Biogeochemical fluxes through the Strait of Otranto (Eastern Mediterranean)

A series of seasonal cruises and Eulerian current measurements in the Otranto Strait were carried out to study the biogeochemical characteristics of the strait and to estimate the exchange of water, dissolved and particulate matter between the Adriatic and the Ionian Sea. Analysis of data shows that on an annual scale, the Adriatic Sea exports dissolved nutrients (nitrate and phosphate) to the Ionian, and imports particulate organic carbon and nitrogen. Estimate of the mean annual water flux for the first time based on direct Eulerian current measurements gives value of 0.9 Sv that is appreciably higher than those found in literature. Calculations of the ratio of new and total primary production based on an annual phosphate subsurface export suggest that the trophic status of the Adriatic Sea on the whole is close to that of an oligotrophic sea. From the biogeochemical distributions obtained, an active role for the Adriatic in supporting the well-known N:P ratio anomaly of the Mediterranean is hypothesized. Further studies are needed to estimate the contribution of the dissolved organic forms to the nutrient exchanges through the strait, and to establish the total budget of N and P in the Adriatic Sea.