Tropical Process and Its Periodicity in the Deep Sea Records

The earth'sorbital geometry configurates eccentricity, obliquity and precession, which control the seasonal and latitudinal distribution of the insolation on the earth's surface. In the periodic variations of the insolation, the precession cycles of 23 ka and 19 ka are significant at any latitude, and the obliquity cycle of 41 ka is evident only at high and middle latitudes, whereas the eccentricity cycles of 413 ka and 100 ka are nearly faint at any latitude. The traditional orbital theory emphasizes the insolation at high northern latitudes which controls global ice volume and climate change and probably transfers its periodicity to the linear climate system. However, the periodicity of the climatic proxies from the tropics is not identical to that of the insolation. Both the insolation and the tropical process perform strong precession and less strong obliquity cycles, highlighting the dominant control of the precession modulated insolation on the tropical climatic changes. Nevertheless, the tropical process especially the monsoon system commonly performs strong eccentricity cycles of 100 ka and 413 ka, as well as significant semi-precession cycles around 10 ka, which are nearly absent in the insolation. These features indicate that the non-linear tropical climatic process doesn't simply respond to the insolation change, nor is completely controlled by the high northern latitudes, but possesses feature of its own.