The N:Si:P molar ratio in the strait of Gibraltar -: art. no. 1506

[1] All existing descriptions of nutrient distributions in the Strait of Gibraltar suggest that the Atlantic water brings to the Mediterranean Sea nutrients in the Redfield ratio (N: Si: P = 16: 15: 1). Here, the N: Si: P molar ratios (+/- Standard Error), obtained in April 1998, are used to show that in the Atlantic water at the western entrance of the Strait this ratio is lower (13.8(+/-0.5): 12.1(+/-1.0): 1) than the classical Redfield ratio; it is close to the Redfield ratio in the middle of the Strait (15.6(+/-0.6): 10.7(+/-0.9): 1), and increases dramatically to 23.6(+/-3.4): 29.1(+/-4.5): 1 at the eastern entrance of the Strait. In the Mediterranean water, the N: Si: P ratio has a quite similar trend with 31.5(+/-6.0): 26.5(+/-3.6): 1 in the east, 20.4(+/-0.2): 31.5(+/-11.1): 1 in the middle and 18.1(+/-0.6): 17.6(+/-0.7): 1 in the west of the Strait. The physical and biological processes that account for the observed spatial variability of the N: Si: P ratio along the Strait are identified. We estimated that in the Atlantic water entering the Mediterranean Sea, about 84% of the variability in N: Si: P molar ratio is due to biological and 16% to physical processes.