Variability in sea ice extent and primary productivity at IODP Site U1339 (Umnak Plateau, Bering Sea) during Marine Isotope Stage 11: a multi-proxy approach
Abstract
The recent rapid decline in Arctic sea ice extent has prompted concerns about the fate of sea ice in the future, and the stability of sea ice dependent ecosystems. By studying the natural variability of sea ice cover and primary productivity during past warm intervals, we can better understand the long-term response of sea ice to a warming climate. Proxy records from the Umnak Plateau (IODP Site U1339) in the Bering Sea afford the chance to examine changes in sea ice and primary productivity during a long-lived interglacial known as Marine Isotope Stage (MIS) 11 (424-374 ka), which is often considered a good analogue for future change. This work uses a multi-proxy approach (sediment grain size, diatom assemblages and stable isotopic analyses) to describe variability in sea ice extent and primary productivity at the Umnak Plateau during MIS 11. The occurrence of coarse (>150μm) sediment grains, interpreted as ice-rafted material, suggests that ice was consistently present in some parts of the Bering Sea during MIS 11. The presence of sea ice diatoms throughout the core is further evidence that sea ice persisted in the Umnak Plateau region throughout MIS 11. Specifically, the relative percent abundance of sea ice associated diatoms shows a steady increase following deglaciation, reaching a maximum during the peak interglacial warmth of Late MIS 11. Sea ice and open water diatom species co-occur in the sediments, indicating that the sea ice cover was likely seasonal. Laminated sediments at the boundary between MIS 12 and 11 point toward an interval of enhanced seasonal productivity during deglaciation. High productivity during deglaciation is also characterized by an increase in organic and inorganic carbon, and by a significant increase in Chaetoceros resting spores (RS), a diatom species associated with high productivity environments. In addition, the onset of MIS 11 is marked by an increase in the relative abundance of Neodenticula seminae, a diatom associated with the warm Alaskan Stream, suggesting a greater influence of Pacific water at the site. Changes in δ15N values are consistent with changes in Chaetoceros RS, reflecting either a change in the δ15N of source water at the site or enhanced surface nitrate utilization during intervals of high productivity.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2016
- Bibcode:
- 2016AGUFM.C31B0749T
- Keywords:
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- 0738 Ice;
- CRYOSPHEREDE: 1630 Impacts of global change;
- GLOBAL CHANGEDE: 4813 Ecological prediction;
- OCEANOGRAPHY: BIOLOGICAL AND CHEMICALDE: 4901 Abrupt/rapid climate change;
- PALEOCEANOGRAPHY