Award: OCE-0934025

The ANACONDAS (Amazon iNfluence on the Atlantic: CarbOn export from Nitrogen fixation by DiAtom Symbioses) project was an interdisciplinary study of the the biogeochemistry of the Amazon plume, focusing on its impacts on phytoplankton diversity and production and the N and C cycles of the Tropical Atlantic. This was a field-oriented project with multiple cruises to the Western Tropical North Atlantic to capture the behavior of the Amazon plume and its interactions with surrounding waters at different times of year. Multiple institutions and investigators were involved in this project, providing an integrative study of the biogeochemical interactions between the Amazon plume and adjacent oceanic waters. Within the overall project, the specific responsibilities of the Montoya lab focused on measurements of nutrient concentrations, the elemental (C & N) and isotopic composition of particles and zooplankton, and the rates of activity of nitrogen fixing organisms in the plume and surrounding waters. The first two cruises of this project sampled the Amazon plume during the low- and high-flow periods of 2010 and 2011, respectively. The structure of the plume was quite different in the two years, with a much larger plume extending well to the east of the South American coastline in 2011. Although the Amazon River introduces substantial quantities of dissolved nutrients to the Atlantic, nutrient concentrations decreased rapidly within the plume as water moved away from the river mouth, and the ratio of nutrients in surface waters was consistent with strong nitrogen limitation of primary production. The isotopic composition of particles and zooplankton provided an index to the relative importance of different nutrients sources in supporting biological production, and we found that nitrogen fixation contributed a significant fraction of the total nitrogen needed by plankton in this region. Interestingly, the highest rates of nitrogen fixation occurred in fresher water than we originally expected, suggesting that the plume proper is a critical site of this important biogeochemical process. Measurements of the isotopic composition of zooplankton provided strong evidence for close coupling of secondary (animal) production to nitrogen fixation throughout the region. The third ANACONDAS cruise in 2012 was the first to sample within Brazilian waters, providing our first direct access to the high nutrient and high sediment-load source waters of the Plume. The major contributions of the Montoya group to the ANACONDAS project included extensive measurements of the concentrations of nutrients in the Western tropical Atlantic as well as the first assessments of the flow of nitrogen through the planktonic community from phytoplankton to zooplankton. The broader impacts of this project included extensive training of students at all levels, technicians, and postdoctoral scholars in oceanographic field research. One undergraduate student who received REU supplement support is pursuing a career in ocean science, and one of the two postdoctoral scholars involved in this project has moved to a faculty position in Germany. Our findings have been incorporated into course materials at Georgia Tech and have been shared with the general community through lectures and other public presentations. Last Modified: 02/05/2015 Submitted by: Joseph P Montoya