Geochemical investigations of Quaternary paleoclimate and environmental change from Lake Titicaca, South America and Prydz Bay, Antarctica

This dissertation is comprised of multi-proxy investigations of Quaternary paleoclimatic and environmental change from two regions of importance to the global climate system: the Central Andes of South America and East Antarctica.; A study of the stable isotopic, elemental, and sedimentary characteristics of a unique set of mid-Holocene age laminated sediments from Lake Titicaca provides a high-resolution record of climate variability for the northern Altiplano region of South America. The results of this study indicate that the mid-Holocene multi-millennial drought featured at least three multidecadal-century scale arid episodes in which lake level dropped by up to 30 meters. Each of these episodes would have required instantaneous reductions of 10–50% in precipitation or 2–8°C increases in temperature. A study of the distribution of three different classes of lipid molecular fossils gives clues to the ecological history of Lake Titicaca over the past 25,000 years. Sharp changes in lake ecology occurred during the mid-Holocene in response to the long-term drought. Mid-Holocene Lake Titicaca is distinguished from other periods by being dominated by a few opportunistic algal species, probably one or two dinoflagellate and chrysophyte species that are presently rare or absent in the lake. The presence of long-chain alkenones in mid-Holocene sediments gives a relative indicator of lake temperature and the possibility of an indicator of absolute lake temperature if the source organism can be identified.; Changes in the size of the Lambert Glacier-Amery Ice Shelf system serve as a proxy for the larger East Antarctic Ice Sheet. Stable isotopic measurements of Neogloboquadrina pachyderma (s.) planktonic foraminfers coupled with sedimentary data from Ocean Drilling Program Hole 1167A drilled in the Prydz Channel Trough Mouth Fan suggest long-term cooling and ice sheet growth since the early Pleistocene. A “warm” interglacial indicated by lowered δ18O values and sedimentary evidence occurred between 0.9–1.38 Ma. Stable isotopic results indicate only two glacial-interglacial cycles stratigraphically between the Brunhes-Matuyama paleomagnetic reversal (780 Ka) and a much younger date at the top of the core (36.9 Ka), raising the possibility that there have been few extreme advances of the ice sheet across Prydz Bay since mid-Pleistocene time.