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

Pavia, Frank J. and Anderson, Robert F. and Pinedo-Gonzalez, Paulina and Fleisher, Martin Q. and Brzezinski, Mark A. and Robinson, Rebecca S. (2020) Isopycnal Transport and Scavenging of ²³⁰Th and ²³¹Pa in the Pacific Southern Ocean. Global Biogeochemical Cycles, 34 (12). Art. No. e2020GB006760. ISSN 0886-6236.

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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.

Item Type:Article
Related URLs:
URLURL TypeDescription ItemDissolved Th and Pa data ItemDissolved and biogenic silica data ItemCTD data
Pavia, Frank J.0000-0003-3627-0179
Anderson, Robert F.0000-0002-8472-2494
Pinedo-Gonzalez, Paulina0000-0003-4613-1113
Fleisher, Martin Q.0000-0002-1141-8723
Brzezinski, Mark A.0000-0003-3432-2297
Robinson, Rebecca S.0000-0002-8072-1603
Alternate Title:Isopycnal Transport and Scavenging of 230Th and 231Pa in the Pacific Southern Ocean
Additional Information:© 2020 American Geophysical Union. Issue Online: 25 November 2020; Version of Record online: 25 November 2020; Accepted manuscript online: 12 November 2020; Manuscript accepted: 02 November 2020; Manuscript revised: 19 October 2020; Manuscript received: 21 July 2020. This work was supported by U.S. National Science Foundation grant OPP‐1542962 to LDEO and an NSF Graduate Research Fellowship to F. J. P. (DGE‐1644869). We thank the captain and crew of the R/V Nathaniel B. Palmer for their support in difficult conditions on the NBP1702 cruise. Discussions with Spencer Jones and Sophie Hines improved the quality of the paper, as did comments from Matthieu Roy‐Barman and an anonymous reviewer. Data Availability Statement: Dissolved Th and Pa data are available online through BCO‐DMO (at https://www.bco‐ Dissolved and biogenic silica data can be found online (at https://www.usap‐, and CTD data can be found through MGDS (at http://www.marine‐
Funding AgencyGrant Number
NSF Graduate Research FellowshipDGE-1644869
Subject Keywords:Thorium; Protactinium; Southern Ocean; Isopycnal Mixing; GEOTRACES
Issue or Number:12
Record Number:CaltechAUTHORS:20201116-140728988
Persistent URL:
Official Citation:Pavia, F. J., Anderson, R. F., Pinedo‐Gonzalez, P., Fleisher, M. Q., Brzezinski, M. A., & Robinson, R. S. (2020). Isopycnal transport and scavenging of 230Th and 231Pa in the Pacific Southern Ocean. Global Biogeochemical Cycles, 34, e2020GB006760.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:106682
Deposited By: Tony Diaz
Deposited On:16 Nov 2020 22:36
Last Modified:25 Nov 2020 17:44

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