Research Highlights

Indian summer monsoon melted ice sheets in northern hemisphere

doi:10.1038/nindia.2019.35 Published online 20 March 2019

Long before the end of the last Ice Age, a rise in sea-surface temperature in the Bay of Bengal, followed by a brief, intense spell of Indian summer monsoon (ISM), triggered a thawing of large ice sheets that covered most of the globe, according to new research1.

This research provides fresh insights into millennial-scale climatic changes, highlighting the previously overlooked roles of the ISM in global climate change. 

The ISM is the dominant monsoon subsystem in terms of heat transport across the equator, making it one of Earth’s most dynamic drivers of ocean–atmosphere interactions. Yet, the ISM is grossly under-represented in the ancient records of Asian monsoons.

To pin down the roles of the ISM in global climate change, an international research team, including a scientist from the Indian Institute of Science in Bangalore, India, collected a core sediment that was deposited in the Bay of Bengal between 127,000 and 139,000 years ago.

They then isolated fossilised, surface-dwelling single-celled sea creatures from the sediment and analysed the levels and ratios of oxygen isotope, calcium, magnesium and neodymium in these creatures and the sediment. This analysis revealed the past sea-surface temperature, water salinity, monsoon-induced rainfall and debris run-off from the Ganges and the Brahmaputra into the Bay of Bengal. 

They found that the ISM briefly intensified around 134,000 years ago, preceded by an increase in sea-surface temperature by one degree Celsius. This warming coincided with the early melting of ice sheets in the southern hemisphere. The warm seawater and the intense ISM then transported heat across the equator to the northern hemisphere, causing a rapid retreat of ice sheets there.


1. Nilsson-Kerr, K. et al. Role of Asian summer monsoon subsystems in the inter-hemispheric progression of deglaciation. Nat. Geosci.(2019) doi: 10.1038/s.41561-019-0319-5