Total organic carbon distribution and budget through the Strait of Gibraltar in April 1998

Abstract

In order to investigate total organic carbon (TOC) exchange through the Strait of Gibraltar, samples were taken along two sections from the western (Gulf of Cadiz) and eastern (Western Alboran Sea) entrances of the Strait and at the middle of the Strait in April 1998. TOC was measured by using a high-temperature catalytic oxidation method. The results referenced here are based on a three-layer model of water mass exchange through the Strait, which includes the Atlantic inflow, Mediterranean outflow and an interface layer in between. All layers were characterised by a decrease of TOC concentrations from the Gulf of Cadiz to the Western Alboran Sea: from 60–79 to 59–66 M C in the Atlantic inflow and from 40–60 to 38–52 M C in the Mediterranean waters, respectively. TOC concentrations in the modified North Atlantic Central Water varied from 43 to 55 M C. Intermediate TOC values were measured in the interface layer (43–60 M C). TOC concentrations increased from the middle of the Strait towards continents indicating a contribution of organic carbon of photosynthetic origin along Spain and Morocco coasts or TOC accumulation due to upwelling in the northeastern part of the Strait. Our results indicate that the short-term variability caused by the tide greatly impacts the TOC distribution, particularly in the Gulf of Cadiz. The TOC input from the Atlantic Ocean to the Mediterranean Sea through the Strait of Gibraltar varies from 0.9×104 to 1.0×104 mol C s?1 (or 0.28×1012 to 0.35×1012 mol C year?1, respectively). This estimate suggests that the TOC inflow and outflow through the Strait of Gibraltar are two and three orders of magnitude higher than reported via the Turkish Straits and Mediterranean River inputs.