CORAL RECORD OF RAPID SEA LEVEL RISE IN HAWAII AFTER THE LAST GLACIAL MAXIMUM

Global records indicate roughly 120 m of sea level rise from the onset of deglaciation at ca 20 ka until the start of the Holocene, yet the details regarding variations in rate and local scale impact over that interval continue to be debated. A newly discovered, intact, well-preserved, fossil coral record from offshore Molokai in the Hawaiian Islands provides information about sea level rise and coral accretion in the central Pacific during this time. Observations on dives using the Hawaii Undersea Research Lab submersible indicate nearly continuous, morphologically fresh fossil coral colonies of Porites on a pre-existing submerged island slope from 170 m to 125 m water depth. These are dominated by large (10-15 m tall) head structures at depth, transitioning to smaller heads and then into smaller encrusting morphologies at the shallowest elevations. U-series dating of this record is underway. Thus far, ages of pristine skeletal material from 162 m to 125 m water depth indicate a linear relative sea level (RSL) change of 0.021±.003 m/yr from 17 to 14.8 ka. Such a rate implies that coral accretion occurred as a thick veneer on pre-existing substrate, wherein large heads were abandoned after several hundred years of growth in favor of new accretion immediately upslope. This pattern allowed the ecosystem to generally keep pace with this rapid sea level rise by driving new growth at the front of the rising water. The local setting (limited wave action, strong light penetration, limited upslope watershed, lack of a fringing reef) likely helped corals survive this rapid rate of RSL change. Corals may have grown nominally up to 40 m deeper than reference sea levels over this interval because of these ideal conditions. We will discuss the implications of this observation for the absolute value of local sea level at this time, considering factors such as growing depth limitations, geoid factors, and vertical motion of the island, and also consider where the apparently missing accretion record from 18-20 ka lies.