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Ref. No. [UMCES] CBL 2016-010

ACT VS16-01

43

Moored Deployment at Michigan Tech Great Lakes Research Center

The

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 is

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 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 87 - 137 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 were noted on three occasions during

the test. Upon inspection it was determined that these shifts 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. Adjusted values are

noted within each figure.

The AroW-USB operated successfully throughout the entire 15 week deployment and

generated 9859 observations based on its 15 minute sampling interval, for a data completion result of

100%. Time series results of the AroW-USB and corresponding reference DO results are given in

figure 2 (top panel). Ambient DO measured by the AroW-USB ranged from 8.669 to 15.076 mg/L

compared to the range captured by reference samples of 10.918 to 14.007 mg/L. The sharp excursion

observed the second week of April was real and was picked up by all instruments and correspondingly

seen in specific conductance and temperature variability across the instrument rack (Fig. 1).