BENTHIC ISOTOPE EVIDENCE FOR CHANGES OF THE MEDITERRANEAN OUTFLOW DURING THE LATE QUATERNARY

A suit of sediment cores close to and south of the Strait of Gibraltar (12 degrees-36 degrees N, 500-2800 m water depth) were analyzed for stable isotopes in epibenthic for aminifers Cibicidoides wuellerstorfi and Planulina ariminensis During peak glacial times, the data exhibit higher delta C-13 values of up to 1.6 degrees/oo at intermediate depths near the Strait of Gibraltar (36 degrees N). The values decrease to the south as evidenced by our data, but also to the north as revealed by data of intermediate depth cores north of 38 degrees N (in Duplessy et al. [1987]). Thus, the distribution pattern of delta C-13 provides crucial evidence for an increased influence of nutrient depleted Mediterranean Outflow Water (MOW) on the glacial northeast Atlantic hydrography. During oxygen isotope Terminations I and II, the meridional carbon isotope gradient indicates a significantly decreased but still active MOW. As deduced from the delta O-18 fluctuations, the temperatures of the MOW in the Atlantic were lower during glacial times by as much as 5 degrees C. During glacial times and during Termination I the maximum delta C-13 values of the MOW correlate with minimum values of the North Atlantic Deep Water (NADW) and viceversa. This inverse response to climatic change of the carbon isotope signals of both water masses indicates, that the supply of saline MOW to the north Atlantic may be less important for the formation of NADW than previously assumed.