The ocean contains a large reservoir of dissolved organic carbon (DOC) with an average radiocarbon age of about five thousand years. This “old” and abundant DOC reservoir sequesters carbon dioxide from the atmosphere, and thus any change in the DOC pool size or residence time can affect Earth’s carbon cycle that shapes the global climate.
Recent studies have challenged the paradigm that the main fate of DOC exported to the deep ocean is aging with deep ocean circulation. Druffel et al.  respond to the debate by providing the first transect of radiocarbon age of DOC in the Pacific. Their findings confirm that the radiocarbon signal of DOC and DIC are tightly coupled in the deep Pacific and not substantially altered by other processes, including decomposition of sinking particulate carbon.
Thus, this study confirms that aging (radioactive decay) is the main control on DOC in the deep Pacific over a timescale of more than 600 years and distances of the entire Pacific basin. The finding may help constrain predictions on how future warming will affect deep ocean circulation, and, in turn, the deep ocean DOC reservoir.
Citation: Druffel, E. R. M., Griffin, S., Wang, N., Garcia, N. G., McNichol, A. P., Key, R. M., & Walker, B. D. . Dissolved organic radiocarbon in the Central Pacific Ocean. Geophysical Research Letters, 46. https://doi.org/10.1029/2019GL083149
—Rose Cory, Editor, Geophysical Research Letters