Events

Abstract: The Messinian Salinity Crisis (MSC; 5.97-5.33 Ma) is considered an extreme environmental event driven by changes in climate and tectonics, which affected global ocean salinity and shaped the biogeochemical composition of the Mediterranean Sea. Yet, after more than 50 years of research, MSC chronology and events remains controversial. Recently drilled offshore wells in the Levant Basin retrieved for the first time a complete sedimentary record of the deep-basin Mediterranean MSC salt deposits and the underlying Pre-Evaporite unit. Analysis of this dataset changes the way these deposits have been perceived since the 1970’s, when they were first penetrated in their uppermost part during DSDP expeditions. Using sedimentology, chemistry, seismic interpretation, biostratigraphy, and astronomical tuning we show that Messinian salt deposition in the Eastern Mediterranean began during stage 1, and not stage 2 of the MSC. In contrast to the present paradigm, salt was deposited synchronously with gypsum deposition in the marginal and intermediate-depth basins. This occurred significantly earlier than the 50 kyr interval coined as the ‘MSC acme event’, ~300 kyr after the crisis began. The one-kilometer-thick lower part of the evaporitic unit is composed of essentially pure halite, except for a thin transitional anhydrite layer at its base. The halite is undisturbed and homogeneous, lacking diverse features apparent in more proximal sections, indicating a deep-sea depositional environment. We find that distinct, meters-thick non-evaporitic intervals interbedded with the halite, previously thought to be clastic layers, are diatomites. While XRD analysis confirms an increase in clastic components in these sediments, they are composed primarily of well-preserved marine and freshwater planktonic diatoms. The occurrence of marine planktonic diatoms in these intervals indicates the input of Atlantic waters into the Mediterranean Basin during the deposition of the massive halite unit. In the second part of this talk I will couple lipid biomarker analysis with faunal and taxonomic evaluation of the diatom assemblages to try and answer the following question: why do we see this extreme abundance of diatoms, but a complete absence of calcareous-shelled forms of life within the MSC salt deposits? This study demonstrates that brine formation, salt precipitation, and faunal extinction occurred at least in part in a deep, non-desiccated basin, with a restricted yet open Mediterranean-Atlantic connection that allowed inflow of oceanic water. A coeval onset of basinal halite and marginal gypsum precipitation calls for a revaluation of global-scale climatic and oceanographic models of the MSC, while substantially altering our understanding of the mechanisms governing the deposition of salt giants. ...»

Abstract: During the last decade, seismic sensing with optical fibers has become a reality. By analyzing the effect of seismic deformation on the fiber’s optical response, state-of-the-art Distributed Acoustic Sensing (DAS) now offers a 1-meter sensor resolution for tens of kilometers of fiber. In other words, a single DAS system can record up to 40,000 data channels at once – two orders of magnitude more than the entire earthquake-monitoring seismic network in Israel. In this talk, I will first introduce the underlying operating principles of DAS acquisition. These measurements are very different from conventional seismic sensors and need to be analyzed accordingly. Subsequently, most of the talk will revolve around DAS applications in various scenarios. We use the ambient seismic field, recorded on a standard telecommunication fiber deployed around the Stanford campus, to analyze subsurface properties. We also acquired DAS data from a downhole fiber deployed in the SAFOD well and utilized it to reconstruct the earth’s structure and detect earthquakes. Finally, we study DAS data from an unconventional gas field and show how to conduct a simple analysis that unveils reservoir properties. ...»

Abstract: We have shown that microorganisms (bacteria, yeast and fungi) were present in clouds and were metabolically active. As a consequence a new scientific question rose: are they able to modify the chemical composition of clouds and be an alternative route to radical chemistry? In the past we have mainly studied the biotransformation of simple carbon compounds (acetate, succinate, formate, methanol, formaldehyde), and oxidants (H2O2). We showed that biodegradation rates were within the same range of order than photo-transformation rates. More recently we investigated their potential biodegradation activity towards atmospheric pollutants. Using GCxGC-HRMS technique we were able to detect and identify over 100 semi-volatile compounds in 3 cloud samples collected at the puy de Dôme station (1465 m, France). Among these compounds, 10 priority pollutants from the US EPA list were identified and quantified. We focused our work on the biodegradation of phenol and catechol in clouds using two strategies. 1) A metatranscriptomic analysis showed in cloud activity of microorganisms. We detected transcripts of genes coding for phenol monooxygenases (and phenol hydroxylases) and catechol 1,2-dioxygenases. These enzymes were likely from Gamma-proteobacteria (Acinetobacter and Pseudomonas genera). 2) 145 bacterial strains isolated from cloud water were screened for their phenol degradation capabilities, 93% of them (mainly Pseudomonas and Rhodococcus strains) were positive. These findings highlighted the possibility of phenol degradation by microorganisms in clouds. To go further we measured the biodegradation rates of Phenol and Catechol by one of the most active strain (Rhodococcus enclensis) and compared them with the transformation rates resulting from the reactivity of °OH and NO3°radicals. In the cloud water phase, both phenol transformation rates were within the same range of order, while biodegradation of catechol was ten times quicker than chemical transformation. The experimentally derived biodegradation rates were included in a multiphase box model to compare the chemical loss rates of phenol and catechol in both the gas and aqueous phases to their biodegradation rate in the aqueous phase under atmospheric conditions. In conclusion our results suggest that cloud microorganisms could play a role in atmospheric chemistry. ...»

Abstract: The soil spectroscopy discipline has been progressed over the past two decades quite remarkably. Many portable point spectrometers became available through that time where recently also image spectrometers have become quite popular. The technology was used in the laboratory, field, and airborne levels and provided a new capability for a rapid and quantitative view of a large number of samples. At the same time platforms were also developed to carry the new family of sensors for remote sensing applications of large areas using ground and airborne vehicles ( manned and un-manned) and recently even satellites. This progress has led to a large number of activities in exploiting the spectroscopy for many applications within the soil science discipline. As the data acquisition increases and the soil spectral database has been enlarged, a new technique to compile soil spectral database together with methods to effectively analyze them has also been developed. To that end, activities to deal with the data mining process using big databases were successfully adopted from other disciplines while also designed especially for the soil spectroscopy activity. The results demonstrated that soil spectroscopy could be used for many applications from different domains such as soil mapping, precision agriculture, and laboratory work and can progress the soil science discipline quite forward. In this talk, we will review the history of soil spectroscopy from the first spectrometer and platform to the present situation. A particular emphasis will be given to the recent applications that have been developed in our group and to the future capability of this critical technology from all perspectives and to the new horizon it may open as expressed by space agencies such as NASA, ESA, ASI, JAXA, ISA and DLR. ...»

Abstract: Many planetary bodies experience tides, which produce time-varying stresses. Seismic activity on the Moon is modulated by tides, and there are hints of similar effects on Earth (but not, so far, Mars). In this talk I'll describe two other places where tides modulate geological activity at different periods: Io, a highly volcanic moon of Jupiter; and Enceladus, a small icy moon of Saturn. In both cases we can use remote-sensing observations of the modulation to make inferences about the properties of these bodies' interiors. One could imagine similar approaches being used for tidally-distorted exoplanets (e.g. the TRAPPIST system). ...»

Abstract: Recent droughts and floods in California have drawn attention to the vulnerability of our water-supply system to present and future climate variability. A recent analysis of climate-model simulations suggests that wet and dry conditions in California may be predictably linked to tropical and high-latitude conditions, a hypothesis that should be testable using paleoclimate records. Abundant paleoclimate evidence indicates that natural whiplash between wet and dry conditions characterized California’s climate throughout the last 4000 years, especially during the Medieval Climate Anomaly (~AD 950 to 1250), but the chronologies of the records are not precise enough to correlate to tropical and high-latitude records in order to test the model prediction. Our recent work at Mono Lake, a climatically sensitive lake on the arid eastern side of the Sierra Nevada mountain range, has focused on exploring and developing radiocarbon dating of pollen purified by flow cytometry as a tool for high-resolution dating of lake records. Our results suggest that pollen can be reliably separated and dated, but (like everything in lakes) must be interpreted within the specific geologic system where it was produced, deposited, and preserved. If pollen dating proves robust in many lake systems, it may provide the high-precision chronologies required for spatial mapping of past terrestrial climate changes. ...»

Abstract: The management of harmful species, including invasive species, pests, parasites, and diseases, is a major global challenge. Harmful species cause severe damage to ecosystems, biodiversity, agriculture, and human health. In particular, the management of harmful species often requires cooperation among multiple agents, such as land‐owners, agencies, and countries. Each agent may have incentives to contribute less to the treatment, leaving more work for other agents, which may result in inefficient treatment. A central question is, therefore, how should a policymaker allocate the treatment duties among the agents? Specifically, should the agents work together in the same area, or should each agent work only in a smaller area designated just for her/him? I will present a dynamic game-theoretic model, where a Nash equilibrium corresponds to a possible set of contributions that the agents could adopt over time. In turn, the allocation by the policymaker determines which of the Nash equilibria could be adopted, which will allow us to compare the outcome of various allocations. I will show that fewer agents abate the harmful species population faster, but multiple agents can better control the population to keep its density lower. This is proven in a general theorem and demonstrated numerically for two case studies. Therefore, following an outbreak, the better policy would be to split and assign one or a few agents to treat the species in a given location; but if controlling the harmful species population at some low density is needed, the agents should work together in all the locations. ...»

Abstract: Observations and climate simulations show that polar regions warm faster than the rest of the globe in response to radiative forcing. Feedback diagnostics in models show that a large fraction of this enhanced polar warming is due to strong positive lapse-rate feedback. However, there is little mechanistic understanding for why this feedback is positive and what controls its strength. Here, I discuss a mechanism for high-latitude lapse rate feedback and show it functioning in a set of simplified GCM simulations. The mechanism hinges crucially on low cloud response. In this sense, high-latitude lapse-rate feedback is a cloud feedback in disguise. ...»

Abstract: The preservation of the organic matter (OM) occurs as a result of post-depositional abiotic sulfurization, condensation and polymerization processes that convert the OM into stable macromolecular material termed kerogen. Different sulfurization processes, pathways and rates affect the 34S values of organic and inorganic S compounds. These sulfurization processes are affected by the redox conditions and paleo-environmental conditions (e.g. organic matter and Fe availability). Therefore, studying the organic and inorganic S distribution and their associated 34S values could be useful for understanding the paleo-environmental history associated with the deposition of ancient organic rich sediments. Until recently, only bulk phases of S could be measured for their 34S values, usually excluding organic S. A new method was developed that allows for S isotope analysis of specific organic S compounds (OSCs) at the sub- nanogram level. In my talk I will give an overview about the utility of compound specific S isotope analysis (CSSIA) for the study of different geochemical environments (e.g., immature organic rich sediments). Applying CSSIA to immature organic rich sediments from the Monterey and Ghareb formations I will show the combination of biomarkers and their S isotope composition in a single analysis. This provides a more detailed and in-depth understanding of the S and C cycles than bulk measurements of organic and inorganic S species alone. ...»

Abstract: Rivers are the most effective agent of erosion on earth, transporting massive amounts of detrital and dissolved matter into depositional basins, making them a significant part of the rock cycle. To better understand the relationship between denudation of continents and the rivers that drain them, numerous studies examine the pathways of sediment transport through large drainage systems. However, due to the complex nature of sediment storage and transport dynamics in large-scale fluvial systems, the amount of time sediment spends in the sedimentary system is poorly constrained. We measured cosmogenic 21Ne to quantify the exposure time of sediments within large-scale fluvial systems in large rivers: the modern Colorado river, the Miocene Hazeva River (~18 Ma), and the Lower Cretaceous (~130 Ma) Kurnub fluvial system. We observe that fluvial transport dynamics in large rivers are complex and that sediment transport time varies significantly and can last between very rapid (faster than our analytical measurement limitation ~103 yr) and 105 yr. To better understand the nature of fluvial transport dynamics in large rivers, we constructed a stochastic model that simulates repeated episodes of burial and exposure and examines the changes in concentrations of cosmogenic 26Al, 10Be, and 21Ne. We compared the simulated results to the concentrations measured in the Colorado River, and we predict that the total that sediment spent both buried and exposed – the residence time in large rivers is ~103-105 years. These observations suggest that the time-scales of sediment transport in large rivers have not changed significantly over the past 130 Myr and have remained significantly fast compared to other processes in the rock-cycle. ...»

Abstract: The oxygen isotopic signature of marine deep-sea cherts was previously used to reconstruct past ocean temperature and bottom water δ18O through the Cenozoic and Mesozoic periods. Oxygen isotopes of deep-sea cherts, which were never exposed to meteoric water, exhibit a wide range of values indicating that the evolution and maturation of biogenic amorphous opal (opal-A) to opal-CT and microquartz chert is accompanied by isotopic changes. We measured δ18O of diatom opal-A, opal-CT, and microquartz chert from deep sea cores retrieved from the Japan Sea. The δ18O of opal-CT and microquartz chert phases correspond to the depth in the sediments where these transitions occur, ~400 m and 40 °C for opal-A to opal-CT and ~500 m and 60 °C for opal-CT to microquartz chert. The δ18O values of opal-CT and microquartz chert appear to reflect equilibrium formation temperatures of silica, corresponding to the geothermal gradient and the local porewater δ18O. The δ18O of opal-CT and microquartz chert are controlled by the geothermal gradient and compositions of pore waters during polymorphic transformations deep within the sediment, indicating that the δ18O of these phases cannot be used to determine temperature or composition of seawater during diatom growth. Opal-A is the most susceptible phase for isotope alteration. We separated opal-A (i.e., diatoms, radiolaria, and siliceous sponge spicules) of Cenozoic age and measured its isotope composition. The results do not indicate any significant change in δ18O. This will be discussed within the general framework of global climatic change. ...»

Abstract: More than one-third of the 4000+ planet candidates found by NASA’s Kepler spacecraft are associated with target stars that have more than one planet candidate, and such “multis” account for the vast majority of candidates that have been verified as true planets. The large number of multis tells us that flat multiplanet systems like our Solar System are common. Virtually all of the candidate planetary systems are stable, as tested by numerical integrations that assume a physically motivated mass-radius relationship. Statistical studies performed on these candidate systems reveal a great deal about the architecture of planetary systems, including the typical spacing of orbits and flatness. The characteristics of several of the most interesting confirmed Kepler & TESS multi-planet systems will also be discussed. ...»

Abstract: Recent discoveries have shown that habitable environments likely exist in subsurface water oceans within the outer planet moons of Europa and Enceladus. On Titan, the largest moon of Saturn, lakes and seas of liquid hydrocarbon exist in addition to a vast subsurface water ocean. These places represent ideal locations for hydrothermal environments that could sustain life as we know it and, in Titan’s case, perhaps even life as we don’t. The next generation of uncrewed planetary spacecraft will be designed to search for the signs of life in one or more of these worlds. This lecture will begin with a brief review of the discoveries that have motivated a renewed importance for Ocean World exploration, before diving into Titan's lakes and seas to discuss recent findings related to its hydrocarbon-based hydrologic cycle and setting the stage for the newly selected Dragonfly quadcopter set to explore Titan in the mid 2030s. ...»

Abstract: Equatorially trapped waves account for a large portion of the perturbations within the tropical atmosphere and ocean. In the atmosphere, these disturbances are coupled to convection and determine a significant amount of rainfall variability on synoptic to intraseasonal time scales. Numerical models used for both weather and climate forecasting universally still have great difficulty simulating these convectively coupled disturbances. We assess the quantitative precipitation forecasts (QPF) skill of NOAA's Global Forecast System (GFS) and the European Centre for Medium Range Weather Forecasting Integrated Forecast System (IFS) operational models used for short term forecasts out to 10 days. Forecast skill was assessed by comparison with virtually independent GPM and CMORPH satellite precipitation estimates. Skill was quantified using a variety of metrics including pattern correlations for various latitude bands, temporal correlation at individual grid points, and space-time spectra of forecast precipitation over the global tropics and extratropics. Results reveal that, in general, initial conditions are reasonably well estimated in both forecast systems, as indicated by relatively good scores for the 6-12 hour forecasts. Since precipitation estimates are not directly assimilated into these systems, this indicates that the initialization of dynamical and thermodynamical fields is able to produce a reasonable QPF field, at least for the larger scales. We present evidence that the specification of the mass circulation rather than the moisture field is the primary source of this initial skill. Model skill is substantially better overall in the extratropics, however, tropical QPF in both systems is not considered useful by typical metrics much beyond a few days. A portion of this lack of tropical skill in can be traced back to inadequate treatment of equatorial wave activity coupled to convection. It is also demonstrated that extratropical forecast skill is positively correlated to preceding tropical skill, strongly suggesting that improvements in the treatment of tropics will lead to improved extratropical forecasts on the weekly and longer timescale. ...»

Abstract: This talk will use photographs and diagrams to illustrate and explain some of the beautiful optical phenomena observable in nature, such as ice‐crystal halos, rainbows, and sky colors, and will relate them to ongoing research into the spectral and spatial distribution of polarization in the atmosphere. Our group at Montana State University has pioneered all‐sky imaging methods to study skylight polarization and relate it to properties of airborne particles, clouds, and the underlying surface. Brief results from a deployment of all‐sky polarization imagers at the August 2017 solar eclipse will be shown and related to a more general discussion of atmospheric optical effects that can be seen by eye. The talk takes its title from my 2017 book, which describes optical phenomena in nature, especially as seen through airplane windows. ...»

Abstract: The effects of ocean circulation on the climate’s response to anthropogenic emissions at low and high latitudes are examined. At high latitudes, we examine the effects of ocean circulation on the North Atlantic sea surface temperature, which has large climate impacts in the Northern Hemisphere. In recent years and in climate projections a cooling trend is found in the North Atlantic surface (the North Atlantic warming hole). Using observations and large ensemble of model simulations, we find that since the beginning of 21st century there has been a reduction in surface meridional heat advection, which cools the North Atlantic midlatitudes and is part of an emerged forced response to anthropogenic emissions and not part of internal climate variability, and thus projected to continue in coming decades. At low latitudes, the Hadley cell plays an important role in setting the strength and position of the hydrological cycle. Climate projections show a weakening of the Hadley cell, together with widening of its vertical and meridional extents. These changes are projected to have profound global climatic impacts. Current theories for the Hadley cell response to increased greenhouse gases account only for atmospheric and oceanic thermodynamic changes, but not for oceanic circulation changes. Here, the effects of ocean circulation changes on the Hadley cell response to increased greenhouse gases are examined. First, using a hierarchy of ocean-model configurations under increased greenhouse gases or arctic sea-ice loss, we show that, by cooling the surface and atmosphere, ocean circulation contracts and strengthens the Hadley cell, and thus reduces its projected response. ...»

Abstract: Micro-algae greatly influence present and past oceans. Recently we have come to realize that bacteria interact with micro-algae in various ways, ranging from pathogenicity to mutualism. My research investigates physical and chemical interactions between micro-algae and bacteria across multiple scales; from the chemical crosstalk to the influence these interactions have on the marine environment. In my talk I will introduce Emiliania huxleyi, the most prevalent micro-alga in modern oceans. I will discuss the role of bacteria as hidden farmers that control the life cycle of algae, determining how fast algae will grow and how fast they will die. I will link laboratory findings to work conducted at sea and demonstrate the importance of these findings in the study of proxies for climate reconstructions. ...»

Abstract: Moist processes, and in particular the release of latent heat in ascending airstreams, can modify the mid-latitude flow and contribute to the formation of prolonged circulation anomalies such as atmospheric blocking. Blocking represents a challenge to numerical weather and climate forecasting, because it may lead to high impact weather in a situation of increased forecast uncertainty. The causal link between latent heating and blocking is still not well understood. In this study, we explore the effect of latent heating in ascending airstreams on the characteristics of atmospheric blocking using a combination of climatological analysis and modelling approaches. The results of this study illustrate how the physics within ascending airstreams play a crucial role in the formation of blocking anticyclones and in the upper-level wave dynamics in general. ...»

Abstract: The large-scale midlatitude flow is dominated by Rossby wave activity along the upper-level midlatitude wave guide and jet stream. This activity often occurs in preferred quasi-stationary, persistent, and recurrent states, so-called weather regimes (e.g. Vautard, 1990). Many of these regimes are dominated by a blocking anticyclone. In the Atlantic-European region, weather regimes explain most of the atmospheric variability on sub-seasonal time scales. From a forecasting perspective, the onset, persistence, and transition of weather regimes present a severe challenge in current numerical weather prediction models (Ferranti et al., 2015). In this presentation Atlantic-European weather regimes are revisited in order to elucidate their linkage to the eddy-driven jet, atmospheric blocking, and the physical and dynamical processes governing their life cycles. For the latter, the focus is on air mass transport into the upper troposphere through "diabatic outflow" driven by latent heat release in ascending air streams associated with synoptic-scale weather systems (e.g. Grams and Archambault 2016). Next to dry dynamics, this process has recently been shown to be of first-order in blocking onset and maintenance (Pfahl et al. 2015). Challenges in predictability of weather regime life cycles imposed by diabatic outflow are exemplarily demonstrated for a recent forecast bust. We further briefly discuss the modulation of weather regime life cycles by climate modes on sub-seasonal time scales such as the stratosphere and Madden-Julian Oscillation. Finally, the role of weather regimes in extreme weather and the relevance of the weather regime paradigm for socio-economic activities are demonstrated. ...»

Abstract: Chemical composition and Sr-Nd isotope ratios of sediments from lake Huguangyan Maar and its vicinity are used to infer the hydro-climatic conditions that prevailed during the last Glacial and early- to mid-Holocene periods in South China. Variations in 87Sr/86Sr ratios in the lake sediments indirectly indicate two modes of climate conditions: wet intervals during which the lake sediments are mainly derived from the volcanic-lake rim materials, expressed in low 87Sr/86Sr, and dry intervals during which fine particles from the nearby granitic soils are windblown to the lake and supply local dust with high 87Sr/86Sr ratios to the sediments. These wet and dry intervals generally correspond to regional climate records (e.g., speleothem δ18O profiles in southeast China) and correlate with global climate events, (e.g., Heinrich events). While δ18O records of speleothems from southeast China caves are dominated by the precession signal, the Huguangyan Maar Sr record mainly correlates with obliquity. This most likely reflects masking of the precession signal due to regional climate variability, accentuating the obliquity signal. These local effects may also account for some of the differences that have been observed between the various East Asian monsoon records in the region. More importantly, the masking of the precession signal reveals the influence of obliquity on the hydro-climate regime in South China. ...»

Abstract: Light-absorbing organic aerosol commonly termed as Brown carbon (BrC) is a significant contributor to radiative forcing of the Earth’s climate and also is of toxicological concern. Understanding the environmental effects of BrC, its sources, formation, and aging processes requires fundamental knowledge of its chromophores and characterization of their light-absorption properties. This seminar will highlight our recent analytical chemistry developments and applications in the area of molecular-level characterization of BrC that provided first insights into diverse composition and properties of its common chromophores. We present the chemical analysis of chromophores reported in a number of case studies of BrC materials associated with emissions from biomass burning and anthropogenic secondary organic aerosols. The results show that BrC chromophores include organic molecules with various structures, polarities, and volatilities. Understanding their chemical identity requires multi-modal analysis employing complementary separation and ionization approaches in combination with high resolution mass spectrometry. These studies allow assessment of BrC optical properties and relating them to fractional contributions from different classes of chromophores such as aromatic carboxylic acids, nitro-phenols; substituted, heterocyclic and pure polycyclic aromatic hydrocarbons. ...»

Abstract: Precariously Balanced Rocks (PBR) cannot withstand strong ground motion. When a strong earthquake occurs in their vicinity they are likely to break or topple. By evaluating the stability of PBR and determining their age, it is possible to constrain the maximum ground motions that occurred at PBR sites during their life time. This methodology has been proven as effective in determining the maximal earthquake magnitude of faults in the USA, and has been applied to improve both deterministic and probabilistic seismic hazard analysis. In the Negev, slender, in-situ, slenderrock pillars constitute a particularly important subset of PPRs as their seismically induced motion may be amplified. This amplification occurs in pillars with a natural frequency of 1-10 Hz, corresponding to dominant seismic wave frequency away from the source rupture of earthquakes. In the Negev, several pillars that were found to be ~10,000 years old, were used to explore potential implications for constraining the maximum magnitude of earthquakes along the Negev-Sinai Sear Zone faults and the Arava Fault. We show that assuming a plausible amplification of motion, the pillar analysis may yield strong constraints on fault seismicity parameters and may indicate a need to re-evaluate ground acceleration maps. Ongoing dating and stability analysis of PBR and pillars may therefore provide important new insights for regional seismic hazard studies. ...»

Abstract: The atmospheric circulation determines the structure of Earth’s climate. Changes in the circulation, such as meridional shifts in the circulation patterns can lead to dramatic changes in the local climate. Increased greenhouse gas emission is expected to change the vertical and meridional temperature profile and affect the atmospheric circulation. Climate models predict that greenhouse gas-induced climate change would cause a warming of the troposphere and cooling of the stratosphere, as well as a poleward and upward shift of the midlatitude jet stream and storm tracks - the major components of the extratropical circulation. The response of the atmospheric circulation to climate change is difficult to explain, due to nonlinear dynamical feedbacks within the system. Previous studies have attempted to explain the poleward shift of the jet stream in response to climate change based on different dynamical mechanisms. Here we propose an alternative approach of connecting the energy and momentum flux in order to explain the jet shift based on energy balance considerations. ...»

Abstract: The Gulf of Lion (GoL) is an ideal location for investigation of past ecological changes and processes affecting sedimentary deposition. Previous work has highlighted the impacts of climatic and glacio-eustatic changes on the GoL stratigraphic organization, but also on terrestrial exports of organic matter. We analyzed the isotopic composition of organic carbon and nitrogen preserved in sediment core PRGL1-4, and the results highlight the importance of river runoff during warm periods of the last 200 kyr. Regional intercomparison with terrestrial and marine records indicates that these river exports result from an increase in precipitation over the North Mediterranean borderland. The location of PRGL1-4 is outside the Mediterranean cyclogenetic area, and we suggest that these pluvial events occurred in response to enhanced passage of North Atlantic atmospheric perturbations into the Western Mediterranean basin. We also measured pyrite sulfur isotopes over the last 500 kyr, and find stratigraphic variations (>76‰) that are among the largest ever observed in pyrite. Interestingly, the stratigraphic variations in pyrite sulfur isotope ratios are in phase with glacial-interglacial sea level variations. These results suggest that there exist important but previously overlooked depositional controls on sedimentary sulfur isotope records. Two different mechanisms influencing the isotopic fractionation can explain the observed dataset: (i) a climatic modulation of the microbial activity and isotope fractionation, and/or (ii) a local early diagenetic sedimentary modulation of microbial fractionation that responds to sea level variations and to associated properties of the depositional environment. ...»

Abstract: The present climate in the Levant is highly variable and suffers from periodic droughts. There is a strong meridional gradient in precipitation and evaporation and influence from both tropical and northern hemisphere climates. The ICDP Dead Sea Deep Drilling Project cores allow for the first time reconstruction of past climate during the warmest and driest periods in the region. We focus here on the Holocene and Marine Isotope Stage (MIS) 5e intervals. These contain thick layers of halite, reflecting the driest periods over the past 220 ky. The fast sedimentation rate (up to several cm per year) allows identification of climatic changes at high temporal resolution. From salt and major element (Mg, Cl and Na) balances in pore waters and fluid inclusions, we have quantified the average runoff, which was 30-50% of the present-day (pre-1964 diversion of the Jordan River) during that time, reaching 20% during the most arid intervals, lasting decades to centuries. 234U/238U activity ratios in authigenic minerals (aragonite, gypsum and halite), which reflect the water sources around the Dead Sea watershed, show drastic shifts in the lake’s hydrology during the driest times, both during MIS 5e and the Holocene. 234U/238U activity ratio decreased during the driest periods from the typical value of ~1.5 to ~1.1, indicating a shift from the typical Mediterranean (northern/western) influence toward tropical (southern/ eastern) influence. Combining the ICDP core record with other climate records and with NCAR climate model (CCSM3) runs of the last interglacial (130, 125 and 120 ka) highlights the temporal variability due to changes in the orbital forcings between 125 ka (peak summer insolation) and 120 ka. While 125 ka, which is salt-free in the core, is characterized by summer and winter precipitation, 120 ka, which is reflected by the thickest salt accumulation, is characterized by dry winters, increases in fall season precipitation and scarce but intense rainfall flooding events. ...»

Abstract: The Global Burden of Disease relates premature mortality to a range of causes, including air pollution by ozone and fine particulate matter (PM2.5). Quantifying the role of air pollution has been a challenge, in part due to uncertainty about human exposure to air pollution worldwide. We present results from a global atmospheric chemistry model, combined with population data, country-level health statistics and pollution exposure response functions. We calculate that outdoor air pollution, mostly by PM2.5, leads to about 4.5 million premature deaths/year worldwide, predominantly in Asia (75%). This is three times the rate by HIV/AIDS and malaria together. Contrary to the common view that traffic, industry and power generation are dominant sources, we show that residential energy use (e.g. heating, cooking) is the largest category worldwide due to its prevalence in India and China. Strong control measures are needed to substantially lower morbidity and mortality from air pollution. Clean air is a human right, being fundamental to many sustainable development goals of the United Nations. ...»

Abstract: Sedimentary basins are commonly viewed as archives of ancient depositional environments and geochemical signals measured in these basins are frequently interpreted as proxies for ancient Earth-surface environments. However, in the course of the sedimentary basins life-cycle, sedimentary rocks can undergo alteration in diagenetic, epigenetic and metamorphic environments. When put in the correct context, these altered geochemical records are valuable sources of information that reflect the complex thermal, compositional, and deformational histories experienced by the sedimentary rocks. Additionally these measurements can serve as key observations in the study of the interactions among the Earth’s surface and internal processes. In the talk, I will demonstrate how carbonate clumped isotope thermometry (a relatively new temperature-proxy) can be used to study the thermal history of the Colorado Plateau (southwestern N. America), and constrain the oxygen isotope composition of the Phanerozoic Ocean. Clumped and single isotope compositions of calcite and dolomite minerals collected from the Paleozoic sedimentary sequence at the Grand Canyon are consistent with isotopic alteration through open-system recrystallization and/or solid-state isotopic reordering at elevated burial temperatures. By comparing these values with modeled predictions of isotopic signal alteration, we constrain the peak burial temperatures and thermal gradient, and infer the total overburden and exhumation above the top Paleozoic datum at the Colorado Plateau. We also use our data to back-calculate the oxygen isotope composition of dolomite parental water and our results indicate that the oxygen isotope composition of seawater has remained stable throughout the Phanerozoic. This stability suggests that the fluxes of globally averaged oxygen isotope exchange, associated with weathering and hydrothermal alteration reactions, have remained proportional through time. This observation is consistent with the hypothesis that a steady-state balance exists between seafloor hydrothermal activity and surface weathering. ...»

Abstract: Atmospheric flows are characterized by chaotic dynamics and recurring large-scale patterns. These two characteristics point to the existence of an atmospheric attractor defined by Lorenz as: “the collection of all states that the system can assume or approach again and again, as opposed to those that it will ultimately avoid”. While this dynamical systems perspective can seem horribly abstract, it has immediate applications to the study of large-scale atmospheric patterns and extreme weather events. I will first show that we can compute measures of the stability and complexity (dimension) of instantaneous atmospheric fields in a (relatively) easy way. Next, I hope to convince you that these two quantities are actually useful! Their extreme values correspond to specific large-scale atmospheric patterns, and match extreme weather occurrences. They can also be used to identify "maximum predictability" states of the atmosphere, where the flow at positive lags of up to one week is particularly stable and with a small number of degrees of freedom. Finally, there is a significant correlation between the time series of instantaneous stability and complexity of an atmospheric field and the mean spread at lead times of over two weeks of an operational ensemble weather forecast initialised from that state. ...»

Abstract: The deep space climate observatory (DSCOVR) spacecraft resides at the 1st Lagrangian point about one million miles from Earth, where roughly the solar pull balances the terrestrial one. A polychromatic imaging camera onboard delivers nearly hourly observations of the entire sun-lit face of the Earth. Many images contain surprisingly bright flashes of light over both ocean and land. We construct a yearlong time series of flash latitudes, scattering angles and oxygen absorption to demonstrate that the flashes over land are specular reflections off tiny cloud ice platelets. Such deep space detection of tropospheric ice can be used to constrain the likelihood of oriented crystals and their contribution to Earth albedo. These glints may help detecting starlight glints off faint companions in our search for habitable exoplanets. ...»

Abstract: Wastewater treatment plants consolidate high loads of fecal and environmental bacteria and residual concentrations of antibiotics and consequentially, effluents released from these facilities may contribute to antibiotic resistance in downstream ecosystems. This is especially relevant in arid and semi-arid environments, where treated wastewater (TWW) is used for irrigation. The goal of this study was to pinpoint key antibiotic resistance genes (ARGs) in wastewater effluents and to determine the impact of TWW irrigation on antibiotic resistance in terrestrial and food-associated microbiomes. The diversity and abundance of ARGs was evaluated in wastewater effluents, in TWW -irrigated soils and in crops irrigated with TWW using state of the art molecular, genomic and bioinformatic analyses. Three specific methods were applied: (A) a novel high-throughput amplicon sequencing methodology that specifically targeted ARGs associated with integron gene cassettes in effluents from 12 wastewater treatment facilities across Europe and in pristine vs. wastewater effluent-saturated soil; (B) quantitative PCR that assessed the abundance of selected ARGs along freshwater- and TWW-irrigated, water-soil-crop continuum; and (C) comparative in-silico-based analyses of human gut, wastewater and soil metagenomes to determine specific associations between wastewater and soil resistomes. Our results reveal that wastewater effluents contain a diverse array of ARGs, and that specific ARGs and class 1 integrons (mobile genetic elements that often harbor ARGs) are profuse and strongly associated with wastewater effluents. In contrast we found that other ARGs that are ubiquitous to soil regardless of TWW irrigation suggesting that these elements are common in environmental microbiomes. Collectively, the study indicates the distribution of ARGs in the environment is highly complex and is impacted by both natural and anthropogenic factors, and that while the impact of wastewater-derived ARGs in TWW-irrigated soils is limited, there is evidence that plasmid- and integron-associated ARGs are disseminated to soil microbiomes. ...»

Abstract: A sediment core was collected from the unsaturated zone of Nizzanim, Israel, from the surface to the water table at 20m. At 3m depth a live root of retama was found and at 10.5m depth a live rootlet was found. The mineralogy of the sediment core alternated between high quartz (low clay) and low quartz (high clay) due to variation in climate regimes. 14C in the organic fraction of the sediment core was measured to 14m depth. The data divides into two groups: insitu, at the extant surface, and exsitu, at the depth of the roots from the extant insitu data. The correlation of the insitu data is 0.9897 and the average rate of sedimentation is 0.77mm/yr. The average depth of the roots below the extant surface is 8.6±2.6m. The dating of the core made possible attributing geologic information to different depths: 1. The little ice age 2. The flooding of the black sea 3. The younger Dryas The age of the sediment at the depth of 12m is 14Kyear. Thus it seems that there was no unsaturated zone in the site and therefore no Coastal Aquifer. The sea level was at that time 80 below the present level and 15km to the west. Our ancestors followed the coast westward the then returned eastward. ...»

Abstract: The polar vortex has "made headlines" in recent years, following anomalously cold Eastern US winters alongside continuing drought conditions in California which were associated with strong undulations in the tropospheric jet stream which bring cold polar air southward over the Eastern part of the continent, and warm dry conditions over the south west. Recent studies have associated these undulations with anomalous tropical Pacific SST anomalies. We propose that these jet undulations are associated with the North American part of the Circumglobal Teleconnection Pattern - a pair of zonally oriented waves of zonal wavenumber 5 which are in zonal quadrature with each other. While the PNA is associated with the first circumglobal wave pattern, Eastern North American extreme cold events are associated with the second pattern. The implications of this association regarding the physical drivers of such cold events will be discussed, in particular Asian wavepacket precursors and the possible relation to SST anomalies. ...»

Abstract: The Snowball Earth episodes may have affected the development of life on Earth through increasing atmospheric oxygen and spurring evolution. Considering the habitability and increase in complexity of life on other planets therefore requires thought about Snowball climate states. Using an energy balance model and global climate model, I will show that it is unlikely a tidally locked planet could experience a Snowball Earth bifurcation. Instead the planet would smoothly transition to global ice coverage. This is due to the difference in the shape of the insolation, which increases strongly toward the substellar point on a tidally locked planet. I will then change focus slightly and explain how climate oscillations between a warm state and a Snowball state can occur on a planet within the habitable zone that has a small CO2 outgassing rate. I will develop analytical relations to understand these cycles and outline scalings in variables such as the cycle period as a function of important climatic and weathering parameters. Work of this type should help us understand the context of planetary habitability and focus on appropriate targets as we seek to find the first inhabited exoplanet. ...»

Abstract: I will begin with introducing my group, studying fluid flow in complex porous media. Most of the talk will describe a study where simulations, experiments and theory are combined to decipher the mechanisms underlying fluid displacement in partially-wettable porous media. I will present a novel pore-scale model that captures wettability and dynamic effects, overcoming a long-standing computational challenge. We find that increasing the wettability of the invading fluid (the contact angle) promotes cooperative pore filling that stabilizes the invasion; this effect is suppressed as the flow rate increases, due to viscous instabilities. Similarly, reducing pore size heterogeneity increases the displacement efficiency, minimizing the fluid-fluid interfacial area, by suppressing (i) trapping at low rates and (ii) viscous fingering at high rates. Scaling analysis is used to derive dimensionless numbers explaining the mode of displacement. Our findings bear important consequences on sweep efficiency and fluid mixing and reactions, which are key in applications ranging from microfluidics to carbon geosequestration, energy recovery, and soil aeration and remediation. ...»

Abstract: Clouds play a major role for the hydrological cycle, the radiation budget and climate on Earth. They are also the largest factor of uncertainty in the scientific understanding and prediction of climate change. The CLOUD experiment at CERN allows to study aerosol and cloud formation under atmospheric conditions at a new level of precision. A focus of investigations are ion-induced aerosol formation processes using an elementary particle beam from CERN. Here, the potential role of galactic cosmic rays - and their modulation by the sun - for aerosols, clouds and climate is studied. The role of ionization for aerosol formation by different chemical systems of natural and anthropogenic origin is quantied. The experiments therefore yield a new understanding of pre-industrial and present-day aerosol sources and their influences on clouds and climate. Most recently, an important new mechanism based on purely biogenic precursor compounds was discovered and its role for climate was assessed. Furthermore, the results from many experiments performed over the past years were parameterized and combined in a global model to predict the role of different particle formation mechanisms in the different regions of the atmosphere. The talk presents an introduction on the role of aerosols and clouds for climate, an overview of the CLOUD chamber at CERN, and of the fi ndings and implications from recent experiments. ...»

Abstract: Uncertainty in the air-sea fluxes of heat, freshwater, CO2 and other properties constrains our ability to understand and model our changing climate. As the air-sea interface is approached, there is a progressive change in scale and greater interdependence of processes. An important process is turbulence, which is quantified with the dissipation rate of turbulent kinetic energy. Turbulence in the surface ocean boundary layer (SOBL) is key for deepening the mixed layer depth, and therefore it is critical to correctly scale the different types of turbulence arising from wind, waves, and buoyancy. Turbulence is also a key process for increasing the exchange between the ocean and atmosphere. Here is presented observations of upper ocean turbulence using the autonomous profiling instrument ASIP (Air-Sea Interaction Profiler) in different ocean basins which have enabled studies on the diurnal jet, air-sea exchange of CO2, and the impact of rainfall on upper ocean salinity. ...»

Abstract: Despite much effort in the past decades, uncertainties in both climate impacts and health effects of atmospheric aerosols remain large. During the last ten years, aerosol mass spectrometry (AMS) has shown that sub-micron aerosol chemical composition is roughly 50:50 inorganic and organic worldwide, with secondary highly oxidized organics dominating the latter. Parallel application of ToFMS has provided the first observation of molecular cluster ions involved in atmospheric nucleation. Chemical ionization mass spectrometry (CIMS) has extended detection to neutral molecules and clusters, detecting highly oxidized multifunctional (HOM) organics in the gas phase. Ambient sampling and photochemical chamber experiments have resolved the interaction of H2SO4 and HOM in nanoparticle nucleation and growth. These results will be discussed in the context of their impact on atmospheric aerosols, clouds and climate. ...»

Abstract: Rock surfaces support microbial communities that may be involved in weathering processes. In arid and hyper-arid environments microbes dominate rock surfaces and were linked to weathering because the scarcity of water excludes classical mechanisms that erode rocks. We studied subaerial biofilms coating arid rocks, focusing on sedimentary rocks that feature comparable weathering morphologies but different lithologies. We hypothesized that weathering is fashioned by salt erosion and mediated by biofilms that play dual roles: stabilizing the rock surfaces by coating, and enhancing salt crystallization by preventing rapid desiccation (thus mitigating and facilitating erosion processes, respectively). We used a combination of microbial and geological techniques to characterize the rocks morphologies and their subaerial biofilms. Deep sequencing and microscopy analyses suggest that bacterial diversity is low, dominated by Proteobacteria, Cyanobacteria and Actinobacteria. Together these phyla formed laminar biofilms that secrete extracellular polymeric substances to aggregate microfabrics and mitigate desiccation, reducing water loss by over 40%. The biofilm was detected only in rocks exposed to the atmosphere, present distinct architecture and burrowed up to 9 mm beneath the surface, protected by sedimentary deposits. A closer inspection revealed that the composition of the biofilm was tightly linked to dust bacterial communities but distinct from soil communities. Moreover, the biofilm composition changed according to the rock location rather than its’ lithology, suggesting that microclimate (dew, relative humidity and radiation) play an important role in arid weathering. Our results contradict common dogmas that considered biofilms as degrading agents and propose their role as mitigators of geomorphic processes. ...»

Abstract: Increasing concentrations of atmospheric carbon dioxide are expected to affect photosynthesis, evapotranspiration (ET) and ultimately plant growth. Numerical tools that simulate land-surface and vegetation dynamics are typically used to represent future scenarios of terrestrial carbon and water cycles. However, these tools are rarely tested to perform well in conditions different from the historical climate. A combination of numerical modeling and observations from flux-towers and free air CO2 enrichment (FACE) experiments is adopted to illustrate strengths and weaknesses of the mechanistic modeling approach in simulating hydrology and vegetation behavior of different ecosystems exposed to elevated CO2 concentrations. Additionally, an ecosystem model (T&C) is used to investigate the relative contributions of direct (through carbon assimilation) and indirect (via soil moisture savings due to stomatal closure, and changes in leaf area index) effects of elevated CO2. The simulations suggest that the indirect effects of elevated CO2 on net primary productivity are large and variable, ranging from less than 10% to more than 100% of the size of direct effects. For ET, indirect effects are on average 65% of the size of direct effects. Indirect effects tend to be considerably larger in water-limited sites, portraying a critical response of semi-arid ecosystems to elevated CO2. A further analysis demonstrates that introducing subtle changes in plant physiological traits in the simulations can also explain the unexpectedly large increase in water use efficiency (WUE) observed during the last two decades in forests across the north hemisphere. These results have major implications for our understanding of the CO2-response of ecosystems and for global projections of CO2 fertilization because they emphasize the role of indirect effects and the importance of ecosystem adaptability in controlling water, carbon and energy fluxes with potential consequences for climate change and supply of ecosystem services. ...»

Abstract: Abstract: Motivated by the physical picture of shape-dependent drag and, consequently, shape-induced differential sedimentation of dust particles, we searched for and found evidence of dust particle asphericity affecting the evolution and distribution of dust-scattered light depolarization ratio (δ). We examined a large data set of Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) observations of Saharan dust from June to August 2007. Observing along a typical transatlantic dust track, we find that (1) median δ is uniformly distributed between 2 and 5 km altitudes as the lifted dust leaves the west coast of Africa, thereby indicating random mixing of particle shapes with height; (2) vertical homogeneity of median δ breaks down during the westward transport: between 2 and 5 km δ increases with altitude and this increase becomes more pronounced with westward progress; (3) δ tends to increase at higher altitude (>4 km) and decrease at lower altitude (<4 km) during the westward transport. All these features are captured qualitatively by a minimal model (two shapes only), suggesting that shape-induced differential settling and consequent sorting indeed contribute significantly to the observed temporal evolution and vertical stratification of dust properties. By implicating particle shape as a likely cause of gravitational sorting, these results affect the estimates of radiative transfer through Saharan dust layers. ...»

Abstract: The reconstruction of thermal history is key to study the geodynamic evolution of sedimentary basins through burial, metamorphism, magmatism, deformation and exhumation. Carbonate clumped isotope thermometry enables such reconstructions in carbonate minerals, and complements ‘conventional’ low-temperature thermochronometers (e.g. apatite and zircon fission-tracks or U-Th/He systems) by constraining the peak burial temperature and the cooling rate. Most published uses of carbonate clumped isotope thermometry aim to measure depositional temperatures of Earth-surface sedimentary carbonates. However, it has also been shown that carbonate clumped-isotope measurements of minerals formed or re-equilibrated at elevated temperatures can constrain thermal histories of sub-surface rocks. Only very recently have we had the experimental constraints on solid-state isotopic reordering to translate clumped-isotope measurements of such materials into quantitative statements about burial and exhumation. These data have led to a new generation of conceptual models describing changes in clumped-isotope composition during heating and cooling; taken together, these experiments and models enable a new approach to the study of burial, metamorphism and exhumation over long timescales and large areas. This presentation will discuss applications of this approach to constrain the thermal history of carbonate rocks exhumed in back-arc (Naxos, Greece) and mid-continental (Colorado Plateau) basins. The exhumation of Naxos metamorphic core-complex entailed a complex thermal history, mineral-mineral and water-rock reactions, and deformation. These processes were registered in the bulk and clumped isotope composition of marbles. Calcite and dolomite marbles from Naxos show large variation of carbonate clumped-isotope values, in association with deformation and secondary mineralization fabrics. Results suggest that dynamic recrystallization of calcite can reset the carbonate clumped-isotope signal, which consequentially records the minimum temperature of dynamic recrystallization in natural samples. Carbonate clumped isotope data from the center of Naxos core-complex are consistent with the thermal history as recorded by multiple ‘conventional’ thermochronometers, but require a faster cooling rate than previously suggested, consistent with a heat shock driven by magmatic and hydrothermal activities. Carbonate clumped isotope thermometry is used to study the burial, uplift and exhumation histories of the Colorado Plateau (USA). There, carbonate rocks were not recrystallized to marbles, and therefore their clumped isotope signals are expected to be sensitive to the peak-burial temperature. Given such constrains on the thermal history, it is straightforward to infer the thermal gradients during peak burial, and calculate total-exhumation (i.e. the volume of rock removed) in-situ. Preliminary results from the southwestern rim and the interior of the Plateau are so far consistent with published constrains on peak burial temperatures. ...»

Abstract: Understanding the response of East Asian monsoon (EAM) rainfall patterns to different climate forcings is cardinal for constraining future climate change over East Asia. The magnitude and rate of EAM rainfall changes during the late Pleistocene-Holocene is reconstructed using the first well-dated Northeastern China lake-area record from a closed-lake basin, which enables reconstructing quantitative absolute paleo-rainfall amounts. In addition, compound specific hydrogen isotopes from long-chain alkanes (Dleafwax) in the lake-sediments were used to reconstruct the isotopic composition of rainwater and lake water. Lake-levels were 60m higher than present during the early and middle Holocene. This requires an absolute increase in mean annual rainfall to at least two times higher than today. The EAM intensity and northern extent alternated abruptly between wet and dry periods on time scales of a few centuries. Both the onset (~60 m rise at 11.5 ka BP) and termination (~35 m drop at 5.5 ka BP) of the Holocene humid period occurred abruptly, within centuries. The co-variation of lake-area and Dleafwax show, for the first time, that the “amount effect” is the cardinal driver of the isotopic composition of paleo tropical rainfall. Thus, resolving a current debate regarding the ability to use the isotopic composition of rainwater as a proxy for rainfall amount and validating the “intensity-based” interpretations of the Chinese cave deposit records. ...»

Abstract: Fears of global climate change and its potential outcomes have stimulated intensive efforts to update current climate models. Nevertheless, most of the existing models lack inputs specific to peatlands and/or to microorganisms. Peatlands store up to 30% of the world’s soil carbon and contribute up to 30% of atmospheric methane, thus their response to climate change is of special interest. Peatlands are mostly found at northern high latitudes where nutrient poor conditions foster Sphagnum as a keystone plant species. My studies focus on understanding the response of peatland ecosystems to climate change at the Marcell Experimental Forest (MEF) in northern Minnesota, USA. At MEF, the U.S. DOE has created a unique multi-faceted large scale climate manipulation experiment known as SPRUCE (Spruce and Peatland Response Under Climatic and Environmental Change), initiated in June 2014. From June 2014 to June 2015, we evaluated the responses of microbial communities, both in structure and metabolic potential, to 5 soil warming treatments (+0°C; +2.25°C; +4.5°C; +6.75°C; +9°C). Methane flux was correlated with temperature in the treatments, suggesting that increases in soil temperature apparently drive the emission response. However, multiple lines of evidence, including laboratory incubations, indicate that CH4 emission increased due to surface processes and not degradation of deep carbon. Characterization of in situ microbial communities indicated no significant effect of temperature or time on community composition or function. Specifically, the potential activity of extracellular lignin oxidative enzymes showed that one year of soil warming had a limited effect on microbial activity. While the physiology and ecology of Sphagnum have been well-studied, the structure, function and response of their microbiome to climate change is less understood. Sphagnum-associated, nitrogen-fixing bacteria are thought to play a major role in plant functioning and the peatland nitrogen cycle. Therefore, we conducted intensive sampling of the S. magellanicum phyllosphere-associated microbial communities. Our results revealed a significant geographical effect on general and nitrogen-fixing microbial communities. Interestingly, the nitrogen-fixing core-microbiome contained only 2 members, taxonomically affiliated with Nostoc azollae (symbiotic Cyanobacteria) and Methyloferula stellate (an obligate methanotroph). Potentially synergistic interactions between these nitrogen-fixing bacteria not only provide the plant with sufficient nitrogen, but may also reduce methane emission from peatlands. Our observations of evolutionary conserved nitrogen-fixing bacteria among representative peatland sites further knowledge of the benefits of the microbiome to Sphagnum host fitness and to ecosystem function. ...»

Abstract: The nature of the large-scale flow below the cloud level on Jupiter is still unknown. The observed surface wind might be confined to the upper layers, or be a manifestation of deep cylindrical flow. Moreover, it is possible that in the case where the observed wind is superficial, there exists deep flow that is completely separated from the surface. During the years 2016-17 Juno will both perform close flybys of Jupiter, obtaining a high precision gravity spectrum for the planet. This data can be used to estimate the depth of Jupiter observed cloud-level wind, and decipher a possible deep flow that is decoupled from the surface wind. In this talk I will discuss the Juno gravity experiment and the possible outcomes with regard to the flow on Jupiter. We explore the possibility of complex wind dynamics that include both the upper-layer wind, and a deep flow that is completely detached from the flow above it. The surface flow is based on the observed cloud-level flow and is set to decay with depth. The deep flow is constructed synthetically to produce cylindrical structures with variable width and magnitude, thus allowing for a wide range of possible setups of the unknown deep flow. The combined 3D flow is then related to the density anomalies via a dynamical model and the resulting density field is then used to calculate the gravitational moments. An adjoint inverse model is constructed for the dynamical model, thus allowing backward integration of the dynamical model, from the expected observations of the gravity moments to the parameters controlling the setup of the deep and surface flows. We show that the model can be used for examination of various scenarios, including cases in which the deep flow is dominating over the surface wind. The novelty of our adjoint based inversion approach is in the ability to identify complex dynamics including deep cylindrical flows that have no manifestation in the observed cloud-level wind. Furthermore, the flexibility of the adjoint method allows for a wide range of dynamical setups, so that when new observations and physical understanding will arise, these constraints could be easily implemented and used to better decipher Jupiter flow dynamics. ...»

Abstract: The complex pattern of river networks has inspired decades of studies. However, the evolution and the dynamics of a growing channel remain elusive. Here we show that the principle of local symmetry, a concept originating in fracture mechanics, explains the path followed by growing streams fed by groundwater. Although path selection does not by itself imply a rate of growth, we additionally show how local symmetry may be used to infer how rates of growth scale with water flux. Our methods are applicable to other problems of unstable pattern formation, such as the growth of hierarchical crack patterns and geologic fault networks, where dynamics is not well understood. ...»

Abstract: Tropical cyclones are generally thought of as being of too small scale to be simulated adequately in the global climate models in use for studies of global warming. But these models are gradually moving to higher resolution and are beginning to provide realistic simulations of the statistics of tropical cyclones. In addition to providing some information on how tropical cyclone statistics might change in the future, these models now provide a framework for studying how the climatology of tropical cyclones is controlled. I will describe a hierarchy of models with which we are beginning to address this issue. ...»

Abstract: The high-latitude vertical structure of temperature is poorly understood, yet is an important factor in the polar amplification of climate change. To better understand the high-latitude lapse rate and its sensitivity to various forcings, we explore two perspectives on the high-latitude temperature structure. The first is the Lagrangian perspective of Arctic air formation. We prescribe the initial sounding of the atmosphere representing an air column starting over the ocean, then allow the air mass to evolve for two weeks in the absence of any solar heating and with a very low heat capacity surface underneath (representing the movement of the air column over high-latitude sea ice or a continental interior). Using a single-column model, we find that a low-cloud feedback slows cooling of the surface and amplifies continental warming, increasing the continental surface air temperature by roughly two degrees for each degree increase of the initial maritime surface air temperature. We discuss extension with a 2D cloud-resolving model, and applications to past and future warm climates. The second is the Eulerian perspective of radiative-advective equilibrium. High latitude temperature profiles are generally stable to convection, with frequent surface-based inversions, especially in winter. Such profiles result from the stabilizing influences of advective heat flux convergence and atmospheric solar absorption, which dominate over the destabilizing influences of surface solar absorption and subsurface heating. We formulate an analytical model for the high-latitude temperature profile, using prescribed heat flux convergence and either gray- or windowed-gray thermal radiative transfer. We discuss how climate feedbacks in this state depend on the type of forcing, and compare temperature feedbacks in high-latitude radiative-advective equilibrium to the more familiar case of low-latitude radiative-convective equilibrium. ...»

Abstract: Dry air intrusions (DAIs) are large-scale descending airstreams. A DAI is typically referred to as a coherent airstream in the cold sector of an extratropical cyclone. Emerging evidence suggests that DAIs are linked to severe surface wind gusts. However, there is yet no strict Lagrangian definition of DAIs, and so their climatological frequency, physical characteristics as well as their seasonal and spatial distributions are unknown. Furthermore, it is unclear how many of the DAIs occur together with a cyclone, and the dynamical interaction between DAIs and strong surface winds is not fully understood. Here, we suggest a Lagrangian definition for DAI air parcels, namely a minimum pressure increase along a trajectory of 400 hPa in 48 hours. Based on this criterion, the open questions are addressed by: (i) a novel global Lagrangian climatology for the ECMWF ERA-Interim reanalysis dataset for the years 1979-2014; (ii) examples for the interaction between DAIs and strong surface winds, shown with composite analysis and with a case study of a high-impact cyclone, using a mesoscale regional model simulation. We find that DAIs occur predominantly in winter, with higher occurrence frequency in the northern hemisphere. DAIs coherently descend from the upper troposphere (its stratospheric origin is small), to the mid- and low levels, where they mix with their environment and diverge. Different physical characteristics typify DAIs in the different regions and seasons, and when occurring together with a cyclone. Finally, we demonstrate the different mechanisms by which DAIs can destabilize the boundary layer and facilitate the formation of strong surface winds. ...»

Abstract: Stabilization of the Dead Sea (DS) level Is the Red Sea-Dead Sea Water Conveyance a feasible solution? By Michael Beyth, Geological Survey The seminar will discuss the: • Limnological background-DS a hypersaline terminal lake. • Environmental impacts of the DS level decline-sinkholes and infrastructure. • The idea- from 1840. • Is the Red Sea – Dead Sea Conveyance a feasible solution?-the only solution to manage the DS level. • The recent feasibility study 2008-2013. The three major goals for the project defined in this recent study were: 1. to stabilize the Dead Sea water level by conveying up to 1,200 MCM/y of reject; 2. to desalinate up to 850 MCM/y mainly for Jordan; 3. to serve as a symbol of peace between the three Beneficiary Parties, Jordan, Israel and the Palestinian Authority. The project was managed by the World Bank navigated by the Steering Committee of the Beneficiary Parties,. This study followed Harza (1996) pre-feasibility study. Six reports were published • Tech./econo. feasibility study by Coyne et Bellier. • Environmental and social assesment by ERM. • Dead Sea Study by Tahal&GSI. • Red Sea study by Tethis&IINS,Jur.Uni., IOLR. • Study of Alternatives by Allen, Malkawi and Tsur. • Chemical industry analysis study (Zbranek). The reports are available at Web-site (www.worldbank.org/rds). Pilot-first phase –tender stage now • a limited desalination plant of ~80 MCM/y at Aqaba. • 35 MCM/y of desalinated water will be bought by Israel and transferred to the Israeli Arava Valley. • The rest will be used by Jordan for Aqaba and dilution of the DISI aquifer pipeline to Amman. • The reject brine together with more sea water (should be 200 MCM/y together) will be piped to the Lisan "Lagoon", at the south-east corner of the Dead Sea. • Possible small Hydro-Electric plant will be built in Ghor Pipa, Jordan, producing ~30 MW. • On December 9th 2013 an MOU was signed in Washington by Israel, Jordan and the Palestinian Authority, speaking also about Israel to sell to Jordan another 50 MCM/y from Lake Kinneret and about Israel to sell the Palestinian Authority another 20-30 MCM/y of water through the current water supply system. • On February 26th 2015 an implementation agreement was signed between Israel and Jordan that defines the implement process of the Red – Dead Pilot, including water swap between the countries. . ...»

Abstract: Impact crater are useful tools to study planetary surfaces. First, they are natural drills into planetary crusts. I will present a combination of studies of the martian crust by the analyses of the composition of central peaks of martian impact craters. These results are part of an ERC project eMars dedicated to the geological evolution of Mars. As part of this project too, a martian data processing application has been built allowing the teleprocessing of imagery data, topographic data and hypespectral data from the 4 last martian orbiters dedicated to the surface of Mars. Secondly, impact crater statistics have recorded both bombardment and the complex geological evolution of a planetary surfaces. I will present how martian crater statistics allow to decipher the climatic evolution of the planet ...»

Abstract: The estimated magnitude of aerosol cloud mediated radiative forcing has evolved during the IPCC assessments, but its large uncertainty remained essentially unchanged and constituted a major component of the total uncertainty in climate forcing. In fact, paradoxically, the advancements in understanding impacts of cloud aerosol interactions on radiation increase the uncertainty, because we discover additional pathways by which aerosols affects clouds much faster than developing our ability to quantify these effects observationally. In other words, we discover more of what we should know that we don't know. This inherently increases the known uncertainty. The presentation will review the various known and recently discovered aerosol cloud mediated radiative effects and the methods that may be used to quantify them. The major challenges in doing so are measuring CCN from satellites and disentangling the impacts of CCN and updrafts on cloud properties. New breakthrough capabilities that give hope that it may be achievable from current satellite measurements will be presented. ...»

Abstract: The poles of Saturn, Uranus and Neptune each have a 'hot spot' that is observable from Earth. Saturn, which has been observed in great detail by the orbiting Cassini mission, exhibits Earth-sized hurricane-like cyclones on each pole. These massive cyclones have been present since they were first observed in 2004 and may be permanent. Our study proposes a mechanism for their creation: numerous small, moist convective thunderstorms. These thunderstorms are ubiquitous small scale features on Jupiter and Saturn. Hundreds of simulations suggest that these very small, short-lived storms can build and maintain a deep, rapid, large polar cyclone like we see on Saturn. Furthermore, an exploration of cyclone sensitivity to the deformation radius and total energy input suggests that Uranus and Neptune have transient polar cyclones, and Jupiter will not exhibit them. This last prediction will be tested for the first time next year, when the NASA Juno mission reaches Jupiter and finally observes the Jovian poles. ...»

Abstract: The general circulation of the ocean is forced by surface fluxes of momentum, heat, and freshwater at basin scales. The kinetic and available potential energy sources associated with these external forces drive a circulation which exhibits flow features that vary on a wide range of spatial and temporal scales. Understanding how the different forcing mechanisms lead to the observed large-scale ocean circulation patterns and to what degree do the various smaller scale processes modify them have been long standing problems for oceanographers. A large fraction of the kinetic energy in the ocean is stored in the mesoscale eddy field. This `balanced' eddy field is expected, according to geostrophic turbulence theory, to transfer energy to larger scales. In order for the general circulation to remain approximately steady, sub-mesoscale instabilities leading to `loss of balance' (LOB) have been hypothesized to take place so that the eddy kinetic energy (EKE) may be transferred to small scales where it can be dissipated. We examine the kinetic energy pathways in fully resolved direct numerical simulations of flow in a flat-bottomed re-entrant channel, a configuration that resembles the Antarctic Circumpolar Current. The flow is allowed to reach a statistical steady state at which point it exhibits both a forward and an inverse energy cascade. We show that EKE is dissipated preferentially at small scales near the surface via sub-mesoscale instabilities associated with LOB and a forward energy cascade rather than by bottom drag after an inverse energy cascade. These results highlight the importance of sub-mesoscales dynamics to the general circulation of the oceans. ...»

Abstract: Cyanobacteria play a key role in marine photosynthesis, which contributes to the global carbon cycle and to the world oxygen supply. Genes encoding the photosystem-II reaction centre are found in many cyanophage (viruses that infect cyanobacteria) genomes, and it was suggested that the horizontal transfer of these genes might be involved in increasing phage fitness. Recently, evidence for the existence of phages carrying photosystem-I genes was also reported. Even more, phages carrying both photosystem-II and photosystem-I gene suites are also found. In this lecture I will discuss viral ‘photosynthesis’, that is the possible contribution of viral proteins to cyanobacterial photosynthesis. The implications to oceanic photosynthesis and to the carbon cycle will be discussed. ...»

Abstract: Flash floods caused by convective rain storms are highly sensitive to space-time characteristics of rain cells. In several recent studies we exploited the high space–time resolution of the radar data to study the characteristics of rain cells in the arid, semi-arid and Mediterranean parts of Israel. A unique approach was applied to examine the impact of convective rain cell characteristics on flash flood magnitude. A rain cell model was applied to the radar data of an actual storm and the rain fields represented by the model were further served as input into a hydrological model. Global sensitivity analysis was applied to identify the most important factors affecting flash flood peak discharge. As a case study we tested an extreme storm event over a semi-arid catchment in southern Israel. We found that relatively small changes in the rain cell’s location, speed and direction could cause a three-fold increase in flash flood peak discharge at the catchment outlet. Based on analysis of space-time rainfall patterns and synoptic conditions in the Mediterranean climate regions of Israel, a stochastic high-resolution rainfall model (“weather generator”) was developed and used to study the potential impact of predicted climate change on streamflow in the Ramot Menashe region. ...»

Abstract: The spring phytoplankton bloom is a major, extensively studied phenomenon in temperate and high latitude seas. Much less information isavailable on blooms in subtropical oligotrophic seas, where the water column is usually stratified. Yet, even in temperate seas the processes determining phytoplankton dynamics during the mixed-layer deepening and the factors triggering the initiation of the bloom are controversial. Here we use long-term measurements of chlorophyll concentration, nutrients, mixed-layer depth and grazing rates to examine the validity of three bloom-initiation processes for the Gulf of Aqaba (northern Red Sea): the Critical Depth Hypothesis, the Dilution-Recoupling Hypothesis, and the Critical Turbulence Hypothesis. The Gulf is a unique water body in the subtropics, where convective mixing during winter reaches hundreds of meters in depth, leading to conspicuous spring blooms. Here we show that neither the critical depth mechanism nor the dilution-recoupling hypothesis explain the phytoplankton dynamics during the winter and spring in the Gulf. Instead, our findings indicate that this dynamics is governed by the interplay between three main processes: (1) nutrient-driven primary production in the upper, illuminated layer; (2) physical ‘homogenization’ of phytoplankton by convective mixing; and (3) accumulation of phytoplankton in the upper layer after the termination of sea-surface cooling. The latter mechanism is responsible for the onset and magnitude of the spring bloom. ...»

Abstract: The sunlit surface layer of the world’s oceans is a critical biome for the functioning of the Earth system. It constitutes the habitat to a tremendous diversity of viral, bacterial and unicellular eukaryotic groups (autotrophic and heterotrophic) whose intricate populations structure and trophic interactions drive nearly half of the global primary productivity and is central in regulation of elemental cycles and climate homeostasis. In a decade where genomic tolls are enabling a robust assessment of the marine microbial biodiversity our understanding of the mechanisms underlying trophic interactions and the complexity of organisms’ life cycles is still fragmentary. Here, I present two studies that I have been developing over the last years. In a first study, we showed using both field observation and laboratorial experiments that copepods, abundant migrating crustaceans that graze on phytoplankton, as well as other zooplankton can accumulate and act as viral-vectors mediating the transmission of viruses infecting Emiliania huxleyi, a bloom-forming marine microalgae that plays an important role in the carbon cycle. We propose that such zooplankton-driven mechanism can boost host-virus contact rates and potentially accelerate the demise of large-scale phytoplankton blooms in the oceans. In a second study, we explore the mechanisms by which viral infections impact the life cycle of E. huxleyi. In earlier studies we demonstrated that the haploid phase of E. huxleyi is unrecognizable and therefore resistant to viruses that specifically kill the diploid phase, and that exposure of diploid cell to virus induces transition to a phenotypically-like haploid phase. We proposed that such escape strategy via life phase switch, the ‘‘Cheshire Cat’’ escape strategy, enables diploid blooming cells to evade viral attack. Recent morphological and genetic characterization of cells exposed to viruses starts now to shed light on the mechanisms underlying life phase transition dynamics, opening new perspectives of future research. ...»

Abstract: Gaia is a space observatory which ESA has launched in December 2013. Its proclaimed mission is to study the origins and subsequent evolution of our Galaxy, the Milky Way. In order to attain its goals it is performing a survey of about a billion stars, allowing the construction of the most accurate three-dimensional map to date of the Galaxy. The talk will describe the Gaia space mission, its scientific context, and its expected impact, beyond its proclaimed mission. Specifically, it will look deeper into the prospects of detecting extrasolar transiting planets ...»

Abstract: The origin of Solar System satellites is actively debated. We know understand that, despite the morphological analogy between a satellite system and a planetary system, the formation processes of satellites may be significantly different from planetary formation processes. in addition, satellites evolve quickly under the effects of tides. Different scenarios seem to be required for different types of planets (terrestrial, giant or ice giant). In this talk I will quickly review our current understanding of satellite formation and the different constrains. Based on Cassini images and numerical simulation, I will show that there is today on-going accretion processes at the edge of Saturn's rings, pointing to a new satellite formation process. I will show that satellite formation may be deeply linked to the evolution of planetary rings, to the point that it is very probable that most of Solar System’s regular satellites may have born inside rings, either massive, like the protolunar disk,or light, like giant planet’s rings. I will illustrate this vividly in the case of Saturn using numerical simulations and CASSINI images. Case of Ice giants, Mars and Jupiter will be also discussed. Some extension to the case of exoplanets’ regular satellites will be attempted. ...»

Abstract: Submesoscale processes may strongly influence the depth and stratification of the ocean surface boundary layer, yet the prevalence of these motions throughout the ocean as well as the conditions that trigger them have been difficult to ascertain. Previous observational programs have focused on regions of strong frontal currents, such as the Gulf Stream and Kuroshio, where conditions are favorable for submesoscale instabilities. Here we present results from a unique times series of hydrographic observations, obtained at submesoscale resolution, from a region with a weak mean flow. As part of the Ocean Surface Mixing, Ocean Submesoscale Interaction Study (OSMOSIS) program, glider pairs occupied a small 20 km by 20 km region over the Porcupine Abyssal Plain in the northeast Atlantic from September 2012 to September 2013. Measurements from the gliders were complemented by a suite of nine mooring arrays in the same region. We analyze the in situ evolution in the context of the background conditions from satellite data, including sea surface temperature, sea surface height and surface forcing from wind stress reanalysis. We also analyze three months of a 1/48-degree ocean model in the same region. This data set provides an opportunity to study the physical processes that contribute to upper ocean mixed-layer variability over a full seasonal cycle. ...»

Abstract: Earth climate varies on long and short time scales and its patterns have been derived by a variety of geochemical proxies. The most commonly used paleoclimate proxy is the oxygen isotopic composition in carbonates (δ18O). δ18O, however, is not a direct paleo-thermometer, and temperature reconstructions rely on independent estimates of water isotopic compositions. This caveat is particularly challenging on land, due to the complexity of hydrological variations that control the δ18O of the relevant waters. Carbonate clumped isotope (Δ47) thermometry is a new method for estimating paleo-temperatures that is independent of water isotopic compositions. It is therefore particularly useful as a temperature proxy in terrestrial environments. When combined with carbonate δ18O, it can also serve as a hydrological indicator. Here I will show the application of this method to the study of Late Pleistocene climate in terrestrial settings in the Levant and East Africa. Glacial-Interglacial climate in the Northern Jordan Rift Valley (Israel) was examined by applying the clumped isotope thermometer to modern and fossil fresh water snails from water bodies in the region. The observed Glacial-Interglacial temperature change is similar to regional records but absolute temperatures are warmer. Paleo-water δ18O values have an opposite trend for the last glacial termination compared to the global ocean trends and regional records that reflects a change in the snow-rain dominance of the region’s rivers and changes in evaporation. An integration of Δ47 and δ18O measurements of land and freshwater mollusks from Lake Victoria, East Africa, provide information on past climatic conditions in the region. Results show no significant increase in precipitation for a time interval during which lake levels were significantly higher than in modern-day. These findings support non-climatic mechanisms for the lake level increase, such as tectonically driven change in lake drainage. ...»

Abstract: A 10-yr climatological study of Tropical Plumes (TPs) observed over the Middle East was undertaken. Several tools were used to identify and analyze these mid-tropospheric elongated cloudbands: satellite images, reanalysis and radiosonde data, backward trajectories, and cluster analysis. In order to conduct an in-depth examination of the synoptic conditions controlling this tropical–extratropical phenomenon, a dual methodology was adopted. In the first analysis, the identified 45 plumes were classified to precipitative and non-precipitative. In the second analysis, backward trajectories of the plumes were clustered in order to detect their moisture origins and pathways. In addition to the well documented south-western plumes originating in West Africa, a more southern pathway was identified, in which moisture was transported from Central to East African sources. The ‘south-western’ plumes are associated with a southwards penetration of mid-latitude troughs, associated with an intensified thermal wind and a longer jet streak, extending as far as Northwestern Africa. In the ‘southern’ category the Sub-Tropical Jet is associated with an anticyclonic flow over the south of the Arabian Peninsula, serving as an essential vehicle advecting moisture from tropical origins. This moisture pathway is considerably shorter than the south-western one. Several conditions favor precipitation induced by TPs over the domain: a northward migration of the jet streak resulting in a weakening of the wind speed over the target area, a deeper trough at the 500 hPa level and a shorter moisture corridor. ...»

Abstract: Long-term averages of the isotopic composition of precipitation from 15 sites in Israel and reanalyzed vapor data from the Mediterranean are used to assess the full modern hydrological cycle of sea surface water–vapor–distillation–precipitation–evaporation in the E. Mediterranean and the Levant. The results combined with modeling efforts show that once the source effect is accounted for, the long-term isotopic composition of precipitation in Israel is governed primarily by distillation that is a function of the sea-land temperature gradient. These processes govern the amount, altitude and the distance from the ocean effects. Based on our understanding of the modern processes, we modeled the distillation as a function of relative humidity during the LGM using d18O values from Soreq Cave stalagmites and Mediterranean foraminifera. Our model suggests a possible reconciliation of the conundrum between the Lake Lisan high-stand during the LGM and the similar offset between the d18O from Soreq Cave stalagmites and Mediterranean foraminifera in modern and LGM times. ...»

Abstract: The Madden-Julian oscillation (MJO) is the dominant mode of variability in the tropics on the intraseasonal time scale (say, 20-90 day periods) and one of the most important coherent, quasi-periodic modes of natural variability in the global climate system altogether. Though it was discovered over 40 years ago, we still do not understand the MJO, in the sense of being able to state an agreed-upon, simple mathematical model that explains its basic features. I will present evidence that the MJO is what some of us now call a "moisture mode", best analyzed by examining the budget of moist static energy or moist entropy. I will argue that cloud-radiative feedbacks are important to the maintenance of the MJO, while horizontal advection of moisture is important to its eastward propagation. I will present evidence from observations, theory, general circulation models, and cloud-resolving models to this effect. ...»

Abstract: Fractures which are always present underground drastically influence the transport properties of porous media on the large scale. Applications such as water flows, transport of contaminants, and reservoir models in the oil industry necessitate the prediction of the transport properties of fractured porous media from easily measurable field quantities. Versatile numerical tools devised to study these properties extensively, will be briefly presented and illustrated. Isotropic networks of uniformly distributed identical fractures are studied first; then, the studies are genereralized to anisotropic networks, to fractures distributed according to power laws and to non uniform distributions. The results can be rationalized in terms of the excluded volume of fractures and their number ' per excluded volume. When the percolation threshold of the fracture network, and the macroscopic permeability are plotted as functions of ', they become independent of the fracture shapes, which is a decisive simplification for the applications. ' can be estimated from measurements performed on intersections of fracture networks with lines, planes, and galleries. These intersections are visible on outcrops, cliffs, quarries, wells and tunnels. Some remarkable relations hold for convex fractures of all shapes. Applications of this approach to several practical cases will be discussed. ...»

Abstract: Abstract: We will consider different examples of flows on the beta-plane in a rotating tank . These flows include eddies, zonal jets and Rossby waves and are relevant to meso- and large-scale dynamics of the Earth's oceans and atmosphere. The flows are generated by a barotropic or baroclinic forcing either spatially localized or distributed over the domain. Laboratory (optical) altimetry is used to measure the surface elevation and to obtain the velocity fields of the flow, not unlike satellite altimetry used by oceanographers. The beta-plume mechanism will be discussed as a concept which unifies all these different flows. ...»

Abstract: The isotopic similarity of the Earth and Moon has motivated a recent investigation (Cuk and Stewart, 2012) of the formation of the Moon with a fast-spinning Earth. Angular momentum was found to be drained from the system through the evection resonance, a resonance between the pericenter of the Moon and motion of the Earth about the Sun. However, tidal heating within the Moon was neglected. Here we explore the coupled thermal-orbital evolution of the early Earth-Moon system, taking account of tidal heating within the Moon. Large tidal heating in the Moon significantly changes the tidal parameters in the Moon, with consequent early escape from the evection resonance. Insufficient angular momentum is withdrawn from the system to be consistent with the current configuration of the Earth-Moon system. ...»

Abstract: Critical transitions have attracted a great deal of attention due to their relevance to many natural and social systems. Much research has been devoted to the characterization and identification of imminent critical transitions. In spatially extended systems, the dynamics (close to and away from the critical point) is more complicated due to the expansion, shrinking and coalescence of alternative-state domains. Pattern-forming systems introduce additional complexity due to the patterned nature of one of the stable states. In this talk, I will present several works in which we used the context of drylands vegetation dynamics to study various aspects of this additional complexity: (i) Using a minimal model, we showed that in systems exhibiting a bistability of a patterned state with a uniform state, a multitude of intermediate stable localized states may appear, giving rise to step-like gradual shifts with extended pauses at these states. This result suggests that a combination of abrupt-shift indicators and gradual-shift indicators might be needed to unambiguously identify regime shifts. (ii) The existence of these localized states in models for the dynamics of drylands vegetation and the response of the systems described by these models to local perturbations will be discussed. (iii) We show how a simplified version of a model for drylands vegetation dynamics can explain the emergence and the observed dynamics of the spectacular phenomenon of “fairy circles” in southern Africa. If time permits, I will present recent results demonstrating the effects of heterogeneity on the pattern formation, survivability and resilience of water-limited vegetation. ...»

Abstract: The Eocene (56-34My ago) is one of the best analogs for a greenhouse climate, with high CO2 concentrations, generally high temperatures, and no polar ice caps. A major feature of the Eocene geochemical records suggests a reduced latitudinal gradient, in which most of the warming occurs in polar regions (possibly exceeding 30°C in the Antarctic margin), but less in the tropics. These results could have profound implications for understanding polar amplification of greenhouse warming, but they are not captured in climate models, pointing to important gaps in climate models and to major uncertainties in the geochemical data. We combine two temperature proxies - carbonate clumped isotopes in fossil bivalve shells and archaeal lipid TEX86 in the sediment associated with the bivalves - to constrain Eocene temperatures in Southern high latitudes. Clumped isotope paleothermometry is a thermodynamically controlled temperature proxy that is not dependent on the isotopic composition of seawater, and presents a novel opportunity to reduce uncertainties in Eocene sea surface temperature estimates. We use it to constrain the calibration of TEX86 in order to compare paleotemperatures in the Antarctic Peninsula (Seymour Island) to those in the South Pacific (Eastern Tasman Plateau), both at ~65°S paleo-latitude. The data indicates middle to late Eocene paleotemperatures of 10-17C in Seymour Island and ~7°C higher in the Eastern Tasman Plateau, suggesting a pronounced zonal heterogeneity in southern high latitude sea surface temperatures. ...»

Abstract: Globally correlatable marine magnetic anomalies record past polarity reversals and changes in the strength of the dipolar geomagnetic field. Traditionally, plate reconstruction models rely on reversals-related anomalies leading to a well-known major temporal gap and tectonic ambiguities in the existing kinematic models for the Cretaceous normal superchron (83.5-120.6 Ma), a long period when no polarity reversal took place. Recent findings on the behaviour of the geomagnetic field during the superchron (Granot et al., 2012) provide new time markers that may be used to define internal isochrones within the Quiet Zones. Based on these features I present a new kinematic model for the opening of the South Atlantic. New sets of finite rotation parameters illuminate in details the break-up and initial drift of Africa and South America. Based on these new rotations I present the first magnetically-constrained opening model for the Equatorial Atlantic Gateway. ...»

Abstract: In this talk I will introduce my research on scale interactions in oceanic processes and the implications of these interactions on the large-scale circulation. I will discuss the nature and importance of scale interactions in the physics of the ocean and the ocean's role in the climate system, and why our understanding of these interactions is critical to our ability to model the ocean in climate models, interpret our observations and simulations of the oceanic circulation, and design effective observing systems. I will then describe two examples from my current research that aim to further our understanding of specific ocean processes in which scale interactions are key: 1. a study of eddy-mean flow interactions in oceanic western boundary current systems such as the Gulf Stream and Kuroshio Extensions, and 2. work on wave-mean flow-turbulence interactions in a Southern Ocean mixing hotspot. Each considers different interacting scales and examines different processes which in turn have different impacts on the larger-scale circulation. They share however a common aim, to understand the physical mechanisms underpinning the observed system behaviour, as well as a common approach, uniting process-targeted observations and idealised process modelling. ...»

Abstract: What is an optimal particle shape for scattering, e.g., shape causing minimal extinction among those of equal volume and randomly oriented? Guided by the isoperimetric property of a sphere, relevant in the geometrical optics limit of scattering by large particles, we examine an analogous question in the low frequency (induced dipole moment) approximation, seeking to disentangle electric and geometric contributions. To that end, a simple proof is supplied of spherical optimality for a coated ellipsoidal particle and a monotonic increase with asphericity is shown in the low frequency regime for orientation-averaged induced dipole moments and scattering cross-sections. Physical insight is obtained from the Rayleigh-Gans (transparent) limit and eccentricity expansions. We propose linking low and high frequency regime in a single sweeping minimum principle valid for all size parameters, provided that reasonable size distributions wash out the Mie resonances. This proposal is further supported by the sum rule for integrated extinction. Implications for environmental remote sensing are discussed throughout the talk. ...»

Abstract: The Gulf of Eilat is an elongated, deep basin in the northern Red Sea. We investigate various mixing processes using recent observational data acquired from a combination of moored platforms and HF coastal radar. We present the first regular ,high vertical resolution profiles of density and velocity and the first deep, long-term profiles of velocity and high frequency temperature measurements collected in the Gulf of Eilat. > The variability of the stratification and its effect on the magnitude of alongshore semi-diurnal tidal currents in the northern Gulf of Eilat/Aqaba are examined using recent observational data acquired from a combination of moored platforms. The variability of the stratification consists of both periodic and episodic components and occurs over a range of time scales, from hourly to seasonal. Large amplitude, tidally-driven internal waves were observed throughout the year under different stratification conditions. Episodic cooling and warming events were observed during convective mixing in winter and re-stratification in spring. The magnitude of the alongshore semi-diurnal tidal currents is strongly correlated with the stratification. > Lateral mixing is examined using surface current measured by HF radar. Here, we modify the traditional random-walk stochastic model to include a large-scale flow (obtained from a numerical model, satellite measurements, or HF radar surface current measurements) that varies in both space and time. A stochastic term is added to represent sub-grid-scale, or unresolved, turbulence and is related to the horizontal eddy diffusivity and thousands of virtual particles are transported by the large-scale flow and the stochastic "jumps." The magnitude of the eddy diffusivity is increased until the barrier is no longer present in the flow field, thus providing an estimate of the upper bound of the horizontal eddy diffusivity. ...»

Abstract: Water-rock interactions in the Earth's crust often modify the pore space and permeability of rocks, soils, and sediments, changing the way fluids flow in the subsurface. Crucially, such geochemical reactions are often controlled by nano-scale processes. In this study, we use atomic force microscopy to examine dissolution rates of limestone; crucially, our measurements show that the rate of mineral dissolution within micron-size pores is much lower than the rate of dissolution on surrounding polished mineral surfaces. In addition, we use numerical simulations to show that this difference cannot be explained using a diffusion - surface reaction model. We propose that the observed variation in reaction rates could instead be due to the elevated density of reactive high curvature features on the polished surfaces. These features can strongly affect local interfacial free energy, making surfaces more prone to dissolution. As a result, polished surfaces should be more reactive than pore surfaces that have effectively been smoothed during prolonged contact with natural fluids. As standard rate experiments routinely use polished and powdered samples, our findings may help to explain the widely reported discrepancy between lab and field-based dissolution rates. ...»

Abstract: The ocean covers 70% of the earth surface, and influences almost every aspect in our life, such as climate, fuel, security, and food. All over the world, including Israel, depleting resources on land are encouraging increased human activity in the ocean, for example: gas drilling, desalination plants, port constructions, aquaculture, bio-fuel, and more. These expanded activities influence the delicate ecology that is already threatened by global warming and ocean acidification, and present a risk of over-exploitation. The ocean is a complex, vast, foreign environment that is hard to explore and therefore much about it is still unknown. Interestingly, only 5% of the ocean floor has been seen so far. As human access to most of the ocean is very limited, optical imaging systems can serve as our eyes in those remote areas. However, optical imaging underwater is challenging due to intense pressures at depth, strong color and distance dependent attenuation, refraction at the interface air/water, and the ever-changing and rugged conditions of the natural ocean. In this talk I describe several imaging systems I developed and show how they can be used to solve acute scientific problems. These include an underwater in-situ high-resolution benthic microscope and systems for in-situ wide-scale multispectral and fluorescence imaging. ...»

Abstract: Fractures are abundant in many geological formations and are often the main pathways for fluid flow. They hence control many different geological processes, ranging from oil production from the world's largest hydrocarbon reservoirs to heat extraction from enhanced geothermal systems, subsurface storage of greenhouse gases, or the migration of methane in gas-bearing sediments - even the formation of many world class ore deposits is, primarily, controlled by the presence of fractures. Yet, it is often the fluid transfer between fractures and matrix, driven by capillary forces, which determines, for example, how well hydrocarbons can be extracted from the subsurface or how readily greenhouse gases are trapped in a geological formation. This talk will discuss how novel pore-scale modelling techniques can be used to analyse the emergent behaviour of capillary forces in complex porous media, how capillary-driven exchange between fractures and matrix can be quantified using a universally applicable scaling law, and how both aspects can be combined to develop more robust and much-needed conceptual models that describe multi-phase flow in fractured geological formations. ...»

Abstract: Organic material accounts for a large fraction of atmospheric aerosol, with the majority being secondary organic aerosol (SOA) formed through oxidation processes. Primary emissions leading to SOA include thousands of chemicals from a variety of natural and anthropogenic sources ranging over approximately 15 orders of magnitude of volatility. As organics are oxidized they fragment to form smaller volatiles or add functionality leading to SOA formation, dramatically increasing the complexity of compounds present. A continuing challenge in aerosol research is to elucidate the sources, structure, chemistry, fate, climate and health impacts of these organic atmospheric constituents. The complex chemical composition of organic aerosols presents unique measurement challenges. My group and close collaborators have developed the Thermal Desorption Aerosol Gas chromatograph (TAG) system for hourly in-situ speciation of a wide range of primary and secondary organic compounds in aerosols. This instrument combines a particle collector with thermal desorption followed by GCMS detection to provide hourly separation, identification, and quantification of organic constituents at the molecular level. We incorporated two-dimensional chromatography (GCxGC), providing dramatically enhanced speciation. We developed a semivolatile collection and analysis system that allows simultaneous measurement of specific organics in the gas and particle phases, enabling analysis of their partitioning. We also developed a combined TAG-AMS (Aerosol Mass Spectrometer) instrument for simultaneous measurements of the total and speciated aerosol composition. We are currently exploring soft ionization with vacuum ultraviolet radiation using a high resolution time of flight mass spectrometer (GCxGC/VUV-HRTOFMS) to more fully separate and identify compounds in complex mixtures such as diesel fuel, motor oil, fire emissions, in controlled oxidation studies, and in ambient samples. This talk will review recent developments (TAG, 2DTAG, SVTAG, TAG-AMS, GCxGC/VUV-HRTOFMS), and present new atmospheric observations, source characterizations, and controlled oxidation studies to more fully characterize atmospheric organic sources and transformation processes. ...»

Abstract: Abstract: Today, hundreds of extrasolar planets have been detected and their number is increasing at a rapid pace. The discovery of planets outside the solar-system opens an opportunity to learn about planets as a class. However, a substantial improvement in our understanding of extrasolar planets, in particular, their physical properties, is not possible without detailed investigation and better understanding of the solar-system planets. I will briefly discuss how planetary interiors are modeled, and will present interior models of the four solar-system outer planets, i.e., Jupiter, Saturn, Uranus and Neptune, including the main uncertainties in planetary composition and interior structure. Recent results, open questions, and future investigations will be presented. ...»

Abstract: Do all raindrops fall at terminal speed? Recent speed versus size measurements of drops during natural rainfall show that sub-mm raindrops often fall up an order of magnitude faster than expected. Furthermore, images of drop clusters reveal that these ‘‘super-terminal drops’’ are differently sized fragments of a recent break-up, moving with the speed of the parent drop and relaxing towards steady fall. Immediately after breakup, the pieces, disembarking off a common carrier, move at about the same (relatively high) speed. Along with reviewing the physics of drop breakup, I shall discuss possible implications, e.g., disdrometers and Doppler radars. ...»

Abstract: In the highly spectrally variable world of atmospheric radiation, some simple algebraic combinations of single scattering albedo, reflected and/or transmitted radiation spectra depend little on wavelength. As an example, under some rather general conditions, the ratio of the radiation leaving clouds to single scattering albedo is a linear function of the same radiation. In the talk we will identify these spectrally-invariant combinations and discuss the physics (and some mathematics) behind them. Using the results of SBDART simulations, we will test the extent to which the assumptions behind spectral invariance are valid for cloudy atmospheres. Finally, the applications of spectral invariance for climate and remote sensing problems will be briefly crystal-balled. ...»

Abstract: Abstract Nonlinear interactions between sea waves and the bottom are a main mechanism of energy transfer between the different wave frequencies in the near-shore region. In this region, nonlinear interactions act much faster than in deep water due to quadratic resonance interactions. One of the methods for solving this flow regime is using quadratic nonlinear mild-slope (MS) type wave models. These models consist of a linear mild-slope type equation for each wave harmonic coupled by quadratic nonlinear terms to all other harmonics. The first part of the talk will discuss the various options for formulating the magnitude of the wave number rather than the commonly used heuristic choice. This allows constructing models that allow for different types of solution methods, and gives a better overview for extending the formulation to two-dimensions. The second part will discuss the phase functions and the directions of the wavenumber vectors. This information is needed for constructing this type of models, and the problem of its formulation is what limits these models to one-dimensional propagation, or to two-dimensional ones with some crude assumptions. In the present work, governing equations for the wavenumber vectors and the phase functions are constructed in order to allow for rigorous derivations of each type of solution method for various wave propagation characteristics. This allows constructing equations for the two-dimensional propagation of oblique incident waves in various angles that interact both with each other and with the seabed. A perturbation approach is used in order to simplify these equations while keeping superior accuracy with respect to other models. Another extension to the commonly used models that will be presented, is the inclusion of nearly resonant interactions. For oblique propagation toward a beach with parallel bathymetry lines, this inclusion allows constructing a higher order correction that changes the nature of the solution causing the waves to evolve also in the lateral direction. In order to address as well people that are not from the field of water waves, some basic concepts of wave propagation will be discussed, and the main mechanisms for nonlinear energy transfer will be explained in an intuitive manner. ...»