As ice ages on Earth waxed and waned over time spans of thousands of years, there were substantial fluctuations in monsoon intensity over India. But while the rains in north-eastern India declined during the last ice age, the monsoon in East Asia remained remarkably robust, a new study has found. During an ice age, vast sheets of ice and glaciers cover much of the planet. The last ice age occurred 75,000 to 20,000 years ago.
A team of Chinese scientists, along with colleagues in the U.S., used levels of isotopes of thorium and oxygen found in stalagmites in a cave in south-western China to reconstruct how the monsoon over north-eastern India, the Himalayan foothills, Bangladesh and northern Indochina fluctuated over the past 2,52,000 years. Their research has just been published in the Proceedings of the National Academy of Sciences.
The paper reconfirms earlier work showing that the Indian monsoon weakened during the ice ages, observed J. Srinivasan of the Centre for Atmospheric and Oceanic Sciences at the Indian Institute of Science, Bangalore.
In their paper, Yanjun Cai and the other scientists also drew on previously collected isotopic data from caves in eastern China as well as computer simulations. Rains over north-eastern India were reliant on moisture transported from the northern Bay of Bengal, which declined during the last ice age. In contrast, East Asian rains could draw on moisture from the Indian Ocean, the South China Sea as well as the Pacific Ocean, and hence was strong during that frigid period, they noted.
