A large system of rotating currents in the North Atlantic is likely behaving very strangely because it is approaching a tipping point, a new analysis of Clamshell shows.
The North Atlantic subpolar Gaia plays an important role in transporting heat to the Northern Hemisphere and is part of a much larger network of ocean currents called the Atlantic Meridian Surrounding Circulation (AMOC). However, new evidence suggests that the suburban thyroid has lost its stability since the 1950s. This means that Gyre’s circulation could be significantly weakened in the coming decades, researchers report in a study published today (October 3) in Journal Science Advances.
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The North Atlantic subpolar gaia are the limbs of the AMOC, but can cross a tipping point independently of a huge network of currents. In particular, the results of European climate are similar to those caused by the collapse of AMOC, but may not be as intense as AMOC is much larger. But she warned, “even if the outcome is not as devastating as the AMOC collapse, weakening of Gaia below the extreme could have a major climate impact.”
Previous studies suggest that AMOC may collapse in the near future. Because its main engine (a dense water cascade from the North Atlantic and Arctic Ocean to the seabed) is failing. Previously made from extremely cold and salty water, this cascade is diluted by meltwater and warmed by rising earth temperatures. (Cold and salty water is warmer and more denser than less water.)
A similar fate is expected for the North Atlantic subpolar thyroid. This also depends on surface waters that subside at the seabed. According to Arelano Nava, the dense water cascade at Gaia’s core keeps rotating currents moving. However, she said that the system is partially driven by the wind, so a complete collapse is unlikely.
As the North Atlantic subpolar thyroid is a branch of AMOC, the collapse of AMOC necessarily involves a dramatic weakening of the thyroid. Conversely, weakening of the extremely inferior thyroid does not automatically mean that AMOC has collapsed, Arerano Nava said.
“Gaia at the very bottom can suddenly become weak without the AMOC collapse,” she explained. “That was what happened during the transition to the small ice ages that took place in the 13th and 14th centuries.”
The small ice age that lasted from the late 1800s to the late 1800s was one of the coldest recorded periods in the Northern Hemisphere since the end of the last ice age. According to New Yorkers, the average temperature is around 3.6 degrees Fahrenheit (2 degrees Celsius), freezing rivers and North American solids in Europe and North America, causing an agricultural crisis and roughly casting medieval society. Factors such as volcanic eruptions and reduced solar activity contributed to the onset of small glacial ages, but the North Atlantic subpolar thyroid gland is believed to have played a major role in strengthening it.
With climate change now dramatically different from the 13th century, scientists don’t know if another small ice age is possible, Arerano Nava said. Nevertheless, it shows some of the climate impacts that our way of doing things may come.
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Clam’s guide
For new research, Arerano Nava and her colleagues analyzed existing datasets derived from the shells of two Aram species living in the North Atlantic: Arctic Island and Glyceymelis glycimelis. Clams record information about the ocean as their shells grow. It can absorb a variety of forms of elements, such as oxygen, for example, and provide researchers with clues about marine processes over time.
“With Crum’s records, each layer has that lovely date,” Areranonava said. “They’re like a sea ring.”
Researchers have compiled 25 datasets to construct high-resolution images of the North Atlantic subpolar thyroid gland over the past 150 years. They found two powerful signals of instability. The latest one is ongoing, suggesting that Gaia, below the extreme, is approaching a tipping point, as a result of global warming that supports previous observations and research, Arerano Nava said.
But the other signals were a complete surprise, she said. CLAM data revealed that Gaia, at the very bottom, had been unstable for several years, leading to changes in the North Atlantic regime in the 1920s. This previously described event was characterized by the enhancement of the gyre flow. The instability of Subpolar Gaia likely caused a shift in government in the 1920s, and the timeline suggests that periods of instability may reflect the recovery of Subpolar Gaia from its small ice age collapse, Arelanonava said.
“At some point it had to be restricted, but that’s not something we have full evidence because we didn’t jump into those mechanisms,” she said.
Whether or not the instability of the early 20th century is indeed a signal that the thyroid below the extreme is returning to full strength, the overlap between the signal in clam data and the North Atlantic regime shift in the 1920s indicates that the results are robust.
“If a rapid change occurs following a loss of stability, I am sure these are early warning signals for sudden changes,” she said.
However, another expert was not very convinced. “The dataset is very useful as it is very well outdated and allows insight into climate change over the years,” David Thornalley, professor of marine and climate science at London University of London, who was not involved in the research, told Live Science in an email.
However, in this analysis, the absence of direct linking the patterns observed in clam data to ocean physical features also does not strongly support changes in the mode of operation of subpolar gaias, said Sonaly. “I’m skeptical of interpretation,” he said.
Regarding the continued destabilization of the North Atlantic subpolar thyroid, Arelano Nava said she and her team were trying to map potential climate trajectories that this could be unleashed.
“I don’t know exactly what the turning point is,” she said. “It could be AMOC, but we may be watching the Gaia below the extreme first weaken, which is definitely a concern.”
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