Sr isotope ratios in the estuarine bivalve, Rangia cuneata, as a proxy for salinity, Neuse River Estuary, North Carolina (2016)

Undergraduates: Aleah Walsh, Lauren Graniero Drew Coleman

Faculty Advisor: Donna Surge
Department: Geology

---

Paleoenvironmental reconstructions using the oxygen isotope ratios (??18O) recorded in carbonate hard part remains require knowledge of either temperature or the ??18O 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 (??87Sr) recorded in bivalve shells from San Francisco Bay (SFB) have been used to reconstruct changes in estuarine salinity during the Holocene based on the ??87Sr-salinity relation. Here, we test the hypothesis that ??87Sr 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 ??18O-salinity relation. This approach will allow us to use ??87Sr shell values to estimate salinity, and hence, the ??18O value of water, and then estimate temperature from the ??18O shell value.