KLIWAS

Seite  11

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  foodweb
  (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