New insights into C, N and P stoichiometry in the Mediterranean Sea: The Adriatic Sea case

Vertical distributions of dissolved organic carbon (DOC), nitrogen (DON) and phosphorous (DOP) were studied in the Southern Adriatic basin in two contrasting periods: autumn (high stratification) and winter (high extent of mixing). These data provide the first observations of dissolved organic matter (DOM) stoichiometry in a key area of the Mediterranean Sea. d DON values are similar to those reported for other areas of the Mediterranean Sea as well as for tropical and temperate regions of the oceans. Surface DOP values are about one order of magnitude lower than those reported for the oceanic waters, confirming the low availability of P in the Mediterranean Sea. Consequently, surface DOM (C:N:P=1189–1411:86–88:1) has higher proportions of C and N with respect to P than in the oceans. DOM stoichiometry in the deep waters of the Southern Adriatic ranged between 993:85:1 and 1693:108:1, indicating a depletion of DOC (or an elevation of DON and DOP) with respect to the old western Mediterranean deep waters. This finding can be explained by the young age of the water masses in the Southern Adriatic, which can mask the effect of mineralization. Our data clearly show that physical processes (water mass circulation, deep water formation and extent of stratification) affect both distribution and stoichiometry of DOM. Finally, we discuss the role of the Adriatic Sea in maintaining the high N:P ratio observed in the Eastern Mediterranean Sea.