Ancient Rain: Historic monsoons could help us respond to climate change

Researching the Indian summer monsoon can allow us to develop a better understanding of our changing climate says PhD student, Katrina Nilsson-Kerr.

Image for post
Image for post
The valleys of Madhya Pradesh, India, during monsoon season — Rajarshi MITRA under Creative Commons BY 4.0 license

Late Pleistocene: Time of the Ice Ages

The climate of the past ~1.2 million years has been characterised by fluctuations between warm interglacial periods and subsequent growth of ice-sheets during glacial periods recurring every 100,000 years. These cycles are thought to be regulated by variations in the amount of solar insolation received on Earth due to changes in the Earth’s position relative to the sun. Coupled with this external climate forcing, internal climate feedbacks (such as greenhouse gas concentrations) act to amplify the climate response to insolation. Assessing the behaviour of the monsoon during the penultimate deglaciation (~140–130 thousand years ago), subsequent warmth of the last interglacial (~130–118 thousand years ago) and return to glacial conditions, we intend to unlock the behaviour of the monsoon to ‘natural’ (i.e. non-anthropogenically influenced) climate changes and assess its relationship with other aspects of Earth’s internal climate system (e.g. ice volume).

Image for post
Image for post
Seven Sister Waterfall in Gangtok, India — Rajarshi MITRA under Creative Commons BY 4.0 license

Tiny fossils, big information

Changes in rainfall, river runoff and temperature forced by past Indian Summer Monsoon variability can be revealed in the shell chemistry of tiny (about the size of a sand grain) ocean-dwelling organisms called foraminifera. These organisms build their shells from calcium carbonate, soaking up the chemistry of the seawater surrounding them as they do this. The chemistry of the seawater that they lock into their shells can record the temperature of the seawater that they grew in and how fresh or salty the water was. At the end of their life cycle, these calcium carbonate shells remain intact, sink and are buried on the ocean floor. A wealth of information on past climate can be accessed by drilling into the ocean floor to retrieve marine sediment cores in which these fossils can be found and subsequently analysed using geochemical techniques. Applying these techniques to foraminifera that once lived in the waters of the northern Bay of Bengal, receiving both monsoon rainfall and induced river runoff from the Ganges-Brahmaputra systems, provides clues to unlocking how the monsoon reacted to past climate changes.

Written by

The home of free learning from The Open University.

Get the Medium app

A button that says 'Download on the App Store', and if clicked it will lead you to the iOS App store
A button that says 'Get it on, Google Play', and if clicked it will lead you to the Google Play store