Physico-chemical trends since 1970 at the Catalan Sea (NW Mediterranean Sea)

Abstract

Temperature and salinity in Western Mediterranean Deep Water (WMDW) and Levantine Intermediate Water (LIW) are increasing, specially since 1955 (Béthoux et al., 1990; Rohling and Bryden, 1992; Béthoux and Gentili, 1996; Painter and Tsimplis, 2003). This has been related to global warming, positive NAO index and to damming of the rivers that discharge into the Black and Eastern Mediterranean Sea. Those increases in salinity and temperature have been observed on several parts of the Mediterranean Sea. Parallel to the increases in temperature and salinity, Béthoux et al., (1998) detected in deep waters of the Algerian and Provençal sub-basins, positive trends on the concentration of nitrate and phosphate, from 1970 to 1994. Here we study the trends in the Catalan Sea (0 – 4,5 W; 38,7 – 42,4 N) of temperature, salinity, density, inorganic nutrients and dissolved oxygen. The study is based on the oceanographic data of 30 cruises, between 1970 and 2003. Our results confirm previous findings, since we observe also an increase of temperature and salinity and of nitrate and phosphate in the WMDW and in the LIW. In addition we also have observed an increase in silicate and in apparent oxygen utilization, associated with a decrease in dissolved oxygen. These findings confirm Bethoux’s prediction (1989) of an increase in oxygen consumption. We explore possible sources of this increase, which leads to the augment of inorganic nutrients in deep waters which will be in addition to the increases due to anthropogenic input as suggested by Béthoux et al. (1998). Béthoux, J.P. (1989). “Oxygen consumption, new production, vertical advection and environmental evolution in the Mediterranean Sea. Deep – Sea Res. 36 (5) : 769-781. Béthoux, J.P., B. Gentili (1996). “The Mediterranean Sea, coastal and deep – sea signatures of climatic and environmental changes”. J. Mar Sys. 7 : 383-394. Béthoux, J.P., B. Gentili, J. Raunet, D. Tailliez (1990). “Warming trend in western Mediterranean deep water”. Nature, 347 : 660-662. Béthoux, J.P., P. Morin, C. Chaumery, O. Connan, B. Gentili, D. Ruiz-Pino (1998). “Nutrients in the Mediterranean Sea, mass balance and statistical analysis of concentrations with respect to environmental change”. Mar. Chem., 63 : 155-169. Painter, S.C., M.N. Tsimplis (2003). “Temperature and salinity trends in the upper waters of the Mediterranean Sea as determined from the MEDATLAS dataset”. Cont. Shelf Res 23 : 1507-1522. Rohling, E.J., H.L. Bryden (1992). “Man – induced salinity and temperature increases in Western Mediterranean Deep Water”. J. Geophysical Res. 97 (C7) : 11191-11198