Compound-specific hydrogen isotope ratios (dD) of biomarker compounds (e.g. n-alkanes, fatty acids, sterols etc.) have recently emerged as a new tool to track changes in the water cycle over the geological past. The proposed project will apply this new palaeoclimate proxy for the first time to reconstruct the dominant mode of global climate variability on multi-year timescales, the El Nino Southern Oscillation phenomenon (ENSO) throughout the Holocene. To achieve this objective lake sediment cores from Islands in the Tropical Pacific, where ENSO events dramatically alter precipitation patterns and therefore the isotopic composition of meteoric water, will be recovered and analysed for their biomarker dD values. The sites cover the entire Tropical Pacific Region, from Indonesia via Galapagos to the South American West Coast. This approach will result in the first direct reconstruction of ENSO variability throughout the Holocene.
The reconstructed meteoric water dD values for specific time periods, where significant changes occur, will be evaluated using a state-of-the art Global Circulation Model (GCM) with a built in water isotope module (ECHAMiso). By variation of the models input parameters the climate of the selected time periods will be simulated. Comparing the models¿ predicted isotopic composition of the meteoric water with the reconstructed values, we will be able to identify the main forcing mechanisms of ENSO in the Holocene. The proposed project features a bottom-up organic geochemical reconstruct ion approach, using a recently available novel climate proxy and a top-down modelling approach, using an advanced GCM with built in water isotope diagnostics. Combining these two novel approaches will greatly improve our understanding of ENSO variability and its causes in the recent geological past, which are a prerequisite for credible predictions of changes in ENSO frequency or intensity caused by human interference with the climate system.
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