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Abstract
Interdecadal modes of tropical Pacific ocean-atmosphere circulation have a strong influence on global temperature, yet the extent to which these phenomena influence global climate on multicentury timescales is still poorly known. Here we present a 2,000-year, multiproxy reconstruction of western Pacific hydroclimate from two speleothem records for southeastern Indonesia. The composite record shows pronounced shifts in monsoon rainfall that are antiphased with precipitation records for East Asia and the central-eastern equatorial Pacific. These meridional and zonal patterns are best explained by a poleward expansion of the Australasian Intertropical Convergence Zone and weakening of the Pacific Walker circulation (PWC) between ∼1000 and 1500 CE Conversely, an equatorward contraction of the Intertropical Convergence Zone and strengthened PWC occurred between ∼1500 and 1900 CE. Our findings, together with climate model simulations, highlight the likelihood that century-scale variations in tropical Pacific climate modes can significantly modulate radiatively forced shifts in global temperature.
Highlights
Interdecadal modes of tropical Pacific ocean-atmosphere circulation have a strong influence on global temperature, yet the extent to which these phenomena influence global climate on multicentury timescales is still poorly known
These meridional and zonal patterns are best explained by a poleward expansion of the Australasian Intertropical Convergence Zone and weakening of the Pacific Walker circulation (PWC) between B1000 and 1500 CE an equatorward contraction of the Intertropical Convergence Zone and strengthened PWC occurred between B1500 and 1900 CE
The two stalagmites used in this study (LR06-B1 and LR06-B3) were collected from Liang Luar, an B1.7-km-long cave situated on the east Indonesian island of Flores (8° 32’N, 120° 26’E; 550 m above sea level; Fig. 1 and Supplementary Figs 1 and 2)
Summary
Interdecadal modes of tropical Pacific ocean-atmosphere circulation have a strong influence on global temperature, yet the extent to which these phenomena influence global climate on multicentury timescales is still poorly known. There are different hypotheses regarding the precise drivers of tropical Pacific hydroclimate over the past millennium, and the relative importance of meridional forcing from the extratropics versus zonal ENSO-like shifts inherent to the tropics To further examine these interactive climate systems, we have constructed a high-resolution multi-proxy hydroclimate record for southeast Indonesia spanning the last B2,000 years based on stalagmite oxygen (d18O) and carbon (d13C) isotopes, elemental ratios (Mg/Ca, Sr/Ca), and initial 234U/238U activity ratios. The influence of the PWC to amplify the radiatively forced warming and cooling trends of the past millennium is limited in the models These results have important implications for future projections of global temperatures because they show that state-of-the-art last millennium (AD 850–1850) and historical (AD 1850–2005) CGCM experiments may be underestimating the potential for low-frequency shifts in the tropical Pacific mean state to modulate Earth’s climate
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