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Ref. No. [UMCES] CBL 2015-014
ACT VS15-07
38
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.
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 18. 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 (RBR solo and SBE 26) 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 will be minimized because the sampling bottle integrates across the
mooring space.
The EXO sonde deployed for the Hawaii field deployment also 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. The sonde operated for the first 16 days, but by November
30
th
the battery voltage had dropped to 4.7 volts and the sonde stopped measuring. Both probes
recorded 1445 observations measured at 15 minute intervals during the first 16 days of operation.
Time series results of the EXO-pH1 and corresponding reference pH results are given in figure
19. Ambient pH measured by the EXO-pH1 ranged from 7.90 to 8.33, compared to the range
measured from reference samples of 7.814 to 8.084. The bottom panel presents the time series
of the difference between instrument and reference pH measurements for each matched pair
(n=29 observations out of a possible 101 for the total deployment). The average and standard
deviation of the difference between EXO-pH1 and reference pH over the total deployment was
0.20 ± 0.02 with a total range of 0.17 to 0.23.