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High-resolution oxygen isotope (δ18O) profiles of six stalagmites from Sanbao Cave in Hubei province, central China, established with 1413 oxygen isotope data and 65 230Th ages, provide a continuous history of East Asian Summer Monsoon (EASM) intensity for the period from 13—0.2 thousand years before present (ky BP, relative to AD 1950). The δ 18O record includes four distinct stages in the evolution of the EASM: (1) an abrupt transition (~11.5 ky BP) into the Holocene; (2) a period of gradual increase in monsoon intensity (11.5—9.5 ky BP); (3) the maximum humid period (9.5—6.5 ky BP); and (4) a period of gradual decline in monsoon intensity (6.5—0.2 ky BP). Comparison of Sanbao with regional records of comparable resolution reveals that the timing of the beginning and end of the Holocene Optimum (as defined by the minimum in δ18 O) was similar in the Indian and East Asian monsoon systems. This supports the idea that shifts in the monsoon tied to shifts in the mean position of the Inter-Tropical Convergence Zone (ITCZ) may control monsoon intensity throughout the entire low-latitude region of Asia on orbital timescales. This observation also supports the idea that the fluctuations in δ18 O recorded across southern Asia reflect broad changes in the monsoon, as opposed to local meteoric precipitation. The EASM records from Sanbao largely follow orbital-scale insolation changes, yet exhibit similar variability to Greenland ice core δ18O on millennial to centennial scales during the early to middle Holocene ( r = 0.94).

Cave calcite deposits (speleothems) provide long and continuous records of paleoenvironmental conditions in terrestrial settings. Typical environmental proxy measurements include speleothem growth rate and variations in elemental and isotope geochemistry. Commonly the assumption is made that speleothems grow continuously and at a constant rate throughout the year. However, seasonal variation of growth rate may be the rule in many caves. Here we apply observations of modern calcite growth and cave-air CO 2 concentrations and a model of factors controlling cave ventilation to construct a global model predicting where cave calcite growth may be seasonal. Previous models and measurements of calcite precipitation in caves demonstrate the retardation of speleothem growth by high cave-air CO 2 . Elevated CO 2 is commonly dissipated by ventilation driven by density differences between cave and surface air. Seasonal cycles in atmospheric temperature, pressure, and humidity commonly drive these density contrasts. Modeling these changes latitudinally and globally indicates a geographic control on seasonal cave ventilation and thus on a principal controlling factor of speleothem growth. The model predicts that given constant water, calcium, and CO 2 inputs, speleothems from temperate to boreal continental regions commonly accumulate more calcite in the cool season and less or none in the warm season. These models predict that proxies from temperate to boreal speleothems may be seasonally biased due to seasonal ventilation, whereas tropical and maritime records should not.