TIMING AND STRUCTURE OF THE YOUNGER DRYAS EVENT RECORDED BY A STALAGMITE FROM NORTHERN JIANGXI, CHINA

The Younger Dryas (YD) event is the major and most extensively studied climatic event during the transition from the last glacial period into the present Holocene interglacial, so far it has been reported in many geological archives/records in the world. However, due to dating uncertainties and/or temporal-resolution, the precise timing and structure of the YD event and its trigger mechanism remain in debate. Shennonggong Cave (28°42'39“N, 117°15'4.2“E; 383 m a.s. l.) is located in Wannian Town, Shangrao City, Jiangxi Province, Southeastern China. The cave developed in the Carboniferous limestone of the Chuanshan and Huanglong groups, which are mainly composed of limestone and interbedded dolostone. The thickness of the cave roof ranges from about 20 m to about 80 m, with average of ca. 50 m. The length of the cave is 7200 m. The temperature inside the cave varied from 16.5? to 21.5? and the relative humidity inside was close to 100% during the period of 2011~2013. This region is strongly influenced by the East Asian summer monsoon (EASM). The annual average temperature is 18.5? and the mean precipitation is 1875 mm. A stalagmite (SN29) was collected 200 m behind the cave entrance with 426 mm in height. This study focuses on the 220~388 mm of distance from the top. A total of 169 subsamples for stable isotopic measurements were drilled along the central axis of SN29 at an interval of 1 mm. We provide a new precisely dated high-resolution (12 yrs) stalagmite δ¹⁸ record (SN29) from Shennonggong Cave, which characterized in detail the timing and structure of the weakened EASM during the YD event. The study section of the stalagmite SN29 spans time range from 13614 a B. P. to 10811 a B. P., and the δ¹⁸ record is reconstructed by 169 δ¹⁸ data and 20 high-precision ²³⁰Th dates. The sample SN29 is composed of aragonite with high growth rate, which allows us to reconstruct a high-resolution record with an unparalleled age constraints with typical errors less than 20 yrs. The YD event in our record manifests a heavier δ¹⁸ excursion from 12851 a B. P. to 11575 a B. P. with an amplitude of 1.7 %, indicating a significantly weakened summer monsoon period. Our results show that the onset of the EASM YD began at 12851±16 a B. P. and lasted for ca. 249 yrs, The end of the YD began at 11575±19 a B. P. and lasted for ca. 146 yrs. The duration of the event is thus 1276±35 yrs. The timing of the YD event in the SN29 δ¹⁸ record is within errors consistent with previously reported stalagmite δ¹⁸O records in the EASM region. A close comparison with other records from high and low latitudes supports a current notion that the weakened EASM during the YD event might be caused by the southward shift of the Intertropical Convergence Zone resulted from the reduction of the Atlantic Meridional Overturning Circulation and cooling of the Northern Hemisphere, which is possibly triggered by fresh water injection into the North Atlantic Ocean.