2522 
F. Große et al.: Looking beyond stratification 
Biogeosciences, 13, 2511-2535, 2016 
www.biogeosciences.net/13/2511/2016/ 
58° N 
56° N 
54° N 
52“ N 
50° N 
60° N 
58° N 
54° N 
52“ N 
50“ N 
Figure 6. Spatial distributions of (a) and (b) longest continuous stratification period derived from simulated T according to Eq. (1), (c) and 
(d) simulated annual minimum bottom От concentrations for the years 2002 (a, c) and 2010 (b, d). Same scales for (a), (b), and (c), (d). 
trations north of the Dogger Bank in August 2010, however, 
they found the minimum concentrations a bit further north 
around 57° N. 
The discrepancy between minimum 0 2 concentrations 
in the 2 years and the quite similar stratification patterns 
demonstrates that stratification is an important prerequisite 
for low 0 2 conditions, but other physical or biological fac 
tors do have a strong effect on the 0 2 dynamics in the North 
Sea. 
3.3 An 02-related characteristic of the North Sea 
3.3.1 Key parameters 
Table 1 shows the 2000-2012 summer (1 April to 30 Septem 
ber) averages of the quantities considered potentially relevant 
for 0 2 for the regions A-D (see Fig. 2). The quantities were 
calculated relative to a D ic \ of 25 m. In addition, the strati 
fication period (fstrat). average MLD (D m id), average bottom 
depth ( /) bol ) and area of the regions are provided. 
The mixed layer net primary production, PP m id- is 
strongest in the coastal region A and shows decreasing val 
ues towards the central North Sea. In the SCNS region B, 
PP m id accounts for about 87 % of that in the highly produc 
tive coastal region A. The corresponding value for the NCNS 
region C and NNS region D is about 80 and 88 %, respec 
tively. 
Despite the highest PP m id in the coastal region A, the 
SCNS region B shows the strongest contribution of gross ad- 
vection of organic matter, ADH org i n and ADH org out . Both 
regions show positive net advection of organic matter, while 
the two northern regions C and D are characterised by nega 
tive net advection, i.e., advective loss in organic matter. The 
latter regions are located north of the Dogger Bank, thus, they 
are affected by the northern Atlantic inflow. In this region, 
net advection results in a loss in organic matter as the recir 
culated northward flowing water has higher concentrations 
of organic matter than the incoming Atlantic water. 
The vertical export of organic matter, EXP org , below D re f 
consistently adds up to about 12-14% of PP m id, indicating 
the clear link between these quantities. Region B yields an 
EXP org of 75 % of that in the coastal region A, which cor 
responds to a higher net advective import of organic matter 
of 6.7 g Cm -2 in region A, compared to only 1.6 g Cm -2 in 
Region B. EXP org in region C and D reach about 69 % and 
79 % relative to region A, respectively.