RB-04-06
NURP Deep Sea Corals 2004 Cruise Readme File

Ship:			NOAA research vessel Ronald H. Brown
Cruise Start:		Boston, MA, June 17, 2004
Cruise End:		Portsmouth NH, June 28, 2004
Chief Scientist:	Les Watling
System Operator:	Jonathan Shannahoff
Expocode:               33RO20040618

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.	Any values outside the range of the standards (294.06, 357.18, & 423.28 ppm) 
should be considered approximate (within 5 ppm).  While individual data points above 
423 or below 294 may not be accurate, the general trends should be indicative of the 
seawater chemistry.
2.	Elevated air xCO2 values of greater than 380 ppm were recorded at several points
during the cruise.  Since these could not be attributed to stack gas, it was assumed
that they were caused by shore-based sources and they have been left in the data set.
3.	The ship's salinity sensor readings drifted down relative to our Seabird sensor 
near the equilibrator beginning on June 22 at midnight and ending on June 27 at 0922.  
This drift resulted in the ship's readings being offset by as much as 1.5 units less than 
our TSG.  I suspect the problem is with the ship's salinity readings because of large 
discontinuities in the plot of ship's salinity readings vs. time.  I used the apparently
good readings from the beginning of the cruise to the end of June 21 to compute an average 
offset of .1005 (Seabird - ship salinity) with a standard deviation of 0.02.  I then replaced 
all the ship's salinities during this time period with values of Seabird salinity + 0.1005
in the final data file.


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