The deglaciation of coastal areas of southeast Greenland

Abstract

Large marine-terminating glaciers around the margins of the Greenland Ice Sheet have retreated, accelerated, and thinned over the last two decades. Relatively little is known about the longer-term behaviour of the Greenland Ice Sheet, yet this information is valuable for assessing the significance of modern changes. We address this by reporting 11 new beryllium-10 ( 10 Be) exposure ages from previously uninvestigated coastal areas across southeast Greenland. The new ages are combined with existing data to assess the timing of glacier retreat across the region.Results show that deglaciation occurred first in the north of the region (~68°N), and progressed southwards. This north-south progression is attributed to the influence of the warm Irminger Current on the ice margin. Areas in the south of the region were isolated from the warm waters by the shallow bathymetry of the continental shelf. This demonstrates that oceanographic forcing paced the deglaciation of southeast Greenland through the Younger Dryas and early Holocene. In most areas of southeast Greenland bedrock ages are systematically older than their counterpart boulder samples; this offset is likely the result of inherited 10 Be content in bedrock surfaces. This suggests that subglacial erosion during the last glacial cycle was insufficient to completely remove pre-existing 10 Be content. Alternatively, this pattern may be the signature of a substantial retreat and advance cycle prior to final Holocene deglaciation.

Younger Dryas ice margin retreat in Greenland: new evidence from southwestern Greenland

“…In areas where the dated record goes back only to the middle YD, such as most of our area, or areas where the ice remained on the shelf until early Preboreal times, as shown by recent cosmogenic dates from coastal southeastern Greenland and the Sisimiut area (Fig. 4) (Dyke et al, 2018;Rainsley et al, 2018;Levy et al, 2020;Young et al, 2020), the ice margin retreat may be seen as a response to the slow warming in the latter portion of the YD (Vacco et al, 2009;Buizert et al, 2018). Therefore, while the dated records going back to Allerød times do not show evidence of ice margin readvance or stillstand at the initial YD cooling, a readvance may have occurred in other areas, considering the large variation in YD ice margin behaviour seen in the dated records.…”

“…4). More recently, GrIS retreat during the YD has been corroborated from the Disko Bugt shelf (Hogan et al, 2016;Oksman et al, 2017) and from eastern and southern Greenland (Levy et al, 2016;Andrews et al, 2018;Dyke et al, 2018;Rainsley et al, 2018).…”

“…The fresher and lighter water eventually sealed off the Atlantic surface circulation from the atmosphere and impeded the Atlantic Meridional Overturning Circulation (AMOC). However, warm water from the subtropical areas was still driven into the North Atlantic but as subsurface currents (Marcott et al, 2011;Ezat et al, 2014). The subsurface water followed the path of the present North Atlantic surface circulation in the Irminger Current running south along southeastern Greenland, continuing around Greenland's southern tip, and heading northwards as the West Greenland Current (Fig.…”

“…Today warm subsurface water from these currents, below a cap of fresher water, causes extensive melting of floating outlet glaciers in Greenland (e.g. Mayer et al, 2000;Motyka et al, 2011), and during the early phase of deglaciation when the GrIS had its entire margin on the shelf it was especially sensitive to the advection of warm subsurface water, causing ice margin retreat even when temperatures were dropping, as discussed extensively in the literature (Kuijpers et al, 2003;Jennings et al, 2006;Knutz et al, 2011;Rinterknecht et al, 2014;Winsor et al, 2015b;Sheldon et al, 2016;Sinclair et al, 2016;Jennings et al, 2017;Oksman et al, 2017;Andrews et al, 2018;Dyke et al, 2018;Rainsley et al, 2018).…”

An updated radiocarbon-based ice margin chronology for the last deglaciation of the North American Ice Sheet Complex

“…Although recent work has taken place in these regions (Winsor et al, 2015;Sinclair et al, 2016;Corbett et al, 2017a;Larsen et al, 2017;Levy et al, 2017;Dyke et al, 2018), the resulting glacial chronologies are heavily reliant on cosmogenic exposure dating and thus include assumptions and sources of error not discussed in this largely radiocarbon-based review. Readers interested in updated ice margin maps from these regions are encouraged to read local studies.…”