A possible 20th-century slowdown of Southern Ocean deep water formation

Chlorofluorocarbon-11 inventories for the deep Southern Ocean appear to con firm physical oceanographic and geochemical studies in the Southern Ocean, which suggest that no more than 5 x 10(6) cubic meters per second of ventil ated deep water is currently being produced. This result conflicts with con clusions based on the distributions of the carbon-14/carbon ratio and a qua si-conservative property, PO4*, in the deep sea, which seem to require an ; average of about 15 x 10(6) cubic meters per second of Southern Ocean deep ventilation over about the past 800 years. A major reduction in Southern Oc ean deep water production during the 20th century (from high rates during t he Little Ice Age) may explain this apparent discordance. If this is true, a seesawing of deep water production between the northern Atlantic and Sout hern oceans may lie at the heart of the 1500-year ice-rafting cycle.