R/V KNORR FASTEX 1996/1997 Cruise Readme File Class of Data: Surface ocean carbon dioxide concentrations Dataset Identifier: KNORR_96_97 Statement of how to cite dataset: R/V KNORR FASTEX cruise website: http://www.aoml.noaa.gov/ocd/gcc/knorr_fastex 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 the AOML ocean carbon group receives fair credit for our work. Please consult with us prior to use so we can insure that the quality and limitations of the data are accurately represented. Cruise Information: This cruise was part of the Fronts and Atlantic Storm Track Experiment (FASTEX). FASTEX addressed the life cycle of cyclones evolving over the North Atlantic Ocean in January and February 1997 with the objective of improving the forecasts of end-of-storm-track cyclogenesis in the North Atlantic. The Woods Hole Oceanographic Institution’s R/V Knorr departed Woods Hole, Massachusetts on October 27, 1996 and returned to Woods Hole, Massachusetts on March 15, 1997. Measurements taken aboard the R/V Knorr were used to examine the near- surface environment and air-sea interaction processes during 10 frontal systems. Underway measurements of surface pco2, temperature and salinity were taken during this cruise. Lead scientist from October 27, 1996 to December 5, 1996: Michael S. McCartney Woods Hole Oceanographic Institution 266 Woods Hole Rd. Woods Hole, Massachusetts 02543 mccartney@whoi.edu Lead scientists from December 23, 1996 to January 26, 1997: Chris Fairall NOAA/ESRL 325 Broadway Boulder, Colorado 80305 chris.fairall@noaa.gov Ola Persson CIRES/NOAA/ESRL University of Colorado Boulder, Colorado 80309 opersson@cires.colorado.edu Lead scientist from January 30, 1997 to March 15, 1997: Robert S. Pickart Woods Hole Oceanographic Institute 266 Woods Hole Rd. Woods Hole, Massachusetts 02543 rpickart@noaa.gov Scientists responsible for technical quality of dataset: Rik Wanninkhof NOAA/AOML/Ocean Chemistry Division 4301 Rickenbacker Causeway Miami, Florida 33149 Rik.Wanninkhof@noaa.gov Timestamp for initial submission of dataset: 7/8/2010 Timestamp for the most recent update of dataset: 7/8/2010 Timestamp period the dataset refers to: 11/21/1996 - 3/13/1997 Geographic area the dataset refers to: 35 N to 65 N 5 W to 65 W List of variables included in this dataset: COLUMN HEADER EXPLANATION 1. GROUP_SHIP: AOML_Knorr 2. CRUISE_ID: Knorr_96_97 3. JD_GMT: Decimal year day 4. DATE_DDMMYYYY: Date 5. TIME_HH:MM:SS: GMT time 6. LAT_DEC_DEGREE: Latitude in decimal degrees (negative values are in the southern hemisphere) 7. LONG_DEC_DEGREE: Longitude in decimal degrees (negative values are in the western hemisphere) 8. xCO2W_PPM: Mole fraction of CO2 in the equilibrator headspace (dry) at equilibrator temperature 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. EQTEMP_C: Water temperature in equilibrator, in degrees centigrade 12. SST_C: Sea surface temperature from the ship's remote temperature sensor, in degrees centrigrade 13. SAL_PERMIL: Salinity from the ship's thermosalinograph (SBE45) on the Practical Salinity Scale. 14. fCO2W@SST_uATM: Fugacity of CO2 in sea water in microatmospheres 15. fCO2A_uATM: Fugacity of CO2 in air in microatmospheres 16. dfCO2_uATM: Sea water fCO2 - air fCO2 in microatmospheres (This uses the average air value for the current hour) 17. QC_FLAG: 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 The following fields have been QC'ed by the CO2 group: GROUP_SHIP CRUISE JD_GMT DATE_DDMMYYYY TIME_HH:MM:SS LAT_DEC_DEGREE LONG_DEC_DEGREE xCO2W_PPM xCO2A_PPM PRES_EQUIL_hPa EQTEMP_C PRES_IR_hPa fCO2W@SST_uATM fCO2A_uATM dfCO2A_uATM QC_FLAG The following fields are from the ship's onboard systems and the quality of this data cannot be verified: SST_C SAL_PERMIL 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 to the equilibration chamber. The chamber contains a water spray head, an enclosed gaseous 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: 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 (82.0578 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 +/- 1 °C warmer than sea surface temperature. The empirical temperature correction from equilibrator temperature to SST is outlined in Takahashi et al (1993): fCO2W = fCO2eq Exp(0.0423 (SST-Teq)) NOTES ON DATA: Columns have a default value of -9 in case of instrument malfunction or erroneous readings. Furthermore, if a suspicious xCO2 value, pressure or temperature value is encountered which cannot readily be extrapolated, the fCO2 is not calculated. INSTRUMENT DESCRIPTION: The general principle of operation of the instrument 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 6262 analyzer passes IR radiation through two 6" cells. The reference cell is flushed with a gas that passes through beds of soda lime and magnesium perchlorate to remove CO2 and water. The sample cell is flushed with the standard or sample gas. The standards used on the cruise are: STANDARD CONCENTRATION STD1 299.22 STD2 524.87 STD3 343.00 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 for fCO2w and for SST at fCO2a. Estimated overall uncertainty of measurement: The xCO2eq measurements are believed accurate to 1 ppm. The fCO2@SSTDa measurements are believed to be precise to 2 ppm. Bibliography: 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 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. Data QC: Pre Cruise: October 10th 1996 A 6K resistor was placed in parallel between the CH2 hi and CH2 low on the AD board to decrease the resistance necessary to measure the temperatures below 6 C. The measurable range of temperatures is now 2.5 to 30 degrees Celsius.The temperature range has been expanded to -2.5 to 30 degrees Celsius without the resistance range increasing. The Knorr left WHOI around Oct 27, 1996. The cruise plan was to go from Woods Hole to the Azores and then to Southampton, England. The ship inported on December 5th. The chief scientist was Mike McCartney (mmccartney@whoi.edu). Evidently, the ship had significant trouble eliminating air bubbles from the bow intake for the TSG. This resulted in having to repeatedly turn off the TSG and the pCO2 system. Therefore the data recorded does not maintain a continuous time record. The group maintaining the system decided that they would save the data daily to assure that no usable data would be left out. Furthermore, there seems to be a significant problem with the quality of TSG data. FASTEX Cruise: In Southampton, the UW data was retrieved and a temperature calibration was performed that was logged in the UW notebook. CDR. Marty Mulhern was trained to maintain the system for the FASTEX cruise. The ship left Southhampton, UK on December 23rd, heading for Cork, Ireland first and then out into the Atlantic to watch for storms. December 2nd-4th 1996 Bow pump off, system shut down for this leg December 20th-23rd 1996 Thermistor calibration, problems with bow pump which was shut off and turned back on. The ship was still having problems maintaining pure water suction. The bow pump was turned continually on and off. Marty Mulhern tried his best to keep logging the on and offs of the intake. On 12/28 the KNORR pulled into Cork, Ireland. On 12/29 at 2000 hrs the ship sailed from Cork. A new seawater intake pump was installed, but there were still problems. On 1/6/97, it appears that there was water in the bow-air intake line at about 0930 hrs. December 24th 1996 The pump was turned on. December 27th-29th 1996 No data December 30th 1996 There was no data after 1500 due to a leak in bow pump piping. December 31st 1996 The pump was turned back on at around 0300. January 1st to 6th There was no data due to pump failure. Jan 7th 1997 The diaphragm was changed on the air pump, a new pump installed and the system was back up at 0135 UTC. Jan 8th 1997 There was no data due to high seas and clogged water filters. Jan 13th 1997 The pump was off due to high seas, no data from 1030 to 2219. Jan 14th-15th 1997 The pump was off, no data from 1947 to 1254. Jan 16th 1997 The pump was off on station, no data from 1230 to 2019. Jan 17th 1997 The pump was off on station, no data from 0147 to 1315. Jan 20th 1997 The pump was off on station, no data from 0051 to 1119. Jan 22nd 1997 The pump was off. Lost suction due to high seas, no data from 0026 to 0324 and 0851 to 2015. Jan 24th 1997 There was no data from 1151 to 2215 Jan 25th-26th 1997 The pump was off due to high seas and on station, no data from 2321 to 0628. Jan 26th 1997 The system shut down at 1259. The ship was inported in Halifax, Nova Scotia from 1/26 to 1/30. A temperature calibration was performed by David Ho. Feb 6th-7th 1997 The pump was off due to high seas, no data from 1256 to 1715. Feb 9th 1997 The pump was off, no data from 1051 to 1815. Feb 10th-12th 1997 The pump was off, no data from 1721 to 1615. Feb 19th-20th 1997 The pump was off, no data from 0847 to 0915 Feb 21st 1997 The joint on bow air line was severed at 1600 during deicing on starboard deck, unclear how long this has been the case, xCO2 air looked ok, line repaired. Feb 22nd-23rd 1997 The pump was off, no data from 0800 to 2115. Feb 24th-25th 1997 The pump was off, no data from 1800 to 1715. Mar 3rd-5th 1997 The pump was off, no data from 0517 to 1715. Mar 13th 1997 There was no data after 1217. Mar 15th 1997 The system shut down and the equipment was packed and shipped back to AOML by Esa Peltola. Post-cruise: The TSG data set has been continually found to contain errors. Finally in March of 1998, we received the corrected TSG conductivity and temperature readings for the FASTEX cruise. Salinity conversion equations from Ernie Lewis were used to convert the conductivity.