RB-04-06 NURP Deep Sea Corals 2004 Cruise Readme File Ship: NOAA research vessel Ronald H. Brown Cruise Start: Boston, MA, June 17, 2004 Cruise End: Portsmouth NH, June 28, 2004 Chief Scientist: Les Watling System Operator: Jonathan Shannahoff Expocode: 33RO20040618 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 (294.06, 357.18, & 423.28 ppm) should be considered approximate (within 5 ppm). While individual data points above 423 or below 294 may not be accurate, the general trends should be indicative of the seawater chemistry. 2. Elevated air xCO2 values of greater than 380 ppm were recorded at several points during the cruise. Since these could not be attributed to stack gas, it was assumed that they were caused by shore-based sources and they have been left in the data set. 3. The ship's salinity sensor readings drifted down relative to our Seabird sensor near the equilibrator beginning on June 22 at midnight and ending on June 27 at 0922. This drift resulted in the ship's readings being offset by as much as 1.5 units less than our TSG. I suspect the problem is with the ship's salinity readings because of large discontinuities in the plot of ship's salinity readings vs. time. I used the apparently good readings from the beginning of the cruise to the end of June 21 to compute an average offset of .1005 (Seabird - ship salinity) with a standard deviation of 0.02. I then replaced all the ship's salinities during this time period with values of Seabird salinity + 0.1005 in the final data file. For questions or comments contact: Bob Castle 4301 Rickenbacker Causeway Miami, FL 33149 305-361-4418 robert.castle@noaa.gov