README FOR Ronald H. Brown UNDERWAY fCO2 FILES The electronic data in comma delimited ASCII form (.CSV) can be found at: http://www.aoml.noaa.gov/ocd/gcc For further information or special requests regarding data format contact: Mr. Bob Castle Atlantic Oceanographic and Meteorological Lab 4301 Rickenbacker Causeway Miami, FL 33149 email: robert.castle@noaa.gov Phone: 305-361-4418 ********************************************************************* * Use of AOML CO2 Underway Data * * Adapted from NOAA Climate Monitoring and * * Diagnostics Laboratory (CMDL) * * Carbon Cycle Greenhouse Gases (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. Use of these data implies an agreement to reciprocate. 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 * * 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. INSTRUMENTATION: ANALYZER: LI-COR 6262 SN1335 (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. ADDITIONAL SENSORS: Seabird SBE-45 TSG (SN 4559728-0329) attached to the underway system provides salinity and temperature measurements of the water flowing into the equilibrator. Only the salinity measurements are used in the final data file. A Hart Model 1521 temperature probe was used to electronically log the equilibrator temperature and was mounted through the top of the equilibrator and its tip was submerged about 5 cm. It 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 are believed accurate to well within 0.02 °C. The barometric pressure was measured with the internal pressure sensor of the Licor. A Setra Model 239 differential pressure transducer is mounted at the inlet of the equilibrator. The Setra output was added to the Licor pressure value since the Licor pressure measurement is made at ambient pressure by opening the 3-way solenoid to the vent. LI-COR 6262 pressure transducer specifications: Accuracy (with software correction): +/- 0.1% full scale. Resolution: 0.002 kPa typical ( = 0.02 hPa). Signal Noise (peak-to-peak): 0.002 kPa typical ( = 0.02 hPa). Setra Model 239 differential pressure transducer specifications: Range: 0 - 0.5 psi ( = 0 - 36 hPa) Accuracy: 0.11% FS ( = 0.04 hPa) SHIP'S SENSORS: SST: SBE 21 located in bow thruster room with the intake ~5 m below the water line. Barometric pressure: Sensor is mounted on the forward mast 10 m above the water line and data is corrected for sensor altitude. SBE-21 specifications: Temperature: Initial Accuracy = 0.01 C Salinity(PSU): Initial Accuracy = 0.001 Unless noted all sensors are calibrated or cross-checked annually and meet or exceed requirements to determine the fCO2_SW @ SST to within 2 uatm and xCO2 to within 0.1 ppm as outlined in Pierrot et al. 2009. ********************************************************************** New data file format April, 2010 Beginning with cruise RB1001, several columns have been removed from the data file. These columns are from ship's instruments and are not directly used in computations of fCO2 or xCO2. Anyone interested in this data should contact Bob Castle (address at top of this file). The columns in the new data files are as follows: Group_Ship: AOML_BROWN for all Ron Brown data Cruise ID: RBYYNNGO where YY is the 2 digit year and NN is the cruise number for that year JD_GMT: Decimal year day DATE_UTC__mmddyyyy: Date in European format (01042008 = April 4, 2008) TIME_UTC_hh:mm:ss: GMT time (24 hour clock) LAT_dec_degree: Latitude in decimal degrees LONG_dec_degree: Longitude in decimal degrees xCO2_EQU_ppm: Mole fraction of CO2 in the equilibrator at equilibrator temperature xCO2_ATM_ppm: Mole fraction of CO2 in air in parts per million (ppm) xCO2_ATM_interpolated_ppm: Bracketing average air values interpolated to time of current Equ measurement PRES_EQU_hPa: Barometric pressure in the equilibrator in hectopascals *PRES_ATM@SSP_hPa: Barometric pressure from ship's barometer, corrected to sea level in hectopascals TEMP_EQU_C: Equilibrator water temperature in degrees centigrade *SST_C: Sea surface temperature in degrees centigrade SAL_permil: Salinity from the Micro TSG in the Hydro Lab practical salinity units fCO2_SW@SST_uatm: Fugacity of CO2 in sea water in microatmospheres fCO2_ATM_interpolated_uatm: Fugacity of CO2 in air in microatmospheres interpolated to time of Equ measurement dfCO2_uatm: Fugacity of CO2 in sea water - fugacity of CO2 in air in microatmospheres WOCE_QC_FLAG: Quality control flag for Equ fCO2 values and Atm xCO2 values (2 = good, 3 = questionable, 4 = bad) QC_SUBFLAG: Subflag text string for values flagged as 3 ********************************************************************* ********************************************************************* New system installed March, 2008 Beginning with the cruise RB200802, a new underway system was installed on the Ron Brown. The system was built by General Oceanics (GO) and is described in Pierrot et al. (2009). While the basic principle of operation is the same for both instruments, there are several differences. The GO system uses a smaller (~ 2 liter) equilibrator and consequently has a lower water flow (~1.5 l/m instead of ~11 l/m). It uses a Licor 6262 with pressure sensor and water channel instead of the Licor 6251. It uses a Nafion dryer instead of glass condensors to dry the sample gas stream. It uses 4 standard gases instead of 3 and performs a zero and span of the Licor approximately once per day. There is a GPS connected directly to the GO system. It also has a fully programmable measurement cycle which has been set to the following: 1. Zero and span 2. Four standard gases 3. Five air samples 4. Fifty equilibrator headspace gas samples 5. Repeat steps 2 - 4 nine more times 6. Restart from step 1 Measurement cycles are somewhat shorter in duration (~2-1/2 minutes as opposed to 4 - 4-1/2 minutes with the old system). The first measurement in each group is ~ 4 minutes to insure full flushing of the Licor and only the following measurements are reduced in time. A Seabird Micro TSG (SBE-45) in the Hydro Lab sink is connected directly to the new system and provides temperature and salinity measurements. Some changes have been made to the format of the final data file. Temperature and pressure of the Licor have been removed and there is now a column for interpolated atmospheric xCO2. All good (flag 2) air and Equ measurements are now included in the data file and all bad measurements (flag 4, either Equ or Atm) are usually omitted. The date is now given in European format and includes slashes between day, month, and year (DD/MM/YYYY). There is now a subflag column which is used to provide additional information about points that have been flagged as 3. The QC flag applies to the fCO2 values of Equ measurements and to the xCO2 values of Atm measurements. In many cases, the xCO2 value of an Equ measurement with a flag of 3 will be good. The new column headers are: Group_Ship: AOML_BROWN for all Ron Brown data Cruise ID: RBYYNNGO where YY is the 2 digit year and NN is the cruise number for that year JD_GMT: Decimal year day DATE_UTC__mmddyyyy: Date in European format (01042008 = April 4, 2008) TIME_UTC_hh:mm:ss: GMT time (24 hour clock) LAT_dec_degree: Latitude in decimal degrees LONG_dec_degree: Longitude in decimal degrees xCO2_EQU_ppm: Mole fraction of CO2 in the equilibrator at equilibrator temperature xCO2_ATM_ppm: Mole fraction of CO2 in air in parts per million (ppm) xCO2_ATM_interpolated_ppm: Bracketing average air values interpolated to time of current Equ measurement PRES_EQU_hPa: Barometric pressure in the equilibrator in hectopascals *PRES_ATM@SSP_hPa: Barometric pressure from ship's barometer, corrected to sea level in hectopascals TEMP_EQU_C: Equilibrator water temperature in degrees centigrade *SST_C: Sea surface temperature in degrees centigrade *SAL_permil: Salinity from ship's TSG or Micro TSG in the Hydro Lab practical salinity units fCO2_SW@SST_uatm: Fugacity of CO2 in sea water in microatmospheres fCO2_ATM_interpolated_uatm: Fugacity of CO2 in air in microatmospheres interpolated to time of Equ measurement dfCO2_uatm: Fugacity of CO2 in sea water - fugacity of CO2 in air in microatmospheres WOCE_QC_FLAG: Quality control flag for Equ fCO2 values and Atm xCO2 values (2 = good, 3 = questionable, 4 = bad) QC_SUBFLAG: Subflag text string for values flagged as 3 WATER_FLOW_L/MIN: Water flow through the equilibrator in liters per minute GAS_FLOW_IR_ML/MIN: Gas flow through the Licor sample cell in milliliters per minute SHIP_SPEED_KNOT: Ship's speed from the ship's computer system in knots SHIP_HEADING_TRUE_DEGREE: Ship's heading from the ship's computer system in degrees (0 = north, 90 = east, etc.) *AIR_TEMP_C: Outside air temperature in degrees centrigrade *WIND_DIR_TRUE_DEGREE: Absolute (true) wind direction in degrees *WIND_SPEED_TRUE_M/S: Absolute (true) wind speed in meters per second *WIND_SPEED_REL_M/S: Wind speed in meters per second relative to the ship *WIND_DIR_REL_DEGREE: Wind direction in degrees relative to the ship *FLUORO_uG/L: Reading from the Turner 10-AU fluorometer in micrograms per liter All data columns marked with a * are from the ship's computer system and have not been quality-controlled. See below for the location of quality-controlled ship's data. ********************************************************************* ********************************************************************* Web Site Changes April, 2004 Our web site for underway pCO2 data from the NOAA ship Ronald H. Brown has undergone a facelift and now has a new address: http://www.aoml.noaa.gov/ocd/gcc/rvbrown_introduction.php. The data for each year can now be accessed from a drop-down list box on this page. Cruise tracks are now color coded to show the approximate partial pressure of CO2 in surface water over the ship's course. Master maps of cruise tracks for a four year period are now at: http://www.aoml.noaa.gov/ocd/gcc/rvbrown_cruisetracks.php. In addition to these cosmetic changes, cruise data files now have a new 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 fluorometer data, 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. Data files from 2003 have all the new fields except for air temperature, ship's speed and ship's course. 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 from the ship's computer system "as is" with no quality control checking. All 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. To get quality controlled meteorological from the Ron Brown, visit the Center for Ocean-Atmosphere Prediction Studies web site at: http://www.coaps.fsu.edu/RVSMDC/cgi-bin/nonwoce-ship.cgi?id=WTEC The following list gives the new data fields with units and notes about changes in format. 1. GROUP/SHIP: AOML_Brown for all Ron Brown data (NEW). 2. CRUISE_DESIGNATION: RBYYYYNN. All Ron Brown data will give the cruise designation RB followed by the 4-digit year and the 2-digit cruise number (NEW). 3. JD_GMT: Decimal year day (same as in old files). 4. DATE_DDMMYYYY: The date format has been changed to comply with the IOCCP recommendations (CHANGED). 5. TIME_HH:MM:SS: GMT time (same as in old files). 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 hemisphere). 8. xCO2W_PPM: Mole fraction of CO2 in the equilibrator at equilibrator temperature (Teq) in parts per million. 9. xCO2A_PPM: Mole fraction of CO2 in air in parts per million. 10. PRES_EQUIL_hPa: Barometric pressure in the lab in hectopascals [1 hectopascal = 1 millibar]. 11. PRES_SEALEVEL_hPa: Barometric pressure from ship's computer system, corrected to sea level in hectopascals [1 hectopascal = 1 millibar] (NEW). 12. EqTEMP_C: Temperature in equilibrator water in degrees centrigade. 13. SST(TSG)_C: Temperature from the ship's thermosalinograph in degrees centrigrade. 14. SAL(TSG)_PERMIL: Salinity from the ship's thermosalinograph in [Practical Salinity Scale]. 15. WATER_FLOW_L/MIN: Water flow through equilibrator in liters per minute (NEW). 16. GAS_FLOW_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 computer system in degrees with 0 = North and 90 = East (NEW). 20. SHIP_SPEED_KNOT: Ship's speed from ship's computer system in knots (NEW). 21. WIND_DIR_REL_DEGREE: Wind direction relative to the ship from ship's computer 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 computer system in meters per second (NEW). 23. fCO2W@SST_uATM: Fugacity of CO2 in sea water in microatmospheres. 24. QC_FLAG_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. 26. QC_FLAG_AIR: Quality control flag for air xCO2 and fCO2 with 2 = good value, 3 = questionable value, 4 = bad value, and 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. 28. FLUORO_uG/L: Reading from the Turner 10-AU fluorometer in micrograms per liter (NEW). 29. WIND_SPEED_TRUE_M/S: True wind speed in meters per second (NEW). 30. WIND_DIR_TRUE_DEGREE: True wind direction in degrees where 0 = North and 90 = East (NEW). 31. AIR_TEMP_C: Outside air temperature from ship's computer system in degrees centrigrade (NEW). ********************************************************************* February, 2004 The YSI thermosalinograph was replaced with an SBE micro TSG from Seabird that includes temperature and conductivity sensors. The data from this unit is only used for quality control checks and is not included in the final data file. It can be obtained from Bob Castle (robert.castle@noaa.gov) if necessary. ********************************************************************* September, 1997 FILE FORMAT Column Explanation JD Julian Day Date Date (month, day, year) Time Greenwich Mean Time Lat Latitude (decimal degrees) Long Longitude (decimal degrees) xCO2,w Mixing ratio of CO2 (dry) in headspace of equilibrator. Water comes from a bow intake 5 m below the water line (in ppm) xCO2,a Mixing ratio of CO2 (dry) from the bow of the ship (15 m above water) EqTemp Temperature in equilibrator measured with a calibrated thermistor (in degrees C) Pressure Pressure in laboratory (in mB) SST(TSG) Sea surface temperature measured at the water intake 5 m below the water line (in degrees centigrade) Sal(TSG) Salinity measured at the water intake (5 m below water line) fCO2w,eq Fugacity of water in equilibrator calculated according to DOE (1994) in microatmospheres) fCO2w,in situ Fugacity of water at SST calculated from algorithm of Weiss et al. (1982) fCO2a Fugacity of CO2 in air dfCO2 Water-air fugacity difference 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: fCO2a/eq = xCO2a/eq(P-pH2O)exp(B11+2d12)P/RT where fCO2a/eq is the fugacity in ambient air or 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 0.2 °C warmer than sea surface temperature. 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. NOTES ON DATA: Columns have a default value of -999.99 in case of instrument malfunction or erroneous readings. Furthermore, if a suspicious xCO2 value, pressure or temperature value is encountered which cannot be readily extrapolated, 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 analyses are done with an infrared analyzer calibrated with three standard gases spanning the anticipated range of water and air values. The standard gases come from NOAA/CMDL in Boulder and are directly traceable to the WMO scale. The system also includes a YSI thermosalinograph (TSG) that contains temperature, salinity, and dissolved oxygen sensors. The uncontaminated sea water line is teed off with one pipe going to the equilibrator and the other going to the YSI. Data from the YSI is logged by the program to the raw data file but is not included in the final data file. In addition, a feed from the ship's computer system provides the program with date, time, latitude, longitude, SST, and salinity. This data feed has been expanded over the years to include wind speed and direction (both absolute and relative) and data from the ship's underway fluorometer. These additional parameters are logged to the raw data file but do not appear in the final data file. Requests for the raw data may be submitted to Mr. Bob Castle, whose contact information appears at the beginning of this file. Sampling Cycle: The system runs on an hourly cycle during which 3 standard gases, 3 air samples from the bow tower and 8 surface water samples (from the equilibrator head space) are analyzed on the following schedule: Mins. after hour Sample ================ ====== 4 Low Standard 8 Mid Standard 12 High Standard 16.5 Water 21 Water 25.5 Water 30 Water 34 Air 38 Air 42 Air 46.5 Water 51 Water 55.5 Water 60 Water Units: All xCO2 values are reported in parts per million (ppm) and fCO2 values are reported in microatmospheres (uatm) assuming 100 % humidity at the equilibrator temperature. 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.