It should come as no surprise that we have more detailed maps of the Moon than the deep seafloor. The surface of the Moon is much easier to see because there’s no huge, deep ocean covering it up.
With a telescope and a clear night, anyone can get a good idea of what the Moon looks like, at least on the side facing towards us. What’s more, the Moon is around ten times smaller than the deep seafloor, which covers two-thirds of the entire surface of the Earth.
That huge area, more than 335 million square kilometres (around 129.3 million square miles), together with the deep’s inaccessibility far offshore, explains why – even with all the technologies now available – scientists have explored only a tiny fraction of the deep seafloor.
Recently, a team of scientists put together a Global Dive Dataset containing information from around 44,000 dives into the deep. These were carried out by scientists inside submersibles, as well as remotely operated vehicles (ROVs) and autonomous robots that steer themselves.
Collectively, these deep submergence vehicles, as they’re known, filmed and photographed an area equal to less than 0.001 per cent of the deep seafloor. That’s roughly the same as Rhode Island, the smallest US state. If the same statistics applied to land-based exploration, all we’d know about terrestrial ecosystems would have come from an area roughly the size of Greater London.
To make matters worse, the minuscule portion of the seafloor that people have explored is an immensely biased sample of the entire deep sea.
Sixty-five per cent of the exploratory dives into the deep have taken place within 200 nautical miles of either the US, Japan or New Zealand. And almost all observations of the deep seafloor – around 97 per cent – were carried out by those three countries, plus France and Germany.
What’s more, explorers have for the most part been focusing on a very narrow range of the deep-sea features. Masses of research effort has been channelled towards exploring the craggy seascapes of deep canyons and escarpments, glossing over other geographical elements like the vast abyssal plains.
Another limitation to deep-sea exploration revealed by the Global Dive Dataset is depth. Over the decades, while the number of dives per year has increased, they’ve been going ever shallower.
Back in the 1960s, more than half of the dives went deeper than 2km down (around 1.2 miles). But by the 2010s, only a quarter of dives were going that far beneath the waves.
And that’s a big problem because the majority of the ocean (around 75 per cent) lies between 2km and 6km below sea level (1.2 to 3.7 miles).
It’s clear that modern day deep-sea explorers are missing an awful lot of the seafloor. Most countries are not involved in deep-sea exploration, and most regions of the deep remain completely unseen and unknown.
Efforts are now underway to fix that, by making deep-sea tools more accessible and less expensive, and by directing dives towards lesser-known sites to help find out what’s actually down on the deep seafloor all around the world.
This article is an answer to the question (asked by Charlotte Preston, Southampton) 'How much of the ocean floor have we actually explored?'
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