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Sy,  A.  et  al.  (2002):  Upper  Ocean  Climate  Ship-of-Opportunity  Programme  of  BSH  -  A  Status  Report

The  AX-11  time  series  from  the  upper  750  m  of  the  subtropical  and  tropical  Atlantic  indicate  a
gradual  warming  from  1991  to  2000  (Figs.  18  bottom,  19).  This  coincides  with  conclusions  by
Yang  (1999)  who  found  a  significant  correlation  between  observed  LSW  thickness  and  the
equatorial  SST  dipole,  with  a  time  lag  of  5  years,  and  suggested  a  dynamic  linkage  between
these  two  features.  The  long  period  of  gradual  warming  which  matches  the  lagged  last  period  of
intensified  LSW  formation  (Sy  et  al.,  1997)  gives  rise  to  the  speculative  question  whether,  and
how,  changes  in  LSW  production  affect  the  northward  flow  in  the  upper  ocean.
In  order  to  take  a  step  forward  and  overcome  the  limited  analysis  of  our  single  SOOP  lines  AX-3
and  AX-11  towards  a  reconstruction  of  the  North  Atlantic  circulation,  we  extended  the  data  base
by  including  additional  XBT  data  from  lines  AX-2,  AX-4,  AX-7,  AX-10,  AX-20,  AX-29  and  AX-32
which  are  to  be  combined  with  a  dynamical  model  developed  in  the  framework  of  CLIVAR  at
AWI,  Bremerhaven,  Germany.  Model  and  measurements  will  be  combined  by  applying  a
variational  assimilation  technique,  also  known  as  the  adjoint  method.  For  further  information  see
www.awi-bremerhaven.de.
The  locations  of  these  lines  together  with  the  10-year  mean  field  of  heat  content  of  the  upper
750  m  is  shown  in  Fig.  20.  In  Fig.  21  the  corresponding  annual  time  series  of  mean  heat  content
anomalies  are  displayed.  Compared  to  the  mean,  the  upper  North  Atlantic  Ocean  was
significantly  colder  from  1993  to  1995  and  warmer  from  1997  to  1999.  No  clear  correlations
between  patterns  can  be  found  which  could  be  indicative  of  the  existence  of  propagation  paths
of  anomalies  of  the  upper  ocean  temperature  field.

3.3  Future  plans
Although  the  SOOP  has  been  extremely  cost-effective  in  scientific  use  and  operational
applications,  it  has  been  argued  that  it  is  time  for  a  change  of  direction  and  a  new  focus.  A  plan
for  a  new  world  wide  network  of  some  3,000  autonomous  profiling  floats  was  developed  in  the
late  90s  (ARGO,  1998),  which  may  affect  the  classical  XBT  network  (Smith  et  al.,  2000).  This
Array  for  Real-time  Geostrophic  Oceanography  (ARGO)  is  now  being  implemented.
Autonomous  profiling  float  technology  is  a  novel  and  very  effective  tool  in  sampling  of  the  upper
ocean  climate  variability,  especially  when  combined  with  an  appropriate  XBT/XCTD  SOOP
network.  Therefore,  an  ARGO  proposal  for  the  A-2  corridor  has  been  drafted  by  BSH  in
conjunction  with  proposals  by  Institut  für  Meereskunde,  Kiel,  and  Alfred  Wegener  Institute  for
Polar  and  Marine  Research,  Bremerhaven,  and  submitted  to  the  German  Ministry  of  Education
and  Research  (BMBF)  in  October  2002.
The  main  objectives  of  BSH’s  ARGO  proposal  are
the  investigation  of  baroclinic  variability  in  time  and  space  in  the  transition  zone  between
subtropical  and  subpolar  gyres,
improvement  of  a  T/S  climatology,
evaluation  of  this  ARGO  contribution  as  a  tool  for  ocean  climate  monitoring  and,  in  this
context,
evaluation  and  optimisation  of  the  AX-3  SOOP.