Abundance variations of planktonic foraminifers during the mid-Pleistocene climate transition at ODP Site 1144, northern South China Sea

Abstract

The abundances of planktonic foraminifers are documented in samples from the interval between 300 and 518 meters composite depth at Site 1144, northern South China Sea. With resolution of ~500–1000 yr, this work represents the first high-resolution study of the climate changes between 0.5 and 1.0 Ma recorded in planktonic foraminifers from the western Pacific. Faunal responses at this site to orbital forcing of climate variations during the mid-Pleistocene transition are found to have been mainly gradual and progressive, accompanied by swift shifts in the abundances of some individual species. Warm-water species represented by Globigerinoides spp. decrease from an average of 60% in marine isotope Stage (MIS) 29 and older intervals to <40% at MIS 22, followed by a steady increase in cool-water species toward younger intervals. Cool-water species including Neogloboquadrina pachyderma and Globorotalia inflata increased from <20% prior to MIS 23 to >35% in MIS 15 and 14. The deep-dwelling warm-water species Sphaeroidinella dehiscens decreased to a minimum during MIS 22 and remained extremely rare, 0%–4%, throughout the upper part of the section. This contrast is also reflected in the estimated sea-surface temperature, which shows a maximum winter temperature difference of 11°C (17°–28°C) during MIS 22. Since then, a stronger association started to develop between species abundance fluctuations and glacial–interglacial cycles. These planktonic foraminifer changes during MIS 22 mark the mid-Pleistocene revolution (MPR) at 0.9 Ma. The MPR event also led to a well-stratified upper water column and a more constrained thermocline, as indicated by abundance changes of deep-dwelling species. The major cooling at MIS 16 almost completely eliminated such deep-dwelling warm-water species as Globorotalia tumida. The planktonic foraminifer results from Site 1144 sample orbital forcing climate changes from 41 to 100 k.y. cyclicities during the mid-Pleistocene climate transition.