Flood rains caused by cyclones and monsoon storms, as well as other catastrophic events, are responsible for moving huge amounts of fresh wood to a watery grave deep beneath the ocean, according to earth scientists.
Their research, published in Proceedings of the National Academy of Sciences On October 21, it shows the first evidence that trees can travel thousands of miles from their mountain homes to settle in the vast sediments that extend beneath the river mouth.
An ancient tree found in the deep sea
An international research team led by Sarah Feakins, Associate Professor of Earth Sciences at USC Dornsife College of Letters, Arts and Sciences, has examined cores of samples taken from the ocean floor over a thousand miles off the coast of Bangladesh, in the Bay of Bengal.
Once at an offshore target, the US research vessel R / V Joides Resolution, part of the International Ocean Discovery Program, extended the drilling mechanism more than two miles from the ocean surface to its bottom and drilled more than half a mile down into the sediments.
The samples were then taken back to the laboratory, where the research team combed the obtained core samples. They discovered wood chips in sandy layers dating back as far as 19 million years.
Their analysis showed that the wood in most layers came from lowland sources, but one layer contained wood from trees high in the mountains.
"We found intact pieces of conifers," Feakins said. "These trees grow two miles above the sea, up in the Himalayas."
The trees were probably uprooted during the last ice age by the massive discharge of water from violations of a natural dam created by the property of a glacier, landslide or similar soil. The trees, because of the rush of water, rode the rivers thousands of kilometers from Nepal, across Bangladesh, all the way to Bengal worshipers, the largest reservoir of underwater sediment in the world.
Scientists searched other layers in the core sample and found wood from the lowlands. These wood chips were probably taken to the sea by torrential rain and floods during the monsoon or cyclone that occurred many times over 19 million years.
Rivers export trees
In addition to discovering stunning trees, trees can transport rivers into the sea due to natural events, research shows that this tree is an important part of the carbon cycle.
Most of the carbon on the planet is in rock, but the rest flows in various forms between land, air, and ocean, breaking through plants, animals, and germs as they do so.
In the air, carbon can be part of carbon dioxide, methane, or other greenhouse gases that can trap heat in the atmosphere, causing the greenhouse effect.
On the other hand, plant-bound carbon remains separated from the atmosphere until its metabolism, breakdown or combustion releases it, usually shortly after death. Yet, rapid transport events by rivers bypass the decay that usually accompanies the fall of trees and instead bring in fresh wood to feed into the sediment on the seabed.
The findings indicate a previously unacknowledged way in which carbon can remain locked, effectively removed from the carbon cycle, for millions of years. The abundance of wood suggests that previous carbon estimates imported by the modern Ganges-Brahmaputra rivers were low.
Now, counting wood, the amount of carbon exported and buried may be 50% higher than previously thought.
"As we were trying to calculate the amount of carbon in all parts of the carbon cycle, we did not know about this forest of fragmented trees buried in the ocean floor," Feakins said. "Now we have to add it to the equation."
Feakins added that the findings underscore the importance of free flowing rivers in carbon sequestration.
"Over the last 50 million years, average global temperatures have dropped significantly," Feakins said, as well as atmospheric CO2 levels.
This is due to natural processes – such as weather on rocks (including the Himalayas) and burying plant carbon into the coast – that draw carbon out of the atmosphere. This research indicates the need to inventory millions of years of carbon excretion in these elusive woody sediment layers without which greenhouse gases would maintain high temperatures.
Furthermore, the cooling trend of 50 million years has been reversed in recent decades thanks to human activity, which has raised CO2 levels to near 3 million years ago.
Feakins notes that, in conjunction with emission reductions, understanding the carbon offsetting services that the natural ecosystem and rivers provide can inform decisions about forest management, embankment removal and other issues, given their potential to help manage the carbon cycle.
Is the theory of Earth's climate wrong in the last 15 million years?
Hyejung Lee el al., "Permanently Buried Wood in Bengal Fan for the Last 19 of My Years." PNAS (2019). www.pnas.org/cgi/doi/10.1073/pnas.1913714116
Catastrophic events carry forests of trees thousands of miles to burial at sea (2019, October 21)
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