Cooling and ventilating the abyssal ocean

The abyssal ocean is filled with cold, dense waters that sink along the Ant arctic continental slope and overflow sills that lie south of the Nordic Se as. Recent integrations of chlorofluorocarbon-11 (CFC) measurements are sim ilar in Antarctic Bottom Water (AABW) and in lower North Atlantic Deep Wate r (NADW), but Antarctic inputs are approximate to 2 degreesC colder than th eir northern counterparts. This indicates comparable ventilation rates from both polar regions, and accounts for the Southern Ocean dominance over aby ssal cooling. The decadal CFC-based estimates of recent ventilation are con sistent with other hydrographic observations and with longer-term radiocarb on data, but not with hypotheses of a 20(th) -century slowdown in the rate of AABW formation. Significant variability is not precluded by the availabl e ocean measurements, however, and interannual to decadal changes are incre asingly evident at high latitudes.