This proposal logically builds upon our previous research on the climatic controls on stable water isotopes (d18O, dD) in precipitation at low latitude proxy sites. Our main goal is to analyze what controls stable isotope variability at various low latitude ice core locations (tropical Andes, Tibet, Himalaya) both at present and in the past, which will help to resolve some of the controversy surrounding the interpretation of paleorecords derived from tropical ice cores. Our specific goals are to:

•    investigate the modern climatic controls such as temperature, amount affect, moisture source variability and atmospheric circulation on stable isotopes (d18O, dD) at tropical ice core drill sites and analyze the influence of main climate modes such as ENSO or Asian monsoon intensity on stable isotope variability (experiments with prescribed SST-forcing over the last decades),

•    analyze the influence of changed orbital parameters (mid-Holocene conditions, 6ky) upon stable isotope distribution and potential climatic controls related to tropical ice cores,

•    investigate the effect of LGM boundary conditions upon low latitude stable isotope distribution by prescribing new, more realistic reconstructions of glacial tropical  SST data,

•    explore the use of the deuterium excess d in tropical ice cores as an additional climate proxy for improved reconstructions of tropical oceanic conditions, and

•    perform a model evaluation by comparing the simulated results with the available proxy data and with IAEA-GNIP and NCEP-NCAR reanalysis data for the modern experiments.

As in our prior NSF project, all experiments will again be based on the GISS II (4° lat. * 5° lon., with new improved topographic control over the Andes) and the ECHAM-4 (T30 and T106 spectral resolution) models. All these experiments (except the 21 ky simulations) have already been performed as part of prior projects, but have not yet been analyzed or applied toward the interpretation of tropical ice cores.

The intellectual merit of our project is to combine and directly address several research areas, which are currently at the forefront of paleoclimate research, such as the study of the sensitivity of the Earth system to variations in climate forcing factors, the evaluation of numerical model simulations and the investigation of the causes, patterns, mechanisms, processes and linkages between different elements of the marine-terrestrial-atmosphere-cryosphere system [ESH Program Announcement NSF-02-191].

for more information and data access please visit Columbia University's Center for Climate System Research.