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Months of heavy rainfall followed by half a year of drought – the monsoon of South Asia, characterized by seasonal rainfall and changing wind direction, has always strongly influenced the lives of inhabitants of the Indian Ocean. It is of crucial importance for agriculture and therefore for the food supply of billions of people. At the same time, floods and landslides in densely populated areas can be catastrophic.
But how exactly does this important climate system work? And how will this change in response to future global warming? "Even the best coupled ocean-atmosphere models are still struggling to simulate South Asian monsoon rains," says Dr. Daniel Gebregiorgis, senior author of the GEOMAR Ocean Research Center Helmholtz Kiel, who currently works in Georgia. State University in Atlanta. (Georgia, United States). With his colleagues from Kiel and the United States, he investigated the new climate records of the South Asian monsoon story, which highlight links and factors of the monsoon in the United States. Southern hemisphere that have so far been the subject of little attention. The study was published today in the international journal Nature Communications .
In its simplest form, the monsoon is fueled by pressure and temperature differences between the Asian continent and the southern subtropical Indian Ocean. "The variability of the moss during recent geological periods would be due to changes in solar sunshine in the northern hemisphere, caused by the regularly changing tilt of the Earth's axis" says Dr. Gebregiorgis.
The reconstruction of the history of the monsoon relies mainly on two climatic records: cores of sediments from the Arabian Sea and stalagmites from caves in China. "The first, however, provide only information on wind conditions and not on rainfall on the Indian subcontinent, while it has long been thought that the latter reflected the monsoon rains of the East Asia: The two reactions are markedly different from the changes in the summer insolation of the northern hemisphere over the summer, "says Ed Hathorne of GEOMAR, co-author of
He and his colleagues for the first time evaluated East Indian Ocean sediment cores obtained from the International Ocean Discovery program, a chemical badysis of the tiny plankton shells that were deposit and are preserved on the seabed allows to reconstruct the temperature and the amount of fresh water to the sea surface during the life of the organisms. "Thanks to this, we have been able to reconstruct the precipitation in the # 39; e st of the Indian Ocean for a million years, "says Dr. Hathorne.
New data generally indicate that monsoon rains in South Asia were lower during the ice peak. and stronger during warm interglacial times like today. "However, we were able to badociate only 30% of the variability of monsoon rainfall in the eastern Indian Ocean with fluctuations in the tilt of the axis of the Indian Ocean. This means that it only plays a secondary role in the monsoon fluctuations, "says Dr. Gebregiorgis. . Instead, the scientists' findings have highlighted important links with the warming phases of the southern hemisphere and the transport of moisture across the equator to the north. "This process has hardly been considered until now," says Dr Gebregiorgis.
"The evaluation of the new climatological records shows that we have not yet fully understood the monsoon.As long as it is not the case, it is difficult to evaluate the reactions from this important climate system to an atmosphere of global warming ", summarizes Professor Martin Frank of GEOMAR, head of the working group.
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Documents Provided by Center for Oceanographic Research Helmholtz Kiel (GEOMAR) . Note: Content can be changed for style and length.
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