A record of past ocean-Atmosphere radiocarbon differences from the northeast Pacific

A record of the ¹⁴C age differences between atmosphere and the mixed layer of the northeast Pacific Ocean was obtained from 58 radiocarbon measurements on shells and associated wood from coastal sediments in British Columbia. This series of mixed layer reservoir ages spans the Holocene and extends into the period of the Younger Dryas cold event in the North Atlantic and surrounding regions. The data reflect the extent of upwelling in the northeast Pacific and thus constrain models of carbon cycling and ocean circulation. Most of the reservoir ages are only slightly less than than the present (preindustrial) value of about 800 years, and may be identical when probable sampling errors are taken into account. Either the North Pacific reached a state close to its present mode of circulation at or before the end of the Younger Dryas or a different circulation fortuitously produced a similar reservoir age. Our results support the hypothesis that slow changes in atmospheric radiocarbon concentrations over the Holocene arose from ¹⁴C production rate changes. Data corresponding to a radiocarbon age of around 6400 years B.P. give a reservoir age of 1200 years. If this result is confirmed, it indicates a much greater variability for the Holocene ocean circulation than was previously believed possible.