Today, the ocean thermohaline circulation transports half of the Pa-231 produced by radioactive decay in the Atlantic Ocean water column to the Southern Ocean. This export respectively imparts low and high Pa-231/Th-230 ratios to the surface sediments of these oceans. Ocean sediments from the Last Glacial Maximum bear a similar isotopic fingerprint, implying that advection of North Atlantic Deep/Intermediate Water into the Circumpolar Deep Water of the Southern Ocean occurred at a similar-or slightly higher-rate during the last glacial period.