It carries over 100 times more water than all the world's rivers combined. Its length reaches from the ocean surface to the ocean floor, and its diameter is 2,000 kilometers. It connects the Indian, Atlantic, and Pacific Oceans and plays an important role in regulating the Earth's climate. It continues to swirl around the southernmost continent, Antarctic circumpolar current is by far the most powerful and important water mover in the world. Its rate has accelerated in recent decades, but scientists are wondering whether it has anything to do with human-induced global warming and whether amplifying ocean currents offset some of the warming effects. I'm not sure if I will.
In a new study, an international team of researchers charted the relationship between the ACC and climate over the past 5.3 million years using sediment cores from some of the roughest and most remote oceans on Earth. Their key finding was that during past natural climate fluctuations, ocean currents moved in conjunction with global temperature, slowing down in colder months and speeding up in warmer months; rise caused significant loss of Antarctic ice. This suggests that today's acceleration will continue as anthropogenic warming increases. It could accelerate the depletion of Antarctic ice, raise sea levels and affect the ocean's ability to absorb carbon from the atmosphere.
The results of the survey have just been published in diary Nature.
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„This is the most powerful and fastest current on Earth. It is probably the most important current in the Earth's climate system,“ said the study's co-authors. Gisela Winklergeochemist at Columbia University Lamont-Doherty Earth Observatory Co-led a sediment sampling expedition. The study suggests that „the retreat or collapse of Antarctic ice is mechanistically linked to the strengthening of the ACC current, which is the scenario we are observing today under global warming. Yes,” she said.
Conditions for the ACC were set about 34 million years ago, after tectonic movements separated Antarctica from other continental masses further north and ice sheets began to accumulate.Currently It seems that it has started to flow It took its current form between 12 and 14 million years ago. Driven by persistent westerly winds and with unobstructed landmass, each of the 165 to 182 million It carries 10,000 cubic meters of water. Number 2.
Scientists believe that winds in the Southern Ocean Strength has increased by about 40% over the past 40 years. Among other things, this accelerates the ACC, activating massive eddies within it, moving relatively warm ocean water from high latitudes toward Antarctica's giant floating ice shelves, and blocking even more extensive inland glaciers. In parts of Antarctica, especially in the west, these warm waters are eroding the underside of ice shelves. This is the main reason why we are depleting ice rather than increasing temperatures.
„If you leave an ice cube in the air, it takes a long time to melt,“ Winkler said. „If you put it in hot water, it will progress rapidly.“
„This ice loss could be due to increased heat transport to the south,“ said the study's lead author. Frank Lamy, of the Alfred Wegener Institute, Germany. „A strengthened ACC means warmer, deeper water will reach the edges of Antarctic ice shelves.“
Through a series of complex processes, the seawater that currently surrounds Antarctica Absorbs about 40% of carbon What humans bring into the atmosphere. It's unclear whether faster ACC will compromise this, but some scientists fear it will.
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About 40 scientists from 12 countries participated in the study. At sea, the researchers collected seafloor sediments beneath the nearby ACC aboard the drilling vessel Joydess Resolution. point nemoIt is the furthest point from land anywhere in the southwestern Pacific Ocean, approximately 2,600 kilometers from the tiny Pitcairn Islands.of 2 month cruise The incident took place during the harsh southern winter period from May to July 2019, when there was little daylight and waves as high as 20 meters threatened the ship.
The ship's crew dropped the drill string approximately 3,600 meters from the surface to the ocean floor. Next, they penetrated the floor and removed 150 and 200 meters of sediment cores, respectively. Scientists then used advanced X-ray techniques to analyze the layers that had accumulated over millions of years. Because small particles tend to settle when the flow is slow and large particles tend to settle when the flow is fast, they were able to graph the change in ACC velocity over time. Compared to the average flow over the past 12,000 years (the period since the last Ice Age, which includes the development of human civilization), flow has been reduced by as much as half in colder periods and almost doubled in warmer periods.
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use Previous research on the West Antarctic Ice SheetThey correlated periods of fast flow with repeated bouts of ice retreat. These were interrupted by cold periods when glaciers advanced. The warmest period in 5.3 million years of record was the Pliocene, which ended about 2.4 million years ago. Then came the era called the Pleistocene. Dozens of cold ice ages alternated with so-called interglacial periods, during which temperatures rose, ocean currents sped up, and ice retreated. Currently, most of the West Antarctic ice sheet is frozen onto land below sea level, making it highly susceptible to warm ocean water intrusion. If completely melted, global sea levels would rise by about 190 feet.
„These findings provide geological evidence supporting further increases in ACC flow with continued global warming,“ the researchers wrote in their paper. „If this is true, future increases in ACC flows with climate warming will indicate a continuation of the pattern observed in the instrumental record, likely with negative consequences.“