Growth of Antarctic ice sheet triggered warming in the Southern Ocean
Scientists of the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI), have deciphered a supposed climate paradox from the Miocene era by means of complex model simulations.
The Southern Ocean
The expansion of the Antarctic ice shield 14 million years ago was followed by a warming of the Southern ocean's surface temperature. Photo: Frank Roedel, Alfred-Wegener-Institut
When the Antarctic ice sheet grew to its present-day size around 14 million years ago, it did not get colder everywhere on the Earth, but there were regions that became warmer. A physical contradiction?
No, as AWI experts now found out, the expansion of the ice sheet on the Antarctic continent triggered changes in winds, ocean currents and sea ice in the Southern Ocean that in the end led to the apparently contrary developments. The scientists report this in a new study published online in the journal Nature Geosciences.
From a geological perspective, the ice sheet of Antarctica is still relatively young. As climate researchers know from sediment samples and calcareous Foraminifera shells, the ice sheet grew to its present-day size around 14 million years ago. At the same time the surface temperature of the Southern Ocean rose by up to three degrees Celsius back then – a seemingly contradictory development, for which climate scientists had no logical explanation for a long time.
“If you imagine that the Antarctic ice sheet grew to its present size in a period of 100,000 years, it seems reasonable to suppose that self-reinforcing climate processes set in during this growth period and further boosted the cooling effect. One could assume, for instance, that the expanding ice sheet reflected more and more solar energy into space, as a result of which the air over the continent became colder and strong offshore winds swept over the ocean, cooled the water and created a huge amount of sea ice. Our climate data, however, paint a different picture,” says AWI climate researcher Dr. Gregor Knorr.
He and his AWI colleague Prof. Dr. Gerrit Lohmann succeeded in depicting the climate conditions at that time in a coupled atmosphere-ocean model and in this way examined what changes the formation of the Antarctic ice sheet triggered in the climate system.
“Our simulation results show that the air temperature over the continent actually decreased by up to 22 degrees Celsius when the ice sheet grew, which led to cooling in some regions of the Southern Ocean. At the same time, however, the surface temperature in the Weddell Sea rose by up to six degrees Celsius,” says Gregor Knorr.
The AWI climate scientists looked for the causes of these contrary changes in their model experiments and found them in the wind. “The expansion of the Antarctic ice sheet led to changes in the wind patterns over the Weddell Sea, for example. As a consequence, there was a shift in the flow of warm water towards the pole and the sea ice in this marine region declined,” explains the AWI climate modeller.
These changes on the surface of the ocean brought about further changes in deep water, which in turn boosted the temperature rise in the surface water in a way unknown to the researchers up to now.
“Our model calculations helped us to develop a new understanding of the Earth system processes back then. Today we can explain what influence the formation of the Antarctic ice sheet had on temperature curves in the Southern Ocean of that time and how the recorded climate changes came about in marine sediment cores,” says Gregor Knorr.
At the same time a great challenge arises for climate scientists as a consequence of these new insights. “On the one hand, our results show that we can understand climate processes by means of models to interpret data from climate history. On the other hand, the results also confirm that feedback mechanisms between individual climate factors are substantially more complex than we had previously assumed,” says Gerrit Lohmann.
Can these new model calculations and insights be used for forecasts regarding current climate change? Gregor Knorr: “No, not directly. Models used to simulate climate change scenarios for the coming 100 years have a much finer resolution and ice sheet changes are not taken into account. For us it was important to gain a better understanding of how the climate system reacts to dramatic changes over a period of 100,000 years and more. Nevertheless, we cannot rule out that similar mechanisms might also play a role for climate changes in the distant future.”
Notes for Editors:
Please find printable images at http://www.awi.de/en/news/press_releases/. The original paper was published under the following title in the online portal of Nature Geoscience on 6 April 2014:
Gregor Knorr / Gerrit Lohmann: Climate Warming during Antarctic ice sheet expansion at the Middle Miocene transition. Nature Geoscience, Vol. 7, April 2014, DOI: 10.1038/NGEO2119 (Link: http://www.nature.com/ngeo/journal/vaop/ncurrent/full/ngeo2119.html)
Your scientific contact persons at the Alfred Wegener Institute are:
• Dr. Gregor Knorr (tel.: 0049 471 4831-1769, e-mail: Gregor.Knorr@awi.de)
• Prof. Dr. Gerrit Lohmann (tel.: 0049 471 4831-1758, e-mail: Gerrit.Lohmann@awi.de)
Your contact person in the Dept. of Communications and Media Relations is Sina Löschke , tel. 0049 471 4831-2008 (e-mail: email@example.com).
Follow the Alfred Wegener Institute on Twitter and Facebook. In this way you will receive all current news as well as information on brief everyday stories about life at the institute.
The Alfred Wegener Institute conducts research in the Arctic, Antarctic and oceans of the high and mid-latitudes. It coordinates polar research in Germany and provides major infrastructure to the international scientific community, such as the research icebreaker Polarstern and stations in the Arctic and Antarctica. The Alfred Wegener Institute is one of the 18 research centres of the Helmholtz Association, the largest scientific organisation in Germany.
Ralf Röchert | idw - Informationsdienst Wissenschaft
Arctic melt ponds form when meltwater clogs ice pores
24.01.2017 | University of Utah
New Study Will Help Find the Best Locations for Thermal Power Stations in Iceland
19.01.2017 | University of Gothenburg
For the first time ever, a cloud of ultra-cold atoms has been successfully created in space on board of a sounding rocket. The MAIUS mission demonstrates that quantum optical sensors can be operated even in harsh environments like space – a prerequi-site for finding answers to the most challenging questions of fundamental physics and an important innovation driver for everyday applications.
According to Albert Einstein's Equivalence Principle, all bodies are accelerated at the same rate by the Earth's gravity, regardless of their properties. This...
An important step towards a completely new experimental access to quantum physics has been made at University of Konstanz. The team of scientists headed by...
Yersiniae cause severe intestinal infections. Studies using Yersinia pseudotuberculosis as a model organism aim to elucidate the infection mechanisms of these...
Researchers from the University of Hamburg in Germany, in collaboration with colleagues from the University of Aarhus in Denmark, have synthesized a new superconducting material by growing a few layers of an antiferromagnetic transition-metal chalcogenide on a bismuth-based topological insulator, both being non-superconducting materials.
While superconductivity and magnetism are generally believed to be mutually exclusive, surprisingly, in this new material, superconducting correlations...
Laser-driving of semimetals allows creating novel quasiparticle states within condensed matter systems and switching between different states on ultrafast time scales
Studying properties of fundamental particles in condensed matter systems is a promising approach to quantum field theory. Quasiparticles offer the opportunity...
19.01.2017 | Event News
10.01.2017 | Event News
09.01.2017 | Event News
24.01.2017 | Earth Sciences
24.01.2017 | Life Sciences
24.01.2017 | Physics and Astronomy