Minimal Holocene retreat of large tidewater glaciers in K\xf8ge Bugt, southeast Greenland

Laurence M Dyke,Tavi Murray,Marit-Solveig Seidenkrantz,John F Hiemstra,Camilla S Andresen,David A Sutherland,Flor Vermassen,Anders A Bjørk,Anna L C Hughes

doi:10.1038/s41598-017-12018-x

Abstract

Køge Bugt, in southeast Greenland, hosts three of the largest glaciers of the Greenland Ice Sheet; these have been major contributors to ice loss in the last two decades. Despite its importance, the Holocene history of this area has not been investigated. We present a 9100 year sediment core record of glaciological and oceanographic changes from analysis of foraminiferal assemblages, the abundance of ice-rafted debris, and sortable silt grain size data. Results show that ice-rafted debris accumulated constantly throughout the core; this demonstrates that glaciers in Køge Bugt remained in tidewater settings throughout the last 9100 years. This observation constrains maximum Holocene glacier retreat here to less than 6 km from present-day positions. Retreat was minimal despite oceanic and climatic conditions during the early-Holocene that were at least as warm as the present-day. The limited Holocene retreat of glaciers in Køge Bugt was controlled by the subglacial topography of the area; the steeply sloping bed allowed glaciers here to stabilise during retreat. These findings underscore the need to account for individual glacier geometry when predicting future behaviour. We anticipate that glaciers in Køge Bugt will remain in stable configurations in the near-future, despite the predicted continuation of atmospheric and oceanic warming.

Highlights

Southeast Greenland has experienced dramatic glaciological changes over the last two decades
Modern temperatures at depth in Køge Bugt are around 4 °C (Fig. S1), the warm water indicator species Cassidulina neoteretis is absent from modern sediments (Fig. 4a)
The high abundance of Cassidulina neoteretis in the early-Holocene suggests that deep ocean temperatures at this time were at least as warm as the present-day (i.e. ~4 °C)

Summary

Introduction

Southeast Greenland has experienced dramatic glaciological changes over the last two decades. We analyse ice-rafted debris abundance, foraminiferal assemblages, and sortable silt grain size to constrain glacier behaviour and oceanographic conditions through the last 9100 years We use these results to assess the stability of glaciers in Køge Bugt in response to changing ocean and climatic conditions during the Holocene. The only oceanographic measurements from within Køge Bugt are temperature profiles which were obtained using sensors mounted on marine mammals[21,22] These data show a similar pattern to the continental shelf; surface waters are cold (~0 °C) to a depth of around 300 m, these are underlain by warmer (~4 °C) water masses (Fig. S1)

Methods

Results

Conclusion