KLIWAS 
Seite 10 
KLIWAS 
Climatology 
of North Sea 
Fronts 
2 Climate Change, Oc e a nie Fronts and 
theirpartic ularlmportanc e for KLIWAS: 
An Intro d uc tio n 
In our daily life we experience fronts as a directly sensible phenomenon by the 
passage of meteorological fronts which separates different air masses: The weather 
changes and we feel a change of wind speed and direction, temperature, precipitation 
and/or cloudiness. Comparable phenomena also exist in the ocean: Oceanic fronts are 
distinct boundaries between water bodies with different properties. They are 
associated with horizontal and vertical transports and have a great impact on local 
dynamics, ecology, marine economy and on the ocean’s uptake of CO2. Climate 
related changes in the North Sea will inevitably have an impact on the location of 
fronts and the strength of their gradients. These changes and their consequences have 
to be assessed within the marine part of KLIWAS. 
Due to a worldwide meteorological monitoring network running for many decades we 
are well informed about the dynamics and impacts of atmospheric fronts. However, 
our knowledge about oceanic fronts is still limited. Now, after more than two decades 
of satellite-borne remote sensing of the oceans, we have the possibility to compile a 
reliable climatology of frontal positions and gradients by analysing long time-series 
to set-up a reference data set as a basis for the assessment of possible changes in the 
oceans due to climate change. This climatology of North Sea fronts is a valuable 
addition to the new KLIWAS North Sea Climatology for oceanic and atmospheric in- 
situ data which was developed in a close co-operation of the Federal Maritime and 
Hydrographic Agency (BSH), the German Meteorological Service (DWD) and the 
Integrated Climate Data Center (ICDC) of the University Hamburg 1 . Both 
climatologies complement each other and provide together a solid set of reference 
data. 
Oceanic fronts are important dynamic meso-scale structures which have a significant 
impact on local dynamics, biology, ecology and - due to their ability to transport CO2 
into greater depths - also on climate. The coastal areas of the North Sea, especially 
the German, Dutch and UK coasts, are dominated by river plume fronts (RPF) with 
strong salinity and turbidity gradients between the fresh water run-off of the big 
continental rivers and the coastal North Sea waters. Roughly following the 30 m 
isobath, tidal mixing fronts (TMF) separate the seasonally (about end of March until 
September) thermal stratified parts of the deeper North Sea from the shallower coastal 
areas which are vertically mixed due to wind and tidal mixing. Other frontal 
structures are caused, e.g., by the intrusion of the brackish Baltic outflow into the 
1 http://icdc.zmaw.de/knsc.html