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Why submarine canyons form in places where the seafloor is particularly steep

Geoscientists Professor Anne Bernhardt of Freie Universität Berlin and PD Dr. Wolfgang Schwanghart of the University of Potsdam have uncovered a surprising insight using a global statistical model: The primary factor influencing the formation of submarine canyons is the steepness of the seafloor—not, as commonly assumed, the role of rivers and where they transport sediment into the ocean.

Their study, "," has been published in Science Advances.

To investigate the causes behind the global distribution of submarine canyons, the researchers used a spatial statistical model incorporating over 2,000 canyons across the world.

They analyzed the relationship between the frequency of canyons and sixteen geoscientific variables, including tectonic, geomorphological, and climatic factors. By means of modern point pattern analysis, they found that the gradient of the seafloor offshore of the continents is by far the most important predictor, ahead of other factors such as proximity to river mouths, sediment load, or seismic activity.

"Our analysis shows that tectonic and thermal processes shaping the slope of the ocean floor ultimately determine where canyons most frequently form," explains lead author Anne Bernhardt.

"These deep underwater valleys are major transport routes for sediment and carbon into the deep ocean, a process that affects Earth's climate across geologic time scales."

The study also reveals that once a canyon has eroded the continental shelf, it begins to interact with nearshore processes, especially with sediment input from rivers or coastal currents. This creates a kind of competitive dynamic: a canyon that gains an advantageous position can effectively "outcompete" neighboring canyons by capturing more sediment.

From this point on, terrestrial processes such as the nature of the underlying bedrock or the volume of river discharge become increasingly important, especially when canyons extended to the ancient coastline during periods of low sea level, allowing direct contact with terrestrial sediment sources.

"These physical processes and their interactions occur on geological time scales and are quite complex. The fact that they happen far beneath the ocean surface certainly does not make them any easier to observe," says Wolfgang Schwanghart.

"This is why we chose a statistical model, as it allowed us to better understand how submarine canyons form using comprehensive global data."

The findings challenge the widely held assumption that rivers and their sediment load are the primary drivers behind the formation of submarine canyons. Instead, the results show that the steeper the seafloor, the more likely it is that such canyons will form –a process largely driven by tectonic uplift, thermal cooling, and slope instability.

The study provides fundamental insights into the interactions between the geodynamics of Earth's crust and the global carbon cycle, thus establishing the basis for better understanding the role of oceans as long-term carbon sinks.

The implications of the findings extend beyond geoscience: Submarine canyons transport organic carbon to the deep sea, contributing to long-term climate regulation. By identifying where and why these types of canyons are most likely to form, the researchers hope to improve our understanding of global carbon sinks.

"Our findings will help us to identify regions in which carbon reaches the deep sea particularly efficiently," says Bernhardt. "This is essential for improving Earth system models and forecasts related to the stability of natural carbon reservoirs."