The Loch Lomond Readvance on north Arran, Scotland: glacier reconstruction and palaeoclimatic implications

摘要

Geomorphological mapping of northern Arran provides evidence for two advances of locally nourished glaciers, the younger being attributable to the Loch Lomond Stade (LLS) of ca. 12.9-11.5 k yr BP, primarily through the mutually exclusive relationship between glacial limits and Lateglacial periglacial features. The age of the earlier advance is unknown. Inferred LLS glacier cover comprised two small icefields and eight small corrie or valley glaciers and totalled 11.1 km2. ELAs reconstructed using area-altitude balance ratio methods range from 268 m to 631 m for individual glaciers, with an area-weighted mean ELA of 371 m. ELAs of individual glaciers are strongly related to snow-contributing areas. The area-weighted mean ELA is consistent with a north-south decline in LLS ELAs along the west coast of Great Britain. This decline has an average latitudinal gradient of 70 m 100 km-1, equivalent to a mean southwards ablation-season temperature increase of ca. 0.42℃ 100 km-1. Mean June-August temperatures at the regional climatic ELA, estimated from chironomid assemblages in SE Scotland, lay between 5.7±0.1℃ and 4.1±0.2℃. Empirical relationships between temperature and precipitation at modern glacier ELAs indicate equivalent mean annual precipitation at the ELA lay between 2002±490 mm and 2615±449 mm. These figures suggest that stadial precipitation on Arran fell within a range between +8% and -33% of present mean annual precipitation.