South Atlantic Central Water Intrusion in the Southeast Brazil Bight and its impacts

Abstract

The responses of biogeochemical cycles and ecosystems are influenced by a variety of physical conditions, including but not limited to temperature, moisture, and nutrient availability. The ecological significance of cold and nutrient-rich water inflow into coastal embayments is well-established and is often attributed to the presence of an upwelling system in the adjacent area. The Southeast Brazil Bight (SBB) provides a sheltered environment for both the Cabo Frio upwelling system and Guanabara Bay. The water mass from the Cabo Frio upwelling system is known as the South Atlantic Central Water (SACW), and cold water events related to it have a particular impact on Guanabara Bay. To understand the ecosystem’s response to cold water events in the SBB during the 2014–2015 austral summer, a compilation of datasets including temperature time series, satellite chlorophyll-a data, meteorological station data, tidal gauge readings, and biogeochemical model results were used. The results revealed an east-to-west cold water flow, with a 43-hour delay in the response observed in Guanabara Bay after it was observed in Cabo Frio. There was no indication of a second upwelling system near Guanabara Bay. The biogeochemical analysis indicated that each area presents a different limitant nutrient, resulting in unique and distinct trophic webs in both areas.