The Eastern Mediterranean tritium distribution in 1987

We describe and evaluate the distribution of the transient tracer tritium in the Eastern Mediterranean, on the basis of approximately 700 data points obtained from cruise M5/6 of F/S METEOR, Aug.–Sept. 1987. The horizontal resolution provided by the dataset is limited, but the vertical resolution is sufficient to resolve most of the principal features of the tritium distribution, and the data quality is good. Previous results concerning the thermohaline circulation of the Eastern Mediterranean based on tracer data are confirmed. Up to 1987 Eastern Mediterranean Deep Water (EMDW) was replenished from the Adriatic Sea, a near-bottom replenishment from the Aegean Sea contributing at most about 10%. A comparison with tritium data from a 1978 METEOR cruise gives evidence of a transfer of near-surface waters into the EMDW during the period between the two surveys. Cretan Intermediate Water (CIW) with a core depth of approximately 700 m and replenished from the Aegean Sea is found to be a prominent water mass. CIW spreads primarily westward, and is bordered in the Levantine Sea by EMDW which in this region extends to about 500 m depth. We infer that CIW replenishment has been rather steady since at least some decades, with a turnover time on the order of 10 years, and we name evidence that suggests a possible contribution of CIW to the dense water formation in the Adriatic Sea. Specific differences between the distribution of tritium and that of the chlorofluorocarbon tracer CFC 12 are noted. Tritium concentrations in the near-surface waters are found to be somewhat variable. The explanation is that for this tracer redistribution within the water column is particularly relevant.