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Researchers hope to fill gaps in sea science with gliders

Right now, Fisheries and Oceans Canada sends out a ship twice a year to take water samples along a line that stretches about 200 kilometres southeast of Halifax. But the department is hoping a plan to buy autonomous gliders will give it near constant access to information about the sea off our shores.
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Physicist Clark Richards explains the basic workings of a Slocum ocean glider at the Bedford Institute of Oceanography on Monday. The glider is used to gather a variety of underwater data. (CHRISTIAN LAFORCE / Local Xpress)

Right now, Fisheries and Oceans Canada sends out a ship twice a year to take water samples along a line that stretches about 200 kilometres southeast of Halifax.

But the department is hoping a plan to buy autonomous gliders will give it near constant access to information about the sea off our shores.

“The idea with the gliders is that we can occupy these lines pretty much all the time,” said Clark Richards, a research scientist at the Bedford Institute of Oceanography.

Using ship-based sampling doesn’t give the physicist or his DFO colleagues a constant picture of what’s happening on the Scotian Shelf.

“A lot of things can happen very quickly. Changes can occur on very short time and spatial scales. So using the gliders is really a way to try and fill in the gaps,” Richards said.

The gliders — which can measure temperature, salinity and the amount of dissolved oxygen in seawater — aren’t meant to replace ship-based sampling, he said.

“They’re really complementary programs.”

But the scientific world is coming up with more and more sensors that can be attached to the gliders.

“Every year there’s kind of a new range of sensors you can put on these things to try and look at different water quality properties, or try to answer different scientific questions related to biology, or chemistry, or physics.”

The gliders use buoyancy to move in an undulating pattern. They employ an electric pump in the nose that can make the device either positively or negatively buoyant by moving oil into or out of a bladder.

“You put some wings on it, so when it sinks, it doesn’t sink straight down, it sinks sideways,” Richards said. “And that’s why we call it a glider, because it essentially kind of glides through the water, driven by these wings.”

When a glider reaches a depth set by its operator, the pump kicks in again, making the device head up for the surface. The wing acts somewhat like a sail, turning the upward thrust into forward motion.

“It has a rudder so that it can control the direction that it’s heading,” Richards said, demonstrating with a bright yellow glider that looks like a torpedo and belongs to Defence Research and Development Canada.

The gliders are usually pre-programmed with waypoints that give them a course to navigate.

“But then, typically, somebody is watching it pretty closely to see if it’s actually getting to the points that you told it to go to,” Richards said.

“If it’s not, then you might have to intervene, and give it some new points. They don’t move very fast. They probably sink at about 10 or 15 centimetres per second. So their horizontal speed is only centimetres per second.”

Fisheries scientists get to use data gathered by gliders that belong to defence scientists. They also have access to observations gathered by similar devices that belong to Dalhousie University’s Ocean Tracking Network, named Slocum gliders after famed Nova Scotian Joshua Slocum, the first man to sail single-handedly around the world.

“There are periods, still, where we’re missing data,” Richards said. “It’s actually hard to get gliders out in the winter because we tend to have a lot of storms. They don’t like really rough seas because they do have to come to the surface sometimes. And it’s also harder to launch and recover them.”

Now Richards and his colleagues are planning to buy four gliders — two for Nova Scotia and another pair for the West Coast — at the price of about $200,000 each.

The gliders are equipped with enough batteries to go to sea for as long as three months.

“Typically for the coastal ones you have to fight currents a lot more and the density change tends to be bigger, so it might be more like three to six weeks instead of three months.”

Richards is hoping to always have a glider at sea.

“In theory, the idea of having at least two (on this coast) is that they’re just continuous. So one of them is going while the other one is being prepped. And when one comes back, we just put the next one out again.”

The gliders can dive to about 200 metres below the waves. They surface every six hours to send information back to their operators about what they sense in the sea.

A boat can recover the gliders once they’ve completed their set course.

“The idea is you’ll use them for years and years and years because you keep getting them back,” Richards said.

The devices can be programmed to glide out to sea for 200 kilometres, turn around and come back to Halifax Harbour, he said.

“Then we can go get it with a Zodiac if we want.”

Equipped with global positioning systems, the gliders can communicate through satellites, so they can tell the operators where they are.

“They actually send their data back over the air as they’re going, because, unfortunately, you have to be prepared that if you put something in the ocean, you might not get it back, even if you intend to.”

Dalhousie, for example, lost a glider last fall as it was coming through the Cabot Strait on Thanksgiving weekend.

“It came to the surface right when that big storm came through,” Richards said. “At one point, they recorded it in seven- or eight-metre waves. It was stuck at the surface … and after the storm passed, they didn’t hear from it again. They put out a notice to mariners saying ‘Please look for a small, yellow sausage.’ But nobody saw it.”

Richards is keen to use the new gliders to learn more about the physics of the ocean. Compared to ships, which would stop at a half-dozen stations to take water samples, the gliders will be taking measurements all the time.

“We might see very different water properties (like temperature or salinity) between the two stations and if you don’t know what happened in between, it’s hard to come up with a physical model for why that’s different.”

Information from the gliders will tell Richards more about currents off our coasts.

“Currents are intimately linked with the temperature and salinity structure,” he said.

“As a physicist, I’m really interested in temperature and salinity because that determines the water density, and water density therefore determines the circulation.”

The Gulf Stream moves around but is often about 600 kilometres south of Nova Scotia, he said.

“It sheds eddies pretty regularly. It’s kind of a wiggly current and sometimes those wiggles turn into a blob of water that will, say, move northwards towards Nova Scotia. It might pinch off a blob of warm water from further south and that will drift up toward the Scotian Shelf.”

That brings warm water, which can change conditions on the Shelf, where the ocean’s typically kind of cold, or subarctic, due to the upstream influence of the Labrador Sea, he said.

“Aside from just the temperature properties, it can bring nutrients with it, for example,” Richards said. “It could actually bring a closed-off community of phytoplankton from further out in the Atlantic and they start to bump up against the Shelf and interact with the oceanography that’s happening here.”

Richards, who earned his PhD at Dal, has a background in how water masses mix.

“We can typically identify those by their temperature and salinity properties,” he said. “One of the things that’s really interesting about that is you can use them as a fingerprint for where water came from.”  

That means Richards will be able to use measurements taken by the gliders to track which water masses are important on the Scotian Shelf at any given time.

“The mixing is interesting from an ecosystem standpoint because you’re bringing nutrients and other things along with them,” Richards said. “But from a physics perspective, I’m actually quite interested in understanding a lot of processes that control that mixing.”

Physical oceanographers are typically playing catch-up, he said.

“You look at the data and you say there must have been mixing happening between these, but I don’t really understand why that much mixing would have happened, or why, in this case, we didn’t get the mixing that we would have expected.”

Richards is hoping the detailed data the gliders collect can improve models scientists use to predict what will happen next in the ocean.

“More observations and better observations will ultimately lead to better understanding, but also better prediction of the marine environment.”

While that could lead to fishermen hitting their quotas faster because they’re working more efficiently, it would also mean fishing boats burn less fuel and disrupt the ocean less because they have a better idea where their quarry lies.

DFO put out a tender for the new gliders late last year and is now analyzing bids from several manufacturers.

“Operational by spring is the hope,” Richards said.



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Chris Lambie

About the Author: Chris Lambie

Chris Lambie is a journalist based in Halifax, Nova Scotia. He has worked at newspapers from Newfoundland to the Northwest Territories.
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