Scientists Blame Tectonic Plates for Pacific Ocean's Shrinking

The world's biggest ocean is also its most doomed one. Now, scientists are worried and they are blaming the tectonic plates for it all. The Pacific Ocean, which is the largest single feature on the surface of the Earth is slowly getting smaller and the irony of it all is as surprising as shocking.

Diving into the Pacific

According to NOAA Ocean Exploration, the Pacific covers more than 155 million square kilometres, roughly 60 million square miles. The total land area of every continent and island on the planet only comes to about 149 million square kilometres. Thus, the Pacific, on its own, is larger than all of that with more room left over. It covers about a third of the Earth's surface and holds roughly half of all the water in the world's oceans. The Atlantic, which most picture as this vast water body, only contains half as much water as the Pacific does. About 200 to 250 million years ago, when the supercontinent Pangaea broke apart, leading to a break in the ancient super ocean Panthalassa, the Pacific Ocean was formed. As tectonic plates moved the land apart, the Atlantic Ocean opened up and the giant Panthalassa shrank into what we now call the Pacific Ocean.

Why the Pacific Ocean is shrinking

The reason comes back down to plate tectonics and specifically to the difference between how the ocean floor is made and destroyed. New sea floor is created where plates pull apart at mid-ocean ridges, with molten rock rising to fill the gap. Old sea floor is destroyed at subduction zones, where one plate dives beneath another and sinks back into the mantle. An ocean grows or shrinks depending on which process wins around its edges. The Pacific is almost ringed by subduction zones. This is the Ring of Fire, the belt of trenches, earthquakes and volcanoes that traces the ocean’s rim from New Zealand up through Japan and around to the Andes. The Pacific does have a spreading ridge of its own, the East Pacific Rise, but so much of its floor is being consumed at those surrounding trenches that the basin is narrowing overall. Those trenches are also where the ocean reaches its extremes. The Mariana Trench in the western Pacific is the deepest place on Earth, bottoming out at close to 11,000 meters, about 36,000 feet which is more than the height of Mount Everest turned upside down. It is a subduction zone, one of the seams where Pacific crust is bending down and sliding back into the planet. The deepest point in any ocean sits over the exact process that is slowly closing this one. The Pacific is losing ground at broadly comparable speeds, which is to say very slowly, and only measurably over millions of years.

What will happen to the Pacific Ocean?

In the long run, the Pacific Ocean could close up entirely. In 2022, a team led by Chuan Huang at Curtin University in Australia ran supercomputer simulations of where the continents are heading. Their result, published in the journal National Science Review and summarised by the university, was that the Pacific will most likely close in 200 to 300 million years, drawing the continents together into a new supercontinent they call Amasia, as the Americas eventually meet Asia. Australia is already drifting toward Asia at about 7 centimetres a year. Other simulations of the deep future close the Atlantic instead and keep the Pacific open, producing different supercontinents with different names. However, two points need to be remembered. The water inside the ocean is not disappearing. What changes is the shape and area of the basin that holds it, as the plates beneath rearrange themselves. It has nothing to do with climate change or anything else. And secondly, this event is going to take time. For now, the Pacific is as permanent as the ground you are standing on.