Methane cycling in Arctic shelf water and its relationship with phytoplankton biomass and DMSP

Damm, Ellen; Kiene, Ronald P.; Schwarz, J.; Falck, Eva; Dieckmann, Gerhard

doi:10.1016/j.marchem.2007.12.003

Cited by 114 publications

(112 citation statements)

References 54 publications

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“…Net oxidation rates of the long-incubation treatments at 10× (46 days) and 200× (41 days) methane concentration fall into the mid-range of rates published for Arctic and subarctic environments (Damm et al, 2015;Gentz et al, 2014;Lorenson et al, 2016;Mau et al, 2013Mau et al, , 2017Steinle et al, 2015) or marine sites with high oxidation rates at oil spills or gas flares (Leonte et al, 2017;Redmond et al, 2010;Valentine et al, 2010), as discussed in Uhlig and Loose (2017a). The fractionation factors (α ox ) that we observed are higher than previously reported from cold marine environments with a range of α ox from 1.002 to 1.017 (Cowen et al, 2002;Damm et al, 2008;Grant and Whiticar, 2002;Heeschen et al, 2004;Keir et al, 2009;Tsunogai et al, 2000). However, some of these fractionation factors, which were calculated from in situ data, might be underestimates due to mixing effects in the water column (Grant and Whiticar, 2002).…”

Section: Methane Dynamics At Different Methane Concentrationssupporting

confidence: 64%

Methane-oxidizing seawater microbial communities from an Arctic shelf

et al. 2018

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Abstract. Marine microbial communities can consume dissolved methane before it can escape to the atmosphere and contribute to global warming. Seawater over the shallow Arctic shelf is characterized by excess methane compared to atmospheric equilibrium. This methane originates in sediment, permafrost, and hydrate. Particularly high concentrations are found beneath sea ice. We studied the structure and methane oxidation potential of the microbial communities from seawater collected close to Utqiagvik, Alaska, in April 2016. The in situ methane concentrations were 16.3 ± 7.2 nmol L −1 , approximately 4.8 times oversaturated relative to atmospheric equilibrium. The group of methaneoxidizing bacteria (MOB) in the natural seawater and incubated seawater was > 97 % dominated by Methylococcales (γ -Proteobacteria). Incubations of seawater under a range of methane concentrations led to loss of diversity in the bacterial community. The abundance of MOB was low with maximal fractions of 2.5 % at 200 times elevated methane concentration, while sequence reads of non-MOB methylotrophs were 4 times more abundant than MOB in most incubations. The abundances of MOB as well as non-MOB methylotroph sequences correlated tightly with the rate constant (k ox ) for methane oxidation, indicating that non-MOB methylotrophs might be coupled to MOB and involved in community methane oxidation. In sea ice, where methane concentrations of 82 ± 35.8 nmol kg −1 were found, Methylobacterium (α-Proteobacteria) was the dominant MOB with a relative abundance of 80 %. Total MOB abundances were very low in sea ice, with maximal fractions found at the icesnow interface (0.1 %), while non-MOB methylotrophs were present in abundances similar to natural seawater communities. The dissimilarities in MOB taxa, methane concentrations, and stable isotope ratios between the sea ice and water column point toward different methane dynamics in the two environments.

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Section: Methane Dynamics At Different Methane Concentrationssupporting

confidence: 64%

Methane-oxidizing seawater microbial communities from an Arctic shelf

et al. 2018

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“…Dissolved methane concentrations of up to 55 nM in surface waters on the shelf to the south of Spitsbergen (Storfjorden) have been attributed to in situ methanogenesis [Damm et al, 2008]. In this setting, methane is able to accumulate because oxidation is slow and waters are strongly stratified, preventing exchange with the atmosphere.…”

Section: 1002/2015jc011084mentioning

confidence: 99%

Fluxes and fate of dissolved methane released at the seafloor at the landward limit of the gas hydrate stability zone offshore western Svalbard

et al. 2015

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Widespread seepage of methane from seafloor sediments offshore Svalbard close to the landward limit of the gas hydrate stability zone (GHSZ) may, in part, be driven by hydrate destabilization due to bottom water warming. To assess whether this methane reaches the atmosphere where it may contribute to further warming, we have undertaken comprehensive surveys of methane in seawater and air on the upper slope and shelf region. Near the GHSZ limit at ∼400 m water depth, methane concentrations are highest close to the seabed, reaching 825 nM. A simple box model of dissolved methane removal from bottom waters by horizontal and vertical mixing and microbially mediated oxidation indicates that ∼60% of methane released at the seafloor is oxidized at depth before it mixes with overlying surface waters. Deep waters are therefore not a significant source of methane to intermediate and surface waters; rather, relatively high methane concentrations in these waters (up to 50 nM) are attributed to isopycnal turbulent mixing with shelf waters. On the shelf, extensive seafloor seepage at <100 m water depth produces methane concentrations of up to 615 nM. The diffusive flux of methane from sea to air in the vicinity of the landward limit of the GHSZ is ∼4–20 μmol m−2 d−1, which is small relative to other Arctic sources. In support of this, analyses of mole fractions and the carbon isotope signature of atmospheric methane above the seeps do not indicate a significant local contribution from the seafloor source.

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“…As far as we are aware, no sub-sea thawing permafrost has been reported for Godthåbsfjord. Damm et al (2008) suggested that methane plumes in the water originate from sediments during winter and from in situ production during phytoplankton blooms during the summer. As our studies took place before the algal bloom, one of the main methane sources should be the sediment.…”

Section: Methanementioning

confidence: 99%

CO<sub>2</sub> and CH<sub>4</sub> in sea ice from a subarctic fjord under influence of riverine input

et al. 2014

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Abstract. We present the CH 4 concentration [CH 4 ], the partial pressure of CO 2 (pCO 2 ) and the total gas content in bulk sea ice from subarctic, land-fast sea ice in the Kapisillit fjord, Greenland. Fjord systems are characterized by freshwater runoff and riverine input and based on δ 18 O data, we show that > 30 % of the surface water originated from periodic river input during ice growth. This resulted in fresher sea-ice layers with higher gas content than is typical from marine sea ice. The bulk ice [CH 4 ] ranged from 1.8 to 12.1 nmol L −1 , which corresponds to a partial pressure ranging from 3 to 28 ppmv. This is markedly higher than the average atmospheric methane content of 1.9 ppmv. Evidently most of the trapped methane within the ice was contained inside bubbles, and only a minor portion was dissolved in the brines. The bulk ice pCO 2 ranged from 60 to 330 ppmv indicating that sea ice at temperatures above −4 • C is undersaturated compared to the atmosphere (390 ppmv). This study adds to the few existing studies of CH 4 and CO 2 in sea ice, and we conclude that subarctic seawater can be a sink for atmospheric CO 2 , while being a net source of CH 4 .

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Methane cycling in Arctic shelf water and its relationship with phytoplankton biomass and DMSP

Cited by 114 publications

References 54 publications

Methane-oxidizing seawater microbial communities from an Arctic shelf

Methane-oxidizing seawater microbial communities from an Arctic shelf

Fluxes and fate of dissolved methane released at the seafloor at the landward limit of the gas hydrate stability zone offshore western Svalbard

CO<sub>2</sub> and CH<sub>4</sub> in sea ice from a subarctic fjord under influence of riverine input

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Methane cycling in Arctic shelf water and its relationship with phytoplankton biomass and DMSP

Cited by 114 publications

References 54 publications

Methane-oxidizing seawater microbial communities from an Arctic shelf

Methane-oxidizing seawater microbial communities from an Arctic shelf

Fluxes and fate of dissolved methane released at the seafloor at the landward limit of the gas hydrate stability zone offshore western Svalbard

CO&lt;sub&gt;2&lt;/sub&gt; and CH&lt;sub&gt;4&lt;/sub&gt; in sea ice from a subarctic fjord under influence of riverine input

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CO<sub>2</sub> and CH<sub>4</sub> in sea ice from a subarctic fjord under influence of riverine input