Late Miocene development of the western Pacific warm pool: Planktonic foraminifer and oxygen isotopic evidence

The disappearance at ~10 Ma of the deep dwelling planktonic foraminifer Globoquadrina dehiscens from the western Pacific including the South China Sea was about 3 Myr earlier than its final extinction elsewhere. Accompanying this event at ~10 Ma was a series of faunal turnover characterized by increase in mixed layer, warm-water species and decrease to a minimum in deepwater species. Paleobiological and isotopic evidence indicates sea surface warming and a deepened local thermocline that we interpret as related to the development of an early western Pacific warm pool. The stepwise decline of G. dehiscens and other deep dwelling species from the NW and SW Pacific suggests more intensive warm water pileup than equatorial localities where surface bypass flow through the narrowing Indonesia seaway appears to remain efficient during the late Miocene. Planktonic delta18O values from the South China Sea consistently lighter than the tropical western Pacific during the Miocene also suggest, similar to today, more variable hydrologic conditions along the periphery than in the core of the warm pool. Stronger hydrologic variability affected mainly by monsoons and increased thermal gradient along the western margin of the late Miocene warm pool may have contributed to the decline of deep dwelling planktonic species including the early extinction of G. dehiscens from the South China Sea region. The late Miocene warm pool became influential and paleobiologically detectable from ~10 Ma, but the modern warm pool did not appear until about 4 Ma, in the middle Pliocene.

Foraminifer datums, opal content and opal accumulation rate of ODP Site 184-1143 sediments

Since the 1970s, Ocean Drilling Program (ODP) and Deep Sea Drilling Program (DSDP) studies have documented high accumulations of biogenic silica and carbonate in the late Miocene-early Pliocene Indian-Pacific Ocean. This high biogenic productivity event, or the "Biogenic Bloom Event," has been dated from 9.0 to 3.5 Ma (Leinen, 1979, doi:10.1130/0016-7606(1979)90<801:BSAITC>2.0.CO;2; Theyer et al., 1985, doi:10.2973/dsdp.proc.85.133.1985; Farrell et al., 1995, doi:10.2973/odp.proc.sr.138.143.1995; Dickens and Owen, 1996, doi:10.1016/0377-8398(95)00054-2, 1999, doi:10.1016/S0025-3227(99)00057-2; Dickens and Barron, 1997, doi:10.1016/S0377-8398(97)00003-0; Berger et al., 1993, doi:10.2973/odp.proc.sr.130.051.1993). It is unknown, however, whether the Biogenic Bloom Event existed in the South China Sea (SCS). High-quality Cenozoic sediment cores taken from the SCS during ODP Leg 184 provide an opportunity to investigate this question. The purpose of this study is to trace and illustrate the change in biogenic productivity in the southern SCS since the late Miocene and the Biogenic Bloom Event in terms of the content and accumulation rate of opal and carbonate at Site 1143.