Trees from Ancient Forests Discovered in Deep Ocean, Thousands of Miles from Their Origin

The remains of ancient forests have been discovered deep beneath the sea, thousands of miles from their mountainous origins, with scientists finding 19 million-year-old wood chips in sediment layers at the bottom of the Bay of Bengal.

Researchers led by Sarah Feakins, from the University of Southern California, Los Angeles, drilled down over two miles from the surface of the ocean, retrieving sediments from half a mile beneath the sea floor. By analyzing the core sample, the team was able to look at how trees were swept into the ocean millions of years ago before getting trapped in the ground.

By looking at the wood chips in the core, the team was able to determine where the trees had come from. In most cases, they found the wood was from trees that grew in lowlands, near the ocean. However, one layer was found to have wood from trees that would have grown high in the Himalayan mountains, about two miles above sea level.

In their study, published in PNAS, the team argues that trees within an ancient forest were uprooted by a huge release of water—potentially by a natural dam created by a glacier or a landslide. These trees would have then been transported for thousands of miles along a huge surge of water—from cyclones, monsoons or floods, the scientists suggest—before being released in the Bengal Fan.

The team say this is the first evidence showing trees can be transported for thousands of miles, from mountains to the deep ocean. Their findings also shed light on the role of wood in Earth's carbon cycle—the way carbon travels from the atmosphere into the planet and its organisms, and back out again.

Carbon stored in plants is released when it is eaten, decays or is burned. Because the trees were transported shortly after being uprooted—the point of death—they did not decompose. Instead, the fresh wood was locked into the seafloor sediment—potentially representing a previously unrecognized means by which carbon can be stored for millions of years.

"The discovery of woody fragments in the coarse-grain layers of turbidite beds across 19 [million years] indicates that woody input may be a neglected contributor to the [organic carbon] cycle in the Bengal Fan and in other continental margins over geologic timescales," the researchers wrote, adding that the findings suggest the organic carbon locked in continental margins may be higher than once thought. "The rapid export and burial of wood represents a highly efficient pathway of atmospheric CO2 sequestration," they said.

Understanding how much carbon may be locked away as a result of forests being washed into the ocean is important in understanding future climate change, Fearkins said. "As we've tried to calculate the amount of carbon in all parts of the carbon cycle, we didn't know about this forest of fragmented trees buried in the ocean floor," she said in a statement. "Now we need to add it to the equation."

Scientists are currently working to understand the carbon cycle, with researchers in the U.S. launching the Deep Carbon Observatory (DCO) over a decade ago. A report recently released by the group showed that less than 1 percent of Earth's total carbon is above surface—in the oceans, on land and in the atmosphere. The rest is all locked away in the planet's crust, mantle and core.

Correction 10/22 7.16 a.m. The headline and opening paragraph of this article originally said the trees were thousands of miles from land. This has been corrected to say thousands of miles from their origin.