A method for the calculation of anaerobic oxidation of methane rates across regional scales: an example from the Belt Seas and The Sound (North Sea–Baltic Sea transition)
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Estimating the amount of methane in the seafloor globally as well as the flux of methane from sediments toward the ocean–atmosphere system are important considerations in both geological and climate sciences. Nevertheless, global estimates of methane inventories and rates of methane production and consumption through anaerobic oxidation in marine sediments are very poorly constrained. Tools for regionally assessing methane formation and consumption rates would greatly increase our understanding of the spatial heterogeneity of the methane cycle as well as help constrain the global methane budget. In this article, an algorithm for calculating methane consumption rates in the inner shelf is applied to the gas-rich sediments of the Belt Seas and The Sound (North Sea–Baltic Sea transition). It is based on the depth of free gas determined by hydroacoustic techniques and the local methane solubility concentration. Due to the continuous nature of shipboard hydroacoustic measurements, this algorithm captures spatial heterogeneities in methane fluxes better than geochemical analyses of point sources such as observational/sampling stations. The sensibility of the algorithm with respect to the resolution of the free gas depth measurements (2 m vs. 50 cm) is proven of minor importance (a discrepancy of <10%) for a small part of the study area. The algorithm-derived anaerobic methane oxidation rates compare well with previous measured and modeling studies. Finally, regional results reveal that contemporary anaerobic methane oxidation in worldwide inner-shelf sediments may be an order of magnitude lower (ca. 0.24 Tmol year–1) than previous estimates (4.6 Tmol year–1). These algorithms ultimately help improve regional estimates of anaerobic oxidation of methane rates.
KeywordsMethane Flux Methane Hydrate Anaerobic Oxidation Anaerobic Methane Oxidation Methane Cycle
We wish to thank Kerstin Jerosch for her help with the grain size classification system. Gerald Dickens, an anonymous reviewer and the editor provided constructive comments that improved the paper. This study was funded by NWO Vidi Award #864.05.007: Marine methane flux and climate change: from biosphere to geosphere, by the European Community’s Seventh Framework Programme (FP/2007–2013) under grant agreement number 217246 made with the joint Baltic Sea research and development programme BONUS, and by the government of the Brussels-Capital Region (Brains Back to Brussels award to P. Regnier). Further funding is acknowledged from the European Union’s Seventh Framework Program (FP7/2007-2013) under grant agreement no 283080, project GEOCARBON.
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