A stalagmite-inferred hydroclimate record over the past 1200 years in a western Pacific island

Abstract:

Over the last millennial, the climate is conventionally characterized by several century-long climate periods such as the Mediaeval Climate Anomaly, the Little Ice Age (LIA) and the anthropogenic global warming. For example, in East Asia, a compilation of the past climate data suggests contract of the Intertropical Convergence Zone (ITCZ) during the LIA. However, spatial distribution of high-resolution proxy data is spares, especially in the western Pacific Ocean away from the continent. In this study, we measured isotopic records of a Holocene stalagmite, collected in Minami Daito Island, Okinawa, located in the eastern margin of East Asian monsoon territory and the northern limit of the ITCZ rain belt. Stable isotopic ratios of oxygen and carbon were measured by using Gas-bench CF-IRMS (Delta V advantage). An age model was established with precise U-Th ages (23 depths, 2-sigma error of 10-38 years) from present to 1.2 thousand years ago. Before the settlement started in 1900 CE, this island had been uninhabited. After 1900 CE, the land-use change due to sugar-cane plantation is clearly recorded as an abrupt shift of the carbon isotope record. The oxygen isotope record shows broad links with Indian and Asian climate records on centennial time scale. On decadal-centennial time scale, our oxygen isotope data are similar to those from the central India.