Dissolved organic carbon in the Atlantic, Southern and Pacific oceans

Abstract

THE amount of dissolved organic carbon (DOC) in sea water is controversial^1,2 Using a high-temperature catalytic oxidation (HTCO) technique, Sugimura and Suzuki³ reported that surface waters contained ^2–4 times as much DOC as that measured previously using wet chemistry and ultraviolet oxidation techniques^4,5. They also observed a relationship between DOC content and apparent oxygen utilization suggesting that the consumption of DOC is responsible for oxygen depletion in the deep sea. How to reconcile the apparent differences between these techniques has not been clear. Here we provide independent confirmation of the findings of Sugimura and Suzuki. We collected surface and deep waters from the equatorial Pacific Ocean, the Drake passage and the Atlantic Ocean south of Iceland, and analysed their DOC content using the HTCO methodology³. We found DOC concentrations ^2–3 times higher than those measured previously. These results imply that the carbon content of the oceans has previously been underestimated by 10¹² (1,000 billion) tonnes, and that the new estimated total of 1,800 billion tonnes represents one of the largest carbon reservoirs on Earth⁶. We found no evidence of a cause-and-effect relationship between DOC and apparent oxygen utilization.