20 / 48
Ref. No. [UMCES] CBL 2015-012
ACT VS15-05
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 36.81°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 3. 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 mounted at the same depth and different locations across the mooring
rack. The average temperature difference observed across the space of the mooring rack 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 SeaFET operated successfully throughout the entire deployment and generated 2576
observations based on its 15 minute sampling interval. Time series results of the SeaFET and
corresponding reference pH results are given in figure 4. Ambient pH measured by the SeaFET
ranged from 7.795 to 8.106 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
standard deviation of the measurement difference over the total deployment was - 0.008 ± 0.029
with a total range of -0.107 to 0.063.