Late pleistocene changes in the Peru current based on planktonic foraminifera

• Main Author: Feldberg, Melissa J.
• Other Authors: Mix, Alan C., College of Oceanic and Atmospheric Sciences, Oregon State University. Graduate School
• Format: Master Thesis
• Language: English; unknown
• Published: Oregon State University
• Subjects: Foraminifera; Fossil > Peru Current; Paleontology > Paleocene; Planktonic foraminifera
• Online Access: https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/zw12z878h

Planktonic foraminiferal faunal assemblages were used to estimate sea-surface temperatures (SST) in the southeast Pacific Ocean during the Last Glacial Maximum (LGM) and off the coast of Peru over the last 150,000 years. Temperatures along the eastern boundary of South America were 6-8° C cooler during the LGM than at present and have varied by as much as 10° C over the past 150,000 years. A likely source of ice-age cooling along the eastern boundary is an increase in the strength and a corresponding decrease in the temperature of water advected northward in the Peru Current. Evidence for this mechanism of cooling comes from incursion of subpolar foraminiferal species northward into the eastern Pacific during the LGM. We infer from this change in the fauna and decreased temperatures that stronger northward advection of eastern boundary current (EBC) waters was influential in driving cooling of the Eastern Tropical Pacific (EEP) during the LGM. The 150,000-year SST records from the Nazca Rise further reveal that changes in the strength of the Peru Current have influenced temperatures in the Eastern Equatorial Pacific on glacial-interglacial timescales. The effects of changes in the eastern boundary current on EEP temperatures are evaluated using a simple heat budget model in which equatorial SSTs are predicted from Peru Current temperatures. Variations in EBC temperatures account for about one third of the variability in equatorial SSTs. The remaining variance near the equator is probably associated with local wind-driven upwelling and is linked to the orbital cycles. We infer from this model that temperature changes in the Eastern Equatorial Pacific reflect both a direct response of equatorial upwelling to insolation and changes in eastern boundary current advection.