Controls on the transport of oceanic heat to Kangerdlugssuaq Glacier, East Greenland

TOM COWTON,DAVID WILTON,PETER NIENOW,ANDREW SOLE,DONALD SLATER,EDWARD HANNA

doi:10.1017/jog.2016.117

Abstract

ABSTRACTGreenland's marine-terminating glaciers may be sensitive to oceanic heat, but the fjord processes controlling delivery of this heat to glacier termini remain poorly constrained. Here we use a three-dimensional numerical model of Kangerdlugssuaq Fjord, East Greenland, to examine controls on fjord/shelf exchange. We find that shelf-forced intermediary circulation can replace up to ~25% of the fjord volume with shelf waters within 10 d, while buoyancy-driven circulation (forced by subglacial runoff from marine-terminating glaciers) exchanges ~10% of the fjord volume over a 10 d period under typical summer conditions. However, while the intermediary circulation generates higher exchange rates between the fjord and shelf, the buoyancy-driven circulation is consistent over time hence more efficient at transporting water along the full length of the fjord. We thus find that buoyancy-driven circulation is the primary conveyor of oceanic heat to glaciers during the melt season. Intermediary circulation will however dominate during winter unless there is sufficient input of fresh water from subglacial melting. Our findings suggest that increasing shelf water temperatures and stronger buoyancy-driven circulation caused the heat available for melting at Kangerdlugssuaq Glacier to increase by ~50% between 1993–2001 and 2002–11, broadly coincident with the onset of rapid retreat at this glacier.

Highlights

Many of Greenland’s marine-terminating outlet glaciers underwent a phase of rapid retreat and acceleration in the late 1990s and early 2000s (Rignot and Kanagaratnam, 2006), with the consequent discharge of ice into the ocean responsible for 58% of total mass loss from the ice sheet over the period 2000–05 (Enderlin and others, 2014)
In the first mechanism, the exchange is driven by density gradients, which form between the fjord and shelf as a result of variability in shelf water properties, during the passage of coastal storms (e.g. Arneborg, 2004; Jackson and others, 2014)
We find that current velocities in Kangerdlugssuaq Fjord (KF) are commensurate with those observed during large wind events at SF when we force the model with Δhi = 100 m, which is at the upper end of the range of isopycnal fluctuations observed at that fjord (Jackson and others, 2014), and t = 2 d (Figs 3 and 4)

Summary

Introduction

Many of Greenland’s marine-terminating outlet glaciers underwent a phase of rapid retreat and acceleration in the late 1990s and early 2000s (Rignot and Kanagaratnam, 2006), with the consequent discharge of ice into the ocean responsible for 58% of total mass loss from the ice sheet over the period 2000–05 (Enderlin and others, 2014). This retreat was coincident with a period of ocean warming around Greenland (e.g. Hanna and others, 2009; Rignot and others, 2012), leading to suggestions that retreat may have been triggered by increased submarine melting at the calving fronts of marine-terminating glaciers The relative efficacy of these processes, and how they may differ between fjords and over time, remains poorly understood (Straneo and others, 2013)

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