Clams Tell Us Why Earth Tipped Into a Mini Ice Age Hundreds of Years Ago



In order to better foresee when the temperature of our world would tip over into dangerous zone, some scientists are becoming into clam "whisperers."

It may seem strange for scholars to pay attention to a bivalve with a tight lip, but as we are learning, clams are great natural historians.

The growth bands on their shells, like the rings on a tree, store important information about the environment and how it has evolved through time.

These complex paragraphs can be dissected and examined by scientists centuries after they were first "written," much like the lines of a diary.

In fact, more than five hundred million years ago—nearly three hundred million years before dinosaurs appeared—clams' ancestors began carving out tunnels in the stone calcite, providing an unrivaled insight into past temperatures.

These antiquated records are currently issuing a grave warning. A potentially disastrous tipping point in the Earth's climate has been discovered by a fresh analysis of three bivalve records from the North Icelandic shelf.

The results show that an eight-hundred-year-old change in our planet's climate was caused by a feedback loop that weakened the stability of a climate system in the North Atlantic Ocean and forced it into a new, colder state of normal.

The North Atlantic saw the beginning of the "Little Ice Age" in the 13th century, and it lasted until manmade warming stopped the natural trend.

Clam shells suggest that this mini-ice age may have been brought on by an abrupt weakening of subpolar ocean current patterns in the North Atlantic, although scientists are still unsure of the precise cause.

Ocean currents may have been weakened as a result of sea ice melting into the Arctic Ocean as a result of rising temperatures in the North Atlantic, according to researchers.

The scientists speculate that this may have reduced the amount of heat carried by the currents towards the pole, "ultimately reinforcing sea-ice expansion through a positive feedback."

The scene was prepared for a return to the ice and snow age.

Even if we are moving in the opposite direction now, fresh study indicates that the North Atlantic may be nearing another unsettling tipping point.

The authors warn that a subpolar gyre tipping point could once more result in rapid and long-lasting regional climate change. "If rapid loss of Arctic sea-ice, accelerating melting of the Greenland ice sheet, and associated export of freshwater into key convective regions in the North Atlantic continue," they write.

Clam shells are only a limited proxy for historical maritime climates, yet they are very trustworthy.

Some of the longest-living organisms on Earth are quahog clams (Arctica islandica), which were utilised in the current investigation. A deep-sea quahog clam that had endured to its 507th year was discovered in 2013, making it the oldest creature ever discovered.

The chemical makeup of clam development lines can encode annual variations in the marine environment, such as seawater temperature, salinity level, and dissolved carbon, because clams draw oxygen and carbon isotopes out of the water to lay down their calcite shells.

On the basis of these measurements, scientists have recently discovered a recurring pattern in long-lived, deep-sea clams that points to two periods when the subpolar currents in the North Atlantic weakened.

Shortly after a few volcanic eruptions, the first weakening phase took place between 1180 and 1260 CE, and the second between 1330 and 1380 CE (though their role in this turbulent transition is debated).

Carbon isotopes in the clams and shell growth between these episodes indicate that the ecosystem adapted to the changing environment. However, the authors noticed a reduction in shell growth beginning approximately 1300 CE during the second episode.

This shows that the region's rising sea ice levels may have disrupted primary production and food supplies to the sea floor below, depriving clams of essential nutrients. The environment never really recovered to its original state after then.

It seems as though its resilience has deteriorated.

The beginning of the [Little Ice Age] may have taken place as a result of the subpolar gyre system reaching a tipping point, according to the evidence presented here for loss of resilience in the subpolar North Atlantic before 1260 and evidence for the weakening of the potentially bistable, subpolar gyre.

These results require further investigation, particularly studies that compare several climate proxies. For instance, several research utilizing a range of data sources suggest that the North Atlantic currents may have collapsed around 1300 CE, which would have coincided with the Little Ice Age.

This area of the planet may be in even greater peril than we imagined if the North Atlantic is as weak as these studies indicate.

Nature Communications published the study.

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