Yanguang Liu

Trend analysis of sediment grain size and sedimentary process in the central South Yellow Sea

With the method of trend analysis of sediment grain size, the sediment transport trend of the fine-grained sediments area in the central South Yellow Sea was studied. The results demonstrated that there is a sedimentation center around the point of 123.4° E, 35.1° N, and the sediments outside the center are transported to it. The patterns of sediment transportation and deposition in the Yellow Sea should be controlled by cyclonic circulation (including the Yellow Sea Cold Water Mass) and cold water gyre. The study also showed that the method of trend analysis of sediment grain size has prospective utilization in the fine-grained sediment deposited area on large-scale continental shelf.

Distribution of major and trace elements in surface sediments of Hangzhou Bay in China

The Inductively Coupled Plasma Optical Emission Spectrometer was used to analyze sediment samples collected from the Hangzhou Bay to determine major and trace elemental concentrations. Based on these concentrations, the study area can be classified into three geochemical provinces. Province I covers the northern Hangzhou Bay area and contains high concentrations of Al2O3, Fe2O3, MgO, Na2O, K2O, MnO, Cr, Cu, Ni, Pb, V, Co and Zn. Province III is located in the western Hangzhou Bay, near the Qiantang River mouth, and contains high concentrations of SiO2, Na2O, P2O5, TiO2, Cr, Sr, Zr. Province II is located in the middle and eastern Hangzhou Bay, with the medium concentrations of major and trace elements. The results also demonstrate that the grain size is the dominating factor controlling the spatial variations of elemental concentrations, and the Changjiang River (Yangtze River) and Qiantang River sediments play an important role in the distribution of these elements. Anthropogenic impact on heavy metal concentrations (especially Cr, Sr and Zr) can be detected in the surface sediments near the Qiantang River mouth.

Magnetostratigraphy of a greigite-bearing core from the South Yellow Sea: Implications for remagnetization and sedimentation

Sediments from the continental shelf are sensitive to sea level, climatic changes, and local tectonic history. In this study, we carried out a high-resolution magnetostratigraphic investigation on the longest core (NHH01, 125.64 m) recovered from the South Yellow Sea (SYS). An abnormal interval dominated by negative inclinations was discovered by applying alternating field demagnetization (AFD) on samples from a greigite-bearing layer (44.90–51.80 m). In contrast, the inclinations of most greigite-bearing samples changed from negative to positive when heated to ~360°C. This strongly indicates that this inclination anomaly revealed by the AFD alone is not a true negative subchron. After neglecting the effects of greigite-bearing layers, the straightforward correlation of the interpreted magnetostratigraphy defines the Matuyama-Brunhes boundary (781 ka) and the Jaramillo top (990 ka) at 68.64 m and 101.54 m, respectively. The linearly extrapolated basal age of the core is ~1.10 Ma. In addition, several short-lived inclination anomalies can be tentatively assigned to magnetic excursions, which indicates that the sedimentation could be continuous even at the millennial time scale at depth intervals bracketing these fast geomagnetic events. Moreover, the excellent correspondence between clay content variations of the core and the marine oxygen isotope record indicates the potential of clay content as a paleoclimatic proxy in the studied region in the past ~1 Ma. In brief, our study provides not only a robust age model in the SYS but also a methodological guide for paleomagnetic studies in continental shelf region.

Reconstructing sea surface temperature, sea surface salinity and partial pressure of carbon dioxide in atmosphere in the Okinawa Trough during the Holocene and their paleoclimatic implications

The sediment core DGKS9603 collected from the Okinawa Trough was used as research target. By use of unsaturated indexU37k of long-chain alkenone, δ13C of POC and of planktonic foraminifera (G. sacculifer), the evolutions of sea surface temperature and partial pressure of carbon dioxide in the atmosphere during the Holocene were reconstructed in the Okinawa Trough. And in combination of δ18O of planktonic foraminifera, the relative difference of sea surface salinity during the Holocene was also reconstructed. Consequently, three cooling events (E1-E3) were identified, each of which occurred at 1.7-1.6, 5.1-4.8 and 8.1-7.4 kaBP (cal), respectively. Of the three events, E2 and E3 are globally comparable, their occurrence mechanism would be that the main stream of the Kuroshio Current shifted eastward due to the enhanced circulation of the northeastern Pacific Ocean, which was driven in turn by amplified intensity of sunshine and subsequent enhancement of subtropical high pressure; E1 corresponds to the Small Ice-Age Event occurring between 1550 and 1850AD in China. In the Oki-nawa Trough, E1 might be also related to the eastward shift of main stream of the Kuroshio current driven by powerful Asia winter monsoon.

The distribution and variation of elements in sediments off the Huanghe (Yellow) River mouth

Surface sediment samples collected off the Huanghe (Yellow) River mouth during the period 2007–2009 were analyzed for major and trace element concentrations. Concentrations of 16 elements were measured using X-ray fluorescence spectrometry. Results demonstrate that sediment grain size is the dominant factor controlling the spatial variations of elemental concentrations. Correlation and cluster analyses allowed classification of the study area into four geochemical regions: Regions I and III are characterized by high concentrations of Al2O3, Fe2O3, MgO, Na2O, K2O, Cr, Cu, Mn, Ni, Pb, V, and Zn, and contain fine-grained sediments with mean grain size (Mz)<22 μm; and; Regions II and IV contain mostly coarse-grained sediments, and are characterized by high concentrations of SiO2, Na2O, and Zr. The sediment entering the sea from the Huanghe River and its tributaries is enriched in Ca. Thus, the Ca/Al ratio was used as an indicator of the proportion of sediments in the study area that originated from the Huanghe River. Ca/Al ratios decrease from Regions I and II (located in the nearshore zone of the Huanghe River delta) to Regions III and IV (distributed in the offshore zone of the northern Huanghe River delta, southern and southeastern Laizhou Bay area).

Gravity and magnetic field and tectonic structure character in the southern Yellow Sea

The research of the geophysical survey in the east of the southern Yellow Sea (SYS) (122°-125°E) in 1999 reveals that the SYS has a structure of three-uplifts and two-basins. The structure can be well concordant with the gravity and magnetic anomalies. In the basins, most of the gravity and magnetic anomalies are low and gentle. As well in the uplifts, the gravity anomalies are high positive ones, but the magnetic anomalies are plus and minus variant ones. Seismic data show that the mid-uplift is a Cenozoic one. The Paleozoic is under the Q+N strata, the thickness of which is less than 1 km, with no Palaeogene. The Wunansha uplift area and the Sunan uplift area have good continuity, which indicates that they belong to the same geological unit. The basin in the northern part of SYS, which developed in the late Cretaceous period, is a Cenozoic one mainly made up of Cenozoic sediment. On the contrary, the basin in the southern part is the seaward extension of Subei basin and is a medial Cenozoic sediment basin mainly made up of Cenozoic sediment. Because of the striking left-lateral sense translation of Tanlu fault zone, the east plate of fault zone moved northward on a large scale, which generated a massive north-south pull-apart stress field to make the earth crust pulled apart, revolved and tilted, and the pulling-apart basin came into being in the upper part of the crust.

Contribution of phytoliths to total biogenic silica volumes in the tropical rivers of Malaysia and associated implications for the marine biogeochemical cycle

The contribution of phytoliths to total biogenic silica (BSi) volumes in rivers worldwide, and the associated implications for the biogeochemical cycle, require in-depth study. Based on samples from rivers in Peninsular Malaysia, this project investigated the source and characteristics of BSi found in Asian tropical rivers, as well as the process of reverse weathering taking place in these fluvial systems. Results indicated that BSi samples collected in sediments consisted of phytolith, diatom and sponge spicules. Phytoliths, predominantly of the elongate form, comprised 92.8%–98.3% of BSi in the Pahang River. Diatom BSi in this river consisted mainly of pennatae diatoms, but represented a relatively small proportion of the total BSi volume. However, diatom BSi (predominantly of the Centricae form) was more prevalent in the Pontian and Endau Rivers with shares of 68.8% and 79.3% of the total BSi volumes, respectively, than Pahang River. Carbon contents of the BSi particulates ranged from 1.85% to 10.8% with an average of 4.79%. These values are higher than those recorded in other studies to date, and indicate that BSi plays a major role in controlling permanent carbon burial. This study suggests that phytoliths from terrestrial plants are the primary constituents of BSi in the rivers of Peninsular Malaysia, and therefore represent a significant proportion of the coastal silica budget.

Paleoceanographic records in the sedimentary cores from the middle Okinawa Trough

Two gravity piston cores (Cores 155 and 180) involved in this study were collected from the middle Okinawa Trough. Stratigraphy of the two cores was divided and classified based on the features of planktonic foraminifera oxygen isotope changes together with depositional sequence, millennium-scale climatic event comparison, carbonate cycles and AMS14C dating. Some paleoclimatic information contained in sediments of these cores was extracted to discuss the paleoclimatic change rules and the short-time scale events presented in interglacial period. Analysis on the variation of oxygen isotope values in stage two shows that the middle part of the Okinawa Trough may have been affected by fresh water from the Yellow River and the Yangtze River during the Last Glacial Maximum (LGM). The oxygen iso-tope value oscillating ranges of the cores have verified that the marginal sea has an amplifying effect on climate changes. The δ13C of benthic foraminifera Uvigerina was lighter in the glacial period than that in the interglacial period, which indicates that the Paleo-Kuroshio’s main stream moved eastward and its influence area decreased. According to the temperature difference during the “YD” period existing in Core 180 and other data, we can reach the conclusion that the climatic changes in the middle Okinawa Trough area were controlled by global climatic changes, but some regional factors had also considerable influence on the climate changes. Some results in this paper support Fairbanks’s point that the “YD” event was a brief stagnation of sea level rising during the global warming up procession. Moreover, the falling of sea level in the glacial period weakened the exchange between the bottom water of the Okinawa Trough and the deep water of the northwestern Pacific Ocean and resulted in low oxygen state of bottom water in this area. These procedures are the reasons for carbonate cycle in the Okinawa Trough area being consistent with the “Atlantic type” carbonate cycle.

Persistent effects of the Yellow River on the Chinese marginal seas began at least ~880 ka ago

The Yellow River (or Huanghe and also known as China’s Sorrow in ancient times), with the highest sediment load in the world, provides a key link between continental erosion and sediment accumulation in the western Pacific Ocean. However, the exact age of its influence on the marginal sea is highly controversial and uncertain. Here we present high-resolution records of clay minerals and lanthanum to samarium (La/Sm) ratio spanning the past ~1 million years (Myr) from the Bohai and Yellow Seas, the potential sedimentary sinks of the Yellow River. Our results show a climate-driven provenance shift from small, proximal mountain rivers-dominance to the Yellow River-dominance at ~880 ka, a time period consistent with the Mid-Pleistocene orbital shift from 41-kyr to 100-kyr cyclicity. We compare the age of this provenance shift with the available age data for Yellow River headwater integration into the marginal seas and suggest that the persistent influence of the Yellow River on the Chinese marginal seas must have occurred at least ~880 ka ago. To our knowledge, this study provides the first offshore evidence on the drainage history of the Yellow River within an accurate chronology framework.

Bacterial and archaeal community structure of pan-Arctic Ocean sediments revealed by pyrosequencing

This study was to investigate bacterial and archaeal community structure of pan-Arctic Ocean sediments by pyrosequencing. In total, investigation of three marine sediments revealed 15 002 bacterial and 4 362 archaeal operational taxonomic units (OTUs) at the 97% similarity level. Analysis of community structure indicated that these three samples had high bacterial and archaeal diversity. The most relatively abundant bacterial group in Samples CC1 and R05 was Proteobacteria, while Firmicutes was dominant in Sample BL03. Thaumarchaeota was the most relatively abundant archaeal phylum in Samples CC1 and R05, and the relative abundance of Thaumarchaeota was almost as high as that of Euryarchaeota in Sample BL03. These two phyla accounted for nearly 100% of the archaeal OTUs. δ-Proteobacteria and γ-Proteobacteria were the two most relatively abundant classes at Proteobacterial class level, and their relative abundance was more than 60% in Samples CC1 and R05. There were also differences in the top 10 relatively abundant bacterial and archaeal OTUs among the three samples at the 97% similarity, and only 12 core bacterial OTUs were detected. Overall, this study indicated that there were distinct microbial communities and many unique OTUs in these three samples.