Repeated surging and rapid retreat of a tidewater glacier in Scotland (Younger Dryas / Greenland Stadial 1)

Abstract

This paper presents evidence of glacier surging in the British landform record. We use new high-resolution multibeam-echosounder bathymetry data to map the submarine geomorphology of a former tidewater glacier that drained the Skye Icefield, NW Scotland, during the Younger Dryas Stadial (Greenland Stadial 1) ca. 12.5-11.7 ka. Our onshore and offshore mapping identifies a glacial landform assemblage indicative of surge-type behaviour followed by rapid retreat and stagnation. We delimit three separate fjord-mouth advances of the Ainort Glacier – interpreted as palaeo-surges – successively decreasing in extent. During the quiescent phase of the final surge cycle the glacier deposited a suite of cross-fjord De Geer moraines, interpreted here as annual moraines. Their pattern and spacing suggest net annual glacier retreat rates increased significantly from around 25-75 ma-1 to 150 ma-1 to >300 ma-1, probably in the presence of seasonal sea ice. On this basis, we find that final post-surge retreat of the Ainort Glacier, from fjord mouth to marine limit (a distance of 3.5 km), was very rapid – probably taking just 20 years. Once wholly terrestrial, the glacier stagnated and did not experience further frontal oscillations. This work highlights one potential cause of asynchronous ice-mass responses in the Younger Dryas Stadial of Scotland and reinforces the importance of identifying surge-type glaciers in palaeo-glaciological studies.