Isopycnal Transport and Scavenging of ²³⁰Th and ²³¹Pa in the Pacific Southern Ocean

Authors

Frank J. Pavia, Lamont-Doherty Earth Observatory
Robert F. Anderson, Lamont-Doherty Earth Observatory
Paulina Pinedo-Gonzalez, Lamont-Doherty Earth Observatory
Martin Q. Fleisher, Lamont-Doherty Earth Observatory
Mark A. Brzezinski, University of California, Santa Barbara
Rebecca S. Robinson, University of Rhode Island

Document Type

Article

Date of Original Version

12-1-2020

Abstract

The Southern Ocean hosts complex connections between ocean physics, chemistry, and biology. Changes in these connections are hypothesized to be responsible for significant alterations of ocean biogeochemistry and carbon storage both on glacial-interglacial timescales and in the future due to anthropogenic forcing. Isotopes of thorium (230Th and 232Th) and protactinium (231Pa) have been widely applied as tools to study paleoceanographic conditions in the Southern Ocean. However, understanding of the chemical behavior of these isotopes in the modern Southern Ocean has been limited by a paucity of high-resolution observations. In this study, we present measurements of dissolved 230Th, 231Pa, and 232Th on a meridional transect along 170°W from 67°S to 54°S in the Pacific sector of the Southern Ocean, with high vertical and meridional sampling resolution. We find Th/Pa fractionation factors below 1, highlighting the preferential removal of Pa relative to Th in a region with low lithogenic inputs where the particle flux is dominated by biogenic opal. We also find steep gradients in all three of these isotopes along neutral density surfaces from north to south, demonstrating the importance of isopycnal mixing in transporting these nuclides to the Southern Ocean. Our results suggest that 231Pa and 230Th in the Southern Ocean are highly sensitive tracers of physical transport that may find use in studies of Southern Ocean biogeochemical-physical connections in the past, present, and future.

Publication Title, e.g., Journal

Global Biogeochemical Cycles

Volume

34

Issue

12

Citation/Publisher Attribution

Pavia, Frank J., Robert F. Anderson, Paulina Pinedo-Gonzalez, Martin Q. Fleisher, Mark A. Brzezinski, and Rebecca S. Robinson. "Isopycnal Transport and Scavenging of ²³⁰Th and ²³¹Pa in the Pacific Southern Ocean." Global Biogeochemical Cycles 34, 12 (2020). doi: 10.1029/2020GB006760.