Abstract:Although methanogenesis is considered a strictly anaerobic process, oxygen‐replete surface open‐ocean waters are usually supersaturated with methane (CH4), a phenomenon termed the oceanic methane paradox. Here, we report that abiotic methane photoproduction from chromophoric dissolved organic matter (CDOM) significantly contributes to this paradox. Methane photoproduction was observed during solar‐simulated irradiations of various waters collected along the land‐ocean continuum. Methane photoproduction rates d… Show more
“…In particular, photochemical reactions in subtropic ocean gyres are responsible for an annual production of 118 Gg of CH 4 (35–71% of the total oceanic CH 4 production), while contributions from coastal, sub-polar, and Polar Regions are minimal (Fig. 4 ) [ 138 ]. Photodegradation by UV radiation, with contributions from other wavelengths of solar radiation, together with microbial degradation therefore contribute to global warming through the release of CH 4 and CO 2 .…”
Section: Biogeochemical Cyclesmentioning
confidence: 99%
“… Fig. 4 Depth-integrated methane photoproduction rate (top 150 m) calculated with a photochemical model based on remote sensing reflectance data (Figure by Rachele Ossola, adapted from Li et al [ 138 ]) …”
The Environmental Effects Assessment Panel of the Montreal Protocol under the United Nations Environment Programme evaluates effects on the environment and human health that arise from changes in the stratospheric ozone layer and concomitant variations in ultraviolet (UV) radiation at the Earth’s surface. The current update is based on scientific advances that have accumulated since our last assessment (Photochem and Photobiol Sci 20(1):1–67, 2021). We also discuss how climate change affects stratospheric ozone depletion and ultraviolet radiation, and how stratospheric ozone depletion affects climate change. The resulting interlinking effects of stratospheric ozone depletion, UV radiation, and climate change are assessed in terms of air quality, carbon sinks, ecosystems, human health, and natural and synthetic materials. We further highlight potential impacts on the biosphere from extreme climate events that are occurring with increasing frequency as a consequence of climate change. These and other interactive effects are examined with respect to the benefits that the Montreal Protocol and its Amendments are providing to life on Earth by controlling the production of various substances that contribute to both stratospheric ozone depletion and climate change.
“…In particular, photochemical reactions in subtropic ocean gyres are responsible for an annual production of 118 Gg of CH 4 (35–71% of the total oceanic CH 4 production), while contributions from coastal, sub-polar, and Polar Regions are minimal (Fig. 4 ) [ 138 ]. Photodegradation by UV radiation, with contributions from other wavelengths of solar radiation, together with microbial degradation therefore contribute to global warming through the release of CH 4 and CO 2 .…”
Section: Biogeochemical Cyclesmentioning
confidence: 99%
“… Fig. 4 Depth-integrated methane photoproduction rate (top 150 m) calculated with a photochemical model based on remote sensing reflectance data (Figure by Rachele Ossola, adapted from Li et al [ 138 ]) …”
The Environmental Effects Assessment Panel of the Montreal Protocol under the United Nations Environment Programme evaluates effects on the environment and human health that arise from changes in the stratospheric ozone layer and concomitant variations in ultraviolet (UV) radiation at the Earth’s surface. The current update is based on scientific advances that have accumulated since our last assessment (Photochem and Photobiol Sci 20(1):1–67, 2021). We also discuss how climate change affects stratospheric ozone depletion and ultraviolet radiation, and how stratospheric ozone depletion affects climate change. The resulting interlinking effects of stratospheric ozone depletion, UV radiation, and climate change are assessed in terms of air quality, carbon sinks, ecosystems, human health, and natural and synthetic materials. We further highlight potential impacts on the biosphere from extreme climate events that are occurring with increasing frequency as a consequence of climate change. These and other interactive effects are examined with respect to the benefits that the Montreal Protocol and its Amendments are providing to life on Earth by controlling the production of various substances that contribute to both stratospheric ozone depletion and climate change.
“…Methane also has poorly quantified other sources where placeholder flux guesses from the 1980s still maintain footholds in computer models of atmospheric chemistry and transport. Examples include fluxes from termites (but see [ 118 ]); from geological sources (but see [ 5 ]); from shelf seas, especially the Arctic, and from the open ocean (but see [ 146 , 147 ]). Also, soil sinks need further study (but see [ 43 ]).…”
The causes of methane's renewed rise since 2007, accelerated growth from 2014 and record rise in 2020, concurrent with an isotopic shift to values more depleted in
13
C, remain poorly understood. This rise is the dominant departure from greenhouse gas scenarios that limit global heating to less than 2°C. Thus a comprehensive understanding of methane sources and sinks, their trends and inter-annual variations are becoming more urgent. Efforts to quantify both sources and sinks and understand latitudinal and seasonal variations will improve our understanding of the methane cycle and its anthropogenic component. Nationally declared emissions inventories under the UN Framework Convention on Climate Change (UNFCCC) and promised contributions to emissions reductions under the UNFCCC Paris Agreement need to be verified independently by top-down observation. Furthermore, indirect effects on natural emissions, such as changes in aquatic ecosystems, also need to be quantified. Nitrous oxide is even more poorly understood. Despite this, options for mitigating methane and nitrous oxide emissions are improving rapidly, both in cutting emissions from gas, oil and coal extraction and use, and also from agricultural and waste sources. Reductions in methane and nitrous oxide emission are arguably among the most attractive immediate options for climate action.
This article is part of a discussion meeting issue 'Rising methane: is warming feeding warming? (part 1)'.
“…To determine the contributing factors and resolve the spatial distributions, mobile sampling platforms such as small vessels (Müller et al, 2016;Brase et al, 2017;Tait et al, 2017) and autonomous vehicles (Manning et al, 2019) are essential. Recent improvements in gas sensors and in technology such as sonar and ebullition sensors will further increase our ability to measure dynamic fluxes (Maher et al, 2019;Lohrberg et al, 2020). Improvements to the quality and quantity of CH 4 and N 2 O measurements in coastal systems will enable the development of iterative forecast models, further improving estimates of global coastal CH 4 and N 2 O fluxes.…”
Section: Ch 4 and N 2 O In Shallow Marine Environmentsmentioning
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.
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