Radiocarbon-based circulation age of the world oceans

The distributions of deep ocean Δ¹⁴C data are often used to illustrate the rate of deep ocean circulation. The associated conventional ¹⁴C ages show a difference of 1000 years between the North Atlantic and the Southern Ocean and a difference of another 1000 years between the Southern Ocean and the North Pacific. These differences may be interpreted directly and mistakenly as the timescale of circulation. The characterization of the deep ocean circulation being millennial is common. Using objectively gridded, natural Δ ¹⁴C "data" of Key et al. (2004), I recast Δ¹⁴C in terms of circulation by accounting for (1) long-surface ocean reservoir ¹⁴C ages and (2) two sources of deep water formed in the North Atlantic and around Antarctica. The new distribution of "circulation ¹⁴C ages" is more consistent with the deep ocean being characterized by a centennial timescale than a millennial timescale. Also, the role of the southern sourced deep water is now made more obvious. By accounting for the two important controls on oceanic ¹⁴C that are not well known outside the field of chemical oceanography, the new map will be useful as an illustration of global deep ocean circulation to the wider scientific community and as a pedagogical tool to new students in Earth sciences and oceanography.