Research on viable carbon dioxide removal (CDR) pathways is becoming more urgent as climate change impacts are increasing in frequency and severity. Due to the ocean’s great capacity to absorb and store carbon, interest in marine CDR (mCDR) methods such as ocean alkalinity enhancement (OAE) are rising. Along with the need to monitor, report, and verify (MRV) the carbon removal efficacy of these approaches, increased understanding about environmental and ecological impacts are critical to inform decisions about viable and responsible mCDR techniques. To date, research has rarely explored how mCDR methods could affect nitrogen cycling, such as the net removal of greenhouse gases (GHG) through air-sea fluxes of nitrous oxide (N₂O) and/or altered nutrient dynamics (i.e. through ammonia/ammonium vs. nitrate phytoplankton uptake) that could have cascading ecological effects on higher trophic levels. In this project, we develop a new, open-source nitrogen cycle model that includes the generation of N2O, which can be coupled with established biogeochemical models that are being applied for mCDR MRV and environmental and ecological monitoring. This presentation will share results from model scenarios that assess nitrogen cycling during OAE experiments and evaluate N2O fluxes, ammonia/ammonium vs. nitrate uptake, and outputs from biogeochemical feedbacks that can inform ecosystem level models. We evaluate thresholds that lead to positive and negative environmental impacts and present learnings that can help weigh the benefits and risks related to mCDR techniques.
 

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