Showing papers by "Erik R. Ivins published in 2019"

Contributions of GRACE to understanding climate change.

Abstract: Time-resolved satellite gravimetry has revolutionized understanding of mass transport in the Earth system. Since 2002, the Gravity Recovery and Climate Experiment (GRACE) has enabled monitoring of the terrestrial water cycle, ice sheet and glacier mass balance, sea level change and ocean bottom pressure variations and understanding responses to changes in the global climate system. Initially a pioneering experiment of geodesy, the time-variable observations have matured into reliable mass transport products, allowing assessment and forecast of a number of important climate trends and improve service applications such as the U.S. Drought Monitor. With the successful launch of the GRACE Follow-On mission, a multi decadal record of mass variability in the Earth system is within reach.

Slowdown in Antarctic mass loss from solid Earth and sea-level feedbacks

Abstract: INTRODUCTION Geodetic investigations of crustal motions in the Amundsen Sea sector of West Antarctica and models of ice-sheet evolution in the past 10,000 years have recently highlighted the stabilizing role of solid-Earth uplift on polar ice sheets. One critical aspect, however, that has not been assessed is the impact of short-wavelength uplift generated by the solid-Earth response to unloading over short time scales close to ice-sheet grounding lines (areas where the ice becomes afloat). Here, we present a new global simulation of Antarctic evolution at high spatiotemporal resolution that captures solid-Earth processes stabilizing and destabilizing ice sheets. These include interactions with global eustatic sea-level rise (SLR), self-attraction and loading (SAL) of the oceans, Earth’s rotational feedback to SAL, and elastic uplift of the solid Earth. RATIONALE In Antarctica, dynamic thinning and retreat of ice streams has been the main driver of mass loss over the past decades, largely controlled by how grounding lines migrate and interact with bedrock pinning points. Studies have shown that the physical representation of grounding-line dynamics (GLD) can only be captured through simulations with a horizontal resolution higher than 1 km. Current models of SLR that incorporate solid-Earth processes with viscoelastic response tend to involve GLD that is resolved at much coarser resolutions (25 to 100 km) and involve time steps on the order of decades. Such resolution bounds are incompatible with capturing the complex bed topography of the ice streams of West Antarctica that are vulnerable to rapid retreat. In addition, a resolution of 25 to 100 km is inherently too coarse to capture short-wavelength elastic uplift generated by fast GLD. Elastic uplift generated by a 2-km grounding-line retreat, modeled as loss of 100-m-thick ice from a disk of 2-km radius, can reach 52 mm near the grounding line (centroid of the equivalent disk). At coarser resolutions (say, 16 km), the same model generates uplift one order of magnitude lower. This implies that uplift generated in simulations at coarse resolutions might underestimate how much uplift is generated during ungrounding of active areas of Antarctica such as Thwaites Glacier (TG), where highly complex grounding-line geometries and associated retreat are observed over short time scales on the order of years. Our goal was therefore to carry out a sensitivity study of sea level– and ice flow–related processes that incorporate kilometer-scale resolutions and global processes involving solid-Earth dynamics. RESULTS Our sensitivity study spans 500 years and demonstrates how in Antarctica, TG is particularly prone to negative feedback from SAL and elastic uplift. At year 2350, including these feedbacks leads to a ~20-year delay in dynamic mass loss of TG, corresponding to a 26.8% reduction in sea-level contribution, along with a reduction in grounding-line retreat of 38% and elastic uplift rates reaching ~0.25 m/year. At year 2100, though, this negative feedback is considerably lower, with a 1.34% reduction in sea-level contribution only. Not including a kilometer-scale resolution representation of such processes will lead to projections of SLR that will significantly overestimate Antarctic Ice Sheet contribution over several centuries. CONCLUSION For 21st-century projections, the effects we have modeled here remain negligible. However, for the period starting 2250 and after, SLR projections that would not account for such dynamic geodetic effects run the risk of consistently overestimating (by 20 to 40%) relative sea-level estimates. Our approach shows that significant stabilization in grounding-line migration occurs when uplift rates start approaching 10 cm/year. This has strong implications for late Quaternary reconstructions of SLR, for example, in which the inclusion of these solid-Earth processes will allow SLR modelers to gain a better grasp of the time scales involved in reaching maximum coastal inundation levels during extended warm periods.

Sea-level fingerprints emergent from GRACE mission data

Abstract: . The Gravity Recovery and Climate Experiment (GRACE) mission data have an important, if not revolutionary, impact on how scientists quantify the water transport on the Earth's surface. The transport phenomena include land hydrology, physical oceanography, atmospheric moisture flux, and global cryospheric mass balance. The mass transport observed by the satellite system also includes solid Earth motions caused by, for example, great subduction zone earthquakes and glacial isostatic adjustment (GIA) processes. When coupled with altimetry, these space gravimetry data provide a powerful framework for studying climate-related changes on decadal timescales, such as ice mass loss and sea-level rise. As the changes in the latter are significant over the past two decades, there is a concomitant self-attraction and loading phenomenon generating ancillary changes in gravity, sea surface, and solid Earth deformation. These generate a finite signal in GRACE and ocean altimetry, and it may often be desirable to isolate and remove them for the purpose of understanding, for example, ocean circulation changes and post-seismic viscoelastic mantle flow, or GIA, occurring beneath the seafloor. Here we perform a systematic calculation of sea-level fingerprints of on-land water mass changes using monthly Release-06 GRACE Level-2 Stokes coefficients for the span April 2002 to August 2016, which result in a set of solutions for the time-varying geoid, sea-surface height, and vertical bedrock motion. We provide both spherical harmonic coefficients and spatial maps of these global field variables and uncertainties therein ( https://doi.org/10.7910/DVN/8UC8IR ; Adhikari et al. , 2019 ). Solutions are provided for three official GRACE data processing centers, namely the University of Texas Austin's Center for Space Research (CSR), GeoForschungsZentrum Potsdam (GFZ), and Jet Propulsion Laboratory (JPL), with and without rotational feedback included and in both the center-of-mass and center-of-figure reference frames. These data may be applied for either study of the fields themselves or as fundamental filter components for the analysis of ocean-circulation- and earthquake-related fields or for improving ocean tide models.

The rapid and steady mass loss of the patagonian icefields throughout the GRACE Era: 2002-2017

Abstract: Fil: Richter, Andreas Jorg. Universidad Nacional de la Plata. Facultad de Cs.astronomicas y Geofisicas. Laboratorio Maggia.; Argentina. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - La Plata; Argentina. Technische Universitat Dresden; Alemania