Events

Abstract: Decadal Climate Predictions Using Sequential Learning Algorithms Ensembles of climate models are commonly used to improve climate predictions and assess the uncertainties associated with them. Weighting the models according to their performances holds the promise of further improving their predictions. Using an ensemble of climate model simulations from the CMIP5 decadal experiments, we quantified the total uncertainty associated with these predictions and the relative importance of model and internal uncertainties. Sequential learning algorithms (SLAs) were used to reduce the forecast errors and reduce the model uncertainties. The reliability of the SLA predictions was also tested, and the advantages and limitations of the different performance measures are discussed. The spatial distribution of the SLAs performance showed that they are skillful and better than the other forecasting methods over large continuous regions. This finding suggests that, despite the fact that each of the ensemble models is not skillful, the models were able to capture some physical processes that resulted in deviations from the climatology and that the SLAs enabled the extraction of this additional information. If time permits I will also present a method for estimating the uncertainties associated with ensemble predictions and demonstrate the resulting improved reliability. References: 1. Improvement of climate predictions and reduction of their uncertainties using learning algorithms, Atmospheric Chemistry and Physics 15, 8631-8641 (2015). 2. Decadal climate predictions using sequential learning algorithms, Journal of Climate 29, 3787-3809 (2016). 3. The contribution of internal and model variabilities to the uncertainty in CMIP5 decadal climate predictions, Climate Dynamics 49, 3221 (2017). 4. Quantifying the uncertainties in an ensemble of decadal climate predictions. Journal of Geophysical Research: Atmospheres 122, 13,191–13,200 (2017). 5. Learning algorithms allow for improved reliability and accuracy of global mean surface temperature projections. Nature Communications 11, 451 (2020). Close abstractClose abstract

Abstract: The maker movement (cheap electronics + sharing), automated microscopy, autonomous platforms and small footprint satellites have been revolutionizing oceanography, opening a variety of new avenues for research and requiring a different education model. In this talk I will summarize a few activities my lab has been involved in that are associated with these disruptive technologies and why I am very optimistic for the future of our field in the coming years. Close abstractClose abstract

Abstract: It is by now well established that certain stratospheric flow configurations may alter tropospheric dynamical variability. Such flow configurations include the aftermath of sudden stratospheric warming events (SSWs) or strong polar vortex events (SPVs). Although the detailed mechanisms behind this stratosphere-troposphere coupling remain elusive, most aspects of it are well-known. For example, the coupling involves feedbacks between upward propagating planetary waves of tropospheric origin and the mean flow, the tropospheric response involves synoptic-scale eddy feedbacks, SSWs tend to project onto negative anomalies of the Arctic and North-Atlantic Oscillation (AO, NAO), whereas SPVs tend to project onto positive anomalies of the AO and NAO. Here I will highlight some recent results on 1) the potential role of a planetary wave source near the tropopause in troposphere-stratosphere coupling, 2) the stratospheric influence on the evolution of baroclinically unstable waves during their non-linear decay phase, 3) the improved quantification of the stratospheric modulation of AO extremes from extended-range ensemble forecasts. Close abstractClose abstract

Abstract: The Great Lakes of the Earth are freshwater seas, and many of the geochemical processes that take place in their bottom sediments parallel those that happen in marine environments. The conditions, however, are different enough to significantly modify the geochemical cycles of key elements. By analyzing those differences, we can not only understand the functioning of the planet's largest freshwater ecosystems, but can also gain insight into the elemental cycling (C, N, P, S...) in the oceans during the past geological epochs. Close abstractClose abstract

Abstract: By economy of scale, imaging sensors can now be deployed densely and operated in a coordinated manner at large numbers in space, air, underwater and on the ground. Such distributed imaging systems enable multi-view setups across heterogeneous media of importance to geoscience. These create new observation modes. One outcome is 4D volumetric spatiotemporal recovery of scatterers in the atmosphere, specifically cloud content (the core of the CloudCT space mission). This is in addition to computed tomography of underwater sediment suspension and atmospheric turbulence distributions. We describe several such systems - demonstrated in the field, including both distributed imaging and the basis of the algorithms to analyze the data. Close abstractClose abstract

Abstract: Extreme temperatures have warmed substantially over recent decades and are expected to continue warming in response to future climate change. Warming of extreme temperatures is projected to be amplified over land, with severe implications for human health, wildfire risk and food production. Using simulations from coupled climate models, I show that hot days over tropical land warm substantially more than the average day. For example, warming of the hottest 5% of land days is a factor of 1.2 larger than the time-mean warming averaged across models. The climate-change response of extreme temperatures over tropical land is interpreted using a theory based on convective coupling and the weak temperature gradient approximation. According to the theory, warming is amplified for hot land days because those days are dry: this is termed the “drier get hotter” mechanism. Changes in near-surface relative humidity further increase tropical land warming, with decreases in land relative humidity particularly important. The theory advances physical understanding of the tropical climate and highlights climatological land-surface dryness as a key factor determining how extreme temperatures respond to climate change. Close abstractClose abstract

Abstract: Natural hazards such as extreme wind, rainfall and ocean waves can have severe impacts on built and natural environments, contributing to the occurrence of disastrous events in some cases. These hazards are often caused by weather systems such as cyclones, fronts and thunderstorms. We have used a number of objective techniques to identify these weather system types, in order to understand the links between the weather systems and hazards in observations. We have then used this understanding to evaluate climate models and to better understand the response of the weather systems and the high impact hazards to a warmer climate. Close abstractClose abstract

Abstract: The vast majority of detected planets are observed indirectly, using their small perturbation on the light emitted by the host stars. In recent years, however, the world's largest ground based telescopes have succeeded in directly imaging the light coming from some planets themselves. I will present our comprehensive theory for the mass, luminosity, and spin of gas giant planets during their final stages of formation - when they simultaneously contract and accrete gas from a disk. I will apply this theory to the luminosity and spectrum obtained by the novel direct-imaging technique, highlighting the recently discovered PDS 70 system, where two planets were directly observed during formation for the first time. Close abstractClose abstract

Abstract: Persistent summer weather can have significant socio-economic impacts. Prolonged hot-dry conditions may lead to crop yield losses, while consecutive rainy days (e.g. associated with stalling cyclones) can cause flooding. Both observational and climate model analyses indicate that global warming weakens the hemispheric-wide circulation in boreal summer, yet it is still largely unclear what this weakening implies for the persistence of regional weather conditions. Here, I present multiple lines of evidence supporting that weather persistence in summer has been increasing over the last 40 years over most mid-latitude regions and will continue to do so under future global warming. Methodologically, we use a persistence metric rooted in dynamical systems theory, which does not require partitioning instantaneous atmospheric states in an arbitrary number of clusters. This makes it ideally suited to detect subtle changes in atmospheric motions including weather-persistence. I discuss relevant recent literature and argue that there is now substantial evidence for increasing weather persistence over mid-latitude regions, providing enhanced extreme weather risks for society. Close abstractClose abstract

Abstract: Ice sheets can dramatically impact the state of climate. This is due to their capacity to modify the planetary energy balance through variations in the ice cover and mass. A major question is how rapidly could such modification occur and to what extent ? This question can be addressed by investigating phenomena that involve relatively large mass flux of ice into the ocean, such as ice calving and rifting, ice streams, and melting. Many of these processes involve interactions between the ice sheet and the underlying bedrock or ocean. We model ice sheets as buoyancy-driven flows of nonlinear (non Newtonian) fluid and explore the resulted flow dynamics and stability due to different friction conditions along the base of the ice. I will show results from scaled laboratory experiments and theoretical modelling of several flows under different friction conditions that evolve patterns reminiscent to those that emerge in glacier ice flows. Specifically, the basal friction that we consider ranges from no-slip conditions, in which radially symmetric flows are stable, to free-slip conditions, in which such flows are unstable, developing patterns reminiscent to ice rifts and ice bergs. Under mixed conditions of friction, an initially radially symmetric flow can be either stable, or develop patterns reminiscent to ice streams. Our insights may have implications to predicting ice flow on Earth and possibly on other planetary objects. Close abstractClose abstract

Abstract: The study of past warm climates with high atmospheric CO2 concentrations provides important tools for understanding present trends and developing mitigation strategies for future scenarios. The Pliocene is the last long lasting warm interval characterized by similar global climate circulation patterns and continental settings as today. Reconstructing Pliocene climate change from well-dated geological archives provides valuable insights into the climate forcing and pathways that modulated the transfer of heat and humidity and disentangle regional impacts without anthropogenic influence. To address this challenge, the current presentation shows initial results from a comprehensive study that amalgamates high-resolution multi-proxy analyses from both marine and lacustrine records from the Levant region aiming to provide an important reference for future climate and environment change scenarios under high atmospheric CO2 concentrations. Close abstractClose abstract

Abstract: Layered halite sequences were deposited in deep hypersaline basins throughout the geological record. These sequences are of research interest for hydrocarbon extraction, mineral exploration, tectonics and structural geology and paleoclimate research. Modern analogs and the processes leading to deposition of thick halite sequences were studied only through analyses of the common modern, shallow environments, which are fundamentally different in their nature from halite-depositing, deep waterbodies. Thus, the spatiotemporal evolution of halite sequences remained ambiguous. I will present, first, a study of the active precipitation of halite layers from the only modern analog in the world for deep, halite-precipitating basin; the hypersaline Dead Sea. Then the implications of these results to the geological record will be emphasized. Novel in situ observations in the Dead Sea link seasonal hydroclimatic conditions, thermohaline stratification, halite saturation, and the characteristics of the actively forming halite layers. The main findings of this study are: (a) Halite deposition dynamics is directly related to the development of the thermohaline stratification and it is primarily temperature controlled; it is counter-intuitive to the common approach that focus on the role of the hydrological budget in the study of hypersaline environments. (b) A pronounced depth dependency of the degree of halite saturation and halite deposition. (c) A well-defined seasonality of halite deposition on the deep lakefloor. (d) Preferential halite accumulation at the deep, hypolimnetic lake floor (>25m depth) due to intensive halite dissolution at the shallow epilimnetic lakefloor, and its re-deposition at depth, in a process termed “halite focusing”. (e) Halite accumulates at high rates in the deep lakefloor, doubling (or even more) the expected thickness without halite focusing. (f) Freshwater inflows further amplify halite thickness at the drier parts of the lake. These findings provide insights and quantify the processes required for reconstructing past hypersaline environments from halite sequences, in the Dead Sea and worldwide. Close abstractClose abstract

Abstract: Sand seas on Mars are riddled with eolian landforms created by accumulating sand particles. When the sand supply is limited and the wind is approximately unidirectional, these landforms take the shape of crescentic barchan dunes, whose slip-faces are approximately perpendicular to the dominant wind direction, and their horns are oriented downwind. The morphology of barchan dunes is thus routinely used to infer wind conditions on Mars by manually analyzing aerial or satellite imagery. Despite the effectiveness of this technique on a local scale, employing it on a global scale remained challenging thusfar - as manually outlining individual dunes globally is impractical, and automatic detection methods have been largely ineffective at accurately segmenting dunes in images. Here we use Mask R-CNN, an instance segmentation convolutional neural network, to detect and outline dunes globally on Mars in images obtained by the Mars Reconnaissance Orbiter Context Camera (MRO CTX). We measure the morphometrics of dunes from their detected outlines, and infer the direction of the winds that formed them. By comparing the global wind distribution we derived to a global climate model, we study Mars' past and recent climate, and constrain global sand mobility thresholds which offer insight into the erosion and dust lifting capabilities of the atmosphere of the Red Planet. Close abstractClose abstract

Abstract: Near the ocean surface, mixing and turbulence modulate the transfer of heat, momentum, carbon and other properties, between the atmosphere and ocean interior. Accurate representation of these processes in General Circulation Models (GCMs) is crucial for simulating atmosphere-ocean interactions. However, all of these processes, generally known as boundary layer turbulence and submesoscale mixing, are on scales smaller than the grid used in GCMs, even at the highest possible resolution. Current submesoscale parameterizations represent the bulk of mixing developed across submesoscale fronts– the sharp interface between waters of different densities– but it has been shown to be too simplistic and unfitting in many circumstances. The presence of turbulence has been missing from these dynamics, and in this talk I will discuss the long-lasting problem of how to correctly include them. 
Building toward a more complete understanding of these processes, a theoretical approach of perturbation analysis is used to include the effects of turbulence as a correction to classic frontogenesis (frontal sharpening) theory. This approach is next extended into a more realistic environment, using a suite of high resolution, turbulence resolving, numerical simulations. It is found that a variety of turbulent processes resulting from winds, waves, convection, and instabilities affect the formation of fronts. Furthermore, this analysis exposes severe limitations in existing techniques to predict potential vorticity dynamics in highly turbulent regimes. Lastly, I will discuss modifying the submesoscale parameterization in GCMs to represent the complex interactions with boundary layer turbulence. Close abstractClose abstract

Abstract: The Atlantic Meridional Overturning Circulation (AMOC) is a circulation pattern of great climatic importance. Its northward heat flux at the upper water column moderates European winter climate, and its descending branch captures atmospheric CO2 into the deep ocean, hence buffering the anthropogenically induced rise in global temperature. The Deep Western Boundary Current (DWBC) has classically been considered to be the main AMOC conduit southward at depth. However, tracer data have shown in recent decades that the DWBC "leaks" most of its material to the ocean interior in a small region of the North Atlantic, and that this leaked material continues southward in different, complex routes. These pathways and their causes are still little-explored and not well understood. In this talk I will present analysis of the DWBC leakiness properties and dynamics, based on existing datasets of passively drifting floats, a new high resolution regional numerical model, and theoretical analysis. Several alternative mechanisms of leakiness are considered, and a novel finding is that a leading cause for the leakiness is inertial separation of the current from the seafloor, near underwater capes. The role of eddies and their interaction with the separation process is investigated as well. Implications for the robustness of the deep AMOC pathways are discussed. Close abstractClose abstract

Abstract: The rapid retreat of the Dead Sea during the past decades led the exposure of unique structures of massive gypsum and aragonite crusts: large capes pointing towards the open lake (termed here “gypsum deltas”) and numerous small gypsum mounds scattered on the lake’s exposed shores. Geological field relations, 14C and 34S measurements and thermodynamic calculations provide evidence that the gypsum deltas and the mounds were formed during time-intervals of low lake stands (~420±10 m below mean sea level), when sulfate-rich Ca-chloride brines discharged from the coastal aquifer via saline springs, mixed with the Dead Sea brine and precipitated the gypsum. This mixing process describes a mechanism of “gypsum outsalting”, which is completely different from the conventional view of gypsum as a product of evaporative deposition. Condition for enhanced saline springs discharge and “gypsum outsalting” occurred in the mid to late Holocene period (~ 6.6 to 0.6 ka), and were mainly intensive at the latest stages of regional aridity cycles when lake level was still low and the Dead Sea salinity was at its highest. The ages of formation of the gypsum structures coincide with times of North Atlantic cooling events and grand solar minima suggesting a direct impact of the latter on the Dead Sea hydrology and high sensitivity of the regional hydrology (controlling lake level) to global solar-related events. The frequency of appearance of the gypsum structures seems to follow the Hallstat Cycle that approached minimum at ~3000 2000 years ago. Close abstractClose abstract

Abstract: Global climate models represent small-scale processes, such as clouds and convection, using subgrid models known as parameterizations. Traditional parameterizations are usually based on simplified physical models, and inaccuracies in these parameterizations are a main cause for the large uncertainty in climate projections. One alternative to traditional parameterizations is to use machine learning to learn new parameterizations which are data driven. However, machine-learning parameterizations might violate physical principles and often lead to instabilities when coupled to an atmospheric model. I will show how machine learning algorithms, such as neural networks and random forests, can be used to learn new parameterizations from the output of a three-dimensional high-resolution atmospheric model, while obeying physical constraints such as energy conservation. Implementing these parameterizations in the atmospheric model at coarse resolution leads to stable simulations that replicate the climate of the high-resolution simulation, and capture important statistics such as precipitation extremes. I will also discuss how machine-learning parameterizations can give further insights into the parameterization problem. Specifically, I will show that failures of machine-learning parameterizations can be used to better understand the relationship between large-scale fields and subgrid processes. Close abstractClose abstract

Abstract: Hydrological systems are inherently non-linear and exhibit an enormous structural and functional heterogeneity. Strikingly, we can nevertheless successfully simulate stream flow generation and the water balance of river catchments with rather simple models that are largely incompatible with the frequently reported subscale process heterogeneity and non-linearity. Here we argue that subscale structural heterogeneity and randomness must not prevent the emergence of functional simplicity. On the contrary, we found simplicity to emerge at rather small scales, reflecting self-organization in hydrological functioning not despite but due to subscale small-scale heterogeneity and the dissipative nature of hydrological process. While we acknowledge that hydrological landscapes are heterogeneous, they are by no means a random product. Catchments exhibit a considerable spatial organisation, which manifests through structured patterns of topography, soil, vegetation, self-similar surface and subsurface drainage networks and most prominently through ubiquitous preferential flow phenomena. While this organized “catchment from” does strongly determine present storage, cycling and release of water, energy and chemical species, this catchment form has in turn been shaped by of water, energy, and nutrients of the past. Is this “co-evolution” just chance or manifested self-organization? This question has been inspiring many scientists to search for thermodynamic principles that link form and function in the Earth system. Here we will present evidence that a thermodynamic and information theoretic perspective opens up new avenues for (i) diagnosing and explaining self-organization in hydrological dynamics, (i) upscaling of constituting relations and (i) using thermodynamic optimality for hydrological predictions. Close abstractClose abstract

Abstract: A subset of megathrust earthquakes produce anomalously large tsunamis for their magnitude. All of these recorded ‘tsunami earthquakes’ in the past 50 years had extensional aftershocks in the upper plate. These include the two largest and most destructive earthquakes of that period, the 2004 Sumatra–Andaman and the 2011 Tohoku events. Evidence from the region of Tohoku indicates that normal fault slip in the upper plate during the earthquake may have contributed to the tsunami size. Here we present a numerical model that shows how a reduction of the dip of a subducting slab, on a timescale of millions of years, can result in an extensional fault failure above a megathrust earthquake on timescales of seconds to months. Slab dip reduction bends the upper plate so that the shallow part fails in extension when a megathrust rupture relieves compressional stress. This results in a distribution of extensional aftershocks comparable to that seen above the Tohoku megathrust. Volcanic arc migra- tion and uplift data for Tohoku and several other tsunami earthquakes is consistent with slab dip reduction. The collection of more such data might identify other areas of tsunami hazard related to slab dip reduction. Close abstractClose abstract

Abstract: Forests and agricultural orchards are becoming increasingly susceptible to drought, ‎insect ‎‎outbreaks, and disease due to climate change worldwide. Thus, forest ‎and ‎agricultural systems management needs to be proactively targeted to improve their ‎resilience to anthropogenic and ‎climate change. The potential of remote sensing ‎data for ‎agriculture and forestry has long been recognized. The global coverage and repositories of different ‎types ‎of satellite data extending integrating with developing UAVs and ‎sensor ‎capabilities provide a unique database, which allows us to develop, test, and ‎implement ‎innovative measures to adapt agriculture and forest to the foreseen climate ‎scenarios. ‎However, there is still a considerable gap between data and information. ‎Remote sensing ‎applications integrated with innovative artificial intelligence techniques ‎could make ‎fundamental discoveries for sustainable environmental management. Thus, ‎the seminar ‎aims to present advanced remote-sensing applications for agriculture and ‎forest to climate ‎change adaptation. Four case studies will be presented, including (1) ‎mapping woody ‎species distribution and richness along the climatic gradient; (2) ‎developing canopy ‎geometry traits to characterize and monitor tree structure using LiDAR ‎applications; and (3) ‎Incorporation winter tree physiology in deciduous orchard into ‎forecast- models of bloom ‎and yield, and (4) leaf to landscape approach to study ‎forest responses to drought. Close abstractClose abstract

Abstract: Contamination of drinking water sources by a variety of organic and inorganic compounds demands more efficacious and reliable treatment technologies. However, conventional water treatment technologies remain chemically demanding, energy intensive, and ineffective in removing key trace contaminants. As such, nanotechnology-based approaches have been increasingly explored to enhance or replace traditional remediation methods because of the high reactivity and tunable-properties of nanomaterials. In her talk, Dr. Zucker will provide an overview on the current status of nano-enabled water decontamination, including promising opportunities and barriers for implementation. Specifically, the application of molybdenum disulfide (MoS2) for heavy metal removal will be extensively discussed as a case study, where material properties, removal mechanisms, and large-scale applications are optimized. Close abstractClose abstract

Abstract: Conventional hydrogeologic models employed to compute ocean island sustainable yields and aquifer storage neglect the nearshore and onshore submarine environment’s complexity. However, the onshore aquifer at the island of Hawaiʻi exhibits a significant volumetric discrepancy between high-elevation freshwater recharge and coastal discharge. This study presents a novel transport mechanism of freshwater moving from onshore to onshore via a multilayer formation of water-saturated layered basalts with interbedded low-permeability layers of ash/soil, as revealed by marine-controlled source electromagnetic (CSEM) imaging. We propose that this newly discovered transport mechanism of fresh water may be the governing mechanism in other volcanic islands. Additionally, our water column CSEM imaging detects multiple vertical freshwater plumes extending from the seafloor to the ocean surface. These findings provide valuable information to elucidate hydrogeologic and oceanographic rocesses affecting biogeochemical cycles in coastal waters worldwide. Close abstractClose abstract

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