****************** Use of AOML CO2 Underway Data ************************** * [Adapted from NOAA Climate Monitoring and Diagnostics Laboratory (CMDL) * ************* Carbon Cycle Greenhouse Gasses (CCGG) web site] ************* These data are made freely available to the public and the scientific community in the belief that their wide dissemination will lead to greater understanding and new scientific insights. The availability of these data does not constitute publication of the data. We rely on the ethics and integrity of the user to assure that AOML receives fair credit for our work. Please send manuscripts using this data to AOML for review before they are submitted for publication so we can insure that the quality and limitations of the data are accurately represented. *********************** Reciprocity Agreement ***************************** * [Adapted from NOAA Climate Monitoring and Diagnostics Laboratory (CMDL) * ************* Carbon Cycle Greenhouse Gasses (CCGG) web site] ************* Use of these data implies an agreement to reciprocate. Laboratories making similar measurements agree to make their own data available to the general public and to the scientific community in an equally complete and easily accessible form. Modelers are encouraged to make available to the community, upon request, their own tools used in the interpretation of the AOML data, namely well documented model code and any additional information necessary for other scientists to repeat the work and to run modified versions. *************************************************************************** The electronic data in comma delimited ASCII form (.CSV) can be accessed by entering the year under the "Explorer Data" prompt to the left and then entering "GO". The data can also be found at:
"http://www.aoml.noaa.gov/ocd/gcc/explorer_introduction.php" For further information or special requests regarding the Explorer data contact: Betty Huss Atlantic Oceanographic and Meteorological Lab 4301 Rickenbacker Causeway Miami, FL 33149 email: betty.huss@noaa.gov Phone: 305-361-4395 WEB SITE CHANGES APRIL, 2009 Beginning with cruise EX0824, the Explorer of the Seas cruise data files have a new 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. xCO2A_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 Quality control flag for seawater fCO2 values with 1 = outside standard range, 2 = bad SST, 3 = bad EqT, 4 = bad ΔT, 5 = excess warming, 6 = bad salinity, 7 = bad pressure, 8 = low gas flow, 9 = bad air value, 10 = interpolated standard and 11 = miscellaneous. ********************************************************************************* WEB SITE CHANGES MARCH, 2004 The Explorer of the Seas cruise data files now have a new file format that includes auxilliary meteorological, oceanographic and ship's navigation data. These changes have been 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 consist of new field headers and new fields. One field, the "Date" field, has been changed to a new format. Additional data fields include relative wind speed and direction, sea level pressure, ship speed and course, air temperature, QC flags, and diagnostics. Beginning with the first cruise of 2004, all new data fields will be present in the data files. Older data files will be updated to the new format 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. 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 new 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. ********************************************************************************* CO2 ANALYTICAL SYSTEM: The concentration of carbon dioxide (CO2) in surface ocean water is determined by measuring the concentration of CO2 in gas that is in contact with the water. Surface water is pumped from an inlet in the ship's bow to the equilbration chamber. The equilbration chamber has an enclosed volume of gas, or headspace, and a pool of seawater that continuously overflows to a drain. As the water flows through the chamber, the dissolved gases (like CO2) partition between the water and the headspace. At equilibrium, the ratio of CO2 in the water and in the headspace is influenced most by temperature, and that relationship is known. By measuring the concentration of CO2 in the headspace and the temperature in the chamber, the partial pressure (or fugacity) of CO2 in the surface water can be calculated. 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 increase of fCO2 due to heating of the water from passing 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. NOTES ON DATA: Columns have a default value of -9 in case of instrument malfunction, erroneous readings or missing data. Furthermore, if a suspicious xCO2 value, pressure or temperature value is encountered, the fCO2 is not calculated. INSTRUMENT DESCRIPTION The general principle of instrumental design can be found in Wanninkhof and Thoning (1993), Ho et al. (1995), and Feely et al. (1998). The concentration of CO2 in the headspace gas is measured using the adsorption of infrared (IR) radiation, which results from changes in the rotational and vibrational energy state of the CO2 molecule. The LI-COR detector passes IR radiation through two 6" cells. The reference cell is flushed with a gas of known CO2 concentration. The sample cell is flushed with the headspace gas. A vacuum-sealed, heated filament is the broadband IR source. The IR radiation alternates between the two cells via a chopping shutter disc spinning at 500 Hertz. An optical filter selects an adsorption band specific for CO2 (4.26 micron) to reach the detector. The solid state (lead selenide) detector is kept at -12 degrees C for excellent stability and low signal noise (less than 0.2 ppm). Several steps are taken to reduce interferences and to increase the accuracy of the measurements. The IR adsorption band for water vapor is close to the band for CO2. After the equilibration chamber, the headspace travels through a drying trap to remove water vapor. During each analysis, the headspace gas is compared to a reference gas of known concentration. To improve the accuracy of the measurements, three different gaseous standards for CO2 are analyzed once an hour instead of the headspace gas. Analyzer: LI-COR 6252 (analog output) infrared (IR) analyzer. Method of Analysis: Differential analyses relative to a reference gas which is close to the CO2 concentration of the middle standard. Measures dried equilibrator headspace gas. Gas flow is stopped prior to IR readings. Drying Method: The equilibrator headspace sample gas first goes through an air filter and a thermoelectric refrigerator (~6 C). The sample and standard gases pass through a Perma Pure (Nafion) dryer and a short column of magnesium perchlorate before reaching the analyzer. The counter flow in the Perma Pure tube is the reference gas. Equilibrator (setup, size, flows): The equilibrator was fabricated using a filter housing (ColeParmer, U-010509-00) with ~0.5 L water reservoir and ~0.8 L gaseous headspace. Water flow rate is ~1.5 L/min. Headspace recirculation rate is ~80 ml/min. Sampling Cycle: The system runs on an hourly cycle during which 3 standard gases, a reference gas and 20 surface water samples (from the equilibrator head space) are analyzed on the following schedule: Mins. after hour Sample ================ ====== 0:00 Low Standard 2:15 Mid Standard 4:30 High Standard 6:45 Reference 9:00 Water 11:33 Water 14:06 Water 16:39 Water 19:12 Water 21:45 Water 24:18 Water 26:51 Water 29:24 Water 31:57 Water 34:30 Water 37:03 Water 39:36 Water 42:09 Water 44:42 Water 47:15 Water 49:48 Water 52:21 Water 54:54 Water 57:27 Water REFERENCES PRIOR TO 2006: 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, 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.REFERENCES PRIOR TO 2006: REFERENCES FROM 2006 TO PRESENT: 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, 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. 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.
