Monterey Canyon: A Grand Canyon beneath the waves

This animation uses data collected over the past 22 years by MBARI’s mapping team to bring Monterey Canyon to life in an unprecedented level of detail. The highest-resolution animation of Monterey Canyon ever created, it uses a combination of ship-based multibeam data at 25 meters (82 feet) in resolution and autonomous underwater vehicle (AUV) multibeam mapping data at one meter (three feet) in resolution. MBARI scientists worked together with Frame 48, a Los Angeles-based film production company, to make these data come to life and give people a chance to see an amazing geologic feature that is otherwise invisible.

About the Canyon

Monterey Canyon is one of the deepest submarine canyons on the west coast of the United States. The canyon is home to an abundance of deep-sea life, but drain the water out of Monterey Bay and you would see the canyon’s stunning underwater topography with huge walls, trenches, and meanders that rival the Grand Canyon in size and grandeur. Repeated efforts to map and observe the canyon have revealed that it is an extremely active feature that changes every few months and plays an important role in transporting carbon to nutrient-deprived deep-sea communities. The fascinating geological processes shaping Monterey Canyon aren’t just relevant to marine geologists—they can help us better understand how submarine canyons might be tied to geohazards like local tsunamis and damage to telecommunications infrastructure.

Researchers in locations with broad continental shelves, like the east coast of the US, oftentimes steam for 10 hours or more to reach deep-ocean sites. The Monterey Bay Aquarium Research Institute (MBARI) is incredibly fortunate to have the Monterey Canyon in its backyard as it provides unprecedented access to the deep. In just a little over two and a half hours, MBARI’s remotely operated vehicles (ROVs), the Doc Ricketts and Ventana, can explore areas more than a mile deep to discover and study the myriad and often bizarre-looking creatures of the deep sea.

If you walked down into the deepest part of the Grand Canyon, the walls would be roughly 1,830 meters (6,000 feet) high. If you walked down into the deepest part of Monterey Canyon, the walls would be roughly 1,700 meters (5,580 feet) high. So, without counting the water above the canyon walls, Monterey Canyon is just slightly shallower—by around 130 meters (430 feet)—than the deepest section in the Grand Canyon. Monterey Canyon and the channel that extends from it ends on the Monterey Deep Sea Fan, which is a flat muddy expanse beyond the canyon mouth. From there, the canyon flattens and merges with the abyssal plain after reaching a depth of more than 4,000 meters (2.5 miles) from the sea surface to the seafloor.

 

If you draw the boundary of Monterey Bay as a straight line from Santa Cruz to Cypress Point (see map), then the deepest part of the bay falls within the canyon axis at a depth of 1,500 meters (4,900 feet) from the sea surface to the canyon floor.

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Modern multibeam sonars use numerous narrow beams of sound to map wide swaths of the seafloor. Using multiple transponders in an array yields higher resolution data compared to a single transponder.

Quick facts about Monterey Canyon

  • Main channel extends to over 470 kilometers (292 miles) offshore
  • Canyon is 12 kilometers (7.5 miles) across at its widest point
  • Canyon walls reach up 1,700 meters (5,580 feet) high
  • Main channel continues into the Monterey Deep Sea Fan at depths below 3,000 meters (1.8 miles)
  • The canyon ends at a depth greater than 4,000 meters (2.5 miles) on the abyssal plain

Canyon formation and change

Monterey Canyon is very similar in scale and shape to the Grand Canyon, but the process that has carved it out over time is remarkably different. The Colorado River cut the Grand Canyon by scouring the rocks as the surrounding plateau uplifted, widening and deepening the canyon’s axis over millions of years. A river of water does not flow through Monterey Canyon. Instead sediment, including coarse sand and gravel from Santa Cruz and Monterey beaches, is carried along the coast by waves and piles up at the canyon head near Moss Landing. Most of the time, the sediments sit relatively undisturbed in the canyon. Different triggers, including storm waves, vibrations from fault activity, and random failures in the canyon walls can cause the built-up sediment to slump. As the sediment is destabilized, it becomes a fast-moving slurry of seawater and sand—similar to an underwater avalanche—called a turbidity current.

Marine geologists were originally unclear how frequently such turbidity currents occur. When MBARI researchers deployed tools to measure turbidity currents and conditions of the canyon, they found a surprisingly active canyon axis. These currents occur multiple times a year and are strong enough to bury, displace, or destroy oceanographic instruments.

Researchers have measured individual turbidity currents which travel at least 50 kilometers (31 miles) snaking down through the main axis at speeds up to 700 centimeters per second (16 miles per hour) along the seabed and produce large changes in bathymetry. Over millions of years, the flowing sand grains carve through even the hardest granite bedrock at the bottom of the canyon.

The transport of material through the canyon is discontinuous. While turbidity currents occur more often than once per year in the upper 20 kilometers (12 miles) of the canyon, the frequency decreases with water depth. Turbidity currents which transport material through the deeper parts of the canyon are rare. Sediments are presently building up within the canyon with some areas acting as reservoirs where materials are stored up until catastrophic events dislodge them.

Understanding how Monterey Canyon changes over time can also provide insight into how submarine canyon activity might impact coastal communities. We have yet to observe a full canyon flushing event and researchers believe that these large-scale events that clear sediment out of the further reaches of the canyon only occur between hundreds to thousands of years. Catastrophic failures of the canyon walls could cause massive enough deposits of sediment to slump into the canyon and set off a local tsunami making it critical for researchers to understand canyon dynamics. Large sediment transport events in canyons around the world are potentially damaging enough to cut off critical telecommunications infrastructure installed on the seafloor.

Flows in Monterey Canyon move more than just sediment into deeper waters. MBARI researchers have recorded trash like balloons, chip bags, and even desk chairs that have come to rest on the canyon floor exposing how the canyon acts as a pathway for trash to the deep seafloor. Early results from analyzing deep-sea sediment cores also show evidence of microplastics—a sobering reminder of how our everyday products can end up in the deep sea. 

Researchers at MBARI have used a variety of methods to estimate the origin and age of different sediments sampled from the deep seafloor. They found evidence of DDT, an agricultural pesticide commonly used between 1945 and 1969, in sediments throughout the canyon and on the Monterey Deep Sea Fan. This indicates that the canyon has moved a substantial amount of sediment from the coastal zone to the deep sea in modern times.

Carbon highway to the deep sea

The turbidity currents responsible for the evolution of Monterey Canyon’s geology are also closely linked to carbon transport to the deep sea. Very little food is available for animals living in the deep sea. Most organisms either feed on each other or on marine snow—flakes made up of organic material like feces and dead animals—that drift from the well-lit, productive surface waters to the darker seafloor.

MBARI researchers measured the amount of carbon consumed by animals inhabiting the Monterey Deep Sea Fan and discovered that the vertical transport of nutrients could not account for the total amount of benthic activity observed. They determined that Monterey Canyon acts like a carbon highway, carrying nutrient-rich organic material like sunken kelp from the sea surface out to the abyssal plain. A single large turbidity flow could account for up to 85 percent of the annual organic carbon transport from the shore to the deep sea in a year.

Not only is this carbon conduit important for nourishing life in the deep sea, but it also plays an important role in our climate system. Plants and marine algae like kelp pull carbon dioxide—from both natural and human sources—out of the atmosphere to grow, and once they sink to the seafloor, can trap carbon for thousands or even millions of years. Over long periods of time the trapped organic carbon in the sediment can become deeply buried and pressed into solid rock and converted into oil and gas deposits.

Abundant life from the surface to the seafloor

Diverse life can be found in several different habitats throughout Monterey Canyon, including the sandy canyon floor, the mud-draped rocks on the canyon walls, and dark midwater zones. Although most of these species aren’t only found in Monterey Canyon, their close proximity to shore enables MBARI researchers to more readily observe them in their natural habitat.

Few large animals live in the sandy channel in the upper reaches of the canyon, where turbidity currents often occur, but some of the most important organisms that live there are the miniature worms, clams, and crustaceans that feed in between the grains. Sea pens and sea cucumbers colonize areas of the seafloor farther from the head of the canyon where mud settles on top of the sand and is less frequently churned up by flows. Animals like sponges, deep-sea corals, tunicates, and anemones cling to the exposed bedrock on the floor and walls of the canyon.

Some of the most spectacular creatures seen in Monterey Canyon are those that float in the midwater with creative adaptations for surviving untethered in the dark water. Many, like the bloody-belly comb jelly, use red pigments—which act like a cloak of invisibility in the deep sea—to conceal themselves against the dark backdrop. Others use stunning bioluminescent displays to communicate and draw in unsuspecting prey.

Currents in Monterey Canyon also sweep large pieces of debris like decaying kelp, wood, and dead animals down the main channel, where they come to rest on the canyon floor. Carcasses of bigger animals such as dead whales become a microhabitat for specialized animals such as bone-eating worms in the Osedax genus, which use root-like appendages to extract proteins from the bones. Biologists believe there are at least 19 different species of these worms in Monterey Bay alone. Some organisms that live on the walls or deeper parts of the canyon are chemosynthetic, relying on bacteria in their gut to thrive in areas where hydrogen sulfide is available just beneath the surface.

Mapping and studying MBARI’s backyard with innovative technology

Less than 10 percent of the seafloor has been mapped at the same level of detail as the entire dry surfaces of the Moon and Mars. MBARI began mapping Monterey Canyon in 1998 and has since developed technology that brings us closer to creating a clear picture of this uncharted frontier beneath the ocean’s surface.

Sonar has long been used to map the seafloor, usually with equipment mounted on a ship’s hull. The ship travels back and forth, sending sound waves toward the ocean floor. When the sound waves hit the bottom, they bounce back to the surface, where the sonar receivers use the time it takes for the signals to return to the ship to indicate the depths of the seafloor. Modern multibeam sonars use numerous narrow beams to cover wide swaths of the seafloor to create maps like the bathymetric map shown here. The more detailed maps overlaid on the base map were created with MBARI’s mapping autonomous underwater vehicle (AUV). Although the AUV uses the same sonar technology as those found on ships, it flies closer to the bottom, allowing higher resolution maps to be made. The AUV bathymetric maps show details as small as one meter (three feet) across, and are among the most detailed maps ever made of the deep seafloor. Researchers use these detailed maps to understand seafloor morphology and the movement of sediment within submarine canyons. 

As MBARI’s mapping technology yields higher and higher resolution data, scientists are also acquiring a much clearer picture of biological communities. Sonars and lasers attached to vehicles flying even closer to the seafloor can create images that distinguish features as small as one centimeter in size. This allows biologists to observe changes in animal communities like sponges and corals over time. In addition to tracking changes in biological communities, one of the next goals for MBARI researchers is to repeatedly map the canyon with enough precision to observe changes in the canyon’s shape over time.

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Monterey Canyon: A Grand Canyon beneath the waves
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