A wideband acoustic method for direct assessment of bubble-mediated methane flux

Weidner, Elizabeth; Weber, Thomas C.; Mayer, Larry A.; Chernykh, Denis; Semiletov, I. P.

doi:10.1016/j.csr.2018.12.005

Cited by 22 publications

(18 citation statements)

References 55 publications

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“…This has bearing for the understanding and future model parametrizations especially of CH 4 fluxes in arctic and subarctic shelf systems, i.e., a comprehensive understanding of spatial and seasonal CH 4 accumulation and flare distribution in sediments as stimulated by heat waves is needed to quantify CH 4 fluxes from shallow coastal waters. Acoustic methods directly addressing bubble-mediated methane flux are becoming more available (Weidner et al, 2019) and similar studies using mid-water sonar systems near Spitzbergen have shown that CH 4 partly originating from ebullition and transformed into the dissolved pool during upward transport is efficiently trapped below the halocline at some 200 m water depth for at least part of the year, which prevents outgassing to the atmosphere (Gentz et al, 2014). This is corroborated by our findings in the deeper stratified Northern Baltic Proper where even a strong upwelling event led to strong outgassing of CO 2 (Figure 4C), but only moderate increased CH 4 concentrations were observed (Figure 4D).…”

Section: Discussionmentioning

confidence: 99%

High Emissions of Carbon Dioxide and Methane From the Coastal Baltic Sea at the End of a Summer Heat Wave

et al. 2019

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The summer heat wave in 2018 led to the highest recorded water temperatures since 1926 -up to 21 • C -in bottom coastal waters of the Baltic Sea, with implications for the respiration patterns in these shallow coastal systems. We applied cavity ringdown spectrometer measurements to continuously monitor carbon dioxide (CO 2 ) and methane (CH 4 ) surface-water concentrations, covering the coastal archipelagos of Sweden and Finland and the open and deeper parts of the Northern Baltic Proper. This allowed us to (i) follow an upwelling event near the Swedish coast leading to elevated CO 2 and moderate CH 4 outgassing, and (ii) to estimate CH 4 sources and fluxes along the coast by investigating water column inventories and air-sea fluxes during a storm and an associated downwelling event. At the end of the heat wave, before the storm event, we found elevated CO 2 (1583 µatm) and CH 4 (70 nmol/L) concentrations. During the storm, a massive CO 2 sea-air flux of up to 274 mmol m −2 d −1 was observed. While water-column CO 2 concentrations were depleted during several hours of the storm, CH 4 concentrations remained elevated. Overall, we found a positive relationship between CO 2 and CH 4 wind-driven sea-air fluxes, however, the highest CH 4 fluxes were observed at low winds whereas highest CO 2 fluxes were during peak winds, suggesting different sources and processes controlling their fluxes besides wind. We applied a box-model approach to estimate the CH 4 supply needed to sustain these elevated CH 4 concentrations and the results suggest a large source flux of CH 4 to the water column of 2.5 mmol m −2 d −1 . These results are qualitatively supported by acoustic observations of vigorous and widespread outgassing from the sediments, with flares that could be traced throughout the water column penetrating the pycnocline and reaching the sea surface. The results suggest that the heat wave triggered CO 2 and CH 4 fluxes in the coastal zones that are comparable with maximum emission rates found in other hot spots, such as boreal and arctic lakes and wetlands. Further, the results suggest that heat waves are as important for CO 2 and CH 4 sea-air fluxes as the ice break up in spring.

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Section: Discussionmentioning

confidence: 99%

High Emissions of Carbon Dioxide and Methane From the Coastal Baltic Sea at the End of a Summer Heat Wave

et al. 2019

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“…A quantitative measure of seafloor ruggedness, sometimes referred to as roughness, can be computed using several different methods (e.g. Wilson et al, 2007;Pike et al, 2008). Here we calculate terrain ruggedness index (TRI) using the algorithm available within the open-source SAGA (System for Automated Geoscientific Analyses) tools (Conrad et al, 2015).…”

Section: Geomorphometrymentioning

confidence: 99%

“…Midwater echo sounders permit remote observations of thermohaline stratification (Stranne et al, 2017), turbulence (Farmer and Dungan Smith, 1980;Moum et al, 2003), and suspended particles (Young et al, 1982;Hay and Sheng, 1992), as well as individual fish, fish schools, and zooplankton (Chu et al, 1994). Advantages of the new type of wideband echo sounders that we used in this study compared to conventional narrow-band systems include increased signalto-noise ratio and increased range resolution (Stanton and Chu, 2008), as well as the ability to study the frequency response of individual targets to help identify the source of the acoustic backscatter (Weidner et al, 2019;Irish et al, 2010). While this kind of frequency response analysis has not been done on the data presented here, we can still visually identify some specific features in the acoustic mid-water profiles such as fish schools, zooplankton or suspended particles, thermohaline stratification (verified with co-located CTD data) and turbulence (Fig.…”

Section: Adding the Midwater Perspectivementioning

confidence: 99%

Bathymetric properties of the Baltic Sea

et al. 2019

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Abstract. Baltic Sea bathymetric properties are analysed here using the newly released digital bathymetric model (DBM) by the European Marine Observation and Data Network (EMODnet). The analyses include hypsometry, volume, descriptive depth statistics, and kilometre-scale seafloor ruggedness, i.e. terrain heterogeneity, for the Baltic Sea as a whole as well as for 17 sub-basins defined by the Baltic Marine Environment Protection Commission (HELCOM). We compare the new EMODnet DBM with IOWTOPO the previously most widely used DBM of the Baltic Se aproduced by the Leibniz-Institut für Ostseeforschung Warnemünde (IOW), which has served as the primary gridded bathymetric resource in physical and environmental studies for nearly two decades. The area of deep water exchange between the Bothnian Sea and the Northern Baltic Proper across the Åland Sea is specifically analysed in terms of depths and locations of critical bathymetric sills. The EMODnet DBM provides a bathymetric sill depth of 88 m at the northern side of the Åland Sea and 60 m at the southern side, differing from previously identified sill depths of 100 and 70 m, respectively. High-resolution multibeam bathymetry acquired from this deep water exchange path, where vigorous bottom currents interacted with the seafloor, allows us to assess what presently available DBMs are missing in terms of physical characterization of the seafloor. Our study highlights the need for continued work towards complete high-resolution mapping of the Baltic Sea seafloor.

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“…Gas apparently releases all year round, judging by the ubiquitous presence of methane bubbles entrapped within the sea ice (recovered from boreholes of ~0.3 m average diameter) [36]. About 90 gas seeps were discovered in the Herald Canyon and around Wrangel Island on the Chukchi shelf in 2014 during a cruise as part of a joint German-Russian-American project [70]. The seeps occurred on the relatively flat shelf part at a sea depth of 50 to 95 m. Zones of intense gas emission, with 4-6 mm bubbles, were detectable in processed acoustic images (Figure 12).…”

Section: Natural Gas Emissionmentioning

confidence: 99%

Evidence of Gas Emissions from Permafrost in the Russian Arctic

et al. 2020

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The active emission of gas (mainly methane) from terrestrial and subsea permafrost in the Russian Arctic has been confirmed by ample evidence. In this paper, a generalization and some systematization of gas manifestations recorded in the Russian Arctic is carried out. The published data on most typical gas emission cases have been summarized in a table and illustrated by a map. The tabulated data include location, signatures, and possible sources of each gas show, with respective references. All events of onshore and shelf gas release are divided into natural and man-caused. and the natural ones are further classified as venting from lakes or explosive emissions in dryland conditions that produce craters on the surface. Among natural gas shows on land, special attention is paid to the emission of natural gas from Arctic lakes, as well as gas emissions with craters formation. In addition, a description of the observed man-caused gas manifestations associated with the drilling of geotechnical and production wells in the Arctic region is given. The reported evidence demonstrates the effect of permafrost degradation on gas release, especially in oil and gas fields.

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A wideband acoustic method for direct assessment of bubble-mediated methane flux

Cited by 22 publications

References 55 publications

High Emissions of Carbon Dioxide and Methane From the Coastal Baltic Sea at the End of a Summer Heat Wave

High Emissions of Carbon Dioxide and Methane From the Coastal Baltic Sea at the End of a Summer Heat Wave

Bathymetric properties of the Baltic Sea

Evidence of Gas Emissions from Permafrost in the Russian Arctic

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