Reconstruction of Asian monsoon intensity changes using a lacustrine sediment core from Lake Biwa, Japan : Contradiction of Milankovitch=Kutzbach theory and solution

Abstract

The Chinese loess-palaeosol sequences and speleothems are two of the most representative records of past monsoon intensity changes. While the former suggests that monsoon intensity is most closely linked to the glacial-interglacial cycles, the latter shows very convincingly that the main cause of monsoon changes is the insolation changes, generating unsolved contradiction between the two opposing views. Nakagawa et al. (2008) tried to solve this problem by quantitatively reconstructing seasonal climate changes of the last 450 kyr, using pollen data of a sediment core from Lake Biwa, Japan. In their results, both Siberian and Pacific air mass temperatures typically oscillate at glacial-interglacial cycle. However, the signals of the glacial-interglacial cycles are cancelled-out in the land-ocean temperature gradient and summer monsoon proxies. Instead, they were typically controlled by the insolation changes which (at this latitudinal zone) show a dominant 23-kyr precession cycle. An exception to this rule was the period of relatively low insolation amplitude, during which the glacial-interglacial cycle exerts more important control over monsoon changes. Here we argue the following points : first, we introduce a relatively simple model/theory which is able to account for all those observations. Second, we propose a possible link between monsoon changes and the 23-kyr super ENSO. Finally, we discuss a problem involved in the loess-palaeosol sequences as the recorder of the monsoon intensity changes.