Early Holocene history of the west Greenland Ice Sheet and the GH-8.2 event

Abstract

The margin of the Greenland Ice Sheet retreated rapidly during the first few thousand years of the Holocene. During this period of relative warmth, known as the Holocene thermal maximum, ice core records identify a significant short-lived cooling event at approximately 8.4–8.0 ka cal. yr BP (the ‘GH-8.2 event’) associated with a 5–7 °C fall in mean annual air temperature over the centre of the ice sheet. In this paper we constrain the history of the ice sheet margin in Disko Bugt (west Greenland) and that of a major ice stream, Jakobshavns Isbrae, during the early Holocene, which incorporates the interval of the GH-8.2 event. Our work is based on a new relative sea-level curve and minimum age estimates for the timing of deglaciation from two field sites, combined with a review of previously published research from the study area. We identify important differences in the chronology of ice margin recession during the early Holocene, most noticeably, the margin of Jakobshavns Isbrae retreated well inland of the adjacent ice sheet at this time. We conclude that the early Holocene ‘Fjord Stade’ moraines in Disko Bugt do not record a uniform ice sheet margin response to the GH-8.2 event. Rather, these moraines are diachronous and formed between c. 10–8 ka cal. yr BP, their age varying as a function of the interplay between topography and ice sheet/ice stream dynamics. We hypothesise that one cause for the lack of an identifiable response to the GH-8.2 event is because topographic controls dominated ice sheet behaviour at this time. In lowland areas, any increase in ice sheet mass balance was probably associated with an increase in calving rather than any major advance of a grounded ice sheet margin.