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Ref. No. [UMCES] CBL 2016-015
ACT VS16-06
30
Michigan Tech Great Lakes Research Center Field Deployment Site
A
15 week deployment under ice took place from January 9 through April 22 in the
Keweenaw Waterway adjacent to the Great Lakes Research Center in Houghton, MI. The
deployment site was located at 47.12° N, 88.55° W, at the end of the pier at the Great Lakes
Research Center docks. This site is located on the south side of the Keweenaw Waterway, and is
connected to Lake Superior in both the NW and SE directions. The instrumentation rack was
lowered off of the end of the pier with a ½ ton crane and rested on the bottom, under the ice, in
4.5m of water. A small shelter was constructed at the end of the pier to provide shelter for
processing the reference samples during winter sampling efforts.
Photo 1.
Aerial view of the Keweenaw Waterway (left) and dockside mooring deployment (right).
Time series results of ambient conditions for temperature and specific conductivity are
given in figure 1. Temperature ranged from 0.04 - 5.3
o
C and specific conductivity from 49 - 110
µS/cm over the duration of the field test. The bottom panel displays the maximum difference
recorded between all reference thermistors mounted at the same depth as the sensors sampling
intakes as well as a meter above, at different locations across the mooring rack. The average
temperature difference observed across the space of the mooring rack was 0.01
°
C with a maximum
of 0.98
o
C. Differences between instrument and reference readings resulting from this variability
should be minimized as the sampling bottle integrates across the mooring space.
Unexpected shifts between adjacent reference samples of magnitudes were noted on three
occasions (during the test. Upon inspection it was determined that these excursions occurred
during changes in the batches of Winkler reagents. A correction to reference values was
subsequently made based on the magnitude of change observed between the adjacent Winkler
measurements after adjusting for ambient changes determined by the average of all seven DO
sensors deployed on the mooring. The magnitude of adjustment was 0.27, 0.26, and 0.13 mg/L on
1/19, 2/23, and 3/16, respectively. Adjusted values are noted within each figure.
The EXO2 sonde operated successfully throughout the entire 15week deployment and
generated 9859 observations based on its 15 minute sampling interval for a data completion result
of 100%. Time series results of the EXO2 and corresponding reference DO results are given in
figure 2 (top panel). Ambient DO measured by the EXO2 ranged from 9.01 to 14.03 mg/L