Variations in the Oxygen/Nitrogen Ratios of Air: Implications for the Global Carbon Cycle

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This project makes use of measured O2/N2 (oxygen/nitrogen) and Ar/N2 (argon/nitrogen) ratios to improve understanding of processes related to the carbon cycle. The O2/N2 measurements provide information on sequestration of CO2 (carbon dioxide) by the terrestrial biosphere and the ocean, and aid in the understanding of ocean fertility and interaction between oceanic circulation and biogeochemical fluxes. The Ar/N2 measurements provide information on upper ocean heat content, upper ocean mixing and ventilation, gas exchange rates, and atmospheric tracer transport. This information helps to constrain upper ocean biogeochemistry and carbon exchange needed for physical ocean models. Atmospheric mixing processes are also constrained by these observations that can lead to improvement in inverse models aimed at characterizing atmospheric CO2 sources and sinks based on atmospheric CO2 distributions. Therefore, the combination of the two ratio measurements will be deployed as important tools for studying the carbon cycle.This will be accomplished by placing automated samplers at a number of existing measurement sites (Barrow, Samoa, Amsterdam Island, Cape Grim, Macquarie, and Syowa), and aboard a NOAA research vessel (Ka'imimoana). Two additional measurement sites will be added (Sable Island and Bermuda), and preparations will begin to quantify the O2/N2 gradient across the continental United States. These measurements are similar to those of Ralph Keeling, but are based on different analytical methodology, with some overlapping sites and some complementary ones. Detailed intercomparison exercises with Keeling's group will be an ongoing part of this study.Products of this research will include an updated anthropogenic carbon balance available because of improved understanding of terrestrial biosphere and ocean carbon sequestration. The seasonal cycles and meridional gradients of the observed quantities will provide improved understanding of oceanic biological processes and upper ocean dynamics, as well as atmospheric transport phenomena.This study will provide important information on anthropogenic influences on the global carbon cycles due to fossil fuel combustion and changes in the biosphere. This information can be used in a number of arenas including coupling between components of the Earth system in response to global climate change, predicting environmental consequences associated with given emission scenarios, assessing possible mitigation efforts, and as part of a scientific basis for policy decisions. Two post-doctoral fellows will receive training as part of this work.