Bamber
Jonathan L.
Bamber
Jonathan L.
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ArticleBedMachine v3 : complete bed topography and ocean bathymetry mapping of Greenland from multibeam echo sounding combined with mass conservation(John Wiley & Sons, 2017-11-01) Morlighem, Mathieu ; Williams, Chris N. ; Rignot, Eric ; An, Lu ; Arndt, Jan Erik ; Bamber, Jonathan L. ; Catania, Ginny ; Chauché, Nolwenn ; Dowdeswell, Julian ; Dorschel, Boris ; Fenty, Ian ; Hogan, Kelly ; Howat, Ian M. ; Hubbard, Alun ; Jakobsson, Martin ; Jordan, Tom M. ; Kjeldsen, Kristian K. ; Millan, Romain ; Mayer, Larry A. ; Mouginot, Jeremie ; Noël, Brice P. Y. ; O’Cofaigh, Colm ; Palmer, Steven ; Rysgaard, Soren ; Seroussi, Helene ; Siegert, Martin J. ; Slabon, Patricia ; Straneo, Fiamma ; Van den Broeke, Michiel ; Weinrebe, W. ; Wood, Michael ; Zinglersen, Karl BrixGreenland's bed topography is a primary control on ice flow, grounding line migration, calving dynamics, and subglacial drainage. Moreover, fjord bathymetry regulates the penetration of warm Atlantic water (AW) that rapidly melts and undercuts Greenland's marine-terminating glaciers. Here we present a new compilation of Greenland bed topography that assimilates seafloor bathymetry and ice thickness data through a mass conservation approach. A new 150 m horizontal resolution bed topography/bathymetric map of Greenland is constructed with seamless transitions at the ice/ocean interface, yielding major improvements over previous data sets, particularly in the marine-terminating sectors of northwest and southeast Greenland. Our map reveals that the total sea level potential of the Greenland ice sheet is 7.42 ± 0.05 m, which is 7 cm greater than previous estimates. Furthermore, it explains recent calving front response of numerous outlet glaciers and reveals new pathways by which AW can access glaciers with marine-based basins, thereby highlighting sectors of Greenland that are most vulnerable to future oceanic forcing.
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ArticleGreenland freshwater pathways in the sub-Arctic Seas from model experiments with passive tracers(John Wiley & Sons, 2016-01-25) Dukhovskoy, Dmitry S. ; Myers, Paul G. ; Platov, Gennady A. ; Timmermans, Mary-Louise ; Curry, Beth ; Proshutinsky, Andrey ; Bamber, Jonathan L. ; Chassignet, Eric P. ; Hu, Xianmin ; Lee, Craig M. ; Somavilla, RaquelAccelerating since the early 1990s, the Greenland Ice Sheet mass loss exerts a significant impact on thermohaline processes in the sub-Arctic seas. Surplus freshwater discharge from Greenland since the 1990s, comparable in volume to the amount of freshwater present during the Great Salinity Anomaly events, could spread and accumulate in the sub-Arctic seas, influencing convective processes there. However, hydrographic observations in the Labrador Sea and the Nordic Seas, where the Greenland freshening signal might be expected to propagate, do not show a persistent freshening in the upper ocean during last two decades. This raises the question of where the surplus Greenland freshwater has propagated. In order to investigate the fate, pathways, and propagation rate of Greenland meltwater in the sub-Arctic seas, several numerical experiments using a passive tracer to track the spreading of Greenland freshwater have been conducted as a part of the Forum for Arctic Ocean Modeling and Observational Synthesis effort. The models show that Greenland freshwater propagates and accumulates in the sub-Arctic seas, although the models disagree on the amount of tracer propagation into the convective regions. Results highlight the differences in simulated physical mechanisms at play in different models and underscore the continued importance of intercomparison studies. It is estimated that surplus Greenland freshwater flux should have caused a salinity decrease by 0.06–0.08 in the sub-Arctic seas in contradiction with the recently observed salinification (by 0.15–0.2) in the region. It is surmised that the increasing salinity of Atlantic Water has obscured the freshening signal.
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ArticleInfluence of ice-sheet geometry and supraglacial lakes on seasonal ice-flow variability(Copernicus Publications on behalf of the European Geosciences Union, 2013-07-26) Joughin, Ian ; Das, Sarah B. ; Flowers, G. E. ; Behn, Mark D. ; Alley, Richard B. ; King, Matt A. ; Smith, B. E. ; Bamber, Jonathan L. ; van den Broeke, Michiel R. ; van Angelen, J. H.Supraglacial lakes play an important role in establishing hydrological connections that allow lubricating seasonal meltwater to reach the base of the Greenland Ice Sheet. Here we use new surface velocity observations to examine the influence of supraglacial lake drainages and surface melt rate on ice flow. We find large, spatially extensive speedups concurrent with times of lake drainage, showing that lakes play a key role in modulating regional ice flow. While surface meltwater is supplied to the bed via a geographically sparse network of moulins, the observed ice-flow enhancement suggests that this meltwater spreads widely over the ice-sheet bed. We also find that the complex spatial pattern of speedup is strongly determined by the combined influence of bed and surface topography on subglacial water flow. Thus, modeling of ice-sheet basal hydrology likely will require knowledge of bed topography resolved at scales (sub-kilometer) far finer than existing data (several km).
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ArticleArctic circulation regimes(The Royal Society, 2015-09-07) Proshutinsky, Andrey ; Dukhovskoy, Dmitry S. ; Timmermans, Mary-Louise ; Krishfield, Richard A. ; Bamber, Jonathan L.Between 1948 and 1996, mean annual environmental parameters in the Arctic experienced a well-pronounced decadal variability with two basic circulation patterns: cyclonic and anticyclonic alternating at 5 to 7 year intervals. During cyclonic regimes, low sea-level atmospheric pressure (SLP) dominated over the Arctic Ocean driving sea ice and the upper ocean counterclockwise; the Arctic atmosphere was relatively warm and humid, and freshwater flux from the Arctic Ocean towards the subarctic seas was intensified. By contrast, during anticylonic circulation regimes, high SLP dominated driving sea ice and the upper ocean clockwise. Meanwhile, the atmosphere was cold and dry and the freshwater flux from the Arctic to the subarctic seas was reduced. Since 1997, however, the Arctic system has been under the influence of an anticyclonic circulation regime (17 years) with a set of environmental parameters that are atypical for this regime. We discuss a hypothesis explaining the causes and mechanisms regulating the intensity and duration of Arctic circulation regimes, and speculate how changes in freshwater fluxes from the Arctic Ocean and Greenland impact environmental conditions and interrupt their decadal variability.
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ArticleRole of Greenland freshwater anomaly in the recent freshening of the subpolar North Atlantic(American Geophysical Union, 2019-04-26) Dukhovskoy, Dmitry S. ; Yashayaev, Igor ; Proshutinsky, Andrey ; Bamber, Jonathan L. ; Bashmachnikov, Igor ; Chassignet, Eric P. ; Lee, Craig M. ; Tedstone, AndrewThe cumulative Greenland freshwater flux anomaly has exceeded 5,000 km3 since the 1990s. The volume of this surplus freshwater is expected to cause substantial freshening in the North Atlantic. Analysis of hydrographic observations in the subpolar seas reveals freshening signals in the 2010s. The sources of this freshening are yet to be determined. In this study, the relationship between the surplus Greenland freshwater flux and this freshening is tested by analyzing the propagation of the Greenland freshwater anomaly and its impact on salinity in the subpolar North Atlantic based on observational data and numerical experiments with and without the Greenland runoff. A passive tracer is continuously released during the simulations at freshwater sources along the coast of Greenland to track the Greenland freshwater anomaly. Tracer budget analysis shows that 44% of the volume of the Greenland freshwater anomaly is retained in the subpolar North Atlantic by the end of the simulation. This volume is sufficient to cause strong freshening in the subpolar seas if it stays in the upper 50–100 m. However, in the model the anomaly is mixed down to several hundred meters of the water column resulting in smaller magnitudes of freshening compared to the observations. Therefore, the simulations suggest that the accelerated Greenland melting would not be sufficient to cause the observed freshening in the subpolar seas and other sources of freshwater have contributed to the freshening. Impacts on salinity in the subpolar seas of the freshwater transport through Fram Strait and precipitation are discussed.