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 spatiotemporal 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.

A Pseudo‐Lagrangian Transformation to Study a Chlorophyll‐a Patch in the Ría de Vigo (NW Iberian Peninsula)

“…Moreover, in vitro experiments to estimate growth and mortality rates should be carried out simultaneously. Finally, sampling strategies combing high‐resolution temporal but also spatial data (Broullón et al., 2021) will be needed in order to describe the horizontal uniformity in the flow and chlorophyll‐a fields. This would allow to determine the validity of the assumptions required for the 1D (along‐Ría axis) approach carried in this study, and even evaluate the possibility for a 2D approach (along and across Ría axes).…”