Document Type

Thesis

Degree

M.S.

Degree Granting Department

Marine Science

Major Professor

Amelia Shevenell

Keywords

foraminifera, Fram Strait, isotopes, meltwater, paleoceanography, radiocarbon reservoir age

Abstract

The Arctic and North Atlantic underwent significant climactic changes since the Last Glacial Maximum (25,000 years before present (1950 AD); ka BP), but offsets in the timing of events between the two regions are poorly constrained due to age model uncertainties that arise from changing radiocarbon reservoir ages. Here, we use a relatively high-resolution, multi-proxy stable isotope and sedimentologic dataset from Eastern Fram Strait (ODP Leg 162 Site 986) marine sediments to constrain the timing of Svalbard/Barents Sea Ice Sheet decay and infer deglacial reservoir ages over the last 30 ka. We use magnetic susceptibility, inorganic and organic carbon, foraminiferal assemblage counts, planktonic foraminiferal isotopes, and iceberg-rafted debris proxies to infer glaciomarine and paleoclimactic processes in Eastern Fram Strait. Significant negative Neogloboquadrina pachyderma (sinistral) δ18O episodes from background levels at 18.8 ka (-3.0 /) and 20.4 ka (-0.8 /) (on a radiocarbon-based age model) are shown to indicate meltwater discharge events from the Svalbard/Barents Sea Ice Sheet during the early glacial termination (21-14.7 ka). To allow for direct comparison between the timing of Eastern Fram Strait meltwater events and North Atlantic climate changes, the ODP Site 986 age model is correlated to the well-dated Greenland Ice Sheet Project 2 (GISP2) ice core δ18O record. The refined age model suggests that 16.0 and 18.1 ka are more realistic estimates for the meltwater events, inferring surface ocean reservoir age shifts of 1750 ± 1050 years in Eastern Fram Strait during the early glacial termination. Trends in reservoir ages throughout the last deglaciation mirror Nordic Sea deep ocean circulation changes and previously reported trends in the sub-polar North Atlantic; however, reservoir ages appear to be greater in Eastern Fram Strait. We hypothesize that processes affecting the distribution of reservoir ages in the North Atlantic and Arctic (e.g. sea ice cover, meltwater input, and ocean circulation) may have resulted in larger reservoir ages in polar regimes than in sub-polar ones during the last deglaciation, analogous to contemporary distributions. In contrast to previous radiocarbon age model-based studies in the Nordic Seas that predict a significant meltwater event at ~19 ka, these findings show that rapid Svalbard/Barents Sea Ice Sheet decay began at 16 ka and suggest that uncertainty on the order of thousands of years may exist in previous paleoclimate studies with radiocarbon-based age models from the deglacial Nordic Seas and Arctic.

Share

COinS