Loch Lomond Stadial glaciers in North Harris, Outer Hebrides, North-West Scotland: glacier reconstruction and palaeoclimatic implications

Abstract

Geomorphological mapping of North Harris provides evidence for the former existence of 10 glaciers with a total area of ca 35 km2. A Loch Lomond (Younger Dryas) Stadial age (ca 12.9-11.5 kyr BP) for this glacial episode is inferred from glacier configuration, landsystems dominated by hummocky recessional moraines, and relationships with Lateglacial periglacial phenomena. Equilibrium line altitudes (ELAs) of 150-289 m were calculated for individual glaciers. ELA variability mainly reflects differences in snow-contributing area. The area-weighted mean ELA (204 m) is consistent with a northwards decline in ELAs along the western seaboard of the British Isles of 69.5 m (100 km)-1, equivalent to a northwards ablation-season temperature decrease of 0.42 °C (100 km)-1. This latitudinal temperature gradient implies a mean July sea-level temperature of ca 7.2 °C for the coldest part of the stade, roughly 6 °C lower than at present. Sea-level precipitation at the time of the LLS glacial maximum is inferred to have been between ca 1970±200 and 2350±200 mm yr-1, implying that LLS precipitation was up to 25% greater than now. Patterns of recessional moraines indicate that the glaciers remained close to climatic equilibrium as they retreated to their sources, though moraine belts implying near-stationary or readvancing ice margins on flat valley floors are separated by moraine-free zones indicating uninterrupted retreat. Calculation of ELAs for 'residual' glaciers in former source areas suggests that summer warming of ≤1.0 °C would have resulted in shrinkage of the glaciers to their sources. © 2007 Elsevier Ltd. All rights reserved.