For the first time in the western Pacific, planktonic foraminifer responses to the MPT at an average resolution of 500–1000 yr were studied in 475 samples taken from the 300- to 518-mcd interval of Site 1144, northern South China Sea. The studied interval covers MIS 14–29, with an undecided age for the bottom part of the section below 500 mcd. Abundant warm-water species typified by Globigerinoides occur in the lower part of the section, with 60% average abundance from MIS 29 and older intervals. Their abundances decrease to <40% during MIS 22 and younger glacial periods. In contrast, cool- and cold-water species including G. bulloides, N. pachyderma, and G. inflata increase from <20% prior to MIS 23 to >35% in MIS 15 and 14. The deep-dwelling warm-water species S. dehiscens decreased to minimum during MIS 22 and remained extremely rare (0%–4%) throughout the upper part of the section. These planktonic foraminifer changes across the MIS 22/23 boundary mark the mid-Pleistocene revolution at 0.9 Ma.
Paleo-SST estimated using transfer function FP-12E shows smaller changes in summer and winter temperatures and their difference before the MPR. The average SST was 29°C for summer and 23.6°C for winter before the MPR but changed to 28.5°C and 21°C, respectively, after the MPR. A maximum winter temperature difference of 11°C (17°–28°C) was recorded during MIS 22.
As indicated by deep-dwelling species, the MPR event also led to a well-stratified upper water column and a more constrained thermocline that fluctuated neatly with glacial–interglacial cycles after 0.9 Ma. Beginning from the MPR, a stronger association started to develop between fluctuations of species abundances and glacial–interglacial cycles. The great cooling at MIS 16 almost completely eliminated several deep-dwelling warm-water species including G. tumida. Most planktonic foraminifer species exhibit abundance changes closely coherent with climate transition from 41- to 100-k.y. cyclicities, as well as with fluctuations of glacial–interglacial cycles. Although marked by a profound shift in some individual species across the MPR, the overall planktonic foraminifer responses to orbital forcing climate changes during the mid-Pleistocene transition were gradual and progressive.