Ocean regulation hypothesis for glacier dynamics in southeast Greenland and implications for ice sheet mass changes

K. Scharrer,T. Murray,A. L. C. Hughes,A. Luckman,T. D. James,N. Selmes,S. R. Dye,E. Hanna,S. Cook,P. Huybrechts,A. D. Booth

doi:10.1029/2009jf001522

Abstract

Synchronous acceleration and thinning of southeast (SE) Greenland glaciers during the early 2000s was the main contributor that resulted in the doubling of annual discharge from the ice sheet. We show that this acceleration was followed by a synchronized and widespread slowdown of the same glaciers, in many cases associated with a decrease in thinning rates, and we propose that ice sheet–ocean interactions are the first‐order regional control on these recent mass changes. Sea surface temperature and mooring data show that the preceding dynamic thinning coincides with a brief decline in the cold East Greenland Coastal Current (EGCC) and East Greenland Current. We suggest this decline was partly induced by a reduction in ice sheet runoff, which allowed warm water from the Irminger Current to reach the SE Greenland coast. A restrengthening of the cold waters coincides with the glaciers' subsequent slowdown. We argue that this warming and subsequent cooling of the coastal waters was the cause of the glaciers' dynamic changes. We further suggest that the restrengthening of the EGCC resulted in part from cold water input by increased glacier calving during the speedup and increased ice sheet runoff. We hypothesize that the main mechanism for ice sheet mass loss in SE Greenland is highly sensitive to ocean conditions and is likely subject to negative feedback mechanisms.

Highlights

[2] During the early 2000s, the Greenland Ice Sheet’s annual ice discharge doubled, primarily as the result of widespread glacier acceleration and consequent thinning of the ice sheet’s southeast (SE) sector [Luthcke et al, 2006; Rignot and Kanagaratnam, 2006; Howat et al, 2008; Wouters et al, 2008]
[6] In this paper, we describe the oceanographic setting of the SE Greenland region and undertake two analyses to explore the relationship between oceanic processes and glacier dynamics
The analyses in our paper provide further evidence that the relative contribution to the East Greenland Coastal Current (EGCC) of sea ice melt and ice sheet runoff vary through the summer months and between years, and we show that sea surface temperature data evidence warm water diverted to the coast during the summer along the Kangerdlugssuaq trough

Summary

Introduction

[2] During the early 2000s, the Greenland Ice Sheet’s annual ice discharge doubled, primarily as the result of widespread glacier acceleration and consequent thinning of the ice sheet’s southeast (SE) sector [Luthcke et al, 2006; Rignot and Kanagaratnam, 2006; Howat et al, 2008; Wouters et al, 2008]. [4] Atmospheric warming can cause increased surface meltwater and, if this water reaches the glacier bed, affect glacier speeds by increasing lubrication and basal sliding. This is a well‐known effect for valley glaciers and was first reported to occur on the Greenland Ice Sheet by Zwally et al [2002]. We present evidence that that the speedup was probably terminated in part by increased discharge from the glaciers themselves, which increased ice sheet runoff and iceberg calving This discharge introduced additional cold water strengthening the East Greenland Coastal Current (EGCC).

Methods

Results

Conclusion