BGD Biogeosciences Discussions BGD 1810-6285 Copernicus GmbH Göttingen, Germany 10.5194/bgd-8-7623-2011 Timescales for the development of methanogenesis and free gas layers in recently-deposited sediments of Arkona Basin (Baltic Sea) Mogollón J. M. 1 5 Dale A. W. 2 Fossing H. 3 Regnier P. 1 4 Department of Earth Sciences – Geochemistry, Utrecht University, P.O. Box 80.021, 3508TA Utrecht, The Netherlands Leibniz-Institut für Meereswissenschaften, IFM-GEOMAR, Kiel, Germany National Environmental Research Institute, Department of Marine Ecology, Aarhus University, Aarhus, Denmark Département des Sciences de la Terre et de l'Environnement, Université Libre de Bruxelles, Brussels, Belgium now at: Marine Geochemistry, Alfred Wegener Institute for Marine and Polar Research, Bremerhaven, Germany 01 08 2011 8 4 7623 7669 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.biogeosciences-discuss.net/8/7623/2011/bgd-8-7623-2011.html The full text article is available as a PDF file from http://www.biogeosciences-discuss.net/8/7623/2011/bgd-8-7623-2011.pdf

Arkona Basin (southwestern Baltic Sea) is a seasonally-hypoxic basin characterized by the presence of free methane gas in its youngest organic-rich muddy stratum. Through the use of reactive transport models, this study tracks the development of the methane geochemistry in Arkona Basin as this muddy sediment becomes deposited during the last 8 kyr. Four cores are modeled each pertaining to a unique geochemical scenario according to their respective contemporary geochemical profiles. Ultimately the thickness of the muddy sediment and the flux of particulate organic carbon are crucial in determining the advent of both methanogenesis and free methane gas, the timescales over which methanogenesis takes over as a dominant reaction pathway for organic matter degradation, and the timescales required for free methane gas to form.

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