UC Santa Cruz

The late Paleocene and early Eocene (LPEE; ca. 59 to 52 Ma) was an interval of warming superposed on the abrupt carbon release events (or hyperthermals) of the early Eocene. The LPEE provides an opportunity to test the coupling of carbon release (and associated long- and short-term warming), to other climate-carbon cycle feedbacks (e.g., ocean acidification and shifts in the hydrologic cycle). Much work has focused on determining the sensitivities of sea surface pH, climate and the hydrologic cycle to carbon release during the largest hyperthermal of the Cenozoic, the Paleocene-Eocene Thermal Maximum (PETM; ca. 56 Ma). However, Eocene Thermal Maximum 2 (ETM-2; ca. 54 Ma) provides a secondary calibration point on assessing the sensitivity of carbon cycle-climate feedbacks to carbon release. Additionally, it has been hypothesized that the long-term carbon storage and release mechanisms (e.g., marine clathrates and organic carbon) are linked to the hyperthermal events, however, constraints on long-term changes in carbonate chemistry are lacking for the interval.

This thesis aims to characterize the nature of changes in the climate and carbon cycle associated with the onset of the LPEE warming, and subsequent cyclicity up to ETM-2 with the overarching goal of testing hypotheses for the origin of both the LPEE and ETM-2. To this end, a multiproxy approach utilizing boron- based (δ11B and B/Ca) and paleothermometry proxies (Mg/Ca and δ18O) is applied to determine the magnitude of shifts in climate, marine carbonate chemistry, and, on shorter timescales, the hydrologic cycle using materials collected from ODP Sites 1209, 1210, 1262 and 1265 (Legs 198 and 208; subtropical Pacific and Atlantic, respectively). Further, I present the first LOSCAR carbon cycle/climate numerical simulations to model the release of carbon to the atmosphere during ETM-2, constrained by the CCD, δ13C, and proxy-based observations of changes in temperature and pH. Additionally, changes in long-term Pacific sea surface pH are used to assess the validity of previously published carbon cycle simulations of the LPEE.