A multi-axial growth analysis of stable isotopes in the modern shell of Saxidomus gigantea: implications for sclerochronology studies
Abstract
In this study we use stable-isotope ratios of two modern Saxidomus gigantea specimens from Namu, British Columbia to investigate intra- and inter-specimen isotopic variation. Seasonal stable isotope profiles (δ13Cshell, δ18Oshell) were generated along the axis of maximum growth: a standard method for sclerochronolgical investigations. The profiles show that analogous seasonal variation is recorded in δ18Oshell however, significant variability is recorded in δ13Cshell. We suggest this is caused by differences in metabolic activity between the individuals. Intra-shell variability was evaluated using a Hendy-type test and a multi-axial growth analysis. Isotopic analysis along growth horizons (Hendy-type test) produced good reproducibility for δ13Cshell, but significant variability in δ18Oshell, especially at the sinistral margin. The multi-axial growth analysis generated several profiles crossing a prominent growth band from a single specimen. Similar seasonal variations are recorded in δ18Oshell along all axes analyzed. δ13Cshell show significantly less co-variation and is possibly caused by internal metabolic activity. This study shows that δ18Oshell profiles generated from any portion of the shell are useful in evaluating seasonal fluctuations, and may be an excellent method to evaluate the types and rates of shell growth. These results have implications for stable isotope sclerochronological studies involving the use of fragmented shell material, such as that derived from archaeological sites (e.g., shell middens) or sediment cores.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2007
- Bibcode:
- 2007AGUFM.B31D0616K
- Keywords:
-
- 0424 Biosignatures and proxies;
- 1041 Stable isotope geochemistry (0454;
- 4870);
- 4235 Estuarine processes (0442);
- 4800 OCEANOGRAPHY: BIOLOGICAL AND CHEMICAL (0460);
- 4924 Geochemical tracers