By Rowenna Hoskin | Science Editor
Scientists at Cardiff University claim to have found the ‘missing link’ in the process that leads to an ice age forming on Earth; the team’s findings have been published in Nature.
The ice age process has been shrouded in mystery, the mechanics of how small variations in solar energy can trigger such dramatic shifts in the Earth’s climate.
Scientists say that the key to the mystery is melting icebergs in the Antarctic: the liquefaction of icebergs triggers a series of chain reactions that plunge Earth into a long period of cold temperatures.
Scientists have known for a long time that ice ages are affected by periodic changes in the orbit of Earth around the sun, which in turn alters the amount of solar radiation that reaches the Earth’s surface.
In their study, the team proposed that given the specific conditions of Earth’s orbit, Antarctic icebergs melt further and further away from Antarctica, causing a shift of high volumes of freshwater away from the Southern Ocean and into the Atlantic Ocean.
This shift of freshwater means that the Southern Ocean gets saltier and the North Atlantic gets fresher; thus the overall ocean circulation patterns begin to dramatically change. In this way CO2 is extracted from the atmosphere and the greenhouse effect is subsequently reduced.
As the planet no longer has the added gas to trap the sun’s solar energy, the planet does not heat up; instead, Earth is pushed into ice age conditions.
In their study, scientists used multiple techniques to reconstruct past climate conditions, which included identifying minuscule fragments of Antarctic rock dropped in the open ocean by melting icebergs.
These fragments, known as Ice-Rafted Debris, were obtained from sediments recovered by the International Ocean Discovery Program (IODP) Expedition 361. They represent over 1.6 million years of history and one of the longest detailed archives of Antarctic icebergs.
Ice-Rafted Debris appeared to consistently lead to changes in ocean circulation, reconstructed from the chemistry of deep-sea fossils called foraminifera.
In addition to these fragments, the team used a new climate model simulation to run their hypothesis, discovering that huge volumes of freshwater could be moved by the icebergs.
The lead author of the study Aidan Starr, from Cardiff University’s School of Earth and Environmental Sciences, said: “We were astonished to find that this lead-lag relationship was present during the onset of every ice age for the last 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.”
Professor Ian Hall, the study’s co-author and the co-chief scientist of the IODP Expedition, also from the School of Earth and Environmental Sciences, said: “Our results provide the missing link into how Antarctica and the Southern Ocean responded to the natural rhythms of the climate system associated with our orbit around the sun.”
Over the course of the last 3 million years, the planet has regularly been plunged into ice age conditions, but currently, it is situated within an interglacial period where the temperatures are warm.
Unfortunately, the increase in anthropogenic CO2 emissions have directly caused an increase in temperature which research suggests has disrupted the natural ice age cycle. The Southern Ocean is predicted to become too warm for Antarctic icebergs to travel far enough to trigger the necessary ocean circulation that is required for an ice age to develop.
Professor Hall believes that the results can be used to further our knowledge in how our climate will 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.
The Cardiff University-led study was funded by NERCScience and Technology Rowenna Hoskin