EX0924 Readme


Class of Data:  Surface ocean carbon dioxide concentrations

Dataset Identifer:  EX0924

Expocode: 33KF20090723

Statement of how to cite dataset:

     For information on dataset citation and more, please see Master Readme File.
     Explorer website: http://www.aoml.noaa.gov/ocd/gcc/explorer_introduction.php

Measurement platform identifier:  EX0924/Explorer

Data quality issues:

     Near the end of the cruise, it was suspected that the three-way valve that allows
     analyzed headspace to return to the equilibrator was faulty.  The analyzed 
     headspace was being vented; the removed headspace was made up with ambient
     air inside the wet box.  Around 12:00 on 31 July, the extra outside air exiting the 
     ballast (source gas for Nafion counterflow) was directed into a vented enclosure.
     The ambient gas being pulled into the equilibrators came from this enclosure.

     During this cruise the ship’s scientific infrastructure was being converted to full 
     automation.  Data was not collected during the early and late parts of the cruise 
     because of control software development issues.  Data was collected during the 
     southernmost transits using the control software’s earliest version.  The connections 
     to and configuration of auxiliary sensors (TSG, SST, etc.) were also being optimized.  
     These changes resulted in loss of data being logged by the pCO2 software program. 

     On 26 July between 15:16 and 16:42, there was no GPS position recorded.  Since 
     this gap occurred during a ship transit day, the positions were extrapolated from the 
     constant speed and direction between 13:54 and 14:17. 

     On 26 July between 13:15 and 22:21 the TSG, SST, and atmospheric pressure 
     sensors were not logged.  For this time interval, the default value of 35 was assigned 
     to salinity.  The difference between the equilibrator and SBE38 temperatures was 
     calculated for the 1190 analyses when both were logged (average= 0.17 +/- 0.25 C).  
     For the above time interval, the SST was estimated by subtracting 0.15 C from the 
     equilibrator temperature.

     The difference between the Licor and atmospheric pressures was calculated for the 
     1056 analyses when both were logged (average= 4.96 +/- 0.33 mbar).  When the 
     atmospheric pressure was not logged, it was estimated by subtracting 4.96 mbar 
     from the Licor pressure.  This estimation was done during the above time interval, 
     on 30 July between 17:17 and 19:61, and between 30 July 20:43 and 31 July 08:08.  

     There were single analyses that did not successfully record all the auxiliary sensors.
     These single drop-outs were interpolated from the neighboring data.  The frequency 
     of the drop-outs decreased significantly as the cruise progressed.
     
     Several times during the transits between islands, the air analyses were slightly 
     higher than expected.  Terrestrial influence of the atmospheric CO2 concentrations 
     was suspected, and the results are reported.

     The applied time offset between the SST and equilibrator temperature data is 0.3
     minutes.  The changes in temperature recorded by the SBE38 were recorded in
     the equilibrator 18 seconds later.

     The SST and salinity data are provided as a reference.  These data have not
     undergone rigorous quality control processes.

     Standard Gases and Reference Gas:  The three standard gases come from CMDL
     in Boulder and are directly traceable to the WMO scale.  The reference gas
     is a non-calibrated gas from a commercial company.  Any value outside the
     range of the standards (300 ppm, 360 ppm, and 420 ppm) should be considered
     approximate (5 ppm).  While individual data points above 450 or below 320 may
     not be accurate, the general trends should be indicative of the seawater
     chemistry.  The standards used on the cruise are:

           STANDARD          TANK #       CONCENTRATION       VENDOR
           STD1                                 0.00         Commercial
           STD2              CA02020          458.04           CMDL
           STD3              CA02040          319.82           CMDL                                               
           STD4              CA02030          377.14           CMDL                                               

     Units:  All xCO2 values are reported in parts per million (ppm) and fCO2
     values are reported in microatmospheres (uatm) assuming 100% humidity at the
     equilibrator temperature.

Contact person for this dataset:  

     Kevin Sullivan
     (305)361-4382
     Kevin.Sullivans@noaa.gov

Timestamp for dataset reduction:  8/10/2009

Timestamp for most recent update of dataset:  8/10/2009

Matlab version used for reduction: 1.05

Time period the dataset refers to:  7/23/2009 - 8/1/2009

Geographic area the dataset refers to:

     Day 1  - Bayonne, New Jersey (40.7 N/74.1 W)
     Day 3  - Kings Wharf, Bermuda (32.3 N/64.8 W)
     Day 5  - Philipsburg, St. Maarten (18.0 N/63.0 W)
     Day 6  - Charlotte Amalie, St. Thomas (18.3 N/64.9 W)
     Day 7  - San Juan, Puerto Rico (18.5 N/66.1 W)
     Day 10 - Bayonne, New Jersey (40.7 N/74.1 W)