Seasonal isotope and trace-metal profiles of serially-sampled Conus gastropods: proxies for paleoenvironmental change

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Title: Seasonal isotope and trace-metal profiles of serially-sampled Conus gastropods: proxies for paleoenvironmental change
Author: Gentry, David Keith
Abstract: We test the fidelity of shallow -water gastropod skeletons as multi -proxy archives of seasonal paleo -environmental change by performing isotopic and trace -metal analyses on specimens of Conus ermineus from the Gulf of Mexico . Four adult specimens were collected from Stetson Bank in the Flower Garden Banks National Marine Sanctuary during the summer of 2002 . Shell samples were milled along axes of growth to produce time -series profiles spanning up to eight years . We corrected the profiles for growth rate effects and compared the tuned results with in situ temperature and salinity records at the reef surface and temperature profiles from nearby surface buoys . Examination of sample densities in & #948 ;18O cycles shows that shell growth is faster during summers and slower during winters . Tuning the profiles versus time yields & #948 ;18O values that co -vary closely with seasonal temperatures to a high degree of coherency (R2 = 0 .84 ) . The & #948 ;13C profiles show cyclic variation modified by ontogenetic decreases in & #948 ;13C . These ontogenetic trends are attributable to decreasing metabolic efficiency , while seasonal cycles reflect hydrographic changes in the gastropods ? ? habitat . Salinity and & #948 ;13C of dissolved inorganic carbon show a strong correlation at Stetson Bank (R2 = 0 .80 ) , and early summer shell & #948 ;13C minima coincide with local salinity minima during times of peak river discharge . The terminations of these & #948 ;13C minima occur during annual upcoast reversals of shelf currents in this area . These effects are augmented by summer stratification and productivity minima that further decrease seawater & #948 ;13C . Sr /Ca ratios increase through ontogeny , most likely due to decreasing metabolic efficiency . However , seasonal variations in Sr /Ca profiles show strong similarity with & #948 ;18O profiles , confirming the temperature dependence of Sr /Ca and minimal influence of salinity on shell & #948 ;18O at Stetson Bank . The results of this study show that tuned & #948 ;18O and Sr /Ca profiles can be used to reconstruct seasonal paleotemperatures . Carbon isotope profiles and environmental data also demonstrate the utility of Conus & #948 ;13C as a proxy for freshwater flux and shelf circulation .
URI: http : / /hdl .handle .net /1969 .1 /3871
Date: 2006-08-16

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Seasonal isotope and trace-metal profiles of serially-sampled Conus gastropods: proxies for paleoenvironmental change. Available electronically from http : / /hdl .handle .net /1969 .1 /3871 .

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