A new study has found that India summer monsoon rainfall and the Arabian Sea fish supporting upwelling are influenced by sunlight in different hemispheres, challenging the long held view that the South Asian monsoon functions as a single system.
Researchers Qin Wen of Nanjing Normal University and Zhengyu Liu of Ohio State University analysed climate records spanning the past 150,000 years. They compared rainfall evidence preserved in cave formations across India and China with Arabian Sea sediment records that capture changes in ocean upwelling.
The study found that stronger Northern Hemisphere summer sunlight strengthens rainfall over the Indian subcontinent. However, Arabian Sea upwelling is more closely linked to Southern Hemisphere summer sunlight.
According to the researchers, warming over southern Africa can trigger rising air and atmospheric changes that weaken southwesterly winds over the Arabian Sea. Weaker winds reduce the movement of surface water away from the coast, resulting in less cold nutrient rich water rising from below.
This upwelling supports plankton growth and plays an important role in sustaining Arabian Sea fisheries.
The findings could have implications for future food and water security. Climate projections indicate heavier monsoon rainfall over land but potentially declining nutrient supplies and marine productivity in the Arabian Sea.
The study was published in the Proceedings of the National Academy of Sciences.