Earth’s atmosphere revealed by temperature changes and climate shifts

A research team from Hokkaido University has investigated temperature changes and climate shifts to reveal the evolution of the Earth’s atmosphere.

What have scientists investigated to reveal this information?

Scientists have discovered argon trapped in air-hydrate crystals in ice cores, which can be utilised to reconstruct past temperature changes and climate shifts.

On the gigantic sheets of ice that stretch across Greenland and Antarctica, the temperature is so low that not even the summer Sun can melt the snow deposited onto them. As the snow accumulates without melting and settles deeper into the ice sheet, it traps air from the atmosphere, which forms small air bubbles when the snow transforms into ice.

Over centuries or millennia, the ice builds up, increasing the pressure and dropping the temperature in the bubbles, until the trapped atmospheric molecules convert into cage-like crystals, preserving the ancient air samples for hundreds of thousands of years. These crystals, called ‘air-hydrate crystals,’ could reveal exactly how the Earth’s atmosphere, and climate, has shifted over hundreds of thousands of years— so long as their composition is accurately measured.

How is this new method improved?

Previous measurement methods were limited to a couple of elements, such as oxygen and nitrogen. Now, this research team has developed a new approach to identify more elusive, previously unconfirmed constituents, such as argon, which could help reconstruct a more precise understanding of past climates.

These findings were published in the Journal of Glaciology.

“The air bubbles in an ice core are the only known paleoenvironmental archive of the actual ancient atmosphere with a time axis in the depth direction,” explained Tsutomu Uchida, lead author and an Associate Professor in the Faculty of Engineering at Hokkaido University.

He explained that argon could be extracted from the ice via melting or cutting, but its location in the undisturbed ice was a mystery. “If we can understand where argon is located in ice, we can improve our understanding of the movement of gas molecules in ice and contribute to improving the accuracy of environmental reconstruction.”

The researchers examined five air-hydrate crystals in an ice core extracted from Greenland and containing ice dating to about 130,000 years ago. They utilised a combination of scanning electron microscopy and energy-dispersive X-ray spectroscopy to visualise and identify the molecules contained in the air-hydrate crystals—this revealed the presence of argon.

An ice core from the Greenland ice sheet Photo Credit: Tsutomu Uchida.

What does this mean for temperature changes and climate shifts?

“Argon was assumed to be in the air-hydrate crystals, but was never confirmed directly by microscopic analysis,” added Kumiko Goto-Azuma, co-author, and Professor with The Graduate University for Advanced Studies, SOKENDAI, and the National Institute of Polar Research.

“Such direct observation is difficult because it has a very small mixing ratio with neighbouring elements and it is an inert gas, which makes it hard to measure by the common methods used for nitrogen and oxygen.”

The researchers plan to refine their approach to better understand the distribution of argon in ice with the goal of elucidating the mechanism of changes. This will enable more accurate estimations of the impact of human activities on temperature changes, climate shifts, and the overall impact on the global environment. 

“With this new approach, we believe that we can improve the accuracy of ice core analysis to elucidate how much argon existed in the ancient atmosphere and how it has changed with the Earth’s environment,” concluded Tomoyuki Homma, co-author, and an Associate Professor in the Graduate School of Engineering at Nagaoka University of Technology.

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