Millenial simulation of global water isotope distribution with the ECHAM4 AGCM

The water isotopic composition of precipitation (δ18OPrec or δDPrec) is a physical tracer of hydro-climatic conditions both today and for the past. In high-latitudes the δPrec composition is strongly linked to condensation temperatures whereas in low latitudes precipitation amount, surface temperatures in the oceanic source areas or recycling intensity affect the isotopic signal. The isotopic signal is archived in many different continental systems such as high altitude or polar glaciers, speleothems, tree ring cellulose or fresh water lake sediments. Many of the records obtained from these archives have an excellent time control with often annual resolution well suited for an analysis of millennial variability. Within this context there is considerable potential for incorporating water isotope diagnostics into a general circulation model (GCM). This can allow both to answer questions concerning the water isotope cycle within the dynamics of the model simulations and also to compare the outputs with real isotopic data. Here we analyse a simulation made with the GCM ECHAM4, equipped with water isotope diagnostics and integrated over the last millennium. This model was driven with sea surface temperatures taken from a 1000 yr forced simulation with the ECHO-G Atmosphere (ECHAM4)- Ocean (HOPE-G) GCM that did not include an isotope dynamics scheme. The ECHO-G simulation was forced by estimates of solar variability, volcanic activity and greenhouse gases through the last millennium. This work will present results of the isotope simulation focusing on: i) a description of the spatial and temporal variability of the isotopic signal in the context of the natural and anthropogenic forcing changes as simulated along the last millennium and ii) how isotopic changes are influenced by temperature and precipitation variability as well as changes in the main modes of large scale circulation (PDO, NAO, ENSO ...). The comparison and evaluation of the simulation is based on a global data base of paleo water isotope records from many different continental archives.