KLIWAS 
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Skagerrak area and by topographically induced up- or down-welling above the 
Norwegian Trench. At the northern boundary of the North Sea, Atlantic Water, the 
mixed Scottish Shelf and North Sea waters are separated by fronts which give 
valuable indications on the dynamics of exchange processes due to their spatial 
structure and eddy displacements. 
Frontal structures are also characterised by strong biological activity and the 
adjacent stratified regions play a key role in marine ecosystems. They affect 
ecosystem components at all levels, directly or through cascading across the food- 
web (ICES 2006). Fronts, with their strong vertical velocities, can lift nutrients into 
the euphotic layer and enhance the productivity of the ocean. They can also increase 
light exposure by modulating the rate at which phytoplankton is mixed below the 
euphotic layer (Ferrari 2011). This high biological activity, stimulated by both high 
inputs and efficient use of nutrients, mediates the drawdown of CO2 from the 
atmosphere and its subsequent export to subsurface layers. The ultimate outflow of 
such CCF-enriched subsurface waters to the open deep ocean constitutes the so-called 
‘shelf sea pump’, a mechanism which transfers CCF to the open ocean and which is 
thought to substantially contribute to the global ocean’s uptake of atmospheric CCK 
The North Sea acts as a sink for CO2 over wide areas throughout the entire year 
except during the summer months in southern parts of this region. More than 90% of 
the CO2 taken up by the North Sea from atmosphere is exported into the North 
Atlantic. Extrapolating the North Sea’s CO2 uptake over all shelf sea areas worldwide 
results into a global net uptake of 20% of all anthropogenic CO2 by the ocean due to 
shelf sea pumping (Thomas et al. 2004). 
Climate related changes in the North Sea and in the adjacent North Atlantic will 
impact atmospheric and oceanic circulation patterns, tides, sea level, precipitation 
patterns and intensity, salinity and continental river run-off volumes. These changes 
in turn will have an influence on the position, strength and dynamic of oceanic fronts 
and thereby on biology, ecology and the intensity of shelf sea pumping. ICES (2006) 
stated: ‘an understanding of fish response to climate compatible with process 
understanding requires that meso-scale oceanic features can be detected and tracked 
over long periods of time.’ Such an operational monitoring is possible only by the use 
of satellite earth observation (EO) data and with algorithms being able to detect 
different types of fronts automatically. To assess alterations caused by climate 
change, there is an urgent need for reliable information about positions and intensities 
of fronts and their seasonal and wind dependent variability. Ferrari (2011) asked: 
‘Given the importance of frontal physics and biogeochemistry, how are we going to 
make substantial progress in understanding and quantifying the effect of fronts on the 
global climate system?’ 
The KLIWAS climatology of North Sea fronts, realised by a co-operation of 
Brockmann Consult and BSH, is a contribution to answer these questions. The new 
method for front detection called GRADHIST is basing on the combination and 
KLIWAS 
Climatology 
of North Sea 
Fronts