Vents 2000 Leg 3 Readme File

Ship:			NOAA research vessel Ronald H. Brown
Cruise Start:		Victoria, BC, July 20, 2000
Cruise End:		Seattle, WA, August 4, 2000
Chief Scientist:	Ed Baker
System Operator:	Jonathan Shannahoff
Expocode:               33RO20000720

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. In several instances, water concentrations outside the range
of the standard gases (281.16, 356.99, & 420.47) were encountered, 
especially near the beginning and end of the cruise.  Any such values
should be considered to be rough estimates only.
2. Due to high variation in air xCO2 values I replaced all air xCO2 values 
with 363.00, which I derived from climatology records provided by CMDL in Boulder.  
I used values from the station in Cape Meares, OR from 1989 to 1997.  There were
no good values for 1993 and 1995.  For each year I averaged all readings taken 
between July 20 and August 4 and plotted them by year.  I used a linear fit to 
extrapolate to the year 2000 to arrive at the value of 363.00.  This value is
in close agreement with the minimum air values observed during the cruise.
3. On July 29 at approximately 1800 GMT the difference between the equilibrator
temperature (EqT) and SST drops about 0.11 degrees C (from ~ 0.42 to ~ 0.31)
and stays that way for the remainder of the cruise.  EqT is measured at the 
equilibrator in the Hydro Lab and SST is measured at the seawater intake in the 
bow of the ship.  For SST in the range of 16-17 degrees C, the normal difference
is about 0.4 degrees.  I will attempt to find out more information about this
discrepancy.

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