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 factors
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 September)
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 stratification
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 values
towards the central North Sea. In the SCNS region B,
PP m id accounts for about 87 % of that in the highly productive
coastal region A. The corresponding value for the NCNS
region C and NNS region D is about 80 and 88 %, respectively.
Despite the highest PP m id in the coastal region A, the
SCNS region B shows the strongest contribution of gross advection
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 negative
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 recirculated
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 corresponds
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.
