Research Outreach Blog
February 10, 2023

Mysteries of Earth’s ocean floor

The sky and the sea have inspired artists and writers for centuries and both hold secrets that have captivated humanity for millennia. In 2022, images from the James Webb Space Telescope revealed some of the mysteries of the visible universe, bringing objects up to 13.6 billion light-years away to the forefront of popular science. But just as many secrets remain to be revealed much closer to home, at the bottom of our own oceans.

The formation of the seabed affects many processes that human civilisation depends on, from the circulation of the oceans to the marine ecosystem that provides food or income for roughly three billion people. Oceanic circulation affects the climate and weather across the globe, which of course impact food and water provision worldwide. It also affects the tides, which could become important sources of renewable energy in the coming decades, along with sediment transport and nutrient cycling, among others. High-resolution maps of the seabed could contribute to a better understanding of all of these processes that are so important for the sustenance of life on this planet. However, much of the ocean floor, including its topography and the species living on it, remains a mystery.

Dima Zel/Shutterstock.com

The HD1 galaxy, lying within the Sextans constellation, was first reported in April 2022 by researchers at Tokyo University. It is currently considered the most distant object within the observable universe, located 33.288 billion light-years from Earth. The Challenger Deep, the deepest point in the ocean, is just 10,920m (about 6.8 miles) below the surface. Comparatively, it doesn’t seem very far. So why is it that, until the past few years, very similar proportions of the observable universe (4%) and the seabed of our own oceans (5%) have been mapped?

Are there not mysteries still to be resolved within the boundaries of the Earth’s atmosphere?

There are challenges associated with oceanography that hinder our ability to record the ocean floor, including technological constraints and the nature of the sea itself. The detection of extra-terrestrial objects is made possible since light emitted can reach a space telescope (such as James Webb) largely uninterrupted by the vast vacuum of space. In contrast, light can only travel about 200m into the ocean, and that’s when the water itself is clear and not muddied by sediment. As such, features beyond this depth – bearing in mind that 72.6% of the seafloor exists at a depth of 3,000–5,750m – must be detected in another way.

The Mariana Trench in the Pacific Ocean is home to the deepest known point on Earth’s seabed: Challenger Deep.

Historically, the seabed was measured by a technique called lead and line sounding. It used a weight, typically composed of lead, attached to a rope. This practice is believed to have been carried out in Roman times, but was mechanised in the 19th century. These methods began to go out of fashion later in the 20th century, when sonar technologies were used to map the shapes and contours of the seabed. Despite this, much of the ocean floor has only been mapped to a resolution of about three miles, meaning that many formations and smaller objects are yet to be discovered. Some parts of the ocean only have depth data from over 100 years ago. Recent technological advancements have improved the resolution of seafloor detection, and there are ongoing projects that aim to improve our understanding of the seabed and map it in its entirety at a much finer resolution. Our oceans will remain just as interesting, but we may soon reach a point where the ocean floors no longer hold as many mysteries as outer space.

Rachel Herbert-Goddard is a freelance writer based in Carmarthenshire, South Wales, with a passion for the marine environment.

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