HR: 0800h
AN: B31D-0611    [Abstracts]
TI: Carbonate-associated sulfate in lucinid (Bivalvia) shells
AU: * Peng, Y
EM: ypeng2@lsu.edu
AF: Louisiana State University, E235 Howe-Russell Geoscience Complex, Baton Rouge, LA 70803, United States
AU: Bao, H
EM: bao@lsu.edu
AF: Louisiana State University, E235 Howe-Russell Geoscience Complex, Baton Rouge, LA 70803, United States
AU: Anderson, L
EM: glande@lsu.edu
AF: Louisiana State University, E235 Howe-Russell Geoscience Complex, Baton Rouge, LA 70803, United States
AU: Engel, A S
EM: aengel@lsu.edu
AF: Louisiana State University, E235 Howe-Russell Geoscience Complex, Baton Rouge, LA 70803, United States
AB: Symbiosis is a fundamental driver of evolution, with examples ranging from mitochondria in eukaryotic cells to barnacle-whale commensalism. The association between sulfur-oxidizing (thiotrophic) bacteria and the lucinid bivalve clade is particularly intriguing because the inferred antiquity of the relationship (>400 m.y.) seems at odds with the relatively loose ecologic linkage of living members. Because only half of genus-level lucinid taxa are extant, and the δ13C of shell carbonate exhibits no systematic difference between symbiotic and non- symbiotic bivalves, a new morphologically-independent proxy to determine whether fossil taxa possessed thiotrophic endosymbionts is needed. The δ34S of carbonate-associated sulfate (CAS) in bivalve shells may hold promise because biogenic carbonate incorporates sulfate into its crystal structure during biomineralization. Incorporation of bacterially derived SO42- (with a more negative δ34S value due to its reduced sulfur origin) into the lucinid-shell crystal lattice would, therefore, impart a distinctly lower δ34SCAS value than that from seawater SO42-, and would be distinguishable from CAS values of co- occurring heterotrophic bivalves. We measured CAS contents, δ34SCAS and δ18OCAS values of 15 sets of lucinid and co-occurring infaunal and epifaunal heterotrophic bivalve shells collected from modern and Cenozoic shallow marine sites. The modern bivalve shells had variable CAS content, from 100 to 2600 ppm. Epifauna often had the highest concentrations relative to the other ecological groups. The δ34SCAS and δ18OCAS clustered at values corresponding to modern seawater sulfate, but with significant scatter. There was no systematic isotope- compositional difference among all bivalves in the same habitat, or among the same lucinid, infaunal, or epifaunal groups across different sites. The fossil bivalve shells tended to preserve lower CAS concentrations and the isotope compositions further deviated from seawater values. These data suggest that 1) pore-water sulfate in shallow sediments is highly heterogeneous in its concentration and isotope composition, probably due to active microbial sulfate reduction, bioturbation, and water-pumping by bivalves and other infaunal filter feeders; 2) CAS is derived from ambient porewater or pumped-in seawater for infauna or epifauna, as well as for lucinids; and 3) CAS concentration and isotope compositions are vulnerable to later diagenetic processes.
DE: 1600 GLOBAL CHANGE
DE: 3600 MINERALOGY AND PETROLOGY
DE: 4870 Stable isotopes (0454, 1041)
DE: 4924 Geochemical tracers
SC: Biogeosciences [B]
MN: 2007 Fall Meeting