Home » Water Science » Oceans » 10 Unsolved Mysteries of the Deep Ocean

10 Unsolved Mysteries of the Deep Ocean

Ocean Mysteries

10 Ocean Mysteries That Remain a Mystery

The ocean is vast and still holds many mysteries. Today, we’re going to dive deep and explore 10 of these fascinating ocean mysteries.

1. The Underwater Pyramids of Yonaguni

Bermuda Triangle Map

Off the coast of Japan, the Yonaguni Monument are underwater structures that some believe could be ancient pyramids (though this is still a subject of debate).

The formations consist of big, flat rocks. Some are arranged like man-made structures with terraces, steps, and right angles. 

Although the origin of the Yonaguni Monument is still uncertain, some researchers and divers think these structures may have formed naturally from rocks breaking apart and eroding because of tectonic activity and underwater currents.

Some people think ancient human civilizations may have shaped or changed the formations, but there isn’t much proof. 

2. The Devil’s Sea (Dragon’s Triangle)

Devil's Triangle

The Devil’s Sea, also called the Dragon’s Triangle, is a part of the western Pacific Ocean. It is between the Japanese coast, the Bonin Islands, and Taiwan.

Many people think of it as being like the Bermuda Triangle, with mysterious disappearances and unexplained events. But it’s not as well-known.

Similar to the Bermuda Triangle, people know the Devil’s Sea for ships and planes disappearing, and strange supernatural encounters. 

Many of these claims are unverified. Natural factors like ocean currents, weather, and seismic activity can make navigation dangerous taking away some of the intrigue. 

3. The Sargasso Sea

Sargasso Sea

The Sargasso Sea is unique because it is the only sea on Earth that is entirely surrounded by ocean currents. This means it does not have a land boundary and it’s bounded by 4 ocean currents.

Within this sea, there are vast mats of free-floating Sargassum seaweed. Scientists still don’t fully understand the Sargasso Sea’s ecosystem with its distinctive marine species and seaweed.

While the Sargasso Sea is not a mystery in the sense of unexplained phenomena, it is a region that scientists continue to explore. Ongoing research is gradually shedding light on the many facets of this fascinating part of the ocean.

4. Underwater Crop Circles


There have been reports of intricate patterns and circular formations on the ocean floor. But these “underwater crop circles” are not created by mysterious forces, as the term “crop circles” might suggest.

Male pufferfish create circular patterns in their nests. They create these intricate patterns on the seabed by swimming and flapping their fins as a form of courtship display.

Other underwater circular patterns can be the result of geological and environmental factors. Circular features can form on the ocean floor due to sediment deposition, ocean currents, or underwater geological formations.

5. The Baltic Sea Anomaly

Baltic Sea Anomaly

The Baltic Sea Anomaly refers to a mysterious object that was discovered in the Baltic Sea in 2011 by a Swedish ocean exploration team.

The object is oval-shaped with a diameter of about 60 meters (200 feet). But it’s also been described as having a stone-like or metallic surface, which is not common for underwater formations.

Some people think it could be a shipwreck underwater. Others have more unusual ideas, like a sunken UFO or a natural rock formation.

6. The Mariana Trench

Mariana Trench Challenger Deep

The Mariana Trench is the deepest part of our oceans. The southern end is the “Challenger Deep”. It reaches a depth of about 36,070 feet (10,994 meters).

The trench is very deep and mysterious. It is one of the least explored and understood places on Earth because it is hard to reach. 

Despite the extreme pressure and darkness of the trench, it hosts a variety of unique and poorly understood life forms.

These creatures can survive in extreme conditions. The more we learn about the Mariana Trench, the more it can teach us about life’s limits on Earth and our geologic history and timeline.

7. Earth’s Hum

Earth Background Noise

The “Earth’s hum” refers to a persistent and faint vibration or oscillation of the Earth itself. It’s only been recently that scientists have gained a better understanding.

Earth’s hum is a very low-frequency vibration that’s ringing all the time. They’re typically between 2 and 7 millihertz (mHz), making it below the threshold of human hearing.

We still don’t completely understand the exact source of the Earth’s hum. But scientists believe they are driven by ocean waves interacting with the seafloor and the movement of ocean currents

These processes can generate subtle seismic waves that propagate through the Earth, creating the hum. While the Earth’s hum is generally imperceptible to human senses, it still remains a bit of a mystery.

8. The Bermuda Triangle

Bermuda Triangle Map

The Bermuda Triangle is located in the ocean between Florida, Puerto Rico, and Bermuda. It’s where some airplanes and ships have gone missing.

People have come up with all sorts of stories about it, like aliens and sea monsters. But scientists say there’s nothing really magical happening.

The weather can be stormy there, and sometimes human errors or technical problems can make ships and planes disappear.

The Bermuda Triangle has had some incidents explained, but it still fascinates people because of its history of disappearing aircraft and ships.

9. Cold Water Mirage

Cold Water Mirage

A “cold water mirage” is a visual phenomenon that can occur when the air is significantly colder air below warmer air.

In a cold water mirage, the cold air near the water’s surface can cause the light to bend. This makes distant objects, such as ships or landmasses, appear distorted or displaced.

This effect can create the illusion of objects hovering above the water’s surface. They can even appear upside down, or even as a “mirage” image above their actual location.

10. The Origin of Water

Volcano Degassing

It’s just a mystery why we have oceans. What is the origin of water? There are really two main theories that can explain it

First, did comets transport water in the early stages of Earth’s formation? This theory suggests that the water on our planet may have been partly delivered by these icy celestial bodies.

The other popular theory is that water has been within the Earth all along. It was through volcanic activity, which releases water vapor from the Earth’s interior. Eventually, this became our oceans.


These ocean mysteries have captured the imagination of people for years. Each one has inspired researchers to venture into the deep in search of their secrets.

Have we missed any of the important ocean mysteries?  We’d love to hear from you in the comment section below.