Atlantic Oceanographic & Meteorological Laboratory Global Carbon Cycle
« GCC Home
Explorer Data:

» Introduction
» Master Readme
» Realtime Display
» Cruise Inventory
» Annual Files
» Contact
» Internal QC Plots

Explorer of the Seas Master Readme File

INTRODUCTION:
 
The information presented in this file is applicable to all the data sets collected 
on the RCCL's Explorer of the Seas that are presented at:
 
     "http://www.aoml.noaa.gov/ocd/gcc/explorer_introduction.php"

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 ensure 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 Group at AOML installed an instrument to measure 
CO2 in surface water in the dedicated ocean laboratory on the Royal Caribbean Cruise Ltd 
(RCCL) 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, with the CO2 instrumental system 
being replaced and relocated to the ship's bow thruster space.  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 Kevin Sulliva
     NOAA/AOML/Ocean Chemistry Division
     4301 Rickenbacker Causeway
     Miami, FL 33149
     Rik.Wanninkhof@noaa.gov
     Kevin.Sullivan@noaa.gov

Contact persons for this dataset:

     Betty Huss and Kevin Sullivan
     NOAA/AOML/Ocean Chemistry Division
     4301 Rickenbacker Causeway
     Miami,  FL 33149
     Betty.Huss@noaa.gov
     Kevin.Sullivan@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)
         ftp://ftp.licor.com/perm/env/LI-6252/Manual/LI-6252_Manual.pdf
         CO2 resolution:  0.01 umol/m
         CO2 accuracy:   1 ppm 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 - November 2010)
         ftp://ftp.licor.com/perm/env/LI-7000/Manual/LI-7000Manual.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 (November 2010 - present)
         ftp://ftp.licor.com/perm/env/LI-6262/Manual/LI-6262_Manual.pdf
         CO2 resolution:  0.01 umol/m
         CO2 accuracy:  1 ppm at 350 ppm
         Pressure resolution:  0.02 hPa
         Internal pressure transducer accuracy:  1.2 hPa 
            (manufacturer specifications: 0.1% FS, where FS = 0-1150 hPa) 


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 (March 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)

During the second instrumental configuration, the absolute pressure of the equilibrator 
headspace reported in data files is the sum of the infrared analyzer pressure and the 
differential pressure from the pressure transducer attached to the equilibrator.


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:  0.0001C 
            Accuracy:   0.0013C
   The Hart1560 was used to annually calibrate the Omega 1000 ohm thermistor.  Based on 
   reproducibility of the annual calibrations, the equilibrator water temperatures were 
   believed accurate to 0.02 C.

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


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

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

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


Atmospheric Pressure (maintained by other scientists):
   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 (2002-2007) 
the reference gas contained CO2 with concentration close to outside air.  During the 
second configuration (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 ~6 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 (2002-2007) was the reference gas; during the 
second configuration it 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) 
from an inlet on the bow mast through ~200 feet of tubing (3/8" OD Dekoron) to the analytical 
system.  The flushing rate of the LI-COR analyzer during ATM analyses was ~70-150 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 ~0.8 L gaseous headspace.  
Water flow rate was ~1.5-2.5 L/min.  The rate that the headspace gas was recirculated 
through the analyzer during EQU analyses was ~70 - 150 ml/min. 

During the first configuration, the water temperature in the equilibrator was measured 
with a 20-cm long, 1000 Ohm thermistor from Omega 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.  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.

A typical sequence of the continuous analyses was:

STEP      TYPE                REPETITIONS
 1        Standards (all)         1
 2        ATM                     5
 3        EQU                    55



CALCULATIONS:

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 of dried equilibrated headspace and air are converted 
to fugacity of CO2 in surface seawater and water saturated air in order to determine the fCO2.  
For ambient air and equilibrator headspace the fCO2a, or fCO2eq is calculated assuming 100% 
water vapor content:

	fCO2eq = xCO2eq(P-pH2O)exp(B11+2d12)P/RT
			
where fCO2eq is the fugacity in the equilibrator, pH2O is the water vapor pressure at the sea 
surface temperature, P is the atmospheric pressure (in atm), T is the SST or equilibrator 
temperature (in K) and R is the ideal gas constant (82.057 cm^3atmdeg^-1mol^-1).  The 
exponential term is the fugacity correction where B11 is the second virial coefficient of pure CO2 

   B11 = -1636.75 + 12.0408T - 0.032795T^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^3mol^-1 (Weiss, 1974). 

The calculation for the fugacity at SST involves a temperature correction term for the change 
of fCO2 due to changes in water temperature which when the water passes through the pump and 
through 5 cm ID PVC tubing within the ship.  The water in the equilibrator is 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 SST, 
and Teq is the equilibrator temperature in degrees C.  In 2006, the empirical temperature 
correction from equilibrator temperature to SST was changed to:

        fCO2(SST) = fCO2(eq) Exp (-0.0423 (Teq-SST))

where dln(fCO2) SST is sea surface temperature and Teq is the equilibrator temperature in degrees C.



DATA FILE STRUCTURE (March 2008 - present):

Beginning with cruise EX0801, the data file format:

COLUMN  HEADER                         EXPLANATION
1.      GROUP_SHIP:                    AOML_Explorer

2.      Cruise ID:                     EXYYNN (where YY is year and NN is the cruise number).
 
3.      JD_GMT:                        Decimal year day

4.      DATE_UTC_ddmmyyyy:             UTC Date

5.      TIME_UTC_hh:mm:ss:             UTC 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.      xCO2_EQU_ppm:                  Mole fraction of CO2 in the equilibrator at
                                       equilibrator temperature (Teq) in parts per
                                       million.

9.      xCO2_ATM_ppm:                  Mole fraction of CO2 in air in parts per million.

10.     xCO2_ATM_interpolated_ppm      xCO2 interpolated in parts per million.

11.     PRES_EQU_hPa:                  Barometric pressure in the lab in hectopascals
                                       (1 hectopascal = 1 millibar).

12.     PRES_ATM@SSP_hPa:              Barometric pressure from ship's barometer,
                                       corrected to sea level in hectopascals (1
                                       hectopascal = 1 millibar).

13.     TEMP_EQU_C:                    Temperature in equilibrator water in degrees
                                       centigade.

14.     SST_C:                         Temperature from the ship's thermosalinograph in
                                       degrees centigrade.

15.     SAL_permil:                    Salinity from the ship's thermosalinograph in
                                       [Practical Salinity Scale].

16.     fCO2_SW@SST_uATM:              Fugacity of CO2 in sea water in microatmospheres.

17.     fCO2_ATM_interpolated_uatm:    Fugacity of CO2 in air in microatmospheres.

18.     dfCO2_uatm:                    Sea water fCO2 - air fCO2 in microatmospheres.
                                       This uses the average value between air
                                       measurements.
									 
19.     WOCE_QC_FLAG                   Quality control flag for seawater fCO2 values
                                       with 2 = good value and 3 = questionable.

20.     QC_SUBFLAG                     Description of the problem with the questionable data


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.  The 2002 cruise data files will 
be converted in the future.  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.csv 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 sea water xCO2 and fCO2
                                       values with 2 = good value, 3 = questionable value, 
                                       4 = bad value, and 9 = no measurement taken (NEW).

25.    fCO2a_uatm:                     Fugacity of CO2 in air in microatmospheres (NEW).
                                       This field is not measured on the Explorer of the
                                       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 (NEW).

27.    dfCO2_uatm:                     Sea water fCO2 - air fCO2 in microatmospheres.
                                       This uses the average air value for the current hour
                                       (NEW).  This fields 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_degree:           True wind direction in degrees were 0 = North
                                       and 90 = East.

31.    Air_Temp_C:                     Outside air temperature from ship's computer
                                       system in degrees centrigrade PLEASE NOTE:
                                       Air_Temp_C is inaccurate; the program is
                                       initializing Air_Temp_C to the wrong sensor
                                       (Wind_dir_true instead of Air_Temp_C).  The
                                       data for 2005 and 2006 has the accurate 
                                       Air_Temp_C.  Older data files will be
                                       corrected as time permits (NEW).
									   
32.   Oxygen                           Oxygen data is from the Aanderaa Optode
                                       and is not considered realiable at this time.



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.

Department Logos
US Department of Commerce Logo Office of Oceanic and Atmospheric Research Logo Atlantic Oceanographic and Meteorological Laboratory Logo National Oceanic and Atmospheric Administration Logo US Department of Commerce National Oceanic and Atmospheric Administration Office of Oceanic and Atmospheric Research Atlantic Oceanographic and Meteorological Laboratory