Discovery of Two New Underwater Canyons

Submarine canyons provide habitats for sponges, corals, and benthic invertebrates that support migrating ocean species such as tuna and billfish, while providing feeding grounds for squid, octopus, sharks, and skates.

Woods Hole Oceanographic Institution (WHOI) scientists aboard OceanX discovered two new underwater canyons during an expedition in Northeast Canyons and Seamounts National Monument, an important discovery due to several reasons.

The Canyons Unit

Three submarine canyons and four undersea seamounts form an intricate marine ecosystem in this region, boasting unique geological features and abundant biodiversity. Surrounded by ocean currents and temperature gradients, eddies, fronts that influence upwelling, stratification and mixing processes as well as providing habitats for an array of fish, invertebrate and whale species, protecting these geologic and oceanographic objects as national monuments will ensure they continue being vital research and education resources for generations to come.

Submarine canyons have long been recognized as essential geological formations, yet only recently have scientists come to comprehend their origins. Canyons often begin on continental slopes as steep-walled gullies or scarps which later transition into channel thalwegs – not only producing sediment but also serving marine mammals and coral reefs as vital habitats. Furthermore, submarine canyons act as natural seepage sources, while their turbulent waters can rupture communication cables on the seafloor or destroy subsea infrastructure1.

Submarine canyon formation was previously believed to be determined by erosion processes and cross-slope turbidity currents, however this assumption has recently been disproved by an in-depth study off California’s coast using open-source global images and multibeam sonar data for analysis of two canyons off their coastline. Stanford Earth graduate students led by research director Amy Resch used these tools to examine these structures; ultimately finding that submarine canyons differ fundamentally from land-based ravines; they form through multiple distinct processes.

Researchers discovered that submarine canyons form not through slope erosion but instead when tectonic plates shift to allow deeper waters into the continental shelf, which then become exposed to turbidity currents for erosion by deeper waters than would normally flow onto it from below, cutting much quicker canyons than would otherwise occur due to dense rocks in upper sedimentary layers and slow erosion processes. Evidence shows these canyons likely formed about 8,000 years ago – meaning either that ocean levels were much higher at that time, or that continental slope shifted down by about 8 feet at this time.

The Canyons’ Biology

The deeper seafloor is an immense frontier; only 10 percent has been fully mapped at a level equivalent to that of Mars or the moon. Since 1998, MBARI has pioneered mapping technology that brings us closer to creating an accurate representation of ocean bottom. It’s an essential step toward protecting fragile marine ecosystems from human interference; support has come from agencies including BOEM (the Bureau of Ocean Energy Management), NOAA (which regulates fisheries management), and U.S. Geological Survey which maps and studies Earth surface features.

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To conduct their investigation of canyons, scientists first created detailed maps using multiple sources – multi-beam sonar readings collected by NOAA research ship Okeanos Explorer being one such data source – as well as multi-beam sonar readings. The maps helped scientists to select optimal spots where ROVs could be dropped into each canyon to collect images and samples from its fauna and flora.

Baltimore and Norfolk Canyons were chosen because they are geographically close, sharing similar qualities. But even neighboring canyons can vary significantly, in terms of both physical characteristics and biological diversity. For instance, Norfolk may feature thicker nepheloid layers – fine sediment that fills deep ocean basins – than Baltimore. This could explain why Norfolk experience higher rates of erosion and sediment deposition.

Norfolk and Baltimore both boast unique habitats due to these differences between them. Canyons provide homes for many species ranging from coral reef organisms such as small corals to larger animals like clams and shrimp. The diversity is caused by an accumulation of plant matter; for instance, tree trunks, leaves and kukui nuts from Molokai’s forested shorelines serve as food sources for an array of invertebrates and other invertebrates living within its canyons.

Canyons may boast immense biodiversity, yet are vulnerable to human impacts that threaten other parts of the ocean. Physical impacts include landslides, benthic storms and sediment slumping while anthropogenic impacts such as re-suspension of sediment from lost gear and equipment being dumped, marine debris entanglement & suffocation as well as releases from gas seeps are just some examples of human effects affecting canyons. Acidification will also have an effect on these canyons.

The Canyons’ Geology

More than 70 submarine canyons pierce the continental shelf and slope off of the East Coast of the United States, stretching 50 to 100 miles offshore with their crests plunging hundreds of feet deep into the dark ocean depths.

Submarine canyons can be difficult to explore due to their remoteness, depths, and steep walls. Scientists use trawling nets for sampling sea life while sonar equipment maps out seafloor contours. Unfortunately in canyons these tools often become damaged or lost on rugged terrain.

So far, only about one-third of underwater canyons have been explored by researchers; yet as more researchers visit, more is revealed about these unique environments. One expedition in September 2018 at Northeast Canyons and Seamounts National Monument led by Tim Shank of Woods Hole Oceanographic Institution (WHOI), along with collaborators from OceanX and University of Connecticut confirmed two new species of coral discovered during that voyage through DNA analysis.

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Canyons’ geology is also fascinating: its walls were cut by rivers at a time when sea level was lower than it is now.

During the last ice age, riverbeds formed a network of canyons and channels that transported sediment downstream and deposited it near our coastlines. Rivers also cut through rock layers to form “horst beds”, geologic structures with steep cliffs.

These beds of sediment contain rich sediment deposits that provide unique habitats, including chemosynthetic communities fueled by methane gas leaked from canyon walls. Furthermore, natural gas seeps into the canyon floor in significant quantities, leading to some unique fish species exclusive to canyon environments.

Due to their mysterious characteristics and links with geohazards such as local tsunamis and damaged telecommunications cables, scientists need to gain a comprehensive understanding of submarine canyon environments such as MBARI’s mapping technology is helping scientists uncover more about biological and geological complexity of underwater canyons and their connections.

The Canyons’ Future

Canyons’ remoteness, depth and steep walls contribute to their relative anonymity. Most ocean researchers study continental shelves using techniques like dragging trawling nets to harvest marine life from the seafloor and sonar scanning to map contours – however these approaches don’t work effectively in canyons due to rough terrain that might rip nets off and sonar equipment getting lost on sloped walls.

Scientists employed multi-beam sonar technology to explore Baltimore and Norfolk Canyons. By emitting pulses of sound from ships or robotic vehicles above the sea floor, pulses return as high-resolution images depicting its shape – this data allowed scientists to pinpoint locations within Baltimore and Norfolk Canyons where remote-operated vehicles could be deployed for closer observation.

Scientists discovered that canyons were home to an abundance of organisms, such as corals, fish, and methane seeps. Corals in particular were densely packed in some areas with complex food webs that supported slow growth rates over long timescales. Furthermore, researchers noted that canyons possessed great physical complexity with tide flows, eddies, microhabitats and physical obstacles such as walls to provide protection from predators.

Scientists utilized their expeditions to collect samples for further examination of canyon geology and biology. For instance, they searched for clues to understand how the canyons formed; their investigation suggested they may have formed by periodic landslides caused by extreme steepness combined with seismic activity on the continental shelf.

Future efforts by researchers will focus on protecting these underwater ecosystems from human disturbance, and sharing their results with federal agencies that oversee activities in the Atlantic ocean such as BOEM, NOAA’s Office of Ocean Fisheries and U.S. Geological Survey.

Even in today’s challenging fiscal environment for ocean research, Ross remains hopeful that federal agencies will fund this kind of work. Understanding what lies beneath the surface is vital in making educated decisions on how best to use ocean resources.

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