Estimates of Oceanic Nitrous-oxide Emissions from Global Biogeochemistry Models
Abstract
Emissions of nitrous-oxide (N2O) to the atmosphere have increased over the past century, associated with increases in reactive nitrogen release from fossil fuel combustion and agricultural fertilizer use. Oceanic emissions of N2O provide approximately a third of the natural sources to the atmosphere. N2O is produced in the ocean during the remineralization of organic matter, and its production and consumption processes display significant sensitivity to local oxygen level. In recent decades, the natural cycle of oceanic N2O has been affected by inputs of anthropogenically derived nutrients (via atmospheric deposition and riverine fluxes). The impacts of climate change on the ocean also have implications for marine N2O production (e.g., via impacts on biological productivity and ocean deoxygenation). The most recent IPCC assessment of the global N2O budget (AR5, Ciais et al. 2014) reported a larger uncertainty range on oceanic N2O fluxes (i.e., 3.8 (1.8 - 9.4) Tg N yr-1) in comparison to that of the previous IPCC assessment (AR4 : 3.8 (1.8 - 5.8) Tg N yr-1, Denman et al. 2007).
We report here on an ongoing intercomparison of ocean N2O emission estimates from global ocean biogeochemistry models. This intercomparison forms part of a new joint activity of the Global Carbon Project and the International Nitrogen Initiative to establish an improved global N2O budget and to quantify its component fluxes. We present results from six global ocean biogeochemistry models that include explicit representation of the oceanic N2O cycle. The individual models differ in their physical configuration, meteorological forcing, and in their parameterization of ocean biogeochemistry. Model groups report their best estimates of spatially resolved N2O fluxes at monthly time resolution for the period 1980-2015. We discuss the aggregated model results for oceanic N2O fluxes at global and regional scales, and report on estimates of decadal averages, trends, and interannual variability. We also discuss the model results in the context of alternative estimates of ocean N2O fluxes derived from surface ocean measurements, and from top-down inverse analyses.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.B21K2481S
- Keywords:
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- 3322 Land/atmosphere interactions;
- ATMOSPHERIC PROCESSESDE: 0414 Biogeochemical cycles;
- processes;
- and modeling;
- BIOGEOSCIENCESDE: 0469 Nitrogen cycling;
- BIOGEOSCIENCESDE: 0490 Trace gases;
- BIOGEOSCIENCES