Dissolved Organic Radiocarbon in the West Indian Ocean

We report marine dissolved organic carbon (DOC) concentrations, and DOC Delta C-14 and delta C-13 in seawater collected from the West Indian Ocean during the GO-SHIP I07N cruise in 2018. We find bomb C-14 in DOC from the upper 1,000 m of the water column. There is no significant change in Delta C-14 of DOC in deep water northward, unlike that of dissolved inorganic carbon (DIC), suggesting that transport of deep water northward is not controlling the C-14 age of DOC. Variability of DOC Delta C-14, 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 delta C-13 are present at two of the five stations studied, suggesting a source of low delta C-13 DOC, or additional microbial utilization of deep DOC. Plain Language Summary Dissolved organic carbon (DOC) is the most abundant pool of organic carbon in ocean water. It is thought to form primarily from photosynthetic organisms in surface waters, however the radiocarbon (C-14) ages of DOC in the Atlantic and Pacific oceans are 4,900-6,400 years old. We find aging of deep DOC in the West Indian Ocean is not similar to that for dissolved inorganic carbon, indicating that transport of deep water northward is not the main control of C-14 in DOC. Evidence of young DOC is observed in the deep Indian.

Automated summary

In the West Indian Ocean, the aging of deep DOC differs from that of dissolved inorganic carbon, indicating that transport of deep water northward is not the main control of C-14 in DOC. This suggests that the dissolution of surface-derived organic carbon is a source of modern carbon to deep DOC in the West Indian Ocean.