The sediment-laden ice blocks were rectangular and approximately 1 x 0.4 x 0.25 m in size. The ice blocks were free of air bubbles and each contained enough Bay of Fundy mud to make the ice blocks slightly more dense than seawater. On average, each ice block weighed 135-140 kg and contained about 27 kg of dried mud. The ice blocks were contained within netting just below the surface and instrumented with GPS loggers, PT sensors (above and below), and an HD video camera.2

The sediment-laden ice blocks were deployed in sets of three. The location and timing within the tidal cycle of each deployment was varied. The ice blocks were deployed in the Minas Passage near or immediately after low water, in Cobequid Bay on the ebb, and in the middle of the basin on the flood.

During the deployments, a small boat was used to monitor each ice block drifter. A frame instrumented with another HD video camera and scaling lasers was lowered next to each ice block periodically during the melt. Melt rate will be estimated based on recorded changes in ice block size and compared with model results.

Making ready on deck.

Deploying an ice drifter.

Small boat ready to chase the 3 ice drifters that were just deployed.

Ice drifters deployed from the CCGS Hudson.

Monitoring the ice drifters with a small boat.

Bringing the recovered gear back to the CCGS Hudson.

In July 2012, I had the opportunity to conduct fieldwork in Grand Passage, Nova Scotia. This tidal channel lies between Brier Island and Long Island, along the Digby Neck, and is proposed for in-stream tidal turbine development. We collected acoustic measurements from a bottom-mounted frame with a hydrophone on it.

The greatest moment of suspense every day was when we had to recover the frame. This could only occur during the short time window of low slack tide, as the currents were too great to safely recover at any other time. To recover, an on-board instrument sent an acoustic command to the releases on the frame, and this initiated electrolytic erosion on a hoop of metal. The corrosion of the metal hoop set loose a bungee chord that held down a buoy, causing the buoy and line to float to the surface, and allowing for the frame to be hauled up. However, the buoy may not always surface; signals may not be have been effectively received, the batteries on the releases may have died, or shell hash could have lodged the buoy.

If the frame was not successfully recovered, there could have be delays in field plans, we would have had to hire SCUBA divers to manually release the buoy, or, in the worst case, we could have lost our expensive hydrophones (oh no!). It was always a great relief when the yellow buoy was spotted!

Moment of suspense while we wait for the buoy to surface

As you can see, my supervisor Paul Hill is not one to shy away from heavy work!

Usual hand coring technique.

Hand coring in the Bay of Fundy