Rapid response to coastal upwelling in a semienclosed bay

Abstract

Bays/estuaries forced by local wind show bidirectional exchange flow. When forced by remote wind, they exhibit unidirectional flow adjustment to coastal sea level. Acoustic Doppler Current Profiler observations over 1 year show that the Ria de Vigo (Iberian Upwelling) responds to coastal wind events with bidirectional exchange flow. The duration of the upwelling and downwelling events, estimated from the current variability, was ~3.3 days and ~2.6 days, respectively. Vectorial correlations reveal a rapid response to upwelling/downwelling, in which currents lag local wind by <6 h and remote wind by <14 h, less than the Ekman spinup (17.8 h). This rapidity arises from the ria's narrowness (nonrotational local response), equatorward orientation (additive remote and local wind responses), depth greater than the Ekman depth (penetration of shelf circulation into the interior), and vertical stratification (shear reinforcing shelf circulation). Similar rapid responses are expected in other narrow bays where local and remote winds act together and stratification enhances bidirectional flow.

Temporal variability of diazotroph community composition in the upwelling region off NW Iberia

“…Overall, the compositional heterogeneity observed in response to the temporal shifts in environmental factors may reflect the transition of ecological niches of specific diazotrophs, since the community comprises a diverse group of organisms with different autoecology and physiological constraints. In the future, higher temporal resolution approaches focusing on abundance, diversity and expression of nifH genes will be required to better understand the role of the short-term variability of hydrodynamic forcing, occurring at scales of a few days in this region 43 , in shaping the diazotrophic community. Furthermore, specific observational and experimental approaches, including nutrient addition assays, should be implemented to shed light on the factors driving the activity and growth of UCYN-A sublineages, as well as to demarcate accurately the environmental conditions that define their ecological niches.…”

Biological N2 Fixation in the Upwelling Region off NW Iberia: Magnitude, Relevance, and Players

“…We are aware that a higher number of samplings would be desirable to better characterize averaged physical, chemical and biological fields in this system, where variability happens at short temporal scales of a few days (Casas et al, 1997;Gilcoto et al, 2017).…”

Modulation of the Semidiurnal Cycle of Turbulent Dissipation by Wind‐Driven Upwelling in a Coastal Embayment

“…While in salt wedge estuaries shear‐driven turbulence occurs at the salt wedge interface, in the Ría the turbulence emerges at the interface of the upwelled waters. Furthermore, other than to remote winds over the shelf, the Ría responds to local wind forcing, and this response is faster than to shelf winds, although the two scales of wind forcing tend to reinforce each other due to the orientation of the Ría (Gilcoto et al, ). This fast response of the upper layers of the Ría to the local winds was observed during the second part of CHAOS 1 (Figure a), producing additional shear (Figures c and e) and enhanced dissipation (Figure a).…”

“…As a result of shifting winds, both inflow and outflow weakened, the outflow deepened and a subsurface inflow ( ) developed along the CHAOS 1 sampling. The rapid current reversal of the upper layers is indicative of a response to the local winds, rather than a shelf‐scale adjustment to the remote winds (Gilcoto et al, ). Although not shown here, local winds measured at the Cíes Buoy (Figure ) and remote winds (Figure a) followed a similar evolution.…”

“…The most outstanding characteristic is that the subtidal circulation is controlled, in most situations, by wind‐driven coastal upwelling‐downwelling events over the adjacent continental shelf. The Ría responds to these events through a bi‐directional exchange flow along its main channel (Barton et al, ; Gilcoto et al, ; Piedracoba, ; Souto et al, ), a response that is reinforced and accelerated by local winds (Gilcoto et al, ). Under Equatorward upwelling‐favorable winds, predominant from April to September, the Ría exhibits positive circulation, as the cool ( ), salty ( ), nutrient‐rich Eastern North Atlantic Central Water (ENACW) intrudes as a lower layer into the Ría, and the inner surface waters flush toward the ocean (Álvarez‐Salgado et al, ; Fraga, ).…”