Transit 1997 Leg 3 Readme File



Ship:			NOAA research vessel Ronald H. Brown

Cruise Start:		Panama Canal, November 11, 1997

Cruise End:		Key West, FL, November 14, 1997

Chief Scientist:	None (transit)

System Operator:	Jonathon Shanahoff



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 3:

1. There were problems with valve mistrips that occurred ~ 1.5% of the 

time, causing the wrong gas to be routed through the Licor infrared 

analyzer.  If these occurred during water or air sampling phases, 

they were removed.  When they occurred during standard gas phases, 

the Licor voltage readings of the appropriate standard gas phase 

before and after the bad reading were averaged to produce an 

interpolated reading.

2. Data from the ship's computer system (SST, salinity, wind speed and 

direction) were merged into the system's data file with an 

approximate 3 minute delay factor.  This is to account for the time 

it takes for seawater to travel from the bow intake to the 

equilibrator in the Hydro Lab.

3. The equation used to convert the equilibrator thermistor voltage to 

temperature was incorrect, resulting in values that were 

approximately 0.9 degrees too high.  In addition, relay closures 

affected the voltage readings from the thermistor.  To obtain 

correct equilibrator temperature readings, we assumed that the YSI 

TSG temperature was the same as the equilibrator temperature since 

both sample seawater from the same source in the Hydro Lab.  

However, the YSI TSG temperature readings are known from 

calibration data to be about 0.2 degrees high.  We therefore 

determined a corrected YSI temperature by using calibration data to 

fit a linear equation relating observed YSI temperature to actual 

temperature as given by a Guildline platinum resistance thermometer 

(New YSI T = 1.0026885 * Old YSI T - 0.272854). A new equation 

relating thermistor voltage to the corrected YSI T was then 

determined using all the data from leg 2 of the PACS 1997 cruise (T 

= 6.0955*V^3 -46.862*V^2 + 101.16V - 28.638.



For questions or comments contact:

Bob Castle

4301 Rickenbacker Causeway

Miami, FL 33149

305-361-4418

castle@aoml.noaa.gov