The Ice Core Records – The Million-Year Climate History Trapped in Antarctica

The notion that the actual air that flowed through Earth’s atmosphere more than a million years ago is contained in a column of ice that was drawn from almost two miles below the Antarctic surface is subtly astounding. Not a chemical stand-in for that air. It is not a mathematical model that speculates on potential conditions. The real thing: an ancient atmosphere preserved by pressure, cold, and pure geological luck, contained within pinhead-sized bubbles. It’s difficult not to get the impression that something truly unique is taking place when you’re standing in a chilled lab in Cambridge and watching researchers work through portions of that ice with the kind of concentrated calm that only comes from years of training.

A continuous ice core record dating back at least 1.2 million years has finally been confirmed by the Beyond EPICA – Oldest Ice project, which is led by Italy and involves twelve scientific institutions from ten European nations. The scientific community used an 800,000-year benchmark for 20 years; it was reliable, reputable, and disappointingly lacking. Scientists learned a lot about atmospheric chemistry, greenhouse gas shifts, and glacial cycles from that record. It was unable to look past a significant turning point in the history of Earth’s climate. Now that gap has been filled.

This project’s central mystery is one of those seemingly straightforward questions. The Earth’s ice age cycle changed about a million years ago. Prior to that, variations in Earth’s axial tilt caused the planet to alternate between warmer interglacial and colder glacial periods approximately every 41,000 years. Then something altered. The cycle lengthened to about 100,000 years, which is more in line with the periodicity of Earth’s orbital shape than its tilt. The duration, temperature, and severity of ice ages increased. During the deepest glacial periods, sea levels fell by more than 100 meters. Ice sheets that were kilometers thick spread over Eurasia and North America. There was a five-degree drop in global temperatures. All of that was brought on by relatively small changes in the planet’s relationship to the sun in terms of energy. There has never been a complete explanation of the response’s scale.

This change is linked to falling CO2 levels in the atmosphere, according to a leading theory. It is believed that the threshold for initiating and maintaining a longer, deeper ice age became easier to cross as carbon dioxide levels decreased. The current analysis of the ice core record should either confirm or significantly complicate that theory. A different theory suggests that ice sheets may have become physically more stable over time due to the slow erosion of bedrock beneath them, making them more resistant to melting during warmer interglacial periods. It’s interesting to note that the ice itself records gases released by bedrock, indicating that the core simultaneously contains evidence supporting both theories.

It is worthwhile to take a moment to consider the physical reality of extracting this data. At Little Dome C, a group of sixteen scientists and support personnel endured four Antarctic summers with average temperatures of about -25 degrees Fahrenheit. Before being loaded onto the icebreaker ship Laura Bassi for transportation to Europe at -58°F, the ice core broke up into sections and was handled with extreme care. When reassembled, the entire core is longer than eight end-to-end Eiffel Towers. Then, for more than seven weeks, 190 meters of the oldest sections were continuously melted by a different team of thirty researchers, engineers, and experts from the British Antarctic Survey using a method known as continuous flow analysis. This ultra-slow melt process simultaneously measures dozens of chemical elements, particles, and isotopes from a single pass through the ice.

Compared to marine sediment cores, which have long been used to study ancient climates, ice cores are much more valuable scientifically because of those trapped air bubbles. Glacial cycles can be timed with the help of marine records. The atmosphere is not captured by them. Cores of ice do. With CO2, methane, oxygen, and other gases preserved from the exact moment that snow compressed into ice, cutting off contact with the outside world, each bubble is effectively a sealed sample jar. By directly measuring those concentrations, researchers can create a record of the changes in greenhouse gas concentrations over time that is unmatched by any other archive on Earth.

The exact age of the deepest parts of this core is still unknown. According to the team’s most recent estimate, it is older than 1.2 million years, but determining its exact age necessitates compiling all the data from labs throughout Europe. In the meantime, Australia is conducting a parallel drilling operation at a location known as Dome C North, which is about 50 kilometers from the location of the European team. According to ice flow modeling, the site may produce ice that is up to two million years old. Since replication is the only trustworthy defense against flow disturbance or other ice artifacts at these depths and ages, both teams are purposefully operating independently to enable cross-verification of findings.

It’s hard to overlook the larger context here. At a time when greenhouse gas levels are rising more quickly than at any other point in the ice core record, scientists are extracting a comprehensive record of how Earth’s climate has reacted to changes in these gases over geologic time. The information gathered from these cores won’t alter the current situation. However, it will improve the models used to forecast future events by adding more than 400,000 years of climate cycles to the baseline that scientists use to determine the planet’s true sensitivity. That’s a big deal. The scientific community believes that after this data is thoroughly examined, some long-held beliefs regarding climate feedback mechanisms and the rate of change will be challenged.

Perhaps a rocket launch would have made headlines more than the melting of 190 meters of old Antarctic ice in a Cambridge laboratory. However, answers to questions that have shaped climate science for generations can be found somewhere in those trapped bubbles, in gases that last touched the open air before modern humans existed, before agriculture, and before the first stone cities. Researchers may find that the data supports their preconceived notions. It’s also possible that it will cause new issues that haven’t been considered yet. In any case, the ice has been waiting a very long time to be read.