Modelling stable water isotopes in monsoon precipitation during the previous interglacial

详细信息    查看全文

• 作者：Jesper Sjolte ; Georg Hoffmann
• 关键词：Monsoon ; Eemian interglacial ; Stable water isotopes ; Modelling
• 刊名：Quaternary Science Reviews
• 出版年：1 February, 2014
• 年：2014
• 卷：85
• 期：Complete
• 页码：119-135
• 全文大小：9700 K

文摘

Changes in the tropical hydrological cycle have been recorded world wide in speleothem records dating back more than 200,000 years for some areas. Numerous empirical and modelling studies have demonstrated a strong link between the intensity of the northern hemisphere monsoon and the precessional insolation cycle (鈭?3聽ka (thousand years)). Here we present simulations of the climate conditions of the previous interglacial, the Eemian (115-130聽ka BP), using a general circulation model. We focus on changes in the tropical hydrological cycle and in the monsoon in particular. The model is equipped with a module for computing the water isotopic composition of all water reservoirs represented by the model. Our analysis of the simulated water isotope signals indicates that this key palaeo-proxy, i.e. the ¹⁸O or Deuterium signal in precipitation, is controlled by varying factors in different tropical areas: The main control on ¹⁸O for the Indian summer monsoon is the local precipitation amount, in accordance with the traditional interpretation, while the main control of ¹⁸O for East Asia is downwind depletion of ¹⁸O in vapour along the transport path. Over Africa the model simulates a strong gradient in the ¹⁸O anomalies during the Eemian climatic optimum, with depleted values in the east and relatively enriched ¹⁸O content in the west. This pattern is the result of a combination of the local 鈥渁mount effect鈥?and an anomalous zonal moisture transport. The influence of the SSTs anomalies on the placement of the Intertropical Convergence Zone (ITCZ) is found to be of major importance for the precipitation amount in the coastal regions of tropical South America. For the western part of South America a decrease in precipitation is seen for the Eemian climatic optimum, while an increase is seen for the eastern part. Our results underline the importance of reviewing the mechanisms causing isotopic changes in proxy records and further investigating the causes for past shifts in the ITCZ.