Southern Ocean and Climate Change: Past and Future Perspectives

Eric J. Barron¹, Dan Seidov¹, and Thomas Stocker²

One of the important new findings in climatology is warming of the ocean, including its abyss, by a rate of a half degree ºC or more per century. This ocean warming over the last several decades reflects the linkage between the ocean thermohaline history and global climate change. Historical observations and paleoclimate data reveal significant climate variability on time scales of decades to millennia. The North Atlantic and its associated deepwater formation has been the consensus focal point of this variability for decades. However, new analyses indicate that the southern deepwater source can also change dramatically on millennium and shorter time scale. Climatic impact of such changes depend on the pattern of ocean circulation, and can, in turn, substantially alter this pattern. AGU Special Session OS21 targets the role of the Southern Ocean in climate change that happen during the glacial cycles on different time scales. Glacial cycles of the Pleistocene are one of the hot topics that are addressed in the session. It has recently been discovered that the Southern Hemisphere led Northern Hemisphere changes during parts of the glacial cycles of Pleistocene, implying a seesaw–type oscillation of the global ocean conveyor. Additionally, global warming related melting of sea ice and ice sheets in Antarctica has the  potential to cause a further slowdown of the southern deepwater source. Future changes that can be caused or be influenced by southern meltwater events form another topic of discussion. Millennium-scale variability is thought to be controlled by a so-called ocean bi-polar seesaw and supports a strong case for more focus on the role of the Southern Ocean in the glacial cycles. For example, it is believed that the Little Ice Age was caused by stronger formation of the Antarctic Bottom Water compared to today. Observational, proxy data, modeling and synthesizing work presented in OS21 session reflects a growing demand for a better assessment of the role of the Southern Ocean in driving changes of the global ocean circulation and climate and indicates that the Southern Ocean impact on climate is becoming a new focal point of studying the climate system.