Abstract. Methane and carbon dioxide were measured with an autonomous and continuous running system on a ferry line crossing the Baltic Sea on a 2-3 day interval from the Mecklenburg Bight to the Gulf of Finland in 2010. Surface methane saturations show great seasonal differences in shallow regions like the Mecklenburg Bight (103-507 %) compared to deeper regions like the Gotland Basin (96-161 %). The influence of controlling parameters like temperature, wind, mixing depth and processes like upwelling, mixing of the water column and sedimentary methane emissions on methane oversaturation and emission to the atmosphere are investigated. Upwelling was found to influence methane surface concentrations in the area of Gotland significantly during the summer period. In February 2010, an event of elevated methane concentrations in the surface water and water column of the Arkona Basin was observed, which could be linked to a wind-derived water level change as a potential triggering mechanism. The Baltic Sea is a source of methane to the atmosphere throughout the year, with highest fluxes occurring during the winter season. Stratification was found to promote the formation of a methane reservoir in deeper regions like Gulf of Finland or Bornholm Basin, which leads to long lasting elevated methane concentrations and enhanced methane fluxes, when mixed to the surface during mixed layer deepening in autumn and winter. Methane concentrations and fluxes from shallow regions like the Mecklenburg Bight are predominantly controlled by sedimentary production and consumption of methane, wind events and the change in temperature-dependent solubility of methane in the surface water. Methane fluxes vary significantly in shallow regions (e.g. Mecklenburg Bight) and regions with a temporal stratification (e.g. Bornholm Basin, Gulf of Finland). On the contrary, areas with a permanent stratification like the Gotland Basin show only small seasonal fluctuations in methane fluxes.

In December 2014, the third strongest salt water inflow into the Baltic Sea occurred since 1880. It was assumed that the inflow would turn the entire bottom water of the Baltic Sea from anoxic into oxic conditions for an extended period. However, already in late 2015, the central Eastern Baltic Sea had turned back into anoxic conditions. This rapid oxygen decline was in fact surprising since a weaker inflow in 2003 ventilated the Baltic Sea for a longer period of time. With the aid of an ecosystem model of the Baltic Sea, the two inflows in 2003 and 2014 were analyzed in detail. Although the 2014 inflow event was twice as strong as the 2003 inflow event, oxygen transport continued after the latter one, supplying about the same amount of oxygen again. In addition to the major inflow event, a series of smaller inflows in 2003 supplied the extra oxygen transport. Therefore, the strength of a major inflow event alone cannot be used to predict the oxygenation impact. Instead, it is necessary to consider smaller events, in particular those occurring just before and after a major inflow event, as well. An element tagging method showed that the share of oxygen imported across the Danish Straits on the total oxygen arriving at the central Eastern Baltic Sea is between 10% and 20%. Therefore, the oxygen concentration of the inflowing water seems to be of less importance for the oxygenation effect on the central Baltic Sea due to the strong dilution effect.

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G . ROPKE et al. : Influence of Exciton Gas and Electron-Hole Plasma 2 15 phys. stat. sol. (b) 100, 215 (1980) Corrections to the energy levels of ground state excitons embedded in a gas of excitons, electrons, and holes are obtained within the framework of the Green's function technique. Contributions of the interaction with free carriers and excitons are considered in the first Born approximation, and plasmon effects are taken into account. Numerical values are given for the exciton energy shift linear in the densities a t different temperatures and different electron-hole mass ratios.Im Rahmen der Technik der Greenschen Funktionen werden die Korrekturen zur Grundzustandsenergie eines Exzitom berechnet, das in ein Plasma aus Exzitonen, Elektronen und Lochern eingebettet ist. Es werden die Beitrage der Wechselwirkung mit freien Ladungstragern und mit Exzitonen in der ersten Bornschen Niiherung betrachtet, und Plasmoneffekte werden berucksichtigt. SchlieSlich werden numerische Werte fiir die in den Dichten lineare Verschiebung des exzitonischen Grundzustandes bei verschiedenen Temperaturen und Elektron-Loch-Massen-verhLltnissen gegeben.

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