HR: 1340h
AN: PP23B-1436    [Abstracts]
TI: Inferring Paleoenvironments Using Seasonal Isotope and Trace-Metal Profiles of Serially-Sampled Gastropods
AU: * Gentry, K
EM: dgentry@geo.tamu.edu
AF: Texas A&M University, Department of Geology and Geophysics, 3115 TAMU, College Station, TX 77843 United States
AU: Sosdian, S
EM: sosdian@imcs.marine.rutgers.edu
AF: Rutgers University, Institute of Marine and Coastal Sciences, New Brunswick, NJ 08901 United States
AU: Grossman, E L
EM: e-grossman@tamu.edu
AF: Texas A&M University, Department of Geology and Geophysics, 3115 TAMU, College Station, TX 77843 United States
AU: Lear, C
EM: carrie@earth.cf.ac.uk
AF: Cardiff University, School of Earth, Ocean, and Planetary Sciences, Cardiff, CF10 3YE United Kingdom
AU: Rosenthal, Y
EM: rosentha@imcs.marine.rutgers.edu
AF: Rutgers University, Institute of Marine and Coastal Sciences, New Brunswick, NJ 08901 United States
AB: Early Cenozoic (e.g., Eocene-Oligocene), foraminiferal records of tropical SSTs are controversial, due to the possible alteration of the shells' isotopic and elemental composition by diagenetic recrystalization. Here we test the fidelity of shallow water molluskan skeletons as an alternative archive of tropical SSTs. Because of the long life-spans and rapid growth of mollusks, mollusk shells provide excellent records for Cenozoic seasonality, provided that seasonal variations in the isotopic and trace-metal composition of the carbonate shells reflect the ambient temperature and $\delta^{18}$O of the water in which the organisms grew. To evaluate the fidelity of gastropod skeletons as recorders of such paleoenvironmental information, we performed isotopic and trace-metal analyses on specimens of {\it Conus ermineus} from the Gulf of Mexico. Three adult specimens were collected at Stetson Bank in the Flower Garden Banks National Marine Sanctuary from depths of 21-24 m. Two were sampled alive and remain in aquaria. The shells were milled parallel to growth banding to produce time series profiles along the axes of growth. These profiles were compared with temperature and salinity records from water quality data recorders at the reef surface for the later part of the growth period. For the earlier growth record, we estimated 24 m temperatures using records from nearby surface data buoys. The $\delta^{18}$O and Sr/Ca profiles covary in a saw-tooth pattern, with a high degree of coherency. Such saw-tooth patterns are often interpreted as resulting from slower growth rates during summer and winter months. However, environmental records show that temperatures at 24 m change in a pattern similar to that seen in the profiles, with summer warming at 24 m lagging behind warming at the surface by up to three months. This asymmetric pattern of temperature change suggests that the shapes of isotope and trace-metal profiles may be dominantly controlled by local hydrography, rather than by intra-annual changes in growth rates. The strong similarity between the Sr/Ca profiles and {\it in-situ} temperature records suggests that Sr/Ca can be used as a paleothermometer in aragonitic mollusks. Regression of temporally-tuned metal profiles against temperature records suggests a 5$\pm$0.8% increase in Sr/Ca per degree Celsius over the range of 19$\deg$ to 30$\deg$C. Therefore, using paired $\delta^{18}$O and Sr/Ca measurements in {\it Conus} shells can provide reconstruction of variations in sea surface temperature and salinity in the past.
DE: 9604 Cenozoic
DE: 4870 Stable isotopes
DE: 4875 Trace elements
DE: 3344 Paleoclimatology
DE: 4267 Paleoceanography
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting