Ice cores store atmospheric bubbles from a million years ago

May 12, 2015 by Bob Yirka report
Credit: Newcastle University

(Phys.org)—A team of researchers with members from Princeton University, the University of Maine and Oregon State University has found that greenhouse gasses a million years ago, were only slightly higher than they were between 450,000 and 800,000 years ago. In their paper published in Proceedings of the National Academy of Sciences, the team describes their study of the newly retrieved ice cores and how it is helping to better understand the changes to the Earth's ice ages.

The cores were taken from a part of Antarctica known as Allan Hills—there unique geography has caused glaciers sliding down mountains to slide upwards for a bit. Additional erosion due to wind and precipitation has caused very old (blue) ice to lie close enough to the surface to be extracted via core drilling. Dating has shown the ice to be approximately one million years old, which means the air bubbles trapped inside are the same age as well—the oldest found so far. Those air bubbles offer scientists an opportunity to measure the amount of different gasses in the atmosphere from that time period, and it is helping, the team suggests, to gain a better handle on the changes to cyclic ice ages.

Prior study has shown that before a million years ago, the Earth experienced ice ages approximately every 40,000 years, but after that the cycle grew longer, to approximately 100,000 years and scientists want to know why—they suspect it has to do with changes to the ratios of —most specifically . That is where the in ice core samples come in, they offer direct evidence of carbon dioxide levels. The latest samples show that there were not major swings in greenhouse gas levels at that time, but more ominously, that carbon dioxide levels never rose above 300 ppm over the past million years, until the twentieth century—right now the level is approximately 400 ppm.

The record setting ice cores do not actually answer any real questions about the cyclic nature of ice ages, the researchers acknowledge, but instead add another chapter to a growing body of knowledge—a suggestion that there is indeed a strong correlation between carbon dioxide levels and glacial cycles.

Explore further: Study of Antarctic ice cores reveals atmospheric CO2 history over past thousand years

More information: Atmospheric composition 1 million years ago from blue ice in the Allan Hills, Antarctica John A. Higgins, DOI: 10.1073/pnas.1420232112

Abstract
Here, we present direct measurements of atmospheric composition and Antarctic climate from the mid-Pleistocene (∼1 Ma) from ice cores drilled in the Allan Hills blue ice area, Antarctica. The 1-Ma ice is dated from the deficit in 40Ar relative to the modern atmosphere and is present as a stratigraphically disturbed 12-m section at the base of a 126-m ice core. The 1-Ma ice appears to represent most of the amplitude of contemporaneous climate cycles and CO2 and CH4 concentrations in the ice range from 221 to 277 ppm and 411 to 569 parts per billion (ppb), respectively. These concentrations, together with measured δD of the ice, are at the warm end of the field for glacial–interglacial cycles of the last 800 ky and span only about one-half of the range. The highest CO2 values in the 1-Ma ice fall within the range of interglacial values of the last 400 ka but are up to 7 ppm higher than any interglacial values between 450 and 800 ka. The lowest CO2 values are 30 ppm higher than during any glacial period between 450 and 800 ka. This study shows that the coupling of Antarctic temperature and atmospheric CO2 extended into the mid-Pleistocene and demonstrates the feasibility of discontinuously extending the current ice core record beyond 800 ka by shallow coring in Antarctic blue ice areas.

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Returners
2.3 / 5 (12) May 12, 2015
The record setting ice cores do not actually answer any real questions about the cyclic nature of ice ages, the researchers acknowledge, but instead add another chapter to a growing body of knowledge—a suggestion that there is indeed a strong correlation between carbon dioxide levels and glacial cycles


I bet they'll try to blame this on humans too.
mreda14
1 / 5 (2) May 15, 2015
Very interesting way of estimating CO2 level in air one million years ago. I guess that volcanic activity if present at that time may effect such measurement. Photosynthesis by the Sun make CO2 level in air to vary between day and night. Everyone expect CO2 level to be much higher at night. CO2 level in air is in a dynamic equilibrium with water vapour in the air and the ocean water. CO2 can easily dissolves in water to produce a mixture of carbonate and bicarbonate depending on the pH of the water. I mean what about photosynthesis during day light. It should convert most of the 400 ppm CO2 into sugar in the plant and oxygen in air.
paul_pglaw
1 / 5 (2) May 20, 2015
These studies are interesting but the uncertainties in the science make any conclusions dubious.

Ice core studies used to estimate atmospheric gas concentrations thousands and hundred of thousands of years ago, obviously cannot be verified by observation or by experimentation. There is no way to know how the concentrations of various gases found trapped in ice now, varies from the concentrations of those gases when the gas was first trapped. Gas migrates in ice, molecules diffuse, gases dissolve. Different gases behave differently. Ice moves, up and down and sideways, over time, due to varying pressures. Gas found in bubbles in ice most likely contains gases trapped at different times. It is known that the age of gas trapped in ice varies from the age of the ice in which it is found, even at shallow depths.

Guesses can be made as to ancient atmospheric CO2 concentrations, based on ice cores. The range of uncertainties is unknown. Actual determinations cannot be made.
Vietvet
3.7 / 5 (3) May 20, 2015
@paul_pglaw

Do you have any links to back up your comments?
paul_pglaw
1 / 5 (3) May 20, 2015
Sure, but I am not allowed to post them.
Search for yourself, look for does gas diffuse in ice cores, or something similar. Read PNAS study. You will find articles - they don't admit what they don't know, and will pretend to know more than they do. But they will describe how air is trapped in ice, how ice compresses, moves, how gas molecules diffuse in ice, how the age of ice differs from the age of air trapped in that ice.
Then think - there are no observations as to how air was trapped hundreds of thousands of years ago, nor how ice broke up, moved up, down, and sideways, how different gas molecules diffused at different rates, how gas mixed from different bubbles. So, yes, ice cores show air was trapped, and that it contained CO2. But that isn't enough to determine what atmospheric CO2 was at the time.
True scientists remain humble, and don't try to answer questions when all they have are untestable theories.

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