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[1] Seasonal to interannual variability of satellite derived chlorophyll-a over the Patagonia shelf and shelf break in the western South Atlantic are studied based on 7 years of ocean-color data (1998)(1999)(2000)(2001)(2002)(2003)(2004) from the Sea-Viewing Wide Field-of-View Sensor (SeaWiFS). Strong chlorophyll-a seasonal variability (>4 mg m À3) is observed compared to the open ocean (<1.5 mg m À3 ). North of 45°S, chlorophyll-a blooms initiate in early austral spring (September and October), while south of 45°S blooms begin in late spring to early summer (November through January). The spring maximum (>3.5 mg m À3 ) extends from the midshelf to the shelf break between 37°S and 44°S and southward to 51°S along a narrow shelf break band. In summer the shelf break maximum persists from 37°S to 51°S, and two inner-shelf blooms develop off Valdés Peninsula and along a near-coastal band between 46°S and 52°S (>3 mg m À3 ). Chlorophyll-a concentrations in the northern midshelf sharply decay in late spring, reaching lowest concentrations in summer (February and March) and a secondary maximum in early winter (June). Though all regions present substantial interannual variations, the bloom locations are stable. The shelf break maximum is located inshore of the front between the low salinity shelf waters and the cold, salty, and nutrient-rich Malvinas Current waters. The inner shelf maxima are offshore of fronts separating well-mixed coastal waters from the stratified midshelf. North of 41°S the midshelf bloom is also associated to a bottom trapped thermal front. Thus, all the high chlorophyll-a regions are associated to well-defined fronts.

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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.

High sea surface chlorophyll concentration on the Argentine Continental Shelf frequently extends to the deep ocean in the vicinity of the Brazil/Malvinas Confluence (BMC). The offshore transport of shelf waters likely plays a key role in the biogeochemical balance of the western South Atlantic and promotes the offshore transport of planktonic species. We analyze data from an oceanographic survey carried out in the western South Atlantic shelf between 31°S and 38°S in October 2013. We describe the distribution and circulation of the water masses and focus on the exchanges with the open ocean. On-shelf subsurface intrusions of oceanic waters and river discharge supply nutrients to the shelf. A low-salinity tongue of Río de la Plata (RDP) waters extends northward to 32°S. Below these waters Subantarctic and Subtropical Shelf Waters (SASW and STSW) meet to form the Subtropical Shelf Front. The main SASW branch, oversaturated in oxygen and with high-fluorescence mixes with a detachment of Brazil Current waters at 38°S and is exported offshore along the BMC. A second branch of SASW reaches 33°S mixing along its way with RDP and STSW and returns southward after splitting into an onshore and an offshore branch. The offshore branch is exported to the open ocean through the BMC. These export routes are in overall qualitative agreement with those indicated by a high-resolution reanalysis. We estimate a net off-shelf transport (geostrophic [96.2%] plus Ekman [3.8%]) of 3.44 Sv to the open ocean between 32.1°S and 37.7°S. The majority of the offshore flow occurs between 34.7°S and 37.7°S.