How deep are the five oceans?

Expedition maps hundreds of thousands of miles of previously unexplored seafloor

A jellyfish in the ocean

An expedition to map the seafloors of the Earth’s five oceans has provided new insights into their precise depths and locations, scientists say.

The Five Deeps Expedition explored the “key locations where the seafloor bottoms out” in the Pacific, Atlantic, Indian, Arctic and Southern Oceans in order to provide “the most precise information yet” on the oceans’ deepest points, reports the BBC.

Top of the ocean bottoms

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According to a newly published paper in the Geoscience Data Journal, the Five Deeps Expedition mapped 550,000 sq km (212,356 sq miles) of seafloor, “of which 61% comprised new coverage over areas never before surveyed”.

Conducted between 2018 and 2019, the global survey identified the deepest points as: the Molloy Hole in the Arctic Ocean, at 5,551 metres; an unnamed deep within the Java Trench in the Indian Ocean (7,182m); another unnamed deep within the South Sandwich Trench in the Southern Ocean (7,432m); the Brownson Deep in the Puerto Rico Trench in the Atlantic (8,378m); and the Challenger Deep within the Mariana Trench in the Pacific.

Some of these places, such as the Mariana Trench, “had already been surveyed a number of times”, says the BBC.

“But the Five Deeps project removed a number of remaining uncertainties,” the broadcaster adds.

Prior to the new study, for example, experts were split over whether the deepest point in the Indian Ocean was a section of the Java Trench just off the coast of Indonesia or a fracture zone to the southwest of Australia.

The “rigorous measurement techniques” of the Five Deeps team “confirmed Java to be the winner”, but also revealed that the lowest point in the trench “is 387km from where previous data had suggested the deepest point might be”, the BBC reports.

The explorers also found a new deepest point in the Southern Ocean.

How accurate is the new data?

The Five Deeps Expedition was led by Texan entrepreneur and explorer Victor Vescovo, a former US navy reservist. In September 2019, Vescovo announced that he reached the final destination in his expedition, to the bottom of the Arctic’s Molloy Hole, “making him the first person to descend to the five deepest known spots of the Earth’s oceans”, as the Smithsonian Magazine reported at the time.

Vescovo made the historic descents in a $35m two-seater submersible, called the Deep Submergence Vehicle (DSV) Limiting Factor, while his team of scientists took measurements of the temperature and the salinity of the water from the sea surface to the deepest point in the ocean.

The scientists then used this data to correct depth readings made from the hull of the DSV’s their support ship, the Pressure Drop, which used a multibeam echosounder to measure the distance to the ocean floor.

Although the resulting calculations still have a margin of error of between plus or minus 15m, the data is more accurate than any previously recorded.

And unless major new breakthroughs are made in the field, “refining the observations any further will be extremely hard”, says the BBC.

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