Date of Award
Doctor of Philosophy (PhD)
R. Mark Leckie
Robert M. DeConto
Bering Sea, Diatoms, IP25, Marine Isotope Stage 11, Pacific Decadal Oscillation, Sea Ice
Earth Sciences | Geology
The recent, rapid decline in Arctic summer sea ice extent has prompted questions as to the rates and magnitude of previous sea ice decline and the affect of this physical change on icerelated ecosystems. However, satellite data of sea ice only extends back to 1978, and mapped observations of sea ice prior to the 1970s are sparse at best. Inventories of boreal ecosystems are likewise hampered by a paucity of investigations spanning more than the past few decades. Paleoclimate records of sea ice and related primary productivity are thus integral to understanding how sea ice responds to a changing climate. Here I examine modern sedimentation, decadal-scale climate change in the recent past, and centennial- to millennial-scale changes of the past 400 ka using both qualitative and quantitative diatom data in concert with sedimentology and organic geochemistry.
Diatom taxonomy and corresponding ecological affinities are compiled in this study and updated for the Bering Sea region and then used as recorders of past climate changes. In recent decades, the Pacific Decadal Oscillation and the strength of the Aleutian Low are reflected by subtle changes in sediment diatom assemblages at the Bering Sea shelf-slope break. Farther back in time, the super-interglacial, marine isotope stage (MIS) 11 (428-390ka), began in Beringia with extreme productivity due to flooding of the Bering Land Bridge. A moisture-driven advance of Beringian glaciers occurred while eustatic sea level was high, and insolation and seasonality both decreased at the global peak of MIS 11. Atlantic/Pacific teleconnections during MIS 11 include a reversal in Bering Strait throughflow at 410 ka and a relationship between North Atlantic Deep Water Formation and Bering Sea productivity. Finally, concentrations of the biomarker-based sea ice proxy, IP25, are compared to sea ice concentration across the Bering and Chukchi seas. Changes in the concentration of IP25 in the sediments may be driven by the length of time that the epontic diatom bloom lasts. When combined with a sediment-based proxy for sea surface temperatures, IP25 can be used to reconstruct spring ice concentration.
Caisse, Beth A., "Diatoms as Recorders of Sea Ice in the Bering and Chukchi Seas: Proxy Development and Application" (2012). Open Access Dissertations. Paper 547.