Events

Abstract: Seismic waves excited by human activity frequently obscure signals due to tectonic processes and are discarded as a nuisance. Seismic noise-field analysis is, however, a powerful tool for characterizing anthropogenic activities. In this talk, I will briefly review the seismological fingerprints of anthropogenic noise sources and then present a scheme devised to identify precursory activity leading to the October 7 terrorist attack. The precursory activity in Gaza included massive mobilization, documented by multiple media outlets. Favorable conditions arose due to a temporary lack of anthropogenic activity in Israel, allowing remote seismic stations to record signals due to Gaza vehicle traffic in the early hours of Oct. 7. Seismogram analysis reveals a widespread signal that abruptly emerged above the nighttime noise levels about 20 minutes before the attack began. Statistical analysis suggests the signal is highly anomalous; tests for significance indicate that pre-attack inter-station correlations would emerge by chance only once every 18,000 years. Tripartite array analysis was used to detect surface waves, locate their sources, and demarcate the extent of preattack activity within the Gaza Strip. The signal’s amplitude, frequency, and spatiotemporal distribution appear to be aligned with vehicular traffic emanating from the south-central region of the Gaza Strip and extending towards its peripheries in the half-hour window preceding the invasion. This provides valuable tactical information and suggests embedding seismic noise-field analysis into decision-making protocols could enhance preparedness for terrorist attacks. Close abstractClose abstract

Abstract: Climate change is having an impact on agricultural production and food security. Rising temperatures, changes in rainfall patterns and extreme weather events can reduce crop yields, sometimes dramatically. However, climate change can also offer new opportunities, by generating more favorable climatic conditions for agricultural production in certain regions that were previously less productive. In order to assess the positive and negative impacts of climate change on agriculture and identify effective adaptation strategies, scientists have produced massive amounts of data during the last two decades, conducting local experiments in agricultural plots and using models to simulate the effect of climate on crop yields. In most cases, these data are not pooled together and are analyzed separately by different groups of scientists to assess the effects of climate change at a local level, without any attempt to upscale the results at a larger scale. Yet, if brought together, these data represent a rich source of information that are relevant to analyze the effect of climate across diverse environmental conditions. The wealth of data available has led to the emergence of a new type of scientific activity, involving the retrieval of all available data on a given subject and their synthesis into more robust and generic results. In this talk, I review the statistical methods available to synthesize data generated in studies quantifying the effect of climate change on agriculture. I discuss both the most classic methods - such as meta-analysis - and more recent methods based on machine learning. In particular, I show how this approach can be used to map the impact of climate change on a large scale (national, continental and global) from local data. I illustrate these methods in several case studies and present several research perspectives in this area. Close abstractClose abstract

Abstract: Microorganisms play a crucial role in the weathering processes that transform rock into soil through chemical and physical mechanisms essential for nutrient cycling, nitrogen fixation, carbon storage, and organic matter decomposition. This intricate relationship between microbial life and landscapes forms the backbone of ecosystem dynamics and biogeochemical processes. Microbes influence rock weathering and soil production, adapting to their surroundings and creating distinct communities across various landscapes. These complex interactions and feedback mechanisms are pivotal to understanding the co-evolution of microbial communities and landscapes over time. However, existing research on microbial contributions to weathering and soil production has predominantly focused on relatively short timescales and small spatial scales. Understanding the interplay between the evolution of microbial communities and their role in weathering processes over geomorphic timescales within transient landscapes is important for a more complete understanding of how landscapes evolve as well as the impact of geomorphic changes on microbial community establishment and evolution. The main objective of this study is to elucidate the long-term dynamics of microbial communities and their role in weathering processes over millennial timescales. To achieve this, we focused on recently deglaciated basins in the Eastern Sierra Nevada, CA, examining bacterial community composition in three phases of the weathering process: exposed rock at the surface, saprolite—the weathered rock found beneath soil, and soil. Sampling along an elevational transect, we collected 25 samples of rock, soil, and saprolite, and evaluated their bacterial composition using 16S rRNA and metagenomic sequencing. Results show that both soil and saprolite samples exhibited diverse and similar microbial communities, indicating a developmental relationship between these habitats despite distinct geochemical compositions. In contrast, rock habitats are less diverse, and their composition resembles those of young deglaciated landscapes. Our findings point to a link between microbial community composition and rock-to-soil weathering processes, suggesting that the majority of weathering processes occur within the soil column (saprolite and soil), with exposed rock maintaining a steady state. The stability of these microbial communities over extended timescales suggests a potentially significant role for microbial weathering in landscape evolution. This finding underscores the importance of considering microbial contributions in future geomorphic studies, as they may play a key role in shaping the Earth's surface. Moving forward, we plan on coupling a long-term, landscape-scale geomorphic perspective with 'omics approaches from microbial ecology to comprehensively understand the complex relationships between microbial life and landscapes, ultimately advancing our knowledge of ecosystem dynamics and health. Close abstractClose abstract

Abstract: Aerosol-cloud interactions are extensively studied to understand the climatic effect of anthropogenic aerosols, as the latter can change the radiative properties of clouds. Despite the clear presence of different cloud morphologies (i.e., the spatial variation of cloud thickness), the impact of aerosol-cloud interactions under different cloud morphologies is often overlooked. I will show that accounting for cloud morphology is essential for a better process understanding and for an accurate assessment of the radiative forcing due to aerosol-cloud interactions. Close abstractClose abstract

Abstract: Flood is the outcome of complex processes interacting at a range of scales. Flood generation and its magnitude depend on different precipitation and surface properties. As the climate becomes warmer globally, precipitation patterns are changing and, consequently, altering flood regimes. Resolving the expected changes in flood properties requires examining projections of precipitation features most correlated with floods. While the redistribution of mean annual precipitation amounts is generally known, the trends in many other essential factors controlling floods are yet to be resolved. For example, flash flood magnitude is sensitive to space-time rainstorm properties such as areal coverage or storm speed. Still, knowledge of how these properties are affected by global warming is lacking. Maximal rain rates for duration relevant to the watershed’s response time are also crucial parameters controlling the flood discharge. There is some understanding of how extreme rain rates change, but the magnitude and sign depend on the rain duration considered. Changes in frequency and the intra-seasonal distribution of precipitation events also affect flood regimes. Finally, watersheds of different properties are sensitive to different precipitation features, and thus, different watersheds may respond differently to global warming. In this talk, we will present the complexity of flood response under global warming and then focus on two questions: 1) how does global warming affect heavy precipitation events (HPEs) in the eastern Mediterranean, and 2) how these effects are imprinted in the resulting floods in small-medium Mediterranean watersheds. We simulated 41 eastern Mediterranean HPEs with the high-resolution weather research and forecasting (WRF) model. Each event was simulated twice: under historical conditions and at the end of the 21st-century conditions (RCP8.5 scenario) using the “pseudo global warming” approach. Comparison of precipitation patterns from the paired simulations revealed that heavy precipitation events in our region are expected to become drier and more spatiotemporally concentrated, i.e., we expect higher rain rates on smaller coverage areas and shorter storm durations that, in total, yield lower amounts of rainfall. These effects have some contradicting signs, and their full hydrological impact on streamflow peak discharge and volume was further explored. Ensembles of spatially-shifted rainfall data from the simulated HPEs were input to a high-resolution distributed hydrological model (GB-HYDRA) representing four small-medium-size watersheds (18–69 km2) in the eastern Mediterranean (Ramot Menashe). Flow volume is significantly reduced in future HPEs, while the change in flood peak is more complicated due to the combined effect of precipitation amount (decreasing) and precipitation rate (increasing). For the watersheds examined in this research, which are mostly agricultural, flood peaks at the watershed outlets are mostly reduced. The dynamics of flood generation at sub-watersheds of different sizes and properties are further examined in this research to understand scenarios for lowering or increasing flood peaks. This study emphasizes that detecting and quantifying global warming impact on space-time precipitation patterns is essential for flood regime projection. Close abstractClose abstract

Abstract: Located in a highly sensitive subtropical climate area and a densely populated area, Lake Kinneret is poised to undergo both natural and human-induced transformations in the coming decades. The lake is thermally stratified throughout most of the year and mixes thoroughly each winter when the epilimnion (upper layer) water temperature reaches equilibrium with the hypolimnion (bottom layer) water temperature by surface cooling and turbulence. Both the stratified and the fully mixed periods has a significant role in the Kinneret’s ecological system. Observation shows that air above the Lake is warming in a rate of 0.4oC/decade, while the epilimnion and hypolimnion are warming in a rate of 0.3oC/decade and 0.1oC/decade, respectively, for the last 50 years. Therefore, stratification strength and duration is anticipated to change and impact the lake’s ecosystem. Additionally, the sequence of drought periods and the expected future rise in water demands from Lake Kinneret formed the basis for the government's decision to channel desalinated water, via the natural course of the Tzalmon Stream, to the lake to ensure its operational functionality at high levels. Using a 3D hydrodynamic model forced by short and long-term forecasts the above scenarios are examined and analyzed. A simulation forced by regional atmospheric RCP4.5 climate change scenario spanning from 2010-2070 show continuous warming followed by abrupt cooling of the lake water around the year 2065. This result, presumably due to enhanced latent heat loss, suggest a restrain the dramatic anticipated change in the lake stratification. Close abstractClose abstract

Abstract: Quantifying land-atmosphere fluxes of carbon-dioxide (CO2) and methane (CH4) is essential for evaluating carbonclimate feedbacks. Greenhouse gas satellite missions aim to provide global observational coverage of greenhouse gas concentrations and thus improve inversions of landatmosphere exchange fluxes. However, in key regions such as the humid tropics current missions obtain very few valid measurements. Leveraging recent advances in the global analysis of high-resolution optical imagery on cloudcomputing platforms and deep learning algorithms for cloud segmentation, we quantitatively diagnose the sources for low data yields in the tropics. We find that the main cause for low data yields are frequent shallow cumulus clouds. We find that increasing the spatial resolution of observations to 200 m would increase yields by 2–3 orders of magnitude and allow regular measurements in the wet season. Thus, the key to effective tropical greenhouse gas observations likely lies in regularly acquiring high-spatial resolution data. Close abstractClose abstract

Abstract: The sediment – bottom-water interface is suggested as a key control on the chemical composition of the ocean by studies of trace elements in the ocean water-column, yet data regarding trace element fluxes and interactions taking place in the top ten cm of abyssal sediments are scarce. To bridge this gap, I analysed the trace and major element composition of porewater and sediment of red-clay sediment from the abyssal North Pacific, and hydrothermally influenced sediment from the Mid-Atlantic Ridge. The top sediment at both study regions is aerobic, nevertheless, there is large variability in the porewater concentrations of many elements at the top five cm. The North Pacific red-clay sediment is a source of cobalt, nickel, copper, arsenic, vanadium and barium to the deep-ocean, the magnitude of these fluxes is consistent with fluxes calculated based on the water-column distribution of most elements, and are equivalent to the global supply of these elements by rivers. The hydrothermally influenced sediment is a strong source of copper, zinc and cobalt up to three km from the vent due to oxidation of sulfide minerals. Close to the vents, the sediment is high in iron oxyhydroxides that adsorb the oxyanions vanadate, arsenate and phosphate, acting as a sink for these elements. The results of this study highlight the importance of red-clay sediment in shaping the chemical composition of the ocean, and suggest an important role for hydrothermally influenced sediment in modulating the contributions of hydrothermal vents to ocean biogeochemistry. Close abstractClose abstract

Abstract: The impact of anthropogenic aerosols on clouds is a leading source of uncertainty in estimating the effect of human activity on the climate system. The challenge lies in the scale difference between clouds (~1-10 km) and general circulation and climate (~1000 km). To address this, we utilize three different novel sets of simulations that allow to resolve convection while also including a epresentation of large-scale processes. Our findings demonstrate that aerosol-cloud interaction intensifies tropical overturning circulation. Employing a weak temperature gradient approximation, we attribute variations in circulation to clear-sky humidity changes driven by warm rain suppression by aerosols. In two sets of simulations accounting for sub-tropical-tropical coupling, we show that aerosol-driven sub-tropical rain suppression leads to increased advection of cold and moist air from the sub-tropics to the tropics, thus enhancing tropical cloudiness. The increased tropical cloudiness has a strong cooling effect by reflecting more of the incoming solar radiation. The classical “aerosol-cloud lifetime effect” is shown here to have a strong remote effect (sub-tropical aerosols increase cloudiness in the tropics), thus widening the concept of cloud adjustments to aerosol perturbation with important implications for marine cloud brightening. Close abstractClose abstract

Abstract: The use of SOM in atmospheric science has grown popular over the recent years. The SOM's strength lies in its ability to project the continuum of a given dynamical system to an easily understood spectrum of dominant states. The SOM relies on a neural network, where each grid-point in each node (cluster) is assigned with a specific weight for a given input parameter. The SOM then operates competitively, shifting individual members between the nodes to minimize internal node variability while maximizing the distances between the nodes. Here, two novel SOM applications are demonstrated, recently used to classify Mediterranean cyclones from an upper-level PV perspective. Each approach yields the potential to enhance the understanding of different aspects of Mediterranean cyclone's predictability and is readily applicable to other regions of interest. Close abstractClose abstract

Abstract: Terrestrial sequestration of carbon has mitigated ≈30% of anthropogenic carbon emissions. However its distribution across different pools—live or dead biomass, and soil and sedimentary organic carbon— which has important implications for future climate change mitigation, remains uncertain. By analyzing global observational datasets of changes in terrestrial carbon pools, we are able to partition carbon that has been sequestered on land between 1992-2019 into live biomass and non-living organic carbon pools. We compare our observation-based estimates against predictions of global vegetation models and identify key processes that are not included in most models that can help align the models with observations. We find that most terrestrial carbon gains are sequestered as non-living organic matter, and thus more persistent than previously appreciated, with a substantial fraction linked to human activities such as river damming, wood harvest, and garbage disposal in landfills. Close abstractClose abstract

Abstract: Sub-seasonal forecasting aims to predict the mean weather conditions on weekly time-scales 2-6 weeks ahead. In the midlatitudes, lLarge-scale, quasi-stationary, recurrent, and persistent flow patterns, so-called weather regimes, explain sub-seasonal weather variability in the European region. However, forecast skill and predictability for regimes are mostly very poor on sub-seasonal forecast horizons. In this presentation we shed light on how synoptic-scale processes, affect the predictability and forecast skill of North Atlantic-European weather regimes. We focus on the upper-tropospheric divergent outflow due to latent heat release in ascending air streams, so-called warm conveyor belts (WCBs). We find evidence that a misrepresentation of diabatic WCB outflow at onset of regimes characterised by blocking anticyclones is likely the cause for vanishing regime skill on sub-seasonal time scales. At the same time results suggest that a correct representation of WCB activity might be a window of forecast opportunity for regimes. We further discuss how the occurrence of regimes is modulated by the state of the winter stratosphere and the MJO, which provide another window of forecast opportunity for weather regimes on sub-seasonal time scales. Interestingly, we find again that WCB activity related to synoptic-scale weather systems modulate the MJO teleconnections towards North America and Europe. We conclude that knowledge about physical and dynamical processes on synoptic scales is key for exploiting the potential windows of forecast opportunity for weather regimes on sub-seasonal time scales. Close abstractClose abstract

Abstract: Tsunami events in antiquity had a profound influence on coastal societies. Six thousand years of historical records and geological data show that tsunamis are a common phenomenon affecting the eastern Mediterranean coastline. However, the possible impact of older tsunamis on prehistoric societies has not been investigated. Here we report, based on optically stimulated luminescence chronology, the earliest documented Holocene tsunami event, between 9.91 to 9.29 ka (kilo-annum), from the eastern Mediterranean at Dor, Israel. Tsunami debris from the early Neolithic is composed of marine sand embedded within fresh-brackish wetland deposits. Global and local sea-level curves for the period, 9.91–9.29 ka, as well as surface elevation reconstructions, show that the tsunami had a run-up of at least ~16 m and traveled between 3.5 to 1.5 km inland from the palaeo-coastline. Submerged slump scars on the continental slope, 16 km west of Dor, point to the nearby “Dor complex” as a likely cause. The near absence of Pre-Pottery Neolithic A-B archaeological sites (11.70–9.80 cal. ka) suggests these sites were removed by the tsunami, whereas younger, late Pre-Pottery Neolithic B-C (9.25–8.35 cal. ka) and later Pottery-Neolithic sites (8.25–7.80 cal. ka) indicate resettlement following the event. The significant run-up of this event highlights the disruptive impact of tsunamis on past societies along the Levantine coast. Close abstractClose abstract

Abstract: Mantle fluids are the primary carriers of key volatile elements that make the Earth’s long-term planetary habitability possible. The interaction of such volatile-rich fluids with the mantle rocks, especially the sub-cratonic lithospheric mantle leads to alteration of the mantle as well as its melting. High-density fluids encased inside diamonds are the best natural representation of mantle fluid compositions, suggesting their compositions are saline, silicic or carbonatitic. However, the origin and role in the mantle as well as their role in altering the mantle are still unclear. In my research, we approach these questions by experimentally simulating the interaction of volatile-rich fluids with mantle rocks at known pressure and temperature relevant to the mantle. Examining different mixtures of volatiles (H2O and CO2) and mantle rocks (peridotite and eclogite), we attempt to understand the origin of each type of fluid found in diamonds as well as study the effect of such interaction on the mantle chemistry and mineralogy. Compiling many experimental studies reveals that fluids ranging from silicic to low-Mg carbonatitic are formed in systems of eclogite+H2O+CO2, the more CO2 in the system, the more carbonatitic the fluid is. Fluids ranging from low-Mg carbonatitic to high-Mg carbonatitic in nature are the results of the formation of fluids in the peridotite-H2O-CO2 system. The more CO2 in the system, the more high-Mg carbonatitic the fluid composition is. These results suggest that the various fluids found in the mantle result from changes in the bulk composition of the mantle rocks. The mantle rocks are significantly affected during percolation of such fluids through them. For example, experimentally interacting silicic fluid with peridotite demonstrated the formation of various metasomatic peridotites as a function of pressure and temperature, composing of amphibole and mica. The mineral assemblages, chemistry, and P-T conditions in the experiments are similar to those found in metasomatic xenoliths from Kimberly, South Africa, and surrounding localities. Close abstractClose abstract

Abstract: In recent decades, various temperature proxies have been developed and further established in the scientific community, at both low and high accuracy, however, not every method can be applied without restriction to all minerals or rocks. Evaporitic rocks, for example, are abundant chemical sediments at the Earth's surface that are deposited from supersaturated brines in marine, terrestrial, and lacustrine environments. Halite is the most abundant rock-forming mineral in this group, which during crystal formation entraps tiny water droplets (fluid inclusions, FIs) that store the chemical composition of the parent brine at a specific pressure-temperature dependent density. Such FIs are therefore excellent records of the original physicochemical conditions of the source brine. Brillouin spectroscopy (BS) is a novel laser-based technique that uses density fluctuations in FIs to directly measure entrapment temperatures and thus the initial brine temperature during crystal growth. In this seminar, the BS method will be introduced and two application cases will be presented using salt layers from the Dead Sea which were deposited during two interglacial periods. In addition to the basic principles, both the recommended sampling strategy and pitfalls along with associated limitations will be presented. The conclusion will be that the salt layers commonly deposited in the Dead Sea basin consist of two types that formed preferentially in summer (coarse-grained crystals) and winter (fine-grained crystals), which is mainly controlled by the degree of salt saturation of the lake water. Furthermore, it will be shown how (1) lake bottom temperatures have fluctuated seasonally (summer/winter), and that (2) paleo temperature trends can be reconstructed for an entire halite layer that was deposited during holomictic periods in the Dead Sea basin. This method is particularly promising for evaporites that formed near the surface if the material has not been affected by external processes such as tectonic burial/uplift, erosion, or mineral replacement. Close abstractClose abstract

Abstract: The global oceanic overturning circulation and the transport of heat and dissolved gases are strongly controlled by upper ocean turbulent mixing that is driven by the breaking of internal gravity waves (IWs). Understanding the life cycle of oceanic IWs, from generation to dissipation, is therefore crucial for improving the representation of ocean mixing in climate models, which do not resolve the IW field.  Oceanic IWs are observed to have a continuous energy distribution across spatial and temporal scales – an internal wave continuum – despite being forced primarily at near-inertial and tidal frequencies at large scales. The formation of the IW continuum and the associated energy transfer to dissipative scales have been traditionally attributed to wave-wave interactions and to Doppler shifting of wave frequencies by currents. Here, we provide evidence from realistic numerical simulations that oceanic eddies rapidly diffuse storm-forced wave energy across spatiotemporal scales, thereby playing a dominant role in the formation of the IW continuum and the corresponding spatiotemporal distribution of energy dissipation. We further demonstrate that winds can play an important role in damping oceanic IWs through current feedback.  This results in a substantial reduction in wind power input at near inertial frequencies and a net energy sink for internal tides. Close abstractClose abstract

Abstract: Thermal Pressurization (TP) is expected to be a dominant frictional weakening mechanism during earthquakes. However, due to experimental limitations there is a lack of direct evidence for the activation of TP in controlled laboratory conditions and most of our knowledge is derived from field studies and theoretical predictions. We present experiments performed by a rotary-shear apparatus where TP is activated in localized faults in Frederick diabase under constant normal stress of 50 MPa, confining pressure of 45 MPa and initial pore water pressure of 25 MPa. We show that by changing the permeability of the host rock we can control the shear stress drop during a TP event in the experimental fault. The TP events are short-lived in bare-surface faults as the opening of existing fractures around the fault plane drains the excess pore fluid. Wider, gouge-filled faults show more persistent frictional weakening, but at a slower rate, which is attributed to the compressibility of the gouge. In addition, we test the effects of transient fault dilation on the duration of a TP event through an expansion of the prevailing TP model, using a one-dimensional numerical simulation. We conclude that dynamic changes to the hydraulic diffusivity around the fault plane and persistent fault dilation, due to geometrical irregularities, are the most likely mechanisms to arrest TP during an earthquake. Close abstractClose abstract

Abstract: Carbon efflux from soils is the largest terrestrial carbon source to the atmosphere, yet it remains one of the most uncertain fluxes in the Earth’s carbon budget. A dominant component of this flux is heterotrophic respiration, influenced by several environmental factors, most notably soil temperature and moisture. We developed a mechanistic model from micro to global scale to explore how changes in soil water content and temperature affect soil heterotrophic respiration. Simulations, laboratory measurements, and field observations validate the new approach. Estimates from the model show that heterotrophic respiration has been increasing since the 1980s at a rate of about 2% per decade globally. Using future projections of surface temperature and soil moisture, the model predicts a global increase of about 40% in heterotrophic respiration by the end of the century under the worst-case emission scenario, where the Arctic region is expected to experience a more than two-fold increase, driven primarily by declining soil moisture rather than temperature increase.   Close abstractClose abstract

Abstract: The traditional approach to weather forecasting on one- to two-week timescales utilizes weather forecasting models, but on timescales longer than two weeks, the value of deterministic (or ensemble-based probabilistic) forecasts weakens. This is due to the presence of chaotic variability in the atmosphere. Yet certain modes of variability in the climate system have timescales longer than this two-week threshold, and the key to longer-scale prediction is to take advantage of these modes when they open up windows of opportunity. By understanding the impacts of these modes of variability on surface weather, the potential for improved forecasts on a monthly timescale can be demonstrated and eventually realized.  Two such classes of modes of variability are stratospheric variability (both in the tropical and polar stratosphere) and tropical tropospheric variability (e.g. the Madden-Julian Oscillation and El Nino). For example, both polar stratospheric sudden warmings and the Madden-Julian Oscillation have been shown to influence European and Mediterranean weather, but it is unclear (1) what mechanism(s) underlie these connections, (2) how far in advance the impacts can be predicted, (3) what governs the magnitude of the surface impact, and (4) how well models capture these connections. This talk will review progress made towards addressing these issues over the past several years in my group. Close abstractClose abstract

Abstract: Over the last 2½ millenia, the world economy depended on prevailing currencies: the Athenian owl (530- 168 BCE), the Roman denarius (211 BCE-250 AD), the Spanish piece-of-eight (16th to 18th C), and today the US dollar. These reference monies were accepted everywhere and all, at least in the beginning, were made of silver. What is so special about this metal? Silver is useless and rare, but still abundant enough to match the wealth of nations and of their long-distance trade. Silver ores are associated with rare and recent tectonic environments, the Mediterranean world, notably the periphery of the Aegean Sea and Southern Iberia, and the American cordillera, Peru and Mexico. In contrast, they were markedly scarce in South and East Asia. After the virtual destruction of soils by the Anatolian farmers at the end of the Bronze Age, the Near and Middle East societies depended almost exclusively on the agriculture of Egypt and Mesopotamia. The Late Bronze Age collapse (ca. 1200 BCE) corresponded to the migration of Greek people and resulted in the annihilation of all the empires outside of the flood plains. Silver by weight was nevertheless used to save populations from famine and trade wheat, barley and copper. Military innovations, hoplites and their phalanx, were, with silver mines, the main resources of the Greeks. Mercenaries received their wages in silver, notably through the tributes exacted in silver by the Achaemenid (Persion) kings. By minting silver, the returning Greek mercenaries emerged as strong middle classes . They soon claimed their share of the power, toppled the tyrants, and installed democracy in many poleis from Greece and Southern Italy. Modern economics teaches us that egalitarian distribution of wealth is unfortunately unstable and this case is well illustrated by Syracuse. At the beginning of the common era, the Roman Empire found itself the owner of centuries of silver extracted from Greece and from Iberia. This bullion was used to buy luxury products, frankincense from Arabia, spices and cotton from India, ivory and precious wood from Africa. Leakage of silver towards the Indian Ocean was so strong that coins were quickly debased by copper and by 250 AD most of the silver had been lost. The progressive replacement of silver by a bimetallic system, gold for the rich and bronze for the working class, progressively fractured the society and ushered the brutal Middle Age regimes. Silver famine had finally destroyed the democratic ideal of the Greeks. This is food for thought as disappearing mining resources may severely affect our current vision of societies. Close abstractClose abstract

Abstract: The Mediterranean region stands out among other subtropical regions in its projected drying response to the global rise in atmospheric greenhouse gas concentrations. This drying trend has already emerged out of the normal, random climate variability in the sensitive Eastern Mediterranean (EM) region. To better understand the dynamical mechanisms responsible for this regional sensitivity, we turn to past protracted EM drying states during warm geological epochs. A unique view of the historical and pre-historical hydroclimate of the EM-Levant has been gleaned from the continued study of the sedimentary and geochemical record left by the lakes that filled the tectonic basin of the Dead Sea. We revisit the Late Quaternary sediment record retrieved during the 2010-2011 Dead Sea Deep Drilling Project (DSDDP). The sediments clearly indicate that the Levant was drier during past warm interglacials than during the adjacent glacials but nonetheless experienced large variations in the intensity of the regional aridity. During each interglacial, extended thick deposits of salts accumulated at the Lake bottom, during millennia of significant regional aridity and severely reduced Mediterranean rains. These dry states were interrupted by extended wet intervals, fed by rains that were supplied by a blend of tropical and Mediterranean moisture. To understand the underlying causes of the EM-Levant interglacial hydroclimate variations, we put the Dead Sea record in the context of the Northern Hemisphere orbital insolation variations and their impact on the global climate system. We show that the changes in EM hydroclimate portrayed by the DSDDP record during the interglacials, are entirely consistent with the response of the North Atlantic Ocean and the overlying atmosphere and surrounding land areas to the changes in the latitudinal insolation gradient, as determined by climate models and evident by surface temperature proxies. This perspective provides new information regarding the dynamical processes responsible for the ongoing, greenhouse gas forced, EM drying. Close abstractClose abstract

Abstract: Recent severe summertime weather extremes in the Northern hemisphere extratropics such as the extraordinary 2021 North American Heatwave and the record-breaking floods in central Europe were in part driven by persistent circulation patterns in the tropospheric Jetstream. To what degree such circulation patterns will modulate extreme weather risk in a warming world is still uncertain and remains a highly debated topic in climate science. I will present results from recent studies that investigate physics of extraordinary extremes, future changes in weather persistence diagnosed by a feature tracking algorithm and future risks from concurrent extremes and associated impacts on crop production based on latest GGCMI-runs. A special emphasis will be placed on benchmarking the skill of CMIP5 and CMIP6 models to reproduce atmosphere dynamical mechanisms and associated extreme weather against reanalysis data short bio: Kai Kornhuber is an adjunct Associate Research Scientist at the Lamont-Doherty Earth Observatory, Columbia University in New York and a Senior Fellow on Climate Risks at the German Council on Foreign Relations. His research is concerned with physical drivers of extreme weather and climate events and associated societal impacts and risks under current and future climatic conditions. He is Founding Member of the EarthNetwork on Sustainable and Resilient Living in an Era of Increasing Disasters at Columbia’s Climate School, Co-Chair of the Compound Events Working Group at Risk-Kan, Steering Committee member of the HiWeather Project and a Co- Pi of the Project PERSEVERE within the BMBF Consortium. Close abstractClose abstract

Abstract: Most electrical activity in vertebrates and invertebrates occurs at extremely low frequencies (ELF), with characteristic maxima below 50 Hz. The origin of these frequency maxima is unknown and remains a mystery. We propose that over billions of years during the evolutionary history of living organisms on Earth, the natural electromagnetic resonant frequencies in the atmosphere, continuously generated by global lightning activity, provided the background electric fields for the development of cellular electrical activity. In some animals, the electrical spectrum is difficult to differentiate from the natural background atmosphericelectric field produced by lightning. In this talk I will present evidence for the link between the natural ELF fields and those found in many living organisms, including humans.  Furthermore, recent experiments show links between the ELF fields and photosynthesis in plants. Close abstractClose abstract

Abstract: One of the most surprising discoveries in exoplanet science has been the existence of compact systems of Earth to super-Earth sized planets. These multi-planet systems have nearly circular, coplanar orbits located at distances of only ∼ 0.01 − 0.1 AU, a region devoid of planets in our Solar System. Although compact systems comprise a large fraction of known exoplanetary systems, their origin remains debated. Common to all prior models of compact system origin is the assumption that infall to the stellar disk ends before planets form. However, there is growing observational, theoretical, and meteoritical evidence of the early growth of mm-sized “pebbles” during the infall phase. We propose that accretion of compact systems occurs during stellar infall. As a cloud core collapses, solids are gradually accumulated in the disk, producing favorable conditions for the formation and survival of close-in planets. A key feature of this model is that the reduced gas-to-solids ratio in the planet accretion region can allow for the formation and survival of compact systems, even with Type-I migration. Accretion within infall-supplied disks has been studied in the context of gas planet satellite origin. Formation models predict that the total mass of the satellite system during this evolution maintains a nearly constant mass ratio ∼10^−4 compared to the host planet’s mass. The maximum mass ratio of compact exoplanetary systems compared to the stellar mass are similar to those of the giant satellite system, suggesting that accretion of compact systems may be similar to regular satellite formation. Close abstractClose abstract