Effects of the 2014 Major Baltic Inflow on methane and nitrous oxide dynamics in the water column of the Central Baltic Sea
Jukka-Pekka Myllykangas1, Tom Jilbert1, Gunnar Jakobs1,2, Gregor Rehder3, Jan Werner3, and Susanna Hietanen11Department of Environmental Sciences, University of Helsinki, P.O. Box 65, FIN-00014 University of Helsinki, Finland 2Technical University of Denmark, Frederiksborgvej 399, 4000 Roskilde, Denmark 3Leibniz Institute for Baltic Sea Research Warnemünde (IOW), Seestraße 15, D-18119 Rostock, Germany
Received: 10 Feb 2017 – Accepted for review: 18 Apr 2017 – Discussion started: 19 Apr 2017
Abstract. In late 2014, a large, oxygen-rich salt water inflow entered the Baltic Sea and caused considerable changes in deep water oxygen concentrations. We studied the effects of the inflow on the concentration patterns of two greenhouse gases, methane and nitrous oxide, during the following year (2015) in the water column of the Gotland Basin. Methane which had previously accumulated in anoxic deep waters was largely removed from the Eastern Gotland Basin during the year, predominantly due to oxidation following turbulent mixing with the oxygen-rich inflow. In contrast nitrous oxide, which was previously absent from deep waters, accumulated in deep waters due to enhanced nitrification following the inflow. A transient extreme accumulation of nitrous oxide was observed in the deep waters of the Eastern Gotland Basin towards the end of 2015, when deep waters turned anoxic again and sedimentary denitrification was induced. The Western Gotland Basin gas biogeochemistry was not affected by the inflow.
Myllykangas, J.-P., Jilbert, T., Jakobs, G., Rehder, G., Werner, J., and Hietanen, S.: Effects of the 2014 Major Baltic Inflow on methane and nitrous oxide dynamics in the water column of the Central Baltic Sea, Earth Syst. Dynam. Discuss., doi:10.5194/esd-2017-14, in review, 2017.