Radiogenic Isotopes and Late Pleistocene Climate Changes in the Central Equatorial Pacific

Abstract

This work focuses on reconstructing changes in atmospheric and bottom water circulation in the Central Equatorial Pacific (CEP) through the last 150 000 years, to examine how atmospheric and oceanic system respond to changes in global temperature in glacial-interglacial timescales. This work is part of a larger conversation in paleoclimate and paleoceanography that investigates the link between changes in northern hemisphere insolation and ocean-atmosphere interactions in the Southern Ocean. These focus in these relationship from two different perspectives. Section 2 and 3 examine dust provenance to reconstruct changes in tropical hydroclimate, in particular the changes in the position of the Intertropical Convergence Zone (ITCZ) the zone of maximum precipitation. I study a 7° north-south transect in the CEP at 160° W, across the annual latitudinal range of the modern ITCZ. This dust provenance work relies on measuring the changes in lead (Pb) and neodymium (Nd) isotopes in the chemically isolated dust fraction of marine sediments. First, I look at ITCZ changes from the last 30 kyr to the mid-Holocene, in order to examine the difference between glacial and interglacial conditions. I suggest that the ITCZ reached its southernmost position during glacial times. I identify this shift in the ITCZ by noting an increase in dust of Asian provenance in the more southern cores. During warmer global climate periods, the ITCZ migrates farther north. I also examine the changes in the ITCZ across the penultimate deglaciations by examining samples from 110 to 150 kyr. I found that the southernmost position of the ITCZ occurred during the peak deglaciation (between 136 and 131 kyr), with a subsequent interglacial movement of more than 7° north. I also investigate the changes in deep-water circulation in the CEP over the last two glacial cycles (from the mid-Holocene to 150 kyr ago) using the Nd isotopic composition of fossil fish debris as a water mass tracer. I discovered an interesting response of Nd in fish debris to low oxygen conditions, a critical contribution to the field, as it complicates the paleoceanographic reconstructions that have been published using Nd isotopes as a conservative tracer. By taking a holistic multi-proxy approach, I was able to constrain the sources that affect Nd in fish debris and improve our current understanding of the respired carbon pool that is argued to be ventilated by the Southern Ocean during deglaciations.