Surface transport of DOC acts as a trophic link among Mediterranean sub-basins

Abstract Lateral advection affects the spatial distribution of dissolved substances in the ocean but very few studies, so far, have been devoted to describe and quantify its impact on the distribution of dissolved organic carbon (DOC) which, in oligotrophic environments, accounts for the largest fraction of chemical energy. In this contribution, using an integrated approach, we explore the importance of surface advection on carbon dynamics in the Western Mediterranean Sea, where strong inter-basin differences in primary production do exist. Detailed information on the surface circulation, derived from high-resolution model simulations, is combined with the analysis of spatially resolved, accurate DOC vertical profiles, repeated over time. Our data show that surface circulation plays a crucial role in regulating DOC concentrations and distributions in the Tyrrhenian Sea and that horizontal transport of DOC into the Tyrrhenian Sea is of the same order of magnitude as in-situ DOC production. Our study addresses this process for the first time in the Mediterranean Sea, whose small size allows for fast, inter-basin transfer times which, in turn, favors the preservation of the DOC stock produced elsewhere. We highlight that this mechanism may be important also in other regions of the oceans, where surface advection may set up a sort of compensation among regions with different trophic regimes, thus smoothing trophic gradients. We posit that understanding these transport processes is a crucial and preliminary step to understand and quantify all the other processes (biological, chemical, geological) that influence DOC distribution on a variety of timescales.