Using High Tech Tools to Explore New Areas Along the Western Side of the Mackenzie Trough
With the great potential for oil and gas deposits, the geology of the area underlying the Canadian Beaufort Sea on the eastern side of the Mackenzie Trough has been extensively explored over the past five decades. Thus, a wealth of data exists in this area, including: multichannel seismic data looking deep into the subsurface; large swaths of multibeam data used to make detailed maps of the seafloor, much like topographic land maps; nearly 100 oil and gas industry exploration wells drilled hundreds of metres into the seafloor; and hundreds of five metres or less cores that have been taken for scientific purposes.
In contrast, on the western side of the Mackenzie Trough, east of the U.S.–Canada border, very little data exist, just some low-resolution maps of the bathymetry, a handful of detailed multibeam and low quality seismic lines, and one oil and gas industry well.
As we begin to investigate the western side of the Mackenzie Trough, we aim to understand the seafloor processes occurring there and will compare these findings to those for the eastern side. Much like early explorers who mapped, charted, and described unknown regions of the earth, we, too, are exploring relatively unknown areas, but with high-tech tools instead of compasses and sextants.
With only 15 days of ship-time, we need to target our studies to develop a solid understanding of what looks like postage stamp–sized areas within the maps of the vast area of the Yukon Shelf/Slope.
These high-tech tools increasingly become more precise as we home in on areas of interest. First, we used existing maps of the Arctic Ocean seafloor to identify areas of potential interest. These maps are at a poor resolution — imagine looking at something that is out of focus. We use educated guesses to select targets and use our first tools discussed in the previous post: the ship-based multibeam sonar system to produce a more detailed map of the seafloor and the sub-bottom profiler to produce images of the sediment layers below the seafloor.
These data are collected continuously as the ship moves back and forth along lines, much like mowing a lawn. The results are intriguing. The first impression is that seabed features are similar to those of the eastern trough and include deep scars that cut into the continental shelf and broad flat swaths of seafloor punctuated by mounds, gullies and ridges potentially associated with gas or water release.
After days of ship-based data collection and multibeam data cleaning — inaccurate soundings in the data must be cleaned to make the map useful to geologists — a base map is produced that can be used to find areas of interest so that we can deploy even more precise sampling tools: the high-resolution mapping autonomous underwater vehicle (AUV) and the remotely operated vehicle (ROV).
Photo 1: Examples of multibeam bathymetry collected by the Araon (left) vs. data collected by the mapping AUV (right).
Once areas of interest are selected from the low-resolution, ship-based maps, a mission is designed and sent to the AUV, which then autonomously surveys the seafloor for 16–20 hour missions. The maps are of such high resolution that we can image seafloor features one metre in size.
While the AUV was collecting data during its long mission through the afternoon and into the night, we began using the sub-bottom profiling data we collected to select locations to target for gravity coring.
To get a core, the coring assembly — consisting of hollow steel pipe fitted with a plastic liner — is lowered to the seafloor while suspended from a steel wire. Above the pipe is a heavy lead weight that drives the pipe into the seafloor. The coring system we are using can have steel pipes that are up to 6 m long and has a 250-kg weight at its top. At locations where the sediment is soft, the pipe and liner fills to the full 6-m length with sediment; when the seafloor is hard, we may only get 1–3 metres of sediment or less. The coring system is then pulled out of the sediment and winched up to the surface.
Once back onboard the Araon, the sediment-filled liners provide samples of how the sediments change with dept. Most of the samples will be sealed on the ship and returned to the laboratory at KOPRI, where they will be analyzed in detail using a variety of techniques to determine various properties, including the age of the sediments, their type and source, and the chemistry of water trapped between layers and grains of sediments. Among the topics of special interest is the question of what conditions were like 10,000–12,000 years ago.
Photo 2: a 6-m long gravity core assembly on the back deck of the Araon.
The final and most surgically precise tool in our modern-day tool box is the remotely operated vehicle, or ROV. Outfitted with a high-resolution video camera, a robotic arm, push cores and a sampling box, we survey the seafloor by “flying” the ROV over terrain that we determined to be the most promising from the multibeam bathymetric maps. These ROV ground-truthing surveys allow us to examine, discuss and sample material just like geologists do on land.
Fortunately we do this all while staying warm and dry within the ROV control van. In the last two days of surveying with the ROV, we have conducted four dives, collected approximately 30 rocks and eight push cores. Two push cores were collected in a patch of bacterial mat growing on the seafloor and released a trickle of bubbles upon collection, indications of the presence of methane gas.
Photo 3: ROV pilots in the control van collecting push cores from the seafloor.
Surfacing from its 18-hour deployment, the autonomous underwater vehicle (AUV) was recovered using the small boat and returned safely back on the deck of the Araon.
After three hours of data processing, the initial results revealed a stunning seafloor topography, with linear scarps, elongated depressions and ridges that are usually parallel with the shelf edge. There are also circular mounds up to 10 m high, often with collapsed summits. To our knowledge, the only place where comparable topography has been mapped is on the eastern flank of the Mackenzie Trough. Clearly this finding suggests that — whatever the processes are that form this unusual morphology — they are occurring on both sides of the Mackenzie Trough. The multi-channel seismic data collected at the beginning of the program will help establish the reasons for these similarities.
Photo 4: Scientists retrieving collected specimens from ROV and Araon crew securing the miniROV to the deck.
A great deal of analysis that needs to be done on all these data once they’re back at our respective laboratories onshore. Using all of these tools helps scientists to develop a more complete understanding of geological processes that have occurred and are occurring around the Mackenzie Trough region.
As a result of poor weather, with winds up to 40 knots, we are unable to deploy the AUV or ROV on this day. Thankfully, the Araon is a very robust vessel designed for rough seas, and we weathered the storm quite comfortably!
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