Scientists studying clam and cockle shells have found signs that the currents in the Atlantic Ocean may be approaching a “tipping point”, which could have significant consequences for climate patterns.
The researchers studied the layers of quahog clam and dog cockle shells to find out about past oceanic conditions and understand how patterns in two ocean current systems – the Atlantic Meridional Overturning Circulation (AMOC) and the subpolar gyre (SPG) – are changing.
Their findings – which found evidence that the Atlantic Ocean is approaching a tipping point – are published in the journal Science Advances.
“Anticipating a tipping point requires good data, covering a long period with no gaps,” says Dr Beatriz Arellano Nava from the University of Exeter, who led the study. “We don’t have ocean observations going back into the distant past, but the bands in clam shells give us an unbroken annual record covering hundreds of years.”
Quahog clams are known for their incredible longevity. The oldest known non-colonial animal in the world was a quahog called Ming, which was dredged by researchers from Icelandic waters in 2006. By analysing the growth rings in its shell – in the same way you might count the rings of a tree – the researchers found that this ancient bivalve was 507 years old.
In this study, scientists looked at annual differences in shell growth to get an idea of how the conditions in the marine environment changed each year. In particular, they were looking for periods when the system became destabilised.
“When a system is stable, there will still be variations – but we would typically see a rapid return to the normal state after a change,” says Professor Paul Halloran, from Exeter’s Global Systems Institute. “When a system destabilises, it doesn’t recover as quickly – and this could be a sign of an approaching tipping point.”
Reaching a tipping point would have ripple effects around the world, according to the scientists. If the AMOC collapsed, we could see more severe winters in north-west Europe and a weakening of the subpolar gyre might lead to more frequent extreme weather around the North Atlantic.
The shell records suggested that there have been two 'destabilisation episodes' in the past 150 years. The first instance took place in the early 20th century and may be why the Arctic and North Atlantic became warmer in the 1920s.
The next destabilisation event started around 1950 and is still happening today. This one is stronger than the first. “Although we cannot yet say which part of the system is losing stability, or what may be causing it, our results provide independent evidence that the North Atlantic has lost stability – suggesting that a tipping point could be approaching,” says Arellano Nava.
Although the experts don’t know whether this is being caused by the AMOC or the SPG, the suggestion that the region is coming towards a tipping point is concerning. “Any tipping point would have major implications for the climate,” he adds – but there is hope. “Rapidly reducing greenhouse gas emissions is the best way to prevent tipping points in the Atlantic Ocean.”
Top image: Quahog clam shells. Credit: Paul Butler
More wildlife stories from around the world
- “You’ve got to kill them faster than they can reproduce”: New Zealand's plan to eradicate invasive animals
- Scientists resurrect 40,000-year-old organisms from Arctic ice – now they’re worried
- Cataclysmic volcanic eruption in Hawai'i triggers astonishing explosion of life 1,200 miles away
- Researchers sink lights to bottom of Chicago River. What they find is incredible
