Tectonic and climatic drivers of Asian monsoon evolution

Area of Science:

• Paleoclimatology
• Climate Dynamics
• Earth System Science

Background:

• Asian Monsoon rainfall is crucial for global agriculture and water resources.
• Understanding the drivers of monsoon variability is key to predicting future climate change.
• Previous studies have debated the relative influence of various factors on monsoon evolution.

Purpose of the Study:

• To reconstruct Indian summer monsoon and South East Asian monsoon rainfall over the past 30 million years.
• To determine the dominant drivers of monsoon variability on orbital and longer timescales.
• To elucidate the complex interplay of factors shaping monsoon evolution.

Main Methods:

• Utilized model-based reconstructions of monsoon rainfall.
• Analyzed millennial-resolution data spanning 30 million years.
• Quantified the contributions of orography, precession, atmospheric CO2, ice sheets, and ocean gateways.

Main Results:

• Precession was identified as the dominant direct driver of orbital variability in monsoon rainfall.
• South East Asian monsoon evolution was primarily influenced by orographic development.
• Indian summer monsoon evolution involved a complex combination of factors, with orography (39%) and precession (25%) being major contributors.
• Strengthening of the Indian summer monsoon from 15-5 Ma was linked to orography and glaciation.
• Closure of the Panama gateway facilitated the modern Indian summer monsoon state.

Conclusions:

• Monsoon dynamics are shaped by a complex interplay of orbital forcing, tectonic activity, and cryospheric and oceanic changes.
• The Indian summer monsoon has undergone significant evolution, with distinct phases driven by different mechanisms.
• Understanding past monsoon variability provides critical insights for future climate projections.