Southwest Greenland ice-sheet retreat during the 8.2 ka cold event

[摘要] The century-long 8.2 ka cold event interrupted early Holocene boreal warmth and may have halted retreat of Greenland ice-sheet margins during the last deglaciation. Here, we synthesize new and existing glacial geological data to assess the behavior of the southwest Greenland ice sheet during the 8.2 ka cold event. In southwest Greenland near the town of Kangerlussuaq, existing and new Be-10 surface exposure ages demonstrate that deposition of the Keglen moraines ended at 8.0 +/- 0.1 ka (n = 10, 1 outlier), with prior studies arguing that these moraines represented an ice-margin stillstand in response to the 8.2 ka cold event. However, new Be-10 ages show that the southwest Greenland ice-sheet margin retreated from the Umivit moraines, which lie 5-10 km outboard of the Keglen moraines, at 8.2 +/- 0.2 ka (n = 11). Accordingly, we suggest that the southwest Greenland ice-sheet margin in the Kangerlussuaq region retreated 5-10 km during the 8.2 ka cold event. Farther south and inland from Nuuk, new Be-10 boulder-on-bedrock ages adjacent to the modern ice-sheet margin demonstrate that the ice-margin was retreating with no moraine deposition at 8.2 +/- 0.1 ka (n = 4, 1 outlier), with this retreat continuing up to at least similar to 7.5 ka according to an existing threshold lake record. Therefore, we propose that the southwest Greenland ice-sheet margin underwent continued retreat during the 8.2 ka cold event in response to elevated early Holocene boreal summer insolation that overwhelmed the impacts from century-scale cooling. Caution should be used in assuming climatic causation for moraine deposition based on temporal correlation. (C) 2021 Elsevier Ltd. All rights reserved.

[发布日期] 2021-09-15

[关键词] Holocene;Glaciology;Paleoclimatology;Greenland;Cosmogenic isotopes;8.2 ka cold event