ENSO-Like Pacing of the Asian Summer Monsoon during the Early Holocene

Abstract

We present a 230Th-dated stalagmite oxygen isotope (δ18O) record from Loushanguan Cave in the Yangtze River valley, China. The δ18O record, if viewed as a proxy of the Asian summer monsoon (ASM) intensity, provides an ASM history for the early Holocene with clear centennial-scale variability. A significant approximately 200-yr cycle between 10.2 and 9.1 ka BP (before present, where “present” is defined as the year AD 1950), as revealed by spectral power analyses, is of global significance and is probably forced by the Suess or de Vries cycle of solar activity. Here, we explore a physical mechanism to explain the relationship between the solar activity and the ASM. A strong coherence between the ASM and El Nino-Southern Oscillation (ENSO) has been observed by performing cross-wavelet analyses on this cycle. Our study suggests that a strong (weak) ASM state corresponds to a warm (cold) ENSO, which is consistent with modern meteorological observations but contrasts with previous studies on regions far from the Meiyu rainbelt. We argue that the centennial fluctuations of the ASM are a fundamental characteristic forced by the solar activity, with the ENSO variability as a mediator. The relationship between ENSO and the ASM displayed spatial heterogeneity on the centennial scale during the early Holocene, which is a more direct analogue to the observed modern interannual variability of the ASM.