Vents98 Leg 4 Readme File

Ship:			NOAA research vessel Ronald H. Brown
Cruise Start:		Victoria, BC, Canada, September 23, 1998
Cruise End:		Seattle, WA, October 3, 1998
Chief Scientist:	Hugh Milburn
System Operator:	Marilyn Roberts
Expocode:               33RO19980923 

Method:
Infrared absorption of dry gas.  Measurement of fugacity of Carbon 
Dioxide in surface water and air using continuous sampling methods.  
See Wanninkhof and Thoning, 1993 in Marine Chemistry, 44, 189-205 
for details of the system.  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).

Notes for Leg 4:
1. The ship's salinity sensor began giving erratic readings near the 
end of the previous leg.  By the end of leg 3, the readings settled 
down.  However, the offset between the YSI TSG attached to our 
system and the ship's TSG changed.  For most of leg 3 the YSI gave 
readings about 0.15 higher than the ship's TSG.  From near the end 
of leg 3 and for all of leg 4, the YSI read about 0.07 lower than 
the ship's TSG.  I have left the ship's salinity values as they 
were recorded and used them to compute fCO2, etc for this leg.
2. Problems with the PC clock and the feed from the ship's computer 
system resulted in the loss of about 2-1/2 hour's worth of data at 
the beginning of leg 4 (from 267.014 through 267.109).
Dec. 12, 2000:
3. Starting on Oct. 1 the lat and lon from the ship's computer
system included only 3 significant digits.  I fixed this by 
interpolating latitude and longitude values.

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