Study provides detailed snapshot to date of the last 11,000 summers and winters on Earth – Eurasia Review

By analyzing the Antarctic ice core, University of Colorado Boulder scientists and an international team of collaborators have revealed the most detailed look yet at the planet’s recent climate history, including summer and winter temperatures going back 11,000 years to the beginning of what is known as the Holocene.

Posted in natureThis study is the first seasonal record of temperature from anywhere in the world.

“The research team’s goal was to push the boundaries of what is possible with previous climate explanations, and for us that meant trying to understand climate on the shortest time scales, in this case seasonally, from summer to winter, year after year,” said Tyler Jones, lead author. To study, and research assistant professor and fellow at the Institute for Arctic and Alpine Research (INSTAAR), over thousands of years.

The study also validates one aspect of a long-standing theory about Earth’s climate that had not been previously proven: how seasonal temperatures in the polar regions respond to Milankovitch cycles. Serbian scientist Milutin Milanković hypothesized a century ago that the collective effects of changes in the Earth’s position relative to the Sun – due to slow changes in its orbit and axis – are a powerful driver of the Earth’s long-term climate, including the onset and end of glaciations. Ages (before any significant human impact on climate).

“I am particularly excited because our result confirms a key prediction of the theory used to explain Earth’s Ice Age climate cycles: that the intensity of sunlight controls summer temperatures in the polar regions, and thus also melts ice,” said Kurt Coffey. , a co-author of the study and a professor at the University of California, Berkeley.

This more detailed data about long-term climate patterns in the past also provides an important baseline for other scientists, who study the effects of human-caused greenhouse gas emissions on our current and future climate. By knowing what planetary cycles occur naturally and why, researchers can better determine the human impact on climate change and its effects on global temperatures.

“This research is something humans can really relate to because we experience the world in part through the changing seasons — and documenting how summer and winter temperatures vary over time translates into how we understand climate,” Jones said.

A more accurate definition of the diffusion medium

Scientists around the world have long studied Earth’s past climate using ice cores collected from the poles. These slender, cylindrical columns of ice, drilled from ancient ice sheets (mostly in Antarctica and Greenland), provide valuable long-term, time-crunched data on everything from past atmospheric concentrations of greenhouse gases to past air temperatures. and oceans.

The West Antarctic Ice Sheet (WAIS), the longest ice core ever drilled by US researchers, is 11,171 feet (or more than two miles) long and 4.8 inches in diameter — and contains data going back 68,000 years. Ice cores like this are then carefully cut into smaller sections that can be safely transported and stored or analyzed in ice core laboratories around the country — like the Stable Isotope Lab at CU Boulder.

In this study, the researchers analyzed an ongoing record of water isotope ratios from WAIS ice cores. The ratios between the concentration of these isotopes (elements with the same number of protons but different numbers of neutrons) reveal data about past temperatures and atmospheric circulation, including transitions between ice ages and warm periods in Earth’s past.

It is particularly difficult to measure seasonal changes in our planet’s history from ice core samples, due to the fine detail required for the shorter time scales. A process within the ice sheets known as diffusion, or natural smoothing, can blur these needed details.

These water isotopes tend not to stay in one place in the upper ice sheet, but instead move in interconnected pathways (similar to air pockets in Styrofoam) as they change states between vapor and ice, over decades or centuries, before they sufficiently solidify. This process can “blur” the data researchers are trying to examine. But by using high-quality ice cores from the West Antarctic Ice Sheet, extremely high-resolution measurements and advances in ice core analysis over the past 15 years, the team was able to correct for the spread found in the data and complete the study.

“Even then, we had to develop completely new ways of working with this data, because no one had ever seen it before,” said Jones.

Stable isotope study

While the study details the history of Earth’s climate, the work behind it has a history of its own.

For more than three decades, researchers at INSTAAR’s Stable Isotope Laboratory have been studying a variety of stable isotopes — forms of nonradioactive atoms with unique molecular signatures — found everywhere from inner ice cores and carbon in permafrost to atmospheric air. Jones joined the lab in 2007 as a master’s student and never left.

“I have this distinct memory of walking into my advisor, Jim White’s office around 2013, and showing him that we’re going to be able to pull out the values ​​of summer and winter in this record over the past 11,000 years — which is extremely rare. In our understanding, no one did,” Jones said. That before.” We looked at each other and said, “Wow, this is going to be a really big deal.”

Then it took nearly a decade to figure out the correct way to interpret the data, from ice samples drilled many years before that meeting.

Bruce Vaughn, co-author and lead scientist on the project, director of the Stable Isotope Laboratory, and Bradley Markle, co-author of the study and assistant professor in INSTAAR and the Department of Geology, were there to collect ice in West Antarctica that had been shipped back and analyzed.

The team’s next step is to try to interpret high-resolution ice core samples in other locations — such as Antarctica and northeastern Greenland, where cores have already been drilled — to better understand the variability of our planet’s climate.

“Humans are fundamentally curious about how the world works and what happened in the past, because that can also inform our understanding of what might happen in the future,” Jones said.

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