VENTS 2000 Readme File Ship: NOAA research vessel Ronald H. Brown Cruise Start: Newport, OR, March 24, 2000 Cruise End: Seattle, WA, April 9, 2000 Chief Scientist: System Operator: Jonathan Shannahoff Expocode: 33RO20000324 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: 1. Due to problems getting the system running, no data was collected before April 1. Data in this file covers the period from April 1 at 0000 GMT through April 4 at 0246 GMT. 2. The regulator on the mid standard tank failed and there was no gas flow in that phase for the entire cruise. Examination of the Licor voltage response during the previous cruise showed a relationship between mid standard voltage response and voltage response in the low and high standard phases. This relationship is (VM - VL)/(VH - VL) = 0.421 where VL, VM, and VH are voltages in the low, mid and high standard phases respectively. Using this equation, a synthetic mid standard voltage was created and applied to the previous cruise. The difference between using the real and synthetic voltages for the previous cruise was less than 0.5 ppm. All concentrations for the current cruise were computed using this synthetic mid standard voltage. For questions or comments contact: Bob Castle 4301 Rickenbacker Causeway Miami, FL 33149 305-361-4418 castle@aoml.noaa.gov