Palaeoclimate reconstruction of the Northern Isles of Scotland, and Caithness, during the Last Glacial – Interglacial Transition

Abstract

Reconstructing high-resolution records of atmospheric temperature change is necessary to better understand the oceanic-atmospheric-terrestrial systems of the North Atlantic region. Using chironomid assemblages to reconstruct mean July summer temperatures is a robust method allowing for records of climate change to be made on sub-centennial scales. No records are available for the north coast and Northern Isles of Scotland presently. Sediments from three Scottish sites (Shetland, Orkney and Caithness) spanning the Last Glacial – Interglacial transition (c.15-10k cal a BP) were analysed for chironomid assemblages, micro-XRF geochemical markers, long-chain alkenones and lithology to enhance our understand of palaeoclimate and environmental changes during this time. These sites are located close to the North Atlantic Ocean, are highly sensitive to fluctuations in the thermohaline circulation and are prime localities to study the complex interaction between the ocean-atmosphere-terrestrial systems. Mean July summer temperature records have been inferred from chironomid assemblages found in lacustrine sediments from Orkney and Shetland (Northern Isles) and Caithness (the north coast of Scotland), complemented by the first long chain alkenone (LCA) spring lake temperature record for Scotland (Caithness). The chironomid and LCA records have provided a better understanding of seasonality in the climate records: showing that spring lake temperatures warmed earlier than summer temperatures and shows temporal, and magnitudinal, leads and lags between sites across N.W Europe. Chironomid and alkenone inferred temperatures captured the abrupt cooling phases GI-d (6-7 ̊C), GI-1b (6-7 ̊C) and GS-1(5-6 ̊C) found in the Greenland ice core records. The warming phases GI-1e (10-11 ̊C), GI-1c (8-9.5 ̊C), GI-1a (10-11.5 ̊C) and the Holocene onset (12 ̊C) have also been recorded. Orkney and Caithness record the subtle three-phased event GI-1c, highlighting the warmer GI-1c (1), cooler GI-1c (2) and the warmer GI-1c (3) stage. Summer trends in Shetland are not as abrupt as those in Caithness and Orkney and trends in Shetland are more similar to those in Greenland than in other Scottish sites.