# Total organic and inorganic carbon exchange through the Strait of Gibraltar in September 1997

Abstract : The total organic carbon (TOC) and total inorganic carbon (C T) exchange between the Atlantic Ocean and the Mediterranean Sea was studied in the Strait of Gibraltar in September 1997. Samples were taken at eight stations from western and eastern entrances of the Strait and at the middle of the Strait (Tarifa Narrows). TOC was analyzed by a high-temperature catalytic oxidation method, and C T was calculated from alkalinity}pH 2 pairs and appropriate thermodynamic relationships. The results are used in a two-layer model of water mass exchange through the Strait, which includes the Atlantic in flow, the Mediterranean out flow and the interface layer in between. Our observations show a decrease of TOC and an increase of C T concentrations from the surface to the bottom: 71}132 M C and 2068}2150 mol kg\ in the Surface Atlantic Water, 74 }95 M C and 2119}214 8 mol kg\ in the North Atlantic Central Water, 63}116 M C and 2123}2312 mol kg\ in the interface layer, and 61}78 M C and 2307}2325 mol kg\ in the Mediterranean waters. However, within the Mediterranean out flow, we found that the concentrations of carbon were higher at the western side of the Strait (75}78 M C, 2068}2318 mol kg\) than at the eastern side (61}69 M C, 2082}2324 mol kg\). This di!erence is due to the mixing between the Atlantic in#ow and the Mediterranean out#ow on the west of the Strait, which results in a #ux of organic carbon from the in#ow to the out#ow and an opposite flux of inorganic carbon. We estimate that the TOC input from the Atlantic Ocean to the Mediterranean Sea through the Strait of Gibraltar varies from (0.97+-0.8)10 to (1.81$0.90)10 mol C s\ (0.3;10 to 0.56;10 mol C yr\), while out flow of inorganic carbon ranges from (12.5$0.4)10 to (15.6\$0.4)10 mol C s\ (3.99}4 .90;10 mol C yr\). The high variability of carbon exchange within the Strait is due to the variability of vertical mixing between in flow and out flow along the Strait. The prevalence of organic carbon in flow and inorganic carbon out flow shows the Mediterranean Sea to be a basin of active remineralization of organic material.
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Evgeny Dafner, Melchor Gonzalez-Davila, J. Magdalena Santana-Casiano, Richard Sempere. Total organic and inorganic carbon exchange through the Strait of Gibraltar in September 1997. Deep Sea Research (1953), Elsevier, 2001, 8 (5), pp.1217 - 1236. ⟨10.1016/S0967-0637(00)00064-9⟩. ⟨hal-02063115⟩

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