Transit 1998 Leg 1 Readme File Ship: NOAA research vessel Ronald H. Brown Cruise Start: Miami, FL, July 12, 1998 Cruise End: Panama Canal, July 16, 1998 Chief Scientist: NA System Operator: Jason Masters Expocode: 33RO19980712 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 1: 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. The YSI TSG suffered from an apparent low water flow condition for this entire leg. Salinity values begin to degrade noticeably on YD 195.25 and temperature before that. 3. SCS salinity and temperature data was bad until YD 193.553 approximately the first 13 hours). I did a linear fit of Equilibrator temperature to SCS temperature readings and derived SST by the following equation: SST = (EqT * 1.009079) - 0.331455 with R^2 = 0.989783. For SSS I did an eyeball check of YSI salinity vs SCS salinity for the period from 193.6 to 195 when there was a near constant offset between the two. I then replaced the SCS salinities up to YD 193.553 with computed salinities using the formula SSS = YSI sal - 0.07. 4. The Air Cadet that pumps air from the bow tower to the system went bad on YD 194.3 and was repaired on 195.7. In most cases I used the last of 3 air measurements during this time period. 5. 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