Wind modulation of upwelling at the shelf‐break front off Patagonia: Observational evidence

Abstract

The South‐Atlantic Patagonian shelf is the largest chlorophyll‐a (Chl‐a) hot spot in Southern Ocean color images. While a persistent 1500 km long band of high Chl‐a along the shelf‐break front (SBF) is indicative of upwelling, the mechanisms that drive it are not entirely known. Along‐front wind oscillations can enhance upwelling and provide a nutrient pumping mechanism at shelf‐break fronts of western boundary currents. Here we assess wind‐induced upwelling at the SBF off Patagonia from daily satellite Chl‐a and winds, historical hydrographic observations, cross‐shelf Chl‐a fluorescence transects from two cruises, and in situ winds and water column structure from a mooring site. Satellite Chl‐a composites segregated by along‐front wind direction indicate that surface Chl‐a is enhanced at the SBF with southerly winds and suppressed with northerly winds. Northerly winds also result in enhanced Chl‐a further offshore (∼25–50 km). Synoptic transects as well as mean hydrographic sections segregated by along‐front winds show isopycnals tilted upward for southerly winds. Spring observations from the mooring also suggest that southerly winds destratify the water column and northerly winds restratify, in agreement with Ekman transport interacting with the front. Moreover, changes in water column temperature lag along‐front wind forcing by 2–4 days. Our results suggest that oscillations in along‐front winds, on timescales typical of atmospheric storms (2–10 days), can significantly modulate the upwelling and Chl‐a concentrations at the SBF off Patagonia, revealing the importance of wind‐induced upwelling for shelf‐slope exchange at shelf‐break fronts of western boundary currents.

Synoptic‐to‐planetary scale wind variability enhances phytoplankton biomass at ocean fronts

“…Finally, remote and in situ observations of fronts can be used to assess the relationships between unsteady winds and biogeochemistry and to test whether the observations are consistent with existing models (see Carranza et al . [] for a recent observational study that focuses on the role of synoptic along‐front wind variability in modifying surface chlorophyll at a front, similar to this study). In any case, the analysis presented here builds on and supports existing studies that suggest wind‐driven vertical transport at fronts, via both turbulent mixing and vertical advection, has a significant impact on biology at fronts in real nutrient‐limited open oceans.…”

Seasonal Variation in the Correlation Between Anomalies of Sea Level and Chlorophyll in the Antarctic Circumpolar Current

“…A budget analysis for 〈Fe〉 along the ACC (Figures b and d; see the supporting information for details) quantifies the various mechanisms of iron supply and removal. We only consider areas where bathymetry is deeper than 200 m in order to avoid the direct influence from shelf regions (Carranza et al, ). Iron is supplied to the mixed layer by lateral and vertical advection, vertical mixing, aeolian input of dust, and entrainment associated with changes in the MLD; it is removed through the biogeochemical sink term, which represents phytoplankton uptake and scavenging on sinking particulates.…”

Plankton Multiproxy Analyses in the Northern Patagonian Shelf, Argentina: Community Structure, Phycotoxins, and Characterization of Toxic Alexandrium Strains

“…The Patagonian Shelf Large Marine Ecosystem (PLME) (Heileman, 2009) is one of the widest in the world, one of the most productive (Lutz et al, 2010), and hydrographically complex in the Southern Hemisphere (Palma et al, 2008;Matano et al, 2010;Paniagua et al, 2018). The extensive shelf breakfront and other shelf fronts support high phytoplankton productivity and fisheries incomes (Acha et al, 2004;Carreto et al, 2016;Carranza et al, 2017;Díaz et al, 2018). Moreover, recent studies on satellite images showed that chlorophyll a (chl-a) has notably risen over the last two decades (Marrari et al, 2017), which highlights the role of this large ecosystem in the global carbon uptake and in the regional sustainability of marine resources and stakeholder communities (Bianchi et al, 2009;Marrari et al, 2013).…”