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Ref. No. [UMCES] CBL 2015-010
ACT VS15-03
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 3). Kaneohe Bay, located on the eastern side of Oahu, is a complex estuarine system with
a large barrier coral reef, numerous patch reefs, fringing reefs, and 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 one meter below the surface.
Photo 3.
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 9. 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 Idronaut 305 Plus operated continuously for the first twenty seven days (total
deployment was 88 days) after which there appeared to be a short in the battery which terminated
logging. During its operational period the instrument generated 2756 observations measured at
30 minute intervals. The time series results of the 305 Plus and corresponding reference pH
results are given in figure 10. Ambient pH measured by the 305 Plus ranged from 7.599 to
8.409, compared to a range in reference pH values over the same time of 7.814 to 8.084. The
bottom panel presents the time series of the difference between instrument and reference
measurements for each matched pair (n=62 observations out of a possible 101 for the entire
deployment). The average and standard deviation of the differences were 0.107 ±0.093 with a
total range in the differences of -0.030 to 0.387.
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