Abstract
Abstract. In the current era of rapid climate change, accurate characterization of climate-relevant gas dynamics – namely production, consumption, and net emissions – is required for all biomes, especially those ecosystems most susceptible to the impact of change. Marine environments include regions that act as net sources or sinks for numerous climate-active trace gases including methane (CH4) and nitrous oxide (N2O). The temporal and spatial distributions of CH4 and N2O are controlled by the interaction of complex biogeochemical and physical processes. To evaluate and quantify how these mechanisms affect marine CH4 and N2O cycling requires a combination of traditional scientific disciplines including oceanography, microbiology, and numerical modeling. Fundamental to these efforts is ensuring that the datasets produced by independent scientists are comparable and interoperable. Equally critical is transparent communication within the research community about the technical improvements required to increase our collective understanding of marine CH4 and N2O. A workshop sponsored by Ocean Carbon and Biogeochemistry (OCB) was organized to enhance dialogue and collaborations pertaining to marine CH4 and N2O. Here, we summarize the outcomes from the workshop to describe the challenges and opportunities for near-future CH4 and N2O research in the marine environment.
Highlights
The most abundant greenhouse gases in the troposphere, excluding water vapor, are carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O)
A workshop sponsored by Ocean Carbon and Biogeochemistry (OCB) was organized to enhance dialogue and collaborations pertaining to marine CH4 and N2O
In the surface waters of tropical and temperate oceans, a number of factors contribute to the low supersaturation of CH4 including direct aerobic production arising from the degradation of methylated sulfur compounds by phytoplankton (Klintzsch et al, 2019) and methyl phosphonate in phosphorus-depleted waters (Karl et al, 2008; Sosa et al, 2020), indirect production via grazing (Schmale et al, 2018), and abiotic photoproduction (Li et al, 2020)
Summary
The most abundant greenhouse gases in the troposphere, excluding water vapor, are carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O). Other technological and analytical advances include improved near-continuous spectroscopic analysis that yields greater sampling resolution in surface waters (e.g., Gülzow et al, 2011; Arévalo-Martínez et al, 2013; Erler et al, 2015) and the deployment of analytical devices on robotic vehicles (Nicholson et al, 2018) These scientific advances and an improvement in the quantity and quality of CH4 and N2O observations are timely given that large areas of both the open and coastal ocean remain undersampled (Fig. 1c and d). Environmental impacts on marine CH4 and N2O distributions include increasing seawater temperatures, decreasing concentrations of dissolved oxygen (O2), acidification, retreat of ice and mobilization of carbon substrates from former permafrost altering coastal run-off, and eutrophication (IPCC, 2019) These impacts will undoubtedly alter future CH4 and N2O exchange with the atmosphere, but the directions and magnitudes of these modified fluxes remain insufficiently understood. This article articulates the workshop outcomes framed in the context of current marine CH4 and N2O research and explores future research opportunities and challenges
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