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RESEARCH PRODUCT

Holocene climate and seasonality of shell collection at the Dundas Islands Group, northern British Columbia, Canada—A bivalve sclerochronological approach

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description

article i nfo To analyze environmental changes and the seasonality of shell collection in British Columbia during the Ho- locene, oxygen isotopes were measured from modern and archeological (1337-7438 cal yr BP) shells of the butter clam Saxidomus gigantea. 1697 discrete isotope samples were taken from two modern and 27 arche- ological shells with a high temporal resolution (sub-seasonal up to daily). Archeological shells were collected from five shell midden sites on the Dundas Islands Group, northern British Columbia, Canada. The oxygen iso- tope data reveal clear annual cycles, with the most positive δ 18 Oshell values occurring during the cold season (slower growth, annual growth line formation) and the most negative δ 18 Oshell values during the warm sea- son (period of faster growth). Whereas the most positive δ 18 Oshell values remained relatively constant throughout the Holocene, the warm season δ 18 Oshell values reflected considerable variability. Summer values observed in the early and late Holocene became approximately 1‰ more negative around 2500-3000 and 5500-6000 BP, implying lower salinity during the Mid-Holocene. Variations in the oxygen isotopic composi- tion of marine shells reflect changes in temperature and salinity. Such large changes in δ 18 Oshell are unlikely being caused by temperature changes alone. Furthermore, the large annual δ 18