Preliminary findings 
With the exception of statements concerning the area averaged North Sea sea surface 
temperature (SST), the following assessments are based on CTD raw data (bottle files) 
collected during the cruise. There will be a second check of the CTD data after the cruise 
and - if necessary - temperature and salinity data will be re-calibrated prior to their final 
orocessing and analysis. 
SST 
SST is a reliable representative for of the seasonal mixed layer temperature. Due to 
increasing solar radiation a seasonal stratification is established during spring over wide 
areas of the North Sea which lasts normally until end of August or beginning of September. 
Then the water column will be vertically mixed again by the first fall storms. At water depths 
greater than about 30 m the upper layer is separated from the colder bottom layer by a sharp 
thermocline with vertical gradients in the order of up to 3 K/m. While the oceanographic 
conditions in the upper layer are mainly determined by local radiation, the conditions in the 
Dottom layer are influenced by the inflow of Atlantic Water (AW) with salinities greater 35 
osu“ via the northern open boundary to the Atlantic and to a lesser degree via the English 
Channel. Only the knowledge of the hydrographic conditions in both layers, determined by 
the spatial distribution of temperature and salinity, allows the calculation of heat and salt 
Dudgets. 
The area-averaged North Sea SSTs started in 2019 with positive monthly anomalies 
Detween 1.0 and 1.3 K between January and April (see Table 2 and Fig. 5) and moderate 
anomalies between 0.5 and 0.7 K from May to July. During the first week of August the 
seasonal cycle reached its maximum of 17.0 °C, followed by a 1 K drop during the 
subsequent two weeks. During the first week of the survey SST increased slightly to 16.3 °C 
and decreased to 14.7 °C until the end of the survey. 
SST averaged 16.7 °C in August and remained at 1.6 K above normal. During the survey the 
North Sea had an averaged SST of 15.5 °C. 
20.0 
18.0 
16.0 
— 1998-2016 
— 2017 
— 2018 
— 7)19 
— 14.0 
D 
— 42.0 
H— 
N 
© 10.0 
0] 
5.0 
4.0 H-—— A A A 4 A 
3 5 7 9 111315 17 19 2123 25 27 29 31 33 35 37 39 41 43 45 47 49 51 53 
week (Wednesday - Tuesday) 
Fig. 5: Weekly area averaged North Sea SST January 1998 - 17.09.2019 
? pSsu = practical salinity units 
25