• Coupled GCM
• Overlays
• SSTConversion
• OceanInjection

Mathias Vuille
University of Massachusetts

Martin Werner
Max-Planck-Institute for Biogeochemistry

Richard Healy
Columbia University

Data from GISS Tracer Model II

View the README.TXT, or download the data (Note: 70MB)

In this study we have been analyzing what controls stable isotope variability at various low latitude ice core locations (tropical Andes, Tibet, Himalaya) both at present and in the past. A better understanding of these controls will help resolve some of the controversy surrounding the interpretation of paleorecords derived from tropical ice cores. Our specific goals have been to:

1. 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.
2. Investigate the modern climatic controls such as temperature, amount effect, 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).
3. Explore the use of the deuterium excess d in tropical ice cores as an additional climate proxy for improved reconstructions of tropical oceanic conditions.
4. Analyze the influence of changed orbital parameters (mid-Holocene conditions, 6ky) upon stable isotope distribution and potential climatic controls related to tropical ice cores.
5. Investigate the effect of LGM boundary conditions upon low latitude stable isotope distribution by prescribing new, more realistic reconstructions of glacial tropical SST data.

We have finished the items (1)-(3). Results from these analyses have been published in Climate Dynamics (Vuille & Werner, 2005), Geophys. Res. Lett. (Vuille et al., 2005a), and in J. Geophys. Res. (Vuille et al., 2003a, 2003b, 2005b).

The analysis of climate simulations for the mid-Holocene and LGM (4-5) are still the focus of ongoing research. Simulations and analysis for the LGM have proven to be more of a challenge than initially anticipated. As a result, we ended up employing many more simulations, than initially proposed and investing significantly more time than foreseen. Given the current uncertainty and controversy about tropical SST estimates at the LGM, we have refrained from trying to simulate LGM conditions as closely as possible, but instead ran a set of sensitivity tests. Besides a modern control run and a traditional CLIMAP simulation, we have also performed a simulation where SSTs were lowered by 2K in the tropics as compared to CLIMAP, and one simulation with an additional 1K warming (cooling) imposed at 10S (10N) respectively, on top of the 2K general cooling. This last simulation is intended to simulate a southward-displaced ITCZ over the tropical ocean, in agreement with proxy observations and results from coupled models. Since each of the four simulations varies from the previous one by adding one additional change in the SST-forcing, attribution of the resulting differences in climate and stable isotope distribution will be fairly easy. However, these simulations are clearly meant as sensitivity studies and not as realistic simulations of LGM climate. These sets of simulations were run with both the GISS II and the ECHAM-4 AGCM.



Other collaborators:

Lonnie Thompson (Ohio State Univ), has been involved as data contributor to the project

Francisco Cruz and Steve Burns, (Univ. of Massachusetts), have collaborated on stable isotope records from speleothems in SE Brazil



Publications:

Vuille, M., and M. Werner, "Stable isotopes in precipitation recording South American summer monsoon and ENSO variability - observations and model results", Climate Dynamics, vol. 25, (2005), p. 401.

Cruz Jr., F.W., S.J. Burns, I. Karmann, W.D. Sharp, M. Vuille, and J.A. Ferrari, "A stalagmite record of changes in atmospheric circulation and soil processes in the Brazilian subtropics during the Late Pleistocene", Quat. Sci. Rev., vol. 25, (2006), p. 2749-2761.

Cruz Jr., F.W., S.J. Burns, I. Karmann, W.D. Sharp, and M. Vuille, "Reconstruction of regional atmospheric circulation features during the Late Pleistocene in subtropical Brazil from oxygen isotope composition of speleothems", Earth Planet. Sci. Lett., vol. 248, (2006), p. 494-506.

Vuille, M., M. Werner, R.S. Bradley, and F. Keimig,, "Stable isotopes in precipitation in the Asian monsoon region", J. Geophys. Res., vol. 110, (2005), p. D23108.

Vuille, M., M. Werner, R.S. Bradley, R.S. Chan, and F. Keimig, "Stable isotopes in East African precipitation record Indian Ocean Zonal mode", Geophys. Res. Lett., vol. 32, (2005), p. L21705.

Cruz Jr., F.W., I Karmann, O. Viana Jr., S.J. Burns, J.A. Ferrari, M. Vuille, A.N. Sial, and M.Z. Moreira, "Stable isotope study of cave percolation waters in subtropical Brazil: implications for paleoclimate inferences from speleothems", Chem. Geology, vol. 220, (2005), p. 245.

Cruz Jr., F.W., S.J., Burns, I. Karmann, W.D. Sharp, M. Vuille, A.O. Cardoso, J.A. Ferrari, P.L., Silva Dias, and O. Viana Jr., "Insolation-driven changes in atmospheric circulation over the past 116,000 years in subtropical Brazil", Nature, vol. 434, (2005), p. 63.

Vuille, M., Bradley, R.S., Werner, M., Healy, R., Keimig, F., "2003: Modeling d18O in precipitation over the tropical Americas: 1. Interannual variability and climatic controls." J. Geophys. Res., 108, D6, 4174, doi:10.1029/2001JD002038.

Vuille, M., Bradley, R.S., Healy, R., Werner, M., Hardy D. R., Thompson, L. G., Keimig, F., "2003: Modeling d18O in precipitation over the tropical Americas: 2. Simulation of the stable isotope signal in Andean ice cores." J. Geophys. Res., 108, D6, 4175, doi:10.1029/2001JD002039.



This work is supported by funding from the National Science Foundation Paleoclimate Program.