Dataset: CTD
Deployment: EN198

   PI:              William Broenkow
   of:              Moss Landing Marine Laboratory (MLML)
   dataset:         CTD data with beam attenuation and fluorescence
   dates:           June 30, 1989 to July 06, 1989
   location:        N: 62.945  S: 59.2933  W: -24.205  E: -20.7967
   project/cruise:  North Atlantic Bloom Experiment/Endeavor 198
   ship:            R/V Endeavor
 

Methodology

CTD PROFILES - (Broenkow, MLML)

The MLML CTD/Rosette (Yarbrough et al., 1989) was used to make profiles of conductivity, temperature, dissolved oxygen, beam attenuation and in situ fluorescence. Conductivity was measured with a Sea-Bird conductivity cell and MLML pump, temperature with a platinum thermometer (tau = 0.3 sec) and pressure with a Digiquartz transducer. Data were digitized at 0.8 m intervals. Corrections were applied to temperature, salinity, and pressure using laboratory calibrations done before and after the cruise. Pressure corrections for the compressibility of the Sea-Bird cell were applied using the algorithm provided by Sea-Bird Electronics. Corrected data were compared with salinity and temperature field calibration data provided by the Scripps CTD group. Scripps corrected CTD data and ours show excellent agreement. Maximum salinity differences between the SIO and MLML profiles are about +/- 0.02 S.

Oxygen

The oxygen electrode data were obtained with a Beckman polarograph electrode modified at MLML to obtain near-membrane temperatures. The data have been corrected to oxygen concentrations by comparison with titrated calibration samples obtained during ATLANTIS II 119.5. Most of these calibration samples were analyzed by MLML personnel, and the RMS difference with Scripps titrations was 3 umole/kg. Oxygen concentrations were computed from oxygen reduction current via the WHOI algorithm (Owens and Millard, 1984) using near-membrane temperatures and in situ pressure. Corrections for membrane porosity changes may be large, and cynicism is advised when using these data.

Beam Attenuation

The MLML transmissometer is a modified Martek instrument based on the Scripps Visibility Laboratory design (Petzolf and Austin, 1968). Beam attenuation is measured through the folded 1 m path with a Wratten 45 (480 nm) filter and an IR blocking filter. Calibration is done in the laboratory by adjusting instrument gain to a transmission reading of 85.5% in dry air. Drift is estimated aboard ship before and after each cast by diligent cleaning of the windows using alcohol.

Fluorescence

The MLML profiling fluorometer uses Variosens electronics (Frungel and Koch, 1980) and produces log-scaled signals. Excitation is via a Xenon flash lamp and a broad band filter (350-550 nm half power). Fluorescence emission was detected by silicon diode through a 670 nm (half power) long pass filter. These raw data are converted to "rescaled fluorescence" units by comparison with extracted pigment analyses. We provided our own chlorophyll calibrations during ATLANTIS II 119.5 by fluorometric analysis of acetone extracts of water filtered through Whatman GF/F (0.7 micron) filters. The "rescaled fluorescence" units are numerically equivalent to chlorophyll-a concentrations in ug/liter. The term "rescaled fluorescence" is used to acknowledge the fact that fluorescence and chlorophyll concentrations may not covary because of variation in quantum yield. The RMS difference between "rescaled fluorescence" and extracted chlorophyll was 0.27 ug/liter.

Depth calculation for the CTD data files

The depth values in these CTD files have been calculated from pressure by the US JGOFS Data Management Office using the algorithm below. The latitude used in computation was the latitude recorded in the CTD data file. The CHECKVALUE was used to verify the accuracy of the computation. The stated accuracy of this algorithm is 0.1 meters. The calculated depths have been rounded to the nearest whole meter.

function DEPTH=depth(P,LAT); DEPTH Computes depth given the pressure at some latitude D=DEPTH(P,LAT) gives the depth D (m) for a pressure P (dbars) at some latitude LAT (degrees). Fofonoff and Millard (1982). UNESCO Tech Paper #44. Notes: (ETP3, MBARI) This algorithm was originally compiled by RP @ WHOI. It was copied from the UNESCO technical report. The algorithm was endorsed by SCOR Working Group 51. The equations were originally developed by Saunders and Fofonoff (1976). DSR 23: 109-111. The parameters were re-fit for the 1980 equation of state for seawater (EOS80). CHECKVALUE: D=9712.653 M FOR P=10000 DECIBARS, LAT=30 DEG CALCULATON ASSUMES STD OCEAN: T = 0 DEG C; S = 35 (IPSS-78) X = sin(LAT/57.29578); X' = X*X; GR = GRAVITY VARIATION WITH LAT: ANON (1970) BULLETIN GEODESIQUE GR = 9.780318*(1.0+(5.2788E-3+2.36E-5*X')*X') + 1.092E-6*P D = DEPTH BEFORE GRAVITY CORRECTION D = (((-1.82E-15*P+2.279E-10)*P-2.2512E-5)*P+9.72659)*P DEPTH = D/GR

   PI:              William Broenkow
   of:              Moss Landing Marine Laboratory (MLML)
   dataset:         CTD data with beam attenuation and fluorescence
   dates:           June 30, 1989 to July 06, 1989
   location:        N: 62.945  S: 59.2933  W: -24.205  E: -20.7967
   project/cruise:  North Atlantic Bloom Experiment/Endeavor 198
   ship:            R/V Endeavor
 
Methodology
 CTD PROFILES - (Broenkow, MLML)
  The MLML CTD/Rosette (Yarbrough et al., 1989) was used to make profiles of conductivity, 
  temperature, dissolved oxygen, beam attenuation and in situ fluorescence. Conductivity 
  was measured with a Sea-Bird conductivity cell and MLML pump, temperature with 
  a platinum thermometer (tau = 0.3 sec) and pressure with a Digiquartz transducer. 
  Data were digitized at 0.8 m intervals. Corrections were applied to temperature, 
  salinity, and pressure using laboratory calibrations done before and after the 
  cruise. Pressure corrections for the compressibility of the Sea-Bird cell were 
  applied using the algorithm provided by Sea-Bird Electronics. Corrected data 
  were compared with salinity and temperature field calibration data provided 
  by the Scripps CTD group. Scripps corrected CTD data and ours show excellent 
  agreement. Maximum salinity differences between the SIO and MLML profiles are 
  about +/- 0.02 S. 
  
Oxygen
  The oxygen electrode data were obtained with a Beckman polarograph electrode 
  modified at MLML to obtain near-membrane temperatures. The data have been corrected 
  to oxygen concentrations by comparison with titrated calibration samples obtained 
  during ATLANTIS II 119.5. Most of these calibration samples were analyzed by 
  MLML personnel, and the RMS difference with Scripps titrations was 3 umole/kg. 
  Oxygen concentrations were computed from oxygen reduction current via the WHOI 
  algorithm (Owens and Millard, 1984) using near-membrane temperatures and in 
  situ pressure. Corrections for membrane porosity changes may be large, and cynicism 
  is advised when using these data. 
  
Beam Attenuation
  The MLML transmissometer is a modified Martek instrument based on the Scripps 
  Visibility Laboratory design (Petzolf and Austin, 1968). Beam attenuation is 
  measured through the folded 1 m path with a Wratten 45 (480 nm) filter and an 
  IR blocking filter. Calibration is done in the laboratory by adjusting instrument 
  gain to a transmission reading of 85.5% in dry air. Drift is estimated aboard 
  ship before and after each cast by diligent cleaning of the windows using alcohol. 
  
Fluorescence
  The MLML profiling fluorometer uses Variosens electronics (Frungel and Koch, 
  1980) and produces log-scaled signals. Excitation is via a Xenon flash lamp 
  and a broad band filter (350-550 nm half power). Fluorescence emission was detected 
  by silicon diode through a 670 nm (half power) long pass filter. These raw data 
  are converted to "rescaled fluorescence" units by comparison with extracted 
  pigment analyses. We provided our own chlorophyll calibrations during ATLANTIS 
  II 119.5 by fluorometric analysis of acetone extracts of water filtered through 
  Whatman GF/F (0.7 micron) filters. The "rescaled fluorescence" units are numerically 
  equivalent to chlorophyll-a concentrations in ug/liter. The term "rescaled fluorescence" 
  is used to acknowledge the fact that fluorescence and chlorophyll concentrations 
  may not covary because of variation in quantum yield. The RMS difference between 
  "rescaled fluorescence" and extracted chlorophyll was 0.27 ug/liter.
 

Depth calculation for the CTD data files

   The depth values in these CTD files have been calculated from
pressure by the US JGOFS Data Management Office using the algorithm
below.  The latitude used in computation was the latitude recorded 
in the CTD data file.  The CHECKVALUE was used to verify the 
accuracy of the computation.  The stated accuracy of this algorithm 
is 0.1 meters.  The calculated depths have been rounded to the 
nearest whole meter.



 function DEPTH=depth(P,LAT);

  DEPTH   Computes depth given the pressure at some latitude
          D=DEPTH(P,LAT) gives the depth D (m) for a pressure P
              (dbars) at some latitude LAT (degrees).

          Fofonoff and Millard (1982). UNESCO Tech Paper #44.

  Notes:  (ETP3, MBARI)
          This algorithm was originally compiled by RP @ WHOI.
          It was copied from the UNESCO technical report.
          The algorithm was endorsed by SCOR Working Group 51.
          The equations were originally developed by Saunders
              and Fofonoff (1976).  DSR 23: 109-111.
          The parameters were re-fit for the 1980 equation of
              state for seawater (EOS80).

  CHECKVALUE: D=9712.653 M FOR P=10000 DECIBARS, LAT=30 DEG

  CALCULATON ASSUMES STD OCEAN: T = 0 DEG C; S = 35 (IPSS-78)


  X = sin(LAT/57.29578);
  X' = X*X;


  GR = GRAVITY VARIATION WITH LAT: ANON (1970) BULLETIN GEODESIQUE

  GR = 9.780318*(1.0+(5.2788E-3+2.36E-5*X')*X') + 1.092E-6*P


  D = DEPTH BEFORE GRAVITY CORRECTION

  D = (((-1.82E-15*P+2.279E-10)*P-2.2512E-5)*P+9.72659)*P

  DEPTH = D/GR