Science at Sea » CCGS Hudson

Muddy ice in Minas Basin

Laura deGelleke — Tue, 09 Jul 2013 19:40:04 +0000

In June 2013, researchers from DFO (BIO), Dalhousie, and Acadia sailed on the CCGS Hudson to do some science. During the cruise, we deployed twelve sediment-laden ice blocks in Minas Basin to assess melt rates and observe drift. This work is part of a larger project aiming to survey the occurrence of sediment-laden and occasionally negatively buoyant ice blocks forming in tidal river estuaries of the upper Bay of Fundy. Melt rate and transport are of concern for assessing risk of collision with bottom-mounted tidal turbines.

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 oceanographic rosette

Mathieu Dever — Mon, 08 Apr 2013 01:56:14 +0000

A rosette is not an oceanographic instrument itself. It is a round frame tied to a winch on which different instruments can be mounted. During the AZMP (Atlantic Zone Monitoring Program) cruise in April 2013, the rosette for a typical profile includes two CTDs, two optodes, two fluorometers, two ADCPs (one looking up, the other looking down) and up to 24 Niskin bottles. Sometimes, we used additional space to include other sensors for calibration purposes (e.g. MicroCats).

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.

Grand Banks/Flemish Cap geoscience

Laura deGelleke — Thu, 15 Sep 2011 17:42:17 +0000

In August 2011, I had the opportunity to sail on the CCGS Hudson for a seismic and sediment coring expedition to the Grand Banks and Flemish Cap. We collected over 60 piston cores in 15 days and made seismic transects all night! … and I made some great friends and got screeched in while we stopped in St. John’s, Newfoundland for a crew change