Reconstructing the history of fluid flow at cold seep sites from Ba/Ca ratios in vesicomyid clam shells

Abstract

Hydrogen sulfide discharge at cold seep sites is recorded as enrichment in the barium to calcium (Ba/Ca) ratio in shells of vesicomyid clams collected live from cold seeps in Monterey Canyon and the Cascadia margin. A direct relationship between increased Ba fluxes from cold seeps and Ba incorporation into shells was established for the Cascadia margin site. For the Monterey canyon site, a 2-yr episode of high fluid flow centered on 1992 was inferred from coherent changes in the Ba/Ca profiles of three Calyptogena kilmeri shells. Comparison with precipitation and δ18O data indicates that this high-flow period may have been driven by an increase in rainfall after the 1988-1990 California drought. High-resolution records preserved in clam shells are shown to be useful in elucidating characteristics, history, and possible mechanisms driving fluid discharge at continental margin seeps, thus establishing their potential use as paleotracers of fluid seepage events.