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Lai Z.,Sun Yat Sen University | Lai Z.,Key Laboratory of Marine Resources and Coastal Engineering in Guangdong Province | Ma R.,Sun Yat Sen University | Huang M.,Sun Yat Sen University | And 5 more authors.
Journal of Geophysical Research: Oceans | Year: 2016

The estuarine plume dynamics under a downwelling-favorable wind condition were examined in the windy dry season of the Pearl River Estuary (PRE) using the PRE primitive-equation Finite-Volume Community Ocean Model (FVCOM). The wind and tide-driven estuarine circulation had a significant influence on the plume dynamics on both local and remote scales. Specifically, the local effect of downwelling-favorable winds on the plume was similar to the theoretical descriptions of coastal plumes, narrowing the plume width, and setting up a vertically uniform downstream current at the plume edge. Tides tended to reduce these plume responses through local turbulent mixing and advection from upstream regions, resulting in an adjustment of the isohalines in the plume and a weakening of the vertically uniform downstream current. The remote effect of downwelling-favorable winds on the plume was due to the wind-induced estuarine sea surface height (SSH), which strengthened the estuarine circulation and enhanced the plume transport accordingly. Associated with these processes, tide-induced mixing tended to weaken the SSH gradient and thus the estuarine circulation over a remote influence scale. Overall, the typical features of downwelling-favorable wind-driven estuarine plumes revealed in this study enhanced our understanding of the estuarine plume dynamics under downwelling-favorable wind conditions. © 2016. American Geophysical Union. All Rights Reserved. Source


Zhang M.,CAS Guangzhou Institute of Energy Conversion | Zhang M.,University of Wisconsin - Madison | Zhang M.,Sun Yat Sen University | Konishi H.,University of Wisconsin - Madison | And 6 more authors.
Journal of Asian Earth Sciences | Year: 2014

In order to understand the response of authigenic pyrite to gas hydrate geo-systems, pyrite tubes or rods at the sulfate-methane transition (SMT) zone of core GC10 from the northern continental slope of the South China Sea (SCS) were investigated. In situ X-ray diffraction (XRD) results show that the pyrite tube consists of pyrite micro-crystals with trace amount of graphite in the inner tube. Scanning electron microscope (SEM) observations of pyrite tubes indicate various aggregations in the form of framboidal, euhedral, and colloidal pyrite microcrystals. Typical framboidal pyrite is considered as packing of octahedral microcrystals. Interestingly, many framboids in the tubes consist of round or irregular microcrystals and have an outer crust that consists of secondary pyrite. The size of the framboids in the inner wall of the tube is larger than that in the middle wall or foraminifer-filled pyrite. High-resolution transmission electron microscopic (HRTEM) images show marcasite lamellae defects in the spherulitic pyrite crystals, which reveal different solution conditions during the pyrite precipitation. Nano-foil-like graphitic carbon was observed to be closely associated with the pyrite spherules. The occurrence of both marcasite layers and nano-foil-like graphitic carbon suggest that the migration of methane from deep sediment. It is suggested that the formation of pyrite serves as a catalyst during the reaction from methane to elemental carbon under the anaerobic oxidation of methane. Meanwhile, this reaction results in local acidification of the solution inside the pyrite tubes, which favors marcasite lamellae growth on the host pyrite substrate. © 2014 Elsevier Ltd. Source


Sun X.,Sun Yat Sen University | Sun X.,Key Laboratory of Marine Resources and Coastal Engineering in Guangdong Province
Geotectonica et Metallogenia | Year: 2014

There exists a large number of diabase rock bodies at the Yinachang iron-copper deposit in Wuding, central Yunnan Province, southwest China. So far, few research works have been carried out on the mafic rocks within this ore district, thus the age of the diabases remains poorly understood. In this paper, we report the zircon U-Pb age of the Haizi diabase obtained by LA-ICP-MS method, and the weighted mean 206Pb/238U age is 1728±4 Ma (MSWD=1.8, n=11). The age of the diabase in the Wuding area is consistent with the contemporary magmatism in the southwestern Yangtze Block, as well as the breakup of the Columbia supercontinent. Therefore, it is suggested that these diabases formed in response to the global breakup event of the Columbia supercontinent. Moreover, the age of the Haizi diabase is roughly comparable with metallogenetic epoch of the typical iron-copper deposit, implying the possible metallogenetic significance of Late Paleoproterozoic magmatism in the southwestern Yangtze Block. This large-scale magmatic event might have been the main sources of ore-forming materials, such as Cu and Fe. In addition, the "Meidang Formation" should be older than the diabase that intruded it. Therefore, we propose that the so called "Meidang Formation", which may be considered as the more ancient basement strata existed before continental extension of the Kunyang rift, should be included in Paleoproterozoic Tangdan Group. Source


Zhang M.,CAS Guangzhou Institute of Energy Conversion | Zhang M.,Sun Yat Sen University | Konishi H.,University of Wisconsin - Madison | Xu H.,University of Wisconsin - Madison | And 5 more authors.
Journal of Asian Earth Sciences | Year: 2014

In order to understand the response of authigenic pyrite to gas hydrate geo-systems, pyrite tubes or rods at the sulfate-methane transition (SMT) zone of core GC10 from the northern continental slope of the South China Sea (SCS) were investigated. In situ X-ray diffraction (XRD) results show that the pyrite tube consists of pyrite micro-crystals with trace amount of graphite in the inner tube. Scanning electron microscope (SEM) observations of pyrite tubes indicate various aggregations in the form of framboidal, euhedral, and colloidal pyrite microcrystals. Typical framboidal pyrite is considered as packing of octahedral microcrystals. Interestingly, many framboids in the tubes consist of round or irregular microcrystals and have an outer crust that consists of secondary pyrite. The size of the framboids in the inner wall of the tube is larger than that in the middle wall or foraminifer-filled pyrite. High-resolution transmission electron microscopic (HRTEM) images show marcasite lamellae defects in the spherulitic pyrite crystals, which reveal different solution conditions during the pyrite precipitation. Nano-foil-like graphitic carbon was observed to be closely associated with the pyrite spherules. The occurrence of both marcasite layers and nano-foil-like graphitic carbon suggest that the migration of methane from deep sediment. It is suggested that the formation of pyrite serves as a catalyst during the reaction from methane to elemental carbon under the anaerobic oxidation of methane. Meanwhile, this reaction results in local acidification of the solution inside the pyrite tubes, which favors marcasite lamellae growth on the host pyrite substrate. © 2014 Elsevier Ltd. Source


Lai Z.,Sun Yat Sen University | Lai Z.,Key Laboratory of Marine Resources and Coastal Engineering in Guangdong Province | Yin K.,Sun Yat Sen University | Yin K.,Key Laboratory of Marine Resources and Coastal Engineering in Guangdong Province
Harmful Algae | Year: 2014

Port Shelter is a semi-enclosed bay in northeast Hong Kong where high biomass red tides are observed to occur frequently in narrow bands along the local bathymetric isobars. Previous study showed that nutrients in the Bay are not high enough to support high biomass red tides. The hypothesis is that physical aggregation and vertical migration of dinoflagellates appear to be the driving mechanism to promote the formation of red tides in this area. To test this hypothesis, we used a high-resolution estuarine circulation model to simulate the near-shore water dynamics based on in situ measured temperature/salinity profiles, winds and tidal constitutes taken from a well-validated regional tidal model. The model results demonstrated that water convergence occurs in a narrow band along the west shore of Port Shelter under a combined effect of stratified tidal current and easterly or northeasterly wind. Using particles as dinoflagellate cells and giving diel vertical migration, the model results showed that the particles aggregate along the convergent zone. By tracking particles in the model predicted current field, we estimated that the physical-biological coupled processes induced aggregation of the particles could cause 20-45 times enhanced cell density in the convergent zone. This indicated that a high cell density red tide under these processes could be initialized without very high nutrients concentrations. This may explain why Port Shelter, a nutrient-poor Bay, is the hot spot for high biomass red tides in Hong Kong in the past 25 years. Our study explains why red tide occurrences are episodic events and shows the importance of taking the physical-biological aggregation mechanism into consideration in the projection of red tides for coastal management. © 2013 Elsevier B.V. Source

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