Epic 2001 Leg A Readme File

Ship:				NOAA research vessel Ronald H. Brown
Cruise Start:			San Diego, CA, Sep. 10, 2001
Cruise End:			Santa Cruz, Galapagos Islands, Oct 6, 2001
Chief Scientist:		Chris Fairall
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.	Extremely high pCO2 values were encountered near the end of the cruise.  
Any values outside the range of the standards (292, 401, & 525 ppm) should be
considered approximate (within 5 ppm).  While individual data points below 296 
may not be accurate, the general trends should be indicative of the seawater 
chemistry.
2.	The system was shut down for approximately 6-2/3 days from Sep. 14 to Sep. 20
because of a mechanical failure.
3.	On Sep. 27 at 2230, gas flow in the air phase dropped to zero because of  
clogged tubing.  For the remainder of the cruise I have inserted air values from
the CO2 rug file of Pieter P. Tans and Thomas J. Conway of the NOAA Climate 
Monitoring and Diagnostics Laboratory (CMDL).  This file gives atmospheric CO2 
concentrations by latitude band through 2000.  The replaced air values were derived
by adding 1.6 ppm to the Sep. 30, 2000 values for each latitude band.  The value of 1.6
ppm is the average increase from 2000 to 2001 (personal communication from Tom Conway).

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