12

speed  cm/s  speed  cm/s  speed  cm/s

column  with  an  estimated  volume  transport  of  6xl0 5  m 3 /s  between  3°  30’  E  and  4°  30’  E  (see  Figs.  2  and  3).
At  M9,  the  deepest  station  in  the  trench,  there  is  an  outflow  of  about  2xl0 5  mVs  below  a  depth  of  300  m  and
an  inflow  of  about  4xl0 5  m 3 /s  above  150  m  depth.  At  M7  there  is  a  northwestward  outflow  below  200  m
and  a  westward  outflow  in  the  upper  150  m.  Regarding  the  general  circulation  pattern  as  outlined  in  figure  1
and  the  inflow  at  M8  and  at  M9  in  the  upper  150  metres,  we  would  have  expected  an  inflow  of  AW  at  M7
at  least  in  the  upper  100  metres.  However,  there  is  an  outflow  from  September  7  to  September  29.  Thereafter
the  current  rotates  slowly  anticyclonically,  reaching  its  initial  (outflow!)  direction  on  October  12.  With  the
exception  of  the  first  few  days  the  distinct  directional  tidal  signal  is  suppressed  and  the  (scalar)  velocity  is
enhanced  (see  Fig.  4b).  This  pattern  can  be  observed  in  all  sampling  depths  at  M7.  For  comparison.  Figure
4  shows  the  unfiltered  time  series  of  M8,  M7,  and  M9  in  286  m,  288  m,  and  300  m  depths,  respectively.  Evident ­
  are  the  directional  stability  at  M8  at  the  western  slope  of  the  trench  (Fig.4c)  and  the  great  directional
variability  at  M9,  close  to  the  center  of  the  broad  opening  of  the  Norwegian  Trench  (Fig.4a).  Here  the  time
series  shows  a  steady  succession  of  eddy  structures,  rotating  both  cyclonically  and  anticyclonically.  These
current  structures  represent  a  signal  which  is  evident  in  all  depth  levels.  Especially  in  240  m  depth  the  lowpassed
  current  is  extremly  variable  with  a  stability  factor  of  only  9%  and  negligible  volume  transport  (see
Table  3).

1986  1986  1986
Fig.  4  Time  series  of  current  speed  and  direction  (unfiltered  data):
a)  M9,  300  m  sampling  depth,
b)  M7,  288  m  sampling  depth,
c)  M8,  286  m  sampling  depth.
The  M6  mooring  was  positioned  about  60.5°  N  at  the  western  edge  of  the  Norwegian  Trench.  There  is
an  inflow  of  AW  down  to  a  depth  of  about  250  m,  but  close  to  the  bottom  we  observe  an  outflow  like  that
at  M9.  In  general,  the  stability  factor  is  less  than  32%.

3  Tidal  Streams  and  Tides
3.1  Relating  Tidal  Streams  to  Aberdeen  as  the  Port  of  Reference
The  previous  part  mainly  dealt  with  low-passed  current  meter  data.  Residual  currents  are  shown  to  visualize ­
  the  general  in-  and  outflow  pattern  and  the  respective  volume  transports  are  estimated.  This  part  focusses ­
  on  tidal  streams  and  elevations.  Firstly,  we  give  a  more  qualitative  description  of  the  tidal  streams
and  the  variation  of  tidal  stream  figures  along  our  sections.  In  a  more  quantitative  approach  we  determine
up  to  17  tidal  constituents  by  means  of  harmonic  analysis.  Our  analysis  of  observed  tidal  elevations  will  be
compared  to  model  results.

direction  deg  direction  deg  direction  deg