A TWO-SITE CORAL REEF RECORD OF TIMING AND DURATION OF MELTWATER PULSE 1A IN HAWAII

Meltwater pulse 1A (MWP-1A) is a globally significant uptick in relative sea level (RSL) change during the last deglacation. Regional variation in MWP-1A timing and magnitude has important implications for meltwater sources and short-term regional responses of oceans and ice sheets to rapid climate warming. Coral reef records from Barbados (e.g., Peltier and Fairbanks, QSR, 2006) and Tahiti (Deschamps et al., Nature, 2012) have been interpreted as rapid glacial melt induced RSL changes from a northern hemisphere (NH) or Antarctic plus NH source, respectively, in part because the Tahiti RSL uptick (14.31-14.65 ka) predates the Barbados one (13.61-14.08). Hawaii represents an excellent site to explore MWP-1A RSL because it is far-field from meltwater sources and glacial isotatic adjustments that contaminate many near-continent or glacial near-field records. Using a different approach than these prior studies (which used drilling), we have mapped and grab sampled two well-preserved Hawaiian deglacial coral reef records using the Univ. Hawaii/HURL Pisces V manned submersible and ROV Luukai. One record is on the margin of a carbonate platform west of Molokai and the other is on the flanks of a rejuvenation volcano off Oahu's SE shore. So far, U-series dating of samples collected on 7 dives at the two sites indicate that the timing and duration of the record (i.e., larger depth variation over a specific time interval than the deglacial mean) is the same and in an overlapping depth range at both sites. While more work collecting and dating corals is needed to refine the duration and magnitude of the RSL shift, our current estimates overlap in time with the Barbados record and like it, postdate the Tahiti RSL shift by about 600 yrs. Another inferred MWP-1a record from Hawaii deduced from the flooding of a now 150-m deep reef structure on the rapidly subsiding Big Island of Hawaii (14.62-15.45 ka; Webster et al., Geology, 2012) significantly predates all three other records.