Scientists have revealed new knowledge about Earth's history of climate change.
The lead author of the study, Professor Heiko Pälike, belonging to the University of Southampton and National Oceanography Centre was also the co-chief scientist of the Integrated Ocean Drilling Programme (IODP) cruise conducted in the Pacific Ocean. The IODP was a four-month expedition conducted on board the JOIDES Resolution drilling vessel. Over 100 scientists and technicians took part in the expedition. They drilled at eight locations between water depths of 4.3 and 5.1 km for 6.3 km. The team recovered 6.3 km of sediment cores.
The cores revealed that geochemical processes that took place in the ocean depths influenced the development of the global climate over the past 55 million years. Other processes apart from man-made CO2 have influenced the carbon cycle and global warming.
The study showed that volcanoes are a major contributor of CO2, while weathering of carbonate rocks have helped remove greenhouse gases. The carbonate compensation depth (CCD) of the deep ocean reflects how these processes balance themselves.
CCD is considered to be the depth at which mineral calcite is dissolved in the oceans. This boundary has not been constant over time and has been found to be fluctuating. It has been found to deepen under ice age conditions and shallow during warm climatic conditions.
The cores drilled by the scientists demonstrated that the interplay between the carbon cycle and the global development of climate was a two-way affair. The CCD fluctuated five times within 200 m and 900 m, during the period from 46 to 34 million years ago. During this period, the Earth was an icehouse. The CCD fluctuations corresponded to the cooling and warming phases that existed between 250,000 and one million years ago. The CCD moved up by 600 m 18.5 million years ago and 2.5 million years later, it fell down to 4.7 km. Presently, the CCD in the Pacific is at a depth of 4.5 km.
The study has been published in the journal Nature.
Source: http://www.southampton.ac.uk/
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