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Abstract:
Naturally occurring radiocarbon and anthropogenic chlorofluorocarbons (CFCs) have proven to be very useful in estimating ages of subsurface water masses in the ocean. Radiocarbon provides temporal information on a time scale of several thousand years and CFCs on a time scale of yearly to decadal. We measured these substances in the deep Canadian Basin of the Arctic Ocean in 2015 as part of the Arctic GEOTRACES program. CFC ratios indicate that the inflow of near-surface water to the bottom is an important, ongoing, renewal process. However, very low concentrations in the deep water suggest an extremely slow renewal rate of about 8,000 years. The radiocarbon measurements yielded a radiocarbon age of about 450 years. These data are contradictory if ventilation of the deep Canadian Basin is a steady, or nearly steady, process. We suggest, rather, that there was a major deep water renewal event about 450 years ago, and that since that time, the abyssal waters of the Canadian Arctic have been in a regime of very slow ventilation. The abyssal radiocarbon age reflects radioactive decay of a nearly stagnant water mass, while the CFC data measures the current ventilation rate, with a modern residence time on the order of 8,000 years.
