A LARGE DROP IN ATMOSPHERIC C-14 C-12 AND REDUCED MELTING IN THE YOUNGER DRYAS, DOCUMENTED WITH TH-230 AGES OF CORALS/

Paired carbon-14 (C-14) and thorium-230(Th-230) ages were determined o n fossil corals from the Huon Peninsula, PaPua New Guinea. The ages we re used to calibrate part of the C-14 time scale and to estimate rates of sea-level rise during the last deglaciation. An abrupt offset betw een the C-14 and Th-230 ages suggests that the atmospheric C-14/C-12 r atio dropped by 15 percent during the latter part of and after the You nger Dryas (YD). This prominent drop coincides with greatly reduced ra tes of sea-level rise. Reduction of melting because of cooler conditio ns during the YD may have caused an increase in the rate of ocean vent ilation, which caused the atmospheric C-14/C-12 ratio to fall. The rec ord of sea-level rise also shows that globally averaged rates of melti ng were relatively high at the beginning of the YD. Thus, these measur ements satisfy one of the conditions required by the hypothesis that t he diversion of meltwater from the Mississippi to the St. Lawrence Riv er triggered the YD event.