Regional and global signals in seawater δ18O records across the mid-Pleistocene transition

Heather L Ford,Maureen E Raymo

doi:10.1130/g46546.1

Abstract

Abstract High-resolution seawater δ18O records, derived from coupled Mg/Ca and benthic δ18O analyses, can be used to evaluate how global ice volume changed during the mid-Pleistocene transition (MPT, ca. 1250–600 ka). However, such seawater δ18O records are also influenced by regional hydrographic signals (i.e., salinity) and changes in deep-ocean circulation across the MPT, making it difficult to isolate the timing and magnitude of the global ice volume change. To explore regional and global patterns in seawater δ18O records, we reconstruct seawater δ18O from coupled Mg/Ca and δ18O analyses of Uvigerina spp. at Ocean Drilling Program Site 1208 in the North Pacific Ocean. Comparison of individual seawater δ18O records suggests that deep-ocean circulation reorganized and the formation properties (i.e., salinity) of deep-ocean water masses changed at ca. 900 ka, likely related to the transition to marine-based ice sheets in Antarctica. We also find that an increase in ice volume likely accompanied the shift in glacial-interglacial periodicity observed in benthic carbonate δ18O across the MPT, with increases in ice volume observed during Marine Isotope Stages 22 and 16.

Highlights

Even after decades of research, the mid-Pleistocene transition (MPT) remains a perplexing interval in Earth’s climate history (Shackleton and Opdyke, 1976; Raymo and Nisancioglu, 2003; Elderfield et al, 2012)
We show that deep-ocean circulation reorganization and salinity played an increasingly important role in determining the density structure of the glacial deep ocean over the mid-Pleistocene transition (MPT)
With this first δ18Osw stack across the MPT, we are able to provide an estimate of changes in global ice volume across this important climate transition

Summary

Introduction

Even after decades of research, the mid-Pleistocene transition (MPT) remains a perplexing interval in Earth’s climate history (Shackleton and Opdyke, 1976; Raymo and Nisancioglu, 2003; Elderfield et al, 2012). Another difficulty in evaluating the timing (and mechanisms) is that δ O 18 benthic values, our primary climate proxy, reflect not just the δ18O of seawater (δ18Osw, salinity and ice volume), and bottom-water temperature and the circulation history of the water mass over a particular location (Clark et al, 2006; Ford et al, 2016).

Results

Conclusion