Inter-annual productivity variability in the North Aegean Sea: Influence of thermohaline circulation during the Eastern Mediterranean Transient

Abstract

The North Aegean inter-annual productivity variability was investigated, by means of a coupled hydrodynamic/biogeochemical model simulation, over a multi-year (1985–2001) period covering the Eastern Mediterranean Transient (EMT). The EMT was a historically significant period (1987–1994), characterized by the massive formation of dense waters in the Aegean and their subsequent southward spreading to the Eastern Mediterranean. Our findings suggest that during the dense water formation events, deep nutrient rich water is exported to the South, affecting the N. Aegean nutrient pool. We show that the open sea productivity variability, driven by the deep nutrient pool entrainment to the euphotic zone, is related to both vertical mixing and nutrient fluxes, induced by thermohaline circulation variability. A negative correlation appears between the two processes, as stronger vertical mixing triggers a higher nutrient export. Process oriented experiments adopting maximum and minimum nutrient fluxes to the Southern Aegean revealed a significant impact on the nutrient pool, counterbalancing the effect of different vertical mixing on primary production. The model results presented good correlation with available satellite SST and Chl-a data. The impact of precipitation and BSW inflow variability on the Aegean salinity and dense water formation was investigated, showing a significant contribution by both preconditioning factors.