DROWNING OF THE -150 M REEF OFF HAWAII: A CASUALTY OF GLOBAL MELTWATER PULSE 1A?

Based on new submersible dives off NW Hawaii, we present evidence that the drowning of the –150 m reef around Hawaii may have been caused by rapid sea-level rise associated with meltwater pulse 1A (MWP-1A) during the last deglaciation. A re-interpretation of existing coral conventional 14C dates, U/Th dates and new 14C AMS dates constrain the drowning time of the coral reef to ~14.3-13.4 cal kyr BP (mean 13.9 cal kyr BP). This date appears to be roughly synchronous with meltwater pulse 1A (MWP-1A, ~14.2-13.8 cal kyr BP). Dates measured from overlying coralline algal material gave a mean age of 11.6 ka, ~ 2.3 kyr younger than the mean coral age. A paleoenvironmental reconstruction incorporating all available radiometric dates, high-resolution bathymetry, dive observations and coralgal paleobathymetry data, indicate a dramatic rise in sea-level occurred around Hawaii ~13.4-14.3 cal kyr BP. This caused paleowater depths over the –150 m reef crest to increase rapidly above a critical depth (~30-40 m), drowning the shallow reef building Porites corals. Deepwater coralline algae growth, preserved as a crust/pavement and associated mobile substrates (rhodoliths and smaller cemented nodules) dominated as sea-level rise and subsidence continued to present. Additional paired 14C AMS and U/Th dates will more precisely constrain the timing of coral reef drowning and subsequent deep water coralline algal accretion.