Argon found in air of ancient atmosphere

Date:
March 30, 2022
Source:
Hokkaido University
Summary:
Researchers have discovered argon trapped in air-hydrate crystals
in ice cores, which can be used to reconstruct past temperature
changes and climate shifts.



FULL STORY ========================================================================== Researchers have discovered argon trapped in air-hydrate crystals in
ice cores, which can be used to reconstruct past temperature changes
and climate shifts.


==========================================================================
On the massive 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
on 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 how the Earth's atmosphere,
and climate, has changed over hundreds of thousands of years -- if their composition can be accurately measured.

Previous measurement methods were limited to a couple of elements,
such as oxygen and nitrogen. Now, an international 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. They published their approach and their findings -- including the first direct discovery of argon in air-hydrate crystals -- 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," said first author Tsutomu Uchida, 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 used a combination of scanning electron microscopy
and energy-dispersive X-ray spectroscopy to visualize and identify the molecules contained in the air- hydrate crystals. They found argon.

"Argon was assumed to be in the air-hydrate crystals, but was never
confirmed directly by microscopic analysis," said co-author Kumiko
Goto-Azuma, a 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 neighboring 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 and more accurately estimating the impact of human activities
in 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," said
co-author Tomoyuki Homma, an Associate Professor in the Graduate School
of Engineering at Nagaoka University of Technology.


========================================================================== Story Source: Materials provided by Hokkaido_University. Note: Content
may be edited for style and length.


========================================================================== Related Multimedia:
* An_ice_core_from_the_Greenland_ice_sheet ========================================================================== Journal Reference:
1. Tsutomu Uchida, Wataru Shigeyama, Ikumi Oyabu, Kumiko Goto-Azuma,
Fumio
Nakazawa, Tomoyuki Homma, Kenji Kawamura, Dorthe
Dahl-Jensen. Discovery of argon in air-hydrate crystals in a deep
ice core using scanning electron microscopy and energy-dispersive
X-ray spectroscopy. Journal of Glaciology, 2021; 1 DOI:
10.1017/jog.2021.115 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/03/220330103305.htm

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