Unusual Po-210/Pb-210 ratios in the surface water of the Gulf of Lions

Concentrations of Po-210 and Pb-210 have been measured in sea water collected in the Grand Rhone Canyon. Concentrations of Pb-210 are at similar levels to those found in other Mediterranean seawater samples, and are at the levels which would be expected in comparison with global sea water data. The same applies to the Po-210 concentrations in samples from below 100 m depth. Surface samples from above 100 m have Po-210 at levels rather higher than expected, and their Po-210/Pb-210 ratios are about 1 or more as compared with the usual open ocean ratio of about 0.5. These data can be interpreted as indicating another source of supply of Po-210 to the surface layer in addition to the normal atmospheric input. We suggest that an episodic advective particulate input, probably originating in the output of the Rhone river and perhaps involving resuspension of fine particulates from the bottom sediments as a result of storm conditions, is the most likely candidate for this additional source.