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Ref. No. [UMCES] CBL 2015-012
ACT VS15-05
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, 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.
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 all reference thermistors mounted at the same depth but located 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 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 4211
observations based on its 30 minute sampling interval. Time series results of the SeaFET and
corresponding reference pH results are given in figure 7. Ambient pH measured by the SeaFET
ranged from 7.814 to 8.084 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 SeaFET and
reference measurements for each matched pair (n=101 observations). The average and standard
deviation of the differences were -0.014 ±0.009 with a total range in the differences of -0.042 to
0.019.