Sea-surface temperature reconstruction for sediment core GIK18287-3 in the tropical South China Sea

The timing and magnitude of sea-surface temperature (SST) changes in the tropical southern South China Sea (SCS) during the last 16,500 years have been reconstructed on a high-resolution, 14C-dated sediment core using three different foraminiferal transfer functions (SIMMAX28, RAM, FP-12E) and geochemical (Uk'37) SST estimates. In agreement with CLIMAP reconstructions, both the FP-12E and the Uk'37 SST estimates show an average late glacial-interglacial SST difference of 2.0°C, whereas the RAM and SIMMAX28 foraminiferal transfer functions show only a minor (0.6°C) or no consistent late glacial-interglacial SST change, respectively. Both the Uk'37 and the FP-12E SST estimates, as well as the planktonic foraminiferal delta18O values, indicate an abrupt warming (ca. 1°C in <200 yr) at the end of the last glaciation, synchronous (within dating uncertainties) with the Bølling transition as recorded in the Greenland Ice Sheet Project 2 (GISP2) ice core, whereas the RAM-derived deglacial SST increase appears to lag during this event by ca. 500 yr. The similarity in abruptness and timing of the warming associated with the Bølling transition in Greenland and the southern SCS suggest a true synchrony of the Northern Hemisphere warming at the end of the last glaciation. In contrast to the foraminiferal transfer function estimates that do not indicate any consistent cooling associated with the Younger Dryas (YD) climate event in the tropical SCS, the Uk'37 SST estimates show a cooling of ca. 0.2-0.6°C compared to the Bølling-Allerød period. These Uk'37 SST estimates from the southern SCS argue in favor of a Northern Hemisphere-wide, synchronous cooling during the YD period.

Planktonic foraminiferal stratigraphy, datum levels and ages of ODP Sites 184-1146 and 184-1148, South China Sea

Over 30 first and last occurrence (FO and LO, respectively) planktonic foraminifer datums were recognized from the Oligocene-Miocene section of Ocean Drilling Program (ODP) Site 1148. Most datum levels occur in similar order as, and are by correlation as probably synchronous with, their open-ocean records. Several datum levels represent local bioevents resulting from dissolution and Site 1148's unique paleoceanographic setting in the northern South China Sea. An age of 9.5-9.8 Ma is estimated for the local LO of Globoquadrina dehiscens (257 meters composite depth [mcd]), whereas the local LO of Globorotalia fohsi s.l. (301 mcd) is projected to be at ~13.0 Ma and the local FO of Globigerinatella insueta (367 mcd) is projected to be at ~18.0 Ma. The combined planktonic foraminifer and nannofossil results indicate that the Oligocene-Miocene section at Site 1148 is not complete. Unconformities up to 2-3 m.y. in duration, occurring at and before the Oligocene/Miocene boundary (OHS1, OHS2, OHS3, and OHS4 = MHS1), are associated with slump deposits between 457 and 495 mcd that signal tectonic instability during the transition from rifting to spreading in the South China Sea. Shorter unconformities of <0.5 m.y. duration that truncate the Miocene section were more likely to have been caused by sea-bottom erosion as well as dissolution. A total of 12 Miocene unconformities, MHS1 through MHS12, are mainly affected by dissolution and an elevated carbonate compensation depth (CCD) during Miocene third-order glaciations recorded in deep-sea positive oxygen isotope Mi glaciation events. Respectively, they fall at ~457 mcd (MHS1 = Mi-1), 407 mcd (MHS2 = Mi-1a), 385 mcd (MHS3 = Mi-1aa), 366 mcd (MHS4 = Mi-1b), 358 mcd (MHS5 = MLi-1), 333 mcd (MHS6 = Mi-2), 318 mcd (MHS7 = MSi-1), 308 mcd (MHS8 = Mi-3), 295 mcd (MHS9 = Mi-4), 288 mcd (MHS10 = Mi-5), 256 mcd (MHS11 = Mi-6), and 250 mcd (MHS12 = Mi-7). The correlation of these unconformities with Mi events indicates that some related driving mechanisms have been operating, causing deepwater circulation changes concomitantly in world oceans and in the marginal South China Sea.

Abundance of palynomorphs and dinoflagellate stratigraphy of ODP Hole 184-1148A, South China Sea

Dinoflagellate stratigraphy is described for the section from 364.75 to 843.85 meters below seafloor (mbsf) at Site 1148 (Sections 184-1148A-40X-1 through 76X-6 and 184-1148B-39X-CC through 56X-1) in the South China Sea. Two assemblage zones and two subzones are defined, based on characteristics of the assemblages and lowest/highest occurrences of some key species. These are the Cleistosphaeridium diversispinosum Assemblage Zone (Zone A; Oligocene), with the Enneadocysta pectiniformis Subzone (Subzone A-1) and the Cordosphaeridium gracile Subzone (Subzone A-2), and the Polysphaeridium zoharyi Assemblage Zone (Zone B; early Miocene). The highest concurrent occurrence of Enneadocysta arcuata, Eneadocysta multicornuta, Homotryblium plectilum, and Homotryblium tenuispinosum delineates the upper boundary of Zone A, which appears to mark a hiatus. Subzone A-1 is of early Oligocene age, as evidenced by the highest occurrences of E. pectiniformis and Phthanoperidinium amoenum at the upper boundary of the subzone. Subzone A-2 is of late Oligocene age based on the highest occurrences of C. gracile and Wetzeliella gochtii close to the upper boundary of the subzone and the occurrence of Distatodinium ellipticum and Membranophoridium aspinatum within the subzone. Zone B is dated as early Miocene based on the lowest occurrences of Cerebrocysta satchelliae, Hystrichosphaeropsis obscura, Melitasphaeridium choanophorum, Membranilarnacia? picena, and Tuberculodinium vancampoae within the zone. The present assemblage zones/subzones are correlative to various degrees with coeval zones/assemblages from areas of high to low latitudes in terms of common key species. We have compared the species content of the assemblage Zones A and B, and the subzones A-1 and A-2, with coeval assemblage(s)/zone(s) described from many, often widely distant, high- and low-latitude regions of the world. These comparisons show that, to various degrees and aside from a number of key species, the coordinated presence of certain important species may also help to assign an age to a given assemblage.