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Ref. No. [UMCES] CBL 2015-008

ACT VS15-01

12

Reference Water Sample Collection

– A standard 2.2 or 4.2L Van Dorn water sampler was used

at each field test site to collect water samples for reference pH measurements. Water sample

collections were timed to correspond directly with the instrument readings or sample intake. The

water sampler was lowered to the same depth of the instrument sampling inlets, and as close as

physically possible to the inlets (distant by no more than 0.5 m horizontal distance). The water

sampler was soaked at sampling depth for 1 minute prior to sampling. If water was not flowing,

the sampler was moved to ensure that it was flushed with the ambient water. The water sampler

was triggered to match the programmed sampling times of each instrument. Three replicate pH

samples were collected in clean 10 cm glass spectrometer cuvettes from each individual field

sample. The cuvettes were gravity filled from PTFE tubing connected to the sampling bottle

spigot such that the volume of the cuvette was exchanged three times (about 20-30 secs) before a

final sample is collected. Care was taken to ensure that no bubbles were left within the cuvette

before sealing the ports with their PTFE stoppers. Cuvettes were stored at ambient or slightly

cooled conditions during transport to the laboratory (travel times at various field sites ranged

from 5 to 20 minutes) until they were placed into the temperature equilibration chamber at the

specified temperature for analysis. In addition, at the freshwater site an additional 300 ml BOD

bottle was filled to allow for a lab-based electrode pH measurement on each field reference

sample. All samples were equilibrated to 25°C and analyzed on a lab electrode calibrated daily

before use.

Twice a week (day 1 and day 5) duplicate water samples were collected to characterize

all of the CO

2

parameters. (This sample collection occurred in conjunction with our field

duplicate sampling and one set of external partner samples came from each Van Dorn. This

protocol was mostly to facilitate limitations of volume but also helped to evaluate heterogeneity

at the mooring.) Water samples were collected and preserved for pH, pCO

2

, TCO

2

and TA

measurements following standard oceanic protocols (Dickson et al., 2007). In brief, a 500 mL

glass sample bottle (supplied by Andrew Dickson, SIO) was filled from the Van Dorn sampling

bottle using PTFE tubing and preserved with 110 µL of saturated HgCl

2

solution. Reference

samples shipped to Oregon State University (Burke Hales, OSU) were analyzed for pCO

2

and

TCO

2

. Reference samples shipped to Scripps Institution of Oceanography (Andrew Dickson)

were analyzed for TA and pH. Reference samples shipped to the University of South Florida

(Robert Byrne) were analyzed for pH. These externally sample analyses provided further

estimation of the uncertainty of ACT’s reference sample measurements through both direct pH

measurement and calculated pH from carbonate parameters using CO

2

-Sys (Pierrot et al., 2006).

However, because these samples were not handled in a manner identical to the unpreserved

reference samples that were analyzed within a few hours of collection, they will not be used in

any published direct assessment against the test instruments without agreement of the TAC.

All sampling procedures were practiced by ACT staff prior to the beginning of the

evaluation, and the Chief Scientist verified that all staff were trained in both instrument and

sample collection protocols. A preservation test was done at each site to ensure samples that

were shipped for external analysis were stable.

Sample Handling and Custody Requirements -

All collected reference water samples for all four

field tests were handled in the same manner. All reference samples were processed according to

methods defined within these protocols and cited Standard Operating Procedure documents

(Dickson et al. 2007). Each reference sample was dated and coded according to site, test

condition and sample sequence. The actual sample container was labeled with a number for