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How many oceans are there on Earth? National Geographic now says five

McMurdo Sound in Antarctica.
McMurdo Sound in Antarctica.CHRIS LARSEN

For the first time in the more than 100 years that National Geographic Society has mapped the world’s oceans, it will now recognize five oceans. The organization announced this week that it will recognize the Southern Ocean, a body of water that encircles Antarctica, as the world’s fifth.

"Scientists have long known there's a distinct ecological region around Antarctica," National Geographic Society geographer Alex Tait said in an interview. But at least in the international scientific community, there hasn't always been complete agreement on the name and boundary of this body of water.

National Oceanic and Atmospheric Administration (NOAA) officials said the federal agency recognized the body as the fifth ocean in 1999, when the U.S. Board on Geographic Names approved the name "Southern Ocean."

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When the boundaries of the ocean were proposed in 2000 to the International Hydrographic Organization (IHO), which tracks and charts the world's seas and oceans, not all IHO member countries were in agreement, according to NOAA.

The IHO is one of National Geographic's main references, among other sources, for consulting on place names.

Tait said that while National Geographic has labeled the ocean on its maps before, it came with a disclaimer about the lack of broad agreement.

"But we thought it was important at this point to officially recognize it," he said. "People look to us for geographic fact: How many continents, how many countries, how many oceans? Up until now, we've said four oceans."

Now, Tait said, when National Geographic lists oceans, it will mention five: Arctic, Atlantic, Indian, Pacific, and Southern.

That's key for educational purposes, too, he said. National Geographic has a geography education program and provides online materials to schools and the general public.

"We think it's really important from an educational standpoint, as well as from a map-labeling standpoint, to bring attention to the Southern Ocean as a fifth ocean," Tait said. "So when students learn about parts of the ocean world, they learn it's an interconnected ocean and they learn there's these regions called oceans that are really important and there's a distinct one in the icy waters around Antarctica."

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How the Southern Ocean becomes part of common knowledge and learning can be a somewhat organic process, Tait said, "boosted by reference organizations like National Geographic."

The water body extends from Antarctica's coast to 60 degrees south latitude, according to NOAA. National Geographic said it will also use 60 south latitude as its northern limit, excluding the Drake Passage and the Scotia Sea.

Enric Sala, National Geographic's "explorer in residence," described the Southern Ocean in an email to The Washington Post as a distinct water body characterized by the powerful Circumpolar Current that flows eastward, "perpetually chasing itself around Antarctica."

He referred to the body as an "oceanic ring at the end of the world that connects the Pacific, Atlantic and Indian oceans."

Frank Nitsche, a marine geologist and geophysicist at Columbia University's Lamont-Doherty Earth Observatory, said as a research scientist who works around Antarctica, "we do use the term Southern Ocean."

"But I was always a little unclear how official it is," Nitsche said.

He said National Geographic's announcement was significant because it's a "mapping standard for a lot of other atlases and maps out there."

"Maybe in the science community it was used, even without a strong definition, like a boundary" Nitsche said. "But I think in the general public, there's maybe not a common understanding."

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Tait and Sala said the recognition could raise awareness about the water body's role in the changing climate.

The Southern Ocean, Sala wrote, "contains areas that are warming the fastest on Earth, such as the Antarctic Peninsula." The sea ice on the Southern Ocean plays a role in determining ocean circulation and weather patterns, Sala said, and further warming of the ocean could "disrupt the global climate."

“This is a great opportunity to raise the profile of this vital region and raise awareness about the threats affecting it, and the solutions.”