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The use of stable oxygen (S180) and carbon (SI3C) isotopic ratios of marine shell carbonate is a powerful tool for reconstructing past sea surface temperatures (SST) and estimating season of harvest for shells from coastal archaeological sites. While methods for sampling shells and analyzing the resulting data are established, less is known about the effects of anthropogenic activity on the geochemistry of the shells. Through an experimental study in which we heat carbonate powder from Mytilus californianus shells, we show that mussels cooked by boiling or steaming were unlikely to have their isotopic composition altered by the process. Shells heated over coals, however, show evidence of both visible and structural changes and in some cases are depleted in 8I3C and/or 8180. This indicates that archaeologists should use caution in interpreting past SST or site seasonality from burned shells and should instead test intact, unburned shells. [ABSTRACT FROM AUTHOR]

Marine-shell beads have been recovered from numerous archaeological sites throughout the Intermountain West. Direct radiocarbon determinations and typological cross-dating indicate that groups conveyed beads long distances inland throughout the Holocene. Because the oxygen and carbon isotopic signatures of Callianax (previously OlivellaJ sp. snail shells reflect local sea surface temperature, researchers over the past 15 years have started to assign beads to source regions (stretches of the coast from which people collected shells). We report radiocarbon and stable isotope data for a Callianax biplicata bead from Oregon's Hawksy Walksy Valley, the only bead that has been recovered from this archaeologically important region. These data indicate that the bead was conveyed ~400km. inland at 480-285 cal B.P. from somewhere along the Oregon or northern California coasts. We place these results within the context of other provenance studies of beads in the northern Great Basin to add to our understanding of how, when, and from where coastal producers conveyed shell beads to inland consumers. [ABSTRACT FROM AUTHOR]

Point Bennett, on western San Miguel Island, California, was an important location for sea mammal hunting through time. We use stable oxygen isotopic (δ18O ) measurements from California mussel (Mytilus californianus) shells to reconstruct a seasonal pattern of mussel harvesting by the human occupants of Point Bennett during three time intervals dated to the middle (-7,550-3,600 cal B.P.; CA-SMI-528, Stratum 3) and late (after - 3,600 cal B.P.; CA-SMI-528, Stratum 1; CA-SMI- 602) Holocene. During both periods of occupation at CA-SMI-528, mussel harvesting was primarily during the spring, coincident with onshore sea mammal breeding. This suggests a seasonal pattern of site occupation. At CA-SM1-602, mussel harvesting primarily occurred during the summer and fall. This is opposite when sea mammals are present in highest densities, suggesting year-round occupation. This shows how seasonality of mussel harvesting can be used alongside other indicators like seasonal availability of sea mammals to understand broader patterns of human mobility. [ABSTRACT FROM AUTHOR]