Surprising pulses of ancient warming found in Antarctic ice monsters | Science

Earth’s ice ages are typically considered as seemingly endless periods of bitter cold. But a new study suggests bursts of carbon dioxide (CO.)₂) often entered the atmosphere during these times, providing decades of heat or even centuries of relative heat amidst 10,000-year-old cooling. Such pulses may have caused glaciers and ice sheets to retreat somewhat, forcing new areas to be opened to plants and animals.

Researchers can track fluctuations in atmospheric CO₂ by looking at ice cores being drilled in Antarctica, Greenland, and some high mountains in lower latitudes. The cores contain trapped air bubbles when fluffy snow was compressed into ice by the weight of newer, fresher surface layers.

Some of these climate chronicles go back hundreds of thousands of years. But high-resolution data, following center scales or shorter variations, have been missing, in part because of contamination of techniques used to extract CO₂ out of the ice.

In the new study, Christoph Nehrbass-Ahles, a climate physicist at the University of Cambridge, and his colleagues came up with a way to extract CO₂ of old ice that is about three times more accurate than previous methods. The ice crushing technique they developed does not involve friction between metal parts, which can be a source of fresh CO₂. Due to the new approach, they were able to measure CO₂ concentrations up to within one part per million.

Nehrbass-Ahles’ team then analyzed parts of a 3.5-kilometer-long ice core that was drilled at one of the highest points in eastern Antarctica. Their samples capture times between 330,000 and 450,000 years ago – an interval that includes one full ice age like the hot spells on opposite sides. On average, each data point of about 300 years was separated from its neighbors, a four- to six-fold improvement in time resolution compared to previous surveys.

Over the 120,000 year interval, the researchers identified eight episodes when CO₂ levels up fast. Seven of those eight pulses lasted more than 100 years, and during six of them, CO₂ levels up more than nine parts per million, the researchers report today Science. (For comparison, before human activity began pumping large amounts of CO₂ in the air at the beginning of the Industrial Revolution, the global average of atmospheric CO₂ was about 280 parts per million.)

In the past, researchers have distinguished centuries of kicks in CO₂ only from ice samples representing the late stages of the last ice age. That, to find them in ice that instead accumulated in a warm, interglacial period was a surprise, says Nehrbass-Ahles.

The team’s new analysis shows that the Earth’s climate “may change much faster than we previously thought,” says Shaun Marcott, a paleoclimatologist at the University of Wisconsin, Madison, who was not involved in the new study. The resulting shifts in ecosystems, although short-lived, could have been profound.

Nehrbass-Ahles and his colleagues suggest the jumps in atmospheric CO₂ result of changes in a conveyor belt of ocean currents in the Atlantic Ocean. As the Gulf Stream decreases, that warm current brings less heat to North Atlantic waters. Those changes in temperature at sea level in turn cause weather patterns in the tropics, causing a shrinkage of wetland, says Nehrbass-Ahles. The carbonaceous material stored in those former swampy zones then falls off, sending a pulse of CO₂ in the air to warm the climate.

In modern times, these old pulses would not be impressive: A jump of 10 parts per million in CO₂, which may have worked out more than 100 years or more in pre-industrial times, these days can only take 4 or 5 years to transport.

Nevertheless, says Marcott, “Find these rapid leaps [in CO₂] is quite exciting from my perspective. “The results of the team show sudden pulses of CO₂ occur not only when the ice ages disappear, but can be triggered at any time during the ice age cycle.