A multiproxy palaeolimnological reconstruction of the nature and timing of climatic changes in the Northern Isles from the end of the last glaciation through the early Holocene

Abstract

The Northern Isles are strongly influenced by changes in the North Atlantic Ocean atmosphere system and, as they project northwards from the British Isles, provide an ideal geographical opportunity to study changing climatic gradients during the last glacial/ interglacial transition along with the detection of regime shifts. Three proxies, diatoms, pollen, and micro-XRF sediment chemistry, have been employed to explore the nature and timing of environmental changes within the water columns and the wider catchments of Loch of Sabiston, Orkney, and Loch of Clumlie and Loch of Grimsetter, Shetland to better understand the nature and timing of environmental change within and among the island groups. The records are constrained by radiocarbon dating, supported by tephrochronology, and the Greenland ice core chronology to enable the comparison of the records produced by this study with previous research in the North Atlantic region. The diatom and lithological results from Loch of Sabiston suggest early deglaciation at c. 23,000 cal BP followed by gradual warming (GI-1e) punctuated by the cooling events coeval with GS-1 and GI-1b. However, the pollen record reflects a lagged response in the development from colonising cold tolerant vegetation to more temperate shrub and woodland communities. The Oracadian signal is dominated by the switching on and off of the accumulation of marl which serves as a supporting indicator of warmer conditions. The Shetland landscape appears to have been deglaciated later at c. 16,400 cal BP, but also has clear representation of GI-1e and the cooling events of GI-1b and GS-1. Both the Shetland and Orkney records record the dramatic cooling of the Younger Dryas but also suggest a two stage change from colder and drier to colder and wetter conditions before the onset of the Holocene. Shetland appears to have experienced less extreme climatic changes in comparison to Orkney despite being in the same present phytogeographical region. This is likely due to the former persisting in the arctic domain and the latter being closer to the latitudinal shifts in the warmer ocean circulation of the North Atlantic during the LGIT. Comparison of the three proxies demonstrates that they may differ by several hundred years in their response to dramatic climatic changes and, therefore, highlights the strength of multi-proxy approaches to reconstructing Quaternary environments. Combining proxies such as diatom and μ-XRF scanning techniques will provide a greater understanding of the processes occurring during environmental change in this region.