Measurements of trichloroethylene (C2HCl3) and tetrachloroethylene (C2Cl4) in waters of the North Atlantic are reported. They show that at the times of sampling both gases are supersaturated in the surface ocean and that there are therefore fluxes of each into the atmosphere. The water column profiles are unusual in showing increasing concentrations with depth. It is proposed that both gases may be supplied to the ocean from the atmosphere in winter, when their atmospheric mixing ratios are higher due to diminished loss rates resulting from lower concentrations of the hydroxyl radical. This hypothesis is consistent with literature reports of ocean supersaturations of trichloroethylene and tetrachloroethylene but does not require any natural source. In the western Atlantic several profiles of trichloroethylene have, superimposed on the general increase in concentration with depth, maxima lying just beneath the mixed layer which may be indicative of a biological source. ¿ 2001 American Geophysical Union