A River Runs Under It

Understanding how fresh-water rivers flow beneath oceans

“Rivers are sacred to humans because they deliver sediments and fresh soil to grow our food,” says Dr. S. “Bala” Balachandar, William F. Powers Professor and Distinguished Professor in the Department of Mechanical and Aerospace Engineering at the UF Herbert Wertheim College of Engineering. “Under-ocean turbidity currents serve as underwater rivers that transport sediments to sites where they can be useful. They are very important in carbon distribution, promoting an oasis of life at the bottom of the ocean and controlling the biodiversity of geological and geographical regions.”

As rivers run to the sea, they carry sediments – some as small as a carbon molecule, others as large as a car. When they reach the relatively steeper slopes (1-5%) of the ocean bed along coastlines, their waters form supercritical turbidity currents that quickly dump their sediment load and mix with the ocean. Some turbidity currents, however, become subcritical on flatter slopes (less than 1%) as the fresh water mixed with sediment sinks to the bottom of the ocean due to its higher density. Subcritical turbidity currents transport large amounts of carbon, nutrients and fresh water through oceans and play an important role in global geochemical cycling and seafloor ecosystems. These currents, sometimes reaching as high as the Grand Canyon is deep, travel for hundreds to thousands of kilometers under the ocean.

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