This project has been ongoing since 2007 in collaboration with David Burdige (Old Dominion University), and more recently with Jeff Chanton (Florida State University). Our main goal is to understand the dynamics of pore-water DOC, which is the key intermediate pool in sedimentary organic matter degradation. To evaluate the composition and reactivity of pore-water DOC, we measure natural 14C and 13C in various carbon pools, and interpret the observed distributions using diagenetic models. Starting 2012, we will be expanding our work into methanogenic zones of the sediment column to understand the relationship between DOC production, methane production, and sulfate reduction, and how these processes affect the 14C-age of DOC that is exported out to the water column. Understanding how DOC cycles in sediments should not only help us gain insight into the controls behind organic matter degradation and preservation, but could also provide clues to the origin of refractory DOC in the deep ocean.
We have conducted an incubation experiment to examine pore-water DOC dynamics in near-shore sediments collected from San Francisco Bay. Our results suggest that when organic matter is degraded anaerobically, pre-aged component of sedimentary organic carbon preferentially accumulates as DOC in the pore waters (Komada et al., in press). Our aim is to conduct a similar experiment under oxic or mixed-redox conditions to help us better evaluate the reactivity and radiocarbon ages of DOC exported from these coastal settings.
A good portion of our efforts go into improving the methods used to process environmental samples for isotopic analyses. We have the capability to process samples for natural 14C and 13C in particulate and dissolved forms of both organic and inorganic carbon. We oxidize small-volume pore-water DOC samples using a low-temperature sealed-tube method (Johnson and Komada, 2011 pdf). We are currently working on reducing the sample size required for this analysis.
I also collaborate with other PIs at RTC to work on issues surrounding ocean acidification.