Reading past climates to see the futureThe Southern Ocean refers to the vast circumpolar body of water that surrounds Antarctica, allowing free exchange of seawater between the Atlantic, Pacific and Indian Oceans. With the massive Antarctic Circumpolar Current circling the Southern Ocean, largely preventing north-south flow across it and thereby isolating Antarctica from the subtropics, many scientists believe the existence of the Southern Ocean acts to cool Antarctica. But what other climate patterns might the Southern Ocean control?  Air temperature response to Drake Passage opening The diagram on the right shows the global air temperature response to 'opening' the Drake Passage gap - the ocean chokepoint between the southern tip of South America and the Antarctic Peninsula. Climate modelling by University of New South Wales scientists suggests that the gradual cooling of Antarctica when it was first formed was due in part to the establishment of the Southern Ocean. Professor Matthew England and graduate student Willem Sijp ran a coupled atmosphere-ocean-ice model on the School's high-performance computing facilities. They wanted to find out how the isolation of Antarctica, with the opening of the Drake Passage, affected global climate. The results, published in the Journal of Climate, are likely to help improve global climate models used to predict the severity of human-induced climate change. The opening of the Drake Passage some 30 million years ago was the last chapter in the 50-million-year history of the break-up of Gondwana. The loss of the last land bridge between Antarctica and other landmasses caused the Southern continent to freeze as the Antarctic Circumpolar Current was established. This current transports cold water around Antarctica, cutting the continent off from the warm subtropical waters to the north. In their simulations, Sijp and England tested three landmass configurations.  Geographic isolation and the circumpolar current are important factors affecting Antartica's frozen climate. In one scenario, the southern gateway was open. In another it was open but of a shallow depth. In the third it was closed. They ran an Earth system climate model, which factors in ocean and atmospheric circulation, a hydrological cycle and the impact of sea ice. To isolate the effect of the Antarctic landmass change from other factors, they kept all other parameters, including carbon dioxide levels, constant at modern-day values. They found that the isolation of Antarctica depressed the continent's temperature by up to 7 degrees-C°. The geography of landmasses in the deep south were also found to affect climate in the North Atlantic by controlling ocean circulation north of the Gulf Stream. Our understanding of the future greenhouse world relies in part on inferences made from palaeoclimate records. The UNSW research will help scientists understand Antarctic palaeoclimate data by increasing the knowledge of the role of plate tectonics in past climates. 'These climate models run over a global domain, calculating values for as many as 10 million variables every hour for simulations of thousands of years,' England said. 'This can only be achieved on state-of-the-art computing facilities, such as those housed in the School of Mathematics.' More Information
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