Chromophoric DOM - A Photoactive Tracer of Biogeochemical Process.

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Chromophoric dissolved organic matter (CDOM), the colored fraction of the dissolved organic matter (DOM) pool, plays an important role in and affects our interpretation of the biogeochemistry of the open sea. Light absorption by CDOM drives photochemical reactions affecting many radiatively important trace gases (CO2, DMS, COS, CO, etc.). Further, light absorption by CDOM often obscures our ability to diagnose biogeochemical processes from satellite ocean color imagery. CDOM is an optical property; hence, its concentration can be quantified synoptically over large spatial scales using satellite sensors or in situ from a host of autonomous platforms. Although land-ocean exchanges are well known sources of ocean CDOM, recent observations have shown that open ocean CDOM is created through in situ biogeochemical processes. With funding through this NSF award, researchers at the University of California -- Santa Barbara will continue their research in CDOM biogeochemistry by making the next step towards the first systematic global survey of oceanic CDOM. They will use these observations in conjunction with data from the CLIVAR-Repeat Hydrography program to characterize CDOM in the open ocean. Their specific goals are to: (1) continue a global surveying of CDOM and DOM quality indices on CLIVAR-Repeat Hydrography cruises in the Pacific, Southern and Indian Oceans; (2) use spectrofluorometric excitation / emission matrix and multispectral analyses to characterize CDOM quality (using newly collected and archived samples); (3) assess the connections among global CDOM stocks and diagenetic state of DOM by HPLC quantification of the individual amino acids within the hydrolysable amino acid pool; and (4) develop and test predictive understanding of the open ocean CDOM cycle through data analyses and numerical modeling. Through our continued coupled investigation of CDOM stocks, chemical and spectral characterization, and analysis and modeling the research team expects to synthesize a new understanding of its sources, sinks and distributions within the global oceans. CDOM characterization should also open a new dimension with which to assess the changes in chemical nature and lability of DOM as it cycles through the global ocean.This project is expected to have a number of broader impacts within and beyond the world of academic ocean science. The study will facilitate future study of global marine chemistry that incorporates optical observables. In particular, the data collected should be useful in the design and implementation of future in situ instrumentation and satellite missions. All data will be freely available to interested parties via the CLIVAR-Repeat Hydrography Program website as well as the NASA SeaBASS ocean optics database. The project investigators are active classroom instructors who will incorporate results of this work in their course offerings at both the undergraduate and graduate levels. This research will also support the completion of the dissertations of two graduate students at UCSB. It will also help to support undergraduate students who are assisting in the laboratory and who will participate in undergraduate research conferences at UCSB.