@article{fdi:010075620,
  title = {{N}onmonotonic response of primary production and export to changes in mixed-layer depth in the {S}outhern {O}cean},
  author = {{L}lort, {J}. and {L}evy, {M}arina and {S}allee, {J}. {B}. and {T}agliabue, {A}.},
  editor = {},
  language = {{ENG}},
  abstract = {{O}ngoing and future changes in wind and temperature are predicted to alter upper ocean vertical mixing across the {S}outhern {O}cean. {H}ow these changes will affect primary production ({PP}) remains unclear as mixing influences the two controlling factors: light and iron. {W}e used a large ensemble of 1-{D}-biogeochemical model simulations to explore the impacts of changes in mixed-layer depths on {PP} in the {S}outhern {O}cean. {I}n summer, shoaling mixed-layer depth always reduced depth-integrated {PP}, despite increasing production rates. {I}n winter, shoaling mixed layers had a two-staged impact: for moderate shoaling {PP} increased as light conditions improved, but more pronounced shoaling decreased iron supply, which reduced {PP}. {T}he fraction of {PP} exported below 100 m also presented a nonmonotonic behavior. {T}his suggests a potential future shift from a situation where reduced winter mixing increases {PP} and export, to a situation where {PP} and export may collapse if the {ML} shoals above a threshold depth. {P}lain {L}anguage {S}ummary {I}n the {S}outhern {O}cean, atmospheric warming associated to climate change is altering the depth at which surface waters are stirred, the so-called mixed-layer depth. {A} change in the mixed-layer depth impacts the phytoplankton cells that inhabit it by altering their two main limiting factors: iron and light. {H}owever, the sign and magnitude of this impact are still not clear. {I}n this work we used mathematical simulations to explain how changes in the seasonal mixed-layer depth modify the supply of iron and the amount of light, and how these changes impact phytoplankton activity. {O}ur results show that mixed-layer depth changes in summer and in winter have different impacts. {R}educing summer mixed-layer depth did not change the iron supply, but it reduced the volume of water where phytoplankton thrived. {I}n winter, shallower mixed-layer depth altered iron and light but in opposed ways. {A}t first, phytoplankton increased its activity as more light became available. {H}owever, a continued shallowing of the mixed-layer depth eventually reduced the iron supply and the phytoplankton activity. {O}ur study proposes a new interpretation on how ongoing changes in the {S}outhern {O}cean impact phytoplankton activity and alerts of the presence of threshold depths for the winter mixed layer above which phytoplankton may struggle to survive.},
  keywords = {{S}outhern {O}cean ; carbon export ; phytoplankton ; primary production ; mixed-layer depth ; {CMIP}5 ; {OCEAN} {AUSTRAL}},
  booktitle = {},
  journal = {{G}eophysical {R}esearch {L}etters},
  volume = {46},
  numero = {6},
  pages = {3368--3377},
  ISSN = {0094-8276},
  year = {2019},
  DOI = {10.1029/2018gl081788},
  URL = {https://www.documentation.ird.fr/hor/fdi:010075620},
}