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Ref. No. [UMCES] CBL 2015-014
ACT VS15-07
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Moss Landing Marine Laboratories Field Deployment Site
A month-long moored field test was conducted at the Moss Landing Marine Laboratories
from August 26 to September 22, 2013. The deployment site was located at 36.80°N, 121.79°W,
in the Small Boat Facilities area of Moss Landing Harbor (Photo 2). This secure deployment site
was located in the Harbor on the junction of the northern tributary of the Salinas River and
Elkhorn Slough National Estuarine Reserve on the central coast of California. Instrumentation
was deployed off a floating dock in waters with a tidal range of 2 meters and a maximum depth
below the dock of 4 meters.
Photo 2.
Aerial view of MLML Harbor (left) and dockside mooring deployment (right).
Time series results of ambient conditions for tidal height, temperature, and salinity are
given in figure 13. Temperature ranged from 14.9 to 18.6 and salinity from 30.7 to 33.7 over
the duration of the field test. The bottom panel displays the maximum difference recorded
between all reference thermistors (RBR solo and SBE 26) mounted at the same depth and
different locations across the mooring rack. The average temperature difference observed was
0.11
o
C with a maximum of 0.8
o
C. The difference between the test instruments instantaneous
temperature reading and the final reference temperature will contribute to the variability and
offset to the calculated ambient reference pH. It is not possible to quantify the exact difference
between the averaged reference temperature and that measured by the test instrument, but a
difference of 1
o
C would amount to an approximate offset of 0.015 pH units at ambient
conditions. Additional differences resulting from variation in the actual chemistry of the water
across this space may exist but will be minimized because the sampling bottle integrates across
the mooring space.
The EXO sonde deployed for this field test contained two separate pH probes and each
probe is reported on separately and designated as EXO-pH1 and EXO-pH2 as defined by the
sensor location ID. Both probes operated continuously over the 28 days of the deployment and
each generated 2575 observations at 15 minute intervals. Time series results of the EXO-pH1
and corresponding reference pH results are given in figure 14. Ambient pH measured by the
EXO-pH1 ranged from 7.96 to 8.27, compared to the range captured by reference samples of
7.933 to 8.077. The bottom panel presents the time series of the difference between instrument
and reference pH measurements for each matched pair (n=84 observations). The average and