Apparent loss of CFC-113 in the upper ocean

We report and evaluate data of the chlorofluorocarbon CFC-113, in comparison with concurrent data for CFC-12, from cruises into the temperate North Atlantic, the tropical western Pacific, the Eastern Mediterranean, and the Weddell Sea. We consistently find CFC-113 deficiencies in the warmer upper waters, which we interpret as CFC-113 depletion at rates of the order of 3% per year, with possibly accelerated rates in the mixed layer or near the surface. These results severely limit a tracer utility of CFC-113 in the warm upper waters of the ocean. Tracer applications in the deep waters of the ocean should be much less affected, since CFC-113 loss in such waters appears to be far slower. This also holds for the Eastern Mediterranean, despite its rather warm deep waters. For the Weddell Sea, the data indicate a CFC-113 deficiency (similar to 20%) in the shelf waters, which converts into a similar deficiency in newly formed deep and bottom water. Such CFC-113 deficiency has to be accounted for in Southern Ocean tracer work. Future work is proposed to study CFC-113 loss in the ocean in additional detail and to elucidate the loss mechanism(s), on which our data give little clue.