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Saturday, 2 November 2019

The 2 million years ancient ice reveals crucial information about the Earth's carbon cycle

A team of scientists worked more than two years to achieve these results: the oldest complete ice core provided a reliable snapshot of the atmosphere of our planet as it was nearly 2 million years ago. years. And the data presented is not what we would have expected.

We know that about a million years ago, the cycle of the Earth's ice ages suddenly changed: since that change, deeper and longer gels only occur every 100,000 years or so, once every 40,000 years.

Nothing on our planet could explain this "brutal" change, better known as the middle Pleistocene transition known  as  MPT  (English Mid-Pleistocene transition), and with few other explanations, some hypothesized long-term decline in CO2 concentrations in the atmosphere, cooling the planet to a new threshold.

But the old air bubbles trapped in the Antarctic ice floe revealed somewhat different information. Indeed, dating back to about 1.5 million years ago, these tiny amounts of our ancient atmosphere reveal " incredibly low " CO2 levels , according to palaeoclimatologist Yige Zhang, of Texas A & M University, who did not participate in the study and stated that he found the results "quite interesting".

These are the first direct observations of greenhouse gases in the atmosphere before the intervals between the Ice ages on Earth begin to lengthen. These observations also suggest that something else that a long-term decline in CO2 has been involved in the change in the complete cycle of the ice age of our planet.

Blue ice near the Allan Hills area in Antarctica. Environmental conditions in this area attract old ice to the surface. Scientists analyzed the air trapped in a core of ice drilled in this region, to obtain the first direct measurements of carbon dioxide levels in the atmosphere, dating back two million years ago. Credits: Sean Mackay

The oldest ice sample that we could test for CO2 levels prior to this new core, dates back only 800,000 years ago: other estimates based on sediment chemistry Earth are only useful as indirect indicators of greenhouse gas levels, they are not useless, but additional verifications are needed.

But the new ice analysis, which exploited more precise measurements than before, revealed that: " although the CO2 levels during the glaciations have remained much higher than the troughs recorded in the ice depths during the 800 ' In the last few years, maximum CO2 concentrations during the interglacial periods have not decreased,  "said Eric Wolff, Earth Science Scientist at the University of Cambridge, who wrote a report on the research.

"  One of the important results of this study is that the carbon dioxide level is temperature-related at the beginning of this period, " said Atmosphere Specialist Ed Brook of Oregon State University. " This is an important baseline for understanding climate science and calibrating predictive models of future change ," he added.

In other words, the relationship between CO2 levels and temperature in Antarctica has not changed much during this period. And, according to scientists, the low levels of CO2 during ice ages are probably only a consequence of the shorter glacial periods that occurred before TWA.

The authors also found that the lowest levels of CO2 did not occur during the first 40'000 years after MPT. " Our results seem to contradict the assumptions that attribute the transition to a world from 100,000 years before a change, to a long-term decline in atmospheric CO2, both interglacial and glacial," the researchers write.

In his report of the research, Wolff congratulated the researchers for their precise estimates, but also argues that "  s complete and undisturbed chronological eries" is needed to bring CO2 levels in context.

Fortunately, the old ice core, discovered in the Allan Hills, Antarctica, may soon have company. Indeed, researchers predict that the ice cover dates back to 2.7 million years or more. " We do not know the age limit in this area,  " Brook said.

And, given the extent of ice movement in this region, new cores that researchers will be analyzing soon will most likely come in discontinuous sections. "  There could be much older elements in some places. That's why we're going back. To grow beyond two million years would be truly incredible, "added Brook. As a result, their future information can help us learn more about some of the mysteries of the planet.

VIDEO: Ice reveals crucial information about the ancient Earth's atmosphere


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