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  1. Arabian Sea 2007 data

    Casciotti, Karen
    October 2007 - July 2016

    Data for nitrate and nitrite natural abundance N and O isotope data from Arabian Sea R/V Revelle cruise Sept/Oct 2007, with associated metadata.

  2. Model code, inputs, and output from N isotope global inverse model

    Martin, Taylor
    September 2, 2022

    Model code, ancillary input files, and model output related to Martin et al., Global Biogeochemical Cycles in review

  3. Stable isotopes of nitrite as a tool for understanding nitrogen cycling and loss in oxygen deficient zones

    Martin, Taylor
    [Stanford, California] : [Stanford University], 2018.

    Nitrogen (N), a key nutrient in the global ocean, has a complicated biogeochemical cycle. In the ocean, nitrogen is mainly found as nitrate (NO3-), but it also accumulates as nitrite (NO2-) within oxygen deficient zones (ODZs). Nitrite is a key intermediate in several processes that produce nitrous oxide (N2O), a potent greenhouse gas. Using natural abundance stable isotope measurements of NO3- and NO2- help to capture an integrated signal of the N cycle processes. My doctoral work aims to use stable isotopes of N and oxygen (O) in order to further our understanding of the pathways that produce and consume NO2-, which will help us better predict the global impacts of nitrogen cycling both at present and in the future. Many N cycle processes are microbially mediated and impart one or more unique isotope effects on its N substrates and products, and it is important to quantify these isotope effects in order to use numerical models to elucidate relative contributions of different N cycle processes. In Chapter 1, I use pure culture experiments to better constrain estimates of the N and O isotope effects of microbial nitrite reduction, a key step in the process of denitrification, which leads to loss of bioavailable N. I then use the values from this experiment, in conjunction with previous estimates of other N cycle process isotope effects, to model observed NO3- and NO2- data from the Arabian Sea (Chapter 2) and explore the necessity for oxygen-requiring processes within the ODZ. In Chapter 3, I expand upon the results from previous chapters by applying the results to a global 3D inverse model of the N cycle, which includes isotopic fractionation, in order to examine the NO2- production and consumption processes within marine ODZs. I also examine the sensitivity of NO3- and NO2- concentration and isotope profiles to controlling parameters of N cycle processes, such as oxygen thresholds and isotope effects, in order to examine the roles of individual processes in N loss, and their potential for future change.

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