Indian Monsoon

Monsoon, a major wind system that seasonally reverses its direction—such as one that blows for approximately six months from the northeast and six months from the southwest.
The most prominent monsoons occur in South Asia, Africa, Australia, and the Pacific coast of Central America. Monsoonal tendencies also are apparent along the Gulf Coast of the United States and in central Europe; however, true monsoons do not occur in those regions.
The primary cause of monsoons lies in different warming trends over land and sea, though other factors may be involved. Seasonal changes in temperature are large over land but small over ocean waters, and monsoons blow from atmospheric heat sinks (that is, cold regions with high atmospheric pressure) toward heat sources (warm regions characterized by low atmospheric pressure). Consequently, monsoon winds typically travel from sea to land in summer and from land to sea in winter.

About 180 million years ago, India separated from the ancient supercontinent Gondwana and took a long northward journey of about 9,000 km to join Eurasia. During this journey, the subcontinent moved from the southern hemisphere, crossed the Equator to reach its current position in the northern hemisphere.
Due to these changing latitudes, it experienced different climatic conditions, and the new study has tried to map these climatic variations using leaf fossils.
The evolution of the monsoonal climate in India is still debatable and not fully understood. Though recent data indicates that the monsoon system we experience now dates back to about 25 million years, it is still unclear how the climate was during its long voyage

The team analysed the morphological characters of fossil leaves collected from Deccan Volcanic Province, East Garo Hills of Meghalaya, Gurha mine in Rajasthan and Makum Coalfield in Assam.
The four fossil assemblages were found to be from four different geological ages and helped to study the climate during 65, 57, 54, and 25 million years ago respectively.
It has been observed from across the globe that plant leaf morphological characters such as apex, base and shape are ecologically tuned with the prevailing climatic conditions to adapt for all the seasons throughout the year.
They applied this model to characterise the past monsoon from fossil leaves.
The results indicated that the fossil leaves from India were adapted to an Australian type of monsoon and not the current Indian monsoon system during its voyage. The reconstructed temperature data show that the climate was warm (tropical to subtropical) at all the studied fossil sites with temperatures varying from 16.3–21.3 degrees C. All the fossil sites experienced high rainfall, which varied from 191.6 cm to 232 cm.

India was the only subcontinent to have crossed from the southern hemisphere to the northern hemisphere, it is a laboratory to study bio-geo changes and understand how the flora and fauna changed accordingly.
We can understand the evolutionary history of Indian monsoon and its role in the evolution of biodiversity hot spots in South and Southeast Asia. This will help in the conservation of modern biodiversity hotspots.
Understanding the past dynamics of Indian monsoon will also help in climate modelling for future monsoon prediction

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