RB-06-05B AMMA African Monsoon/Sahara Dust Cruise Leg B Readme File Ship: NOAA research vessel Ronald H. Brown Cruise Start: Recife, Brazil, June 23, 2006 Cruise End: Charleston, S.C., July 14, 2006 Chief Scientist: Claudia Schmid System Operator: Jonathan Shannahoff 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. Any values outside the range of the standards (303.23, 370.90, & 411.42 ppm) should be considered approximate (within 5 ppm). While individual data points above 411 or below 303 may not be accurate, the general trends should be indicative of the seawater chemistry. 2. There were three data dropouts: on July 6 at 0733 for 3 hours, on July 8 at 0120 for 11.5 hours, and on July 12 at 1015 for 29 hours. 3. On July 11 at 0200 there was an abrubt drop in air values from about 382 to about 377.5 ppm and the values remain constant for about 1.25 days when there is a data dropout. After the dropout, the air values return to the 382 ppm level for the remainder of the cruise. A check of the air values from the Carbon Cycle Greenhouse Gas group at NOAA's Earth System Research Laboratory ( http://www.cmdl.noaa.gov/ccgg/ ) shows that the values recorded at the nearest station (St. David's Head, Bermuda) for that time were also in the high 370's. For questions or comments contact: Bob Castle 4301 Rickenbacker Causeway Miami, FL 33149 305-361-4418 robert.castle@noaa.gov