Abstract
AbstractContinental margin sediments are important sites of marine nitrogen cycling and potential contributors to atmospheric N2O emissions. We employed trace‐level N2O microsensors to measure vertical N2O profiles at submillimeter resolutions in intact cores from outer continental margin sediments underlying the NE Pacific oxygen minimum zone. We used mathematical modeling to estimate depth‐dependent rates of N2O production and fluxes to the overlying water along a transect of diminishing bottom water oxygen concentrations. Net sediment efflux was observed at all sites on the outer continental margin, with a mean value of 524 nmol m−2 d−1. N2O efflux increased with decreased oxygen penetration depth in sediments. Enhanced N2O production and efflux were obtained when outer continental shelf sediments were experimentally exposed to lower bottom‐water O2 concentrations, to simulate upwelling conditions. Our results underline the need for further investigation of the drivers of N2O production in continental margin sediments, and the relative importance of these environments to the global N2O budget.
Highlights
MethodsField sampling Field operations were conducted off the west coast of Vancouver Island, Canada, between 29 September and 04 October 2019
Author Contribution Statement: All authors contributed to the conception of the experimental design and data interpretation
Pore-water concentration profiles Mean Oxygen penetration depths (OPD) were deepest in the control cores from 200 m depth, where natural bottom water O2 concentrations were highest, and shallowest in the 850 m cores from the oxygen minimum zones (OMZs) core (Table 1; Fig. 2)
Summary
Field sampling Field operations were conducted off the west coast of Vancouver Island, Canada, between 29 September and 04 October 2019. All data are available through Scholars Portal Dataverse (Jameson et al 2020). A multicorer was used to collect replicate sediment cores = 9.8 cm; length = 52.0 cm) from three sampling stations (200, 475, and 850 m depth) positioned along a transect of increasing depth and diminishing bottom water O2 concentrations (Fig. 1). Bottom water characteristics were measured at each station using a CTD rosette (SBE 43, Sea-Bird Electronics), and bottom water samples were obtained from 5 to 10 m above the seafloor in 2.8-L Niskin bottles. We immediately transferred the bottom water to an N2-flushed reservoir using 3/4 inch Tygon tubing and stored it in the shipboard cold room
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