Dissolved Organic Radiocarbon in the West Indian Ocean

• Published in: Geophysical research letters 2023-10, Vol.50 (19), p.n/a
• Main Authors: Druffel, Ellen R. M., Lewis, Christian B., Griffin, Sheila, Flaherty, Alessandra, Rudresh, Megha, Hauksson, Niels E., Key, Robert M., McNichol, Ann P., Hwang, Jeomshik, Walker, Brett D.
• Format: Article
• Language: English
• Subjects: 13C; 14C; Aging; Carbon; Carbon 13; Carbon 14; carbon cycle; Carbon isotopes; circumpolar deep water; Deep water; Dissolved inorganic carbon; Dissolved organic carbon; DOC; hydrothermal system; Microorganisms; Oceans; Organic carbon; Particulate organic carbon; Photosynthesis; radiocarbon; Radiocarbon dating; Seawater; Surface water; Water circulation; Water column
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2023GL104732

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 bomb 14C 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 the 14C 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. 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 (14C) 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 14C in DOC. Evidence of young DOC is observed in the deep Indian. Key Points 14C aging of deep dissolved organic carbon (DOC) northward is not similar to that of deep dissolved inorganic carbon, showing that transport of deep water is not the main control of 14C in DOC Variability of deep DOC 14C indicates heterogeneity in the DOC pool, perhaps by dissolution of surface‐derived, particulate organic C Low DOC δ13C in deep water from two stations may suggest a source of chemosynthetically produced organic matter