Underway measurements metadata form

• Investigator:
  • Name: Liqi, Chen; Yuanhui, Zhang; Heng, Sun
  • Organization: Third Institute of Oceanography, Stata Oceanic Administration
  • Address:
    Key Laboratory of Global Change and Marine-Atmospheric Chemistry (GCMAC) Third Institute of Oceanography (TIO), State Oceanic Administration (SOA) 178 Daxuelu Xiamen 361005, P.R. CHINA
  • Phone:
  • Email: lqhen@soa.gov.cn
  Investigator #2:
  • Name: Wei-Jun, Cai
  • Organization: University of Georgia
  • Address:
    Department of Marine Sciences University of Georgia Athens, GA 30602-3636
  • Phone:
  • Email: wcai@uga.edu
  Investigator #3:
  • Name: Rik, Wanninkhof; Denis, Pierrot
  • Organization: NOAA/AOML/Ocean Chemistry Division
  • Address:
    NOAA/AOML/Ocean Chemistry Division 4301 Rickenbacker Causeway Miami, FL 33149
  • Phone:
  • Email: Rik.Wanninkhof@noaa.gov, Denis.Pierrot@noaa.gov
• Dataset Info:
  • Dataset ID: Xue_Arctic_08
  • Submission Dates:
    • Initial Submission: 2013/01/21
    • Revised Submission:
• Cruise Info:
  • Experiment:
    • Experiment Name: Underway measurement of atmospheric and surface water pCO2 during the Arctic 2008 Expedition
    • Cruise:
      • Cruise ID:
      • Section:
      • Geographical Coverage:
        • Geographical Region:
          Pacific sector of the Arctic Ocean
        • Bounds:
          • Westernmost Longitude: -179.99
            Degrees, Minutes, Seconds: E
          • Easternmost Longitude: -143.49
            Degrees, Minutes, Seconds: E
          • Northernmost Latitude: 85.42
            Degrees, Minutes, Seconds: N
          • Southernmost Latitude: 62.18
            Degrees, Minutes, Seconds: N
      • Temporal Coverage:
        • Start Date: 2008/07/30
        • End Date: 2008/09/11
      • Ports of Call:
        
  • Vessel:
    • Vessel Name: R/V Xue Long
    • Vessel ID:
    • Country: China
    • Vessel Owner: Polar Research Institute of China (PRIC)
• Variables Info:
  • Variable:
    • Variable Name: pCO2
    • Description of Variable: pCO2 at 100 % humidity and at SST (microstmosphere)
  • Method Description:
    • Equilibrator Design:
      • Equilibrator type: shower head
      • Equilibrator volume:volume of ~0.5 L with a headspace of ~0.8 L
      • Water_Flow_Rate: 2.5
      • Headspace_Gas_Flow_Rate:0.1
      • Vented: No
    • Measurement Method: Non-dispersive Infrared absorption of dried gas
    • Manufacturer of Calibration Gas: Standard gases are supplied by NOAA's Earth System Research Laboratory (ESRL), Global Monitoring Division in Boulder, CO.
    • C0₂ Sensors:
      • Manufacturer: Li-Cor, Inc., USA
      • Model: LI-480
      • Environmental Control:
        
      • Resolution: +/- 0.1 ppm
      • Uncertainty:
      • Calibration:
        LI-840 was calibrated every 2.5 to 3 hours with the CO2 standard gas listed below: STANDARD CYLINDER# CONCENTRATION(ppm) STD1 CA03928 244.32 STD2 CA04455 546.80 STD3 CA02174 420.53 STD4 CA05559 366.87
    • Other sensors:
      • Manufacturer:
      • Model:
      • Resolution:
      • Calibration:
        
    • Method References:
      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, R., H. Lüger,T. Johannessen, A. Olsen, R. A. Feely, C. E. Cosca, 2009. Recommendations for autonomous underway pCO2 measuring systems and data reduction routines, Deep Sea Res 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. 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.
  • Additional Information:
    
  • Data Set References:
    1. Cai, W-J., Chen, L., Chen, B., Gao, Z. Lee, S.H., Chen, J., Pierrot, D., Sullivan, K., Wang, Y., Hu, X., Huang, W.-J., Zhang, Y., Xu, X., Murata, A., Grebmeier, J.M., Jones, E.P., and Zhang, H. 2010. Decrease in the CO2 uptake capacity in an ice-free Arctic Ocean basin. Science 329(5991):556-9. doi:10.1126/science.1189338. 2. Bates, N. R., Cai, W.-J. and Mathis, J. T. 2011. The ocean carbon cycle in the Western Arctic Ocean: distributions and air-sea fluxes of carbon dioxide. Oceanography 24: 186–201. 3. Gao, Z., L. Chen, H. Sun, B. Chen, and W.-J. Cai (2012), Distributions and air–sea fluxes of carbon dioxide in the Western Arctic Ocean, Deep Sea Research Part II: Topical Studies in Oceanography.
  • Citation:
    Xue Long website: http://www.aoml.noaa.gov/ocd/gcc/xuelong_introduction.php 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 Third Institute of Oceanography, Xiamen, China; the University of Georgia; and 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.
• Data Set Link:
  • URL: http://www.aoml.noaa.gov/ocd/gcc/xuelong_arctic2008.php
  • Label: Arctic 2008 Expedition 7/30-9/11/2008
  • Link Note:
    METADATA: [List of variables included in this dataset]: COL HEADER EXPLANATION 1. Group_Ship AOML_XUE 2. Cruise_ID dependent upon expedition's name 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 headspace (dry) at equilibrator temperature, in parts per million 9. xCO2_ATM_ppm Mole fraction of CO2 in outside air (dry), in parts per million 10. 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 11. PRES_EQU_hPa Barometric pressure in the equilibrator headspace, in hectopascals (1 hPa = 1 millibar) 12. PRES_ATM@SSP_hPa Pressure measured by outside barometer, corrected to sea level, in hectopascals 13. TEMP_EQU_C Water temperature in equilibrator, in degrees centigrade 14. SST_C Sea surface temperature from the ship's remote temperature sensor, in degrees centigrade [interpolated, see note below] 15. SAL_permil Salinity from the thermosalinograph (SBE45), on the Practical Salinity Scale 16. fCO2_SW@SST Fugacity of CO2 in sea water, in Microatmospheres (100% humidity) 17. fCO2_ATM_interpolated_uatm Fugacity of CO2 in air corresponding to the interpolated xCO2, in microatmospheres (100% humidity) 18. dfCO2_uatm Sea water fCO2 minus interpolated air fCO2, in microatmospheres 19. WOCE_QC_FLAG Quality control flag for fCO2 values (2 = good value, 3 = questionable value) 20. QC_SUBFLAG Quality control sub flag for fCO2 values provides explanation for atypical data, when QC_FLAG = 3 The quality control flags are provided as an aid to the interpretation of the CO2 data. Quality control flags were adjusted in the following manner. For samples outside the standard range the quality control flags were changed from 3 to 2 while keeping the subflag. We believe that the uncertainty introduced by extrapolations between 0 and the low standard of 244 ppm is less then 1 ppm and does not unduly impact the results. Several samples that clearly were bad but had a flag of 3. These were changed to a flag of 4. [INSTRUMENT DESCRIPTION and CONFIGURATION]: The general principle of operation of the instrument can be found in Wanninkhof and Thoning (1993), Ho et al. (1995), Feely et al. (1998), and Pierrot et al. (2009). Seawater flows through an equilibrator chamber where CO2 exchanges between water and the air above it. An overflow pipe that is loosely covered with an inverted cup maintains the continuously-flushed pool of seawater (~750 ml). Small changes in seawater CO2 concentration are rapidly translated into changes in CO2 concentration in the air of the chamber (~850 ml of enclosed headspace). The mole fraction of CO2 in the headspace gas is measured using a non-dispersive infrared (NDIR) analyzer (LI-840 from LICOR). The analyzer compensates for the presence of water vapor in the sample gas. However, these corrections are minimized by drying the gas before it reaches the NDIR analyzer. The water is first condensed out of the gas stream by cooling to ~5 degrees C and further removed using Nafion gas dryers. The sample gases typically contain less than 3 millimoles/mole of water when they flow through the analyzer. During the cruise the NDIR analyzer is calibrated regularly using four standard gas cylinders from NOAA's Earth System Research Laboratory (ESRL), Global Monitoring Division in Boulder, CO. The analyzer is regularly zeroed using nitrogen and spanned with the most concentrated standard. STANDARD CYLINDER# CONCENTRATION(ppm) STD1 CA03928 244.32 STD2 CA04455 546.80 STD3 CA02174 420.53 STD4 CA05559 366.87 The system also measures the CO2 content of the outside air, which is drawn from an inlet on the instrument tower above the bridge. Atmospheric air was constantly being pulled (6 liters/min maximum flow) through ~200 feet of tubing (3/8" OD Dekoron) to the analytical system located many decks below and aft. The seawater is drawn from the ship's flowing seawater line. The ship has a thermosalinograph (TSG) and a remote temperature sensor. There is a TSG (Sea-Bird SBE45) next to the CO2 instrument. A 'Deck Box' containing a high precision pressure transducer, a GPS and Iridium satellite modem is located outside and several decks above the system on part of the ship's superstructure protected from severe weather. The instrumental system via the deck box records the atmospheric pressure and the position of the ship. The measured pressure is corrected for the height of the barometer above the sea surface with the addition of dgh/u - where d is atmospheric density (1.2 kg/m3), g is gravitational acceleration (9.8 m/sec2), h is height of the barometer above the sea surface, and u is the conversion factor from pascals to desired pressure units. The estimated height of 15 meters resulted in applying an increase of 1.8 mbar in the measured barometric pressoure to correct the pressure at sealevel. The sequence of continuous analyses was: STEP TYPE REPETITIONS 1 Zero gas 1 2 Span gas 1 3 Standards (all four) 1 4 ATM 5 5 EQU 60 6 Loop to STEP 3 5 7 Standards (all four) 1 8 Loop to STEP 1 1 The amount of time between analyses depends on whether the analyses are of the same type of gas (e.g., STD, ATM, EQU) or not. When switching between different gases, the connecting tubes and analyzer are flushed for an initial interval called the 'PRE-FLUSH' time plus an interval called the 'REGULAR FLUSH' time. Between successive measurements of the same type of gas, the system is flushed for only the 'REGULAR FLUSH' time. The gas flow is then stopped. After the 'STOP FLOW' time interval, which is 10 seconds for all analyses, the output of the NDIR analyzer is read. The pre-flush time is set to 180 seconds and the regular flush time is set to 60 seconds for standard and air analyses. Both the pre-flush and regular flush times are 120 seconds for equilibrator headspace analyses. With these settings, a complete set of standards and the atmospheric analyses are done every 3 hours and a full day contains about 480 analyses of the equilibrator headspace. [CALCULATIONS]: 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 fCO2_ATM or fCO2_SW 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, 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 fugacity as measured in the equilibrator is corrected for any temperature difference between sea surface temperature and equilibrator chamber using the empirical correction outlined in Takahashi et al. (1993). fCO2(SST) = fCO2(teq)exp[0.0423(SST-teq)] where fCO2(SST) is the fugacity at the sea surface temperature and fCO2(teq) is the fugacity at the equilibrator temperature. SST and teq are the sea surface and equilibrator temperatures in degrees C, respectively. [Data quality issue]: The data was reduced using the Matlab program pCO2 Sys v1.05. 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. Any value outside the range of the standards should be considered approximate (+/- 5 ppm). While individual data points above 546 or below 244 ppm may not be accurate, the general trends should be indicative of the seawater chemistry. No atmospheric pressure after JD 223. Before JD 223 the atmospheric pressure agreed very well with the equilibrator pressure. Equil Pressure has been used as atmospheric pressure. Right before JD 230, salinity dipped down close to zero and xCO2 went up to 2000. Flagged this area as 4. Region around JD 245, interpolated the low salinities. Using CTD data from the cruise provided by W.J. Cai of UGA, a relationship was established between equilibrator temperature (Teq) and surface temperature values from the CTD at station. The Teq points were averaged at each station. Based on agreement and SST and SSS variations at the stations, data from 32 stations were used from which we obtained a relationship SST = -1.0891 + 1.0326 * Teq with a r^2 of 0.98 and an uncertainty in the calculated SST of 0.3 C. The Teq for each data point was then used with this relationship to determine the SST. The fCO2_SW@SST and fCO2 were recalculated from the relationship: fCO2_SW@SST = fCO2_EQ@Teq * EXP (-0.0423* (Teq-SST)) The amount of time between the sea water entering the ship 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. [Scientists responsible for technical quality of this dataset]: Rik Wanninkhof (305)361-4379 Rik.Wanninkhof@noaa.gov Denis Pierrot (305)361-4441 Denis.Pierrot@noaa.gov Timestamp for dataset reduction: 05/08/09 Timestamp for most recent update of dataset: 12/03/09 Time period the dataset refers to: 7/30/2008 - 9/11/2008