Award: OCE-1155764

Intellectual Merit This project has contributed to the field of oceanography by broadening our understanding about how long-lived marine dissolved organic matter (DOM) is formed in the ocean. DOM in seawater constitutes an important carbon reservoir on Earth?s surface, because it is abundant, and is largely made up of molecules that are long-lived. These qualities together give DOM the potential to sequester carbon over time scales of millenia or longer. There is growing consensus that biological DOM production in the sunlit surface ocean followed by processing of this DOM by the microbial community results in DOM that resists further degradation. However, it remains unclear as to how (or where) long-lived DOM in the deep sea acquires its old radiocarbon age, and whether there are other sources of long-lived DOM to the ocean other than microbial processing of DOM exported from the sunlit surface ocean. Findings from this project support the idea that anoxic marine sediments at the bottom of the ocean are sources of long-lived, and pre-aged, DOM to the ocean?s interior. Most of the DOM produced within the sediments has young radiocarbon ages and is rapidly consumed by microbes, but a small fraction has old radiocarbon ages, and appears to persist in the sediments and in the oxic water column. Although marine sediments have long been suspected to be sources of long-lived DOM molecules in the deep sea, this project was the first to explore this idea rigorously. These findings are likely to influence how the oceanographic community approaches the problem of how DOM cycles in the ocean. Broader Impacts This project provided robust hands-on research training for three Masters students and 8 undergraduate students. Of these, five undergraduate students and one Masters student participated in sample collection on research cruises. A subset of these students has since moved on to pursue higher degrees in science and the medical field. All data generated from this project are available from the Biological and Chemical Oceanography Data Management Office (BCO-DMO), http://www.bco-dmo.org/project/649648. Last Modified: 05/13/2017 Submitted by: Tomoko Komada