Science at Sea » mud

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.

Filling the MUC with muck!

Liz Kerrigan — Sat, 18 May 2013 11:34:52 +0000

Often times ocean scientists are interested in what’s happening below the water, on the ocean floor. One instrument used to sample deep-water ocean sediments is a Multi-Corer or MUC. What’s cool about a MUC is that it keeps the sediment-water interface intact. The ability of the MUC to preserve the most recent (top) sediment layer makes it unique from gravity or piston corers, which essentially sacrifice the top sediment layers for increased penetration depths and longer cores. We send the MUC instrument, which can be seen in the pictures below, to the bottom of the ocean using a winch. Once the instrument has hit the bottom, the tubes are slowly driven into the sediment and sealed before it is hauled back up to the surface. Using a MUC we can see exactly what’s happening at the seafloor surface even though its been pulled up 4000 m from the bottom of the ocean! In the end, we get about 30-40 cm of sediment from the ocean floor in each MUC tube.

Just by looking at the cores and feeling the mud we can identify boundary and redox layers as well as differences in grain size. But to find out more, we take samples of these cores for future analysis.

If you like getting muddy, then you’ll love sediment work! To sub-sample these cores we remove a tube filled with sediment from the MUC and place it on a stand. Once the core is on the stand we can move it down centimeter-by-centimeter revealing 1 cm of sediment at a time and scraping it off. For the first few really wet centimeters we put the sub-samples in a glass jar. After that we fill syringes with sediment every few centimeters until we get to the end of the core. Since we’re dealing with mud, and not water, we have to cut the tip off the syringe and then push it into the sediment core to get our sub-sample. Once we’ve taken these sub-samples we can look at things like nitrogen isotopes, sediment grain size, and multiple other parameters. Ultimately, this information from the sediment helps us reveal a little bit more about what’s happening in the ocean above, both today and in the past.

An empty MUC on the ship before deployment

The MUC coming up!

Cores filled with sediment

Tip-less syringe to be filled with sediment

Putting the core on to the core stand

Sampling the first few muddy centimeters

Sampling with the tip-less syringe

Tropical Pacific geoscience

Laura deGelleke — Tue, 14 May 2013 18:52:54 +0000

It’s always nice to “have” to go to sea in the tropics, especially when it’s 10 C and rainy back in Halifax. Dal MSc student Liz Kerrigan and her supervisor, Prof. Markus Kienast, are currently sailing aboard the 98 m German research vessel RV Sonne between Kaohsiung in Taiwan and Jayapura in the easternmost corner of Indonesia.

The research work being conducted is, in general, geoscience. What does this mean to student scientists onboard? More often than not it means getting muddy. Inevitably on a geoscience cruise, some amount of mud will be brought up from the seafloor and processed. The fate of the mud varies and depends on who wants it and for what, which often determines how it was retrieved from seafloor. Processing onboard can involve splitting, cutting, sub-sampling mud/porewater, logging, and always labeling. You can see Liz sub-sampling a multi-corer tube in 1 cm slices and using a modified syringe in the pictures below.

Every now and then, crafty professors manage to escape the daily grind at the office and actually make it out on one of their cruises. Markus gets points for craftiness here: not only has he managed to make it out on a cruise, he’s selected a tropical location and is keeping his hands clean… or at least mud-free! You can see Markus sampling seawater from niskin bottles in a CTD rosette in the pictures below. He is hoping water column profiles of nutrient concentrations and the isotopic composition of nitrate will help explain water mass distributions in the study area, and aid in ground-truthing the interpretation of paleoceanographic proxy records.

This cruise (SO-228) combines three cruise proposals for research in the Western Pacific. Read more about the proposed research and cruise plans on the MARUM Bremen University website.

Sampling mud flats despite large tides!

Jessica Carriere-Garwood — Mon, 09 Jul 2012 21:00:27 +0000

You might have heard that the Bay of Fundy is home of the largest tides in the world, reaching heights above 16 m. As part of my Master’s project, I needed to obtain sediment cores from mud flats that experience such huge tides. Our usual hand coring technique consists of using a simple device to push plastic barrels into water-covered sediment, seal them, and bring them out. It is usually carried out from a small ship or even by simply walking into the water (see left picture below). This technique, however, was completely useless in the Bay of Fundy! Instead, we set up two semi-permanent pier that allowed us to walk over the mud without disturbing it and manually dig out our cores at low tide (see right picture below).

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