An international team of scientists have created a map of the seafloor using satellite radar measurements of ocean surfaces.
The scientist were able to measure the altitude of the sea surface from space by timing how long it takes a radar beam to reflect from the surface to back to the satellite
"Once you average out waves and currents there’s a static sea surface, and it’s slight undulations actually reflect seafloor topography," said team member Professor Dietmar Müller from the University of Sydney, who is funded through the Australian Research Council Laureate Fellowship to participate in the project.
"So where there’s a seamount or a ridge or plateau on the seafloor it ever so slightly it attracts a mass of water above it and causes a small hump. This hump might be a couple of decimetres in size.
"With modern radio technology, and by combining a lot of data, we can actually map out these tiny undulations – highs and lows – at the sea surface globally to make an inference about the seabed and the sub-seafloor structure."
Existing data from satellites CryoSat-2 and Jason-1 were used to construct a global marine gravity model, with it being two times more accurate than previous models.
“How much do we know about what’s actually down there, let alone about what’s underneath the seabed? We know much more about the topography of Mars than we know about Earth’s seafloor,” said Müller.
“One of the most important uses of this new marine gravity field will be to improve the estimates of seafloor depth in the 80 per cent of the oceans without depth soundings,” Müller said.
“Even after 40 years of mapping by hundreds of ships, one finds that more than 50 per cent of the ocean floor is more than 10 kilometres away from a depth measurement. Between the soundings, the seafloor depth is estimated from marine gravity measurements from satellite altimetry.”
The map can measure uncharted sea mounts, unknown tectonic microplates in the Pacific Ocean, detailed kinks in fracture zones, linear scars on the seafloor that trace out plate motion.
Using the map, scientists were able to discover an ancient, extinct mid-ocean ridge from the Jurassic Period in the Gulf of Mexico and an ancient rift scar in the South Atlantic Ocean formed by a deep-seated hotspot leading to a cracking of the ocean floor.
"It has long been suspected that there must be an extinct mid-ocean ridge in the Gulf of Mexico, because of the Gulf of Mexico opened by the Yucatan block in the Caribbean moving away from North America. But... the ridge itself had never been seen because its buried underneath the large pile of marine sediments," said Müller.
"With our gravity data we can see through the sediments. That’s one of the important advances that has been made possible by this new gravity grid – it allows us to detect hidden features, to map the fine scale features on the sea floor and underneath the sea floor."
The map can also be used to map rough seafloor patches and better understand how deep ocean circulation and ocean mixing affect global climate.
"The mixing of water in the oceans partly determine how heat is taken up by the oceans and how oxygen is transported from shallow water into the deep ocean," said Müller.
"The tools and methodology had been around for several decades, but the existing satellite’s coverage is quite sparse; the data coverage is just not good enough to create a detailed map. It’s only in time that several different satellite missions have been carried out...and we can combine all this data. So for the first time, we’ve now been able to create this very hybrid, illusion map, even though the method has been around for a while.
"By having an accurate map of the very deep ocean, it helps oceanographers to build better models for ocean mixing."
Supercomputer simulations of the Earth’s mantle – the layer that is between the Earth’s surface and core – are also being used to explore some of the unknown forces that cause changes to the tectonic plates.
"Even though we have [got] a lot of data that maps features and tell us where plates are diverging or converging, we still don’t understand the exact forces that result in the variety of plate motion behaviour. We don’t understand exactly how it works because you can’t go down there directly and take samples or observe what’s happening.
"So we need computer simulations to try and model this process. Only recently has high performance computers become powerful enough and software has been developed to allow us to model this entire global system of the connecting deep mantle of the Earth with the plates above to try to understand what actually drives the plates."
He said as Australia is surrounded by water and large offshore territory, there's much opportunity to make new discoveries.
"Australia is surrounded by huge offshore territory and very large sunken bits and pieces of continent, and there’s very little we know about it. What we see at the surface with Lord Howe Island and Norfolk Island, for example, they are just tiny expressions of this vast undersea landscape," Müller said.
This research has been published in the international journal Science.
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