Xue Long Readme

Class of Data:  Surface ocean carbon dioxide concentrations

Dataset Identifer:  Xue_Arctic_08

Statement of how to cite dataset:

     Xue Long website: http://www.aoml.noaa.gov/ocd/gcc/xuelong_introduction.php

     For more information on dataset citation and for a full description of the  
     instrumentation and procedures, see the Master Readme file accessible
     thru the Master Readme link located in the left navigation bar of the
     R/V Xue Long web pages.
 

Measurement platform identifier:  R/V Xue Long

Data quality issues:

     The data was reduced using the Matlab program pCO2 Sys v1.05.

     Data reduced using equilibrator temperature for in-situ temperature.

     Assigned GPS JDay to JDay in the data reduction.
                                         
     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.

     Any value outside the range of the standards should be considered 
     approximate (+/- 5 ppm).  While individual data points above 546 or below 
     244 ppm may not be accurate, the general trends should be indicative
     of the seawater chemistry.

     10/9/08:

     Calculated JDay from XUE and GPS Time and dates -->
     XUE_GPS(730-912).txt.

     Combined all raw pCO2 data and merged GPS data with it -->
     XUE_Arctic08_pCO2_gps-merged.txt.

     Deleted all "::" (see 'gps time' column) and replaced all
     empty cells by -9 then saved in csv format (loaded fine in
     version 1.03)-->XUE_Arctic08_pCO2_gps-merged-Clean.csv.

     4/3/09:

     XUE_Arctic08_pCO2_gps-merged-Clean.csv was the input file
     for the data reduction.

     No atmospheric pressure after JD 223.  Before JD 223 the
     atmospheric pressure agreed very well with the equilibrator
     pressure.  Equil Pressure has been used as atmospheric pressure.

     Right before JD 230, salinity dipped down close to zero and
     xCO2 went up to 2000.  Flagged this area as 4.

     Region around JD 245, interpolated the low salinities.

     12/3/09

     Updated data file:
 
     1. Using CTD data from the cruise provided by W.J. Cai of UGA, 
     a relationship was established between equilibrator temperature 
     (Teq) and surface temperature values from the CTD at station.  
     The Teq points were averaged at each station.  Based on agreement 
     and SST and SSS variations at the stations, data from 32 stations 
     were used from which we obtained a relationship SST = -1.0891 + 
     1.0326 * Teq with a r^2 of 0.98 and an uncertainty in the calculated 
     SST of 0.3 C.  The Teq for each data point was then used with this 
     relationship to determine the SST.  The fCO2_SW@SST and ÆfCO2 were 
     recalculated from the relationship:

          fCO2_SW@SST  = fCO2_EQ@Teq * EXP (-0.0423* (Teq-SST))

     2. Quality control flags were adjusted in the following manner.
     For samples outside the standard range the quality control flags 
     were changed from 3 to 2 while keeping the subflag. We believe 
     that the uncertainty introduced by extrapolations between 0 and 
     the low standard of 244 ppm is less then 1 ppm and does not unduly 
     impact the results.  Several samples that clearly were bad but 
     had a flag of 3. These were changed to a flag of 4.


Scientists responsible for technical quality of this dataset:

     Rik Wanninkhof
     (305)361-4379
     Rik.Wanninkhof@noaa.gov 

     Denis Pierrot
     (305)361-4441
     Denis.Pierrot@noaa.gov

Timestamp for dataset reduction:  05/08/09

Timestamp for most recent update of dataset:  12/03/09

Time period the dataset refers to:  7/30/2008 - 9/11/2008