GU0802-Leg 1 SEAMAP Readme

Class of Data:  Surface ocean carbon dioxide concentrations

Dataset Identifer:  GU0802 Leg1 SEAMAP

Expocode: 33GG20080419

Statement of how to cite dataset:

     Gordon Gunter website: http://www.aoml.noaa.gov/ocd/gcc/rvgunter_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 Gordon Gunter web pages.
 
Measurement platform identifier:  R/V Gordon Gunter

Data quality issues:

     The data reduction for this dataset was done using pCO2 Sys v1.0.

     The LICOR had a faulty Pressure transducer so the Peq has been estimated from the
     Peq-Patm difference during the GU0802_Leg2 (JDay 136-150) cruise. The average
     difference was Peq-Patm= -1.26 ± 0.33 mbar calculated on ~11000 samples. That
     difference was applied to the Atmospheric Pressure (atm press). On 9 occasions
     when ‘atm press’ was zero, it was linearly interpolated between previous and
     following pressures. These estimated pressures are good to within 0.1 mbar.
     It was done because a few of the missing pressures were for standards, which in
     turn affected a lot of seawater measurements if that standard value was missing.
     One of the standard tanks used to regularly calibrate the LICOR was not turned
     on for the first couple of days, which made the LICOR return unreasonable mole
     fractions (xCO2).  These values have been recalculated using the calibration
     coefficients of the analyzer. xCO2 values up to April 23rd, 2008 at 13:00 have
     been re-calculated. The other values are the measured ones output by the LICOR.
     The difference between re-calculated values and the ones output by the LICOR
     is that the re-calculated ones do not have Zero and Span applied to them.
      

     Standard Gases and Reference Gas:  The three standard gases come from Scott-Marrin, Inc.,
     and are calibrated with primary standards that are directly traceable to the WMO scale.  
     The zero gas is a non-calibrated ultra-high purity gas from a commercial company.  Any 
     value outside the range of the standards should be considered approximate (5 ppm).
     While individual data points above 450 or below 245 may be less 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              ja 2280          248.73       Scott-Marrin, Inc.
           STD3              ja 2292          372.88       Scott-Marrin, Inc.  
           STD4              ja 2261          450.59       Scott-Marrin, Inc.                 

                                       
                                      
     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.

Ship Information:

     NOAA Research Vessel Gordon Gunter website:  http://www.moc.noaa.gov/gu/index.html

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:  09/20/08

Timestamp for most recent update of dataset:  10/25/08

Time period the dataset refers to:  4/19/2008 - 5/08/2008

Geographic area the dataset refers to:

     Gulf of Mexico