Sr Isotope Ratios in the Estuarine Bivalve, Rangia cuneata, as a Proxy for Salinity, Neuse River Estuary, North Carolina

Paleoenvironmental reconstructions using the oxygen isotope ratios (δ¹⁸O) recorded in carbonate hard part remains require knowledge of either temperature or the δ¹⁸O value of the ambient water during calcification. Constraining either variable in estuarine environments can be difficult because of variability in freshwater discharge and temperature. Therefore, additional proxies are necessary to estimate changes in estuarine salinity and/or temperature recorded in carbonate hard part remains. Strontium isotope ratios (Δ⁸⁷Sr) recorded in bivalve shells from San Francisco Bay (SFB) have been used to reconstruct changes in estuarine salinity during the Holocene based on the Δ⁸⁷Sr-salinity relation. Here, we test the hypothesis that Δ⁸⁷Sr values in Rangia cuneata shells from the Neuse River Estuary (NRE) in North Carolina reflect estuarine salinity. R. cuneata were collected alive at sites in the upper, middle, and lower estuary to represent the salinity gradient of the NRE. Water samples were collected along the estuary to confirm the mixing relationship between fresh- and seawater end members. We will also establish the δ¹⁸O-salinity relation. This approach will allow us to use Δ⁸⁷Sr shell values to estimate salinity, and hence, the δ¹⁸O value of water, and then estimate temperature from the δ¹⁸O shell value.