AOML's Ocean Chemistry and Ecosystems Division

INTRODUCTION:
 
The information presented in this file is applicable to all the data sets collected 
on the Explorer that are presented at:

   www.aoml.noaa.gov/ocd/ocdweb/explorer/explorer_introduction.html.

Any temporary changes in this information will be noted in the readme files for 
the individual expeditions.

Statement for use of data:

These data are made available to the public and the scientific community in the belief 
that their wide dissemination will lead to greater understanding and new insights. The 
availability of these data does not constitute publication of the data. We rely on the 
ethics and integrity of the user to insure that the AOML ocean carbon group receives 
fair credit for its work. Please consult with us prior to use so we can insure that the 
quality and limitations of the data are accurately represented.

Platform Information:

In February 2002, the Ocean Carbon Cycle (OCC) group at AOML installed an instrument to 
measure CO2 in surface water in the dedicated ocean laboratory on the RCI ship, Explorer 
of the Seas.  Over the next four years, the ship alternately cruised through the eastern 
and western Caribbean Sea.  Starting in May 2006, the ship's home port alternated between 
Miami, FL, and Bayonne, NJ.   The cruise destinations started including Bermuda and 
occasionally the northeast coast of the USA and Canada.   By the end of 2007, Bayonne had 
become the ship's permanent home port.  During 2008, the science operations were transitioned 
to fully automated and unattended systems.   A new instrumental system from General Oceanics 
was installed in the ship's bow thruster space in June 2008.  The new location was closer to 
the seawater intake and other oceanographic instruments.  It has also allowed the installation 
of an air inlet tube so that atmospheric CO2 measurements can be done in conjunction with 
surface water CO2 observations.

Vessel Name: Explorer of the Seas

Class of Data:  Surface ocean carbon dioxide concentrations

Scientists responsible for the technical quality of this pCO2 dataset:

  Rik Wanninkhof and Denis Pierrot
  NOAA/AOML/Ocean Chemistry and Ecosystems Division
  4301 Rickenbacker Causeway
  Miami, FL 33149
     Rik.Wanninkhof@noaa.gov
     Denis.Pierrot@noaa.gov

Contact persons for this dataset:

  Kevin Sullivan and Betty Huss
  NOAA/AOML/Ocean Chemistry and Ecosystems Division
  4301 Rickenbacker Causeway
  Miami,  FL 33149
     Kevin.Sullivan@noaa.gov
     Betty.Huss@noaa.gov


COMPONENT SPECIFICATIONS and ACCURACIES:

The accuracies of all components, when operating optimally, are such that the calculated 
seawater fCO2 has an accuracy of 2 uatm or better and the calculated mole fraction of 
CO2 (XCO2) in air has an accuracy of 0.1 uatm.

Infrared Analyzer:
	  
   LI-COR model 6252 (February 2002 - March 2008)
      Licor_6252_Manual.pdf
      CO2 resolution: 0.01 umol/m
      CO2 accuracy: ±1ppm at 350 ppm
      Pressure resolution: 0.02 hPa
      Internal pressure transducer accuracy: ±1.2 hPa  (1.2 hPa = 1.2 mbar)
      (manufacturer specifications: ±0.1% FS, where FS = 0-1150 hPa) 

   LI-COR model 7000 (August 2008 - 19 November, 2010)
      Licor_7000_Manual.pdf     
      CO2 resolution: 0.01 umol/m
      CO2 accuracy: ±1% nominal
      Pressure resolution: 0.02 hPa
      Internal pressure transducer accuracy: ±1.2 hPa 
      (manufacturer specifications: ±0.1% FS, where FS = 0-1150 hPa) 

   LI-COR model 6262 (19 November, 2010 - present)
      Licor_6262_Manual.pdf
      CO2 resolution: 0.01 umol/m
      CO2 accuracy: ±1 ppm at 350 ppm
 
   Setra model 270  (19 November, 2010 - present)
      http://www.setra.com/ProductDetails/270_Baro.htm        
      Resolution: 0.015 hPa 
      Accuracy: ±0.15 hPa 

For the first two LI-COR analyzers installed with the instrumental systems, the 
internal pressure transducers were used for processing the internal raw signal.  
The LI-COR 6262 used an external Setra 270 pressure transducer for processing its 
internal raw signal. 

	  
Equilibrator Pressure:
   Setra model 270, (February 2002 - March 2008)
      http://www.setra.com/ProductDetails/270_Baro.htm        
     Resolution: 0.015 hPa 
     Accuracy: ±0.15 hPa 
     (manufacturer specifications: ±0.05% FS, where FS = 80-110 kPa)

   Setra model 239, differential pressure (August 2008 - present)
      http://www.setra.com/ProductDetails/model_239.htm           
     Resolution: 0.01 hPa
     Accuracy: ±0.052 hPa 
     (manufacturer specifications: ±0.14% FS, where FS = ± 7.5 inches WC)

From 2002 until May 2008, the main equilibrator was vented to the Ocean Laboratory 
space.  The pressure of the laboratory space was measured with a Setra 270 sensor, 
which was taken as the headspace pressure in the equilibrator.  Since May 2008, the 
instrumental system in the bow thruster compartment included a differential pressure 
sensor (Setra 239) attached to the equilibrator and vented to the bow thruster space.  
The absolute pressure of the equilibrator headspace reported in data files is the sum 
of the Setra 239 differential pressure and the absolute pressure measured at the 
analyzer exit under stopped flow condition.
  

Equilibrator Temperature:	  
   Hart model 1560 (February 2002 - March 2008)
      http://www.instrumart.com/assets/1560_manual.pdf 	          
      with Thermometrics AS125 thermister
      http://www.ge-mcs.com/download/temperature/sases.pdf 	          
      Resolution: 0.0001°C 
      Accuracy: ±0.0013°C
			
   The Hart1560 was used to annually calibrate the 1000 ohm thermistor.  Based on 
   reproducibility of the annual calibrations, the equilibrator water temperatures 
   were believed accurate to ± 0.02 °C.

   Hart model 1521 (August 2008 - present)
      http://www.testequipmentdepot.com/hart/pdfs/1521_1522.pdf  	          
         Resolution: 0.001°C
         Accuracy: ±0.025°C


Sea Surface Salinity and Temperature (maintained by ship):
   SeaBird model SBE-21 (February 2002 - March 2008)
     http://www.seabird.com/pdf_documents/manuals/21_026.pdf   
     Temperature resolution: 0.001°C 
     Temperature accuracy: ±0.01°C
     Salinity resolution: 0.002‰
     Salinity accuracy: ±0.05‰

   SeaBird model SBE-45 (August 2008 - present)
      http://www.seabird.com/pdf_documents/manuals/45_017.pdf  
      Temperature resolution: 0.0001°C 
      Temperature accuracy: ±0.002°C
      Salinity resolution: 0.0002‰
      Salinity accuracy: ±0.005‰

   SeaBird model SBE-38 (August 2008 - present)
     http://www.seabird.com/pdf_documents/manuals/38_013.pdf   
     Temperature resolution: 0.00025°C 
     Temperature accuracy: ±0.001°C

Atmospheric Pressure (maintained by ship):
   RMYoung barometer (February 2002 - present)
     http://www.youngusa.com/products/3/22.html      
     Resolution: 0.1 hPa
     Accuracy: ±0.2 hPa


INSTRUMENT DESCRIPTION and CONFIGURATION:

The general principle of instrumental design can be found in Wanninkhof and Thoning 
(1993), Ho et al. (1995), and Feely et al. (1998) and Pierrot et al. (2009).  The 
concentration of CO2 in the headspace gas was measured using the adsorption of infrared 
(IR) radiation by the CO2 molecule.  The LI-COR® analyzer passed IR radiation through 
two cells.  The reference cell was constantly flushed with a gas of known concentration.
During the first configuration of the instrumental system (February 2002 - March 2008), 
the reference gas contained CO2 with concentration close to outside air.  During the 
second configuration (August 2008 - present), the reference gas was CO2-free air.  
The sample cell was flushed with the gas of interest (standard, outside atmosphere, 
or headspace gas from equilibration chamber).  A vacuum-sealed, heated filament was 
the broadband IR source.  The IR radiation alternated between the two cells via a 
chopping shutter disc spinning at 500 Hertz.  An optical filter selected an adsorption 
band specific for CO2 (4.26 micron) to reach the detector.  The solid state (lead 
selenide) detector was kept at -5 degrees C for excellent stability and low signal 
noise (less than 0.2 ppm),

The effects of water vapor on the sample analyses were kept to a minimum by removing 
as much water as possible.  The water was first condensed out of the sample gas stream 
by cooling to approximately 6 degrees C using a thermoelectric device.  Then water was 
further removed using Nafion® gas dryers before reaching the IR analyzer.  The 
counterflow gas in the dryer during the first system configuration was the reference 
gas.   During the second configuration, the counterflow gas was pre-dried outside air.  
Typical water content of the analyzed gas was less than 3 millimoles/mole with 
approximately 90% of the water being removed.

The infrared analyzer was calibrated regularly using three standard gases (200 - 550 ppm)
from the ESRL laboratory in Boulder, CO, which are directly traceable to the WMO scale.
Any value outside the range of the standards should be considered approximate (+/-5 ppm).
While individual data points above the highest standard or below the lowest standard may 
be less accurate, the general trends would be indicative of the seawater chemistry.  
The exact concentrations of the standards used on a particular cruise are listed in 
the individual readme file.

With its reconfiguration in 2008, the capacity of the instrumental system to measure CO2 
in atmospheric air was added.  Outside air was constantly being pulled (6 liters/min maximum) 
from an inlet on the bow mast through approximately 62 meters of tubing (1 cm OD Dekoron) 
to the analytical system.  The flushing rate of the LI-COR analyzer during ATM analyses 
was 60 - 150 ml/min

The dedicated scientific seawater inlet is just above the bow thruster tunnel at an 
approximate depth of 5 meter.  The scientific seawater was pushed through a spray head 
into an equilibration chamber that was fabricated using a filter housing (ColeParmer, 
U-010509-00).  The chamber had a 0.5 L water reservoir and a 0.7 L gaseous headspace.  
Water flow rate was 1.3 - 2.5 L/min.  The rate that the headspace gas was recirculated 
through the analyzer during EQU analyses was 60 - 150 ml/min. 

During the first configuration, the water temperature in the equilibrator was measured
with a 20 cm long, 1000 Ohm thermistor whose tip was submerged about 5 cm.  The 
thermistor was calibrated annually against a Hart Scientific 1560 Black Stack module 
with platinum resistance NIST traceable thermistor.  Based on reproducibility of the 
annual calibrations, the temperatures were believed accurate to ± 0.02°C.  During the 
second configuration, the water temperature was measured with a Hart 1521 thermometer.

The equilibration chamber was vented to the surrounding space.  During the first 
configuration, the barometric pressure was measured in the lab next to the equilibrator 
using a Setra model 270 barometer.  This pressure was used as the equilibrator pressure.  
During the second configuration, the pressure in the equilibrator relative to the bow 
thruster compartment was measured with a Setra model 239 differential barometer.  The 
LI-COR® barometer measured the barometric pressure of the compartment, and the 
sum of the outputs of the two sensors was used as the equilibrator pressure.

The first instrumental system ran an hourly cycle comprised of the three standard gases
(STD), the reference gas, and twenty equilibrator headspace (EQU) gas analyses.  The 
infrared analyzer was flushed with the chosen gas at 50 - 80 ml/min for least 2.3 
minutes before the flow was stopped.  aer waiting 10 seconds for the analyzer to 
reach ambient pressure, the raw data was recorded.  This data included the infrared 
analyzer, the numerous sensors internal to the CO2 instrumental systems, and the 
ship's sensors chosen for inclusion in the data feed to the instrumental system.  
The timing of the hourly cycle was based on the computer time internal to the 
instrumental system.  The processed data is associated and posted with the UTC 
time logged from the ship's GPS.

The second instrumental system ran a sequence comprised of the three STD gases, five 
ATM analyses, and then at least fifty-five EQU analyses.  When data acquisition was
initiated, the zero and span of the analyzer were set with CO2-free air and the highest 
standard gas, respectively.   At least six complete sequences (3 STD, 5 ATM, 55-65 EQU)
were completed before the zero and span of the analyzer was set again.  For the first 
analysis of any type, the analyzer was flushed for four minutes before the 10 seconds 
of stopped flow and data recording.  For repeated analyses of sample gas (i.e. ATM 
or EQU), the analyzer was flushed 2 - 2.5 minutes.  The analytical sequence was 
configured to calibrate the analyzer every 2.5 - 3 hours and to set the zero and 
span at least once a day.


CALCULATIONS:

For data collected with the first configuration (2002 - March, 2008), the mixing ratios 
of ambient air and equilibrated headspace air are calculated by fitting a second-order
polynomial through the hourly averaged response of the detector versus mixing ratios of 
the standards.  Mixing ratios, or xCO2, of dried equilibrated headspace and air are 
converted to fugacity of CO2 in surface seawater and water-saturated air.  For data 
collected with the second configuration (August 2008 - present), the measured xCO2 
values are linearly corrected for instrument response using the standard measurements 
(see Pierrot et al., 2009).
 
For ambient air and equilibrator headspace, the fCO2a or fCO2eq is calculated assuming 100% 
water vapor content:

   fCO2 = xCO2 P (1-pH2O) exp[(B11+2d12)P/RT]

where fCO2 is the fugacity in ambient air or equilibrator headspace, pH2O is the water vapor 
pressure at the sea surface or equilibrator temperature, P is the equilibrator or outside 
atmospheric pressure (in atm), T is the SST or equilibrator temperature (in K) and R is the 
ideal gas constant (82.057 cm^3·atm·deg^-1·mol^-1). The exponential term is the fugacity 
correction where B11 is the first virial coefficient of pure CO2 
 
   B11 = -1636.75 + 12.0408 T - 0.0327957 T^2 + 3.16528E-5 T^3

and

   d12 = 57.7 - 0.118 T

is the correction for an air-CO2 mixture in units of cm^3·mol^-1 (Weiss, 1974).
 
The calculation for the fugacity at SST involves a temperature correction term for 
the changes in fCO2 due to changes in water temperature while the water passes through 
the pump and connecting tubing within the ship.  For the first configuration, the water 
in the equilibrator was typically 0.4 °C cooler than sea surface temperature.  For all 
data before 2006, the empirical temperature correction from equilibrator temperature 
to SST is outlined in Weiss et al. (1982):

	dln(fCO2) = (Teq-SST)(0.0317 - 2.7851E-4 Teq - 1.839E-3 ln(fCO2eq))

where dln(fCO2) is the difference between the natural logarithm of the fugacity at Teq 
and at SST.Teq and SST are the equilibrator and sea surface temperatures in degrees C, 
respectively.

Starting in 2006, the fugacity as measured in the equilibrator is corrected for the 
temperature difference between equilibrator chamber and SST using the empirical correction 
outlined in Takahashi et al. (1993).

   fCO2(SST) = fCO2(eq) exp[0.0423(SST-Teq)]
   
where fCO2(SST) is the fugacity at the sea surface temperature and fCO2(eq) is the fugacity 
at the equilibrator temperature. 

The amount of time between the sea water passing by the SST (SBE38) sensor and the 
water flowing through the equilibrator is estimated before assigning an SST value to 
each analysis.  The patterns in the temperature records for the equilibrator and for 
SST over time are compared, and a time offset that optimizes the match of these patterns 
is determined.  The time offset is applied to the SST measurements.  A linear interpolation 
between the time-adjusted SST data yields the SST value assigned to each CO2 analysis and 
used in the fugacity calculations.


DATA FILE STRUCTURE (February 2002 - March 2008):

Beginning in March 2004, the Explorer of the Seas cruise data files were changed to a 
new file format that included auxilliary meteorological, oceanographic and ship's 
navigation data.  These changes were made to conform with the recommendations of the 
International Ocean Carbon Coordination Project (http://ioc.unesco.org/ioccp).  The 
purpose of this project is to standardize measurement techniques and QA/QC procedures, 
coordinate international ocean carbon observations, and improve accessibility to carbon 
data sets in order to better meet the needs of the research community.

For the most part, changes to the data files consisted of new field headers and new fields.
One field, the "Date" field, was changed to a new format.  The new data fields included 
relative wind speed and direction, sea level pressure, ship speed and course, air temperature, 
QC flags, and diagnostics.  All the 2003 and 2004 cruises have been converted to the new 
file format.   In cases where the data are not available for a particular field, the column 
will appear with values of -9 in each record from 2002 to 2012 and values of -999 beginning 
in 2013.  Most of the additional data is taken "as is" with no quality control checking 
from the ship's sensors.  All oxygen data, wind speeds and directions, fluorometer readings, 
outside air temperature and pressure, and ship's speed and course have not been quality 
controlled and should only be used with that limitation in mind.  The following list gives 
the data fields with units and notes about changes in format.

COLUMN  HEADER                         EXPLANATION
	 
1.      GROUP_SHIP:                    AOML_Explorer for all Explorer of the
                                       Seas data (NEW).
									   
2.      Cruise:                        ExYYNN where YY is the year and NN
                                       is the cruise number.
 
3.      JD_GMT:                        Decimal year day.

4.      Date_DDMMYYYY:                 The date format has been changed to comply
                                       with the IOCCP recommendations (CHANGED).

5.      TIME_HH:MM:SS:                 GMT time.

6.      Lat_dec_degree:                Latitude in decimal degrees (negative
                                       values are in southern hemisphere).

7.      Long_dec_degree:               Longitude in decimal degrees (negative
                                       values are in western latitudes).

8.      xCO2eq_ppm:                    Mole fraction of CO2 (dry) in the equilibrator
                                       headspace at equilibrator temperature (Teq)
                                       in parts per million.  Water comes from bow
                                       intake 2 m below the water line.

9.      xCO2a_ppm:                     Mole fraction of CO2 in air in parts per million
                                       (NEW).  This field is not measured on the Explorer
                                       of the Seas - all fields initialized to -9.
        
 
10.     Pres_Equi_hPa:                 Barometric pressure in the lab in hectopascals
                                       (1 hectopascal = 1 millibar).

11.     Pres_sealevel_hPa:             Barometric pressure from ship's barometer,
                                       corrected to sea level in hectopascals (1
                                       hectopascal = 1 millibar) (NEW).
									   
12.     EqTemp_C:                      Temperature of equilibrator water in degrees
                                       centigade.  Temperature in equilibrator measured
                                       with a calibrated thermistor.

13.     SST(TSG)_C:                    Temperature from the ship's thermosalinograph in
                                       degrees centigrade.

14.     Sal(TSG)_Permil:               Salinity from the ship's thermosalinograph on the
                                       Practical Salinity Scale.

15.     Water_flow_l/min:              Water flow through equilibrator in liters per
                                       minute (NEW).

16.     Gasflow_IR_ml/min:             Gas flow through the Licor infrared analyzer before
                                       the flow is stopped in milliliters per minute (NEW).

17.     Temp_IR_C:                     Temperature of the Licor infrared analyzer sample
                                       cell in degrees centrigrade (NEW).

18.     Pres_IR_hPa:                   Pressure in the Licor infrared analyzer in
                                       hectopascals.  NOTE:  There is no pressure sensor 
                                       in the Licor but since it is vented to atmosphere
                                       prior to measurement, this value is the same as
                                       number 10 above. (1 hectopascal = 1 millibar) (NEW).

19.     Ship_heading_true_degree:      Ship's heading from ship's navigation system in
                                       degrees with 0 = North and 90 = East (NEW).

20.     Ship_speed_knot:               Ship's speed from ship's navigation system in
                                       knots (NEW).

21.     Wind_dir_rel_degree:           Wind direction relative to the ship from ship's
                                       navigation system in degrees with 0 = from the bow
                                       and 90 = from starboard (NEW).

22.     Wind_speed_rel_m/s:            Wind speed relative to the ship from ship's
                                       navigation system in meters per second (NEW).

23.     fCO2W@SST_uatm:                Fugacity of CO2 in sea water in microatmospheres
                                       calculated as outlined below.

24.     QcFlag_water:                  Quality control flag for seawater xCO2 and fCO2
                                       values with 2 = good value, 3 = questionable value, 
                                       4 = bad value and 9 = no measurement taken (NEW)									   
									   								   
25.     fCO2_uatm:                     Fugacity of CO2 in air in microatmospheres (NEW).
                                       This field is not measured on the Explorer of 
                                       Seas - all fields initialized to -9

26.     QcFlag_air:                    Quality control flag for air xCO2 and fCO2 with
                                       all fields initialized to -9, no measurement taken
		 
									   
27.     dfCO2_uatm:                    Sea water fCO2 - air fCO2 in microatmospheres.
                                       This uses the average air value for the current
                                       hour (NEW).  This field is not measured on the
                                       Explorer of the Seas - all fields initialized to -9
									 
28.     Fluoro_ug/l:                   Reading from the fluorometer in micrograms per liter

29.     Wind_speed_true_m/s:           True wind speed in meters per second

30.     Wind_dir_true_m/s:             True wind direction in degrees were 0 = North and 
                                       90 = East
									   
31.     Air_Temp_C:                    Outside air temperature from ship's computer
                                       system in degress centigrade.  PLEASE NOTE:
                                       Air_Temp_C is inaccurate; the program is 
                                       initializing Air_Temp_C to the wrong sensor
                                       (Wind_dir_true_m/s instead of Air_Temp_C).
                                       The data for 2005 and 2006 has the accurate 
                                       Air_Temp_C.  Older data will be corrected
                                       as time permits (NEW)
									   
32.     Oxyten:                        Oxygen data is from the Aanderaa Optode and
                                       is not considered reliable at this time.
								   						   
									   
DATA FILE STRUCTURE (February 2002 - March 2008):

Beginning with cruise EX0801, several columns of data not directly used in computation 
of fCO2 or xCO2 were removed from the final data file format.  Also, columns for 
Interpolated ATM xCO2 and fCO2 and for QC_SUBFLAG as described in Pierrot et al. 
(2009) were added.   Starting with cruise EX1311 in 2013, the column for EXPOCODE 
was added.

COLUMN  HEADER                         EXPLANATION

1.      EXPOCODE:                      Expedition code, where '33KF' is the NODC identifer
                                       YYYYMMDD is the UTC date that the ship starts the
                                       expedition

2.      GROUP_SHIP:                    AOML_Explorer

3.      Cruise ID:                     EXYYNN, where YY is year and NN is the cruise number
 
4.      YD_UTC:                        Decimal year day

5.      DATE_UTC_ddmmyyyy:             UTC Date

6.      TIME_UTC_hh:mm:ss:             UTC Time

7.      LAT_dec_degree:                Latitude in decimal degrees (negative
                                       values are in southern hemisphere)

8.      LONG_dec_degree:               Longitude in decimal degrees (negative
                                       values are in western latitudes)

9.      xCO2_EQU_ppm:                  Mole fraction of CO2 in the equilibrator at
                                       equilibrator headspace (dry) at equilibrator
                                       temperature, in parts per million

10.     xCO2_ATM_ppm:                  Mole fraction of CO2 in air (dry), in parts per million

11.     xCO2_ATM_interpolated_ppm      xCO2 in outside air associated with each water
                                       analysis.  These values are interpolated between
                                       the bracketing averaged good xCO2_ATM analyses,
                                       in parts per million

12.     PRES_EQU_hPa:                  Barometric pressure in equilibrator headspace,
                                       in hectopascals (1 hectopascal = 1 millibar)

13.     PRES_ATM@SSP_hPa:              Barometric pressure by outside barometer,
                                       corrected to sea level in hectopascals (1
                                       hectopascal = 1 millibar)

14.     TEMP_EQU_C:                    Temperature in equilibrator water, in degrees
                                       centigade.

15.     SST_C:                         Sea surface temperature from the remote temperature
                                       note above)
									   
16.     SAL_permil:                    Salinity from the ship's thermosalinograph, on
                                       Practical Salinity Scale

17.     fCO2_SW@SST_uATM:              Fugacity of CO2 in sea water, in microatmospheres
                                       (100% humidity)

18.     fCO2_ATM_interpolated_uatm:    Fugacity of CO2 in air, in microatmospheres.

19.     dfCO2_uatm:                    Sea water fCO2 minus interpolated air fCO2, 
                                       in microatmospheres
									 
20.     WOCE_QC_FLAG                   Quality control flag for fCO2 values
                                       (2 = good value, 3 = questionable value)

21.     QC_SUBFLAG                     Quality control sub flag for fCO2 values provides
                                       explanation for the atypical data when WOCE_QC_FLAG = 3
									   
The quality control flags are provided as an aid to the interpretation of the CO2 data.
Stringent minimum and maximum values for numerous parameters (e.g. temperature difference 
between the equilibrator temperature and SST) have been established by CO2 researchers 
(see Pierrot et al., 2009).  These ranges were chosen so that if each parameter were 
within their stringent range, the resulting CO2 data would almost certainly be good.  
If a parameter is outside its range or if a parameter is estimated from surrounding good 
values, the quality flag of that data record is set to 3 (questionable value).  The 
resulting CO2 data could be good; however, investigators should determine whether 
these data are valid for their purposes.
									   

REFERENCES:

DOE (1994). Handbook of methods for the analysis of the various parameters of the carbon 
	dioxide system in sea water; version 2. DOE.
Feely, R. A., R. Wanninkhof, H. B. Milburn, C. E. Cosca, M. Stapp and P. P. Murphy (1998). 
	A new automated underway system for making high precision pCO2 measurements onboard 
	research ships. Analytica Chim. Acta 377: 185-191.
Ho, D. T., R. Wanninkhof, J. Masters, R. A. Feely and C. E. Cosca (1997). Measurement of 
	underway fCO2 in the Eastern Equatorial Pacific on NOAA ships BALDRIGE and 
	DISCOVERER, NOAA data report ERL AOML-30, 52 pp., NTIS Springfield, 
Pierrot, D., C. Neill, K. Sullivan, R. Castle, R. Wanninkhof, H. Luger, T. Johannessen,
    A. Olsen, R. A. Feely, and C. E. Cosca (2009).  Recommendations for autonomous 
    underway pCO2 measuring systems and data-reduction routines.  Deep Sea Research II,
    56: 512-522. 
Wanninkhof, R. and K. Thoning (1993) Measurement of fugacity of CO2 in surface water using 
	continuous and discrete sampling methods. Mar. Chem. 44(2-4): 189-205.
Weiss, R. F. (1970). The solubility of nitrogen, oxygen and argon in water and seawater. 
	Deep-Sea Research 17: 721-735.
Weiss, R. F. (1974). Carbon dioxide in water and seawater: the solubility of a non-ideal gas. 
	Mar. Chem. 2: 203-215.
Weiss, R. F., R. A. Jahnke and C. D. Keeling (1982). Seasonal effects of temperature and 
	salinity on the partial pressure of CO2 in seawater. Nature 300: 511-513.
Takahashi, T., J. Olafsson, J. G. Goddard, D. W. Chipman, and S. C. Sutherland (1993).
    Seasonal variation of CO2 and nutrients in the high-latitude surface oceans: a comparative
    study, Global Biogeochem. Cycles, 7, 843-878.