Precise temporal correlation of holocene mollusk shells using sclerochronology

Annual growth bands of mollusk shells record several types of paleoenvironm ental information, including geochemical proxies for water properties and m orphological characteristics of growth and mortality. Sclerochronology, the marine counterpart of dendrochronology, offers a way to link individual sh ells together to form long continuous records of such parameters. It also a llows for precise dating of recent shells and identification of contemporan eous fossil individuals. The longevity of the ocean quahog Arctica islandic a (commonly >100 yr) makes this species well suited for sclerochronology, B and width records of contemporaneous A. islandica specimens from the same r egion exhibit high correlations (p = 0.60-0.80 for spans of greater than or equal to 30 bands), indicating some common enviromental influences on shel l growth. By adopting several strict criteria, fossil (dead-collected) shel ls can be linked into composite sclerochronologies. A seven-shell 154-yr ch ronology was constructed for Georges Bank using three live-collected and fo ur dead-collected shells. Band width matching indicates that the dead-colle cted individuals died in A.D, 1950, 1971, 1978, and 1989, Sclerochronologic al age assignments were verified using aspartic acid racemization dating. C onstruction of a 1000-yr sclerochronology is judged to be feasible using th e described methods. (C) 2000 University of Washington.