Indoex99 Leg 2 Readme File

Ship:			NOAA research vessel Ronald H. Brown
Cruise Start:		Male, Maldives, March 4, 1999
Cruise End:		Male, Maldives, March 23, 1999
Chief Scientist:	Tom Carsey
System Operator:	Drew Hamilton
Expocode:               33RO19990304 

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 2:
1. The system was down for approximately 8 hours beginning on YD 73.380 
for calibration of the YSI TSG.
2. The system was down for approximately 8 hours beginning on YD 
77.213.
3. The Air Cadet that pumps ambient air from the bow mast began to fail 
on YD 77.857.  Flow through the Licor IR analyzer dropped steadily 
for the rest of the leg and for the last day there were no usable 
air measurements.  When possible, I used the third of each group of 
three air readings, but in some cases complete flushing of the 
sample cell did not occur.  Since the second half of the leg was 
spent steaming south from Male to about 13S and then turning around 
and steaming north back to Male, I used average air xCO2 values from 
the southbound section and pasted them into northbound spots that 
corresponded in latitude.  This allowed me to match the gradient 
from 2N to 5S where xCO2 levels dropped about 2 ppm.  The north and 
south bound sections were no more than 3 degrees of longitude apart.
4. The PC clock was reset prior to this leg to match GMT as it had 
become off by about 3 minutes.  However, this PC has an annoying 
habit of changing the date when the time is reset and in the raw 
data file dates went from 2/9 to 2/28.  I changed these to the 
correct dates in the final data file.
5. The low standard tank was changed on YD 69.285 from 283.26 to 298.46 
ppm.
6. On several occasions, large changes in water xCO2 values were 
observed.  I believe these were caused by intermittent air leaks in 
the uncontaminated seawater line feeding the equilibrator.  This 
problem recurred 2 months later in a non-intermittent form.  I 
removed about 130 water values that I suspected were bad.  I left in 
2 water xCO2 spikes (on YD 77.6 and 78.2) that are likely real due 
to rapid changes in temperature and fluorometer readings.

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