UC Santa Cruz

As humanity embarks on a global experiment in climate warming associated with increased levels of atmospheric greenhouse gases, we require a thorough understanding of the mechanisms, dynamics, and spatial extent of current and past environmental change on a range of timescales. In the past 1.5 million years (Pleistocene and Holocene), glacial-interglacial cycles emerge as the dominant pattern of orbital-scale global temperature change with millennial-scale oscillations superimposed. The ~100-ka glacial cycles are especially well recognized in the oceanographic and geologic records, though the climate-ocean dynamics and feedback mechanisms responsible for these glacial cycles are often a source of debate. Past sea-surface temperature (SST) is an especially useful indicator of past environmental conditions and a multitude of paleotemperature indicators exist. I make use of a number of geochemical signals for SST including the magnesium-calcium ratio of biogenic calcite, oxygen isotopes, and the alkenone unsaturation index from lipid ketones in order to better understand the mechanisms and dynamics of the current and past climate system.

The California Current and the tropical Pacific are two of the major features that influence climate in California, the tropics, and across the globe through direct effects (e.g., upwelling, sea surface temperature changes) and atmospheric teleconnections. This dissertation examines past oceanic and atmospheric change in these two critical regions and linkages with high-latitude climate, insolation, and radiative greenhouse gas forcing. The coastal California chapter addresses questions regarding the regional and local strength of the California Current, upwelling intensity, and precipitation variability in the Holocene. Tropical Pacific chapters deal with the spatial distribution of tropical Pacific sea-surface temperatures as a reflection of oceanographic change and a driver of global climate. Each of these regions offers lessons for understanding climate variability from the late Pleistocene to the present and future climates.