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We report marine dissolved organic carbon (DOC) concentrations, and DOC Δ¹⁴C and δ¹³C in seawater collected from the West Indian Ocean during the GO‐SHIP I07N cruise in 2018. We find bomb¹⁴C in DOC from the upper 1,000 m of the water column. There is no significant change in ∆¹⁴C of DOC in deep water northward, unlike that of dissolved inorganic carbon (DIC), suggesting that transport of deep water northward is not controlling the¹⁴C age of DOC. Variability of DOC ∆¹⁴C, including high values in the deep waters, is more pronounced than in other oceans, suggesting that dissolution of surface derived particulate organic carbon is a source of modern carbon to deep DOC in the West Indian Ocean. Low δ¹³C are present at two of the five stations studied, suggesting a source of low δ¹³C DOC, or additional microbial utilization of deep DOC.

We report marine dissolved organic carbon (DOC) concentrations, and DOC Δ¹⁴C and δ¹³C values in seawater collected from the Southern Ocean and eastern Pacific GOSHIP cruise P18 in 2016/2017. The aging of¹⁴C in DOC in circumpolar deep water northward from 69°S to 20°N was similar to that measured in dissolved inorganic carbon in the same samples, indicating that the transport of deep waters northward is the primary control of¹⁴C in DIC and DOC. Low DOC ∆¹⁴C and δ¹³C measurements between 1,200 and 3,400 m depth may be evidence of a source of DOC produced in nearby hydrothermal ridge systems (East Pacific Rise).