Rapid Fluctuations of the Subsurface Chlorophyll Maximum in Response to
Wind Forcing in a Long, Narrow Bay
Abstract
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.