engleski

The influence of Northern Hemisphere climate patterns on the Adriatic Sea pelagic ecosystem

We investigated Northern Hemisphere climate effects on the long term variability of the marine ecosystem in the middle Adriatic Sea during the period 1961-2005. Air temperature, precipitation, evaporation, air-sea fluxes and the North Atlantic Oscillation index covary with the patterns observed in temperature and salinity data. The use of a sequential algorithm for regime shift detection (SARS) applied to the primary production and sardine/anchovy ratio revealed three periods with significantly different mean levels of productivity: 1961-1979, 1980-1996 and 1997-2002. Moreover, the years 1980 to 1996, with the highest primary production, showed contrasting periods of productivity. While the years 1980-1986 showed an increasing trend, the years 1987-1996 were characterized by an inverse pattern. Such opposite patterns appeared to be linked to modifications in thermohaline circulation related to the Eastern Mediterranean Transient (EMT) whose effects prevented warm and nutrient rich water mass intrusions into the Adriatic and reduced productivity. Weak ventilation in the Adriatic was also evident in the lower than normal sea temperature and oxygen concentrations below the thermocline. These results provide evidence on connections between shifts in primary production in the middle-Adriatic with the Northern Hemisphere climate system via changes in regional atmospheric conditions, and highlight the role atmospheric variability may play as a triggering factor for ecosystem-wide changes.

influence; Northern Hemisphere climate patterns; Adriatic Sea; pelagic ecosystem

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