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.

The R/V Planet is unlike any ship that I have ever seen. The ship is owned by FWG (WTD 71), a German naval research organization. While at first glance it appears to be a type of catamaran, it is actually a SWATH (Small Waterplane Area Twin Hull) vessel. The main difference between the two is in the volume of the ship that comes in contact with wave energy. Both ships are stabilized by twin hulls, but a catamaran has two conventional hulls, while a SWATH ship’s design is more like a platform built on top of two submarines. Because of this, only the parts of the ship that connect the platform to the submarines will be affected by wave energy. This makes the R/V Planet very stable in rough seas, which is beneficial for acoustic research work. Additional measures, such as suspending the ship’s diesel generators on springs, have been taken to minimize ship noise that may contaminate acoustic measurements.

This was the R/V Planet’s first trip across the Atlantic Ocean to collaborate with American scientists. The goal of our expedition was to better understand how mines bury in carbonate sediments and to classify the seafloor off the coast of Cape Canaveral, Florida, where carbonate sediments are known to be abundant. Additionally, we were able to collect information to expand dbSeabed, a database managed by Dr. Chris Jenkins (University of Colorado at Boulder) that provides geographic seafloor substrate data by compiling thousands of individual datasets.

We collected our data primarily using 3 instruments: 1. sidescan sonar, 2. a van Veen grab, and 3. a Burial Recording Mine produced by FWG. An underwater camera was also deployed as an additional means of ground truthing. The sidescan sonar provided images of the seafloor by transmitting a fan-shaped sound beam and interpreting the acoustic backscatter, or echoes, returned to the receiver. The sidescan data allowed us to categorize the seafloor by it’s acoustic profile. Grab samples were collected periodically along short transects to determine the relationship between actual seafloor properties and the acoustic backscatter data collected by the sidescan. For example, we observed higher backscatter in regions with courser grains and lower backscatter in regions with finer grains. We also deployed a Mine Burial Recorded (MBR), a tool developed by FWG to test seafloor mine burial. The MBR uses the case of an old mine that has three rings of light sensors attached. As the mine buries, the light sensors become covered and it is possible to tell how deeply the mine penetrated the seafloor.

What an experience!

Deploying the sidescan sonar from the R/V Planet.

The Mine Burial Recorder (MBR) developed by FWG – Kiel.

All of these instruments make in-situ measurements. But sometimes there is no instrument capable of measuring the quantity we are interested in (radioactive isotopes concentration, bacterial analysis, etc). That is why we use Niskin bottles to take water samples. They are tied open in the wet lab and then remotely triggered to seal shut and trap water at a given depth. But you have to make sure you fire these bottles on the way up! If a bottle is sealed on the way down, the extra pressure at depth, compared to the pressure of the sampled water, is going to crush the bottle. While on the way up, the extra pressure of the trapped water can be released without contaminating the water sample.

Once the rosette is back on deck, we transfer the required volume of water into labeled bottles for future processing in the laboratory.