Award: OCE-1737078

This project explored the factors that shape planktonic communities in the Western Tropical North Atlantic, a region strongly affected by the plume of the Amazon River. The Amazon Plume region supports diverse assemblages of phyto- and zooplankton within a dynamic system driven by nutrients supplied by transport from the river as well as nutrients entrained from offshore waters by physical mixing and upwelling. This creates strong interactions among physical, chemical, and biological processes across a wide range of spatial and temporal scales that are biologically relevant, leading to shifts in the composition and activity of plankton across multiple scales. This was a field-oriented project and we carried out two dedicated research cruises to the Amazon Plume region in 2018 and 2019 and took part in a third, collaborative cruise aboard a German research vessel in 2021. These three expeditions allowed us to sample the full range of the Plumes influence from the mouth of the Amazon to waters over a thousand km to the north during the high-flow season. During these expeditions, we collected samples of water for analysis of dissolved nutrients and plankton for measurement of their elemental and isotopic composition. These measurements provide critical insight into the sources of nitrogen and carbon supporting the planktonic ecosystem at each sampling site. We also carried out focused experiments to quantify the rates of nitrogen- and carbon-fixation by phytoplankton; these experiments measure the rate of addition of organic matter to the ecosystem by the primary producers at the base of the planktonic food web. Our field samples required extensive processing and analysis in the laboratory ashore, and in parallel with this lab work, we integrated our hydrographic measurements with our data as well as ancillary data from colleagues to explore the factors that shape the planktonic ecosystem using a variety of statistical and numerical tools. Our synthesis of field and laboratory work has allowed us to identify and delineate planktonic habitats in this highly dynamic region of the Tropical Atlantic and to characterize the sources of nitrogen supporting biological production in these habitats. These findings have been shared through multiple publications and presentations at professional meetings as well as in classroom materials for courses in introductory biology and oceanography. Beyond the scientific impact of this project, multiple undergraduate and graduate students took part in the field and laboratory work, gaining valuable experience in ocean science. We also worked closely with foreign collaborators from Guyana, France, and Germany, providing our students with important professional connections abroad. Our findings have also been incorporated into teaching materials at Georgia Tech and elsewhere. In all, this project has supported eleven scientific publications and a similar number of presentations at conferences and at other institutions. Two technicians, three graduate students and five undergraduates have played key roles in carrying out this research and have gained hands-on experience in ocean science. Last Modified: 02/02/2024 Submitted by: JosephPMontoya