A study of the dynamics of the British Ice Sheet during Marine Isotope Stages 2 and 3, focusing on Heinrich Events 2 and 4 and their relationship to the North Atlantic glaciological and climatological conditions
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A high-resolution investigation into the stratigraphy of core MD95-2006 from the Barra fan, NW Scottish continental slope has been carried out. The study focuses on key palaeoceanographic proxies (percentage Neogloboquadrina pachyderma (s), planktonic foraminiferal stable isotopes, planktonic foraminiferal and ice-rafted debris concentrations) throughout the interval between and including Heinrich Event 4 and Heinrich Event 2. A newly constructed age model produced through ties to the GRIP Greenland ice core record places this interval at approximately 20-48 ka BP. The interval covers the end of Marine Isotope Stage 3 and the start of Marine Isotope Stage 2, dating the MIS3/2 transition at 25.34-26.57 ka BP. Results reveal novel information on the dynamics of the British Ice Sheet (BIS) through this period and their relationship with other circum-North Atlantic ice sheets through a particular focus on the structure and provenance of Heinrich Events 2 and 4 within MD95-2006. The study reveals that at the time of Heinrich Event 4, placed at 36.2-36.7 ka BP, the BIS was of limited extent and significant ice sheet expansion only occurred after ca. 26.5 ka BP, coinciding with the MIS3/2 transition in the MD95-2006 record. It appears that the margin of the BIS reached the continental slope around 25 ka BP and it is likely that the period between 21.5 and 25 ka BP, represents the maximum extent of the NW Scottish ice sheet. At the time of H4, the BIS was of limited extent whereas the Laurentide Ice Sheet (LIS) was already significantly expanded, thus the dominant radioisotopic signal seen in H4 sediment in MD95-2006 is that of LIS icebergs, overcoming the BIS contribution. In contrast, H2 (21.56-21.72 ka BP) occurs at a time of increased delivery of icebergs from all North Atlantic ice sheets however the MD95-2006 record dominated by the influence of the proximal BIS. This is revealed in both the increased background level of IRD delivery and the correspondence of background and peak IRD radioisotopic ratios tending towards British provenance.
Thesis, MPhil Master of Philosophy
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