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Rapid Fluctuations of the Subsurface Chlorophyll Maximum in Response to Wind Forcing in a Long, Narrow Bay
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  • Esperanza Broullón,
  • Peter J.S. Franks,
  • Bieito Fernández Castro,
  • Miguel Gilcoto,
  • Beatriz Mourino-Carballido
Esperanza Broullón
Universidade de Vigo

Corresponding Author:[email protected]

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Peter J.S. Franks
Scripps Institution of Oceanography
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Bieito Fernández Castro
University of Southampton
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Miguel Gilcoto
Instituto de Investigaciones Marinas- CSIC
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Beatriz Mourino-Carballido
Universidade de Vigo
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Bays within eastern boundary upwelling systems (EBUS) are ecological hot-spots featuring a diverse range of spatio-temporal dynamics. At the EBUSs’ poleward limit, upwelling occurs in short-lived (<1 week) pulses modulated by synoptic wind variability. The circulations in long, narrow bays can respond to these fluctuations within few hours. The short-term biological response to these pulses was investigated in two of these bays (Rias Baixas, NW-Iberia) with a two-week quasi-synoptic spatio-temporal survey in the summer 2018. A four-day-long upwelling pulse caused deep, nutrient-rich isopycnals to rise into the euphotic zone inside the bays, triggering a rapid (~1.7 days) nutrient uptake and formation of a subsurface chlorophyll maximum (~3.8 days). The phytoplankton biomass was transported rapidly toward deep, offshore waters when the winds weakened. These results suggest that high productivity in narrow bays is controlled by the transient exposure of deep, nutrient-rich waters to light during upwelling pulses.