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We present observational evidence that a significant regime change occurred around the year 2000 in the formation of Warm Core Rings (WCRs) from the Gulf Stream (GS) between 75° and 55°W. The dataset for this study is a set of synoptic oceanographic charts available over the thirty-eight-year period of 1980–2017. The upward regime change shows an increase to 33 WCRs per year during 2000–2017 from an average of 18 WCRs during 1980 to 1999. A seasonal analysis confirms May-June-July as the peak time for WCR births in agreement with earlier studies. The westernmost region (75°-70°W) is least ring-productive, while the region from 65°W to 60°W is most productive. This regime shift around 2000 is detected in WCR formation for all of the four 5-degree wide sub-regions and the whole region (75°-55°W). This might be related to a reduction of the deformation radius for ring formation, allowing unstable meanders to shed more frequent rings in recent years. A number of possible factors resulting in such a regime shift related to the possible changes in reduced gravity, instability, transport of the GS, large-scale changes in the wind system and atmospheric fluxes are outlined, which suggest new research directions. The increase in WCRs has likely had an impact on the marine ecosystem since 2000, a topic worthy for future studies.

The Brazil Current (BC) originates with the arrival and bifurcation of the southernmost branch of the South Equatorial Current (sSEC) between 10–20°S. Previous climatological studies showed a stratified sSEC bifurcation and that the resulting southern branch formed a shallow BC ‐ a weak western boundary current. The analysis of three recent synoptic surveys and global model outputs challenge the description of a continuous BC. The sSEC bifurcation signal near the continental margin was unclear in the analyses, and the velocity fields were dominated by mesoscale eddies. Recurrent anticyclones that seemed to be related to the meandering BC led us to construct a picture of a flow strongly influenced by topography and probably very unstable. Given this new emerging scenario, we hypothesize that the Brazil Current is eddy‐dominated to the north of 20°S.

The development of phytoplankton blooms in Von Kàrmàn vortex streets in island wakes has been investigated using a coupled bio‐physical model which evolves a geostrophically balanced flow past a relatively small (L = 10 km) oceanic island. Three major processes associated with the “island mass effect” are found to occur in series in our numerical experiment. First, increases in phytoplankton were observed in the lee due solely to passive advection from the deep maximum. Second, following the shedding of cyclonic eddies, upwelled nitrate enhances local primary production in the surface euphotic layer resulting in a phytoplankton bloom. The bloom peaks appeared about two weeks downstream from the island. Third, a weaker bloom is also found in the immediate lee of the island, associated with nutrient injection and longer residence time of upwelled water. The demonstrated detailed features of island mass effect are remarkably consonant with previously observed phenomena in the real ocean.

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