Modified dendrochronological methods can improve the temporal resolution of environmental reconstruction from bivalve mollusk shells. Mollusks grow by periodic accretion of skeletal material leaving daily, fortnightly and annual growth increments bordered by distinctive growth lines in their shells. Cross-dating individual growth increment time-series can help to find and verify overlapping life spans among different specimens from a given region. "Clam-ring" chronologies from individuals with overlapping life spans can be strung together to form master chronologies, which comprise much longer time periods than individual life spans. Master chronologies provide a source for the analysis of longer-term environmental periodicities and fluctuations.

We measured annual growth increment widths in 67 Chione cortezi, C. fluctifraga and C californiensis specimens collected alive at different times in the 1990s in the intertidal zone of the northern Gulf of California, Mexico. The specimens average seven to eight years in ontogenetic age. Standardized growth index time-series calculated from each specimen were cross-dated and strung together. Inter-annual growth patterns in specimens with overlapping life spans are strikingly similar. The Chione master chronology covers the period from 1982 to 1999. 75% of the variability in growth rates during the past ten years can be explained by water temperature and salinity.

This study demonstrates that even relatively short-lived bivalve mollusks can be used to establish master chronologies, which reveal high-resolution environmental information over periods that are longer than the individual mollusk's life span.

Check out other C.E.A.M. pages:

CEAM publications

Back to CEAM abstracts

Back to 2001 abstracts

C.E.A.M. Home

Return to U of A Geosciences Homepage