Scientists say they have found the ‘missing link’ in the process leading to an ice age on Earth.
A melting Antarctic iceberg is the key, say the team from Cardiff University, triggering a series of chain reactions that collapse on Earth to a prolonged period of cold temperatures.
The findings were announced today in Nature from an international consortium of scientists from universities around the world.
It has long been known that ice age cycles undergo periodic changes in the Earth’s solar orbit, which in turn changes the amount of solar radiation that reaches the Earth’s surface.
However, so far it has remained a mystery as to how small changes in solar energy can induce such dramatic shifts in the Earth ‘s climate.
In their study, the team suggests that when the Earth’s orbit around the sun is just right, the Antarctic iceberg begins to melt further and further away from the Antarctic, moving amounts of freshwater away from the South Sea and into the Atlantic Ocean.
As the South Sea becomes more salty and the North Atlantic becomes more modern, large ocean circulation patterns begin to change dramatically, drawing CO2 out of the atmosphere and reducing the so-called greenhouse effect.
This in turn pushes the Earth to ice age conditions.
As part of their study, the scientists used a number of methods to reconstruct climatic conditions, which included identifying tiny fragments of Antarctic rock that had been deposited in the open ocean by melting of an iceberg.
The rock fragments were recovered from sediments recovered by the 361 International Sea Discovery Program (IODP) Tour, representing over 1.6 million years of history and one of the longest detailed archives of icebergs. Antarctica.
The study found that these deposits, known as ice debris, consistently appeared to lead to changes in ocean deep circulation, reconstructed from the chemistry of deep-sea fossils called foraminifera.
The team also used new climate model simulations to test their hypothesis, finding that freshwater volumes could be moved by the icebergs.
Study lead author Aidan Starr, of Cardiff University ‘s School of Earth and Environmental Sciences, said: “We were surprised to see that this lead – weak relationship was present at the beginning of each ice age for the next 1.6 million years. The key role of the South Sea and Antarctica in global climate has been considered but it was so encouraging to see it so clearly in geological evidence. “
Professor Ian Hall, co-author of the study and co-lead scientist of the IODP Expedition, also from the School of Earth and Environmental Sciences, said: “Our results provide the link needed on how Antarctica and the South Sea dealt with nature. the rhythms of the climate system associated with our orbit around the sun. “
Over the past 3 million years, the Earth has fallen steadily in conditions of ice age, but it is currently within an interspecific period where temperatures are warmer.
However, due to the rise in global temperature due to anthropogenic CO2 emissions, the researchers suggest that the natural rhythm of ice age cycles may be broken down as the South Sea is likely to be too warm for the Antarctic iceberg to travel far enough to encourage the changes in sea circulation. needed to improve ice age.
Dr Hall believes the findings can be used to understand how our climate might address anthropogenic climate change in the future.
“Similarly as we see an increase in major losses from the Antarctic continent and iceberg activity in the South Sea, as a result of warming associated with conventional human greenhouse gas emissions, the Our study confirms the importance of understanding iceberg signals and melting patterns in developing stronger predictions about their future impact on marine circulation and climate, “he said.
Professor Grant Bigg, from the University of Sheffield’s Department of Geography, who contributed to iceberg model simulations, said: “Modern modeling of icebergs within the climate model is essential for identifies and supports the idea of ice debris of the effects of Antarctic ice melting water. which is ahead of glacial bike rides. “
The Cardiff University-led study was funded by NERC.