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Ref. No. [UMCES] CBL 2015-012

ACT VS15-05

Great Lakes Field Test Site

A month-long moored field test was conducted in Lake Michigan from June 21 to July

19, 2014. The Great Lakes deployment site was located at 43.23°N, 86.34°W on a fixed pier at

the Lake Michigan Field Station of the NOAA Great Lakes Environmental Research Laboratory,

in Muskegon, Michigan. The site is located at the outfall of Lake Muskegon into Lake Michigan

with a depth of approximately 3 meters. The temperature range during deployment was 11.6°C

through 24.9°C and salinity averaged 0.031.

Photo 8.

Aerial view of Lake Michigan and Muskegon Lake (left) and rack deployment at GL Site

Time series results of ambient conditions for water depth, temperature, and salinity are

given in figure 12. Temperature ranged from 11.6 to 24.9 and salinity from 0.024 to .035 over

the duration of the field test. While there are no tidal cycles at this site there was significant

exchange between the open lake and the protected basin within the break wall as evidenced by

changes in salinity and water depth. The bottom panel displays the maximum difference recorded

between all reference thermistors (RBR Solo and SBE26) 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 0.08 ±0.18

o

C, with a maximum of 2.53

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 because the sampling bottle integrates across the

mooring space.

The SeaFET operated throughout the entire deployment and generated 2673 observations

based on its 15 minute sampling interval. It should be noted that only results from the internal

pH sensor are reported for this deployment site since the freshwater media does not allow the

external reference electrode to function properly. The internal pH sensor reported ambient pH

over a range from 7.770 to 8.594, compared to 8.013 to 8.526 captured by the reference pH

measurements (Fig. 13). The bottom panel presents the time series of the difference between the

SeaFET and reference pH for each matched pair (n=98 observations). The average and standard

deviation of the difference for the entire deployment was -0.183 ± 0.040 with a total range of -

0.347 to -0.090.