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Science

Scientists Mapping Ocean Depth and Volume

Scientists are now closer than ever to being able to answer what is the volume of Earth’s oceans.

“A lot of water values are taken for granted,” he says. “If you want to know the water volume on the planet, you Google it and you get five different numbers, most of them 30- or 40-year-old values.”

Until now, that is.

[social_buttons]Woods Hole Oceanographic Institute (WHOI) scientists Matthew Charette and Walter H.F. Smith have used the latest technology to not only answer how deep our oceans are, but also give the best answer yet as to the volume of our oceans.

There have been previous measurements of the oceans volume for many years now. John Murray, in 1888, dropped lead weights from a rope off a ship to calculate an ocean volume, calculating the ocean area and mean ocean depth. His figure was only 1.2% greater than the figure that Charette and Smith have conceived.

The WHOI pair is using satellite measurements which have not been used before to answer these questions. Rather than seeing the ocean bottom, satellite measurements detect to minute detail bumps and depressions in the ocean’s surface. These changes in the surface reveal the changes in the ocean bottom such as mountains and ranges.

Subtracting these massive mountains from the depth of the water means that the volume figure is more accurate, as the mountains take up space that water would normally have filled. “Matt and I are seeing a better picture of the shape and volume of oceans,” says Smith.

Satellite measurements have measured almost all the world’s oceans, except for some areas of the Arctic currently covered by ice. But they have their shortcummings as well. “There is a problem of spatial resolution, like an out-of-focus camera. We’re measuring the sea surface that is affected by mountains,” he says, “but we’re seeing only really big mountains, and in a blurry way. The resolution is 15 times worse than our maps of Mars and the moon.”

The researchers believe that ship-based measurements are required to augment the satellite data. However ship-based sonar has only mapped approximately 10% of the Earth’s seafloor. “We have gaps in echosounding measurements as wide as New Jersey,” says Smith. And unless Bill Gates gets on the case, it’s unlikely for a full-scale measurement operation to take place. According to U.S. Navy estimates 200 years for one ship, or 20 years for 10, is needed to measure all the ocean-floor depths with an echsounder. “That would come to about $2 billion,” Smith says. “NASA is spending more than that on a probe to [the Jupiter moon] Europa.”

Measurements like these are one of a multitude of data that are needed to make climate change models as accurate as possible. Additionally, knowing just that it is mountains reducing the volume of the water and not the act of humans helps understand what is going on out at sea.

Source: Woods Hole Oceanographic Institute

Image Source: Tiago Fioreze




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