Chromophoric DOM: An Ignored Photoactive Tracer of Geochemical Process

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ABSTRACTOCE-0241614Chromophoric dissolved organic material (CDOM), the colored fraction of the dissolved organic material (DOM) pool, is a highly dynamic property found throughout the open ocean. CDOM is an optical property; hence, its concentration can be quantified synoptically over large spatial scales using satellite-borne sensors or in situ from a host of autonomous platforms. Recent work demonstrates that net CDOM production is related to heterotrophic bacterial cycling processes while its losses are due to photobleaching. Vertical distributions of CDOM and in particular its surface signature are therefore regulated by how vertical mixing processes redistribute the basic processes of CDOM cycling. This suggests that CDOM may be an excellent tracer of upper ocean exchanges. In this study, researchers at the University of California - Santa Barbara will apply a process-level description of CDOM cycling to test its utility as a geochemical tracer. Specifically the research team will: (1) elucidate CDOM distributions over a range of oceanic regimes on several meridional sections of the CO2/CLIVAR Repeat Hydrography survey; (2) quantify and parameterize CDOM production & destruction processes with the goal of mathematically constraining the cycling of CDOM; (3) evaluate the utility of CDOM as an upper ocean age tracer by comparing with coincident tracer distributions from the Repeat Hydrography survey; and (4) develop a one-dimensional model of CDOM dynamics for use across a wide range of oceanic regimes with the goal of diagnosing mixed layer - thermocline exchanges.The proposed project has broad impacts beyond the world of academic ocean science. The three principal investigators on the project are active instructors, and results of this proposed work (and experiences gained) will be used in their course offerings at both the undergraduate and graduate levels. This research will support a dissertation of a graduate student at UCSB. All data will be freely available to all interested parties via a website at UCSB and the CO2/CLIVAR Repeat Hydrography Program. Finally, tf their scientific hypotheses prove correct, this research could lead to the remote estimation of water mass exchanges between the mixed layer and underlying waters from satellite orbit. A predictive understanding of these exchanges is critical for understanding the oceanic fate of anthropogenic compounds discharged to the atmosphere.