Dichloromethane is an atmospheric trace gas that has a tropospheric lifetime on the order of 5 months and has major anthropogenic sources. Evidence has been presented for an oceanic source. This paper reports measurements of dichloromethane in waters of the North Atlantic and Labrador Sea that are interpreted as showing that the compound has a primarily atmospheric source and appears to persist for years to decades in the intermediate and deep ocean. These characteristics have the potential to yield apparent supersaturation of the gas in surface ocean waters which may be incorrectly interpreted as an oceanic source.