[MIS19-P20] Temperature reconstruction in the late Pleistocene using fossil terrestrial snails and a stalagmite from an archaeological cave in Okinawa
Keywords:fossil snail, stalagmite, oxygen isotope composition, paleo-temperature, Okinawa, archaeological cave
In this study, fossil shells of a freshwater snail Semisulcospira libertina excavated at Sakitari Cave in Okinawa-jima were investigated. These samples were from two sediment layers dated to 13-16 ka and 23 ka in the cave. We measured stable carbon and oxygen isotope ratios and trace element concentrations at intervals of 1 mm along the growth direction of the snails to reconstruct seasonal temperature variations during the Last Glacial Maximum and the last deglaciation. To estimate paleo-temperature and -oxygen isotope composition of precipitation accurately, we also measured oxygen isotope composition of fluid inclusion water in a stalagmite collected near the archaeological site. Comparing with chemical composition of living S. libertina shells collected around the site, estimated annual mean temperature was about 8 °C and 6°C lower at 23 ka and 13-16 ka than at the present. Summer temperature has largely increased from 23 ka to 13-16 ka relative to winter temperature, which is consistent with North Hemisphere insolation changes in summer and winter. Our results indicate that the increase of mean air temperature around Okinawa-jima was larger than that of seawater temperature in the northwestern Pacific Ocean during the last deglaciation. This inconsistency is a significant finding for better understanding of past climate changes associated with the East Asian Monsoon.