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What caused the ice sheet to grow?


What caused the end of a warm climate phase and an expansion of the Antarctic ice sheet 14 million years ago? This is the question addressed by Kiel and Bremen palaeoclimatologists in an article for the latest issue of Nature (24/11/05). Their research uncovered a temporal link between a reduction in carbon dioxide (CO²) levels on earth, ice sheet formation and global cooling. The "global cooling" that took place 14 million years ago is attributed by Dr. Ann Holbourn, Professor Wolfgang Kuhnt, Professor Michael Schulz and Dr. Helmut Erlenkeuser to changes in the marine carbon cycle, associated with variations in Earth’s orbit and tilt.

Kuhnt: "We know that the orbital situation, i.e. the path followed by the Earth around the Sun, changes regularly. One such change occurred during the global cooling period 14 million years ago, bringing with it a period of cool Antarctic summers. The Antarctic ice sheet was no longer melting down in summer and began to grow steadily. For the first time we can reconstruct in great detail the history of this glacial expansion, which took place in about 80,000 years, a short time in geological terms.”

Researchers at the Institute for Geosciences of the Christian-Albrechts-Universität in Kiel and their colleague from DFG Research Center Ocean Margins in Bremen studied marine sediments from two cores in the eastern and western subtropical Pacific. The analysis of oxygen and carbon isotopes in the calcite shells of tiny organisms (foraminifers) living at the sea floor allowed to track changes in ice volume and carbon dioxide levels. The team investigated an interval of about two million years with a sampling resolution of 4,000 years.

The research is funded by the German Research Foundation (DFG) within the framework of the German contribution to the international "Integrated Ocean Drilling Program".

The following images are available already:

Photo 1:

Calcareous shell (about half mm in size) of single cell marine organism (foraminifer), which allow to track climate change 14 million years ago.
Copyright: The Natural History Museum, London

Photo 2:

Messengers from ancient time: calcareous shells of foraminifers (about half mm in size) that lived at the seafloor provide evidence of a major increase in Antarctic ice volume 13-14 million years ago.
Photo: Juergen Haacks, Copyright: University of Kiel

Photo 3:

By analysing the shells of tiny marine organisms found in deep-sea cores Professor Wolfgang Kuhnt and his team reconstruct the expansion of the Antarctic ice-sheet more than 13 million years ago.
Photo: Juergen Haacks, Copyright: University of Kiel

Photo 4:

The Antarctic ice-cap expanded 14 million years ago with dramatic environmental consequences.
Photo: W. Hagen, Copyright: University of Kiel / Institute of Polar Ecology

Susanne Schuck | alfa
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