Secchi depth south of a line Dogger — Fisherbank ranged from 6 — 10 m and north of this line 
down to a maximum of 16 m below surface (Fig 30). 
In conclusion the average temperature maximum in 2007 did not surmount the values of 
2006 due to the lower air temperatures and the vigorous winds. The only increase has been 
observed just above the thermocline in the central North Sea. However, a preliminary esti- 
mate of the heat content of the greater North Sea revealed a very slight increase relative to 
2006. The salinity distribution in the upper part of the water column was typical for wet years 
whereas in the deeper water no changes relative to the preceding year could be observed. 
Cloudy weather conditions in the second quarter of 2007 prevented obviously from higher 
levels in primary production thus, leading to a relatively good visibility in the water column 
and a good oxygen saturation. 
16