Bomb and Natural Dissolved Organic Radiocarbon in the Atlantic Ocean

Dissolved organic carbon (DOC) in the ocean is mostly produced in the surface ocean though, its radiocarbon (¹⁴C) age is thousands of ¹⁴C years old. We report DOC ∆¹⁴C results for water samples that were collected on 4 CLIVAR Repeat Hydrographic Survey cruises (A10, A22, A20, A16N) from 2011 to 2013. We show that a significant fraction of the DOC in the deep North Atlantic is of post-bomb origin. Thus, a revised ¹⁴C age of the pre-bomb DOC pool is approximately 4900 ¹⁴C yrs. We report the first ∆¹⁴C values of DOC in the deep South Atlantic; they fall between those in the North Atlantic and the Southern Ocean. We show that DOC transport time in the deep Atlantic is similar to the transport time of deep dissolved inorganic carbon in southward flowing North Atlantic Deep Water. This is contrary to results from the deep Pacific that showed processes other than deep circulation controlled ∆¹⁴C of DOC [Druffel and Griffin, 2015]. The residence time of DOC in the global deep ocean and implications for the marine carbon cycle are presented.

Druffel, E., and S. Griffin (2015), Radiocarbon in dissolved organic carbon of the South Pacific Ocean, Geophys. Res. Lett., 42, 4096-4101.