DOC dynamics in the meso and bathypelagic layers of the Mediterranean Sea |
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| Affiliation: | 1. Department of Chemistry and Biochemistry, Schmid College of Science and Technology, Chapman University, One University Drive, Orange, CA 98266, USA;2. College of Science and Engineering, Western Washington University, 516 High Street, Bellingham, WA 98225, USA;1. School of Ocean and Earth Science and Technology, Department of Oceanography, University of Hawai''i at Manoa, 1000 Pope Road, Honolulu, HI 96822, United States;2. Department of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, 266 Woods Hole Road, Woods Hole, MA 02543, United States;1. Helsinki University Centre for Environment, , P.O. Box 65, FI-00014 University of Helsinki, Finland;2. Finnish Environment Institute, Marine Research Laboratory, Erik Palménin aukio 1, FI-00560 Helsinki, Finland;3. Finnish Environment Institute, Natural Environment Centre, P.O. Box 140, FI-00251 Helsinki, Finland;4. Agrifood Research Finland, FI-31600 Jokioinen, Finland |
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| Abstract: | Seven years (2001–2008) of dissolved organic carbon (DOC) vertical profiles were examined in order to assess the main processes determining DOC concentration and distribution in the meso- and bathypelagic layers of the Mediterranean Sea. As expected, DOC showed high and highly variable concentrations in the surface layer of 57–68 μM (average values between 0 and 100 m), with a decrease to 44–53 μM between 200 and 500 m. Deep DOC distribution was strongly affected by deep-water formation, with a significant increase to values of 76 μM in recently ventilated deep waters, and low concentrations, comparable to those observed in the open oceanic waters (34–45 μM), where the oldest, deep waters occurred. In winter 2004/2005 a deep-water formation event was observed and the consequent DOC export at depth was estimated to range between 0.76–3.02 Tg C month–1. In the intermediate layer, the main path of the Levantine Intermediate Water (LIW) was followed in order to estimate the DOC consumption rate in its core. Multiple regression between DOC, apparent oxygen utilization (AOU), and salinity indicated that 38% of the oxygen consumption was related to DOC mineralization when the effect of mixing was removed. In deep waters of the southern Adriatic Sea a DOC decrease of 6 μM, together with an AOU increase of 9 μM, was observed between the end of January 2008 and the end of June 2008 (5 months). These data indicate a rate of microbial utilization of DOC of about 1.2 μM C month−1, with 92% of the oxygen consumption due to DOC mineralization. These values are surprisingly high for the deep sea and represent a peculiarity of the Mediterranean Sea. |
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