Climate patterns shape sand deposits in the deep sea
New findings about how sand deposits form in the deep sea during different climate eras reveal mysterious processes miles beneath the ocean’s surface, and could help future-proof offshore operations like wind farms as the Earth warms and water rises.
As weather, earthquakes, and other events erode mountains, sand washes through streams and rivers and eventually reaches the sea, where some is swept into destructive, sediment-filled currents before settling as offshore deposits.
How those deposits form under different conditions not only reveals critical information about the planet’s cycles, but also could help ensure that offshore operations like wind farms and carbon sequestration can withstand changes in undersea sediments as the climate warms and seas rise.
In a recent study that synthesized global data on deep-sea sand deposits, scientists found records of fast-moving turbidity currents formed roughly 50 million years ago during a particularly hot time in the planet’s history when seas were high. The study, published Feb. 8 in Nature Scientific Reports, challenges a theory that deposits from turbidity currents are more likely to form when seas are low, and hints at what we might expect as the climate warms and seas rise.
“This suggests that extreme weather events and exacerbated global climatic conditions contributing to increased erosion of landscapes could amplify delivery of sand into the deep ocean,” said Stanford University adjunct lecturer Zack Burton, PhD ’20, lead author on the study.
In the paper, the researchers present a conceptual model suggesting that conditions like intense precipitation and integrated river drainages can cause abundant sand-rich deep-marine deposits despite exceptionally high sea levels.
“We suspected this was true, but we hadn’t realized the magnitude of examples that have been documented in the literature,” said senior study author Stephan Graham, the Welton Joseph and Maud L’Anphere Crook Professor in the Stanford Doerr School of Sustainability. “There were many more of those deep-water deposits than we had realized.”
Earth during the early Eocene 56 million to 48 million years ago had the highest sea levels – with oceans over 200 feet above current levels – since before the sudden mass extinction of three-quarters of the planet’s plant and animal species about 66 million years ago. There were rainforests in the Arctic, and alligators lived in the Dakotas.
While some of these conditions may be unfathomable, present-day climate change is giving us glimpses of the extreme climate events that besieged the early Eocene.
“As the Earth gets hotter and hotter and sea level rises even further, then we would expect the increasing intensity of storms, higher precipitation rates – based on climate modeling by other people – to have much more impact in terms of sediment getting to the deep sea,” Graham said.
Graham said the power of sediment-laden flows known as turbidity currents that sweep sand out to the deep sea shouldn’t be underestimated for future-proofing the next generations. According to Graham, those currents are like an underwater version of the devastating glowing avalanches that cascade down erupting volcanoes, leaving destruction in their wake.
Researchers first found out about turbidity currents because they were snapping transatlantic telegraph cables in 1929. “They’re very powerful submarine flows of tremendous scale,” Burton said.
With this synthesis of deposits from such a critical time in Earth’s history, the researchers hope others will continue speculating about the aspects of warmer climates that may be impacting the global sedimentary cycle.
“Other factors, like human interactions with sedimentary systems and the terrestrial world we all live in, are combining to influence movement of sediment,” Burton said. “I think it’s hard to consider from an everyday perspective, just because we don’t see these systems – they’re part of the beautiful mystery of the deep ocean which we know so little about.”
Stanford co-authors on the study include Tim McHargue and alumni Chris Kremer (now at Brown University), Jared Gooley (now at the U.S. Geological Survey Alaska Science Center), Chayawan Jaikla (now at Microsoft), and Jake Harrington. The research was supported by the Stanford Project on Deepwater Depositional Systems and Basin Processes and Subsurface Modeling programs.
Danielle T. Tucker
Stanford Doerr School of Sustainability