Cycling of Dissolved Organic Matter in the Pacific and Indian Oceans Using Radiocarbon

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Controls on the Aging of Marine Dissolved Organic CarbonMost of the organic carbon in ocean water is in the dissolved form. Surprisingly, the age of this dissolved organic carbon is thousands of years old, even though it is thought to form during photosynthesis in the surface ocean. One explanation for the age of this carbon is the amount of time that it takes for carbon to circulate through the ocean. Investigators at the University of California Irvine (UCI) will investigate the aging of dissolved organic carbon in the Pacific, Southern and Indian oceans using C-14 isotopes. This work is important for knowing how carbon produced from human activities will be distributed on Earth in the future. This project will support the work of two graduate and two undergraduate students, providing hands-on experience that will prepare them for careers as scientists and educators. Both graduate students will be involved in a variety of educational activities. They will also help teach a short course on applications of C-14 in Ecology and Earth System Science for graduate students, technicians, postdocs and researchers during summer. UCI is a Hispanic-serving institution (27% of undergraduates identify as Hispanic), and 60% of students who attend UCI are first generation family representatives. This study will examine the concentration, isotopic (14C, 13C) and molecular composition of dissolved organic carbon (DOC) in depth profiles from the Pacific, Southern and Indian Oceans. This information will help to determine the main controls on DOC cycling in the world’s oceans. The project will test the hypothesis that circulation is the primary control on DOC cycling in the deepest water (3500 meters). The research will also investigate two alternative processes that could influence the age of DOC in deep water (2000-3000 meters): (1) dissolution of surface-derived particles and (2) input of ancient carbon from hydrothermal vents and flanks. Spectroscopic and spectrometric measurements designed to characterize a portion of the DOC will be performed on surface and deep water. Results will be incorporated into an inverse model of DOC cycling to determine the main processes controlling the DOC cycle in the ocean. DOC may serve as a sink for excess carbon dioxide produced from human activities and the size of the refractory DOC pool in the ocean could increase as circulation slows. Measuring the 14C age of DOC in the surface and deep ocean is important for understanding how the global carbon cycle will change as the Earth's climate shifts.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.