Stable carbon isotopes in bivalve shells as a salinity proxy
Abstract
Stable carbon isotopes of dissolved inorganic carbon (δ13C-DIC) often vary with salinity in estuarine settings. Variations of salinity in estuaries also complicate temperature reconstructions based on oxygen isotope values in biological carbonates. Therefore having a salinity proxy could assist in estuarine temperature reconstruction as well as providing data on freshwater discharge into the estuary. Unfortunately, δ13C values in bivalve shells are potentially influenced by several sources of carbon including DIC, metabolic carbon and sediment pore-water DIC. This study first investigates the influence of these three potential carbon sources in the Manila clam (Ruditapes philippinarum) reared under laboratory conditions and then in the field during a two-year monitoring study. Metabolic carbon remained fairly constant in the laboratory (~12%) and we did not detect any difference between clams living in organic rich sediments and those in sediment free aquaria. There was a strong correlation between δ13C-shell and δ13C-DIC (r2=0.77) indicating that δ13C-shell can be used as a relative salinity indicator. In the field, calculated salinities were within the range of recorded salinities (± 5 salinity units), but there were significant differences between individuals. This study highlights the potential of using δ13C in bivalve shells as a salinity proxy, but also illustrates that large uncertainties are associated with this proxy.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2010
- Bibcode:
- 2010AGUFMPP11A1405G
- Keywords:
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- 0424 BIOGEOSCIENCES / Biosignatures and proxies