T86 Paleoenvironmental Reconstructions from Biogenic Carbonates I

Monday, 5 November 2018
8:00 AM - 12:00 PM
Room 140

DECONVOLVING SEASONAL TEMPERATURES AND SALINITIES FROM CRASSOSTREA VIRGINICA USING A δ13C AND δ18O MULTIPROXY APPROACH

Paper number: T86-12
Program: Technical Sessions
Time: 10:45 AM – 11:00 AM

Authors

Abstract

Researchers have attempted to reconstruct estuarine environmental temperatures and salinities from mollusk shell geochemistry for decades. Because shell carbonate δ18O is controlled by both temperature and δ18Owater (a salinity proxy), a second geochemical proxy is needed in order to uniquely solve for temperature and constrain salinity. Shell calcite Mg/Ca (a temperature proxy) or Ba/Ca (a salinity proxy) have been combined with δ18O measurements to solve this conundrum in other calcifying groups such as foraminifera. Unfortunately, the use of elemental ratios in mollusk shells to reconstruct ambient salinity and temperature has been elusive.

Here we present environmental reconstructions using the Eastern North American oyster, Crassostrea virginica, and water samples from the James River, Virginia that describe estuarine salinity and temperature conditions across four centuries. Water samples were collected from several localities across an annual cycle and analyzed for salinity, δ18Owater and δ13CDIC. James River C. virginica shells of known provenance were sampled along their hinge margins for δ18O and δ13C measurements. James River water data display linear S vs δ18Owater and S vs δ13CDIC relationships. We combine these environmental relationships with measured δ13Cshell and δ18Oshell values to compute the ambient James River δ18Owater values for the environmental chronology recorded by an oyster throughout its life. Converting the δ13Cshell values to salinity using the local S vs δ13CDIC relationship yields ambient salinities that agree remarkably well the environmental data. We conclude that δ13Cshell can be used to compute ambient salinity and, in combination with δ18Oshell and a local S vs δ18Owater relationship, compute environmental temperatures in this mesohaline estuarine region. We present environmental salinity and temperature reconstructions from 5 recent (2002-2006), 4 historical (Jamestown, 1608-1612 AD) and two fossil Pleistocene C. virginica shells from the nearby Yorktown Formation to demonstrate the application of this multiproxy approach for deconvolving environmental salinity and temperatures from C. virginica shell geochemistry.

Geological Society of America Abstracts with Programs. Vol. 50, No. 6

doi: 10.1130/abs/2018AM-321462

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