Constraints on ocean circulation at the Paleocene–Eocene Thermal Maximum from neodymium isotopes

April N Abbott,Brian A Haley,Aradhna K Tripati,Martin Frank

doi:10.5194/cp-12-837-2016

Abstract

Abstract. Global warming during the Paleocene–Eocene Thermal Maximum (PETM) ∼ 55 million years ago (Ma) coincided with a massive release of carbon to the ocean–atmosphere system, as indicated by carbon isotopic data. Previous studies have argued for a role of changing ocean circulation, possibly as a trigger or response to climatic changes. We use neodymium (Nd) isotopic data to reconstruct short high-resolution records of deep-water circulation across the PETM. These records are derived by reductively leaching sediments from seven globally distributed sites to reconstruct past deep-ocean circulation across the PETM. The Nd data for the leachates are interpreted to be consistent with previous studies that have used fish teeth Nd isotopes and benthic foraminiferal δ13C to constrain regions of convection. There is some evidence from combining Nd isotope and δ13C records that the three major ocean basins may not have had substantial exchanges of deep waters. If the isotopic data are interpreted within this framework, then the observed pattern may be explained if the strength of overturning in each basin varied distinctly over the PETM, resulting in differences in deep-water aging gradients between basins. Results are consistent with published interpretations from proxy data and model simulations that suggest modulation of overturning circulation had an important role for initiation and recovery of the ocean–atmosphere system associated with the PETM.

Highlights

IntroductionThe Paleocene–Eocene Thermal Maximum (PETM) represents a time of profound global change with deep-sea temperatures increasing 4–8◦ C (Katz et al, 1999; Kennett and Stott, 1991; Sluijs et al, 2006; Tripati and Elderfield, 2004, 2005; Zachos et al, 2001, 2003, 2006), widespread biological extinctions (e.g., Kennett and Stott, 1991), and ocean acidification marked by widespread carbonate dissolution occurring ∼ 55 million years ago (Ma) (Dickens, 2000; Kump et al, 2009; Ridgwell and Schmidt, 2010; Zachos et al, 2005, 2008; Zeebe and Zachos, 2007)
Our new Nd isotope data are combined with existing δ13C records and published Nd isotope data from fossil fish teeth of the Atlantic, Indian, and Southern oceans (Thomas et al, 2003) in order to obtain a reconstruction of Nd isotope distributions, and deep-ocean circulation, for all major ocean basins across the Paleocene–Eocene Thermal Maximum (PETM) at a resolution comparable to the corresponding δ13C data (Fig. 1, Table 3)
Our study provides new neodymium isotope data from Fe– Mn leachates constraining changes in ocean circulation associated with the PETM

Summary

Introduction

The Paleocene–Eocene Thermal Maximum (PETM) represents a time of profound global change with deep-sea temperatures increasing 4–8◦ C (Katz et al, 1999; Kennett and Stott, 1991; Sluijs et al, 2006; Tripati and Elderfield, 2004, 2005; Zachos et al, 2001, 2003, 2006), widespread biological extinctions (e.g., Kennett and Stott, 1991), and ocean acidification marked by widespread carbonate dissolution occurring ∼ 55 Ma (Dickens, 2000; Kump et al, 2009; Ridgwell and Schmidt, 2010; Zachos et al, 2005, 2008; Zeebe and Zachos, 2007). Abbott et al.: Constraints on ocean circulation at the Paleocene–Eocene Thermal Maximum

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