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