Melting icebergs are key to sequence of an ice age, scientists find

New study unravels long-standing climate mystery and provides insight into how our planet may change in the future

01/14/2021 | 9:06 AM

Scientists claim to have found the ‘missing link’ in the process that leads to an ice age on Earth. Melting icebergs in the Antarctic are the key, says an international team of scientists including earth scientists Martin Ziegler (Utrecht University) and Jeroen van der Lubbe (Vrije Universiteit Amsterdam), triggering a series of chain reactions that plunges Earth into a prolonged period of cold temperatures. The samples for this study were recovered by the International Ocean Discovery Program (IODP) and the findings have been published today in Nature. “Until now we had a good idea how the planet gets out of an ice age. Our results give us now finally some clues on how an ice age is triggered,” Dr Ziegler explains.

It has long been known that ice age cycles are paced by periodic changes to Earth’s orbit of the sun, which subsequently changes the amount of solar radiation that reaches the Earth’s surface. However, up until now it has been a mystery as to how small variations in solar energy can trigger such dramatic shifts in the climate on Earth. 

Shifting of freshwater
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, shifting huge volumes of freshwater 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. Over the past 3 million years the Earth has regularly plunged into ice age conditions, but at present is currently situated within an interglacial period where temperatures are warmer.

Disruption of natural rhythm
However, due to the increased global temperatures resulting from anthropogenic CO2 emissions, the researchers suggest the natural rhythm of ice age cycles may 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 required for an ice age to develop.

Reconstructing the past
As part of their study the scientists used multiple techniques to reconstruct past climate conditions, which included identifying tiny fragments of Antarctic rock dropped in the open ocean by melting icebergs. 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 importance of understanding iceberg trajectories
The team also used new climate model simulations to test their hypothesis, finding that huge volumes of freshwater could be moved by the icebergs. Professor Ian from Cardiff University, who is one of the co-authors of the study believes that 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 the mass loss from the Antarctic continent and iceberg activity in the Southern Ocean, resulting from warming associated with current human greenhouse-gas emissions, our study emphasises the importance of understanding iceberg trajectories and melt patterns in developing the most robust predictions of their future impact on ocean circulation and climate,” he said.

Drilling Activity

Photo: Lucas Lourens