Showing papers by "Noel Gourmelen published in 2023"

Mass balance of the Greenland and Antarctic ice sheets from 1992 to 2020

Abstract: Abstract. Ice losses from the Greenland and Antarctic ice sheets have accelerated since the 1990s, accounting for a significant increase in the global mean sea level. Here, we present a new 29-year record of ice sheet mass balance from 1992 to 2020 from the Ice Sheet Mass Balance Inter-comparison Exercise (IMBIE). We compare and combine 50 independent estimates of ice sheet mass balance derived from satellite observations of temporal changes in ice sheet flow, in ice sheet volume, and in Earth's gravity field. Between 1992 and 2020, the ice sheets contributed 21.0±1.9 mm to global mean sea level, with the rate of mass loss rising from 105 Gt yr−1 between 1992 and 1996 to 372 Gt yr−1 between 2016 and 2020. In Greenland, the rate of mass loss is 169±9 Gt yr−1 between 1992 and 2020, but there are large inter-annual variations in mass balance, with mass loss ranging from 86 Gt yr−1 in 2017 to 444 Gt yr−1 in 2019 due to large variability in surface mass balance. In Antarctica, ice losses continue to be dominated by mass loss from West Antarctica (82±9 Gt yr−1) and, to a lesser extent, from the Antarctic Peninsula (13±5 Gt yr−1). East Antarctica remains close to a state of balance, with a small gain of 3±15 Gt yr−1, but is the most uncertain component of Antarctica's mass balance. The dataset is publicly available at https://doi.org/10.5285/77B64C55-7166-4A06-9DEF-2E400398E452 (IMBIE Team, 2021).

Measuring glacier mass changes from space—a review

Abstract: Glaciers distinct from the Greenland and Antarctic ice sheets are currently losing mass rapidly with direct and severe impacts on the habitability of some regions on Earth as glacier meltwater contributes to sea-level rise and alters regional water resources in arid regions. In this review, we present the different techniques developed during the last two decades to measure glacier mass change from space: digital elevation model (DEM) differencing from stereo-imagery and synthetic aperture radar interferometry, laser and radar altimetry and space gravimetry. We illustrate their respective strengths and weaknesses to survey the mass change of a large Arctic ice body, the Vatnajökull Ice Cap (Iceland) and for the steep glaciers of the Everest area (Himalaya). For entire regions, mass change estimates sometimes disagree when a similar technique is applied by different research groups. At global scale, these discrepancies result in mass change estimates varying by 20%–30%. Our review confirms the need for more thorough inter-comparison studies to understand the origin of these differences and to better constrain regional to global glacier mass changes and, ultimately, past and future glacier contribution to sea-level rise.

Inter-decadal climate variability induces differential ice response along Pacific-facing West Antarctica

Abstract: West Antarctica has experienced dramatic ice losses contributing to global sea-level rise in recent decades, particularly from Pine Island and Thwaites glaciers. Although these ice losses manifest an ongoing Marine Ice Sheet Instability, projections of their future rate are confounded by limited observations along West Antarctica's coastal perimeter with respect to how the pace of retreat can be modulated by variations in climate forcing. Here, we derive a comprehensive, 12-year record of glacier retreat around West Antarctica's Pacific-facing margin and compare this dataset to contemporaneous estimates of ice flow, mass loss, the state of the Southern Ocean and the atmosphere. Between 2003 and 2015, rates of glacier retreat and acceleration were extensive along the Bellingshausen Sea coastline, but slowed along the Amundsen Sea. We attribute this to an interdecadal suppression of westerly winds in the Amundsen Sea, which reduced warm water inflow to the Amundsen Sea Embayment. Our results provide direct observations that the pace, magnitude and extent of ice destabilization around West Antarctica vary by location, with the Amundsen Sea response most sensitive to interdecadal atmosphere-ocean variability. Thus, model projections accounting for regionally resolved ice-ocean-atmosphere interactions will be important for predicting accurately the short-term evolution of the Antarctic Ice Sheet.

Improved Monitoring of Subglacial Lake Activity in Greenland

Abstract: Abstract. Subglacial lakes form beneath ice sheets and ice caps if water is available, and if bedrock and surface topography are able to retain the water. On a regional scale, the lakes modulate the timing and rate of freshwater flow through the subglacial system to the ocean by acting as reservoirs. More than one hundred hydrologically active subglacial lakes, that drain and recharge periodically, have been documented under the Antarctic ice sheet, while only a handful of active lakes have been identified in Greenland. The small size of the Greenlandic subglacial lakes puts additional demands on mapping capabilitie aiming to resolve the evolving surface topography in sufficient detail to record their temporal behavior. Here, we explore the potential for combining data from CryoSat-2, TanDEM-X, and ArcticDEM to document the evolution of four active subglacial lake sites in Greenland. The inclusion of the new data sources provides important information on lake activity, documenting that the ice surface collapse basin on Flade Isblink ice cap was 50 % (30 meters) deeper than previously recorded. We also present evidence of a new active subglacial lake in Southwest Greenland, which shows signs of being hydrologically connected to another subglacial lake in that region. These findings show how improving the measurement capabilities of subglacial lakes, improves our current understanding and knowledge of the subglacial water system and its connection to surface hydrology.

Subglacial Freshwater Drainage Increases Simulated Basal Melt of the Totten Ice Shelf

Abstract: Subglacial freshwater discharge from beneath Antarctic glaciers likely has a strong impact on ice shelf basal melting. However, the difficulty in directly observing subglacial flow highlights the importance of modeling these processes. We use an ocean model of the Totten Ice Shelf cavity into which we inject subglacial discharge derived from a hydrology model applied to Aurora Subglacial Basin. Our results show (a) discharge increases melting in the vicinity of the outflow region, which correlates with features observed in surface elevation maps and satellite‐derived melt maps, with implications for ice shelf stability; (b) the change in melting is driven by the formation of a buoyant plume rather than the addition of heat; and (c) the buoyant plume originating from subglacial discharge‐driven melting is far‐reaching. Basal melting induced by subglacial hydrology is thus important for ice shelf stability, but is absent from almost all ice‐ocean models.

Taskfarm: A Client/Server Framework for Supporting Massive Embarrassingly Parallel Workloads

Abstract: Taskfarm is a client/server framework that can be used to keep track of massive embarrassingly parallel workloads. The system is split up into two packages: (1) a flask server that hands out new tasks via HTTP and (2) a python client that requests and updates tasks. The server stores task progress in a database. This system has been designed to manage a satellite data processing workflow with hundreds of thousands of tasks with variable compute costs. It can be used for any problem that can be solved using a task farm.

Improved Monitoring of Subglacial Lake Activity in Greenland.

Abstract: . Subglacial lakes form beneath ice sheets and ice caps if water is available, and if bedrock and surface topography are able to retain the water. On a regional scale, the lakes modulate the timing and rate of freshwater flow through the subglacial system to the ocean by acting as reservoirs. More than one hundred hydrologically active subglacial lakes, that drain and recharge periodically, have been documented under the Antarctic ice sheet, while only a handful of active lakes have been identified in Greenland. The small size of the Greenlandic subglacial lakes puts additional demands on mapping capabilities 5 aiming to resolve the evolving surface topography in sufficient detail to record their temporal behavior. Here, we explore the potential for combining data from CryoSat-2, TanDEM-X

Glacier Mass Loss Between 2010 and 2020 Dominated by Atmospheric Forcing

Abstract: We generate a high spatial and temporal record of ice loss across glaciers globally for the first time from CryoSat‐2 swath interferometric radar altimetry. We show that between 2010 and 2020, glaciers lost a total of 272 ± 11 Gt yr−1 of ice, equivalent to a loss of 2% of their total volume during the 10‐year study period. Using a simple parameterization, we demonstrate that during this period, surface mass balance anomaly dominated the mass budget, accounting for 89% ± 5% of the total ice loss. Ice discharge anomaly was responsible for 11% ± 1% of the total ice loss, and 28% ± 2% of the ice loss when excluding land‐terminating sectors. Strong discharge anomaly is found over areas of changing oceanic conditions such as in the Barents and Kara Seas or in Antarctica, and areas fringed by lakes and fjords in Patagonia.