Like tree rings, growth lines on oyster shells contain important information about the environment and how it has changed over the years.
Like lines of memory, these complex passages can be separated and read by scholars centuries after they were first “written”.
In fact, the ancestors of oysters left passages in the mineral calcite over five hundred million years, almost three hundred million years before the advent of the dinosaurs, opening an unprecedented window into the climate of the past.
Now these ancient archives are issuing a severe warning. A new reading of data on three bivalves off the northern shelf of Iceland has revealed a potentially dangerous tipping point in Earth’s climate.
The results show that the change in our global climate about eight centuries ago was the result of a feedback loop that undermined the stability of the North Atlantic climate system, pushing it towards a new, colder-than-usual state.
The “Little Ice Age” first began in the 13th century in the North Atlantic and only ended when anthropogenic heating reversed the natural trend.
Scientists are still not sure what exactly caused this small ice age, but oyster shells suggest it could be due to a sudden weakening of subpolar ocean currents in the North Atlantic.
Researchers believe temperatures in the North Atlantic have reached a point where sea ice in the Arctic Ocean is increasingly melting, diluting seawater with fresh water and weakening ocean currents.
This, in turn, reduced the amount of heat carried by the currents to the poles, “eventually enhancing the expansion of sea ice through positive feedback,” the researchers write.
They warn that “if the rapid loss of Arctic sea ice, the accelerating melting of the Greenland ice sheet and the associated export of fresh water to the major convective regions of the North Atlantic continue, the subpolar cyclical tipping point could again lead to climate change.” changes” are fast and long-term.
Because oysters extract oxygen and carbon isotopes from the water to lay their calcite shells, the chemistry of their growth lines can encode annual fluctuations in the marine environment, such as seawater temperature, salt content, and dissolved carbon.
Based on these measurements, the researchers found a pattern in long-lived deep-sea oysters, indicating that subpolar currents in the North Atlantic have weakened twice.
The first episode of vulnerability occurred between 1180 and 1260 AD, and the second between 1330 and 1380 AD, shortly after some volcanic eruptions (although its role in this tumultuous transition is still debated).
Between these episodes, shell growth and carbon isotopes in oysters indicate that the ecosystem is keeping pace with environmental changes. But during the second episode, the researchers noticed a decrease in the growth of the earth’s crust, starting around 1300 AD.
This suggests that the increased presence of sea ice in the area may have disrupted the primary production and food supply of the lower seafloor, depriving the oysters of nutrients. After that, the ecosystem never returned to its original level.
Additional studies are needed to confirm these results. Other studies using various data sources, for example, also point to a possible collapse of the North Atlantic Currents around 1300 AD, which also links it to the Little Ice Age.
And if the North Atlantic is weak, this part of the world could face more problems than we thought.
The study was published in a journal. Connection with nature.
Source: Science Alert.