Characteristics of the Heinrich 1 abrupt climate event inferred from a speleothem record from Xianyun Cave, Fujian Province

Abstract

The climate system of the Earth experienced a series of abrupt changes such as Heinrich events and Dansgaard-Oeschger cycles during the last glaciation. Among them, the Heinrich 1 event (H1 event) is the most prominent cold event. It was recorded in Greenland ice cores, deep sea sediments, loess, stalagmites and lacustrine sediments and was proposed to be a global climate event. During H1 event (~18–15 ka), the ice raft extended southward and large amount of cold and fresh water was integrated into the North Atlantic Ocean. It led to the reduction of the Atlantic Meridional Overturning Circulation (AMOC), cooling of the northern hemisphere, and the weakening of the East Asian summer monsoon (EASM) as the results of the southward shift of the Inter-tropical Convergence Zone (ITCZ). Pausata et al. (2011) used a numerical climate model with an embedded oxygen-isotope model to assess what caused the shifts in the oxygen-isotope signature of precipitation during a climate perturbation designed to mimic the Heinrich event. The simulations reproduced the enrichment of δ 18O over Northern India and East Asia evident in speleothem records during Heinrich events. They then concluded that changes in the δ 18O of Chinese stalagmites associated with Heinrich events reflect changes in the intensity of Indian rather than East Asian monsoon precipitations. The simulation result also shows no significant change in δ 18O in precipitation over southeastern China, where its climate is influenced by EASM only. However, there is a lack of well-dated stalagmite record covering the H1 event from the southeastern China to test this hypothesis. Here we present a high resolution stalagmite isotope record (XYⅣ-3) from Xianyun Cave in western Fujian Province to reveal the detailed precipitation history of the EASM from 16.8 to 15.2 ka BP, based on eight high-precision 230Th ages and 256 oxygen isotope data, yielding an average resolution of 7 a. This high resolution stalagmite δ 18O record constrained detailed changes of the EASM during H1 event. It is characterized by a two-step positive shift process beginning at ~16.2 ka BP with the amplitude of 1.8‰, which indicates a significant weakened monsoon period. This result does not support the model simulation which was proposed by Pausata et al. (2011) that the δ 18O of Chinese stalagmites reflected changes of the Indian Summer Monsoon rainfall. Indeed our record suggests that changes in δ 18O of Chinese stalagmites reflect changes of EASM, especially during Henrich events. Comparing with stalagmite records from Hulu Cave and Qingtian Cave, stalagmites records from all 3 caves captured the H1 abrupt climate changes within dating errors. However, changes in Xianyun Cave are more prolonged (~260 a) than the abrupt (18–19 a) changes in Qingtian and Hulu caves. We conclude that the prolonged process of the Xianyun Cave is influenced, to some extent, by ocean-atmosphere coupling processes over the tropical western Pacific Ocean. The hydroclimate of the tropical west Pacific may cause the different responses. Due to the influence of sea-surface temperature changes in the tropical western Pacific warm pool and ENSO, the response of δ 18O in precipitation in Fujian Province evident by our stalagmites to North Atlantic Ocean change would last longer than other EASM regions.