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“Unexpected”-evidence of the Little Ice Age triggered by sea ice



Glacier mountain

  • Sea ice can act as a driving force for climate change on various time and space scales, not just a passive responder to change.
  • The Little Ice Age may have been “suddenly produced”
    ; by internal changes within the climate system, rather than external pushes caused by volcanic eruptions or other factors.
  • From the 14th to the 15th centuries, distant sea ice pulsations may have caused the demise of the Nordic colonies in Greenland.

A new study finds the triggers of the Little Ice Age that cooled Europe from the 1300s to the mid-1800s, and supports surprising model results showing that under the right conditions, sudden changes in climate can happen spontaneously without external forcing .

The research was published in Scientific progress, The report has carried out a comprehensive reconstruction of sea ice. In the past 1400 years, sea ice has crossed Greenland from the Arctic Ocean into the North Atlantic through the Fram Strait. Reconstruction shows that the Little Ice Age (not a true ice age, but a regional cooling centered on Europe) was triggered by the massive flow of sea ice from the Arctic Ocean into the North Atlantic in the 1300s.

Greenland and adjacent ocean currents

The map shows Greenland and nearby ocean currents. The colored circles indicate that some of the sediment cores used in this study were obtained from the seafloor. A small historical map from the beginning of the 20th century shows the distribution of Storis (sea ice of the Arctic Ocean), which flows down to the east coast of Greenland. Image source: Miles et al., 2020.

Although previous experiments using numerical climate models have shown that increasing sea ice is necessary to explain long-term climate anomalies like the Little Ice Age, physical evidence is lacking. This study excavated the geological records to confirm the model results.

Researchers collected records of marine sediment cores drilled from the Arctic Ocean to the bottom of the North Atlantic Ocean to learn more about sea ice in the entire region for the past 1400 years.

INSTAAR researcher Martin Miles said: “We decided to collect different evidence to try to reconstruct the sea ice from the past one and a half thousand years in space and time, and then see what we found.” Norwegian NORCE Norwegian Research Center and Bjerknes Climate Research Center are dating.

The core includes compounds that algae live in sea ice, the shells of single-celled organisms that live in different water temperatures, and debris absorbed and transported by sea ice over long distances. The core is detailed enough to detect sudden changes in sea ice and ocean conditions over time (decadal scale).

Records indicate that Arctic sea ice exports to the North Atlantic increased suddenly, starting around 1300, reaching a peak in the middle of this century, and ending abruptly at the end of the 1300s.

The occurrence of sea ice and polar water

These figures show the reconstructed time series of past sea ice and polar water changes. The color of the curve corresponds to the location on the map. The blue shading indicates the period when sea ice increased in the 1300s. Image source: Miles et al., 2020.

Myers said: “I am not only fascinated by sea ice as a passive indicator of climate change, but also fascinated by how sea ice interacts with the climate system or actually causes long-term trends in climate change.” “The perfect example is the Little Glacier. century.”

Miles added: “This particular investigation was inspired by partial paleoclimatic reconstructions by INSTAAR colleague Giff Miller and my INSTAAR colleague Anne Jennings, John Andrews and Astrid Ogilvie.” The first paper written by Miller proposed. Sea ice played a vital role in maintaining the Little Ice Age.

Scientists have been arguing about the causes of the Little Ice Age for decades, and many believe that explosive volcanic eruptions are necessary to initiate a cooling period and make it last for centuries. On the one hand, the new reconstruction provides strong evidence that explosive volcanic eruptions may have triggered large-scale sea ice anomalies. On the other hand, the same evidence also supports interesting alternative explanations.

Martin Myers

INSTAAR researchers collaborated with Martin Miles in the fjords of the modern Arctic Circle. Credit: Martin Myers

Run a climate model called a “control model” to understand how the climate system operates over a period of time without being affected by external factors such as volcanic activity or greenhouse gas emissions. A set of recent control model experiments includes describing the results of sudden cold events that have lasted for decades. The results of this model seem too extreme to be realized, the so-called Ugly Duckling simulations, and researchers worry that they show problems with the model.

Miles’ research found that these models may not have any problems.

He said: “We actually found the first place. We do have physical and geological evidence that the decades-old journey of ice and snow in the same area may actually happen.” In the “Ice Age”, “what we reconstruct in space and time is very similar to the development of the “ugly duckling” model simulation. In the ugly duckling model simulation, spontaneous cold events lasted for about a century. As we found here As it does, it involves unusual winds, sea ice exports, and more ice east of Greenland.” Encouraging results indicate that external forcing from volcanic eruptions or other causes may not be necessary for large-scale climate change to occur. Myers continued: “These results strongly suggest…that these things may suddenly appear due to changes within the climate system.”

While disappearing in the 15th century, the heart of the sea also showed the continuous pulsation of sea ice near the Nordic colonies of Greenland. The debate about why the colonies disappeared has been fierce, and it is generally agreed that the cooling climate has increased their resilience. Myers and his colleagues want to take into account the changes in the nearby ocean: For nearly a century, there has been a lot of sea ice and extremely cold water year after year.

Myers said: “In the past and even today, a large number of ice bands flowing from the Arctic have been around the farewell corner to the place where these colonies are located.” He wants to study the ocean conditions more closely with researchers in climate-related social sciences. .

Reference: Martin W. Miles, Camilla S. Andresen and Christian V. Dylmer, “Evidence that the extreme export of Arctic sea ice led to the sudden eruption of the Little Ice Age”, September 16, 2020, Scientific progress.
DOI: 10.1126 / sciadv.aba4320

The co-authors of this study are Camilla S. Andresen of the Geological Survey of Denmark and Greenland, and Christian V. Dylmer of MMT Sweden AB.




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