Currents are being altered by wilder winds. The sea is releasing carbon dioxide. The sea floor is melting.
By HENRY FOUNTAIN
And JEREMY WHIITE
The enormity and inexplicableThe Southern Ocean is known for its devilish swells and howling gales, which have been a test for mariners for centuries. Its true strength lies beneath the waves.
The ocean’s dominant feature, extending up to two miles deep and as much as 1,200 miles wide, is the Antarctic Circumpolar Current, by far the largest current in the world. It is the world’s climate engine, and it has kept the world from warming even more by drawing deep water from the Atlantic, Pacific and Indian oceans, much of which has been submerged for hundreds of years, and pulling it to the surface. It exchanges heat with the atmosphere and then returns to its eternal round trip.
This is what scientists call upwelling. Without it, the world would be even more hotter than it is today due to human-caused greenhouse gasses like carbon dioxide.
“From no perspective is there any place more important than the Southern Ocean,” said Joellen L. Russell, an oceanographer at the University of Arizona. “There’s nothing like it on Planet Earth.”
This ocean was unexplored for centuries. Its extreme conditions made it impossible for sailors to explore its iceberg-infested waters. Measurements taken by explorers and naval ships, as well as occasional research expeditions and whaling vessels, provided fragmentary scientific knowledge.
But more recently, a new generation of floating, autonomous probes that can collect temperature, density and other data for years — diving deep underwater, and even exploring beneath the Antarctic sea ice, before rising to the surface to phone home — has enabled scientists to learn much more.
They discovered that the Antarctic current is being affected by global warming in complex ways. This could impact the ability to combat climate change in future.
Dr. Russell and others believe that the unceasing winds driving the upwelling are becoming stronger as the world heats. This could lead to more carbon dioxide being released into the atmosphere by bringing to surface more of the deepwater that has kept this carbon for centuries.
The Southern Ocean is also warming, which has a significant climate effect. Some of this upwelling water, which is already relatively warm, flows beneath ice shelves on the Antarctic coast that help keep the continent’s vast, thick ice sheets from reaching the sea more quickly.
In effect, “Antarctica is melting from the bottom,” said Henri Drake, an oceanographer at the Massachusetts Institute of Technology.
Scientists say this is already contributing towards sea level rising. It could also contribute to the rise of sea levels, possibly threatening coastlines over the next century.
Although the potential impact of all these factors is still unknown, oceanographers as well as climate scientists believe it is becoming more urgent to understand the interplay of powerful forces and how human activities are changing them. “There’s lots of questions left,” said Lynne Talley, an oceanographer at Scripps Institution of Oceanography in La Jolla, Calif.
Much of humanity’s limitedThe scientific understanding of Southern Ocean was long tied to an industry that saw profit in it: whaling.
As overhunting of whales in the Atlantic and Pacific oceans decreased, whaling ships began moving southward to the Antarctic in the latter part of the 19th century. Many ships set sail for the dangerous southern waters, often sailing for up to a year.
Overhunting became a problem in Southern Ocean too. In order to maintain their population, the British government decided that more information needed to be gained about the environment of the whales and their behavior.
George Deacon was a young Londoner who had studied chemistry and wanted to explore the sea. He was offered the job of sampling the waters in the Southern Ocean as part a mission to save the whaling industry.
Deacon would have a long career in oceanography. He would later help to develop secret submarine detection devices during World War II, lead the National Institute of Oceanography, and eventually be knighted.
He was 21 years old when he set sail for Antarctica on Christmas Eve 1927 aboard the William Scoresby, a small research vessel. Deacon’s work there, even though some of his conclusions were later viewed as incorrect, would shape scientific understanding of the Southern Ocean for years to come.
He spent the best part of the next ten years aboard ships, analysing water samples at different depths. It was dangerous work. Storms would cause the cables and pulleys that lower equipment into the water to become so thickly clogged with ice, that torches were necessary to remove them. Sample bottles, once pulled out of the water, would often freeze before they could reach below decks. This would spoil his tests.
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Deacon overcame all obstacles and eventually sampled enough ocean to get a good understanding of its mechanics. He combined his ideas with those of others in a 1937 book, “The Hydrology of the Southern Ocean,” that became the standard textbook describing the waters around Antarctica.
Deacon and his companions were not the only ones to have experienced the hardships of South Ocean. It was discovered by archeological evidence that it was explored in the 12th or13th century by Indigenous Polynesians. This is about 500 years before Europeans made their first voyage there.
Visitors were rare then — and still are today. Even a modern ship can be difficult to navigate the Southern Ocean.
That’s a result of geography. Cape Horn, the southern tip in South America, is the closest landmass to Antarctica. It is located approximately 500 miles across the Drake Passage. As a result, the ocean’s westerly winds have nothing to impede them, so they sweep completely around the world, building up ferocious strength and creating huge swells.
Researchers still look for data because very few ships have ever ventured there.
It can be found in unexpected places.
Just a few years ago Praveen Teleti, while working on his doctorate on the historical variability of Antarctic sea ice at the University of Cambridge, realized that the logbooks of a British whaling company’s ships contained invaluable climate measurements — air and water temperatures, barometric pressure, wind strength — from the 1930s and 1950s.
Dr. Teleti explained that the logbooks included occasional personal comments, which were often shockingly understated. For example, numbers indicating hurricane-force winds would include a benign comment about gales. “They wrote it as if it’s nothing much,” he said.
Although it is not a complete survey, the 9,000 data points Dr. Teleti discovered are among the few that document the Southern Ocean before any research was done there. They can help scientists better understand the region’s changes as a result of global warming.
However, research efforts increased in the 1950s. More sophisticated and systematic expeditions became commonplace. Instruments that could measure from the bottom to the top were created. In the late 1970s, data was also being collected by polar-orbiting satellites.
The real revolution lies in the people. In the middle of the 2000s, Southern Ocean science was initiated with the use drifting floats. These floats can adjust their buoyancy to mimic fish and allow them to move up or down in the water while taking readings. They only surface occasionally to beam their data to satellites before sinking again below the waves. Some even go below the sea ice.
The floats, part of a worldwide project called Argo, have helped transform oceanographers’ understanding of the Southern Ocean.
Greta Shum/Southern Ocean Carbon and Climate Observatory and Modeling Project
They now know, for instance, that Deacon’s description of the ocean in his 1937 book was incorrect in some ways. Deacon described the water movement as a loop that moved northward through the current. He then called it a Deacon cell.
Oceanographers now know more about the intricate cycle of oceanic currents around the world, of which Antarctic upwelling is just a part. The waters around Antarctica are on an epic journey from the Atlantic and Pacific oceans. They flow southward and slowly cycle upward as if they were climbing an ocean-sized circular staircase.
“This is deep ocean water that hasn’t seen the atmosphere for centuries,” said Veronica Tamsitt, who, as a doctoral student, worked with Dr. Talley, Dr. Drake and others to build computer modelsAll the new data revealed.
Scientists now have a better understanding of how interconnected the Southern Ocean is to the rest, despite it being so far from the rest. The circular flow around Antarctica is in effect a climate engine spinning on continental scale.
Researchers are becoming increasingly concerned about the potential changes in the ocean and current as the Earth warms.
Dr. Russell, an Arizona oceanographer, has dedicated her entire life to this cause. She was raised in the Arctic on the coast of Kotzebue, Alaska’s Chukchi Sea. As a child, she said, “I wanted to know where the sea ice went,” when it retreated from shore every summer.
“You never quite give up what you fall in love with when you’re young,” she said.
As a graduate student she was able to go on many Southern Ocean expeditions. She described the unique terror of working on a 300-foot vessel being tossed around by huge swells. “You’re chugging up the side of the wave and then schuss down the other side until you stick the prow into the next wave and a mountain of water proceeds to just fall on you,” she said.
She was measuring the dissolved oxygen in water during her first voyage and kept getting readings suggesting a startling rate for upwelling. “It was coming from so deep, so fast,” she said. “That’s when my Southern Ocean obsession really started.”
Like other oceanographers, she has been focusing her attention on the carbon dioxide, which is dissolved in large quantities in the deep seas around Antarctica.
One of the most important The exchange of carbon dioxide between the atmosphere and the ocean is one of the processes that takes place in the Southern Ocean. This has important implications for combating climate change.
Global warming is mainly due to carbon dioxide that is released into the atmosphere from the burning of fossil fuels. These emissions are absorbed by the oceans, and heat is absorbed from the atmosphere. They act as a buffer against climate change and keep the world from becoming a livable hothouse.
According to some estimates, the oceans have taken up 25 percent of excess carbon dioxide and more than 90% of excess heat that has resulted in the burning of fossil fuels since the 19th Century. But the deep ocean water that upwells around Antarctica contains even more carbon dioxide — not from current emissions, but dissolved over centuries from organic matter including decaying marine organisms, tiny and immense, that sink when they die.
“It’s been accumulating the rot of ages,” Dr. Russell said.
When this ancient water reaches the surface, some of that carbon dioxide is released, or “outgassed,” as the scientists say.
Since long, scientists have believed that the Southern Ocean absorbs a greater amount of carbon dioxide than it emits. This has a positive impact on climate. This critical balance could shift if more water rises. It would be more difficult to combat climate change. To keep the temperature under control, nations would have to reduce their carbon dioxide emissions even further.
The incessant Southern Ocean winds that push the surface water northward and draw up deep water behind them are what drive upwelling. Warming affects the winds and they have strengthened in recent decades.
A Recent studyThe Southern Ocean may still be absorbing greater amounts of carbon dioxide than it releases. Many researchers believe that the ocean may be outgassing more carbon dioxide now than previously thought. The winds could increase as the world warms, and the upwelling or outgassing could continue to increase.
Scientists point out that more upwelling might actually have one benefit in the effort to fight climate change: It could allow more of the atmosphere’s excess heat to be absorbed. However, they remain concerned.
“We’re excited about it, because it would take up more heat,” Dr. Russell said. “But we’re worried about it because of all that deep-ocean carbon.”
Carbon, however, isn’t the only concern. The water that’s welling up in the Southern Ocean is also relatively warm, and warming more, which spells trouble for the planet in the form of sea level rise.
Some of that warm water reaches Antarctica’s continental shelf, where it flows beneath ice shelves, the tongues of ice at the ends of glaciers. These glaciers act as a support, helping to keep the huge ice sheets that cover Antarctica and are slowly moving toward ocean.
Scientists discovered decades ago that this upwelling of water is melting the ice shelves below. The glaciers lose some ability to keep the ice sheet in check as the ice gets thinner.
Most of this melting is occurring on Antarctica’s western side, where the circumpolar current comes closest to the coast. There, the ice shelves of two large glaciers, Thwaites and Pine Island, hold much of the region’s ice sheet back.
Their melting and thinning has only made a small contribution to rising sea levels. The concern is that the ice shelves could quickly melt, accelerating the movement to the ocean of the glaciers and eventually the entire West Antarctic ice sheet. New researchThis suggests that a collapse of a part of Thwaites’ ice shelf and the resulting acceleration of the flow could occur within the next ten years.
If the West Antarctic Ice Sheet were to melt into the ocean, sea levels could soar by as much as 12 feet in a few centuries.
Already, the rate at which these glaciers melt is increasing. The winds play a crucial role.
According to David Holland, a New York University climate scientist and mathematician, the winds that matter in the case of melting ice-shelf ice are those closest to the continent. The effect is the same. Studies suggest that in the past, these close-in winds kept colder water at surface, preventing warmer water from rising high enough for it to reach the continental shelf, and the ice shelves.
These winds have changed, according to Dr. Holland, who was a pioneer in pioneering research. Through the Thwaites ice shelfBelow is how to measure the water temperature. “Right now the wind is pushing the cold water away, and so the warm water is coming to fill the void,” he said. “And it’s looking like there will be more of that, based on computer models.”
In less than a century, the state of the art has progressed from Deacon’s solitary whaling research ship, to fleets of autonomous oceangoing probes circling the world, to sophisticated computer models.
Today, scientists are poised to get even more data. Argo will soon deploy a new generation, more sophisticated floats worldwide that can measure much more than temperature and salinity.
Of particular interest to Dr. Russell and others are acidity readings, because they can be used to determine the water’s carbon dioxide content. That could help further illuminate the profound importance of deep, ancient, carbon-laden water to the world’s future.
Despite all that has been learned, Dr. Russell said, “Unlike any other field of exploration, we are at the absolute frontier here.”