Preprints
https://doi.org/10.5194/egusphere-2022-1489
https://doi.org/10.5194/egusphere-2022-1489
06 Jan 2023
 | 06 Jan 2023

Satellite data reveal earlier and stronger phytoplankton blooms over fronts in the Gulf Stream region

Clément Haëck, Marina Lévy, Inès Mangolte, and Laurent Bopp

Abstract. Fronts affect phytoplankton growth and phenology by locally reducing stratification and increasing vertical nutrient supply. Biomass peaks at fronts have been observed in-situ and linked to local nutrient upwelling, and reduced stratification over fronts has been shown to induce earlier blooms in numerical models. However observation of these biophysical interactions through satellite imagery have been scarce, despite the opportunity to quantify them at synoptic scales. Here we used twenty years of Sea Surface Temperature (SST) and Chlorophyll-a satellite data in a large region surrounding the Gulf Stream to quantify the impact of fronts on phytoplankton in contrasting regimes, from oligotrophy to bloom, and throughout the year. We computed an Heterogeneity Index (HI) from SST, and used it to sort fronts into weak and strong fronts based on HI thresholds. We observed that the localization of strong fronts corresponded to western boundary current fronts, and weak fronts to more ephemeral submesoscale fronts. We compared Chlorophyll-a distributions over strong fronts, weak fronts and outside of fronts. We assessed three metrics, the local enhancement of Chlorophyll-a over fronts, the global enhancement of Chlorophyll-a due to fronts at the scale of the region, and the lag in spring bloom onset due to fronts. We found that weak fronts lead to a local enhancement of Chlorophyll-a weaker than strong fronts, but because they are also more frequent they contribute equally to the regional Chlorophyll-a budget. We also find the the local enhancement of Chlorophyll-a was two to three times larger for the spring bloom than in the oligotrophic subtropical gyre. We also provide observational evidence that blooms start earlier over fronts, by one to two weeks. Nevertheless our results suggest that the spectacular impact of fronts at the local scale may be misleading, considering their impact on a regional scale budget remains limited.

Journal article(s) based on this preprint

11 May 2023
Satellite data reveal earlier and stronger phytoplankton blooms over fronts in the Gulf Stream region
Clément Haëck, Marina Lévy, Inès Mangolte, and Laurent Bopp
Biogeosciences, 20, 1741–1758, https://doi.org/10.5194/bg-20-1741-2023,https://doi.org/10.5194/bg-20-1741-2023, 2023
Short summary

Clément Haëck et al.

Interactive discussion

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2022-1489', Anonymous Referee #1, 18 Feb 2023
    • AC1: 'Reply on RC1', Clément Haëck, 16 Mar 2023
  • RC2: 'Comment on egusphere-2022-1489', Anonymous Referee #2, 01 Mar 2023
    • AC2: 'Reply on RC2', Clément Haëck, 16 Mar 2023

Interactive discussion

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2022-1489', Anonymous Referee #1, 18 Feb 2023
    • AC1: 'Reply on RC1', Clément Haëck, 16 Mar 2023
  • RC2: 'Comment on egusphere-2022-1489', Anonymous Referee #2, 01 Mar 2023
    • AC2: 'Reply on RC2', Clément Haëck, 16 Mar 2023

Peer review completion

AR: Author's response | RR: Referee report | ED: Editor decision | EF: Editorial file upload
ED: Publish subject to minor revisions (review by editor) (17 Mar 2023) by Peter Landschützer
AR by Clément Haëck on behalf of the Authors (31 Mar 2023)  Author's response   Author's tracked changes   Manuscript 
ED: Publish subject to technical corrections (13 Apr 2023) by Peter Landschützer
AR by Clément Haëck on behalf of the Authors (14 Apr 2023)  Author's response   Manuscript 

Journal article(s) based on this preprint

11 May 2023
Satellite data reveal earlier and stronger phytoplankton blooms over fronts in the Gulf Stream region
Clément Haëck, Marina Lévy, Inès Mangolte, and Laurent Bopp
Biogeosciences, 20, 1741–1758, https://doi.org/10.5194/bg-20-1741-2023,https://doi.org/10.5194/bg-20-1741-2023, 2023
Short summary

Clément Haëck et al.

Clément Haëck et al.

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

Short summary
Phytoplankton vary in abundance in the ocean over of large regions, and with the seasons, but also because of small-scale heterogeneities in surface temperature, called fronts, where phytoplankton growth can be favoured. Here, using satellite imagery, we found that fronts enhance phytoplankton much more where it is already growing well, but despite large local increases the enhancement for the region is modest (5%). We also found that blooms start by one to two weeks earlier over fronts.