Seasonality of Dissolved Organic Carbon Exchange Across the Strait of Gibraltar

Exchange of mass, heat, and solutes across the Strait of Gibraltar is fundamental to understand the circulation and biogeochemistry of the Mediterranean. Here we focus on the exchange of dissolved organic carbon (DOC) using data from 12 surveys conducted between 2008 and 2015. DOC exchange exhibits a marked bimodal distribution with minima in late June and late October and maxima in mid-April and late August. This pattern is mainly due to seasonal variation of the DOC gradient between the Atlantic Surface Water entering the Mediterranean and the deep opposite flow of Mediterranean Overflow Water. The gradient is controlled by the different seasonal cycles followed by the DOC in the two layers. Annual average DOC import from the Atlantic is equivalent to 4.2 +/- 1.5 Tg C yr(-1), which represents 53% of the external DOC inputs and contributes to support 32% of the net heterotrophy of the Mediterranean.