@article{fdi:010087717,
  title = {{S}atellite data reveal earlier and stronger phytoplankton blooms over fronts in the {G}ulf {S}tream region},
  author = {{H}aeck, {C}. and {L}evy, {M}arina and {M}angolte, {I}. and {B}opp, {L}.},
  editor = {},
  language = {{ENG}},
  abstract = {{F}ronts affect phytoplankton growth and phenology by locally reducing stratification and increasing nutrient supplies. {B}iomass peaks at fronts have been observed in situ and linked to local nutrient upwelling and/or lateral transport, while reduced stratification over fronts has been shown to induce earlier blooms in numerical models. {S}atellite imagery offers the opportunity to quantify these induced changes in phytoplankton over a large number of fronts and at synoptic scales. {H}ere we used 20 years of sea surface temperature ({SST}) and chlorophyll a ({C}hl a) satellite data in a large region surrounding the {G}ulf {S}tream to quantify the impact of fronts on surface {C}hl a (used as a proxy for phytoplankton) in three contrasting bioregions, from oligotrophic to blooming ones, and throughout the year. {W}e computed an heterogeneity index ({HI}) from {SST} to detect fronts and used it to sort fronts into weak and strong ones based on {HI} thresholds. {W}e observed that the location of strong fronts corresponded to the persistent western boundary current fronts and weak fronts to more ephemeral submesoscale fronts. {W}e compared {C}hl a distributions over strong fronts, over weak fronts, and outside of fronts in the three bioregions. {W}e assessed three metrics: the {C}hl a excess over fronts at the local scale of fronts, the surplus in {C}hl a induced at the bioregional scale, and the lag in spring bloom onset over fronts. {W}e found that weak fronts are associated with a local {C}hl a excess weaker than strong fronts, but because they are also more frequent, they contribute equally to the regional {C}hl a surplus. {W}e also found that the local excess of {C}hl a was 2 to 3 times larger in the bioregion with a spring bloom than in the oligotrophic bioregion, which can be partly explained by the transport of nutrients by the {G}ulf {S}tream. {W}e found strong seasonal variations in the amplitude of the {C}hl a excess over fronts, and we show periods of {C}hl a deficit over fronts north of 45 circle {N} that we attribute to subduction. {F}inally we provide observational evidence that blooms start earlier over fronts by 1 to 2 weeks. {O}ur results suggest that the spectacular impact of fronts at the local scale of fronts (up to +60 %) is more limited when considered at the regional scale of bioregions (less than +5 %) but may nevertheless have implications for the region's overall ecosystem.},
  keywords = {{ATLANTIQUE}},
  booktitle = {},
  journal = {{B}iogeosciences},
  volume = {20},
  numero = {9},
  pages = {1741--1758},
  ISSN = {1726-4170},
  year = {2023},
  DOI = {10.5194/bg-20-1741-2023},
  URL = {https://www.documentation.ird.fr/hor/fdi:010087717},
}