engleski

Occurrence of seasonal hypoxia and anoxia in the Northern Adriatic sea under different environmental conditions

The northern Adriatic Sea is characterized by highly variable conditions, particularly due to excess primary production during the spring Po River freshets when the water column becomes highly stratified, and the establishment of semi-enclosed circulation patterns. Consequently, the region recurrently suffers oxygen depletion in the bottom layer from August to November, more frequently on the western eutrophic side. The most widespread and severe hypoxia occurred in 1977 and 1989, culminating in anoxia, even in a large part of the eastern oligotrophic area. In 1988, 1990 and 1991 near-anoxic conditions also occurred over most of the basin, whereas in 1996, 1997, 2000, 2001 and 2004, hypoxia was limited to the western part. Remarkably, these events occurred under very different environmental conditions. In most of these years higher than average Po freshets occurred, although in some years the freshwater discharge was very low. However, the Istrian Coastal Countercurrent (ICCC) was well developed during late summer or early autumn of all years when near-anoxia occurred. ICCC probably is an indicator of a substantially reduced water exchange between the northern and central Adriatic.

hypoxia and anoxia ; geostrophic circulation ; Po River ; northern Adriatic

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