Stable Isotopic Constraints on Nitrogen Transformations in Low and High Temperature Hydrothermal Fluids

Woods Hole Oceanographic Institution, Woods Hole MA

Investigators

Abstract

Part 1 This project will address deficiencies in our understanding of Nitrogen transformations under hydrothermal conditions with implications for the fate of bioavailable Nitrogen in the modern subsurface biosphere and of reduced Nitrogen on pre-biotic Earth. Through the PIs the project will advance the utility of Nitrogen isotopic composition in active submarine hydrothermal systems. Three hypotheses will be tested concerning: the reaction temperature and redox state of hydrothermal reaction zones; NH4+ in high temperature vent fluids; and NH4+ and NO3- in low-temperature vent fluids. To address these hypotheses, the PI's plan combined experimental and observational approaches. Well-constrained laboratory experiments will be conducted to determine operative reaction pathways and associated N isotopic fraction during redox dependent reactions involving dissolved N species under hydrothermal conditions. In addition, measurements will be made in high and low temperature hydrothermal vent fluids from existing samples spanning a range of hydrothermal environments to constrain abiotic and microbially mediated processes that influence the abundance of aqueous N species in submarine hot springs. The broader impacts consist of educational opportunities for students at various levels. Part 2 This project aims to address existing deficiencies in our understanding of nitrogen transformations under hydrothermal conditions with implications for the fate of bioavailable nitrogen in the modern subsurface biosphere and of reduced nitrogen on pre-biotic Earth. Through the examination of the controls on reaction pathways, rates, and associated stable isotope systematics, this project will advance the utility of nitrogen isotopic composition in active submarine hydrothermal systems, and help to constrain geologic records of nitrogen isotopic composition. This research is guided by the hypotheses that 1) reaction temperature and redox state of hydrothermal reaction zones regulate the geochemical conversion of nitrate (NO3-) and possibly dinitrogen (N2) to ammonium, that 2) the stable nitrogen isotopic composition of NH4+ in high temperature vent fluids will record the relative roles of these reaction processes and that 3) variations in the abundance and isotopic composition of NH4+ and NO3- in low-temperature vent fluids in concert with their corresponding high temperature endmember source fluids can be used to constrain the nature and extent of subsurface biological processes. To address these hypotheses, the PI?s plan combined experimental and observational approaches. Well-constrained laboratory experiments will be conducted to determine operative reaction pathways and associated N isotopic fraction during redox dependent reactions involving dissolved N species under hydrothermal conditions. In addition, the abundance and N (and O) isotopic composition o NH4+ (and NO3-) will be measured from high and low temperature hydrothermal vent fluids from a rich archive of samples spanning a range of hydrothermal environments to constrain abiotic and microbially mediated processes that influence the abundance of aqueous N species in submarine hot springs. The broader impacts consist of educational opportunities for students at various levels.