The Greenland ice sheet is losing mass at an accelerated rate due to warming global temperatures. It is losing mass through two main processes: 1) subsurface melting due to warm subtropical waters flowing around Greenland's continental shelf and interacting with coastal glaciers, and 2) increased surface melting and runoff due to rising air temperatures. A proposed mechanism is that warm southern waters and cold northern waters circulate in the ocean around Greenland's coastline without fully mixing, allowing the warmer waters to interact with and melt glaciers from below. Understanding the mechanisms driving increased ice discharge from glaciers remains challenging due to limited observational data from the region.

1. 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

2. Outline
o Background on the Greenland Ice Sheet (GrIS)
o Processes resulting in ice mass loss
o Proposed mechanism for GrIS mass loss

3. 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

4. Source: PfefferSource: Pfeffer (2011)
Background

5. 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

6. 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)

7. Cumulative sea level rise (1989–2009)
Source: Van den Broeke, Bamber, Lenaerts & Rignot (2011)
Greenland Ice Sheet
Antarctic Ice Sheet
Total

8. 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

9. 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)

10. 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.

11. 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

12. Cold water from the north;
warm water from the south
(subtropics).
Source: Straneo & Heimbach (2013)
Proposed mechanism

13. 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

14. Concluding thoughts
o Responses to climate change require a cross-disciplinary
focus
o International collaboration
o Modeling from all disciplinary fields
o New instruments on the ground, at sea and in space
o 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.

15. 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.