How is the Greenland ice sheet behaving under global warming and what are the potential impacts of ice mass loss?
Meg Stewart June 5, 2015
Outline
o Background on the Greenland Ice Sheet (GrIS)o Processes resulting in ice mass losso Proposed mechanism for GrIS mass loss
Subpolar location in the northern hemisphere
Ice sheets and glaciers are considered among the most sensitive indicators of climate change
Loss of ice mass believed to be due to 1) submarine melting, and 2) inflow of subtropical waters
Strong seasonal variations – with greater ice mass decreases observed in the summers
Background
Source: PfefferSource: Pfeffer (2011)
Background
Gravity is determined by mass. By measuring gravity anomalies, GRACE shows how mass is distributed around the planet and how it varies over time.
GRACE has been collecting gravity anomaly data since March 2002.
Gravity Recovery and Climate Experiment
or GRACE
Figure 1 - Greenland
Source: Velicogna (2009)
Greenland ice sheet losing mass at an accelerated rate
From 1992 to 2011 Greenland has lost twice the ice mass as the Antarctic ice sheet (Shepherd, et al. 2013)
Cumulative sea level rise (1989–2009)
Source: Van den Broeke, Bamber, Lenaerts & Rignot (2011)
Greenland Ice Sheet
Antarctic Ice Sheet
Total
Source: Harig, Christopher & Simons, Frederik J. (2012)
Where, Total mass balance =
surface mass balance – discharge
1) negative surface mass balance is attributed to a persistent increase in surface melt in southeast and west Greenland.
Processes resulting in ice mass loss
2) Increased ice discharge resulting from the speed up, thinning and retreat of multiple marine terminating glaciers (in contrast to those terminating on land).
Processes resulting in ice mass loss
Helheim Glacier that terminates into Sermilik Fjord in southeast Greenland. Source: Straneo & Heimbach (2013)
External forcings: changes in precipitation on the ice sheet and rising air temperatures increasing surface melting
Change in sea surface temperatures around Greenland have correlated to changes in coastal air temperatures and changes in runoff
Ocean forcing is also a potential driver of changes in the ice mélange
The mechanisms and forcings behind the increased ice discharge, however, remain elusive.
Ice-sheet-ocean interactions occurring at two scales
Warm, ocean waters from the south and Cold, fresh water from the Arctic flows around Greenland’s deep continental shelf.
Source: Straneo & Heimbach (2013)
Proposed mechanism
Cold water from the north; warm water from the south (subtropics).
Source: Straneo & Heimbach (2013)
Proposed mechanism
Source: Straneo & Heimbach (2013)
Cold water and warm water resists mixing
The warmer water works on melting the glacier, producing subglacial discharge
Buoyancy driven circulation
Proposed mechanism
Concluding thoughts
o Responses to climate change require a cross-disciplinary focus
o International collaborationo Modeling from all disciplinary fieldso New instruments on the ground, at sea and in spaceo Rigorous efforts to synthesize the heterogeneous data
streams into a coherent, sustainable and dynamic network.
Full understanding of the Greenland Ice Sheet is complicated by a relative lack of high-quality data. A concerted effort is required to reduce the uncertainty in projected contributions to sea-level rise.
References
o Harig, C. & Simons, F. J. (2012) Mapping Greenland’s mass loss in space and time. Proceedings of the National Academy of Sciences. 109 (49), 19934–19937.
o Pfeffer, W.T. (2011). Land ice and sea level rise: A thirty-year perspective. Oceanography. 24(2):94–111.
o Straneo, F. & Heimbach, P. (2013). North Atlantic warming and the retreat of Greenland’s outlet glaciers. Nature. 504, 36.
o van den Broeke, M. R., Bamber, J. L., Lenaerts & Rignot, E. (2011). Ice Sheets and Sea Level: Thinking Outside the Box. Survey Geophysics. 32, 495–505.
o Velicogna, I. (2009). Increasing rates of ice mass loss from the Greenland and Antarctic ice sheets revealed by GRACE. Geophysical Research Letters. 36, L19503.
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