Deep water arenas and where to find them

This is a sanctioned Spanish translation of an Eos article.

The depths of the sea are filled with sand, but it is surprisingly difficult to study exactly how it got there.

Equally astonishing is the significance of deep-sea sand. The layers of dense but porous sand, known as turbidites, can be filled with oil, and when they are not, their porosity could make them important sites for carbon capture and storage.

In a recent study, researchers highlighted the factors that predict where and when turbidites can form. This information could assist in accurately determining ancient deposits located kilometers below the Earth’s surface. “This could potentially be a paradigm shift,” stated Jacob Covault, a research scientist at the University of Texas at Austin, who was not involved in the study.

How the sand descends

Submarine avalanches, also known as turbidity currents, carry sediments from the continental shelf to the depths of the sea. Once the sediments reach there, they can form porous turbidites, sometimes filled with oil. Since the mid-20th century, oil companies have begun exploring ancient turbidites, predicting their locations based on factors that may have generated them.

According to Zachary Burton from Stanford University, the oil companies viewed sea level as a key factor in controlling turbidite currents. Their belief was that when sea levels are low, the continental shelf can hold less sediment, making it more likely for it to slide into the deep sea.

Burton and colleagues tested this idea by searching for decades of valuable stratigraphic data. The researchers looked for evidence of turbidites formed during the Cenozoic era (approximately 65 million to 35 million years ago). In total, they found 59 deposits spanning all continents except Antarctica. “This was the first global compilation focused on ancient lithological record (of turbidites),” said Burton.

Their findings challenged the prevailing thought: turbidites were formed during the warmer periods of the Cenozoic era, when sea levels were high. While not the first of their kind, these findings were by far the oldest and most widespread, and were located in some of the highest seas on Earth. Therefore, sea levels alone could not explain the formation of turbidites.

Burton and his colleagues developed a new conceptual model that linked turbidity currents with other climatic factors such as precipitation, extreme storms, and river drainage, which may have pushed sand into the sea. Burton noted that these factors could fill the marine environment with sediments and “overflow” the continental shelf, which would otherwise be spacious.

“It may not be as straightforward as the sea level,” Covault stated. “You can have weather forces that cause a significant supply of sediment… and that’s how you transport sediment to deep waters, even when the sea level is globally high.”

The amazing value of sand.

Sand, even when not forming turbidites, is a valuable resource used in products ranging from smartphones to toilets. Concrete, made up of sand and water, is the second most widely used material in the world. The traditional understanding of turbidite currents suggested that when sea levels were high, the sand should remain near the coast, according to Covault. However, the new model suggests that, despite high sea levels, valuable sand could be dragged to inaccessible depths.

Turbidites are not only useful for resource extraction, but can also be used for carbon sequestration. According to Burton, carbon capture and storage reservoirs have many of the same requirements as oil fields.

When selecting a potential reservoir for carbon storage, “you want to try to identify where the sand aggregates are of significant size and then where the muddy parts are located that seal them,” said Covault.

Some scientists argue that carbon storage in deep waters comes with significant warnings. Firstly, the process only captures a portion of existing carbon dioxide emissions, which is insufficient to offset the total emissions. Additionally, if the captured carbon dioxide manages to escape from deep water deposits, it could acidify the environment, which would be catastrophic for many marine creatures.

In addition to serving as a resource and deposit, sand can also pose a danger. A better understanding of turbidity currents will help protect infrastructure such as transoceanic cables, oil and gas platforms, and wind turbines, which could be destroyed by underlying sediment, according to Burton. “If these events become more frequent, they will have implications for any infrastructure we have on the seafloor.”

—Emily Shepherd (@emilyshep1011), Escritora de ciencia

This translation, done by Oriana Venturi Herrera, was made possible through a partnership with Planeteando.

Text © 2023. The authors. CC BY-NC-ND 3.0

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