Melting icebergs key to ice age sequence, scientists say

Scientists claim to have found the “missing link” in the process leading to an ice age on Earth.

Melting icebergs in Antarctica are key, according to the Cardiff University team, triggering a series of chain reactions that plunge the Earth into an extended period of cold temperatures.

The results were published today in Nature an international consortium of scientists from universities around the world.

It has long been known that the cycles of the Ice Age are punctuated by periodic changes in the Earth’s orbit of the Sun, which subsequently changes the amount of solar radiation that reaches the Earth’s surface.

However, until now, how small variations in solar energy can trigger such dramatic changes in Earth’s climate has remained a mystery.

In their study, the team proposes that when Earth’s orbit around the sun is correct, Antarctic icebergs begin to melt further and further away from Antarctica, moving huge volumes of fresh water away from it. the Southern Ocean and the Atlantic Ocean.

As the Southern Ocean becomes saltier and the North Atlantic cools, large-scale ocean circulation patterns begin to change dramatically, attracting CO₂ out of the atmosphere and reducing the so-called greenhouse effect.

This in turn pushes the Earth into Ice Age conditions.

As part of their study, the scientists used several techniques to reconstruct past climatic conditions, including identifying tiny fragments of Antarctic rock dropped into the open sea by melting icebergs.

The rock fragments were obtained from sediments recovered by Expedition 361 of the International Ocean Discovery Program (IODP), representing more than 1.6 million years of history and one of the longest detailed archive of Antarctic icebergs.

The study found that these deposits, known as Ice Debris, appeared to systematically drive changes in deep ocean circulation, reconstructed from the chemistry of tiny deep-sea fossils called foraminifera.

The team also used new climate model simulations to test their hypothesis, finding that huge volumes of fresh water could be displaced by icebergs.

Lead author of the study, Aidan Starr, of the School of Earth and Environmental Sciences at Cardiff University, said: “We were amazed to find that this lead-lag relationship was present at the start of each period. glacial over the 1.6 million years. The leading role of the Southern Ocean and Antarctica in the global climate has been speculated, but to see it so clearly in the geological evidence was very exciting. “

Professor Ian Hall, co-author of the study and co-chief scientist of the IODP expedition, also from the School of Earth and Environmental Sciences, said: “Our results provide the missing link in how Antarctica and the Southern Ocean responded to the rhythms of the climate system associated with our orbit around the sun. “

Over the past 3 million years, the Earth has steadily plunged into Ice Age conditions, but is currently in an interglacial period where temperatures are warmer.

However, due to rising global temperatures resulting from anthropogenic CO₂ emissions, the researchers suggest that the natural rhythm of Ice Age cycles could be disrupted as the Southern Ocean will likely become too warm for Antarctic icebergs to travel far enough to trigger the changes in ocean circulation necessary for the development of a ice Age.

Professor Hall believes the results can be used to understand how our climate may respond to anthropogenic climate change in the future.

Likewise, as we observe an increase in mass loss from the Antarctic continent and iceberg activity in the Southern Ocean, resulting from the warming associated with current human emissions of greenhouse gases, our study highlights the importance of understanding iceberg tracks and melting patterns in developing the most robust predictions of their future impact on ocean circulation and climate, ”he said.

Professor Grant Bigg, Department of Geography, University of Sheffield, who contributed to the iceberg model simulations, said: “The revolutionary modeling of icebergs in the climate model is crucial in identifying and supporting the hypothesis of ice debris on iceberg meltwater impacts in Antarctica. that lead to the beginnings of the glacial cycle. ”