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.

Granulometry, mineralogy and geochemistry of ODP Holes 184-1147A and 184-1148A, South China Sea

Green clay layers are reported from the Pliocene-Holocene intervals in five of the six sites drilled in the South China Sea (SCS) during Leg 184. Centimeter-scale discrete, discontinuous, and bioturbated layers, constituted by stiff and porous green clays, were observed, sometimes associated with iron sulfides and pyrite. Detailed mineralogical and geochemical analyses indicate that they differentiate from the host sediments in their higher content of iron, smectite, and mixed-layered clays and lower amounts of calcite, authigenic phosphorus, quartz, and organic matter. Although no glauconite was observed, the mineralogy and geochemistry of green clay layers, along with their geometrical relation to background sediments, suggest that they most likely represent the result of the first steps of glauconitization. Correlation between green layers and volcanic ash layers was suggested for green laminae observed elsewhere in Pacific sediments but was not confirmed at SCS sites. Statistical analysis of the temporal distribution of green layers in the records of the last million years suggests that green clay layers have become more frequent since 600 ka. Only at Site 1148 does the green layer record show a statistically significant cyclicity which may be related to orbital eccentricity. A possible influence of sea level variations, related both to climatic changes and tectonism, is postulated.

Benthic foraminiferal faunas of Miocene to Holocene sediments of ODP Site 184-1143 from the southern South China Sea

Deep-sea benthic foraminiferal assemblages from Ocean Drilling Program (ODP) Site 1143 located in the southern South China Sea (SCS) were investigated to evaluate the relationship between faunal composition patterns and paleoceanographic changes during the last 6 million years (late Miocene to Holocene). We used multivariate statistics (correspondence analysis) to analyze carbon-flux-related changes in assemblage composition of benthic foraminifers. Additional proxies for carbon flux and deep-water ventilation include delta13C records of epifaunal Cibicidoides wuellerstorfi and infaunal Uvigerina peregrina var. dirupta and Melonis pompilioides, benthic foraminiferal accumulation rates (BFARs), diversity indices, and relative abundances of indicator species. We observe three significant benthic faunal changes in the southern South China Sea during the last 6 million years. Strong fluctuations in BFAR and relative abundance of productivity indicator species between glacial and interglacial stages after the mid-Pleistocene revolution (MPR) at approximately 0.9 Ma, indicating stronger seasonal carbon flux fluctuations, are accompanied by the extinction of such species as Stilostomella spp. Increases in carbon flux indicator species are coupled with an overall decrease in benthic foraminifer diversity around 3.0 Ma in the late Pliocene. This may indicate increasing carbon flux in a period of productivity maximum caused by enhanced offshore upwelling from intensified winter monsoon wind strength.

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.

Climatic impact on Al, K, Sc and Ti in marine sediments: Evidence from ODP Site 1144, South China Sea

Al, K, Sc and Ti concentrations of the terrestrial material-dominant sediments from ODP site 1144 were reported. Comparison between the bulk and the acid-leached sediments indicates that about 20~30% of the Al, K and Sc in the bulk sediments are not hosted in terrestrial detritus, rather they are of authigenic origin. However, authigenic Ti is negligible. The results indicate that Ti rather than Al is the best proxy for terrestrial materials. Significant climate controls are displayed in the Al/Ti, K/Ti and Sc/Ti variation patterns both for the bulk and the acid leached sediments. Such variation patterns can be mainly accounted for in terms of climate change in their provenance areas in South China. Elevated Al/Ti, K/Ti and Sc/Ti ratios during interglacial periods indicate that chemical weathering then was stronger than during glacial periods, which might be related to a more humid climate in interglacial periods.

Uranium-Thorium dating and sea surface temperatures from corals from Hainan Island, South China Sea

Three mid-Holocene sea surface temperature (SST) records spanning more than 30 years were reconstructed for the northern South China Sea using Sr/Ca ratios in Porites corals. The results indicate warmer than present climates between circa 6100 yr B.P. and circa 6500 yr B.P. with the mid-Holocene average minimum monthly winter SSTs, the average maximum monthly summer SSTs, and the average annual SSTs being about 0.5°-1.4°C, 0°-2.0°C, and 0.2°-1.5°C higher, respectively, than they were during 1970-1994. Summer SSTs decrease from circa 6500 yr B.P. to circa 6100 yr B.P. with a minimum centered at circa 6300 yr B.P. The higher average summer SSTs are consistent with a stronger summer monsoon during the mid-Holocene, and the decreasing trend indicates a secular decrease of summer monsoon strength, which reflects the change in summer insolation in the Northern Hemisphere. El Niño-Southern Oscillation (ENSO) cycles were apparent in both the mid-Holocene coral and modern instrumental records. However, the ENSO variability in the mid-Holocene SSTs was weaker than that in the modern record, and the SST record with the highest summer temperatures from circa 6460 yr B.P. to 6496 yr B.P. shows no robust ENSO cycle. This agrees with other studies that indicate that stronger summer monsoon circulation may have been associated with suppressed ENSO variability during the mid-Holocene.

Abundance of mesozooplankton collected in October and November 1991 at 20 stations in the South Aegean Sea during O91

The O91- Mesozooplankton dataset is based on samples collected in mid October-mid November 1991 at 20 stations in the South Aegean, the SE.Ionian Sea and in NW Levantine. Samples were collected at discrete layers (from the surface till 300m. These data are published. Sampling volume was estimated by multiplying the mouth area with the wire length. The entire sample (for deep layers) or aliquot of Taxon-specific mesozooplankton abundance (1/4) (for the upper layer) was analyzed under the binocular microscope. Copepod and cladoceran species were identified and enumerated; the other zooplankters were identified and enumerated at higher taxonomic level (commonly named as zooplankton groups). Taxonomic identification was done by I.Siokou-Frangou, E.Christou, and N.Fragopoulu, using the relevant taxonomic literature. The entire sample (for deep layers) or aliquot of Mesozooplankton total abundance (1/4) (for the upper layer) was analyzed under the binocular microscope. All zooplankters were enumerated.

Speciation of metals in bottom sediments from the south Kara Sea and Ob and Yenisei estuarine zones

Speciation of Fe, Mn, Zn, Cu, Co, Ni, Cr, Pb, and Cd was studied in 52 samples of bottom sediments collected during Cruise 49 of the R/V "Dmitry Mendeleev" to the estuaries of the Ob and Yenisei rivers and to the southwest Kara Sea. Immediately after sampling the samples were subjected to on-board consecutive extraction to separate metal species according to their modes of occurrence in the sediments: (1) adsorbed, (2) amorphous Fe-Mn hydroxides and related metals, (3) organic + sulfide, and (4) residual, or lithogenic. Atomic absorption spectroscopy of the extracts was carried out at a stationary laboratory. Distribution of Fe, Zn, Cu, Co, Ni, Cr, Pb, and Cd species is characterized by predominance of lithogenic or geochemically inert modes (70-95% of bulk contents), in which the metals are bound in terrigenous and clastic mineral particles and organic detritus. About half of total Mn amount and 15-30% of Zn and Cu are contained in geochemically mobile modes. Spatiotemporal variations in proportions of the metal species in the surface layer of sediments along sub-meridional sections and through vertical sections of bottom sediment cores testify that Mn and, to a lesser extent, Cu are the most sensitive to changes in sedimentation environment. The role of their geochemically mobile species notably increases under reducing conditions.