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Ref. No. [UMCES] CBL 2015-008
ACT VS15-01
31
Moored Deployment off Coconut Island in Kaneohe Bay, Hawaii
A three month-long moored field test was conducted in Kaneohe Bay from November 15,
2013 to February 10, 2014. The deployment site was located at 21.46° N, 157.80° W in the
back-reef region of the barrier reef offshore of Coconut Island (HIMB) in a depth of 3 meters
(Photo 4). Kaneohe Bay, located on the eastern side of Oahu, Hawaii, is a complex estuarine
system with a large barrier coral reef, numerous patch reefs, fringing reefs, and several riverine
inputs. Tides in Kaneohe Bay are semi-diurnal with mean tidal amplitude of approximately 68
cm day. The pH instruments were mounted on the Crimp II Buoy (right), about on meter below
the surface.
Photo 4.
An aerial view of HIMB deployment site (left) and sampling at deployment buoy (right).
Time series results of ambient conditions for tidal height, temperature, and salinity are
given in figure 11. Temperature ranged from 22.3 to 26.5 and salinity from 32.8 to 35.2 over
the duration of the field test. The bottom panel displays the maximum difference recorded
between reference thermistors mounted at the same depth across the mooring rack. The average
temperature difference observed across the space of the mooring rack was 0.04 ±0.10
o
C with a
maximum of 0.65
o
C. As noted above, it is not possible to quantify the exact difference between
the averaged reference temperature and that measured by the test instrument, but differences
resulting from this variation and variation in the chemistry of the water across will be minimized
because the sampling bottle integrates across the mooring space.
The CSI operated continuously over the 88 days of the deployment and generated 4211
observations measured at 30 minute intervals. The time series results of the CSI and
corresponding reference pH results are given in figure 12. Ambient pH measured by the CSI
ranged from 7.886 to 8.470, compared to a range in reference pH values of 7.814 to 8.084. The
bottom panel presents the time series of the difference between CSI and reference measurements
for each matched pair (n=101 observations). The average and standard deviation of the
differences were 0.221 ±0.066 with a total range in the differences of 0.076 to 0.316.