Seasonal control of Petermann Gletscher ice-shelf melt by the ocean's response to sea-ice cover in Nares Strait

E. L. SHROYER,A. MÜNCHOW,L. A. STEARNS,R. M. SAMELSON,L. PADMAN

doi:10.1017/jog.2016.140

E. L. SHROYER, A. MÜNCHOW + Show 3 more

Open Access

https://doi.org/10.1017/jog.2016.140

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Abstract

AbstractPetermann Gletscher drains ~4% of the Greenland ice sheet (GrIS) area, with ~80% of its mass loss occurring by basal melting of its ice shelf. We use a high-resolution coupled ocean and sea-ice model with a thermodynamic glacial ice shelf to diagnose ocean-controlled seasonality in basal melting of the Petermann ice shelf. Basal melt rates increase by ~20% in summer due to a seasonal shift in ocean circulation within Nares Strait that is associated with the transition from landfast sea ice to mobile sea ice. Under landfast ice, cold near-surface waters are maintained on the eastern side of the strait and within Petermann Fjord, reducing basal melt and insulating the ice shelf. Under mobile sea ice, warm waters are upwelled on the eastern side of the strait and, mediated by local instabilities and eddies, enter Petermann Fjord, enhancing basal melt down to depths of 200 m. The transition between these states occurs rapidly, and seasonal changes within Nares Strait are conveyed into the fjord within the same season. These results suggest that long-term changes in the length of the landfast sea-ice season will substantially alter the structure of Petermann ice shelf and its contribution to GrIS mass loss.

Highlights

200 million people around the globe live within 1 m of the current sea level (Stern, 2006; Milne and others, 2009), making improved projections of the rate of sea-level rise an international priority
About 80% of the mass flux across the grounding line is lost through basal melting of the Petermann Gletscher ice shelf (PGIS) (Rignot and Steffen, 2008), the remainder being lost through intermittent calving events (Münchow and others, 2014) and through surface sublimation in winter and meltwater runoff in summer
The fixedgeometry ice-shelf representation used here does not allow direct modeling of the quasi-equilibrium balances that determine the large-scale structure of the ice shelf, the results suggest that the long-term stability of the PGIS may relate to the regular establishment of landfast sea ice within Nares Strait

Summary

INTRODUCTION

200 million people around the globe live within 1 m of the current sea level (Stern, 2006; Milne and others, 2009), making improved projections of the rate of sea-level rise an international priority. Over the last two decades, the mass loss rate from Greenland ice sheet (GrIS) has increased rapidly from 1 to 6 cm equivalent global sea-level rise per 100 years (Vaughan and others, 2013), with the greatest loss occurring at marine-terminating outlet glaciers (Straneo and others, 2013) This loss has been attributed to increased oceanic heat flux to the Greenland’s glaciated margins (Holland and others, 2008; Joughin and others, 2012; Straneo and Heimbach, 2013), which has been linked to increased calving rates including collapse of ice shelves and retreat of grounding lines (Pritchard and others, 2009; Pollard and others, 2015). About 80% of the mass flux across the grounding line is lost through basal melting of the Petermann Gletscher ice shelf (PGIS) (Rignot and Steffen, 2008), the remainder being lost through intermittent calving events (Münchow and others, 2014) and through surface sublimation in winter and meltwater runoff in summer. We use an improved, fully coupled ocean and seaice regional model augmented by a fixed-geometry thermodynamically coupled ice shelf to show how the ocean’s response to sea-ice conditions in Nares Strait seasonally modulates basal melting of PGIS

METHODS

OCEAN RESPONSE TO SEA-ICE COVER IN NARES STRAIT

SEASONAL CHANGES IN THE CONNECTION BETWEEN NARES STRAIT AND PETERMANN FJORD

BASAL MELT RATES FOR PETERMANN GLETSCHER ICE SHELF

Findings

DISCUSSION