The Scientific Legacy of NASA’s Operation IceBridge
Joseph A. MacGregorLinette BoisvertBrooke MedleyAlek PettyJ. P. HarbeckRobin E. BellJ. B. BlairEdward Blanchard‐WrigglesworthEllen BuckleyM. S. ChristoffersenJames R. CochranB. M. CsathóEugenia L. De MarcoRoseanne DominguezM. A. FahnestockS. L. FarrellS. GogineniJamin S. GreenbaumChristy HansenM. A. HoftonJ. W. HoltKenneth C. JezekL. KoenigN. T. KurtzR. KwokChristopher F. LarsenC. LeuschenCaitlin Dieck LockeSerdar S. ManizadeSeelye MartinT. NeumannSophie NowickiJohn PadenJ. Richter‐MengeEric RignotFernando Rodríguez‐MoralesMatthew R. SiegfriedB. E. SmithJ. G. SonntagM. StudingerK. J. TintoMartin TrufferThomas WagnerJohn E. WoodsD. A. YoungJames K. Yungel
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Abstract The National Aeronautics and Space Administration (NASA)’s Operation IceBridge (OIB) was a 13‐year (2009–2021) airborne mission to survey land and sea ice across the Arctic, Antarctic, and Alaska. Here, we review OIB’s goals, instruments, campaigns, key scientific results, and implications for future investigations of the cryosphere. OIB’s primary goal was to use airborne laser altimetry to bridge the gap in fine‐resolution elevation measurements of ice from space between the conclusion of NASA’s Ice, Cloud, and land Elevation Satellite (ICESat; 2003–2009) and its follow‐on, ICESat‐2 (launched 2018). Additional scientific requirements were intended to contextualize observed elevation changes using a multisensor suite of radar sounders, gravimeters, magnetometers, and cameras. Using 15 different aircraft, OIB conducted 968 science flights, of which 42% were repeat surveys of land ice, 42% were surveys of previously unmapped terrain across the Greenland and Antarctic ice sheets, Arctic ice caps, and Alaskan glaciers, and 16% were surveys of sea ice. The combination of an expansive instrument suite and breadth of surveys enabled numerous fundamental advances in our understanding of the Earth’s cryosphere. For land ice, OIB dramatically improved knowledge of interannual outlet‐glacier variability, ice‐sheet, and outlet‐glacier thicknesses, snowfall rates on ice sheets, fjord and sub‐ice‐shelf bathymetry, and ice‐sheet hydrology. Unanticipated discoveries included a reliable method for constraining the thickness within difficult‐to‐sound incised troughs beneath ice sheets, the extent of the firn aquifer within the Greenland Ice Sheet, the vulnerability of many Greenland and Antarctic outlet glaciers to ocean‐driven melting at their grounding zones, and the dominance of surface‐melt‐driven mass loss of Alaskan glaciers. For sea ice, OIB significantly advanced our understanding of spatiotemporal variability in sea ice freeboard and its snow cover, especially through combined analysis of fine‐resolution altimetry, visible imagery, and snow radar measurements of the overlying snow thickness. Such analyses led to the unanticipated discovery of an interdecadal decrease in snow thickness on Arctic sea ice and numerous opportunities to validate sea ice freeboards from satellite radar altimetry. While many of its data sets have yet to be fully explored, OIB’s scientific legacy has already demonstrated the value of sustained investment in reliable airborne platforms, airborne instrument development, interagency and international collaboration, and open and rapid data access to advance our understanding of Earth’s remote polar regions and their role in the Earth system.Keywords:
Greenland ice sheet
The Programme for Monitoring of the Greenland Ice Sheet (PROMICE) has measured ice-sheet elevation and thickness via repeat airborne surveys circumscribing the ice sheet at an average elevation of 1708 ± 5 m (Sørensen et al. 2018). We refer to this 5415 km survey as the ‘PROMICE perimeter’. Here, we assess ice-sheet mass balance following the input-output approach of Andersen et al. (2015). We estimate ice-sheet output, or the ice discharge across the ice-sheet grounding line, by applying downstream corrections to the ice flux across the PROMICE perimeter. We subtract this ice discharge from ice-sheet input, or the area-integrated, ice sheet surface mass balance, estimated by a regional climate model. While Andersen et al. (2015) assessed ice-sheet mass balance in 2007 and 2011, this updated input-output assessment now estimates the annual sea-level rise contribution from eighteen sub-sectors of the Greenland ice sheet over the 1995–2015 period.
Greenland ice sheet
Ice-sheet model
Future sea level
Antarctic ice sheet
Elevation (ballistics)
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Greenland ice sheet
Firn
Snowpack
Ice-sheet model
Glacier mass balance
Percolation (cognitive psychology)
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Greenland ice sheet
Ice-sheet model
Wisconsin glaciation
Meltwater
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In the 21st century, polar land ice melting became one of the driving factors of global sea level rise, which is discussed widely by the media and the public. Although the fact of the shrinking ice caps and accompanying changes in the sea level is established, the actual amount of polar ice melting still needs to be quantified in separate regions. Sitting on top of bedrock, the Greenland ice sheet (GrIS) is the second largest ice sheet on Earth. With traditional glaciological methods the change of the Greenland ice sheet is difficult to measure directly, however with the GRACE (Gravity Recovery and Climate Experiment) satellite system the mass changes can be measured directly. There are several sub-drainage areas within the Greenland Ice Sheet. Some of the subsystems may contribute differently to the overall mass changes of GrIS. For instance, while the mass loss in the GrIS ablation zone is enhanced during the last decades, the central high altitude areas experienced increased mass accumulation (Krabill et al., 2000, Thomas et al., 2001, Colgan et al., 2015, Xu et al., 2016). It is important to quantify the regional mass changes because it gives us insight what is going on beyond the realization that the GrIS is shrinking...
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Future sea level
Ice-sheet model
Ice caps
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Greenland ice sheet
Ice-sheet model
Fact sheet
Shelf ice
Groenlandia
Glacier morphology
Wisconsin glaciation
Ice divide
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The Greenland Ice Sheet is the world’s second largest ice sheet, storing an equivalent of 7.3 meters of sea level rise. Due to climate change, the Greenland ice sheet is currently losing mass at an accelerated rate. Ice sheet models are used to project long term melt of the ice sheet, which are often forced by output from climate models. Most of the multi-millennium time scale ice sheet simulations conducted in the past used SMB calculations based on empirical relationships between melt and temperature (Positive-Degree Day schemes). In this thesis, I address the question of the future evolution of the Greenland ice sheet by means of an ice sheet model forced with an elevation dependent SMB field that accounts for the energy available for melt. This work focuses on key variables such as ice thickness, ice area, velocity and contribution to eustatic sea level rise, and assesses the reversibility of the mass loss. For this thesis, I performed uncoupled CISM2.1 simulations which were forced by the elevation- SMB field from a coupled CESM-CISM simulation. The coupled simulation used to force the ice sheet has a length of 160 years and a CO2 concentration that is increased with 1% per year from pre-industrial levels and capped at 4 times CO2. Time segments with 2x, 3x and 4x pre-industrial CO2 concentrations of this CESM-CISM run were used to force the ice sheet on multi-millennium time-scales. In addition, a Recovery from 4x CO2 was conducted in which the pre-industrial forcing from a coupled CESM-CISM simulation is re-introduced after 55% mass loss. The 2x, 3x and 4x CO2 scenarios resulted in a cumulative sea level rise of 0.49 m, 3.0 m, and 8.2 m by year 4,000. The 2x CO2 scenario resulted in limited retreat and stability within 4,000 years. No stability of the ice sheet was attained by year 8,000 in the 3x CO2 simulation, with a final Mass Balance of -108.8 Gt/yr (0.30 ± mm/yr). The 4x CO2 simulation resulted in the complete deglaciation of the ice sheet within 3,000 years. Despite the lower initial topography compared to the pre-industrial ice sheet, the Recovery from 4x CO2 simulation resulted into expansion of the ice sheet. Within 4,000 years, the mass increased from 46% to 67% relative to the pre-industrial ice sheet.
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Elevation (ballistics)
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Abstract. Greenland ice sheet mass losses have increased in recent decades with approximately half of these attributed to increased surface meltwater runoff. However, controls on ice sheet water release, and the magnitude of englacial storage, firn densification, internal refreezing and other hydrologic processes that delay or reduce true water export to the global ocean remain poorly understood. This problem is amplified by scant hydrometerological measurements. Here, ice sheet surface meltwater runoff and proglacial river discharge determined between 2008 and 2010 for three sites near Kangerlussuaq, western Greenland were used to establish the water budget for a small ice sheet watershed. The water budget could not be closed in the three years, even when uncertainty ranges were considered. Instead between 12% and 53% of ice sheet surface runoff is retained within the glacier each melt year (time between onset of ice sheet runoff in two consecutive years). Evidence of the ice sheet summer meltwater escaping during the cold-season suggests that the Greenland ice sheet cryo-hydrologic system may remain active year round.
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Ice-sheet model
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A more accurate assessment of the contemporary evolution of the Greenland ice sheet and its major drainage basins requires a close interaction between observational data and modeling. The main challenge when interpreting satellite and observational data is to separate the ice mass contribution from the contribution of postglacial isostatic rebound, to separate ice-sheet dynamic changes from interannual surface mass balance changes, and to separate long-term ice-dynamic changes from short-term flow fluctuations. Here we report from recent progress towards these goals within the DFG SPP 1257 project 'Assessing the current evolution of the Greenland ice sheet' from studies combining observational data with glaciological modeling. This comprises studies to reconstruct the surface mass balance of the Greenland ice sheet between 1866 and 2006, optical satellite data from ASTER to obtain surface velocities, modelled balance velocities, and simulations with a three-dimensional thermomechanical ice-sheet model. In combination with GRACE data, these studies are expected to contribute to an improved estimate of the present-day contribution of the Greenland ice sheet to global sea-level change and a better understanding of the various contributions to current ice mass changes and their associated uncertainties.
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Groenlandia
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The Greenland Ice Sheet is the largest ice sheet in the northern hemisphere. Ongoing melting of the ice sheet, resulting in increased mass loss relative to the longer term trend, has raised concern ...
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Greenland ice sheet
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Paleoclimatology
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