The northern slope of the South China Sea is a gas-hydrate-bearing region related to a high deposition rate of organic-rich sediments co-occurring with intense methanogenesis in subseafloor environments.Anaerobic oxid...The northern slope of the South China Sea is a gas-hydrate-bearing region related to a high deposition rate of organic-rich sediments co-occurring with intense methanogenesis in subseafloor environments.Anaerobic oxidation of methane（AOM） coupled with bacterial sulfate reduction results in the precipitation of solid phase minerals in seepage sediment,including pyrite and gypsum.Abundant aggregates of pyrites and gypsums are observed between the depth of 667 and 850 cm below the seafloor（cmbsf） in the entire core sediment of HS328 from the northern South China Sea.Most pyrites are tubes consisting of framboidal cores and outer crusts.Gypsum aggregates occur as rosettes and spheroids consisting of plates.Some of them grow over pyrite,indicating that gypsum precipitation postdates pyrite formation.The sulfur isotopic values（δ^34 S） of pyrite vary greatly（from –46.6‰ to –12.3‰ V-CDT） and increase with depth.Thus,the pyrite in the shallow sediments resulted from organoclastic sulfate reduction（OSR） and is influenced by AOM with depth.The relative high abundance and δ^34 S values of pyrite in sediments at depths from 580 to 810 cmbsf indicate that this interval is the location of a paleo-sulfate methane transition zone（SMTZ）.The sulfur isotopic composition of gypsum（from–25‰ to –20.7‰） is much lower than that of the seawater sulfate,indicating the existence of a 34 S-depletion source of sulfur species that most likely are products of the oxidation of pyrites formed in OSR.Pyrite oxidation is controlled by ambient electron acceptors such as MnO2,iron（Ⅲ） and oxygen driven by the SMTZ location shift to great depths.The δ^34 S values of gypsum at greater depth are lower than those of the associated pyrite,revealing downward diffusion of 34 S-depleted sulfate from the mixture of oxidation of pyrite derived by OSR and the seawater sulfate.These sulfates also lead to an increase of calcium ions from the dissolution of calcium carbonate mineral,which will be favor to the formation of gypsum.Overall,the mineralogy and sulfur isotopic composition of the pyrite and gypsum suggest variable redox conditions caused by reduced seepage intensities,and the pyrite and gypsum can be a recorder of the intensity evolution of methane seepage.展开更多
The Taixinan Basin is one of the most potential gas hydrate bearing areas in the South China Sea and abundant gas hydrates have been discovered during expedition in 2013. In this study, geochemical and microbial metho...The Taixinan Basin is one of the most potential gas hydrate bearing areas in the South China Sea and abundant gas hydrates have been discovered during expedition in 2013. In this study, geochemical and microbial methods are combinedly used to characterize the sediments from a shallow piston Core DH_CL_11（gas hydrate free） and a gas hydrate-bearing drilling Core GMGS2-16 in this basin. Geochemical analyses indicate that anaerobic oxidation of methane（AOM） which is speculated to be linked to the ongoing gas hydrate dissociation is taking place in Core DH_CL_11 at deep. For Core GMGS2-16, AOM related to past episodes of methane seepage are suggested to dominate during its diagenetic process; while the relatively enriched δ18O bulk-sediment values indicate that methane involved in AOM might be released from the ＂episodic dissociation＂ of gas hydrate.Microbial analyses indicate that the predominant phyla in the bacterial communities are Firmicutes and Proteobacteria（Gammaproteobacteria and Epsilonproteobacteria）, while the dominant taxa in the archaeal communities are Marine_Benthic_Group_B（MBGB）, Halobacteria, Thermoplasmata, Methanobacteria,Methanomicrobia, Group C3 and MCG. Under parallel experimental operations, comparable dominant members（Firmicutes and MBGB） are found in the piston Core DH_CL_11 and the near surface layer of the long drilling Core GMGS2-16. Moreover, these members have been found predominant in other known gas hydrate bearing cores, and the dominant of MBGB has even been found significantly related to gas hydrate occurrence. Therefore,a high possibility for the existing of gas hydrate underlying Core DH_CL_11 is inferred, which is consistent with the geochemical analyses. In all, combined geochemical and microbiological analyses are more informative in characterizing sediments from gas hydrate-associated areas in the South China Sea.展开更多
The rare earth elements（REE） composition of the polymetallic crusts and nodules obtained from the South China Sea（SCS） were analyzed through inductively coupled plasma mass spectrometry.Results revealed great diff...The rare earth elements（REE） composition of the polymetallic crusts and nodules obtained from the South China Sea（SCS） were analyzed through inductively coupled plasma mass spectrometry.Results revealed great differences in the REE abundances（∑REE） of the SCS polymetallic crusts and nodules; the crusts show the highest ∑REE, whereas the nodules exhibit the lowest ∑REE. The similarity in their NASC-normalized patterns, the enriched light REE（LREE）, the markedly positive Ce anomaly（δCe）, and the non-or weakly positive Eu anomaly（δEu）, suggest that the polymetallic crusts and nodules are of hydrogenetic origin. Moreover, the REE contents and their relevant parameters are quite different among the various layers of the crusts and nodules, which probably results from the different marginal sea environments and mineral assemblages of the samples. The growth profiles of the SCS polymetallic crusts and nodules reveal the tendency ∑REE and δCe to slightly increase from the outer to the inner layers, suggesting that the growth environments of these samples changed smoothly from an oxidizing to a relatively reducing environment; in addition, the crust ST1 may have experienced a regressive event（sea-level change） during its growth, although the REE composition of the seawater remained relatively stable. On the basis of the regional ∑REE distribution in the SCS crusts and nodules,the samples collected near the northern margin were influenced by terrigenous material more strongly compared with the other samples, and the REE contents are relatively low. Therefore, the special geotectonic environment is a significant factor influencing the abundance of elements, including REE and other trace elements. Compared with the oceanic seamount crusts and deep-sea nodules from other oceans,the SCS polymetallic crusts and nodules exhibit special REE compositions and shale-normalized patterns, implying that the samples are of marginal sea-type Fe-Mn sedimentary deposits, which are strongly affected by the epicontinental environment, and that they grew in a more oxidative seawater environment. This analysis indicates that the oxidized seawater environment and the special nano property of their Fe-Mn minerals enrich the REE adsorption.展开更多
Noble gas isotopic compositions of various layers in three-layered （outer, porous and compact layers） cobalt-rich ferromanganese crusts and their basaltic and phosphorite substrates from the western Pacific Ocean we...Noble gas isotopic compositions of various layers in three-layered （outer, porous and compact layers） cobalt-rich ferromanganese crusts and their basaltic and phosphorite substrates from the western Pacific Ocean were analyzed by using a high vacuum gas mass spectrum. The analytical results show that the noble gases in the Co-rich crusts have derived mainly from the ambient seawater, extraterrestrial grains such as interplanetary dust particles （IDPs） and wind-borne continental dust grains, and locally formation water in the submarine sediments, but different noble gases have different sources. He in the crusts derives predominantly from the extraterrestrial grains, with a negligible amount of radiogenic He from the eolian dust grains. Ar is sourced mainly from the dissolved air in the seawater and insignificantly from radiogenic Ar in the eolian continental dust grains or the formation water. Xe and Ne derive mainly from the seawater, with minor amounts of extraterrestrial Xe and Ne in the IDPs. Compared with the porous and outer layers, the compact layer has a relatively high 4He content and lower 3He/4He ratios, suggesting that marine phosphatization might have greatly modified the noble gas isotopic compositions of the crusts. Besides, the 3He/4He values of the basaltic substrates of the cobalt-rich crusts are very low and their R/R. ratios are mostly 〈0.1 R., which are similar to that of phosphorite substrates （0.087 R.）, but much lower than that of fresh submarine MORB （8.75±14 Ra） or seamount basalts （3-43 Ra）, implying that the basaltic substrates have suffered strong water/rock interaction and reacted with radiogenic ^4He and P-rich upwelling marine currents during phosphatization. The trace elements released in the basalt/seawater interaction might favor the growth of cobalt-rich crusts. The relatively low ^3He/^4He values in the seamount basalts may be used as an important exploration criterion for the cobalt-rich ferromanganese crusts.展开更多
目的探究抑制Polo样蛋白激酶1(Polo-likekinase1,PLK1)联合细胞因子诱导的杀伤细胞(cytokine-induced killer cell,CIK细胞)对三阴性乳腺癌(triple-negative breast cancer,TNBC)的杀伤作用,并初步探究其作用机制。方法Ficoll密度梯度...目的探究抑制Polo样蛋白激酶1(Polo-likekinase1,PLK1)联合细胞因子诱导的杀伤细胞(cytokine-induced killer cell,CIK细胞)对三阴性乳腺癌(triple-negative breast cancer,TNBC)的杀伤作用,并初步探究其作用机制。方法Ficoll密度梯度离心法分离健康志愿者外周血单个核细胞,诱导生成CIK细胞并鉴定;使用不同浓度PLK1抑制剂BI-2536处理MDA-MB-231细胞,MTT法检测细胞存活率;以MDA-MB-231细胞作为靶细胞,CIK细胞为效应细胞,MTT法检测不同效靶比下细胞存活率;再以BI-2536联合CIK细胞处理MDA-MB-231细胞,MTT法检测细胞存活率,流式细胞术检测细胞凋亡水平,蛋白质印迹法测定细胞内胱天蛋白酶(caspase)-3与caspase-9蛋白活性;构建TNBC裸鼠移植瘤模型,随机分为对照组、BI-2536组、CIK组和BI-2536+CIK组,按照分组对裸鼠进行处理后,每隔2d测量瘤体,21d后处死裸鼠称重瘤体,苏木精-伊红染色观察肿瘤组织内细胞生长情况,免疫组织化学染色检测肿瘤组织内细胞增殖标记物Ki-67及caspase-3、caspase-9蛋白阳性表达情况。结果与诱导前比较,诱导后CIK细胞亚群中CD3^(+)CD8^(+)和CD3^(+)CD56^(+)细胞比例均增高,CD3^(+)CD4^(+)细胞比例减少(P<0.05);不同浓度BI-2536作用下的MDA-MB-231细胞存活率均下降,不同效靶比的CIK细胞作用下的MDA-MB-231细胞存活率也下降(P<0.05);相较于单独BI-2536或CIK细胞处理,BI-2536和CIK细胞联合作用后细胞存活率下降,细胞凋亡率升高,caspase-3与caspase-9蛋白活性增加(P<0.05)。裸鼠移植瘤模型实验发现,BI-2536和CIK细胞联合作用能够抑制肿瘤组织生长,肿瘤质量减小,肿瘤组织内细胞排列稀疏且增殖受抑制,Ki-67阳性率降低,caspase-3和caspase-9阳性率均增加(P<0.05)。结论使用PLK1抑制剂BI-2536联合CIK细胞能够在体外和体内抑制TNBC肿瘤细胞增殖,并提高对肿瘤细胞的杀伤作用,该机制可能与激活caspase依赖性途径有关。展开更多
Gas hydrates are a significant energy resource and are usually detected by bottom simulating reflection and submarine geochemical anomalies. Authigenic minerals are related to gas hydrates, with carbonates, sulfates a...Gas hydrates are a significant energy resource and are usually detected by bottom simulating reflection and submarine geochemical anomalies. Authigenic minerals are related to gas hydrates, with carbonates, sulfates and sulfides being important tracing minerals. Authigenic tubular pyrites were collected from offshore southwest Taiwan in the South China Sea, and were investigated by scanning electron microscopy(SEM) and high-resolution transmission electron microscopy (HRTEM). Authigenic tubular pyrite was composed of framboidal pyrite, within which nanosized graphitic carbon of low crystallinity was discovered. The graphitic carbon coexisted with pyrite and had a texture similar to carbon nanotubes and nanocones, indicating that they likely precipitated from carbon supersaturated C-H-O fluid. Pyrite may act as a catalyst for the conversion of CH 4 to C. The discovery of nanosized graphitic carbon in pyrite indicated it was deposited in sediments that were supersaturated with methane fluid. Thus, nanosized graphitic carbon may be another tracing species for submarine gas hydrates. The discovery of nanosized graphitic carbon deposited in a low temperature environment will enlighten our understanding of the laboratory synthesis and industrial production of graphitic carbon.展开更多
Elemental sulfur(ES) is one of the intermediates in the inorganic sulfur cycle and thus plays a key role in the fractionation of stable sulfur isotopes in different reservoirs and the marine environment. In this study...Elemental sulfur(ES) is one of the intermediates in the inorganic sulfur cycle and thus plays a key role in the fractionation of stable sulfur isotopes in different reservoirs and the marine environment. In this study, solid ES is discovered in sediments near the Jiulong Methane Reef in the northern South China Sea by scanning electron microscopy and Raman spectroscopy. Combining the morphology and distribution of ES, pyrite concentrations, and sulfur isotopes, we conclude that:(1) solid ES coexists with pyrite microcrystals and sulfide(oxyhydr)oxides as well as clay minerals, and they are mainly distributed on the surface of mineral aggregates;(2) ES mainly occurs within and near the sulfate-methane transition zone(SMTZ) despite little morphological diversity;(3) ES formation might be related to hydrogen sulfide oxidation and is therefore linked with fluctuations in the SMTZ. Within the SMTZ, hydrogen sulfide is produced and pyrite precipitates because of enhanced anaerobic oxidation of methane coupled with dissimilatory sulfate reduction. This enhances the efficiency of the inorganic sulfur cycle and provides favorable conditions for ES formation. The discovery of solid ES in sediments near the Jiulong Methane Reef suggests an important relationship with SMTZ fluctuations that could have implications for the evolution of methane hydrate in the South China Sea.展开更多
基金The Qingdao National Laboratory for Marine Science and Technology under contract No.QNLM2016ORP0210the National Natural Science Foundation of China under contract Nos 41306061,41473080 and 41376076the Scientific Cooperative Project by China National Petroleum Corporation and Chinese Academic of Sciences under contract No.2015A-4813
文摘The northern slope of the South China Sea is a gas-hydrate-bearing region related to a high deposition rate of organic-rich sediments co-occurring with intense methanogenesis in subseafloor environments.Anaerobic oxidation of methane（AOM） coupled with bacterial sulfate reduction results in the precipitation of solid phase minerals in seepage sediment,including pyrite and gypsum.Abundant aggregates of pyrites and gypsums are observed between the depth of 667 and 850 cm below the seafloor（cmbsf） in the entire core sediment of HS328 from the northern South China Sea.Most pyrites are tubes consisting of framboidal cores and outer crusts.Gypsum aggregates occur as rosettes and spheroids consisting of plates.Some of them grow over pyrite,indicating that gypsum precipitation postdates pyrite formation.The sulfur isotopic values（δ^34 S） of pyrite vary greatly（from –46.6‰ to –12.3‰ V-CDT） and increase with depth.Thus,the pyrite in the shallow sediments resulted from organoclastic sulfate reduction（OSR） and is influenced by AOM with depth.The relative high abundance and δ^34 S values of pyrite in sediments at depths from 580 to 810 cmbsf indicate that this interval is the location of a paleo-sulfate methane transition zone（SMTZ）.The sulfur isotopic composition of gypsum（from–25‰ to –20.7‰） is much lower than that of the seawater sulfate,indicating the existence of a 34 S-depletion source of sulfur species that most likely are products of the oxidation of pyrites formed in OSR.Pyrite oxidation is controlled by ambient electron acceptors such as MnO2,iron（Ⅲ） and oxygen driven by the SMTZ location shift to great depths.The δ^34 S values of gypsum at greater depth are lower than those of the associated pyrite,revealing downward diffusion of 34 S-depleted sulfate from the mixture of oxidation of pyrite derived by OSR and the seawater sulfate.These sulfates also lead to an increase of calcium ions from the dissolution of calcium carbonate mineral,which will be favor to the formation of gypsum.Overall,the mineralogy and sulfur isotopic composition of the pyrite and gypsum suggest variable redox conditions caused by reduced seepage intensities,and the pyrite and gypsum can be a recorder of the intensity evolution of methane seepage.
基金The Natural Science Foundation of China under contract Nos 91128101,41273054 and 41373007the China Geological Survey Project for South China Sea Gas Hydrate Resource Exploration under contract No.DD20160211+1 种基金the Fundamental Research Funds for the Central Universities under contract No.16lgjc11the Guangdong Province Universities and Colleges Pearl River Scholar Funded Scheme under contract No.2011
文摘The Taixinan Basin is one of the most potential gas hydrate bearing areas in the South China Sea and abundant gas hydrates have been discovered during expedition in 2013. In this study, geochemical and microbial methods are combinedly used to characterize the sediments from a shallow piston Core DH_CL_11（gas hydrate free） and a gas hydrate-bearing drilling Core GMGS2-16 in this basin. Geochemical analyses indicate that anaerobic oxidation of methane（AOM） which is speculated to be linked to the ongoing gas hydrate dissociation is taking place in Core DH_CL_11 at deep. For Core GMGS2-16, AOM related to past episodes of methane seepage are suggested to dominate during its diagenetic process; while the relatively enriched δ18O bulk-sediment values indicate that methane involved in AOM might be released from the ＂episodic dissociation＂ of gas hydrate.Microbial analyses indicate that the predominant phyla in the bacterial communities are Firmicutes and Proteobacteria（Gammaproteobacteria and Epsilonproteobacteria）, while the dominant taxa in the archaeal communities are Marine_Benthic_Group_B（MBGB）, Halobacteria, Thermoplasmata, Methanobacteria,Methanomicrobia, Group C3 and MCG. Under parallel experimental operations, comparable dominant members（Firmicutes and MBGB） are found in the piston Core DH_CL_11 and the near surface layer of the long drilling Core GMGS2-16. Moreover, these members have been found predominant in other known gas hydrate bearing cores, and the dominant of MBGB has even been found significantly related to gas hydrate occurrence. Therefore,a high possibility for the existing of gas hydrate underlying Core DH_CL_11 is inferred, which is consistent with the geochemical analyses. In all, combined geochemical and microbiological analyses are more informative in characterizing sediments from gas hydrate-associated areas in the South China Sea.
基金financially supported by the National12th Five Year Plan Project(No.DY-125-13-R-05)Natural Sciences Foundation of China(No.40343019.40473024)+2 种基金project from the State Key Laboratory for Mineral Deposits Research in Nanjing University(No.20-15-07)the Project Supported by Guangdong Province Universities and Colleges Pearl River Scholar Funded Scheme(2011)the Fundamental Research Funds for Central Universities(No.121gjc05,091gpy09)
文摘The rare earth elements（REE） composition of the polymetallic crusts and nodules obtained from the South China Sea（SCS） were analyzed through inductively coupled plasma mass spectrometry.Results revealed great differences in the REE abundances（∑REE） of the SCS polymetallic crusts and nodules; the crusts show the highest ∑REE, whereas the nodules exhibit the lowest ∑REE. The similarity in their NASC-normalized patterns, the enriched light REE（LREE）, the markedly positive Ce anomaly（δCe）, and the non-or weakly positive Eu anomaly（δEu）, suggest that the polymetallic crusts and nodules are of hydrogenetic origin. Moreover, the REE contents and their relevant parameters are quite different among the various layers of the crusts and nodules, which probably results from the different marginal sea environments and mineral assemblages of the samples. The growth profiles of the SCS polymetallic crusts and nodules reveal the tendency ∑REE and δCe to slightly increase from the outer to the inner layers, suggesting that the growth environments of these samples changed smoothly from an oxidizing to a relatively reducing environment; in addition, the crust ST1 may have experienced a regressive event（sea-level change） during its growth, although the REE composition of the seawater remained relatively stable. On the basis of the regional ∑REE distribution in the SCS crusts and nodules,the samples collected near the northern margin were influenced by terrigenous material more strongly compared with the other samples, and the REE contents are relatively low. Therefore, the special geotectonic environment is a significant factor influencing the abundance of elements, including REE and other trace elements. Compared with the oceanic seamount crusts and deep-sea nodules from other oceans,the SCS polymetallic crusts and nodules exhibit special REE compositions and shale-normalized patterns, implying that the samples are of marginal sea-type Fe-Mn sedimentary deposits, which are strongly affected by the epicontinental environment, and that they grew in a more oxidative seawater environment. This analysis indicates that the oxidized seawater environment and the special nano property of their Fe-Mn minerals enrich the REE adsorption.
文摘Noble gas isotopic compositions of various layers in three-layered （outer, porous and compact layers） cobalt-rich ferromanganese crusts and their basaltic and phosphorite substrates from the western Pacific Ocean were analyzed by using a high vacuum gas mass spectrum. The analytical results show that the noble gases in the Co-rich crusts have derived mainly from the ambient seawater, extraterrestrial grains such as interplanetary dust particles （IDPs） and wind-borne continental dust grains, and locally formation water in the submarine sediments, but different noble gases have different sources. He in the crusts derives predominantly from the extraterrestrial grains, with a negligible amount of radiogenic He from the eolian dust grains. Ar is sourced mainly from the dissolved air in the seawater and insignificantly from radiogenic Ar in the eolian continental dust grains or the formation water. Xe and Ne derive mainly from the seawater, with minor amounts of extraterrestrial Xe and Ne in the IDPs. Compared with the porous and outer layers, the compact layer has a relatively high 4He content and lower 3He/4He ratios, suggesting that marine phosphatization might have greatly modified the noble gas isotopic compositions of the crusts. Besides, the 3He/4He values of the basaltic substrates of the cobalt-rich crusts are very low and their R/R. ratios are mostly 〈0.1 R., which are similar to that of phosphorite substrates （0.087 R.）, but much lower than that of fresh submarine MORB （8.75±14 Ra） or seamount basalts （3-43 Ra）, implying that the basaltic substrates have suffered strong water/rock interaction and reacted with radiogenic ^4He and P-rich upwelling marine currents during phosphatization. The trace elements released in the basalt/seawater interaction might favor the growth of cobalt-rich crusts. The relatively low ^3He/^4He values in the seamount basalts may be used as an important exploration criterion for the cobalt-rich ferromanganese crusts.
文摘目的探究抑制Polo样蛋白激酶1(Polo-likekinase1,PLK1)联合细胞因子诱导的杀伤细胞(cytokine-induced killer cell,CIK细胞)对三阴性乳腺癌(triple-negative breast cancer,TNBC)的杀伤作用,并初步探究其作用机制。方法Ficoll密度梯度离心法分离健康志愿者外周血单个核细胞,诱导生成CIK细胞并鉴定;使用不同浓度PLK1抑制剂BI-2536处理MDA-MB-231细胞,MTT法检测细胞存活率;以MDA-MB-231细胞作为靶细胞,CIK细胞为效应细胞,MTT法检测不同效靶比下细胞存活率;再以BI-2536联合CIK细胞处理MDA-MB-231细胞,MTT法检测细胞存活率,流式细胞术检测细胞凋亡水平,蛋白质印迹法测定细胞内胱天蛋白酶(caspase)-3与caspase-9蛋白活性;构建TNBC裸鼠移植瘤模型,随机分为对照组、BI-2536组、CIK组和BI-2536+CIK组,按照分组对裸鼠进行处理后,每隔2d测量瘤体,21d后处死裸鼠称重瘤体,苏木精-伊红染色观察肿瘤组织内细胞生长情况,免疫组织化学染色检测肿瘤组织内细胞增殖标记物Ki-67及caspase-3、caspase-9蛋白阳性表达情况。结果与诱导前比较,诱导后CIK细胞亚群中CD3^(+)CD8^(+)和CD3^(+)CD56^(+)细胞比例均增高,CD3^(+)CD4^(+)细胞比例减少(P<0.05);不同浓度BI-2536作用下的MDA-MB-231细胞存活率均下降,不同效靶比的CIK细胞作用下的MDA-MB-231细胞存活率也下降(P<0.05);相较于单独BI-2536或CIK细胞处理,BI-2536和CIK细胞联合作用后细胞存活率下降,细胞凋亡率升高,caspase-3与caspase-9蛋白活性增加(P<0.05)。裸鼠移植瘤模型实验发现,BI-2536和CIK细胞联合作用能够抑制肿瘤组织生长,肿瘤质量减小,肿瘤组织内细胞排列稀疏且增殖受抑制,Ki-67阳性率降低,caspase-3和caspase-9阳性率均增加(P<0.05)。结论使用PLK1抑制剂BI-2536联合CIK细胞能够在体外和体内抑制TNBC肿瘤细胞增殖,并提高对肿瘤细胞的杀伤作用,该机制可能与激活caspase依赖性途径有关。
基金supported by the Project of the 10th and 11th Five-Year Research and Development of International Seabed (DYXM-115-02-1-11)the Specialized Research Fund for the Doctoral Program of Higher Education (20090171120019)+1 种基金the Fundamental Research Funds for the Central Universities (09lgpy09)the Project of Key Laboratory of Marginal Sea Geology, Guangzhou Institute of Geochemistry and South China Sea Institute of Oceanology, CAS (MSGL08-01 and MSGLCAS03-4)
文摘Gas hydrates are a significant energy resource and are usually detected by bottom simulating reflection and submarine geochemical anomalies. Authigenic minerals are related to gas hydrates, with carbonates, sulfates and sulfides being important tracing minerals. Authigenic tubular pyrites were collected from offshore southwest Taiwan in the South China Sea, and were investigated by scanning electron microscopy(SEM) and high-resolution transmission electron microscopy (HRTEM). Authigenic tubular pyrite was composed of framboidal pyrite, within which nanosized graphitic carbon of low crystallinity was discovered. The graphitic carbon coexisted with pyrite and had a texture similar to carbon nanotubes and nanocones, indicating that they likely precipitated from carbon supersaturated C-H-O fluid. Pyrite may act as a catalyst for the conversion of CH 4 to C. The discovery of nanosized graphitic carbon in pyrite indicated it was deposited in sediments that were supersaturated with methane fluid. Thus, nanosized graphitic carbon may be another tracing species for submarine gas hydrates. The discovery of nanosized graphitic carbon deposited in a low temperature environment will enlighten our understanding of the laboratory synthesis and industrial production of graphitic carbon.
基金supported by the National Natural Science Foundation of China(Grants Nos.41472085 and 41172102)the National Basic Research Program of China(Grants Nos.2011CB808805 and 2009CB21950605)the National Project of Exploration and Test Production for Gas Hydrate(Grants Nos.GZH20110030-50603 and GZH20110030-6WX02)
文摘Elemental sulfur(ES) is one of the intermediates in the inorganic sulfur cycle and thus plays a key role in the fractionation of stable sulfur isotopes in different reservoirs and the marine environment. In this study, solid ES is discovered in sediments near the Jiulong Methane Reef in the northern South China Sea by scanning electron microscopy and Raman spectroscopy. Combining the morphology and distribution of ES, pyrite concentrations, and sulfur isotopes, we conclude that:(1) solid ES coexists with pyrite microcrystals and sulfide(oxyhydr)oxides as well as clay minerals, and they are mainly distributed on the surface of mineral aggregates;(2) ES mainly occurs within and near the sulfate-methane transition zone(SMTZ) despite little morphological diversity;(3) ES formation might be related to hydrogen sulfide oxidation and is therefore linked with fluctuations in the SMTZ. Within the SMTZ, hydrogen sulfide is produced and pyrite precipitates because of enhanced anaerobic oxidation of methane coupled with dissimilatory sulfate reduction. This enhances the efficiency of the inorganic sulfur cycle and provides favorable conditions for ES formation. The discovery of solid ES in sediments near the Jiulong Methane Reef suggests an important relationship with SMTZ fluctuations that could have implications for the evolution of methane hydrate in the South China Sea.
