Transit 1998 Leg 2 Readme File Ship: NOAA research vessel Ronald H. Brown Cruise Start: Panama Canal, July 16, 1998 Cruise End: Newport, OR, July 27, 1998 Chief Scientist: NA System Operator: Jason Masters Expocode: 333RO19980716 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 2: 1. This leg (also known as Gasex98 leg 4) has been broken into two sub-legs, from Miami to Panama and from Panama to Newport, OR. 2. Salinity and temperature from the ship's TSG were merged after the cruise with a 3 minute delay to account for the time it takes seawater to travel from the bow intake to the hydro lab. 3. On YD 204.127 the high standard tank was changed from 408.35 to 523.27 ppm because of high surface water xCO2 levels. 4. One hour later the mid standard was changed from 360.62 to 408.35 ppm. 5. On YD 204.836 the low standard was changed from 299.06 to 360.62 ppm. 6. On YD 205.419 the standard tanks were changed from 360.62, 408.35, 523.27, to 299.06, 360.62, 408.35 ppm. 7. For the last day of this leg (nearing Newport) large variations in surface water xCO2 values were observed. I left these in the data file because of simultaneous large changes in SST and SSS. 8. Latitude and longitude values were recorded by the system with only 3 places of precision (e.g. -80.1, 9.97, etc). I merged SCS data provided by the ship into the data file to obtain better values. For questions or comments contact: Bob Castle 4301 Rickenbacker Causeway Miami, FL 33149 305-361-4418 castle@aoml.noaa.gov