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Seven Deadly Seas:Past Present and Future

Updated on June 14, 2020
Dean Traylor profile image

Dean Traylor is a freelance writer and teacher who writes about various subjects including education and creative writing.


Mythologies from around the world are filled with tales of treacherous waters. And there should be no surprise the world's ocean and seas have played a major part in the ancient people’s beliefs. Sea-faring cultures such as the Vikings, Greeks, Romans, and Phoenicians knew firsthand the dangers of trversing the huge waterways.

Even today, sailors, oceanographers, and other researchers are aware of the ocean’s power. They may not associate gods or sea monsters to them, but they understand how fickle and destructive these waterways can be.

And, when scientists view the entire history of Earth, they discover that deadly seas have always existed; especially those that had real monsters swimming in them.

To identify the seven deadliest seas, one has to look at two sets of “sevens”; in other words, there are seven deadly seas in modern times and seven deadly seas from the prehistoric periods.

The “seas” themselves are not exactly seas, either. In many cases they are an entire ocean, portions of major oceans or giant lakes. Either way, these large bodies of waters have spawned unimaginable horrors.

What Makes a Sea Deadly?

There are many factors that contribute to a deadly sea. Most often, it’s the weather patterns or the storms it produces. Also, it can be the shifting tectonic plates under its surface, which can produce underwater volcanoes, earthquakes, and tsunamis. Other natural factors can be shallow reefs or jagged rocks under the surface, icebergs or giant rogue waves.

Also, there are manmade hazards that contribute to a sea’s deadly status. Modern-day pirates, mine-fields or war zones have created many dangers.

In prehistoric time, on the other hand, it had to do with beasts under the waves during the various eras that stretched over millions of years.

Orthoceras, the largest predator
Orthoceras, the largest predator | Source

The Seven Deadly Seas of Prehistoric Times

Recently, BBC Online’s Science and Nature page posted an article detailing the seven deadliest seas of all time. All seven of them existed millions of years ago when the continents of today were either breaking away from a larger land mass or being created by upheavals and eruptions on the sea floors.

The seas – or in this case, the entire marine systems – were listed. They are as follows:

  • The Ordovician – Between 488 and 443 million years ago, life didn't exist on land. The days were shorter (21 hours) and oxygen level was low (15% then, compared to 20% today). The ocean, on the other hand was teeming with life (BBC, 2012).The main predators were sea scorpions and the squid-like Giant Orthocones. The two were behemoths of their times and would stalk anything. Of the two, the Orthocones was the deadliest.Even the sea scorpions were not safe from them!
  • The Triassic – Continental shifts and the Permian-Triassic Extinction Event helped to form this period. Dinosaurs began their rule over the land and seas. The ones who lived on land were small. Those in the ocean were huge. Cymbospondylus, Nothosaur, and the long-necked Tanystropheus hunted the waters around 250 to 200 million years ago.
  • The Devonian – Sharks made their appearance.Some were unique such as the Stethacanthus, which had a dorsal fin shaped like an anvil. Others were ferocious. But, the alpha predator was the armor-plated Dunkleosteus. It hunted all marine animals, and a few land animals unlucky enough to be in coastal waters.


There were other eras for the deadly seas. Many included the time of the dinosaurs while others contained the first prehistoric mammals. Even the sharks made their presences known. These are the eras:

  • The Eocene – Mammals dominated the ocean as well as the land. Brachiosaurus was ancestor of the modern whales. They were sleek hunters with sharp teeth, and they hunted in the deep or near coastal areas.
  • The Pliocene – Four million years ago, the most treacherous area of the ocean was near its center. There, the Megalodon, the largest shark and distant relative of today’s Great White Shark, stalked the deep waters for whales – in particular the bottom dweller, Odobenocetops.
  • The Jurassic – Ancestors to the modern sharks (Hybodus) and crocodiles (Metriorhynchus) lurked the waters during this era. They weren’t alone. By far, the most fearsome beast was the Liopleurodon – a member of the marine reptile family known as pliosaurs. It was considered the largest predator of all time (BBC, 2012). It was also believed to be an extremely efficient hunter.
  • The Cretaceous – the BBC article rank this era as having the most dangerous sea ever. While there were predators under the sea’s surface, there were others above it. The bird, Hesperornis, often stalked the ocean from above. The Halisaurus hunted below the water’s surface – or above, considering it snatched low-flying Hesperornis from the air.

The top preditors of the deep were the giant massaurs and the long-necked plesiosaur, Eeasmosarus. And if that wasn't dangerous enough, the land of the time offered no quarter with such dinosaurs such as Tyrannosaurus Rex on the prowl.

Seven Modern Deadly Seas

Fast forward to modern times, in which humans sail the "seven seas." This term has often been considered a cliche of sorts. Nearly any large body of water can be considered one of the fabled seas of legend.

Most people assume the “seven seas” is a reference to the North Pacific, North Atlantic, Indian Ocean, Arctic Ocean, Antarctic Ocean, South Pacific, and South Atlantic . However, there are several areas designated as seas throughout the world, including the Bering Sea , Sea of Japan, Caribbean Sea, Red Sea , and others.

The Bering Sea
The Bering Sea

Of these watery regions, seven of them are considered deadly. They are:

  • The Bering Sea - Located in the North Pacific between Alaska and Russia -- and just south of the Arctic Ocean -- the Bering Sea is the roughest and deadliest waterway.. If the gigantic swells don’t sink a ship, the violent storms, icy waters, and the occasional iceberg will.
  • North Atlantic - Like the Bering Sea, this hostile region has spawned some of the deadliest storms on Earth. On top of that, there are icebergs! Many ships have lost the battle against this behemoth, including the Titanic.
  • The Mediterranean Sea – this sea’s deadly status has more to do with human activity. Pollution is poisoning the waters. The United Nations estimates that more than 600 million tons of sewage, nearly 130,000 tons of mineral oil, 60,000 tons of mercury, 3,800 tons of lead and 36, 000 tons of phosphates are dumped in these once tranquil waters. As a result, marine life is depleting. For humans, swimming in these waters can be hazardous to their health.
  • The Aegean Sea - Although the waters seem calm, this sea holds a deadly secret. It is seismically active. The countries bordering this sea have been subjected to active volcano eruptions and strong earthquakes. Many ancient civilizations, such as the Minoans on Crete, were destroyed by what this sea hid.

Originally posted at
Originally posted at
  • Drake Passage – technically a route from the southern end of South America to the continent of Antarctica, this large body of water produces some of the most vicious storms in the Southern Hemisphere. Also, it’s a place in which large ships can easily be inundated by huge swells, rogue waves, and extensive patches of icebergs. If that’s not enough, waters near Deception Island are wrought with jagged rocks, which can tear and strand ships.
  • The waters off the coast of Somalia – The Gulf Aden, The Indian Ocean Coast, and even the mouth of the Red Sea are dangerous for one big reason. In recent years, this region has become a hotbed for modern pirates from the war-ravaged and impoverished nation of Somalia.
  • The Caribbean Sea – Don’t let the warm, turquoise waters fool you. This is a deadly sea. The heydays of piracy may have gone by, but it doesn’t mean all of them are gone. Also, this region contains volcanic islands, shallow and hazardous reefs, and plenty of weather. Hurricanes and tropical storms are normal in this area. The weather can change within minutes. One moment you’re sailing in calm water. The next instance, you’re hit by a squall. Many ships have sunk in this area. Also, it’s not uncommon to find small islands that form and disappear under its surface -- sometimes within days.

And now, for a few honorable mentions…

The Great Lakes

There are several deadly waterways that need to be mentioned. The Persian Gulf is a geopolitical hotspot. Once a nearly impossible ocean to sail on, the Arctic Ocean is opening up, thanks to global warming.On top of having iceberg fields, it may become another geopolitical hotbed as several nations including Russia, Canada, and the United States vie for navigational and oil drilling rights.

Although technically not an ocean – or a sea for that matter – the Great Lakes are weather producers. Due to their size and location, the Great Lakes generate freak storms and massive waves that have sunk numerous large ships (anyone remembers the fate of the Edmund Fitzgerald?)

The waters off the southernmost tip of South America and Africa are notorious for their weather and currents. Many ships and sailors have met their fate in these waters. These regions are where oceans currents converge. In South Africa near the Cape of Good Hope, the Atlantic and Indian Ocean meet. Near Cape Horn in South America, the Pacific and Atlantic clash.

Finally, there’s the ocean themselves. The Pacific, Atlantic, Indian Ocean, Arctic and the area known as the Antarctic Ocean (the southern end of the Atlantic, Pacific, and Indian Ocean) are wrought with various forms of treachery. They’re weather producers, home to various predators, and contain powerful geological forces within or under its surface. Also, human activity -- namely pollution -- is making them more toxic than ever.

What Will the Future Hold?

These oceans and seas will get more violent. Global Warming may raise its level, and help to produce bigger and stronger storms. Also, it is likely that small low-lying islands may vanish under its waves. The world’s waterway may be dangerous now, but they’ll become more deadly if the trends of today continue.

New York Under Water
New York Under Water | Source

This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.

© 2017 Dean Traylor


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    • thumbi7 profile image

      JR Krishna 

      3 years ago from India

      Very interesting read

      Thank you


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