HOME
Torres, Marta E. and James A.Barry
Marta E. Torres (COAS, Oregon State University, Corvallis, OR 97331; 541-737-2415; email:mtorres@oce.orst.edu)
James P. Barry (MBARI, 7700 Sandholdt Rd. Moss Landing, CA 95039; 408-775-1726; email:barry@mbari.org
High-resolution profiles of a group of minor and trace elements in shells of bivalves have been obtained by Laser Ablation Inductively coupled mass spectrometry to evaluate their potential as monitors of chemical variations in fluid composition at sites of active fluid discharge. Our current focus is on the chemistry of Ba, Sr, Mn, Pb and U. We hypothesize that although the concentration of these elements in the shell may be complicated by a variety of factors, the ratios between various elements to calcium can be related to the compositional differences in the venting fluids.
The bivalve shells analyzed represent specimens from Calyptogena pacifica and Calyptogena kilmeri collected from the "Clam Field" cold seep site in Monterey Canyon at 904 m. This site is located near outcrops in the hydrocarbon-bearing Monterey Formation. Variations in the chemical profiles document that these specimens grew in contact with fluids of significantly different chemical compositions. The Calyptogena kilmeri specimen records much higher levels of Ba, Pb, Mn and U than the Calyptogena pacifica shell. This is consistent with the observation that Calyptogena kilmeri dominates the vesicomyid population at seeps with high sulfide content, whereas, Calyptogena pacifica is the major species present at seeps with low sulfide levels. Variations within a specimen suggest changes in the composition of the fluids through time, which are consistent with variations in the ¶13C and ¶18 O data obtained from sub-samples of shell material.
Comparison between these specimens with samples recovered from seeps in Cascadia margin and from a Galapagos hydrotherman site show changes in the chemistry and isotope profiles which represent changes in the compositional characteristics of the discharging fluids. The present study indicates that shells of living clams may be used to reconstruct geochemical history of fluid discharge at vents and seeps on the seafloor
WHAT'S NEW - THE INSTITUTE - PROJECTS AND PROGRAMMES - CASE STUDIES
BIBLIOGRAPHICAL SERVICES - PRODUCTS & SERVICES - INTERNET RESOURCES