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Massive underwater rivers discovered off the coast of Australia
Massive, underwater rivers have been discovered hidden off Australia’s coasts by robotic ocean gliders. These rivers could be critical for moving material from the coasts to the deep ocean, scientists have said. Called ‘dense shelf water cascades’, the hidden rivers form when shallow water on the coasts loses heat during the colder months. This water is already highly salty due to evaporation during the summer months. This cold, salty stream of water in the inner portion of the continental shelf – the edge of the continent that’s typically submerged in shallow water – is denser than deeper water. Driven by the difference in density, this river of water flows offshore along the ocean floor.
Now a group of researchers at the University of Western Australia has analysed data collected between 2008 and 2019 with ocean gliders from eight locations on Australia’s coastline. The data “is the equivalent to spending more than 2,500 days at sea,” said Dr. Tanziha Mahjabin, of UWA Oceans Institute.
As part of Australia’s Integrated Marine Observing System, autonomous underwater vehicles deployed along the coasts collected data on the temperature and salinity – salt concentration – of the water. These measurements allowed researchers to deduce the water’s density, revealing the presence of these underwater rivers.
The team of scientists found that the underwater rivers are a regular occurrence during the autumn and winter months in Australia across a span of 10,000 kilometres. They also found that the underwater rivers could withstand high winds and high tides that often stir up the water, a finding that’s a “unique occurrence globally”.
The underwater gliders were also equipped with sensors to detect organic matter and chlorophyll, a green pigment found in plants, algae and cyanobacteria. The underwater rivers in Australia, they found, serve as transport channels for material and matter across the continental shelf and deeper into the ocean.
“The coastal ocean is the receiving basin for suspended and dissolved matter that includes nutrients, plant and animal matter and pollutants and represents an important component of the ocean environment, connecting the land to the deeper ocean,” said Yasha Hetzel, a researcher at the University of Western Australia’s Oceans Graduate School.