Possible Association of Oyster Terrain Mound Features in the Peconic Estuary on Long Island, NY With 8.2ka Meltwater Pulse?

Mound features revealed by multibeam bathymetry and seismic profiles are associated with an oyster terrain that covers an extensive area of the Peconic Estuary on Long Island, NY. These mounds may capture high resolution paleoclimate records of the 8.2ka melt water pulse. One of the puzzles of the 8.2ka event is the lack of a strong signal in the salinity or δ180 near the suggested outburst path via the Hudson Strait and Labrador Sea. The Peconic Estuary is situated where one might find evidence of this outburst, downstream from the modern currents exiting the Labrador Sea and to the north of the signature reported to be found off of Cape Hatteras near the present Gulf Stream North Wall. By examining the characteristics of these features based on the multibeam backscatter and bathymetry data obtained as part of an ongoing project we can distinguish relatively high backscatter regions associated with a mound morphology typified by exposed mounds of approximately 2m in height. The mounds' surfaces are associated with stained unarticulated oyster shells in grab samples, but no living oysters. These oysters are far thicker with many growth bands than the thin young oysters associated with modern Long Island aquaculture or harvested oyster beds and are often full of pits and holes. The mounds topped by oyster shells are hypothesized to be oyster bioherms that started to form around the time of the 8.2ka meltwater pulse (mwp), and as such should serve as proxies of climate around this time period. Examination of seismic profiles over this mound terrain reinforces the idea that these are indeed older features by revealing buried mounds under at least 3m of sediment that fall within the exposed mound range of 6m to at least 18m. It also reveals even greater relief of most exposed mound morphologies below the surface with many buried and exposed mounds reaching greater than 4m in relief. It would have required thousands of years to bury mounds at a steady low sedimentation rate. Cores and dates of the buried mound features are needed to confirm this hypothesis. If these mounds indeed started around that time and continued for several hundred years to millennia after, we may be able to find evidence of a freshening from meltwater pulse sources upstream related to the 8.2ka event in the North Atlantic as well as changes in interannual variability by examining oyster shells from this region.