Do the Pacific Ocean and Atlantic meet?
Images show what appears to be a dividing line between the Atlantic and Pacific oceans, with the waters on either side being different colors, but is this some kind of barrier, or are the two oceans mixing?
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The meeting of the two oceans as seen from a boat.
Lines like this often appear where rivers or glaciers meet the ocean. But these popular videos also claim that the line shows the dividing line between the Pacific Ocean and Atlantic oceans, and then use it as “evidence” to claim that the two oceans don’t mix.
But is this true? Or are the Pacific and Atlantic oceans mixing? “The short answer is yes. The waters are constantly mixing,” said Nadine Ramirez, an oceanographer at the University of Concepción in Chile. The Pacific Ocean and Atlantic mix at different rates in different places, and climate change may actually be changing those rates.
Imagine watching a circle of cream dissolving in coffee: The liquids mix, but slowly. That’s roughly what’s happening in the image showing the dividing line between different oceans. On one side, the water might be saltier, cleaner, or colder; it takes time to average out those differences.
To speed things up, imagine stirring your coffee vigorously. The cream melts faster. That’s what happens when there are storms and big waves at sea.
The Pacific Ocean and Atlantic mix faster in some places than in others. The two oceans meet near the southern tip of South America, where the continent breaks up into a cluster of small islands. The water flows relatively slowly between these islands, and the Strait of Magellan is one of the popular routes through it. In the Beagle Channel, melting glacier water has created a dividing line between fresh and salt water that looks a bit like the lines in YouTube videos.
The Strait of Magellan is another popular route. Where the strait flows into the Atlantic, there’s a line that’s not easy to see with the naked eye, but oceanographers can detect through measurements, Ramirez told Live Science. “You can see a tongue of blue water in the Atlantic,” he said on a chart.
The water coming in from the Pacific Ocean is different because the Pacific has more rain, so the water is less salty. But “it stays separate for a while,” Ramirez said, and then storms and waves blur the line.
In the open ocean between South America and Antarctica, the Pacific and Atlantic border is notorious for turbulence; the Drake Passage is known for waves as high as 60 feet (18 meters). “That improves the mix,” Ramirez said.
Water also mixes deeper into the ocean. Daily tides send water surging back and forth over the rugged seafloor, said Casimir Delavigne, a researcher at Sorbonne University and France’s National Center for Scientific Research (CNRS). “That creates a lot of confusion,” he told Live Science.
But water from different sources can also move through the ocean with little mixing. The ocean is “like a cake with different layers, but they’re all water,” Ramirez explained. These layers, whose properties vary depending on the source of the water, are called undulating layers.
In the intervening layers, far from the surface and the seafloor, water mixes more slowly because there’s less turbulence.
Oceanographers distinguish between mixing and exchanging water. Mixing means “an irreversible transformation of the water,” Delavigne said. When light cream turns into dark coffee and the entire drink is the same color, it’s well mixed.
On the other hand, “you can exchange chunks of water without actually mixing their properties,” he said. The Pacific Ocean and Atlantic Oceans are constantly exchanging water, thanks to global ocean currents.
A powerful current around Antarctica’s Southern Ocean carries water from the Pacific clockwise through the Drake Passage into the Atlantic. It also draws water from ocean basins around the world, “and then pumps it back in,” Delavigne said. Another current carries water from the Pacific across the Indian Ocean, around the tip of South Africa, and into the Atlantic in the other direction.
The edges of these streams always mix water. But because the different layers of water don’t completely mix, oceanographers can track different “packets” of water moving around the globe. Climate change caused by human activity is slowing these currents, Delavigne added.
“It seems to be happening already, especially around Antarctica,” he adds. Cold, salty water sinks, speeding up and forming northward currents. But the poles are warming. The warmer, fresher water from the melting ice sheets won’t sink as much, so the water exchange will slow down.
“The mixing of water also seems to be slowing down,” adds Delavigne. That’s because when the ocean slopes differ more from one another, they take longer to reach an average. As the ice sheets melt, “the density difference between surface water and deep water is growing,” he adds.
These changes are expected to alter how oxygen and nutrients circulate in the ocean, negatively impacting marine life. But the oceans will never completely stop mixing or exchanging water. “As long as there are winds and tides, there will be mixing, there will be currents,” Delavigne says.
