Using seismic facies and pollen analyses to evaluate climatically driven change in a Scottish sea loch (fjord) over the last 20 ka

Abstract

AbstractLoch Sunart is a glacially over-deepened sea loch (fjord) on the west coast of Scotland, UK. The loch is divided into three sub-basins, separated by relatively shallow and narrow sills. A programme of data collection including high-resolution bathymetric sonar and sub-bottom seismic surveys were conducted in the loch as part of an investigation into the sedimentological and climatic change signatures preserved in western sea lochs since the Last Glacial Maximum. Very-high-resolution sub-bottom profiles were obtained using the SEISTEC boomer system. The seismic profiles revealed an igneous and metamorphic basement covered by a 10–70 m thick sediment sequence. Five different acoustic facies were recognized and interpreted in terms of glacial activity, ice retreat and subsequent Holocene sedimentation. These facies have been correlated to sediments sampled in a radiocarbon-dated 12 m long giant piston core (MD04-2833) acquired from the main basin of Loch Sunart. Pollen analyses conducted along the length of the core, together with 14C dating, indicate a complex series of palaeoclimate changes in the loch. In particular, five distinct cooling events have been recognized c. 9.8, 8.2, 5.8, 1.2 cal ka BP and 771–1211 cal a BP (possibly the Little Ice Age), corresponding to phases of Holocene rapid climate change.