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

• Main Authors: Funder, Svend, Sørensen, Anita H. L., Larsen, Nicolaj K., Bjørk, Anders, Briner, Jason P., Olsen, Jesper, Schomacker, Anders, Kjær, Kurt H.
• Format: Text
• Language: English
• Published: 2020
• Subjects: Greenland; glacier; ice core; Ice Sheet; Sea ice
• Online Access: https://doi.org/10.5194/cp-2020-57; https://cp.copernicus.org/preprints/cp-2020-57/

Cosmogenic 10 Be 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 10 Be and 14 C-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.