HR: 0800h
AN: PP31A-0889    [Abstracts]
TI: Entrainment of Meltwaters in Hyperpycnal Flows During Deglaciation Superfloods in the Gulf of Mexico: Implications for Freshwater Outflows in the Climate System
AU: * Aharon, P
EM: aharon@wgs.geo.ua.edu
AF: Dept. of Geological Sciences, Box 870338, The University of Alabama, Tuscaloosa, AL 35487 United States
AB: Climate models have indicated that exceptionally high freshwater discharge outbursts into the ocean may offset the ocean thermohaline circulation (THC) and the North Atlantic Deep Water (NADW) production causing sudden climate instabilities. Verification of the numerical model predictions requires the establishment of phase and amplitude relation between the freshwater outflow events into the ocean and the warming/cooling of the atmosphere during the deglaciation. A case in point is provided by the ongoing controversy regarding the question of coupling between the onset of the global meltwater pulse mwp-1A with either the rapid B\/{o}lling warming event at 14.7 cal ka or with the Older Dryas cold event at 14 cal ka. Were the B\/{o}lling warm event and the global meltwater pulse mwp-1A synchronous, then the implications are that (i) the rapid melting of the ice sheets was in response to the dramatic warming event; (ii) mwp-1A corresponds with an intensification, rather than a weakening, of the THC and a regular NADW production, and (iv) the absence of a coupling between the mwp-1A and a slowdown of the THC offers additional evidence of an Antarctic source for the mwp-1A. In contrast, a causative coupling between mwp-1A and the Older Dryas cold event implies disturbances in the THC and NADW formation in response to the meltwater input from a Laurentide Ice Sheet (LIS) source and massive climate reversals. The validity of the proposed arguments and correlation can be readily tested by comparing the Greenland ice record with the contemporaneous meltwater fluxes in the Gulf of Mexico derived from the receding LIS. It has been argued, however, that the isotopic evidence of meltwater flows into the GOM are inconsistent with the volumes of freshwater required to account for the mwp-1A event. Moreover, the size of the mwp-1A would have required melting of the entire southern section of LIS, a scenario that is unsupported by geological evidence. Here I show that previous reliance on oxygen isotopes of planktonic foraminifera as sole archives of the meltwater events in GOM led to a gross underestimation of the volume of meltwater discharges, and to displaced timing. Oxygen isotopes of depth-stratified foraminifera exhibit unusual inversions at the onset of a succession of meltwater discharges into the Gulf of Mexico from the receding LIS. These isotope inversions document entrainment of $^{18}$O-depleted meltwaters in dense flows reaching the seafloor and rising to the surface as buoyant plumes. The exceptional meltwater fluxes of 0.28 to 0.33 Sv, coeval with a prominent erosion intensity peak in continental cryohydrology, are likely the imprints of meltwaters stored in proglacial lake basins along the ice margins and catastrophically released at 14.23-13.87 cal ka in a rapid succession of dam failures. Correspondence between the torrential floods and the Older Dryas abrupt cold reversal in the Greenland ice record supports climate models advocating a coupling between abrupt freshwater flooding of the ocean and climate instabilities.
DE: 4870 Stable isotopes
DE: 4203 Analytical modeling
DE: 4267 Paleoceanography
DE: 3309 Climatology (1620)
DE: 1600 GLOBAL CHANGE (New category)
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting