99.999% of earth’s deep seafloor yet to be observed

The ‘Candelabra’ hydrothermal vent on the Mid-Atlantic Ridge 3.3 km underwater. In the past, scientists have found evidence of ancient life forms in the precipitates around such vents.
| Photo Credit: MARUM (CC BY 4.0)

Two-thirds of the earth’s surface consists of the deep ocean — parts of the surface 200 m or more below sea level. It’s thus the world’s largest as well as least explored ecosystem. A new study in Science Advances by U.S. researchers has estimated how much of the deep seafloor humans have observed visually so far, to quantify what remains unseen and geographic biases.

Visual imaging is an important way to study deep-sea ecosystems because it yields the context from which biological and geological samples have been extracted and helps calibrate remote-sensing data.

The researchers collected 43,681 records of deep-sea visual dives from 34 institutions in 14 countries, spanning activities in 120 exclusive economic zones and the high seas. These dives were supplemented with data about dive coordinates, depth, dates, operator details, and platform type collected from institutional records, public databases, and published papers.

Then the team used two methods to analyse the data. In the first, they estimated the area imaged by various submersible vehicle types and calculated minimum and maximum seafloor area per dive. Thus they estimated the total visual coverage to be at least 1,259 km² and at most 2,130 km².

In the second, they used dive duration and vehicle speed, among others, from long-running programmes to estimate total coverage to be 3,823 km² over 66 years.

Thus, the researchers concluded, visual observations have covered 0.001% at best of the deep seafloor. Equally starkly, they said more than 97% of all dives have been conducted by just five countries — the US, Japan, New Zealand, France, and Germany — whereas all African and most Latin American countries don’t exist in operator records.

The team also reported that features like canyons and escarpments are over-represented in observations whereas abyssal plains, which dominate the seafloor, are under-represented.The coverage implies scholars have been left to make inferences about marine biodiversity and ecosystem processes based on a sample that collectively covers only half of Goa.