*** Documentation for the CTD data collected on RRS John Biscoe Cruise  06                                                          
(Dec  1985 - Feb 1986) by the British Antarctic Survey,  Cambridge,  U.K.,                                                          
under the direction of R.B. Heywood ***                                                                                             
                                                                                                                                    
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      *  WARNING: Salinity data are highly suspect, see note below  *                                                               
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DATA COLLECTION                                                                                                                     
The   instrument  used was a Neil Brown Instruments System Mark IIIB  CTD.                                                          
Observed  parameters  were  pressure, temperature  and  conductivity.  All                                                          
sensors  were  calibrated before and after the cruise.   Up  to  12  water                                                          
bottles  were  mounted  on  a Rosette sampler and  4  pairs  of  reversing                                                          
thermometers were attached.   Water bottles were triggered on the downcast                                                          
at  10m and at the bottom of the cast,  the remainder being fired  on  the                                                          
upcast  (mainly  for  chemical  samples).   Data  were  collected  on  the                                                          
downcast.                                                                                                                           
                                                                                                                                    
CALIBRATION                                                                                                                         
Reversing  thermometers  were calibrated at the Deacon Laboratory  of  the                                                          
Institute  of Oceanographic Sciences.   The pressure sensor  was  compared                                                          
with  a Bourdon gauge which had been calibrated at the  National  Physical                                                          
Laboratory.  The  accuracy  of  the temperature  data  is  thought  to  be                                                          
+/-0.01degC.                                                                                                                        
                                                                                                                                    
DATA PROCESSING                                                                                                                     
Calibrations  were applied and the data despiked by rejecting data  values                                                          
outside  of predetermined tolerances.  Data values were then  averaged  to                                                          
provide data at 1 decibar intervals.                                                                                                
                                                                                                                                    
** WARNING **                                                                                                                       
The  data  are derived from instruments which were  laboratory  calibrated                                                          
(for  pressure  and temperature anyway), but not  finally  adjusted  using                                                          
reversing thermometers or salinity derived from in situ samples.  The data                                                          
required  for  this final adjustment are either missing or of too  poor  a                                                          
quality for calibration. Therefore these CTD data are of varying quality -                                                          
the  temperature  data are reasonable,  but the salinity data  are  HIGHLY                                                          
SUSPECT and should not be used for detailed physical studies. The salinity                                                          
data  are  probably  just  about good enough for  setting  the  scene  for                                                          
biological  studies  since they can be used to show  relative  changes  in                                                          
space  or  time  but are not accurate enough  to  show  absolute  salinity                                                          
levels.                                                                                                                             
                                                                                                                                    
Note  that  it was not possible to recover and reprocess all of  the  data                                                          
collected  on  this cruise to produce 1 decibar values.  For  those  casts                                                          
which were not reprocessed an earlier version of the data is held by BODC.                                                          
Few  processing details are available for these casts.  Calibrations  were                                                          
applied  and  the  data  despiked by  rejecting  data  values  outside  of                                                          
predetermined  tolerances.   Derived   quantities  were   computed    from                                                          
algorithms  published   by  Fofonoff  and Millard (1983).  The  data  were                                                          
averaged to provide values at the following depths:  5m,  10m,  15m,  20m,                                                          
25m, 30m, 35m, 40m, 45m, 50m, 55m, 60m, 65m, 70m, 75m, 80m, 85m, 90m, 95m,                                                          
100m,  110m, 120m, 130m, 140m, 150m, 160m, 170m, 180m, 190m,  200m,  250m,                                                          
260m,  280m, 300m, 325m, 350m, 375m, 400m, 425m, 450m, 500m,  600m,  700m,                                                          
800m, 900m, 1000m, 1200m, 1500m, 2000m.                                                                                             
                                                                                                                                    
Salinities  from  the  bottle  samples  were  determined  at  the  British                                                          
Antarctic Survey using a Guildline Salinometer. Some time after these data                                                          
were  supplied to BODC the salinometer was found to be faulty which  casts                                                          
doubt on the accuracy of the salinity values. The CTD casts to which these                                                          
comments apply are as follows:                                                                                                      
                                                                                                                                    
BODC Series Reference No.      Originator's Reference                                                                               
                                                                                                                                    
      76287                    JB06/0068                                                                                            
      76447                    JB06/0253                                                                                            
      76459                    JB06/0458                                                                                            
      76460                    JB06/0460                                                                                            
      76484                    JB06/0463                                                                                            
      76496                    JB06/0471                                                                                            
      76503                    JB06/0517                                                                                            
      76527                    JB06/0523                                                                                            
      76539                    JB06/0526                                                                                            
      76540                    JB06/0528                                                                                            
      76552                    JB06/0529                                                                                            
      76564                    JB06/0530                                                                                            
      76576                    JB06/0531                                                                                            
                                                                                                                                    
The  deep water salinity data from the CTD have been compared  with  other                                                          
measurements made in this region and also with the Levitus Atlas. The data                                                          
which  have not been reprocessed are in agreement with data  collected  on                                                          
various cruises including Discovery II (1929-31) and within about 0.02 ppt                                                          
of the Levitus Atlas salinities.  The reprocessed salinity data are  about                                                          
0.04 ppt higher than the data which has not been reprocessed.                                                                       
                                                                                                                                    
References:                                                                                                                         
Fofonoff,  N.P.  and Millard Jr., R.C. 1983 Algorithms for the computation                                                          
of  fundamental  properties  of  sea water.  UNESCO Technical   Paper   on                                                          
Marine Science 44                                                                                                                   
                                                                                                                                    
Levitus,  S.  1982  Climatological Atlas of the  World  Ocean.  NOAA  Pro-                                                          
fessional Paper No. 13. US Government Printing Office. 173pp                                                                        
