Preprints
https://doi.org/10.5194/egusphere-2024-4107
https://doi.org/10.5194/egusphere-2024-4107
16 Jan 2025
 | 16 Jan 2025

Southern Hemisphere tree-rings as proxies to reconstruct Southern Ocean upwelling

Christian Blair Lewis, Rachel Corran, Sara Mikaloff-Fletcher, Erik Behrens, Rowena Moss, Gordon Brailsford, Andrew Lorrey, Margaret Norris, and Jocelyn Turnbull

Abstract. The Southern Ocean plays a key role in regulating global climate and acting as a carbon sink. This region, defined as south of 35° S, is accountable for 40 % of all oceanic anthropogenic CO2 uptake, and 75 % of ocean heat uptake between 1861 and 2005. However, the strength of the Southern Ocean sink (air-sea CO2 flux) is variable – weakening in the 1990s and strengthening again in the 2000s. Typical methods of constraining the flux must grapple with two opposing forces: outgassing of natural CO2 and uptake of anthropogenic CO2. Reconstructions of atmospheric radiocarbon (Δ14CO2) from Southern Hemisphere tree-rings may be a viable method of observing the one-way outgassing flux of natural CO2, driven by Southern Ocean upwelling. Here we present more than 400 tree-ring ∆14C measurements from 13 sites in Chile and New Zealand from the 1980s to the present. These measurements dramatically expand the dataset of Southern Hemisphere atmospheric Δ14CO2 records. We use these records to analyse latitudinal gradients in reconstructed atmospheric Δ14CO2 across the Southern Ocean. Tree-rings from New Zealand’s Campbell Island (52.5S, 169.1E) show Δ14CO2 was on average 3.3±3.5 ‰ lower than atmospheric background, driving a latitudinal gradient among New Zealand sites between 41.1° S and 52.5° S, whereas samples from similar latitudes in Chile do not exhibit such a strong gradient. We demonstrate that the gradient is driven by the combination of CO2 outgassing from the Antarctic Southern Zone (ASZ) and atmospheric transport to the sampling sites.

Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this paper. While Copernicus Publications makes every effort to include appropriate place names, the final responsibility lies with the authors. Views expressed in the text are those of the authors and do not necessarily reflect the views of the publisher.
Share

Journal article(s) based on this preprint

26 Aug 2025
| Highlight paper
Southern Hemisphere tree rings as proxies to reconstruct Southern Ocean upwelling
Christian Lewis, Rachel Corran, Sara E. Mikaloff-Fletcher, Erik Behrens, Rowena Moss, Gordon Brailsford, Andrew Lorrey, Margaret Norris, and Jocelyn Turnbull
Biogeosciences, 22, 4187–4201, https://doi.org/10.5194/bg-22-4187-2025,https://doi.org/10.5194/bg-22-4187-2025, 2025
Short summary Co-editor-in-chief
Christian Blair Lewis, Rachel Corran, Sara Mikaloff-Fletcher, Erik Behrens, Rowena Moss, Gordon Brailsford, Andrew Lorrey, Margaret Norris, and Jocelyn Turnbull

Interactive discussion

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Review', Anonymous Referee #1, 27 Jan 2025
  • RC2: 'Comment on egusphere-2024-4107', Anonymous Referee #2, 27 Jan 2025
  • RC3: 'Comment on egusphere-2024-4107', Anonymous Referee #3, 08 Feb 2025

Interactive discussion

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Review', Anonymous Referee #1, 27 Jan 2025
  • RC2: 'Comment on egusphere-2024-4107', Anonymous Referee #2, 27 Jan 2025
  • RC3: 'Comment on egusphere-2024-4107', Anonymous Referee #3, 08 Feb 2025

Peer review completion

AR: Author's response | RR: Referee report | ED: Editor decision | EF: Editorial file upload
ED: Reconsider after major revisions (02 Apr 2025) by Niels de Winter
AR by Christian Lewis on behalf of the Authors (17 Apr 2025)  Author's response   Author's tracked changes   Manuscript 
ED: Referee Nomination & Report Request started (18 Apr 2025) by Niels de Winter
RR by Anonymous Referee #1 (22 Apr 2025)
ED: Publish subject to minor revisions (review by editor) (23 Apr 2025) by Niels de Winter
AR by Christian Lewis on behalf of the Authors (02 May 2025)  Author's response   Author's tracked changes   Manuscript 
ED: Publish as is (07 May 2025) by Niels de Winter
AR by Christian Lewis on behalf of the Authors (09 May 2025)  Author's response   Manuscript 

Journal article(s) based on this preprint

26 Aug 2025
| Highlight paper
Southern Hemisphere tree rings as proxies to reconstruct Southern Ocean upwelling
Christian Lewis, Rachel Corran, Sara E. Mikaloff-Fletcher, Erik Behrens, Rowena Moss, Gordon Brailsford, Andrew Lorrey, Margaret Norris, and Jocelyn Turnbull
Biogeosciences, 22, 4187–4201, https://doi.org/10.5194/bg-22-4187-2025,https://doi.org/10.5194/bg-22-4187-2025, 2025
Short summary Co-editor-in-chief
Christian Blair Lewis, Rachel Corran, Sara Mikaloff-Fletcher, Erik Behrens, Rowena Moss, Gordon Brailsford, Andrew Lorrey, Margaret Norris, and Jocelyn Turnbull

Model code and software

Code used in this manuscript Christian Lewis https://github.com/christianlewis091/science_projects/tree/main/soar_tree_rings/scripts_EGU_submission

Christian Blair Lewis, Rachel Corran, Sara Mikaloff-Fletcher, Erik Behrens, Rowena Moss, Gordon Brailsford, Andrew Lorrey, Margaret Norris, and Jocelyn Turnbull

Viewed

Total article views: 519 (including HTML, PDF, and XML)
HTML PDF XML Total Supplement BibTeX EndNote
398 95 26 519 45 20 41
  • HTML: 398
  • PDF: 95
  • XML: 26
  • Total: 519
  • Supplement: 45
  • BibTeX: 20
  • EndNote: 41
Views and downloads (calculated since 16 Jan 2025)
Cumulative views and downloads (calculated since 16 Jan 2025)

Viewed (geographical distribution)

Total article views: 501 (including HTML, PDF, and XML) Thereof 501 with geography defined and 0 with unknown origin.
Country # Views %
  • 1
1
 
 
 
 
Latest update: 26 Aug 2025
Download

The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.

Short summary
The Southern Ocean carbon sink is a balance between two opposing forces: CO2 absorption at mid-latitudes and CO2 outgassing at high-latitudes. Radiocarbon analysis can be used to constrain the latter, as upwelling waters outgas old CO2, diluting atmospheric radiocarbon content. We present tree-ring radiocarbon measurements from New Zealand and Chile. We show that low radiocarbon in New Zealand’s Campbell Island is linked to outgassing in the critical Antarctic Southern Zone.
Share