Award: OCE-1756686

Award Title: Collaborative Research: Peptide deamination as a source of refractory dissolved organic matter in marine sediments
Funding Source: NSF Division of Ocean Sciences (NSF OCE)
Program Manager: Henrietta N. Edmonds

Outcomes Report

The scientific community has known for several decades that seawater contains not just water and salt, but also carbon in the form of dissolved organic carbon (DOC). Two surprising facts about this DOC pool are: (1) it is very large comparable to all of the carbon dioxide in the atmosphere; and (2) it is very old it appears to survive thousands of years in the ocean instead of being consumed by microorganisms for energy. These observations have led to a number of key questions including: What is the source of old marine DOC? In this project, we tested the hypothesis that the seafloor (sediments) are sources of DOC that are old and stable enough to persist in the water column. We focused on marine sediments, because they are known sources of DOC to the water column, and sediments contain organic matter that has undergone extensive degradation as well as aging. We therefore surmised that DOC produced from sediments will be equally old and stable against degradation. To investigate the age and stability of DOC produced in sediments, we measured the radiocarbon abundances of various carbon pools (including porewater DOC) collected from different locations in the continental margin offshore California, USA. These locations ranged from low-oxygen sites dominated by microbial processes to high-oxygen sites harboring benthic macrofauna. Our results show that the radiocarbon ages of porewater DOC at these sites range from modern to ancient (tens of thousands of years or older), and that these ages are largely modulated by the radiocarbon ages of bulk sedimentary organic carbon (OC). In stark contrast, radiocarbon ages of a respiration end-product, dissolved inorganic carbon (DIC), were much younger and similar across sites. Together, these findings indicate that DOC that accumulate in sediment porewaters represents a component of sedimentary OC that is older and is not readily respired to DIC. Because our study sites include not only anoxic but also oxygenated environments, DOC produced in these sediments could survive degradation upon export to the oxic water column. To better predict how the marine DOC pool might respond to ongoing climate and environmental change, it is imperative that we understand how it cycles its sources, transformations, and overall fate. Our findings contribute to achieving this goal. Last Modified: 04/23/2025 Submitted by: TomokoKomada
DatasetLatest Version DateCurrent State
2025-06-09Preliminary and in progress
2025-06-09Preliminary and in progress

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Principal Investigator: Tomoko Komada (San Francisco State University)