Coupling between interannual fluctuations of the sea surface temperature and zooplankton biomass in the tropical Atlantic Ocean

Interannual fluctuations of the sea surface temperature (SST) were analysed for the Northern Tropical Atlantic. Two patterns were noticed: a positive interannual trend (from 1960s to 1990s) and fluctuations of SST anomalies with a period from two to eight years, possibly formed by interannual dynamics of the Northern Subtropical Gyre. These dynamics were featured by the Subtropical Temperature Index (STI) revealing the meridional gradient of the SST anomalies between the Sargasso Sea and the Northern Tropical Atlantic. Being employed for a relatively short time series, STI has enabled us to evaluate an event of a sign change in SST anomalies. At STI≥1, positive SST anomalies and negative anomalies of nutrient concentration and zooplankton biomass take place. This qualitative ratio gets reversed at STI≤-1. Overall, interannual decline of zooplankton biomass (from 1960s to 1990s) has been accompanied by a positive trend of SST.