Rapid climate change in the history of the earth
As the "Earth's fridge" and gigantic water reservoir, Antarctica plays a special role as an indicator of the global climate. The examination of drill cores reveals the development within the last million years - meanwhile with a temporal resolution of centuries. "The results exceeded all our expectations," says Rainer Gersonde from the Alfred Wegener Institute for Polar and Marine Research (AWI), describing the success of the recent Ocean Drilling Program (ODP) expedition in the Southern Ocean. "We are now able to record the processes in the ocean during the transition from cold to warm periods in much more detail and to document rapid climate changes and the stability of environmental conditions with a temporal resolution in the range of centuries and shorter. This creates a new dimension for the reconstruction of the Earth's climate history." On March 5, 1998, Dr. Gersonde presented the results of the expedition to the public for the first time at a colloquium of the German Research Foundation (DFG) in Freiburg.
On February 7, the research drilling ship JOIDES Resolution returned to the southern Chilean port of Punta Arenas after a two-month expedition. Together with an international team of 27 geoscientists, deposits on the sea floor were drilled along a section through the Atlantic sector of the Southern Ocean, which can be used to study the climate history of the last 46 million years.
Despite the bad weather, the scientists were able to drill up to 600 meters deep into the deposits of the Southern Ocean at seven positions at water depths between 2000 and 5000 meters. A total of 4000 meters of drill cores are now available to reconstruct the climate and glaciation history of an area that is a key to global climate development.
The ice masses on the Antarctic continent are currently the largest accumulation of ice on earth and are significantly cooling the world ocean. The Antarctic Ocean, which surrounds Antarctica as a ring current, acts as a buffer between the Antarctic ice sheet and the warmer areas further north and plays an important role in the production and distribution of the world's ocean water masses.
One focus of the drilling trip ODP-Leg 177 was the documentation of rapid climate changes as they occurred in the recent geological climate history, i.e. in the last 1.5 million years. Such climate changes were first discovered during drilling through the Greenland ice cap. Investigations show that in the Arctic climate changes with temperature changes of 5 to 10 degrees Celsius have taken place over a period of decades to centuries. The results of the ODP expedition show that there have also been rapid climate changes in the southern polar regions during warm and cold periods. The mechanisms that control these changes are still largely unknown.
Gersonde, who led the expedition together with David A. Hodell from the University of Florida, was already studying deposits extracted during the expeditions with the German research vessel Polarstern. This and studies of ice cores indicate that climate changes in the southern polar regions are ahead of global developments. Whether the Antarctic represents an early detection system for global climate development is to be checked using the newly obtained drill cores. The investigations are carried out at the AWI and five other institutes in the USA and Europe.
First drilling expeditions ten years ago had shown that the Antarctic continent began to ice over 40 million years ago. The result was drastic changes in sea level, global ocean currents and global climate zones. It was only three million years ago that huge masses of ice also formed in the northern hemisphere. The reasons that led to this icing and its timing are not yet known. The interactions between the southern and northern high latitudes and the stability of the Antarctic ice sheets, which if they melted would raise sea levels by 50 to 60 meters, are not well understood. The drill cores from the latest expedition, which document the climate history of the last 46 million years in an exceptionally continuous and well dated manner, are therefore of great importance. First evaluations during the expedition have confirmed this.
The Ocean Drilling Program (ODP) is a joint project involving the USA, Germany, Japan, France, England, Canada and Australia as well as other European and Asian countries. The German contribution is funded by the German Research Foundation (DFG) and the Federal Ministry of Education, Science, Research and Technology. The drill ship JOIDES Resolution has been deployed worldwide as part of the ODP drilling expeditions since 1985. It is fitted with a derrick amidships which rises 62 meters above the waterline. With the help of two main and twelve additional propellers, the ship can be kept precisely above the borehole on the seabed even in great water depths and rough seas of up to seven meters.
The Alfred Wegener Institute, Helmholtz Center for Polar and Marine Research (AWI) in Bremerhaven is part of the Helmholtz Association. It is dedicated to researching the polar regions and also takes a look at topics such as marine biology and climate change.