The hydrographic-hydrochemical state of the Baltic Sea in 2011

The article summarizes the hydrographic-hydrochemical conditions in the western and central Baltic Sea in 2011. Based on meteorological conditions, the horizontal and vertical distribution of temperature, salinity, oxygen/hydrogen sulphide and inorganic and organic nutrients are described on a seasonal scale.

The moderate to severe, long and cold winter 2009/2010 was immediately followed by a similarly strong winter 2010/2011. With the “cold sum” of the air temperature in Warnemünde of 177.7 K d it ranks on place 13 of the coldest winters since the beginning of the record in 1948. The summer “heat sum” 2011 in Warnemünde of 174.5 K d was lower than in the years before and was lying only slightly above the average of 148 K d. The satellite derived sea surface temperature of the entire Baltic Sea reached place 7 of the warmest years since 1990.

In 2011, barotropic inflow events with estimated volumes between 100 and 300 km3 took place four times: in January/February, in March/April, in May and in November/December. The relatively strong inflow signal of November/December 2011 transported about one billion tons (1 Gt) of salt into the Baltic Sea; it remains clearly behind the Major Baltic Inflows in the winter of 2003 (2.0 Gt) and the winter of 1993 (3.4 Gt). Subsequent effects can be documented only in 2012.

In the deep water of the eastern and western Gotland Basin, the stagnation period was continuing undiminished. Nitrate was detected in 2005 for the last time. Phosphate and ammonium stabilized at the previous year’s level and were comparable with those at the end of the last stagnation period in 2002.

Dr. Günther Nausch