Distribution and cycling of total organic carbon across the Almeria‐Oran Front in the Mediterranean Sea: Implications for carbon cycling in the western basin

Abstract

The dynamics of the total organic carbon (TOC) pool were studied during winter 1997–1998 in the Almeria‐Oran jet‐front (AOF) system. This system includes the modified Atlantic Jet, which spreads into the Mediterranean Sea from the Gibraltar Strait, its associated gyre, and the front between the Mediterranean and Atlantic waters. We determined TOC concentrations, bacterial production (BP), and primary production (PP) during field work, and labile dissolved organic carbon (l‐DOC) and bacterial growth efficiency (BGE), which were calculated from biodegradation experiments. Our results showed that the geostrophic Atlantic Jet, which is the most dynamic area (horizontal speed of 80 cm s −1 in the upper 100 m flowing eastward), was characterized by low TOC stocks integrated in the first 100 m (6330–6990 mmol C m −2 ), a proportion of l‐DOC of 5 ± 0.5%, a BGE of 15 ± 2% and moderate residence times of excess‐TOC (42 ± 7 days). Higher TOC stocks were found in the surrounding areas, including the Mediterranean (7298–7400 mmol C m −2 ) and gyre waters (6718–8315 mmol C m −2 ) whereas l‐DOC averaged 6 ± 0.9% and 15 ± 2%, respectively. BGE averaged 7 ± 1% in Mediterranean waters and 21 ± 3% in the gyre giving rise to slightly different excess‐TOC residence times (28 ± 1 days in Mediterranean waters and 109 ± 30 days in the gyre). We estimated that the transport of TOC and excess‐TOC within the Atlantic Jet averaged 8.04 ± 0.32 × 10 4 and 1.68 ± 0.32 × 10 4 mol C s −1 , respectively.