Precise temporal correlation of holocene mollusk shells using sclerochronology

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