Variations in tropical west Pacific climate and its role in glacial-interglacial cycles

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The tropical oceans are a major source of heat and moisture for the high latitudes, making them a key player in the global climate system. Under modern climate conditions, strong inter-annual variability in tropical climate related to El Niño-Southern Oscillation has been observed, which affects climate in the surrounding land masses and also worldwide. While this phenomenon has been well studied for the present-day, the behavior of tropical climate on longer timescales and its role during large global climate shifts is not yet well understood. In the proposed study, we will use stalagmites from Borneo as archives to assess past changes in precipitation and temperature in the tropical west Pacific, covering several glacial-interglacial cycles. Variations in the hydrological cycle will be reconstructed from changes in the oxygen isotopic composition of calcite. As stalagmites allow continuous reconstructions at very high resolution, the proposed work should yield a paleoclimate record that permits assessing not only changes in the mean state but also in the variability of climate. Furthermore, precise age control through U-series dating will allow examining the relative timing of changes in tropical climate in comparison to higher latitudes. In addition to the well-established oxygen isotope approach, we propose to apply two new methods to the stalagmites, namely NanoSIMS for ultra-high resolution measurements of elemental (and potentially isotopic) ratios and a recently proposed paleothermometer based on carbonate isotopologues. The proposed study will therefore both contribute a valuable paleoclimate record and expand the toolbox of paleoclimatologists.