Diving into the mysteries of Smith Sound
The deep waters of Smith Sound, Trinity Bay, hold many mysteries. Why did Smith Sound have a strong and vibrant cod stock during the moratorium? What happened to vessels that sank in the 1890s during an ice storm? Are there really internal standing waves, or seiches, in the waters and what drives them? These are questions surrounding one of the longest fjords along the coast of the island, questions that no one has been able to answer. A team of researchers from Memorial’s Marine Environmental Research Laboratory for Intelligent Vehicles (MERLIN) is searching for the answers in hopes of uncovering the mysteries of Smith Sound.
MERLIN researchers from the faculties of Engineering and Applied Science, Science and Arts are using an explorer-class autonomous underwater vehicle (AUV) called DORA (Deep Ocean Research AUV). Dora the Explorer provides 3D images of the seafloor, information on the seafloor topography and can even detect shipwrecks on the ocean floor.
During phase one, which took place in June 2014, the AUV conducted a preliminary multi-beam survey from the surface. The survey provided an accurate map of the bottom of the Sound.
“Existing charts for the area only provide soundings, or depth measurements, at point locations,” explained Dr. Dan Walker, lead researcher of the project. “That’s fine for a ship or boat at the surface because it’s not in danger of hitting anything in 150 or 200 metres of water.”
For phase two, in early July, the AUV dove to the bottom of the ocean and mapped seabed from approximately 20 metres altitude.
“We used the multi-beam sonar again and improved the bathymetric map developed in phase one,” said Dr. Walker. “The closer the sonar is to the sea floor, the higher the resolution so we were able to see images or obstructions very clearly. The AUV has other types of sonar as well – a side-scan sonar and a sub-bottom profiler. The side-scan sonar sends signals from the side of the vehicle to provide a three-dimensional picture of rocks, wrecks, etc. on sea floor, which determines sizes and shapes of rocks and other objects on the seafloor. The sub-bottom profiler sends a signal into the sediment and can look into the mud to see things that other sonars can not detect.”
The MERLIN team wants to get a clear picture of the Sound’s seafloor. They want to know if it’s rocky, sandy or muddy, and if it’s rocky, they want to know how big the rocks are. This knowledge will help them understand why codfish were plentiful in Smith Sound during the moratorium.
“The principal goal of our research was seafloor characterization, which tells us what type of sediment is on the sea floor, for example mud, silt, rock or sand,” said Dr. Walker. “Based on differing acoustic responses, we can determine patches of mud or rock.
“However, some members of the team have an interest in archeology and were able to use the data we collected to establish potential locations of shipwrecks that may have occurred during the late 1800s, shipwrecks that remain a mystery today.”
While the results of the survey are still being compiled and more work needs to be done, the team is very excited about what they’ve learned so far. Multi-beam results, along with a subsequent bottom ground-truthing program using grab samples, which involves taking, or grabbing, actual samples from the sea floor to determine type of sediment have allowed the team to develop a preliminary habitat map. Initial side-scan results have highlighted potential ship wrecks that can be explored using remotely operated vehicles and future programs will, hopefully, increase their knowledge and expertise when using AUVs to explore deeper locations.