Younger Dryas ice-margin retreat in Greenland, new evidence from Southwest Greenland

Abstract

Abstract. Cosmogenic 10Be dates from bedrock knobs on six outlying tiny islands along a stretch of 300 km of the Southwest Greenland coast, indicate that the Greenland Ice Sheet (GrIS) margin here was retreating on the inner shelf close to the coast during the Younger Dryas (YD) cold period. A survey of recently published 10Be and 14C-dated records show that this unexpected behaviour of the ice-margin has been seen also in other parts of Greenland, but with very large variations in extent and speed of retreat even between neighbouring areas. In contrast to this, landforms appearing in high resolution bathymetry surveys on the shelf, have recently been suggested to indicate YD readvance or long-lasting ice-margin still stand on mid shelf, far from the coast. However, these features have been dated primarily by correlation with cold periods in the ice core temperature records, and therefore cannot inform about the ice-margin/climate relation. Ice-margin retreat during a YD cooling has been explained by advection of warm subsurface water melting the ice-margin, and by increased seasonality of the climate with the temperature drop mainly in winter, with high impact on sea ice extent and duration, but little effect on glacier mass balance. This study therefore adds to the complexity of the climate/ice-margin relation, where local factors may for some time overrule or mute overall temperature change. It also points to the urgent need for climate-independent dating of the rich treasure trove of information coming from the shelf in these years.

Abrupt (or millennial or suborbital) climatic variability: Heinrich events/stadials

“…cold air and SST, widespread sea ice) in the North Atlantic region at that time, although it may resemble the one described in Scotland, Arctic Norway and Greenland during the Younger Dryas event (~12.5 cal ka BP). At this time, glaciers (sensitive to summer-temperature change in these regions) were retreating (Bromley et al, 2014;Funder et al, 2021;Rinterknecht et al, 2014;Wittmeier et al, 2020) while the annual mean temperature over Greenland dropped by 5-9°C (Buizert et al, 2014). The comparison between the Younger Dryas and the HS is not straightforward.…”

“…In other words, most of the seasonality is due to winter air temperature changes (Buizert et al, 2014;Denton et al, 2005) which makes it difficult to isolate the summer signal from marine and terrestrial palaeo-bioclimatic proxies. As a prominent example, palynological records reveal a rapid vegetation response to HS conditions in western Europe with semi-desert or steppic vegetation, particularly Artemisia, replacing open (boreal/temperate) forest indicating colder and drier atmospheric conditions (Fletcher et al, 2010;Sanchez-Goni et al, 2008, 2021. Artemisia is an interesting taxon with regard to the seasonal signal discussed above.…”