Congratulations to Meghan Taylor who successfully defended her dissertation May 11, 2015.
Advisor: Ingrid Hendy
Abstract: During last glacial period, abrupt climate events were recorded in the Greenland ice core and North Atlantic sediment cores suggest major millennial scale variability in the northern North Atlantic, marked by a series of abrupt climate changes from 60 to 20 ka, first characterized by rapid shifts in the Greenland ice core oxygen isotope record. The use of high-resolution marine sediment cores in regions like the Pacific Ocean that are far afield from the region of climatic forcing allows us to evaluate different mechanisms for transmission of these major climate change events. The subarctic northeastern Pacific Ocean was also influenced by the growth and retreat of the smaller, western side of the North American ice sheet, the Cordilleran Ice Sheet (CIS). The last glacial period culminated in the last glacial maximum at ~20 ka, after which continental ice sheets retreated rapidly, discharging meltwater and raising sea level. In this dissertation I investigate the teleconnections between the North Atlantic and North Pacific Oceans during these periods of climate instability, as well as the deglacial history and retreat of the CIS.
In Chapters 2 and 3, I use the δ18Ocalcite and the ratio of Mg/Ca in planktonic foraminifera to reconstruct sea surface temperatures and δ18Oseawater from high-resolution ocean sediment core MD02-2496 offshore of Vancouver Island in the subarctic Northeastern Pacific to reconstruct the effects of ocean temperatures on the marine margin of the CIS during the deglacial. Sediment records capture the response of tidewater glaciers to significant ocean thermal forcing and the ice rafted debris record suggests an increase in calving events that coincide with the retreat of the CIS beginning around 17 ka. From 50 to 10 ka, surface ocean temperature and δ18Oseawater are compared with core sites to the south along the California margin, to examining the relative changes in surface ocean characteristics during Dansgaard-Oeschger events. Warm, relatively saline waters dominate offshore during these intervals, perhaps as a result of increased tropical waters from the south advected northward by the relative strengthening of the California Undercurrent. After 30 ka, as the CIS coalesces and begins to grow, the teleconnections between the North Atlantic and North Pacific appear to weaken.
Chapter 4 is a characterization of sediments in modern Arctic sea ice from sites in the northern Canadian Arctic Archipelago and offshore from Point Barrow, AK. Sea ice aggregates sediments entrained during sea ice formation from multiple sources including atmospheric mineral dust and terrigenous runoff, and may enriched in filterable and particulate metals relative to seawater. Sea ice may therefore contribute to surface ocean Fe concentrations during the early spring melt when surface nitrate concentrations are relatively high. In Chapter 4, elemental data from sea ice cores collected from shallow coastal regions in the Beaufort/Chukchi Sea and the Canadian Arctic are presented, and with successive sediment digestions, I estimate the potentially bioavailable pool of filterable and particulate Fe from sea ice sediments in these regions.