Velocity increases at Cook Glacier, East Antarctica, linked to ice shelf loss and a subglacial flood event

Bertie W J Miles,Stewart S R Jamieson,Chris R Stokes

doi:10.5194/tc-12-3123-2018

Abstract

Abstract. Cook Glacier drains a large proportion of the Wilkes Subglacial Basin in East Antarctica, a region thought to be vulnerable to marine ice sheet instability and with potential to make a significant contribution to sea level. Despite its importance, there have been very few observations of its longer-term behaviour (e.g. of velocity or changes at its ice front). Here we use a variety of satellite imagery to produce a time series of ice front position change from 1947 to 2017 and ice velocity from 1973 to 2017. Cook Glacier has two distinct outlets (termed East and West), and we observe the near-complete loss of the Cook West Ice Shelf at some time between 1973 and 1989. This was associated with a doubling of the velocity of Cook West Glacier, which may also be linked to previously published reports of inland thinning. The loss of the Cook West Ice Shelf is surprising given that the present-day ocean climate conditions in the region are not typically associated with catastrophic ice shelf loss. However, we speculate that a more intense ocean climate forcing in the mid-20th century may have been important in forcing its collapse. Since the loss of the Cook West Ice Shelf, the presence of landfast sea ice and mélange in the newly formed embayment appears to be important in stabilizing the glacier front and enabling periodic advances. We also show that the last calving event at the larger Cook East Ice Shelf resulted in the retreat of its ice front into a dynamically important portion of the ice shelf and observe a short-lived increase in velocity of Cook East between 2006 and 2007, which we link to the drainage of subglacial Lake Cook. Taken together, these observations suggest that the velocity, and hence discharge, of Cook Glacier is highly sensitive to changes at its terminus, but a more detailed process-based analysis of this potentially vulnerable region requires further oceanic and bathymetric data.

Highlights

Ice which is grounded well below sea level in the marine basins of Antarctica with an inland-sloping bed is potentially vulnerable to marine ice sheet instability
The Cook East Ice Shelf last underwent a major calving event at some point between 1963 and 1973 (Figs. 2 and 3). This calving event resulted in the retreat of its ice front deep into the constrained section of its embayment, resulting in the loss of all passive ice and retreat into the dynamically constrained section of the ice shelf (Furst et al, 2016) (Fig. 2)
An inspection of the current morphology of the Cook East Ice Shelf reveals no obvious signs of an imminent calving event, and we suggest another calving event is at least several years away

Summary

Introduction

Ice which is grounded well below sea level in the marine basins of Antarctica with an inland-sloping bed is potentially vulnerable to marine ice sheet instability. Thinning or retreat of these ice shelves reduces their ability to restrain flow from the ice sheet (Pritchard et al, 2012) This is evident in parts of the West Antarctic Ice Sheet (WAIS) where the feedbacks resulting from the rapid thinning of ice shelves (Paolo et al, 2015) has resulted in an increased discharge of ice into the ocean (Mouginot et al, 2014). This oceanic-driven thinning of ice shelves may have destabilized the Thwaites Glacier basin, where marine ice sheet instability may already be underway, and which might undermine much of the WAIS over the coming decades to centuries (Joughin et al, 2014)

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Conclusion