We now know the deepest points in Earth’s five oceans but only 20 percent of the seabeds have been mapped yet

Scientists say we now have the most precise information yet on the deepest points in each of Earth’s five oceans.

The deepest place in each ocean were identified as the Brownson Deep, Puerto Rico Trench in the Atlantic Ocean (8,378 m or 5.2 miles), an unnamed deep within the South Sandwich Trench in the Southern Ocean (7,432 m or 4.6 miles), an unnamed deep within the Java Trench in the Indian Ocean (7,187 m or 4.5 miles), Challenger Deep within the Mariana Trench in the Pacific Ocean (10,924 m or 6.8 miles), and the Molloy Hole in the Arctic Ocean (5,551 m or 3.5 miles)

The key locations where the seafloor bottoms out in the Pacific, Atlantic, Indian, Arctic and Southern oceans were mapped by the Five Deeps Expedition.

Some of these places, such as the 10,924m-deep (6.8 miles) Mariana Trench in the western Pacific, had already been surveyed a number of times.

But the Five Deeps project removed a number of remaining uncertainties.

For example, in the Indian Ocean, there were two competing claims for the deepest point – a section of the Java Trench just off the coast of Indonesia; and a fracture zone to the southwest of Australia.

Likewise, in the Southern Ocean, there is now a new place we must consider that region’s deepest point. It’s a depression called Factorian Deep at the far southern end of the South Sandwich Trench. It lies 7,432m (4.6 miles) down.

There is a location in the same trench, just to the north, that’s deeper still (Meteor Deep at 8,265m or 5.1 miles) but it’s technically in the Atlantic Ocean. The dividing line with the Southern Ocean starts at 60 degrees South latitude.

All of the new bathymetry (depth data) is contained in a paper published in the Geoscience Data Journal.

Better seabed mapping data

The wider context here is the quest to get better mapping data of the seabed in general. Current knowledge is woeful. Roughly 80% of the global ocean floor remains to be surveyed to the modern standard delivered by the likes of the Five Deeps Expedition.

“Over the course of 10 months, as we visited these five locations, we mapped an area the size of continental France. But within that was an area the size of Finland that was totally new, where the seafloor had never been seen before,” explained team-member Dr Heather Stewart from the British Geological Survey.

All of this information is being handed over to the Nippon Foundation-GEBCO Seabed 2030 Project, which aims to compile, from various data sources, a full-ocean depth map by the end of the decade.

Why are better seafloor maps needed?

They are essential for navigation, of course, and for laying underwater cables and pipelines.

They are also important for fisheries management and conservation, because it is around the underwater mountains that wildlife tends to congregate. Each seamount is a biodiversity hotspot.

“For example, there are some major animal groups in the world for which we just don’t know how deep they go. Just last month, we recorded a jellyfish 1,000m deeper than 9,000m, which was the previous record by us. So we’ve now got jellyfish down to 10,000m.

“Three weeks ago, we saw a squid at 6,500m. A squid at that depth! How did we not know this? And during the Five Deeps Expedition, we added 2,000m on the depth range for an octopus.

“These are not obscure animals; it’s not like they’re some sort of rare species. These are big animal groups that are clearly occupying much larger parts of the world than we thought,” Prof Jamieson said.

The deepest place in the Atlantic is in the Puerto Rico Trench, a place called Brownson Deep at 8,378m (5.2 miles). The expedition also confirmed the second deepest location in the Pacific, behind the Challenger Deep in the Mariana Trench. This runner-up is the Horizon Deep in the Tonga Trench with a depth of 10,816m (6.7 miles). [Geoscience Data Journal, BBC, Five Deeps Expedition]

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