地中海深海堆積物(ODP site 974B)で検出された過去450万年間の気候変動 Climatic Changes Recorded in the Deep Sea Sediments (ODP Site 974B) of the Mediterranean Sea during the Last 4.5 Ma
We attempted to clarify changes of magnetic susceptibility and clay mineralogy of the deep-sea sediments in ODP site 974B during the last 4.5 Ma. These sediments are composed mainly of calcareous nannoplankton ooze with organic matters and eolian dusts. Sequential changes of illite crystallinity, expressing as full width of half maximun of 10 A peaks by X-ray diffraction patterns, indicate changes of dry-wet climatic conditions in a supply area.<BR>Due to the atmospheric circulation pattern influenced by the Himalayan -Tibetan Plateau, the tropical easterly jets have lead northern Africa to dry conditions. So, it is possible to settle the uplift age of the Himalayan-Tibetan Plateau from the beginning age of dry climatic condition in northern Africa.<BR>As a results, we could clarify two evidences as follows:<BR>1) Illite concentrations and magnetic susceptibility indicate concentrations of eolia n dust carrying from northern Africa have increased from 3.5 Ma ago. In other words, the recent atmospheric circulation, that is carrying eolian dust into the Mediterranean Sea, has been confirmed from 3.5 Ma ago.<BR>2) Based on oscillations of illite crystallinity during the 4.5 Ma, the northern Africa region became dry condition 0.8 Ma ago. We thought that this event of 0.8 Ma was caused by the uplift of the Himalayan-Tibetan Plateau.