ALBERT

Description: The geological record encodes the relationship between climate and atmospheric carbon dioxide (CO 2 ) over long and short timescales, as well as potential drivers of evolutionary transitions. However, reconstructing CO 2 beyond direct measurements requires the use of paleoproxies and herein lies the challenge, as proxies differ in their assumptions, degree of understanding, and even reconstructed values. In this study, we critically evaluated, categorized, and integrated available proxies to create a high-fidelity and transparently constructed atmospheric CO 2 record spanning the past 66 million years. This newly constructed record provides clearer evidence for higher Earth system sensitivity in the past and for the role of CO 2 thresholds in biological and cryosphere evolution. Editor’s summary The concentration of atmospheric carbon dioxide is a fundamental driver of climate, but its value is difficult to determine for times older than the roughly 800,000 years for which ice core records are available. The Cenozoic Carbon dioxide Proxy Integration Project (CenCO2PIP) Consortium assessed a comprehensive collection of proxy determinations to define the atmospheric carbon dioxide record for the past 66 million years. This synthesis provides the most complete record yet available and will help to better establish the role of carbon dioxide in climate, biological, and cryosphere evolution. — H. Jesse Smith

Description: Groundwater is a crucial resource for drinking water, agricultural irrigation, and industry, and its sustainable management is essential for maintaining economic development and healthy ecosystems. Climate change (e.g., droughts) and human interventions (e.g., land use change, and water withdrawals) increase global reliance on groundwater, leading to more pressure on already depleted aquifers. A lack of direct groundwater observations presents many challenges to assess groundwater stores, especially when under stress caused by groundwater drought. Thomas et al., (2017) developed a framework to evaluate groundwater drought occurrence across California Central Valley (CCV), based on observations from NASA's Gravity Recovery and Climate Experiment (GRACE) satellite mission. The GRACE Groundwater Drought Index (GGDI), a normalized GRACE-groundwater time series, was shown to quantify groundwater storage deficits attributed to groundwater drought. The GGDI demonstrated a good agreement with in-situ groundwater drought timeseries, capturing the characteristics of groundwater drought in the CCV. As applied for the CCV, in-situ records of surface water storage changes were used to derive GRACE-groundwater. However, many follow-on studies have applied GGDI without strict accounting for surface water storage change. Accurate extraction of GRACE-groundwater requires robust estimation of water budget components; thus, it stands to reason that accounting for surface water stores within GGDI would result in a more robust estimate of groundwater drought. The aim of this project is to investigate the influence of accounting for surface water changes within GGDI on capturing groundwater storage deficits. Our findings indicated that a strict accounting of changes in surface water stores improved GGDI’s ability to identify groundwater drought characteristics across large-scale basins.

Description: Observing basin water storage response due to hydroclimatic fluxes and human water use provides valuable insight to the sensitivity of water storage to climate change. Quantifying basin water storage changes due to climate and human water use is critical for water management yet remains a challenge globally. Observations from the Gravity Recovery and Climate Experiment (GRACE) mission are used to extract monthly available water (AW), representing the combined storage changes from groundwater and surface water stores. AW are combined with hydroclimatic fluxes, including precipitation (P) and evapotranspiration (ET) to quantify the hydroclimatic elasticity of AW for global basins. Our results detect consequential global water sensitivity to changes in hydroclimatic fluxes, where 25% of land areas exhibit hydroclimatic elasticity of AW greater than 10, implying that a 1% change in monthly P-ET would result in a 10% change in AW. Corroboration using a Budyko-derived metric substantiate our findings, demonstrating that basin water storage resilience to short-term water deficits is linked to basin partitioning predictability, and uniform seasonality of hydroclimatic fluxes. Our study demonstrates how small shifts in hydroclimate flux may affect available water storage potentially impacting billions globally.

Description: Traditional methods for evaluating groundwater resources rely on in-situ observations, which are often limited due to sparsely distributed monitoring wells and temporal inconsistencies in measurements. However, InSAR techniques have the potential to measure groundwater storage change indirectly through measuring ground deformation. The ground deformation associated with groundwater withdrawal is mainly recoverable or as a result of elastic compression. However, when effective stress exceeds the maximum past stress on the aquifer, inelastic subsidence occurs, which can permanently lower the storage capacity of the aquifer. Thus, in addition to monitoring changes in the volume of groundwater storage, analysing elasticity properties is necessary to fully understand the influence of overextraction on long-term aquifer sustainability. This research aims to investigate the capability of InSAR to contribute to a detailed understanding of groundwater storage change and the sustainability of groundwater use across Delhi, India. Specifically, we apply the ISBAS-InSAR technique to Sentinel-1 SAR data to produce a time-series of deformation across the region and investigate the relationship between in-situ groundwater storage change and ground deformation. Finally, the spatio-temporal variability and trends of elasticity in the underlying aquifer system, quantified using the elastic skeletal storage coefficient, will be analysed by examining the ratio of seasonal deformation signal provided by InSAR and groundwater level change from well measurements across the time-series of observations. These results shall inform both groundwater management in the Delhi region and provide insights into the applicability of InSAR for inferring large-scale aquifer dynamics.

Description: Recent tsunamis demonstrate the urgent need for more densely spaced observations and direct measurements from the oceans. Most of the existing observing capacity is located on land or close to the shore, and often sparse (seismic network, land-based GNSS, tide-gauges and DART array), limiting our ability to predict, detect and respond to tsunamis. We propose a network of ships with GNSS systems as a way to fill this geodetic observation gap in the ocean by tracking changes in sea-surface height, and detecting even small, ~10 cm amplitude tsunamis of different origins. One year of navigation data from the commercial shipping fleet is used to generate statistical coverage maps of large ships for different epochs in the Pacific region which are overlapped with regions source of tsunamis and impacted by tsunamis. Some first results describe what a cargo-ship network might experience in terms of tsunami travel time and tsunami predicted amplitudes based on several tsunami models calculated over the Pacific. They clearly demonstrate that commercial shipping lines provide an excellent temporal and spatial coverage of the ocean globally. A focus on different regions indicates that the highest density of ships is near coastlines, and testing different tsunami origins helps understand more precisely how this network could improve regional early warning. By exploring the geographic relationship between tsunami sources, travel times and amplitudes with the ships locations, the discussion seeks to determine the ability of a defined ship network to provide effective warnings for the communities at risk and improve hazard mitigations.