Arctic shelf edge
MBARI’s Arctic ROV operations on the shelf and slope of the Beaufort Sea
MBARI has participated in three research cruises in the Canadian Beaufort Sea on the Canadian Coast Guard Icebreaker Sir Wilfrid Laurier (SWL). On each of these cruises an inspection class remotely operated vehicle (ROV) has been utilized to visualize the seafloor and to collect samples. This work has been conducted in collaboration with scientists at the Geological Survey of Canada and Fisheries and Oceans Canada. This is also part of a collaborative research network involving participation of the Korean Polar Research Institute.
An overview of the ROV operations that MBARI has conducted from the SWL in 2010, 2012, and 2013 are outlined on this site. In total, 37 dives have been conducted; 8 with a Phantom ROV in 2010 and 29 dives with MBARI’s mini ROV in 2012 and 2013.
The locations of these dives are indicated in the maps below and listed in this table.
ROV dive locations (.csv file)
Mini ROV Specs (.doc file)
Fauna Observation (.csv file)
|Sabellidae||feather duster worm|
|Chionoecetes opilio||snow crab|
|bacterial mat||bacterial mat|
MBARI provides these data “as is”, with no warranty, express or implied, of the data quality or consistency. Data are provided without support and without obligation on the part of the Monterey Bay Aquarium Research Institute to assist in its use, correction, modification, or enhancement.
Expanding capabilities for ROV operations in the Arctic: filling the open niche
ROV’s are among the most effective tools for conducting detailed surveys of seafloor characteristics. However, there has been little use of ROV’s in the Arctic Ocean in water depths below ~150 meters. As a result the appearance of the seafloor along the margins of the Arctic Ocean is largely unknown.
The lack of ROV exploration in the Arctic is largely attributable to logistical difficulties. The presence of a sea ice cover over the outer shelf and slope has historically made access and especially ROV operations difficult. In some areas it is still not possible to operate in some years. In addition, most deep-diving ROV’s require large launch and recovery systems that take up a considerable amount of deck space on the ship of operation and need to be installed in port. They also require a large team of specialized personnel to operate. In practice this means that a ship going into the Arctic would have to be largely if not solely committed to ROV operations for an entire summer field season, which is economically hard to justify.
During the 2010 SWL cruise the ROV sampling targets were gas vents near the edge of the continental shelf in <150 m water depth. For this work a MBARI-owned Phantom ROV was used, which is a small commercially produced vehicle. Phantoms have been heavily used since 1982, sometimes for work on the Arctic shelf.They are small enough to be stowed in the ships hold and are mounted on the deck only during a particular segment of an expedition. Thus, their small size makes them viable to be utilized as an ancillary operation in conjunction with other programs. 150>
After the 2010 field season, the scientific goals shifted from operations near the shelf edge to research targets in up to 1 km water depth, which is beyond the capability of the Phantom. The lack of a versatile, easily deployable, and inexpensive vehicle to operate was identified as a gap in the capabilities of the existing research facilities, which was hindering the advancement of high latitude marine science research. Some commercially available vehicles were considered, however we did not find them optimal for our needs. A decision was made to build a fly-away inspection class ROV system at MBARI (mini ROV specs). The goal was to obtain a capable vehicle which could access ≤ 1 km water depth and be used as an ancillary program on broader expeditions. The most immediate objective was to use it in the ongoing Arctic project, as well as to provide the capability to conduct ROV operations elsewhere in the world from ships of opportunity.
Dale Graves and Alana Sherman at MBARI designed a vehicle to fill this open niche. They then lead a team in building an initially 1000 m capable vehicle. It is now called the mini ROV. The field programs in the Arctic in 2012 and 2013 were the first field deployments where this vehicle was put to use.
The mini ROV is a portable, low cost, inspection class ROV system, needing only a small crew (2 people) to operate. The mini ROV is capable of light duty work functions such as limited sediment and gas sampling, video transects, and instrument deployment and recovery (with a 70 pound instrument payload).The core vehicle is outfitted with the following suite of instruments: HD camera, scanning sonar, lasers to provide visual scale, LED lights (10,000 lumens) and CTD. A five-function manipulator arm (ECA Robotics Arm 5E) was added for the 2013 field program to enable sampling (rock samples, push cores, etc.) and to potentially conduct experimental deployments on the seafloor. In addition, the vehicle has a removable tool sled for mission specific payloads and sampling requirements.
Efforts to enhance the capability of the mini ROV are on-going. For example, since the 2013 field program, a new longer umbilical wire, allowing the vehicle to dive to 1500 m, was acquired. A generator was selected and purchased, which will enable the vehicle system to operate on ships of opportunity without having to interface with the ship’s power. A mid-water sampler was added to the vehicle tool sled.
Evidence of methane venting on the Beaufort shelf and shelf edge
The seafloor under the Arctic Shelf is arguably the part of the Earth that is undergoing the most dramatic change due to the warming caused by Holocene sea level rise over the last 10,000 years (e.g., Paull et al., 2007). In the southern Beaufort Sea, off the north coast of Canada, the shelf area was exposed above sea level during much of the Quaternary period when sea level was ~120m lower than present. As a consequence, many areas of the shelf are underlain by >600m of ice-bonded permafrost, formed when the shelf was exposed to the atmosphere, that conditions the geothermal regime such that the base of the methane hydrate stability zone can be >1000m deep. Marine transgressions have imposed a change in mean annual surface temperature from -15°C or lower during periods of aerial exposure, to mean annual sea bottom temperatures near 0°C when the shelf is covered by the sea. The thermal disturbance caused by the last sea transgression is still influencing the upper 1 km of subsurface sediments. Decomposition of gas hydrate is inferred to be occurring at the base and the top of the gas hydrate stability zone. As gas hydrate and permafrost intervals degrade, released gas will generate excess pore water pressure. The fate of this gas and water and in particular whether they are escaping from the seafloor is a focus of current research.
In the fall of 2010 the goal of the ROV operations was to investigate sites where methane venting possibly associated with decomposing gas hydrate and/or permafrost was inferred to occur. Water column acoustic anomalies related to potential vents sites had been discovered along the shelf edge during multibeam surveys conducted by the ArcticNet project the previous summer (Blasco et al., 2013; Saint-Ange et al., 2015). During the 2010 expedition a Phantom ROV was used to document the nature of these seafloor gas vents. Two different styles of methane venting were observed on this expedition (Paull et al., 2011).
Vigorous Methane Vent (Dive 8: 2010) (Download movie file .wmv .mov. Depending on your web browser you may need to right click on link and save the file to download the clip.) Video clip shows methane venting at a site called Kopanoar in the middle of the Arctic shelf. In this image, bubble releases are observed to migrate along the seafloor, apparently following the tip of a propagating crack in the seafloor. The clouds of sediment were created by the vigorous gas release. Such vigorous venting was only observed at discrete geomorphic features known as Pingo-Like-Features (Paull et al., 2007).
Methane Vent (Dive 3: 2010) (Download movie file .wmv .mov. Depending on your web browser you may need to right click on link and save the file to download the clip.) Video clip shows methane bubbles intermittently emanating from several small holes that are rimmed with white bacterial mats. This style of venting of methane is occurring over a large area along the edge of the continental shelf.
The gases emanating from both areas are predominately composed of methane, have stable isotopic compositions that indicate a microbial origin, and have no radiocarbon (Paull et al., 2011). The methane vents at the Pingo-Like-Features are believed to be sourced from the top of the gas hydrate stability field, while the gas emanating along the shelf edge can be either from release of gas trapped in permafrost or from gas hydrate decomposition. Gas venting from both these shelf environments is to be expected due to the warming of the continental shelf that has been taking place since the last transgression.
Beaufort Sea shelf edge morphologies
ROV dives along the shelf edge of the Beaufort Sea were conducted during the SWL cruises in 2010, 2012, and 2013. Two re-occurring morphologies were observed, including areas of slightly elevated rough topography and exposed gravel deposits.
(a) Areas of rough topography
ROV-observations of the seafloor near the shelf edge in the areas where gas venting was observed (Phantom Dives 1 to 7) documented patches of distinctive slightly elevated rough topography. These patches form isolated small mounds and ridges that are frequently accompanied by a white surface coating interpreted to be bacterial mats. The positive relief of these features may be due to differential erosion, that leaves these more erosion-resistant patches standing higher.
Mounds (Dive 5: 2010) (Download movie file .wmv .mov. Depending on your web browser you may need to right click on link and save the file to download the clip.) Video clip showing an individual patch of rough topography near the shelf edge. This video clip starts when the ROV is hovering over smooth seafloor and shows the transition as it moves onto a patch of rough topography. Rough topography is composed of areas with a white surface coating and with exposed black colored sediment. These white and black colored areas outline subtle ridges that are slightly elevated with respect to the tan-colored sediments of the surrounding smooth seafloor. Field of view is estimated to be ~2 m.
Polygonal Structure (Dive 3: 2010) (Download movie file .wmv .mov. Depending on your web browser you may need to right click on link and save the file to download the clip.) Video clip shows a patch of slightly elevated rough topography near the shelf edge.Within this patch there are ~20 cm wide <5 cm high white and black ridges that appear to be arranged in approximately polygonal patterns. Gas bubbles occasionally emanate from the white and black areas. Field of view is estimated to be ~2 m.
Older Inactive Ridge (Dive 3: 2010) (Download movie file .wmv .mov. Depending on your web browser you may need to right click on link and save the file to download the clip.) Ridge of slightly elevated and rough topography seen near the shelf edge. The ridge is estimated to be ~1 m across and have 10 cm to 20 cm of relief with respect to the surrounding smooth seafloor. Because the size and shape of this ridge, which lacks the typical white and black coloration, are similar to the elevated rough topography where gas venting is occurring nearby, this ridge is inferred to be of a similar origin, but older. Field of view is estimated to be ~2 m.
(b) Gravel deposits along the shelf edge
Gravel deposits were discovered near the shelf edge at a number of sites (2013 mini ROV Dives, 14, 17, 18, 19, 20, 25, 26, & 28 and 2012 mini ROV Dives 7, 9). These deposits are considered to be tills as they are composed of unsorted material containing boulders, cobbles, and pebbles of mixed lithologies, as well as fine sediment. The origin of these tills is the topic of on-going investigations.
Shelf Edge Gravel (Dive 18: 2013) (Download movie file .wmv .mov. Depending on your web browser you may need to right click on link and save the file to download the clip.) Video clip showing extensive fields of gravel exposed on the seafloor near the shelf edge. Red dots are 8 cm apart.
Shelf Edge Gravel (Dive 25: 2013) (Download movie file .wmv .mov. Depending on your web browser you may need to right click on link and save the file to download the clip.) Video clip showing extensive fields of gravel exposed on the seafloor near the shelf edge. Note that sessile organisms are frequently attached to cobbles. Red dots are 8 cm apart.
Appearance of continental slope sediments
(a) Sediment covered areas
A mini ROV dive transect (mini ROV Dive 15) was conducted on the continental slope within a huge landslide scar. The seafloor was observed to be covered with fine sediment, which has apparently accumulated in place. Not a single rock was observed. This is in sharp contrast to areas at the shelf edge and on the headwall faces exposed by slide scars where pebbles, cobbles and even boulders are common.
Background Seafloor (Dive 15: 2013) (Download movie file .wmv .mov. Depending on your web browser you may need to right click on link and save the file to download the clip.) Video clip shows part of an 867 m long transect between 667 and 592 m water depth up the slope of a sediment-draped landslide scar. Bottom has scattered sea pens (distinguished from tubeworms as they do not form clusters). The bottom was monotonously similar along the entire transect. Red dots are 8 cm apart.
(b) Outcrops exposed on the slope
Three mini ROV dives were conducted within slide scars or on the sides of gullies where older materials are exposed. These deposits are also considered to be tills as they are composed of unsorted material containing boulders, cobbles, and pebbles of mixed lithologies, as well as fine sediment. These dives demonstrated that that tills occur on the slope of the Canadian Beaufort Sea down to nearly 1 km water depth.
Scattered Cobbles (Dive 21: 2013) (Download movie file .wmv .mov. Depending on your web browser you may need to right click on link and save the file to download the clip.) Video clip shows the mini ROV’s mechanical arm collecting a cobble from the face of a slide scar in ~950 m water depths, where scattered cobbles were commonly observed during the dive. Some of these cobbles were plucked out of the wall formation. On most dives where cobbles were observed 8 to 14 samples were collected. Red dots are 8 cm apart.
Boulders and Cobbles (Dive 29: 2013) (Download movie file .wmv .mov. Depending on your web browser you may need to right click on link and save the file to download the clip.) Video clip from ~990 m water depths where the mini ROV conducted a transect up the steep sidewall of a slope-cutting gulley. An outcrop sequence ~100 m thick was observed, containing an extremely poorly sorted sequence that included boulders and numerous cobbles. Red dots are 8 cm apart.
(c) Water seepage on the slope
The mini ROV encountered six positive relief features within a slide scar in ~960 m water depths during dives 21 and 22, which were covered with a distinctive orange stain and/or chemical precipitate.These features occur on a steep slope where older strata might be exposed on the sole of the slide. These features are ~1 m high, 2-5 m wide, and appear to occur along the same isobath. They are believed to be present where fluid seeps onto the seafloor.
Shimmering Water (Dive 21&22: 2013) (Download movie file .wmv .mov. Depending on your web browser you may need to right click on link and save the file to download the clip.) Video clip shows shimmering water. This effect is created by the flow from the mound onto the seafloor of water with a different salinity than seawater. A brilliant orange color is seen on freshly exposed faces, where the mini ROV has broken off samples.
Multibeam bathymetric surveys conducted by the ArcticNet project in 2009 provided the first detailed bathymetry for a 100 km long section of the shelf edge and slope of the Canadian Beaufort Sea (Saint-Ange et al., 2014; Fig. 1). These data revealed the existence of large circular morphologic features in water depths of ~282 m, ~420 m, and a cluster of three closely-spaced structures in ~740 m water depths. Water column acoustic anomalies were identified over each of these features, indicating that they are sites of active gas venting and thus initially interpreted as being large mud volcanoes (Blasco et al., 2013; Saint-Ange et al., 2014). Six mini ROV dives focused on exploring and sampling gas from the tops and flanks of these expulsion features.
Gas Collection (Dive 8: 2012) (Download movie file .wmv .mov. Depending on your web browser you may need to right click on link and save the file to download the clip.) Video clip first showing gas bubbles escaping from the top of the mud volcano in 420 m water depth and then being captured into a transparent overturned funnel mounted on the front of the ROV. When a sufficient amount of gas was collected the ROV ascended to 400 m water depth and a heater within the funnel was turned on. The gas hydrate coated bubble mass decomposed over a couple of minutes, forming a gaseous headspace. This gas was later collected by withdrawing it into a pre-evacuated cylinder.
Tubeworm Beds (Dive 5: 2012) (Download movie file .wmv .mov. Depending on your web browser you may need to right click on link and save the file to download the clip.) Video clip showing a characteristic seafloor texture on a generally flat-topped mud volcano in ~282 m water depths on the continental slope of the Beaufort Sea. Clip begins with a close up of a starfish and surrounding tubeworm tubes, then zooms out as the ROV hovers over extensive tubeworm beds and lands to zoom on the worms and seafloor again. Red dots are 8 cm apart.
Mound and Furrow (Dive 5: 2012) (Download movie file .wmv .mov. Depending on your web browser you may need to right click on link and save the file to download the clip.) Video clip showing a characteristic fine-scale texture and topography on the top of a mud volcano in ~282 m water depths on the continental slope of the Beaufort Sea. Tubeworms are abundant and form parallel swaths with varying worm density. Clip begins with a view of an individual elevated mound with a small crack on its top that reveals black sediment rimmed by frosting of white mat. This pattern is interrupted by a distinct furrow which is ~5 cm across and has raised levee-like flanks. Similar furrows and gouges elsewhere have been attributed to excavation by marine mammals (Nelson et al., 1987; Woodside et al, 2006). Red dots are 8 cm apart.
Dense Tubeworm Beds (Dive 6: 2012) (Download movie file .wmv .mov. Depending on your web browser you may need to right click on link and save the file to download the clip.) Video transect across part of a large flat-topped mud volcano in ~740 m water depth. This transect starts in area of isolated clusters of tubeworms and moves into an area where the bottom is carpeted with tubeworms. Red dots are 8 cm apart.
Top of 740 m Mound (Dive 6: 2012) (Download movie file .wmv .mov. Depending on your web browser you may need to right click on link and save the file to download the clip.) Video showing area near top of a conical mud volcano in ~740 m water depths. This area is notably devoid of sessile organisms. The linear furrow crossed by the mini ROV is similar to furrows that have been observed elsewhere and attributed to excavation by marine mammals (Nelson et al., 1987; Woodside et al, 2006). Red dots are 8 cm apart.
Top of 420 m Mound (Dive 24: 2013) (Download movie file .wmv .mov. Depending on your web browser you may need to right click on link and save the file to download the clip.) Video clip showing part of a mini ROV dive transect across the top of a mud volcano in 420 m water depths. Clip starts in an area believed to be a recent mud flow where the seafloor is characterized by its light gray color, rough texture and notable absence of sessile organisms. As the mini ROV moves towards the edge of the flow, the number of mobile organisms increases. The contact between the recent flow and the older surface is marked by a change to a tan color, a slight drop in the surface elevation, a change to a smoother surface texture, and the occurrence of sessile organisms (notably tiny tubeworms and white mats rimming burrows). A linear ridge seen on the older surface outside the flow appears to end where it was buried by the flow. Red dots are 8 cm apart.
Top of 420 m Mound (Dive 24: 2013) (Download movie file .wmv .mov. Depending on your web browser you may need to right click on link and save the file to download the clip.) Video clip showing part of a mini ROV dive transect over a recent flow across the top of a mud volcano in 420 m water depths. This clip starts at the edge of the what is interpreted to be a recent mud flow. Initially the surface is light tan color and has some sessile organism (small tubeworms and white rimmed burrows). The edge of the flow is associated with a change to a light gray color, slight rise in surface elevation, and rougher surface texture. The surface of the flow is notably lacking in sessile organisms. Red dots are 8 cm apart.
Seafloor excavation features
Seafloor excavation features were seen on most of the ROV dives on the Beaufort Sea shelf and slope. These excavation features are typically 2-10 m long and have slightly curving paths. In cross section these features are characterized by smooth rounded central troughs, which are consistently associated with upturned sediments on their flanks. These features occur as tear shaped gouges or longer furrows. The gouges are tapered at one end and get deeper towards the other end where they abruptly end in a semicircular depression. It is common to see clumps of obviously out of place sediments apparently dropped onto the seafloor at the end of these gouges. Similar furrows and gouges elsewhere have been attributed to excavation by marine mammals (Nelson et al., 1987; Woodside et al, 2006).
Whale Mark (Dive 5: 2012) (Download movie file .wmv .mov. Depending on your web browser you may need to right click on link and save the file to download the clip.) Video clip showing an example of a large tear-shaped groove. This groove has clumps of sediment at its end that are lighter colored than the surrounding sediment. This suggests that these clumps were apparently dropped onto the seafloor and that this feature is comparatively fresh. Red dots are 8 cm apart.
The video recorded from the ROV dives in 2010, 2012, and 2013 are archived at MBARI. The video has been reviewed to document the major components of the visually identifiable benthic fauna using VARS (video annotation and reference system). Lists of the identified organism is tabulated here.
This research has been advanced in collaboration with scientists from the Geological Survey of Canada, Fisheries and Oceans Canada and MBARI. Future research cruises will include an expanded research network with participation by the Korean Polar Research Institute.
Blasco, S., Bennett, R., Brent, T., Burton, M., Campbell, P., Carr, E., Covill, R., Dallimore, S., Davies, E., Hughes-Clarke, J., Issler, D., MacKillop, K., Mazzotti, S., Patton, E., Shearer, J., and White, M., 2013, State of knowledge: Beaufort Sea seabed geohazards associated with offshore hydrocarbon development Geological Survey of Canada Open File 6989, 307 p.
Paull, C.K., Ussler, W. III, Dallimore, S., Blasco, S., Lorenson, T., Melling, H., McLaughlin, F., and Nixon, F.M., 2007, Origin of pingo-like features on the Beaufort Sea shelf and their possible relationship to decomposing methane gas hydrates, Geophysical Research Letters, 34, L01603, doi:10.1029/2006GL027977.
Paull, C.K., Dallimore, S., Hughes-Clarke, J., Blasco, S. Lundsten, E., Ussler, W. III, Graves, D., Sherman, A., Conway, K., Melling, H., Vagle, S., and Collett, T., 2011, Tracking the decomposition of permafrost and gas hydrate under the shelf and slope of the Beaufort Sea, 7th International Conference on Gas Hydrate, 12 p.
Nelson, C.H., Johnson, K.R., and Barber, J.H. Jr., 1987, Gray Whale and Walrus Feeding Excavation on the Bering Shelf, Alaska, Journal of Sedimentary Research, v. 57, p. 419-430.
Saint-Ange, F., Kuus, P., Blasco, S., Piper, D.J.W., Hughes-Clarke, J., and MacKillop, K., 2014, Multiple failure styles related to shallow gas and fluid venting, upper slope Canadian Beaufort Sea, northern Canada, Marine Geology, v. 355, p. 136-149.
Woodside, J.M., David, L., Frantzis, A., and Hooker, S.K., 2006, Gouge marks on deep-sea mud volcanoes in the eastern Mediterranean; caused by Cuvier’s beaked whales?, Deep-Sea Research V. 53, p. 1762-1771.