2025 Theses Doctoral

Multi-Proxy Paleoceanographic Reconstructions of the Late Pleistocene Eastern Equatorial Pacific

Pallone, Celeste Teresa

The equatorial Pacific is a dynamic region, characterized by zonal and meridional asymmetries in both the ocean and the atmosphere. The asymmetries in the eastern equatorial Pacific (EEP) reach a maximum in northern hemisphere fall, when southern hemisphere trade winds cross the equator and drive the upwelling of cold, CO₂ and nutrient-rich waters along a shallow thermocline, fueling marine primary production. Interannual perturbations in ocean heat content also result in El Niño or La Niña events, which diminish or amplify these asymmetries.

In this dissertation, multi-proxy paleo-records derived from marine sediment cores are used to reconstruct fundamental aspects of the coupled ocean-atmosphere system in the EEP and to evaluate the hypothesis that changes in the seasonal distribution of equatorial insolation, which were primarily controlled by Earth’s precession, influenced the mean state and variability of the EEP in the late Pleistocene. EEP thermocline depth, reconstructed from the δ18O of multiple species of planktic foraminifera that lived at different depths in the water column, was found to oscillate between a La Niña-like and an El Niño-like state on precession timescales, in close phase with equatorial insolation during northern hemisphere late summer/early fall. EEP export production, reflected in sedimentary 231Pa/230Th, was influenced by changes in high latitude nutrient leakage and upwelling and, at times, varied on precession timescales.

Glacial increases in EEP deep ocean carbon storage, reconstructed from sedimentary authigenic 238U, occurred independently of changes in local export production. Individual δ18O analyses of the surface-dwelling foraminifera Globigerinoides ruber were used to reconstruct EEP sea-surface variability during the last interglacial and penultimate glacial period. While sea-surface variance was not significantly different from that of the late Holocene, the paleo-record suggests that the strength and frequency of ENSO events varied with changes in equatorial insolation during northern hemisphere late summer/early fall and with EEP thermocline depth.