One year of continuous measurements constraining methane emissions from the Baltic Sea to the atmosphere using a ship of opportunity

[摘要] Methane and carbon dioxide were measured with an autonomous andcontinuous running system on a ferry line crossing the Baltic Sea ona 2–3 day interval from the Mecklenburg Bight to the Gulf ofFinland in 2010. Surface methane saturations show great seasonaldifferences in shallow regions like the Mecklenburg Bight(103–507%) compared to deeper regions like the Gotland Basin(96–161%). The influence of controlling parameters liketemperature, wind, mixing depth and processes like upwelling, mixingof the water column and sedimentary methane emissions on methaneoversaturation and emission to the atmosphere areinvestigated. Upwelling was found to influence methane surfaceconcentrations in the area of Gotland significantly during the summerperiod. In February 2010, an event of elevated methane concentrationsin the surface water and water column of the Arkona Basin wasobserved, which could be linked to a wind-derived water level changeas a potential triggering mechanism. The Baltic Sea is a source ofmethane to the atmosphere throughout the year, with highest fluxes occurring during the winter season. Stratification was found to promote theformation of a methane reservoir in deeper regions like Gulf ofFinland or Bornholm Basin, which leads to long lasting elevatedmethane concentrations and enhanced methane fluxes, when mixed to thesurface during mixed layer deepening in autumn and winter. Methaneconcentrations and fluxes from shallow regions like the MecklenburgBight are predominantly controlled by sedimentary production and consumptionof methane, wind events and the change in temperature-dependentsolubility of methane in the surface water. Methane fluxes varysignificantly in shallow regions (e.g. Mecklenburg Bight) and regionswith a temporal stratification (e.g. Bornholm Basin, Gulf ofFinland). On the contrary, areas with a permanent stratification likethe Gotland Basin show only small seasonal fluctuations in methanefluxes.

[学科分类] 地球化学与岩石