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 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 before the final processing and analysis of 
che data. 
SST is a reliable representative for the temperature of the seasonal mixed layer. Due to 
increasing solar radiation the North Sea established a seasonal stratification 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 depth greater 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 bottom layer are influenced by the inflow of Atlantic Water (AW) with 
salinities grater 35 psu“ via the northern open boundary to the Atlantic and to a lesser degree 
via the English Channel. Only the knowledge of the hydrographic condition in both layers, 
determined by the spatial distribution of temperature and salinity, allows the calculation of 
heat and salt budgets. 
During the first eight months of 2016 the monthly anomalies of the area averaged North Sea 
SST varied between 1.3 °C (January) and 0.8 °C (March, May, June, and August) compared 
to the reference period 1971-1993. Regarding the seasonal cycle 2016, the survey lies 
exactly between the two seasonal maxima of 16.2 °C recorded in the seven days periods 
from July 27° to August 2"* and from August 24" to 30". During the survey period from 
August 4" to 23" the area averaged SST was 15.5 °C. That confirms that the survey took 
olace very close to the total seasonal heat maximum of the North Sea which can be 
expected in the bottom layer about 4 weeks after reaching its maximum in the surface layer. 
While the southernmost temperature section along 54° N is vertically mixed due to low water 
depth, the zonal (east-west) temperature sections between 55 and 57° N show a massive 
homogeneous mixed surface layer with a strong thermocline at depth between 30 und 40 m. 
Zurther north, there is still a strong deep thermocline, but the Baltic outflow — which expands 
far to the west in 2016 — together with the Norwegian Coastal current cause slight 
temperature gradients within the surface layer (Fig. 4, 6, and 8). The calculation of the North 
Sea’s total heat budget will be done after the final check of the data. 
The salinity sections show a massive inflow of Atlantic Water (S >35 psu) from the north. The 
main inflow paths through the Fair Isle Channel, the East-Shetland Shelf, and at the western 
slope of the Norwegian Trench at 350 to 400 m depth are clearly visible (Fig. 7). This tongue 
of Atlantic Water intrudes southward to 56° N where it is still covering the whole water 
column from surface to bottom in the central North Sea. It can be expected that the total salt 
content in 2016 will be much higher than in the previous year, however, also the total heat 
Dudget will not be calculated before the final processing of the data and the analysis of over 
200 in-situ salinity samples for CTD calibration. 
? pSsu = practical salinity units 
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