Search

Manganese nodules are a potential source of critical metals such as Cu, Ni, and Co and are widely distributed on the abyssal plains of the global oceans. A polymetallic nodule metallogenic belt with a heterogeneous and spatially clustered nodule distribution was recently discovered in NW Pacific inter-seamount basin (NPIB) areas. However, the geological processes that regulate the nodule occurrence in that region are unresolved. Here, we report on the characteristics of a high-density field of manganese nodules in the abyssal plain north of Suda Seamount. Ship-borne multibeam bathymetric data reveal a typical seamount sector-collapse topography characterized by radial lineaments of debris channels and ridges formed by rapid debris-avalanche flow. Backscatter data linked with underwater observation indicate that manganese nodules are more concentrated (50%–80% areal coverage) along the main body of the debris apron compared to adjacent neighboring areas (

A coupled approach based on grain size and geochemical elements is used to trace the provenance of surface sediments and to confirm the distribution patterns of grain size and elements on the continental shelf off western Guangdong Province and northeastern Hainan Island. The mean grain size ranges from 0.05 ϕ to 7.28 ϕ with a mean value of 5.60 ϕ. The average concentrations of major elements descend in the order of SiO2 >Al2O3 >CaO>Fe2O3 >K2O>MgO>Na2O>TiO2 >P2O5 >MnO, while those of trace elements exhibit a descending order of Sr>Rb >Zn>V>Cr>Pb>Ni>Cu>As>Cd. On the basis of the distribution patterns of elements and results of statistical analysis, the study area is classified into three zones. Zone I locates on the continental shelf off western Guangdong Province, and the sediments are mainly from Pearl River, Taiwanese rivers, and small rivers nearby. Zone II locates in the eastern exit of Qiongzhou Strait and the coastal area off Leizhou Peninsula, and the sediments are mainly from the erosion products of Qiongzhou Strait and Hainan Island. Zone III locates off the eastern Hainan Island and the continental shelf deeper than −50 m isobaths, and the sediments are mainly from Hainan Island and coral reef. The influence from open water should also be considered. Results indicate that the grain size is the main controlling factor for major and trace element contents and that anthropogenic impact and biological activity also play an important role in the distribution of these elements.

Research on seamounts provides some of the best constraints for understanding intraplate volcanism, and samples from seamounts reveal crucial evidence about the geochemical makeup of the oceanic mantle. There are still many seamounts in the West Pacific Seamount Province (WPSP) that have not been studied, meaning their ages and geochemistry remain unknown. A better understanding of these seamount trails and their evolutionary history, investigated with age and geochemistry data, will enable better understanding of the geological processes operating underneath the Pacific Ocean Plate. Here, new 40Ar/39Ar ages and trace element and Sr-Nd-Pb isotopic data for seven basalt rocks from four seamounts in the WPSP are provided. Chemically, these rocks are all Oceanic Island Alkali basalt (OIA type); analysis of olivine phenocrysts shows that the magmas experienced strong olivine fractionation and changed from olivine + plagioclase to olivine + plagioclase + clinopyroxene cotectic during their evolution. Rare earth element (REE) patterns and a spider diagram of the samples in this study show OIB (Ocean Island Basalt) like behavior. The range of 87Sr/86Sr values is from 0.704 60 to 0.706 24, the range of 206Pb/204Pb values is from 18.241 to 18.599, and the range of 143Nd/144Nd values is from 0.512 646 to 0.512 826; together, these values indicate magma sources ranging from EMI to EMII. Finally, new 40Ar/39Ar age data show that these seamounts formed at ~97 and ~106 Ma, indicating that some may have undergone the same formation processes as seamounts in the eastern part of the Magellan Seamount Trail, but other seamounts likely have different origins.

Discontinuities in the magmatic activity along a spreading ridge are usually observed in ultraslow-spreading ridges with a thick crust. However, the reasons for such melting anomaly are unknown. The Dragon Flag Supersegment between the Indomed Fault Zone (FZ) and the Gallieni FZ on the Southwest Indian Ridge (SWIR) is characterised by ultra-thick oceanic crust (up to ~10 km), and it provides a unique opportunity for studying magmatic crustal accretion at an ultraslow-spreading ridge. We determined the compositions of olivine–spinel pairs in mid-ocean ridge basalts (MORBs) collected from Segments 25 and 28 of the SWIR to estimate the temperatures of crystallisation and investigate the source lithologies. The olivine-spinel pairs were carefully screened and only those having crystallized in equilibrium were used for the temperature estimates. The Al-in-olivine thermometer provided crystallisation temperatures that ranged from 1197 ± 37 to 1393 ± 21 °C. The 95th percentile calculated temperature (1345 °C) for the primitive olivine is ~75 °C hotter than for olivines in MORBs from normal ridges but comparable to the data for plume-related oceanic island basalts. The olivines have Fe/Mn ratios and Ni, Ca, and Mn contents that are similar to those of olivines in MORBs from normal ridges, which suggests their derivation from a peridotite-dominant source with little contribution from fertile mantle components. Our results suggest a hot mantle reservoir is present beneath the Dragon Flag Supersegment, and that it is probably related to a mantle plume.

The relationship between the East Asian winter monsoon (EAWM) and East Asian summer monsoon (EASM) during the Holocene is complicated and remains controversial. In this study, analysis of grain size and benthic foraminiferal oxygen isotope, as well as accelerator mass spectrometry 14C dating was performed on a sediment core retrieved from the newly revealed muddy deposit on the northern South China Sea continental shelf. The history of the EAWM and EASM were reconstructed for the last 8200 a BP. Further analysis in conjunction with previously published paleo-climate proxies revealed that the relationship between the EAWM and EASM during the Holocene is more complex than a simple and strict anti-phase one-both negative and positive correlations were identified. The EAWM and EASM are negatively correlated around 7500, 4800, 4200, 3200, and 300 a BP (cooling periods), while positively correlated around 7100, 3700, and 2100 a BP (warm periods). In particular, both the EAWM and EASM intensified during the three positive correlation periods. However, we also found that the relationship between these two sub-monsoons is anti-phase during the final phase of particularly hot periods like Holocene Optimum and Medieval warm period. The possible impact from variations of solar irradiance on the relationship between the EAWM and EASM was also discussed.

A total of 388 surface sediment samples taken from the northern South China Sea (SCS) continental shelf were analyzed to characterize the signature of their rare earth elements (REEs). The average REEs concentration was 192.94 &mu, g/g, with a maximum of 349.07 &mu, g/g, and a minimum of 32.97 &mu, g/g. The chondrite-normalized REEs pattern exhibits a remarkably light REEs accumulation, a relatively flat heavy REEs pattern, and a negative Eu anomaly. We subdivided the study area into three zones using the characteristics of REEs and statistical characteristics. Zone I: continental shelf off western Guangdong Province. Here, the sediment provenance is mainly river-derived from the Pearl River, Taiwanese rivers, and those in the adjacent area. Zone II: Qiongzhou Strait and Leizhou Peninsula. Here, the sediment provenance consists of the Qiongzhou Strait and the Hainan Island. Zone III: Hainan Island and SCS slope sediments are dominated. The REEs compositions are mainly controlled by source rock properties, hydrodynamic conditions, and an intensity of chemical weathering. We reconstructed the sediment dispersal and transport route using the REEs compositions, grain size, and other geochemical characteristics throughout the study area.

Hydrothermal materials in deep-sea sediments provide a robust tracer to the localized hydrothermal activity at mid-ocean ridges. Major, trace and rare earth element (REE) data for surface sediments collected from the ultraslow spreading Southwest Indian Ridge are presented to examine the existence of hydrothermal component. Biogenic carbonate oozes dominate all the sediment samples, with CaO content varying from 85.5% to 89.9% on a volatile-free basis. The leaching residue of bulk sediments by ~5% HCl is compositionally comparable to the Upper Continental Crust (UCC) in SiO2, Al2O3, CaO, MgO, alkali elements (Rb, Cs) and high field strength elements (Nb, Ta, Zr, Hf, Ti). These detritus-hosted elements are inferred to be prominently derived from the Australian continent by means of eolian dust, while the contribution of local volcaniclastics is insignificant. In addition, the residual fraction shows a clear enrichment in Fe, Mn, and Ba compared with the UCC. Combining the positive Eu anomaly of residual fraction which is opposed to the UCC but the characteristic of hydrothermal fluids and associated precipitates occurred at mid-ocean ridges, the incorporation of localized hydrothermal component can be constrained. REE mixing calculations indicate that more than half REE within the residual fraction (~55%–60%) are derived from a hydrothermal component, which is inferred to be resulted from a diffuse fluid mineralization. The low-temperature diffuse flow may be widely distributed along the slow-ultraslow spreading ridges where crustal faults and fissures abound, and probably have a great mineralization potential.

Surface sediments collected from the continental shelf off the western Guangdong Province and northeastern Hainan Island are analyzed for selected heavy metals contents including Cd, Cr, Cu, Pb, Zn, and As to determine spatial distribution, potential ecological risks, and sources. In addition, some of the controlling factors of heavy metals distribution are also discussed. The average heavy metals contents decrease in the order of Zn &gt, Cr &gt, Pb &gt, Cu &gt, As &gt, Cd. The averaged pollution degree, as shown by the index of geo-accumulation (Igeo), decreases in the order of Zn &gt, Cd &gt, As. Due to the barrier of islands, the Igeo values of Zn, Pb, Cr, Cu, and Cd near the Hailing and Xiachuan Islands are larger than those in other areas. Meanwhile, the Igeo value of As near the coastal area off the estuary of Wanquan River is clearly larger than that in other areas. Based on the results of potential ecological risk index, Cd, Cu, and As should be paid more attention for the contamination risk in future. The results of Pearson correlation analysis and principal component analysis indicate that Zn, Cr, Pb, Cu, and Cd are mainly from the Pearl River and surrounding small rivers, whereas As originates from the Hainan Island. The grain size is one of the main controlling factors for heavy metals distribution, and the anthropogenic activity also plays an important role.

In the equatorial western Pacific, iron-manganese oxyhydroxide crusts (Fe-Mn crusts) and nodules form on basaltic seamounts and on the top of drowned carbonate platform guyots that have been swept free of pelagic sediments. To date, the Fe-Mn crusts have been considered to be almost exclusively of abiotic origin. However, it has recently been suggested that these crusts may be a result of biomineralization. Although the Fe-Mn crust textures in the equatorial western Pacific are similar to those constructed by bacteria and algae, and biomarkers also document the existence of bacteria and algae dispersed within the Fe-Mn crusts, the precipitation, accumulation and distribution of elements, such as Fe, Mn, Ni and Co in Fe-Mn crusts are not controlled by microbial activity. Bacteria and algae are only physically incorporated into the crusts when dead plankton settle on the ocean floor and are trapped on the crust surface. Geochemical evidence suggests a hydrogenous origin of Fe-Mn crusts in the equatorial western Pacific, thus verifying a process for Fe-Mn crusts that involves the precipitation of colloidal phases from seawater followed by extensive scavenging of dissolved trace metals into the mineral phase during crust formation.

Seamounts are an integral part of element recycling in global subduction zones. The published trace element and Pb-Sr-Nd isotope data for basaltic lavas from three key segments (Central Lau Spreading Ridge (CLSR), Eastern Lau Spreading Ridge (ELSR), and Valu Fa Ridge (VFR)) of the Lau back-arc basin were compiled to evaluate the contribution of Louisville seamount materials to their magma genesis. Two geochemical transitions, separating three provinces with distinct geochemical characteristics independent of ridge segmentation, were identified based on abrupt geochemical shifts. The origin of the geochemical transitions was determined to be the result of drastic compositional changes of subduction components added into the mantle source, rather than the transition from Indian to Pacific mid-ocean ridge basalt (MORB) mantle, or due to variable mantle fertilities. The most likely explanation for the drastic shifts in subduction input is the superimposition of Louisville materials on ‘normal’ subduction comp...

High-resolution Chirp profiling and coring reveals an elongated (ca. 400 km) Holocene Zhujiang River (Pearl River)-derived mud area (maximum thickness > 20 m) extending from the Zhujiang River Delta, southwestward off the Guangdong coast, to the Leizhou Peninsula. Two depo-centers, one proximal and one distal, are identified. On the continental shelf off the west Guangdong Province, the mud is deposited in water depth shallower than 50 m; while to the southeast of the Zhujiang River Estuary, the mud area can extend to the −120 m isobath. A combined analysis with the stratigraphic sequences of other muddy deposits in the Western Pacific marginal seas (mainly Changjiang (Yangtze) and Huanghe (Yellow) Rivers derived) indicates that the initiation of the Zhujiang River muddy deposit can be further divided into two stages: Stage 1 is before the mid-Holocene sea-level highstand (ca. 7.0 cal. ka BP), the proximal mud was mostly deposited after 9.0 cal. ka BP, when the sea-level rose slowly after the Meltwater Pulse −1C; Stage 2, after the mid-Holocene sealevel highstand, clinoform developed on the continental shelf off the west Guangdong Province, extending ca. 400 km from the Zhujiang River Estuary. The proximal clinoform thins offshore, from ca. 10 m thickness around 5–10 m water depth to less than 1–2 m around 20–30 m water depth. In addition, we also find a developed distal clinoform in the east of the Leizhou Peninsula.

The mineral chemistry and texture of clinopyroxenes in peridotite from the Kingkong tectonic zone of the Southwest Indian Ridge segment in an effort to constrain mantle melting beneath this slow-spreading ridge are reported. There are three types of clinopyroxenes in the abyssal peridotites: coarse-grained, intergranular and exsolved. The compositional variations among these three types suggest that the coarse-grained clinopyroxene is a mantle-derived source. The Al, Na and Ti contents and the Na/Ti ratio of the coarsegrained clinopyroxene may be used to monitor the degree of partial melting, combined with the contradistinction with Spinel Cr#, which is calculated to be between 7.9% and 14.9%, and may represent low degrees of melting in the global ocean ridge system. The along-axis compositional variations in the coarse-grained clinopyroxene suggest that the degree of partial melting is primarily controlled by the transform faults on both sides of the ridge. Nonetheless, the northwestern side of the ridge may be affected by a hypothesised detachment fault as documented by the calculated P-T conditions. Simultaneously high Na and low Ti contents in the coarse-grained clinopyroxene points to mantle heterogeneities along the ridge axis.

The heavy minerals of 408 surface sediment samples collected from the inner shelf of the northwest South China Sea were analyzed in 2008.The results suggested that there are three heavy mineral provinces in this region,dominated by Zircon-Ilmenite-Hematite assemblage,Anatase-White Titanium-Epidote assemblage,and Pyroxene-Hornblende-Epidote assemblage respectively.The three provinces have conspicuous differences in depositional environment,hydrodynamic condition,grain size and redox environment,suggesting that the distribution pattern of heavy minerals is controlled by both provenance and hydraulic conditions.From the provinceⅠwith high hydrodynamic condition to the province Ⅲ with relatively low hydrodynamic condition,or from the river estuary and deltas to the inner shelf and semiclosed bays,the stable heavy minerals of high density gradually decrease and those with less density and lower stability increase.The heavy minerals in the study area came from three major sources,i.e.terrestrial,nearshore and autogenetic sources.Terrestrial heavy minerals were mainly from the Hainan island and Yunkai massif.The heavy minerals from erosion of the coastal islands and surrounding lands are mainly distributed by the Pearl River.

Gas hydrate serves as the largest reservoir in the global carbon cycle. It may release lots of methane into water column and atmosphere due to the global warming and/or sea level falling,which greatly affects climate and environment. Since Dickens et al. proposed the hypothesis that massive methane releasing from gas hydrate is one of the most important reasons of the Latest Paleocene Thermal Maximum (LPTM) in 1995,great research effort has been focused on the evolution of gas hydrate in geological history. A series of climate fluctuations have occurred since the late Quaternary,and scientists have found paleoenvironmental records of carbon isotope negative excursions in Santa Barbara basin,Guaymas basin,Lake Baikal,Greenland Sea,Peru,East Greenland continental shelf,Papua New Guinea,and South China Sea,which are related to the gas hydrate-derived methane. In this study,we compile these records to provide valuable information for future studies of dynamic evolution of gas hydrate.

Sound refraction artifacts are often present in multibeam swath bathymetry data. For a flat array, the artifacts are usually more serious in outer beams than in inner beams. In a 3D topographical mapping they appear as ridges that parallel the tracks of the vessel. To shorten the survey time, the outer beams should be utilized as often as possible. Therefore, the refraction errors should be removed. In this paper, we present a model of reduced sound speed profile that consists of three water layers. The sound speed of the two upper layers has a constant gradient, and the third layer has the same sound speed as the most bottom measured layer. The model parameters can be searched based on the principle of the minimum difference of depth between the overlap of two neighboring swaths. The horizontal position and depth of each beam can be accordingly recalculated using the model parameters. To avoid being trapped in local optimum, the initial search scope is limited according to assumed lunch angle and travel ...

As the latest abrupt cold event, the study on the Younger Dryas event is important to forecast the change of future climate, especially to present global warming. So that what caused the event and how the event worldly spread is crucial to anticipate anything like that. Spatial distribution and relative timing of the Younger Dryas event are central for our understanding of causes and transferring mechanism of it. From the large numbers of the published works on the late Quaternary paleoclimatic research, the evidences of the Younger Dryas event were summarized and the accurate coordinates of these sites were put on the world map with Mapinfo software From more than 200 sites which have the event records, the onset, the termination and duration trend of it are figured and analyzed. The onset time of the event is different from 11.8 cal. ka B.P. to 13.7 cal. ka B.P. The mean value is 12.72 cal. ka B.P. The contour line of 12.8 cal. ka B.P. circle more than half of the earth, from Europe to Qinghai-Tibet Plateau, southwest Pacific, east Antarctica, South Africa, South Atlantic Ocean and South America. The earliest site is 13.7 cal. ka B.P. at MD01-2386 core, West Pacific Warm Pool and at AD91-17, South Adriatic Sea, not at Arctic region. The end time of the event is 7.8-12.53 cal. ka B.P., mean is 11.52 cal. ka B.P. The contour line of 11.5 cal. ka B.P. covers almost north Hemisphere except North Africa and west Pacific, from north to south total tread of the terminative time is younger. The terminative time of the event at continents is earlier than around oceans. The duration of the Younger Dryas event is 0.25-4.46 cal. ka, the mean value is 1.20 cal. ka. The areas more than 1.2 cal. ka is most in low latitude. At the North Africa and the West Pacific Warm Pool the duration is longer than at other places. While at high latitude it is shorter. The results indicate that the origin of the Younger Dryas event is at West Pacific Warm Pool. The trigger is Qinghai-Tibet Plateau. The changing of the atmosphere general circulation is the reason of the beginning and the ending of the event. And the signs of the event are transferred by the air circulation and ocean-air exchanging. Because special factors the local responses of the Younger Dryas event are diversity in different places.

Marine magnetic survey is an important mean of geophysical exploration. The magnetic disturbance magnitude, the start and end time, and perfecting magnetic disturbance model are important for magnetic survey. In this paper, on the basis of that dual-frequency GNSS is able to get the ionospheric total electron content, reflect the nature of the magnetic disturbance characteristics, etc. the study of magnetic disturbance correction in marine magnetism measurements using dual-frequency GNSS is carried out. Through quality controlled by the dual-frequency GNSS phase observations, ionospheric total electron content solved by static and dynamic at slant direction. Comparing the solving with geomagnetic observatories and marine magnetic measurements, the solution showed that there is relatively strong correlation between ionospheric total electron content and marine magnetic surveys. This fact helps to perfect magnetic interference correction model and improve the accuracy of magnetic measurement. Also it is a good foundation for the application of GNSS to carry out new areas.

Zhujiang Submarine Canyon, a large submarine canyon, is located in the northern South China Sea, extending to 300 km southeastward from the shelf break off Zhujiang River estuary, down to deep-sea basin. Based on the full-coverage multi-beam seabed terrain data, the subtle topographic features of Zhujiang Submarine Canyon are analyzed. According to the morphology, trend, and bottom axial gradient, Zhujiang Submarine Canyon is divided into upper, middle and lower segments and deep-sea fan. On the basis of geomorphology, tectonic interpretation indicates that Zhujiang Submarine Canyon is mainly affected by the northeast-trending faulted basin and northwest-trending fault belt since Mesozoic, followed by the east-west-trending fault belt. Zhujiang Submarine Canyon maybe formed by the continuing thermal subsidence and fault depression of northern South China Sea margin caused by South China Sea spreading based on the collision between India-Australian plate and Eurasian plate. The submarine canyon becomes more narrow and deeper at the entrance because of the submarine volcanoes formed by the volcanic eruptions in Neogene. Zhujiang Submarine Canyon is continual eroded and filled by the cyclical sea level changing and massive sediment carried by Zhujiang River. The thick sediments, slump layer and developed fracture are conducive to migration, aggregation and accumulation of hydrocarbon. And the surface hydrocarbon spill formed the seabed pockmark structure on the north slope of the submarine canyon.

Because of device noises, bad sea state or incorrect ship parameter, multibeam bathymetry data easily conceal many outliers. In order to process such large amount of data, we must research an automatic and rapid and robust approach. We present an automatic algorithm for detecting outliers based on density of points. Firstly, each swath data are projected along orthogonal and side direction respectively. On each plane, an initial point can be determined according to the corresponding maximum density. Then a big region will be searched by the connected neighboring points on each plane. Then we adopt erosion and dilation algorithms to eliminate a few outliers which connected with the big region. Afterward we obtain the edge of region by edge tracing. All data beyond of the region will be considered as outliers and deleted. Finally a local window filter is used to delete some outliers which conceal in the scope of real depth. The algorithm is verified by real data. It is a kind of rapid, robust algorithm.