Deglacial patterns of South Pacific overturning inferred from 231Pa and 230Th

Thomas A Ronge,Walter Geibert,Jörg Lippold,Ralf Tiedemann,Finn Süfke,Samuel L Jaccard,Sebastian Mieruch-Schnülle

doi:10.1038/s41598-021-00111-1

Abstract

The millennial-scale variability of the Atlantic Meridional Overturning Circulation (AMOC) is well documented for the last glacial termination and beyond. Despite its importance for the climate system, the evolution of the South Pacific overturning circulation (SPOC) is by far less well understood. A recently published study highlights the potential applicability of the 231Pa/230Th-proxy in the Pacific. Here, we present five sedimentary down-core profiles of 231Pa/230Th-ratios measured on a depth transect from the Pacific sector of the Southern Ocean to test this hypothesis using downcore records. Our data are consistent with an increase in SPOC as early as 20 ka that peaked during Heinrich Stadial 1. The timing indicates that the SPOC did not simply react to AMOC changes via the bipolar seesaw but were triggered via Southern Hemisphere processes.

Highlights

The millennial-scale variability of the Atlantic Meridional Overturning Circulation (AMOC) is well documented for the last glacial termination and beyond
Modeling studies suggested that, depending on boundary conditions, changes in the AMOC may directly impact Pacific overturning via atmospheric teleconnections[13], raising the following questions: (i) can the bipolar seesaw h ypothesis[14], based on Atlantic data explain the reconstructed deglacial changes in the Pacific overturning circulation in general, and the South Pacific overturning circulation (SPOC) ? (ii) did the SPOC react to changes in AMOC, or did it evolve independently?
We reconstruct changes in the SPOC from a depth transect of five sediment cores from the New Zealand Margin and the East Pacific Rise (Fig. 2). These sediment cores are bathed by the major Southwest Pacific deepwater masses, including Antarctic Intermediate Water (AAIW) the Upper and Lower Circumpolar Deep Water (UCDW and LCDW) as well as the Antarctic Bottom Water (AABW)

Summary

Introduction

The millennial-scale variability of the Atlantic Meridional Overturning Circulation (AMOC) is well documented for the last glacial termination and beyond. The formation and dynamics of North Atlantic Deep Water (NADW) and more broadly the AMOC were in the focus of studies reconstructing past changes in the global overturning circulation. Collapsing Antarctic ice sheets[2,3] and rising atmospheric CO2Ref.[4] accompanied enhanced upwelling south of the Antarctic Polar Front, highlighting the importance of Southern Ocean overturning in propelling the global climate system out of the last glacial[8,9,10,11,12]. Modeling studies suggested that, depending on boundary conditions, changes in the AMOC may directly impact Pacific overturning via atmospheric teleconnections[13], raising the following questions: (i) can the bipolar seesaw h ypothesis[14], based on Atlantic data explain the reconstructed deglacial changes in the Pacific overturning circulation in general, and the South Pacific overturning circulation (SPOC) ? We aim to test the applicability of 231Pa/230Th as a paleo circulation proxy in the SW-Pacific (Fig. 2), in the context of gaining further insights into the questions outlined above

Objectives

Methods

Results

Discussion

Conclusion