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Exploring the relationship between sea ice and phytoplankton growth in the Weddell Gyre using satellite and Argo float data

Exploring the relationship between sea ice and phytoplankton growth in the Weddell Gyre using satellite and Argo float data
Exploring the relationship between sea ice and phytoplankton growth in the Weddell Gyre using satellite and Argo float data
Some of the highest rates of primary production across the Southern Ocean occur in the seasonal ice zone (SIZ), making this a prominent area of importance for both local ecosystems and the global carbon cycle. There, the annual advance and retreat of ice impacts light and nutrient availability, as well as the circulation and stratification, thereby imposing a dominant control on phytoplankton growth. In this study, the drivers of variability in phytoplankton growth between 2002–2020 in the Weddell Gyre SIZ were assessed using satellite net primary production (NPP) products alongside chlorophyll-a and particulate organic carbon (POC) data from autonomous biogeochemical floats. Although the highest daily rates of NPP are consistently observed in the continental shelf region (water depths shallower than 2000 m), the open-ocean region’s larger size and longer ice-free season mean that it dominates biological carbon uptake within the Weddell Gyre, accounting for 93 %–96 % of the basin’s total annual NPP. Variability in the summer maximum ice-free area is the strongest predictor of inter-annual variability in total NPP across the Weddell Gyre, with greater ice-free area resulting in greater annual NPP, explaining nearly half of the variance (R2 = 42 %). In the shelf region, the return of sea ice cover controls the end of the productive season. In the open ocean, however, both satellite NPP and float data show that a decline in NPP occurs before the end of the ice-free season (∼ 80 to 130 d after sea ice retreat). Evidence of concurrent increases in float-observed chlorophyll-a and POC suggest that later in the summer season additional factors such as micro-nutrient availability or top-down controls (e.g. grazing) could be limiting NPP. These results indicate that in a warmer and more ice-free Weddell Gyre, notwithstanding compensating changes in nutrient supply, NPP is likely to be enhanced only up to a certain limit of ice-free days.
1812-0792
475–497
Douglas, Clara Celestine
bc11960b-0103-428a-8ecd-30e142533454
Briggs, Nathan
a53aa80d-785a-4ace-99d3-72fa05e94471
Brown, Peter
c6e4857d-84f4-48e5-aded-0a68462bdc7a
Macgilchrist, Graeme
ccfda4b5-26d3-4081-b7db-8d65f22e8b8b
Naveira Garabato, Alberto
97c0e923-f076-4b38-b89b-938e11cea7a6
Douglas, Clara Celestine
bc11960b-0103-428a-8ecd-30e142533454
Briggs, Nathan
a53aa80d-785a-4ace-99d3-72fa05e94471
Brown, Peter
c6e4857d-84f4-48e5-aded-0a68462bdc7a
Macgilchrist, Graeme
ccfda4b5-26d3-4081-b7db-8d65f22e8b8b
Naveira Garabato, Alberto
97c0e923-f076-4b38-b89b-938e11cea7a6

Douglas, Clara Celestine, Briggs, Nathan, Brown, Peter, Macgilchrist, Graeme and Naveira Garabato, Alberto (2024) Exploring the relationship between sea ice and phytoplankton growth in the Weddell Gyre using satellite and Argo float data. Ocean Science, 20 (2), 475–497. (doi:10.5194/egusphere-2023-1068).

Record type: Article

Abstract

Some of the highest rates of primary production across the Southern Ocean occur in the seasonal ice zone (SIZ), making this a prominent area of importance for both local ecosystems and the global carbon cycle. There, the annual advance and retreat of ice impacts light and nutrient availability, as well as the circulation and stratification, thereby imposing a dominant control on phytoplankton growth. In this study, the drivers of variability in phytoplankton growth between 2002–2020 in the Weddell Gyre SIZ were assessed using satellite net primary production (NPP) products alongside chlorophyll-a and particulate organic carbon (POC) data from autonomous biogeochemical floats. Although the highest daily rates of NPP are consistently observed in the continental shelf region (water depths shallower than 2000 m), the open-ocean region’s larger size and longer ice-free season mean that it dominates biological carbon uptake within the Weddell Gyre, accounting for 93 %–96 % of the basin’s total annual NPP. Variability in the summer maximum ice-free area is the strongest predictor of inter-annual variability in total NPP across the Weddell Gyre, with greater ice-free area resulting in greater annual NPP, explaining nearly half of the variance (R2 = 42 %). In the shelf region, the return of sea ice cover controls the end of the productive season. In the open ocean, however, both satellite NPP and float data show that a decline in NPP occurs before the end of the ice-free season (∼ 80 to 130 d after sea ice retreat). Evidence of concurrent increases in float-observed chlorophyll-a and POC suggest that later in the summer season additional factors such as micro-nutrient availability or top-down controls (e.g. grazing) could be limiting NPP. These results indicate that in a warmer and more ice-free Weddell Gyre, notwithstanding compensating changes in nutrient supply, NPP is likely to be enhanced only up to a certain limit of ice-free days.

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Accepted/In Press date: 20 January 2024
e-pub ahead of print date: 4 April 2024
Additional Information: This work was supported by the Natural Environmental Research Council (NE/S007210/1 & NE/X008657/1) and by a European Research Council Consolidator grant (GOCART, agreement no. 724416). GAM was supported by the NSF-funded SOCCOM project (PLR-1425989) and UKRI (MR/W013835/1).

Identifiers

Local EPrints ID: 487936
URI: http://eprints.soton.ac.uk/id/eprint/487936
ISSN: 1812-0792
PURE UUID: 9b92c5cc-b6ed-428a-8fca-588e71041c13
ORCID for Alberto Naveira Garabato: ORCID iD orcid.org/0000-0001-6071-605X

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Date deposited: 11 Mar 2024 17:36
Last modified: 07 Jun 2024 04:01

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Contributors

Author: Nathan Briggs
Author: Peter Brown
Author: Graeme Macgilchrist

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