The hydrographic-hydrochemical state of the Baltic Sea in 2018

For the southern Baltic Sea area, the “cold sum” of the air temperature of 67.7 Kd in Warnemünde amounted to a mild winter in 2017/18 and ranks as 34th warmest winter since the beginning of the record in 1948. The summer “heat sum” of 394.5 Kd ranks on 1st position setting a new record as warmest summer over the past 71 years and is nearly twice as high as the long-term average of 153.5 Kd.

Based on satellite derived Sea Surface Temperature (SST) 2018 was as well the warmest year since 1990 and with 1.19 K far above the long-term SST average. May to August contributed to the record by their high positive anomalies of +4-5 K. March and April were characterized by negative anomalies due to the late winter cold spell in February and March.

The situation in the deep basins of the Baltic Sea was characterized by mainly anoxic to euxinic conditions. The influence of several inflows during 2014-2017 was fading away and phosphate and ammonium concentration were increasing again. Two weak barotropic inflows occurred during September and December transporting volumes 233 km³ and 215 km³ into the Baltic Sea, showing a relatively low mean salinity of around 15 g/kg. Calm summer weather induced several phases of baroclinic inflow events, importing very warm saline surface water of the Kattegat area into the deep basins. A temperature increase of 3-5 K was registered.