Events

Abstract: Diamonds are perfect boxes for delivering samples of fluids and volatile species from the mantle to the surface. While mineral inclusions are often a few >30 micrometer in size and allow easy analysis, fluid inclusions are mostly <1 micrometer. Still, careful analysis allowed us to define carbonatitic, saline and silicic melts in the inclusions. Recently, transmission electron microscopy allowed us to look into even smaller inclusions, 10-30 nm in size where we found solid molecular nitrogen and solid molecular CO2. Contrary to the melts that are low volume mantle melts, the N2 and CO2 are interpreted as exsolutions of N and O atoms that were taken as single atoms in the diamond matrix and later migrated and joined to form tiny octahedrons full of N2 and CO2. Geologically, the solids are an oddity of nature, but the melts can play an important roll in the extraction of trace elements from the mantle and into the crust. Close abstractClose abstract

Abstract: The Hadley circulation is a key element of the climate system. It is traditionally defined as the zonally averaged meridional circulation in the tropics, therefore treated as a zonally symmetric phenomenon. However, differences in temperature between land and sea cause zonal asymmetries on Earth, dramatically affecting the circulation. This longitudinal dependence of the meridional circulation evokes questions about where and when the actual large scale tropical circulation occurs. Here, we look into the connection between the longitudinally dependent meridional circulation, and the actual large scale transport of air in the tropics using a coupled Eulerian and Lagrangian approach. Decomposing the velocity field into rotational and divergent components, we identify how each component affects the actual circulation. We propose an alternative definition for the circulation, that describes the actual path of air parcels in the tropics, as a tropical atmospheric conveyor belt. We further investigate this definition, analyzing the circulation under climate change and its effect on precipitation changes. We show that in order to predict future climate, the regionality and three-dimensionality of the large-scale tropical circulation must be taken into account. We find that the changes in the circulation vary significantly over longitude, and are overlooked when analyzing the zonally averaged meridional circulation. The circulation is strengthening and expanding in the center of the Pacific, a region where the circulation barely existed in past. On the other hand, the circulation is weakening in the Indo-Pacific region, where it was the most significant in the past. These differences appear as a shift in the region of ascent of the conveyor belt, that is revealed when analyzing the decomposed vertical wind. The pattern of weakening of the ascent in the Indo-Pacific and strengthening in the center of the Pacific explains the projected changes in precipitation. The Indo-Pacific region is drying, while the precipitation in the center of the Pacific is intensifying. Close abstractClose abstract

Abstract: Weather and climate extremes such as cold spells, heat waves, heavy precipitation or windstorms have long been considered challenging to adequately predict a few days in advance. Even at shorter time scales, it is sometimes difficult to estimate the magnitude and impact area accurately. Therefore, they have been selected as one of the grand challenges by the World Climate Research Program. Several studies suggest that extreme temperatures or heavy precipitation events may become more frequent and more intense with climate change, making this topic even more pertinent. The ability to predict the development of any dynamical system (a system that evolves in time), depends on: 1) its persistence, meaning that a persistent system will be easier to predict and 2) the number of options the system can develop into/from, meaning that systems with a small number of options will be easier to predict. Recent advances in dynamical systems theory allow to efficiently compute these metrics from model data. Our earlier findings show that the dynamical systems metrics can serve as an extremely informative qualitative method for evaluating the predictability and dynamics of synoptic systems over the Eastern Mediterranean. The talk will discuss this novel dynamic approach and its recent applications in extreme weather forecasting, as well as in climate model projections over the Eastern Mediterranean. Close abstractClose abstract

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 utilize the ambient seismic field, recorded on a standard telecommunication fiber deployed around the Stanford campus, to analyze subsurface properties. The same fiber can also be used to measure changes in traffic patterns due to the COVID-19 lockdown. With downhole DAS arrays deployed in deep vertical wells, we can study previously undetected low-magnitude earthquakes. Finally, we utilize DAS data recorded inside an unconventional gas field to unveil reservoir properties with unprecedented resolution. Close abstractClose abstract

Abstract: Supercooled clouds substantially impact polar surface energy budgets but large-scale models often underestimate their occurrence, which motivates accurately establishing metrics of basic processes. A polar stratiform cloud’s lifecycle is determined by a set of complex interactions and feedbacks between different micro-physical and macro-physical processes, some of which are not fully understood or quantified, leading to uncertainty in climate predictions. These polar clouds are commonly presupposed as being turbulent as a result of intense cloud-top longwave radiative cooling, while experiencing desiccation dominated by precipitating ice. In this talk, I examine some of these underlying assumptions and provide applicable guidance for large-scale model evaluation. I first present observations of persistent formation of drizzle drops at cloud temperatures below -25 °C detected over McMurdo Station, Antarctica. These supercooled drizzle observations supported by large-eddy simulations (LES) used to examine the cloud’s formation and evolution under initially stable, nonturbulent conditions, suggest that drizzle can be common over polar regions and serve as the main cloud moisture sink even well below the freezing temperature. A persistent nonturbulent cloud state suggested by the LES leads to the examination of nonturbulent cloud occurrence in observational datasets from Arctic and Antarctic ground-based sites. Such stable, nonturbulent conditions, surmised to preferentially occur early in cloud lifecycles, are estimated to prevail in a quarter of cloud occurrences over these polar sites. I use LES sensitivity tests to examine how short to intermediate period gravity waves, which are supported by such stable conditions, may catalyze turbulence formation when aerosol particles available for activation are sufficiently small. The observational datasets are also utilized to examine ice precipitation processes, and show that the vast majority of polar supercooled clouds are at least weakly precipitating ice at the cloud base even when they are not seeded from above, consistent with commonly observed supercooled cloud longevity. These results indicate that supercooled cloud layers are a sustained source of ice precipitation, and suggest that ground-based statistics offer valuable guidance for large-scale models. Finally, as an example of how some of these observational and modeling results may be used to evaluate the representations of polar clouds in large-scale models, I briefly describe using the GISS E3 climate model in single-column model (SCM) mode applied to the supercooled drizzle case study. Close abstractClose abstract

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. Close abstractClose abstract

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. Close abstractClose abstract

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. Close abstractClose abstract

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. Close abstractClose abstract

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). Close abstractClose abstract

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. Close abstractClose abstract

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. Close abstractClose abstract

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. Close abstractClose abstract

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. Close abstractClose abstract

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. Close abstractClose abstract

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. Close abstractClose abstract

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. Close abstractClose abstract

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. Close abstractClose abstract

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. Close abstractClose abstract

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. Close abstractClose abstract