Icebergs in the Antarctic gradually melting further and further from the frozen continent could be the trigger that plunges Earth into a new ice age, study finds.

Researchers from Cardiff University reconstructed past climate conditions and identified tiny fragments of Antarctic rock dropped in the open ocean as part of a study designed to understand how ice ages begin.

Ice age cycles over the past 1.6 million years have been paced by periodic changes to Earth’s orbit of the Sun – changing how much solar radiation reaches the surface.

However, before this study little was known about how changes in solar energy from small changes in the orbit could so dramatically change Earth’s climate.

They found that melting icebergs gradually move freshwater from the Southern to the Atlantic Ocean by melting further from Antarctica – causing a change in ocean circulation and plunging the planet into a cold period – triggering an ice age.

The impact of human-created CO2 emissions could make the Southern Ocean too warm for Antarctic icebergs to reach, bringing an end to this 1.6 million year cycle of ice ages starting with melting icebergs, study authors warned.

In their study, the team propose that when the orbit of Earth around the Sun is just right, Antarctic icebergs begin to melt further and further away from Antarctica.

This results in huge volumes of freshwater being shifted away from the Southern Ocean and into the Atlantic Ocean.

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

This in turn pushes the Earth into ice age conditions, according to the team, who reconstructed past climate conditions including finding tiny fragments of Antarctic rock dropped in open ocean by melting icebergs.

The rock fragments were obtained from sediments recovered by the International Ocean Discovery Program (IODP) that represents 1.6 million years of history.

The study found that these deposits, known as Ice-Rafted Debris, appeared to consistently lead to 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 freshwater could be moved by the icebergs.

Lead author of the study Aidan Starr, said they were astonished to find that the link between iceberg melting and ocean circulation was present during the onset of every ice age for the past 1.6 million years.

‘Such a leading role for the Southern Ocean and Antarctica in global climate has been speculated but seeing it so clearly in geological evidence was very exciting,’ he said.

Professor Ian Hall, co-author of the study and co-chief scientist of the IODP Expedition, from Cardiff, said the results provide a ‘missing link’ in ice age history.