Methane fluxes from the sea to the atmosphere across the Siberian shelf seas

Thornton, Brett F.; Geibel, M. C.; Crill, Patrick; Humborg, Christoph; Mörth, Carl‐Magnus

doi:10.1002/2016gl068977

Cited by 107 publications

(138 citation statements)

References 55 publications

(71 reference statements)

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“…For the North Sea in winter, much higher values were obtained (7-62 cm h −1 = 17-150 m d −1 ) (Nightingale et al, 2000). Similar values were reported for a bay in the Baltic Sea, at around 7 cm h −1 = 17 m d −1 (Silvennoinen et al, 2008), but lower values were reported for a Japanese estuary in summer (0.69-3.2 cm h −1 = 1.7-7.7 m d −1 ) (Tokoro et al, 2007). Our values for k 600 ranged from 0.37 to 3.17 m d −1 , with a median of 1.05 m d −1 .…”

Section: Diffusive Methane Fluxsupporting

confidence: 63%

Methane distribution and oxidation around the Lena Delta in summer 2013

et al. 2017

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Abstract. The Lena River is one of the largest Russian rivers draining into the Laptev Sea. The predicted increases in global temperatures are expected to cause the permafrost areas surrounding the Lena Delta to melt at increasing rates. This melting will result in high amounts of methane reaching the waters of the Lena and the adjacent Laptev Sea. The only biological sink that can lower methane concentrations within this system is methane oxidation by methanotrophic bacteria. However, the polar estuary of the Lena River, due to its strong fluctuations in salinity and temperature, is a challenging environment for bacteria. We determined the activity and abundance of aerobic methanotrophic bacteria by a tracer method and by the quantitative polymerase chain reaction. We described the methanotrophic population with a molecular fingerprinting method (monooxygenase intergenic spacer analysis), as well as the methane distribution (via a headspace method) and other abiotic parameters, in the Lena Delta in September 2013.The median methane concentrations were 22 nmol L −1 for riverine water (salinity (S) < 5), 19 nmol L −1 for mixed water (5 < S < 20) and 28 nmol L −1 for polar water (S > 20). The Lena River was not the source of methane in surface water, and the methane concentrations of the bottom water were mainly influenced by the methane concentration in surface sediments. However, the bacterial populations of the riverine and polar waters showed similar methane oxidation rates (0.419 and 0.400 nmol L −1 d −1 ), despite a higher relative abundance of methanotrophs and a higher estimated diversity in the riverine water than in the polar water. The methane turnover times ranged from 167 days in mixed water and 91 days in riverine water to only 36 days in polar water. The environmental parameters influencing the methane oxidation rate and the methanotrophic population also differed between the water masses. We postulate the presence of a riverine methanotrophic population that is limited by sub-optimal temperatures and substrate concentrations and a polar methanotrophic population that is well adapted to the cold and methane-poor polar environment but limited by a lack of nitrogen. The diffusive methane flux into the atmosphere ranged from 4 to 163 µmol m 2 d −1 (median 24). The diffusive methane flux accounted for a loss of 8 % of the total methane inventory of the investigated area, whereas the methanotrophic bacteria consumed only 1 % of this methane inventory. Our results underscore the importance of measuring the methane oxidation activities in polar estuaries, and they indicate a population-level differentiation between riverine and polar water methanotrophs.

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Section: Diffusive Methane Fluxsupporting

confidence: 63%

Methane distribution and oxidation around the Lena Delta in summer 2013

et al. 2017

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“…Thornton et al . [] described a continuous shipboard survey of CH 4 concentrations in the atmosphere and near‐surface waters in much of this same area. They conclude that ebullition does not substantially contribute to the sea‐air CH 4 flux, which they calculate to be less than 2.9 Tg yr −1 CH 4.…”

Section: Climate Susceptibility Of Gas Hydrates By Physiographic Provmentioning

confidence: 99%

The interaction of climate change and methane hydrates

Ruppel

Kessler

2017

Reviews of Geophysics

648

554

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Gas hydrate, a frozen, naturally‐occurring, and highly‐concentrated form of methane, sequesters significant carbon in the global system and is stable only over a range of low‐temperature and moderate‐pressure conditions. Gas hydrate is widespread in the sediments of marine continental margins and permafrost areas, locations where ocean and atmospheric warming may perturb the hydrate stability field and lead to release of the sequestered methane into the overlying sediments and soils. Methane and methane‐derived carbon that escape from sediments and soils and reach the atmosphere could exacerbate greenhouse warming. The synergy between warming climate and gas hydrate dissociation feeds a popular perception that global warming could drive catastrophic methane releases from the contemporary gas hydrate reservoir. Appropriate evaluation of the two sides of the climate‐methane hydrate synergy requires assessing direct and indirect observational data related to gas hydrate dissociation phenomena and numerical models that track the interaction of gas hydrates/methane with the ocean and/or atmosphere. Methane hydrate is likely undergoing dissociation now on global upper continental slopes and on continental shelves that ring the Arctic Ocean. Many factors—the depth of the gas hydrates in sediments, strong sediment and water column sinks, and the inability of bubbles emitted at the seafloor to deliver methane to the sea‐air interface in most cases—mitigate the impact of gas hydrate dissociation on atmospheric greenhouse gas concentrations though. There is no conclusive proof that hydrate‐derived methane is reaching the atmosphere now, but more observational data and improved numerical models will better characterize the climate‐hydrate synergy in the future.

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“…Investigations led by Shakhova et al (2010Shakhova et al ( , 2014 estimated total ESAS emissions from diffusion, ebullition, and storm-induced degassing, at 8-17 TgCH 4 yr −1 . A subsequent measurement campaign led by Thornton et al (2016a), though not made during a stormy period, failed to observe the high rates of continuous emissions reported by Shakhova et al (2014), and instead estimated an average flux of 2.9 TgCH 4 yr −1 . Berchet et al (2016) also found that such values were not supported by atmospheric observations, and instead suggested the range of 0.0-4.5 TgCH 4 yr −1 .…”

Section: Introductionmentioning

confidence: 99%

Detectability of Arctic methane sources at six sites performing continuous atmospheric measurements

et al. 2017

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Abstract. Understanding the recent evolution of methane emissions in the Arctic is necessary to interpret the global methane cycle. Emissions are affected by significant uncertainties and are sensitive to climate change, leading to potential feedbacks. A polar version of the CHIMERE chemistrytransport model is used to simulate the evolution of tropospheric methane in the Arctic during 2012, including all known regional anthropogenic and natural sources, in particular freshwater emissions which are often overlooked in methane modelling. CHIMERE simulations are compared to atmospheric continuous observations at six measurement sites in the Arctic region. In winter, the Arctic is dominated by anthropogenic emissions; emissions from continental seepages and oceans, including from the East Siberian Arctic Shelf, can contribute significantly in more limited areas. In summer, emissions from wetland and freshwater sources dominate across the whole region. The model is able to reproduce the seasonality and synoptic variations of methane measured at the different sites. We find that all methane sources significantly affect the measurements at all stations at least at the synoptic scale, except for biomass burning. In particular, freshwater systems play a decisive part in summer, representing on average between 11 and 26 % of the simulated Arctic methane signal at the sites. This indicates the relevance of continuous observations to gain a mechanistic understanding of Arctic methane sources. Sensitivity tests reveal that the choice of the land-surface model used to prescribe wetland emissions can be critical in correctly representing methane mixing ratios. The closest agreement with the observations is reached when using the two wetland models which have emissions peaking in AugustSeptember, while all others reach their maximum in JuneJuly. Such phasing provides an interesting constraint on wetland models which still have large uncertainties at present. Also testing different freshwater emission inventories leads to large differences in modelled methane. Attempts to include methane sinks (OH oxidation and soil uptake) reduced the model bias relative to observed atmospheric methane. The study illustrates how multiple sources, having different spatiotemporal dynamics and magnitudes, jointly influencePublished by Copernicus Publications on behalf of the European Geosciences Union. 8372T. Thonat et al.: Detectability of Arctic methane sources the overall Arctic methane budget, and highlights ways towards further improved assessments.

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Methane fluxes from the sea to the atmosphere across the Siberian shelf seas

Cited by 107 publications

References 55 publications

Methane distribution and oxidation around the Lena Delta in summer 2013

Methane distribution and oxidation around the Lena Delta in summer 2013

The interaction of climate change and methane hydrates

Detectability of Arctic methane sources at six sites performing continuous atmospheric measurements

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