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: 0.0001°C Accuracy: ± 0.0013°C 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: 0.001°C Accuracy: ± 0.025°C 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: 0.001°C Temperature accuracy: ± 0.01°C 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: 0.0001°C Temperature accuracy: ± 0.002°C 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: 0.00025°C Temperature accuracy: ± 0.001°C 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^3·atm·deg^-1·mol^-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^3·mol^-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.
