When Was MWP-1A? Evidence From Two New Hawaiian Coral Reef Records

Abstract:

Meltwater pulse 1A (MWP-1A) was a rapid, globally significant jump in relative sea level (RSL) within a sequence of events that brought the Earth system out of the ice age. The absolute timing of MWP-1A and the timing relative to the Bolling warming remain controversial. Current coral reef estimates for the start of MWP-1A timing vary over about 1.5 ka, including the Barbados record (13.61-14.08 ka, Peltier and Fairbanks, QSR, 2006), a recent Tahiti record (14.31-14.65 ka, Deschamps et al., Nature, 2012) and an age estimate inferred 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). While the amplitude of the local MWP-1A RSL jump will vary regionally in a manner that reflects the location of the meltwater source(s), the timing at far-field sites should not vary significantly. We present a new record we are developing from Hawaii, a far-field site, that may provide an additional important constraint on this timing. Specifically, we have mapped and grab sampled two well-preserved Hawaiian deglacial coral reef records, including MWP-1A, using the University of Hawaii/HURL Pisces V HOV and ROV Luukai. One site lies west of Molokai and the other off Oahu's SE shore. Preliminary results of U-series dating of samples (e.g., see images below) collected on seven dives at the two sites indicate that the timing and duration of the record is the same and in an overlapping depth range at both sites. More laboratory and field work is required to refine this age constraint. We will discuss our estimate for the initiation timing and duration of the event, and our continuing efforts to refine them, as well as their implications for the ongoing debate regarding the role of MWP-1A in ice age climate change.