Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
4736696 | Quaternary Science Reviews | 2014 | 17 Pages |
•We run an isotope enabled climate model for time slices during the previous interglacial.•The isotopic amount effect in precipitation is investigated for a number of regions.•Seasonality impacts annual mean isotope composition in Western South America.•For East Asia and Africa moisture advection have major impact.•Large scale patterns of isotope anomalies compare well to collection of proxy records.
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 (∼23 ka (thousand years)). Here we present simulations of the climate conditions of the previous interglacial, the Eemian (115–130 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 “amount effect” 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.