THE YOUNGER DRYAS EVENT RECORDED IN A SPELEOTHEM FROM RODRIGUES, SOUTHWESTERN INDIAN OCEAN

The Younger Dryas (YD) event is an abrupt cooling event in the Northern Hemisphere occurred during the last deglaciation, which is triggered likely by fresh water injecting into the North Atlantic Ocean, resulting slowdown of the Atlantic Meridional Overturning Circulation (AMOC) and southward shift Intertropical Convergence Zone (ITCZ). While a large number of YD records have been reconstructed from Northern Hemisphere, the YD records from Southern Hemisphere remain sporadic, especially in southwestern Indian Ocean. This impeded our understanding about climate variations across the YD event to a global extent. Here, we present a high-resolution and precisely dated speleothem (PATA-1) oxygen isotope (δ¹⁸O) record from Patate Cave (19°45'30“S, 63°23'11“E; ca. 20 m a.s.l.) in Rodrigues Island, southwestern subtropical Indian Ocean. The sample is pure calcite around 334 mm long and 95 mm wide with clear yellow, white, dark red or brown layers. The length between 100~169 mm was selected to study, covering the time period from ca. 13.3 ka to 10.8 ka ago, including the YD event. We obtained 19 U-Th dates and 684 δ¹⁸O data, which allows a high-resolution (ca. 3.7 a) reconstruction of a new speleothem δ¹⁸O record to characterize the hydroclimate variability across the YD event in the southwestern subtropical Indian Ocean. Our analyses show that the PATA-1δ¹⁸O record reflects mainly changes in the precipitation amount resulting from local to large scale atmospheric circulations, including ITCZ shift and El Niño -Southern Oscillation (ENSO). The YD variation in the PATA-1 record is characterized by a heavier (or drier) excursion with a gradual onset and a rapid termination, similar to Greenland ice core δ¹⁸O records and speleothem δ¹⁸O records from vast Asian summer monsoon regions. In eastern coast of the Indian Ocean, the existing records also show a drier condition during the YD event, such as the stalagmite records from Palawan and Ball Gown caves located respectively in the northern and southern edges of the Indo-Pacific warming pool (IPWP, defined between 10°N~18°S and 110°~140°E). However, the records near the equator in the IPWP show different climate change during the YD event compared with our PATA-1 record. Along west coast of the Indian Ocean, the climate show a pattern of “dry in north and wet in south” from equatorial eastern Africa to subtropical southern Africa. The hydroclimate variations during the YD event inferred from the PATA-1 record in Rodrigues are in line with the records near equatorial eastern Africa. Although the hypothesis of a ITCZ shift farther south across Rodrigues may explain the drier YD condition observed in our record, it requires a ITCZ shift of more than 11° to south from its modern position, which appears to be difficult in terms of atmospheric physics. Alternatively, a weakened ITCZ intensity and thus its convective activity during the YD event may explain the drier YD condition in Rodrigues, as well as along the Asian summer monsoon pathway in both hemispheres.