The Last Interglacial in the Labrador Sea

• Main Author: Hume, Leila
• Format: Thesis
• Language: English
• Published: 2018
• Subjects: Antarctic; Greenland; Antarc*; Ice Sheet; Labrador Sea; Sea ice; Subarctic
• Online Access: https://ueaeprints.uea.ac.uk/id/eprint/67637/; https://ueaeprints.uea.ac.uk/id/eprint/67637/1/Leila_Hume_PhD_Thesis_March_2018.pdf

A multi-proxy age model protocol was established using Labrador Sea sediment cores U1305 (57°N,48°W) and U1302 (50°N,45°W). These cores provided centennial-scale surface and deep-water records spanning the last interglacial (153-100ka). Ice rafted debris (IRD) counts and meltwater-runoff proxy Ba/Ca were used to investigate ice sheet instabilities; planktonic foraminiferal assemblages, planktonic δ18O and multi-species Mg/Ca records were used to reconstruct temperature and salinity; and fluctuations in Atlantic meridional overturning circulation (AMOC) were inferred from benthic δ13C. Intense cold and ice rafting accompanied Heinrich events H11 (135–130ka) and H12 (140ka), as well as a previously unrecognised Heinrich event (H13; 150–148ka), during which benthic and planktonic δ13C values indicate reduced AMOC and nutrient-rich Antarctic bottom-water (AABW) incursions. During H11, three warm phases preceded cooling and massive IRD pulses. Strongly depleted U1302 planktonic δ18O accompanied all IRD-rich cold periods, particularly H11, attributed to sea-ice formation and enhanced meltwater input. No Younger Dryas-like event was observed. Last interglacial temperatures were 2–5°C warmer in U1305, but similar to modern values at U1302, suggesting differing latitudinal responses to increased insolation (129–126ka). A diatom mat deposited ~128.7–128.6ka in U1305 indicates a proximal subarctic convergence front. Palaeotemperature reconstructions reveal two last interglacial warm maxima. The first (128.5–126.5ka) had the most diverse foraminiferal assemblages and was coeval with continued Greenland ice-sheet melt. A previously reported red layer, linked to a Laurentide outburst flood, has been dated to ~126.5ka and marks the culmination of localised intra-interglacial cooling. Subsequent AABW incursion events suggest rapid AMOC weakening and instability. Mg/Ca results reveal a second warming (123–117ka) associated with a vigorous AMOC, and was attributed to a stronger Irminger Current. IRD, SST and isotopic evidence ...