Regulation of monsoon climate by two different orbital rhythms

By contrast, precipitation at several places on Earth is oscillating at 23,000 year cycles. However, the reason two different climatic parameters (temperature and rain fall) show different rhythms is not well understood. Nakagawa et al. reconstructed climate changes of the past 450,000 years using fossil pollen grains from a Japanese lake sediment.

The results clearly showed that the temperatures of both continental and oceanic air masses fluctuate at 100,000 year cycles, whereas the land-ocean temperature gradient and summer rainfall oscillates at 23,000 year cycles. The land-ocean temperature gradient is the direct cause of the East Asian monsoon, which in turn is responsible for the Japanese summer rain fall. The 23,000 year climatic cycle coincides with the strongest periodicity of changes in the brightness of the sun.

Based on these findings, Nakagawa et al. propose that the direct solar beam is regulating the land-ocean temperature gradient (and hence monsoon intensity and rainfall) through different heat capacities between land and oceans, and this process is essentially independent from glacial-interglacial cycles.-Geological Society of America