Description: This document is the final report for DOE grant number DE-FG02-02ER63472: "The impact of enhanced nitrogen fixation on carbon sequestration: a reassessment of the inorganic carbon system in LNLC regions" to Patricia L. Yager at the University of Georgia School of Marine Programs. This project examined the inorganic carbon system associated with nitrogen fixation in the “low nutrient low chlorophyll” (LNLC) regions of the western tropical North Atlantic (WTNA) and subtropical Pacific Oceans. Total dissolved inorganic carbon (DIC) and alkalinity (ALK) data were measured on seven expeditions. Data have been finalized, checked for quality assurance, and uploaded to the Carbon Dioxide Information Analysis Center website (http://cdiac.ornl.gov/). Two manuscripts using this data are published or in press so far and we are current working on two others. The first (Cooley and Yager, 2006, JGR) uses a mixing model to remove the dilution effects of the Amazon River from the WTNA inorganic carbon data set. Once the physical effect is removed, the paper then estimates net community production (NCP) for each station. Enhanced rates of production (over respiration) are seen in the river plume, establishing a large biogenic atmospheric carbon sink in this region that is otherwise a source of carbon to the atmosphere. We note that this sink occurs in the absence of a measurable nitrate flux, and correlates well with the abundance of diatoms containing endosymbiotic diazotrophs, so it must be supported by nitrogen fixation. The second manuscript (Cooley et al., in press, GBC) compares our WTNA data (from Winter 2001, Spring 2001, and Summer 2003) to previously collected datasets (Ternon et al. 2000, Kortzinger et al. 2003) for the purposes of identifying seasonal and interannual variability in Amazon River-associated carbon sequestration. For the mid-salinity regions of the plume only, we estimate a carbon sink of 15±6 TgC per year. ...
Date: June 27, 2007
Creator: Yager, Patricia L.
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