Wind Control of the Interannual Ocean‐Biogeochemical Variability in the South Atlantic Bight

Abstract In the South Atlantic Bight (SAB), changes in the Gulf Stream (GS), particularly its strength and proximity to the coast, are thought to be primary factors determining the shelf‐break upwelling rate. However, it is still not entirely clear if and to what extent those factors influence cross‐shelf nutrient fluxes and shape the ocean biogeochemistry at interannual and longer timescales. Here, we use a high‐resolution regional ocean‐biogeochemical model and an ocean reanalysis product (1993–2022), along with a satellite‐derived chlorophyll data set (1997–2022), to investigate the interannual ocean‐biogeochemical variability in the SAB. Regional model outputs suggest that year‐to‐year changes in phytoplankton production are indeed largely driven by upwelling of cold and nutrient‐rich water to the shelf‐break. The upwelling variability, reflected in bottom temperature and vertically integrated production patterns, is strongly linked to surface velocity changes in the GS near the shelf break, but weakly related to the depth‐integrated GS transport. The GS's velocity changes, and the temperature and production anomalies, are well correlated to the alongshore wind stress, suggesting that local wind is the leading driver of the shelf‐break upwelling variability at interannual timescales. Those relationships are also supported by circulation patterns from ocean reanalysis and satellite chlorophyll anomalies. Finally, examining the simulated shelf‐slope interchanges in the carbonate system, we find that shelf‐break upwelling significantly increases bottom acidification, a pattern linked to the low carbonate concentration in the slope waters. This study thus provides new insight for understanding and predicting GS and winds impacts on biogeochemical patterns from the SAB.