Wang Rujian

Quaternary biogenic opal records in the South China Sea: Linkages to East Asian monsoon, global ice volume and orbital forcing

Particulate fluxes investigated in the central South China Sea (SCS) during 1993–1996 indicate that opal flux can be used to show primary productivity change, which provides a foundation for tracing the evolutionary relationship between the surface productivity and East Asian monsoon in the SCS during the late Quaternary glacial and interglacial periods. Based on the studies of opal % and their mass accumulation rates (MAR) at the six sites recovered from the SCS during the “Resolution” ODP Leg 184 and “Sonne” 95 cruise of the Sino-Germany cooperation, opal % and their MARs increased evidently in the northern sites since 470–900 ka, and they enhanced and reduced, respectively, during the glacial and interglacial periods. Whereas they increased obviously in the southern sites since 420–450 ka, and they augmented and declined, respectively, during the interglacial and glacial periods. The variability in opal % and their MARs in the late Quaternary glacial cyclicity indicate the “seesaw” pattern of surface productivity in the SCS. The winter monsoon intensified during the glacial periods, surface productivity increased and decreased, respectively, in the northern and southern SCS. The summer monsoon strengthened during the interglacial periods, surface productivity increased and decreased, respectively, in the southern and northern SCS. The cross spectral analyses between the opal % in the northern and southern SCS during the Quaternary and global ice volume (δ18O) and orbital forcing (ETP) indicate that the East Asian winter and summer monsoons could be ascribed to the different drive mechanisms. On the orbital time scale, the global ice volume change could be a dominant factor for the winter monsoon intension and temporal variations. As compared with the winter monsoon, the correlative summer solar radiation with the obliquity and precession in the Northern Hemisphere could be a mostly controlling factor for the summer monsoon intension and temporal variations.

Age estimation of the mid-Pleistocene microtektite event in the South China Sea: A case showing the complexity of the sea-land correlation

The present study confirms the stratigraphical position of microtektite layer being clearly located below the Brunhes/Matuyama (BIM) boundary. Based on the sedimentation rate derived from the stable isotopic and magnetic data of ODP Site 772A, cores 17957 and 17959 in the South China Sea, the age of the mid-Pleistocene impact event was estimated at 1–12 ka earlier than the Brunhes-Matuyama polarity reversal. However, the microtektites were found above the measured BIM boundary in the loess profile due to the downward deviation of the measured B/M boundary from its true position[1]. This demonstrates the complexity of paleo-magnetic records in the loess profiles which, in turn, causes the confusion in the sea-land stratigraphic correlation.

Radiolarian biostratigraphy in the Southern Bering Sea since Pliocene

Detailed radiolarian biostratigraphy in the Plio-Pleistocene was analyzed by using samples from IODP Site U1340 that was drilled to a core depth of 604 m in the southern Bering Sea. A total of 227 species belonging to 102 genera were identified. Based on the distributions of the radiolarian index species at Site U1340, five radiolarian zones since the Pliocene were established in the southern Bering Sea for the first time, and 25 radiolarian bioevents were recognized. Their ages were estimated on the basis of the age-depth plot that was constructed by the synthetical datum of the effective biostratigraphic and magnetostratigraphic events. The radiolarian zones at Site U1340 were systematically compared with those in its adjacent regions since the late Early Pliocene, which further improved and interpreted the biostratigraphic datum as well as their correlations in the middle-high latitude of the North Pacific. In addition, the comparative results of radiolarian zones show that Botryostrobusaquilonaris Zone emended in this paper is equivalent to the upper part of the same zone defined by Hays, 1970, and Druppatractus irregularis-Dorydruppa bensoni Zone as well as Spongodiscus sp. Zone, newly proposed in this paper, are well correlated with Cycladophora sakaii Zone and Stylatractus universus Zone in the subarctic North Pacific, respectively.

Paleoceanographic implications of radiolaria in the southern Okinawa Trough over the last 20,000 years

Quantitative analyses have been carried out on radiolarians from 65 samples of Core 255 in the southern Okinawa Trough. The distribution of taxa and the results of Q-mode factor analysis show that during the last 20 000 years three radiolarian assemblages could be distinguished which can be correlated to high and low productivity levels indicated by the organic carbon content, radiolarian abundance and ratio of Nassellaria/Spumellaria in the sediment. TheTetrapyle quadriloba assemblage of thr last glaciation and deglaciation is associated with high productivity whereas the early HolocenePolysolenia spinosa and the middle and late HoloceneCarposhaera globosa assemblages correspond to low surface productivity. Meanwhile, the variations in the ratio of radiolarian fragments indicate higher SiO2 dissolution during the Holocene than during the last glacial stage.

Lithochemical classification of the arctic depositional environments (Chukchi Sea) by methods of multivariate statistic

This paper presents data on the chemical composition of bottom sediments from the Chukchi Sea and the adjacent Arctic Ocean. Multivariate statistical techniques were used for the analysis of the data set and revealed that grain size fractionation of the original terrigenous component during sedimentation was the major factor of the clustering of the samples. Secondary factors include the accumulation of biogenic siliceous and carbonate material and chemogenic or biochemical accumulation of iron, manganese, and some trace elements. The latter factor was significant in areas of tectonic activity within the graben-rift system of the Chukchi Sea.

Sediment color cycles and their causesin the western Arctic Ocean and Bering Sea

A challenge that limits high-latitude paleo-environment investigations is the lack of foraminiferal shell-bearing sediments for stratigraphy constructions. In the Arctic, the Mn-rich brown layers have been proposed as a new approach to establish glacial-interglacial timescale stratigraphy, but their formation mechanisms remain unclear. Until now, only a limited number of sediment cores with Mn-rich brown layers have been studied, and it has been argued that these layers were formed by diagenesis. During past several years, China expeditions have collected many sediment cores from the western Arctic Ocean and Bering Sea offering an opportunity to investigate sediment color cycles in these regions. In this study, we have studied 14 sediment cores from wide geographic and topographic regions including basin, continental slope, continental shelf, and off-shore deep-sea. First, core images were taken by a line scan camera and high-resolution color reflectance was measured by a spectrometer. Second, core sediments were scanned at 1 cm resolution by an XRF core scanner to obtain element content variations. Third, sediment layers with maxima and minima Mn based on XRF data were analyzed by ICP-OES and ICP-MS to crosscheck the reliability of XRF results and provide precise element concentration. Our results show that 9 cores from slope and basin of the western Arctic bear color cycles which can be effectively indicated by a */ b * ratios, as a * is chromatic value from green to red while b * is chromatic value from blue to yellow. In each of these cores, a */ b * ratios co-vary with contents of Mn and some other redox sensitive trace elements such as Cu, Co, Ni, and especially Mo. Data comparison shows that MnO and Mo concentrations at peak values in the cores gradually decrease, respectively, from 5.22% and 80 ppm on the slope to nearly 1% and 30 ppm in the central basin, whereas minimal MnO and Mo concentrations in these cores always stay around 0.1% and <10 ppm, respectively. By contrast, the 5 sediment cores from Bering Sea, continental shelf and off-shore deep-sea of the Western Arctic show (i) no cycle in color, a */ b *, Mn, or Mo, (ii) no correlation between a */ b *, Mn, or Mo, and (iii) generally very low MnO and Mo contents comparable to average values of weathered continents. Based on independent stratigraphy of several cores and considering previous work in this region, we propose the following mechanism for the formation of sediment color cycles in the Western Arctic. During interglacial, a substantial amount of weathered terrigenous Mn-bearing minerals and Mn2+ containing waters are transported by rivers into continental shelves of the Arctic Ocean, where many minerals are subsequently weathered to release additional Mn2+. Although upper waters on continental shelves are oxidizing, bottom waters are more reducing due to the respiration of organic matter, which prevents Mn2+ in waters from being oxidized into MnO x deposits in sediments. This leaves significant amount of Mn2+ to be transported to the Arctic basin by Pacific waters entered through the Bering Strait. Furthermore, Mn-bearing debris carried by sea ice during winter is moved towards the Arctic basin during summer. On the Arctic slope, Mn2+ is oxidized and deposited in the form of MnO x due to little organic matter, making sediments brown color. Also, most Mn-bearing debris is deposited because summer sea ice boundary is located around the slope. Remaining Mn2+ is then further dispersed into other areas in oxidizing waters by ocean currents and is eventually deposited to form brown sediments at depth. While during glacial periods, cold climate and reduced continent exposure due to more extensive ice cover would decrease Mn transportation to the Arctic, resulting in the formation of yellow or dark-grey sediments with low-Mn. If diagenetic influences can be taken into account, cycles of color and Mn content could be used as indicators for glacial-interglacial cycles in the Western Arctic.

The Mid-Pleistocene Climate Transition Recorded in a 1.6 Myr-Period Lacustrine Sediment Sequence from Mazatage, Tarim Basin

The mid-Pleistocene climate transition(MPT)has been widely reported in worldwide geological events.As a key issue of the Quaternary geology,it has attracted much attention from the paleoclimate community.MPT refers to a period lasting for several hundreds of thousand years,during which the dominant climate periodicity gradually extended from 41 kyr to 100 kyr(Ruddiman et al.,1989),and glacial-interglacial climate difference became more更多还原