BUILDING CONFIDENCE IN SHELL: VARIATIONS IN THE MARINE RADIOCARBON RESERVOIR CORRECTION FOR THE NORTHWEST COAST OVER THE PAST 3,000 YEARS
Jennie N. Deo, John O. Stone, Julie K. Stein
American Antiquity 69 no. 4, 771-786 (2004)
Countless research questions hinge on the ability of archaeologists to construct reliable radiocarbon chronologies of human behavior. Reliability may be challenged and is especially troublesome in the case of dated shell, since marine organisms are subject to a reservoir effect. Marine reservoir corrections have long been known to vary regionally, due in part to global differences in circulation and upwelling, which introduce old carbon into ocean surface waters. It is now acknowledged that reservoir corrections also vary temporally. In this study, a comparison of shell-charcoal pairs in Puget Sound and the Gulf of Georgia suggests that, while most samples dated between 3000-0 cal yr B.P. do support the modern correction value, there was a period of time when the reservoir correction deviated significantly. Between 400 and 1400 cal yr B.P., the reservoir correction dipped below the modern value, potentially reflecting a decrease in offshore upwelling. This information is presented as a regional correction curve for the Late Holocene and should be incorporated into other Northwest Coast chronometric analyses.