Indoex99 Leg 3 Readme File

Ship:			NOAA research vessel Ronald H. Brown
Cruise Start:		Male, Maldives, March 26, 1999
Cruise End:		Male, Maldives, April 2, 1999
Chief Scientist:	Tom Carsey
System Operator:	Drew Hamilton
Expocode:               33RO19990326 

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 3:
1. The system was down for approximately 13 hours beginning on YD 
87.577 when the PC froze up.
2. The Air Cadet that pumps ambient air from the bow mast had failed on 
the previous leg and never pumped enough air to flush the Licor IR 
analyzer during this leg.  All air values for this leg were 
discarded.  I inserted air xCO2 values by using the base value 371.8 
ppm at 4N which was taken from the values observed on the previous 
leg.  I then added 0.15 * (measurement_latitude - 4) to the base 
value to arrive at an xCO2 value for each air measurement.  The 
number 0.15 comes from the CO2 rug file for 1981 - 1995 and is an 
approximation of how much air xCO2 values tend to rise per degree of 
latitude in the latitude range for this cruise leg.
3. Large variations in water xCO2 values cause me to suspect a serious 
air leak in the water line leading into the equilibrator.  I removed 
a large number of data points from the final file.  Further, periods 
of low xCO2 variability seem to coincide with times late at night 
when few if any people would have been in the lab.

For questions or comments contact:
Bob Castle
4301 Rickenbacker Causeway
Miami, FL 33149
305-361-4418
castle@aoml.noaa.gov