The hydrographic-hydrochemical state of the Baltic Sea in 2017

The article summarizes the hydrographic-hydrochemical conditions in the western and central Baltic Sea in 2016. Based on meteorological conditions, the horizontal and vertical distributionof temperature, salinity, oxygen/hydrogen sulphide and nutrients are described on a seasonal scale.

For the southern Baltic Sea area, the “cold sum” of the air temperature of 63.5 Kd in Warnemünde amounted to a mild winter in 2014/15 and ranks as 27^th warmest winter since the beginning of the record in 1948. The summer “heat sum” of 267 Kd is ranked in the “top ten” over the past 69 years and ranks on place 6 of the warmest summers.

The situation in the deep basins of the Baltic Sea was mainly coined by ongoing inflow activity of moderate Major Baltic Inflows (November 2015, January-February 2016) following the Major Baltic Inflow of December 2014, which was the third largest ever observed. Since mid of January, the deep layer in the eastern Gotland Basin was ventilated again. The November 2015 MBI reached the bottom, whereas the following event only water depths between 100-200 m had ventilated. In 2016, furthermore three smaller inflow events with estimated volumes between 171 km³ and 184 km³ occurred in the timespan October to December. In conclusion, the observed phase of intensified water exchange processes with subsequent consequences for the biogeochemical cycles is going on since 2014.