Abstract
AbstractEstimates of oceanic emissions of nitrous oxide (N2O) are surrounded by a considerable degree of uncertainty, particularly regarding the contribution of productive shelf regions, where assessments are based on limited observations. In this paper, we have applied a coupled hydrodynamic‐biogeochemical model resolving N2O dynamics to estimate N2O emissions within the northwest European continental shelf. Based on 10‐year average distributions (2006–2015), dominant seasonal patterns of N2O air‐sea exchange were identified. Within the southwest region of the shelf and deep parts of the North Sea, emissions are highest during winter. Peak emissions during late autumn are typical for the northwest part of the shelf and central North Sea, while in the western English Channel, Irish Sea and western North Sea peak outflux shifts toward early autumn. Within these regions, most N2O production occurs below the seasonal pycnocline, and duration and intensity of stratification defines the timing and rate of its subsequent release to the atmosphere. In contrast, within the southeast North Sea and most of the coastal areas, lack of stratification allows the excess N2O to outgas as soon as it is produced, driven by ammonium availability, resulting in peak emissions in summer. We estimate that N2O emissions from the northwest European shelf contribute 0.02224 Tg N to the atmosphere annually, that is, between 3.3–6.8% of total emissions from European shelves and estuaries.
Highlights
Nitrous oxide (N2O) is the third most important long‐lived greenhouse gas contributing ~6% of the direct anthropogenic radiative forcing, preceded by carbon dioxide and methane which contribute ~76% and ~16%, respectively (IPCC, 2013)
For the purpose of our study we use the 3‐D coupled hydrodynamic‐biogeochemical modeling system NEMO‐FABM‐ERSEM configured on the Atlantic Meridional Margin (AMM7) domain, which is based on an update of Edwards et al (2012)
As the water column gradually starts to mix from September onward, this facilitates earlier outgassing of excess N2O into the atmosphere relative to class A
Summary
Nitrous oxide (N2O) is the third most important long‐lived greenhouse gas contributing ~6% of the direct anthropogenic radiative forcing, preceded by carbon dioxide and methane which contribute ~76% and ~16%, respectively (IPCC, 2013). With a global warming potential about 300 times higher than that of carbon dioxide, N2O plays a significant role in the greenhouse effect (Myhre et al, 2013). The main pathways for natural N2O emissions to the atmosphere are production during microbially mediated nitrification and denitrification processes within soils and in the ocean. N2O is an intermediate product of denitrification, leading to either net production or net consumption flux depending on oxygen conditions (Bianchi et al, 2012; Cohen & Gordon, 1978; Nevison et al, 2003)
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