Clams tell us why the Earth ended up in a mini ice age Hundreds of years ago: ScienceAlert

Some scientists are becoming “clam whisperers” to better predict when our planet’s climate will tip over into dangerous territory.

A tight-lipped bivalve might sound like a strange creature that researchers can turn their ears to, but as we’re learning, clams are outstanding natural historians.

Similar to tree rings, the growth bands on their shells contain crucial information about the environment and how it has changed over the years.

Like the lines of a diary, these intricate passages can be broken down and read by scientists centuries after being “written” for the first time.

In fact, the ancestors of clams traced passages in the mineral calcite for more than five hundred million years, nearly three hundred million years before the dinosaurs appeared, offering us an unprecedented window into the climates of the past.

Now, these ancient archives are issuing a stern warning. A new reading of three bivalve records from the Icelandic North Shelf revealed a potentially dangerous tipping point in the Earth’s climate.

The findings suggest that a change in our global climate some eight centuries ago was the result of a feedback loop that wore down the stability of a climate system in the North Atlantic Ocean, leading it to a new colder state of normalcy.

The “Little Ice Age” first began in the 13th century in the North Atlantic and only stopped when anthropogenic warming reversed the natural trend.

Scientists aren’t sure yet what specifically triggered this mini-ice age, but according to clam shells, it may have had something to do with a sudden weakening of subpolar ocean current patterns in the North Atlantic.

Researchers suspect temperatures in the North Atlantic have reached a point where sea ice has increasingly melted into the Arctic Ocean, diluting seawater with fresh water and weakening ocean currents.

This, in turn, may have led to a reduction in the amount of heat carried by currents to the pole, “ultimately reinforcing sea ice expansion through positive feedback,” the authors write.

The stage was set for a return to an era of snow and ice.

Today we are headed in the opposite direction, but as other recent research suggests, the North Atlantic may be approaching another troubling turning point.

“If rapid Arctic sea ice loss, accelerated melting of the Greenland ice sheet, and associated freshwater export to major North Atlantic convection regions continues, a subpolar vortex tipping point could again lead to climate change. rapid and long-term regional initiatives ”, warn the authors.

Shells are just a proxy of past climates in the marine environment, but they are quite reliable.

Those used in the present study, the quahog clams (Icelandic Arctic), are some of the longest living creatures on planet Earth. In 2013, a deep-sea quahog clam was found that survived to its 507th year, making it the oldest animal ever found.

Since clams extract oxygen and carbon isotopes from the water to lay down their calcite shells, the chemical composition of their growth lines can encode annual fluctuations in the marine environment, such as seawater temperature, salinity and dissolved carbon.

Based on these measurements, the researchers have now found a consistent pattern in long-lived deep sea clams that suggests weakening of the North Atlantic subpolar currents on two occasions.

The first episode of weakening occurred between AD 1180 and 1260, and the second between AD 1330 and 1380, not long after some volcanic eruptions (although their role in this turbulent transition is debated).

In the interval between these episodes, shell growth and carbon isotopes in clams suggest that the ecosystem has kept pace with environmental changes. But during the second episode, the authors observed a decline in shell growth starting around 1300 AD.

This suggests that the presence of increased sea ice in the region likely disrupted the primary production and food supply of the underlying seabed, depriving the clams of nutrients. After that, the ecosystem never returned to baseline.

His resilience seems to have taken a bad turn.

“The evidence presented here for the loss of resilience in the subpolar North Atlantic before 1260, together with the evidence for the weakening of the potentially bistable subpolar vortex, indicate that the onset of [Little Ice Age] it may have occurred in response to the subpolar vortex system having passed a tipping point, “the authors write.

More research is needed to confirm these findings, particularly those that include several climate proxies for comparison. Other studies using a variety of data sources, for example, also point to a possible collapse of the North Atlantic currents around 1300 AD, also linking it to the Little Ice Age.

If the North Atlantic is as vulnerable as these studies suggest, this region of the world may be in even more trouble than we thought.

The study was published in Nature communications.

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