INVESTIGATION OF DEAD OCEAN QUAHOGS (ARCTICA ISLANDICA) SHELLS ON THE MID-ATLANTIC BIGHT CONTINENTAL SHELF

Ocean quahogs, Arctica islandica, are a long-lived, widely dispersed, biomass dominate in the Mid-Atlantic; therefore, quahog shells are valuable resources for studying climate change over time. Recently, dead ocean quahog shells were discovered south and inshore of the present biogeographic range of this animal. The presence of ocean quahog shells outside the current range is presumably a consequence of past regressions and transgressions of the Cold Pool, the bottom-trapped, cool body of water that allows boreal animals to live at lower latitudes. Dead ocean quahog shells were collected offshore of the DelMarVa Peninsula then radiocarbon-dated, evaluated for taphonomic condition, and aged to investigate spatial-temporal changes in growth. One hundred and twenty-one dead shell were dated with birth years ranging from 60-4,400 cal years BP, including ages contemporaneous with four major Holocene cold events. Shells with a longer time-since-death were discolored orange with no periostracum while shells with a shorter time-since-death had their original color, white, with some periostracum. The presence (or absence) of periostracum and discoloration followed a logistic process, with 50% of shells absent of periostracum and 50% discolored in about 1,000 years. This is the longest time series assessing taphonomic processes within the Holocene with the first reported logistic relationship between time-since-death and degradation. Changes in growth throughout time and space is evident when comparing growth curves fit with a Modified Tanaka model to contemporary populations for George’s Bank, Long Island, and New Jersey