Determination of sediment provenance at drift sites using hydrogen isotopes in lipids

• Main Author: Englebrecht, Amy C.
• Format: Thesis
• Language: English
• Published: Massachusetts Institute of Technology and Woods Hole Oceanographic Institution 2004
• Subjects: Marine sediments; Climatic changes; Northwest Atlantic
• Online Access: https://hdl.handle.net/1912/2067

Submitted in partial fulfillment of the requirements for the degree of Master of Science at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution February 2004 Paleoclimate records with sufficient length and temporal resolution to study the occurrence and causal mechanisms of abrupt climate change are exceedingly rare. Rapidly deposited ocean sediments provide the best archive for studying these events through geologic time, but such sites in the open ocean are limited to sediment drift deposits such as the Bermuda Rise in the northwest Atlantic. Using multiple climate proxies in a single core is becoming more common in high-resolution paleoclimate investigations, but a major potential concern for this approach arises from the possibility that the fine fraction of sediment (<63 μm), and the climate proxies within it, may represent conditions far from the deposition site. We hypothesize that hydrogen isotope ratios of alkenones, a class of lipids from phytoplankton, may provide insight into the source of fine fraction sediment. Because of their restricted sources, broad geographic distribution, and excellent preservation properties, alkenones are of particular interest in the emerging field of compound-specific hydrogen isotopic analysis, and the sedimentary abundances, extents of unsaturations, and isotopic compositions of alkenones provide quantitative and near-continuous records. We isolated alkenones from cultured unicellular algae (haptophyte Emiliania huxleyi), surface ocean particulate material, and open ocean sediments to determine the extent and variability of hydrogen isotopic fractionation in the di-, tri-, and tetraunsaturated C37 compounds. We then compared the δD of the alkenones in surface sediments between the Bermuda Rise and the Scotian Margin above which a large (~20%) δD gradient exists. We determined the fractionation between alkenones from suspended particulate samples and the water in which the phytoplankton lived, and examined the variability of ...