Carbon dioxide system in the Canary region during October 1995

Abstract

During the cruise F/S Poseidon 212/3 (September 30-October 8, 1995) determination of carbon system variables was carried out over the section of La Palma-La Graciosa and at the ESTOC station in the Canary Island area. Total alkalinity and pH in the total scale at 25ºC were determined at 24 stations from surface to bottom. In this area, the presence of different water masses can be traced by the carbon system variables. NACW is defined by a strong gradient of AT and pH from 150 to 750 m. MW is characterised by high values of AT and pH between 1000 to 1200 m and AAIW signals are found at around 900 m in the strait between Gran Canaria and Fuerteventura with low AT, low pH and a maximum of fCO2. Assuming an atmospheric mean value of fCO2 of 360 µatm and an average surface value of 393±7 µatm, we can conclude that during this cruise this oceanic area tends to release CO2 into the atmosphere, acting as a weak source with a carbon flux towards the atmosphere of +8.0±1.8 mmol?m^-2d^-1. The saturation levels in the Canary Island area have been found to be higher than 3600 m for calcite and 2700 m for aragonite. The inorganic carbon/organic carbon ratio (IC/OC) varies from 0.07 at 300 m to 0.5 at 3000 m. The IC/OC ratio shows that about a 34% increase in the CT of the deep water is contributed by the inorganic CaCO₃ dissolution. The IC at 300 m is around 7 µmol kg^-1, increasing with depth to 37.5 µmol kg^-1 at 3700 m.