One million years of precipitation history of the monsoon reconstructed

With its wind and precipitation patterns, the South Asian Monsoon influences the lives of several billion people. Recent studies indicate that its drivers are more complex than Scientists from the GEOMAR Helmholtz Center for Ocean Research Kiel have published a report on the history of the Indian Ocean. Nature Communications. It points to connections with controlling processes in the southern hemisphere that have received little attention so far.

The second half of the year is a year of drought-the South Asian Monsoon with its seasonally changing rainfall and wind directions has always strongly influenced the lives of people around the Indian Ocean. It is of crucial importance for agriculture and thus the food supply of several billion people. At the same time, floods and landslides in densely populated areas can be catastrophic.

But how does this important climate system work? And how will it change in response to global warming? "The best coupled ocean-atmosphere models still have problems to simulate the South Asian Monsoon," says lead author Dr. Daniel Gebregiorgis from the GEOMAR Helmholtz Center for Ocean Research Kiel, who is working at Georgia State University in Atlanta (Georgia, USA). Together with colleagues from Kiel and the USA, he investigates new climate records of the history of the South Asian Monsoon, which point to connections and monsoon drivers in the southern hemisphere that have previously received little attention.

In its simplest form, the monsoon is driven by pressure and temperature differences between the Asian continent and the southern subtropical Indian Ocean. "The variability of the recent geological time periods is caused by the earth's axis," explains Dr. Gebregiorgis.

So far, the main reconstruction of the world is based mainly on two climate archives: sediment cores from the Arabian Sea and stalagmites from caves in China. "The form, however, only to provide information on the Indian subcontinent, while the latter is thought to reflect precipitation of the East Asian Monsoon. Timescale, "explains Ed Hathorne of GEOMAR, co-author of the study.

He and his colleagues have been seduced by the International Ocean Discovery Program. The chemical badysis of the shells of tiny plankton that allows for the reconstruction of the temperature of the seawater during the lifetimes. "Using this we have been able to reconstruct the precipitation in the eastern Indian Ocean for the past one million years," says Dr. Hathorne.

The new record shows that the precipitation of the South Asian Monsoon was weaker during the peak season. "However, we were only able to badociate 30 percent of the variability of monsoon precipitation in the eastern Indian Ocean with fluctuations in the earth's axis inclination." This means that it only plays a subordinate role in the fluctuations of the monsoon, "emphasizes Dr. Gebregiorgis. Instead, the results of the survey of the importance of warming in the southern hemisphere and moisture transport in the equator to the north. "This process has hardly been considered so far," says Dr. Gebregiorgis.

"The evaluation of the new climate archives shows that it is difficult to estimate the reactions of this important climate system to a globally warming atmosphere" leader Prof. Dr. Martin Frank from GEOMAR.

Explore further:
East asian monsoon dynamics discovery

More information:
D. Gebregiorgis et al, Southern Hemisphere Forcing of South Asian monsoon precipitation over the past ~ 1 million years, Nature Communications (2018). DOI: 10.1038 / s41467-018-07076-2