Indoex99 Leg 3 Readme File Ship: NOAA research vessel Ronald H. Brown Cruise Start: Male, Maldives, March 26, 1999 Cruise End: Male, Maldives, April 2, 1999 Chief Scientist: Tom Carsey System Operator: Drew Hamilton Expocode: 33RO19990326 Method: Infrared absorption of dried gas. For details of the system see: Measurement of fugacity of Carbon Dioxide in surface water and air using continuous sampling methods. Wanninkhof and Thoning, 1993 in Marine Chemistry 44, 189-205, And: Feely, R.A., R. Wanninkhof, H.B. Milburn, C.E. Cosca, M. Stapp, and P.P. Murphy, A new automated underway system for making high precision pCO2 measurements onboard research ships, Analytica Chim. Acta, 377, 185-191, 1998. The three standard gases come from CMDL in Boulder and are directly traceable to the WMO scale. 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. Notes for Leg 3: 1. The system was down for approximately 13 hours beginning on YD 87.577 when the PC froze up. 2. The Air Cadet that pumps ambient air from the bow mast had failed on the previous leg and never pumped enough air to flush the Licor IR analyzer during this leg. All air values for this leg were discarded. I inserted air xCO2 values by using the base value 371.8 ppm at 4N which was taken from the values observed on the previous leg. I then added 0.15 * (measurement_latitude - 4) to the base value to arrive at an xCO2 value for each air measurement. The number 0.15 comes from the CO2 rug file for 1981 - 1995 and is an approximation of how much air xCO2 values tend to rise per degree of latitude in the latitude range for this cruise leg. 3. Large variations in water xCO2 values cause me to suspect a serious air leak in the water line leading into the equilibrator. I removed a large number of data points from the final file. Further, periods of low xCO2 variability seem to coincide with times late at night when few if any people would have been in the lab. For questions or comments contact: Bob Castle 4301 Rickenbacker Causeway Miami, FL 33149 305-361-4418 castle@aoml.noaa.gov