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Ref. No. [UMCES] CBL 2015-009
ACT VS15-02
11
sampling times were recorded on logsheets and entered into a database for final data
comparisons.
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 external 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