Our planet is dominated by water, with over 70% of its surface covered by oceans. Despite this, a staggering 40% of the global population lives within 100km of the coast, yet our understanding of these vast underwater realms remains surprisingly limited. In many ways, sending humans into space has proven less challenging than exploring the crushing pressures of the deep sea.
While our knowledge of the oceans is constantly expanding, countless mysteries continue to baffle scientists. From unexplained animal behaviors to the very origins of Earth’s water, the deep blue holds secrets that challenge our current understanding.
Unraveling the Ocean’s Enigmas: Mysteries That Stump Scientists
Why Are Orcas Killing Great White Sharks?
A puzzling phenomenon has been unfolding off the coast of South Africa since 2017: great white sharks are washing ashore with their livers precisely removed. Evidence points to a pair of male orcas, or killer whales, known as ‘Port’ and ‘Starboard’ (distinguished by their collapsed dorsal fins), as the culprits.
In May 2022, drone and helicopter footage from Mossel Bay captured Starboard and four other orcas actively hunting great whites, with one kill even recorded. A year later, Starboard was observed killing a juvenile great white alone in just two minutes. During these hunts, orcas cunningly flip the sharks onto their backs, inducing a trance-like state, before extracting and devouring their oil-rich livers.
This behavior raises significant questions about its impact on the local ecosystem, as great whites have been observed fleeing in response to these attacks. Marine biologist Leigh de Necker notes that while orcas are known for specialized hunting, their targeting of great whites is relatively new. “In previous years we had orcas coming to South Africa to hunt dolphins,” de Necker states, “But in 2015 they were documented hunting sevengill sharks for the first time, before being recorded predating on great whites in 2017.”
The reasons behind this shift remain unclear. Theories range from changing fisheries impacting orca prey sources to orcas simply discovering a new, abundant food source.
Where Did Earth’s Water Come From?
Our planet is truly a water world, yet the origin of this immense volume of water, which covers approximately 360 million square kilometers, remains a significant scientific mystery. Earth formed around 4.5 billion years ago, but how it became so “soggy” is still debated.
Dr. Helena Bates, a postdoctoral researcher in meteorite science at the Natural History Museum, London, explains two primary theories. The first suggests Earth formed in a region of space already containing water. The second posits that Earth initially formed in a hot, dry environment, and its water was delivered later by other celestial bodies.
The latter theory gains credence from carbonaceous chondrites, a type of meteorite that can contain up to 10% water. The early Solar System experienced far more bombardments from such objects than it does today. By studying meteorites, scientists can gain insights into the distribution of water throughout the Solar System. Professor Sara Russell, a professor of planetary sciences, highlights the use of hydrogen-deuterium ratios in meteorites to determine their “fingerprint” and potential origins.
Most scientists believe a combination of these factors likely contributed to Earth’s watery abundance. As Bates muses, “I don’t know if we’ll ever work it out. But that’s the joy of it!”
Who – or What – Made the Yonaguni Monument?
Off the coast of Yonaguni, Japan, lies a controversial underwater rock formation discovered by scuba diver Kihachiro Aratake in 1986. This unusual structure features stacked sandstone blocks, parallel joints, a spiraling staircase, and strange etchings. Some believe it’s the sunken remains of an ancient civilization, while others argue it’s a natural phenomenon.
Professor Masaaki Kimura of Ryukyu University is a proponent of the human-made theory, claiming his surveys reveal “artificial topographies constructed about 10,000 years ago beneath the sea… including stepped pyramids, roads and water canals.”
Conversely, Professor Robert Schoch of Boston University, who has extensively dived the site, concludes the structure is natural. He points to the geological characteristics of the region, where rocks naturally break along vertical and horizontal planes, and similar formations can be found on land. He attributes the “etchings” to natural scratches. While he concedes evidence of ancient civilizations on nearby islands, he remains unconvinced about the Yonaguni Monument’s artificial origins.
Where Are Weird Ocean Noises Coming From?
The ocean is a surprisingly noisy environment, filled with sounds from human activity, marine life, volcanic rumbles, and seismic shifts. However, some underwater noises have left scientists perplexed.
One such sound is ‘The Upsweep,’ first recorded by NOAA in 1991 and still detected today. This wailing sound steadily rises in pitch, lasts a few seconds, and appears to originate between New Zealand and South America. Its activity peaks in spring and autumn, but its source remains unknown.
Another mystery is ‘The Ping,’ reported in 2016 from the Fury and Hecla Strait in the Canadian Arctic. Hunters claimed it was scaring away animals. Despite investigation by the Canadian military, the origin of this noise remains unidentified, with various theories, including mining companies and wildlife activists, denying involvement.
Perhaps the most famous enigmatic ocean sound is ‘The Bloop,’ one of the loudest underwater noises ever recorded. Picked up in 1997 by hydrophones thousands of kilometers apart across the Pacific, theories about its origin ranged from military exercises to unknown sea monsters. The latter theory gained traction when its source was reportedly near the fictional emergence point of HP Lovecraft’s Cthulhu. However, in 2005, scientists finally determined that ‘The Bloop’ was the sound of a large iceberg breaking away from a glacier. With climate change, such “Bloops” may become increasingly common as ice melts at an accelerated rate.
What’s Going On With the Seafloor?
Beyond the waves, the ocean floor is a profoundly mysterious place. While satellite data has provided general maps, these often miss entire topographical features like seamounts and intriguing relics such as shipwrecks.
A global initiative, the Seabed 2030 project, aims to map the seafloor with high-resolution technology. As of June 2024, only 26.1% of the seafloor has been mapped in detail, highlighting the vast amount of work still needed. A comprehensive understanding of the seabed could significantly boost our knowledge of ocean circulation and climate change, and even aid in tsunami forecasting.
Furthermore, an improved understanding of the seabed could reshape theories about Earth’s formation. Recent research from the University of Maryland, using seismic imaging, has uncovered evidence of a previously unknown ancient seafloor that may have sunk deep into Earth’s interior approximately 250 million years ago. As study leader Dr. Jingchuan Wang notes, “This is just the beginning. We believe that there are many more ancient structures waiting to be discovered in Earth’s deep interior,” potentially revealing new insights into our planet’s complex past and even other planets.
Where Has All the Plastic Gone?
An estimated eight million tonnes of land-based plastic enter our oceans annually, yet scientists are largely unaware of where the vast majority of it ends up. Research in 2015 by Professor Kara Law suggested that only a tiny percentage (between 6,350 and 245,000 tonnes) floats on the surface. Understanding the fate of this missing plastic is crucial for comprehending its true impact on marine life.
As marine biologist Tom ‘The Blowfish’ Hird explains, “The most notorious [impacts] are the effects of large chunks of plastic – like straws and shopping bags – that impact charismatic animals such as marine mammals, turtles and seabirds. However, these incidents are the tip of the iceberg.” He emphasizes that plastic persists, breaking down into increasingly smaller microplastics, which have become a microscopic component of seawater.
No part of the ocean seems free from plastic pollution. A 2019 study found microplastic particles in the guts of 65 out of 90 amphipods sampled from six different deep ocean trenches. Evidence also suggests that wave action can aerosolize microplastics into the atmosphere, with a recent study even finding microplastics in dolphins’ breath. Hird concludes, “The fact of the matter is that we simply do not have the ability to accurately monitor and gather the correct data to give us the true picture of where plastics are going in our ocean and how they’re getting there.”
Why Do Some Creatures Glow?
The ocean’s depths are often characterized by darkness, yet they are punctuated by flashes of bioluminescence – the generation of light by living organisms. This remarkable trait has evolved independently around 100 times and is widespread throughout marine environments. In the “twilight zone” (200-1,000m deep), up to 90% of animals may produce light for various purposes, including finding mates, camouflage, luring prey, or evading predators.
Professor Jon Copley, a marine ecologist, highlights examples like the “lightsabers” of lantern sharks, which advertise their unappetizing spines. Recent research in 2024 by Dr. Danielle DeLeo’s team found that bioluminescence first emerged in octocorals approximately 540 million years ago.
Despite pinpointing its earliest evolution, the initial spark for animals to emit light remains a mystery. Copley offers a compelling theory: the ocean’s conditions 540 million years ago were vastly different, particularly with much lower oxygen levels. The rise in oxygen during the Cambrian explosion may have spurred the development of new metabolisms. “Bioluminescence is the by-product of an oxidation reaction,” Copley explains. “So perhaps bioluminescent reactions evolved as part of the development of metabolism for more oxygenated conditions – and then the light by-product from those reactions found a use in signalling and camouflage and so on.”
While bioluminescence is crucial for short-range visual communication, Copley reminds us that the ocean is also a world rich in smells and sounds.
The vastness of our oceans continues to hold countless secrets, from the perplexing behaviors of its inhabitants to fundamental questions about our planet’s very formation. As science and technology advance, we inch closer to unraveling these mysteries, deepening our appreciation for the incredible complexity and wonder of the underwater world.
What other ocean mysteries do you find most intriguing?
