The pattern of the global thermohaline circulation of today’s oceans is controlled by deep-water formation at the northern and southern limits of the Atlantic. The apparent lack of deep-water formation in the North Pacific, on the other hand, suggests that this ocean plays only a minor role in the global circulation, but it is unclear whether this was also the case during periods of glaciation-there is conflicting evidence in the sedimentary record for the existence of a deep-water source in the North Pacific during the Last Glacial Maximum(1-4). Here we report the detection of anthropogenic chlorofluorocarbons in the bottom waters of the Aleutian basin in the eastern Bering Sea, which suggests that a small amount of bottom water has formed in this region during the past 40 years. Although the small volumes of water involved are unlikely to play a significant role in determining present-day global circulation patterns, the results lend credence to the possibility that this sea was an important source of deep water for the northwestern Pacific Ocean during the Last Glacial Maximum.