Geometry of the Meridional Overturning Circulation at the Last Glacial Maximum

• Main Authors: Pavia, Frank J., Jones, C. Spencer, Hines, Sophia K.
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: American Meteorological Society 2022
• Subjects: Atmospheric Science; Antarc*; Antarctic; North Atlantic
• Online Access: https://doi.org/10.1175/jcli-d-21-0671.1

Understanding the contribution of ocean circulation to glacial–interglacial climate change is a major focus of paleoceanography. Specifically, many have tried to determine whether the volumes and depths of Antarctic- and North Atlantic–sourced waters in the deep ocean changed at the Last Glacial Maximum (LGM; ∼22–18 kyr BP) when atmospheric pCO₂ concentrations were 100 ppm lower than the preindustrial. Measurements of sedimentary geochemical proxies are the primary way that these deep ocean structural changes have been reconstructed. However, the main proxies used to reconstruct LGM Atlantic water mass geometry provide conflicting results as to whether North Atlantic–sourced waters shoaled during the LGM. Despite this, a number of idealized modeling studies have been advanced to describe the physical processes resulting in shoaled North Atlantic waters. This paper aims to critically assess the approaches used to determine LGM Atlantic circulation geometry and lay out best practices for future work. We first compile existing proxy data and paleoclimate model output to deduce the processes responsible for setting the ocean distributions of geochemical proxies in the LGM Atlantic Ocean. We highlight how small-scale mixing processes in the ocean interior can decouple tracer distributions from the large-scale circulation, complicating the straightforward interpretation of geochemical tracers as proxies for water mass structure. Finally, we outline promising paths toward ascertaining the LGM circulation structure more clearly and deeply. The authors thank Esther Brady, who provided data from the extended CCSM model run, together with Alan Seltzer, Kassandra Costa, Shantong Sun, and Andrew Thompson, who all read the manuscript and provided valuable feedback. Two anonymous reviewers and Andreas Schmittner contributed thorough and insightful reviews that improved the paper. S.K.H. was supported by the Investment in Science Fund at WHOI and the John E. and Anne W. Sawyer Endowed Fund in Support of Scientific ...