Carbon and oxygen isotope and dating analyses of foraminiferan in sediment cores collected from three different areas of the northern slope of the South China Sea were conducted, in order to examine the records of the...Carbon and oxygen isotope and dating analyses of foraminiferan in sediment cores collected from three different areas of the northern slope of the South China Sea were conducted, in order to examine the records of the gas hydrate decomposition events since the late Quaternary under the conditions of methane seepage. The results show that： 1） the δ13C values of the benthic foraminiferan Uvigerina spp. （size range of 0.25-0.35 ram） are from -0.212% to -0.021% and the δ180 values of the planktonic foraminiferan Globigerinoides ruber （size range of 0.25-0.35 ram） are from -0.311% to -0.060%; 2） three cores （ZD2, ZD3 and ZS5） from the bottom of a hole are aged for 11 814, 26 616 and 64 090 a corresponding to the early oxygen isotope stage （MIS） Ⅰ, Ⅲ and Ⅳ final period, respectively; 3） a negative-skewed layer of carbon isotope corresponds to that of MIS II （cold period）, whose degree of negative bias is -0.2%0; and 4） the δ13C compositions of foraminiferans are similar to those of the Blake Ridge and the Gulf of Mexico sediments of the late Quaternary. According to the analysis, the reasons for these results are that the studied area is a typical area of methane seep environment in the area during MIS II due to the global sea-level fall and sea pressure decrease. Gas hydrate is decomposed and released, and a large number of light carbon isotopes of methane are released into the ocean, dissolved to inorganic carbon （DIC） pool and recorded in the foraminiferan shells. A pyrite layer developed in the negative bias layers of the foraminiferans confirms that the δ13C of foraminiferans is more affected by methane and less by the reduction of marine productivity and early diagenesis. The use of foraminiferan δ13C could accurately determine late Quaternary hydrate release events and provide evidence for both reconstructing the geological history of methane release events and exploring natural gas hydrate.展开更多
A comparative study on the phenotypic and genetic characteristics among Acidithiobacillus ferrooxidans （AF2）, a typic strain ATCC23270 and a previously isolated strain AF3 was performed. AF2 can use ferrous ion （F...A comparative study on the phenotypic and genetic characteristics among Acidithiobacillus ferrooxidans （AF2）, a typic strain ATCC23270 and a previously isolated strain AF3 was performed. AF2 can use ferrous ion （Fe^2＋） or elemental sulfur （S^0） as sole energy source, but oxidizes So more effectively than Fe^2＋, which is different from ATCC23270 and AF3. The G＋C content of AF2 is 51.8% （molar fraction）, however, ATCC23270 and AF3 strains have G＋C content of 63.7% and 64.8% （molar fraction）, respectively. The DNA-DNA hybridization results show that AF2 has 41.53% and 52.38% genome similarity to ATCC 23270 and AF3, respectively, but AF3 has a high genome similarity of 89.86% to ATCC 23270 strain. Rusticyanin （rus） and subunit III of aa3-type cytochrome oxidase （coxC） genes are not detected in AF2, but Fe^2＋ oxidase （iro） gene can be detected. To understand the genomic organization of iro gene, a cosmid library of AF2 genome was constructed and iro gene-containing clone was screened. The sequencing result shows that although the nucleotide sequence of iro gene in AF2 is completely identical to that of ATCC 23270 strain, its genomic organization is different from that of ATCC 23270. In AF2, iro is located at downstream ofpurA gene, while it is located at downstream ofpetC-2 gene in ATCC 23270 strain. These results indicate that AF2 is a novel strain ofA. ferrooxidans, and that phenotypic differences among the strains ofA. ferrooxidans are closely correlated with their genetic polymorphisms.展开更多
基金Project(40976035) supported by the National Natural Science Foundation of ChinaProject(2009CB219501) supported by the National Basic Research Program of ChinaProject(908-ZC-I-07) supported by the Special Program of Comprehensive Survey and Assessment Offshore China Sea
文摘Carbon and oxygen isotope and dating analyses of foraminiferan in sediment cores collected from three different areas of the northern slope of the South China Sea were conducted, in order to examine the records of the gas hydrate decomposition events since the late Quaternary under the conditions of methane seepage. The results show that： 1） the δ13C values of the benthic foraminiferan Uvigerina spp. （size range of 0.25-0.35 ram） are from -0.212% to -0.021% and the δ180 values of the planktonic foraminiferan Globigerinoides ruber （size range of 0.25-0.35 ram） are from -0.311% to -0.060%; 2） three cores （ZD2, ZD3 and ZS5） from the bottom of a hole are aged for 11 814, 26 616 and 64 090 a corresponding to the early oxygen isotope stage （MIS） Ⅰ, Ⅲ and Ⅳ final period, respectively; 3） a negative-skewed layer of carbon isotope corresponds to that of MIS II （cold period）, whose degree of negative bias is -0.2%0; and 4） the δ13C compositions of foraminiferans are similar to those of the Blake Ridge and the Gulf of Mexico sediments of the late Quaternary. According to the analysis, the reasons for these results are that the studied area is a typical area of methane seep environment in the area during MIS II due to the global sea-level fall and sea pressure decrease. Gas hydrate is decomposed and released, and a large number of light carbon isotopes of methane are released into the ocean, dissolved to inorganic carbon （DIC） pool and recorded in the foraminiferan shells. A pyrite layer developed in the negative bias layers of the foraminiferans confirms that the δ13C of foraminiferans is more affected by methane and less by the reduction of marine productivity and early diagenesis. The use of foraminiferan δ13C could accurately determine late Quaternary hydrate release events and provide evidence for both reconstructing the geological history of methane release events and exploring natural gas hydrate.
基金Project(200805032) supported by the Scientific Research Program of Marine Public Welfare Industry of China
文摘A comparative study on the phenotypic and genetic characteristics among Acidithiobacillus ferrooxidans （AF2）, a typic strain ATCC23270 and a previously isolated strain AF3 was performed. AF2 can use ferrous ion （Fe^2＋） or elemental sulfur （S^0） as sole energy source, but oxidizes So more effectively than Fe^2＋, which is different from ATCC23270 and AF3. The G＋C content of AF2 is 51.8% （molar fraction）, however, ATCC23270 and AF3 strains have G＋C content of 63.7% and 64.8% （molar fraction）, respectively. The DNA-DNA hybridization results show that AF2 has 41.53% and 52.38% genome similarity to ATCC 23270 and AF3, respectively, but AF3 has a high genome similarity of 89.86% to ATCC 23270 strain. Rusticyanin （rus） and subunit III of aa3-type cytochrome oxidase （coxC） genes are not detected in AF2, but Fe^2＋ oxidase （iro） gene can be detected. To understand the genomic organization of iro gene, a cosmid library of AF2 genome was constructed and iro gene-containing clone was screened. The sequencing result shows that although the nucleotide sequence of iro gene in AF2 is completely identical to that of ATCC 23270 strain, its genomic organization is different from that of ATCC 23270. In AF2, iro is located at downstream ofpurA gene, while it is located at downstream ofpetC-2 gene in ATCC 23270 strain. These results indicate that AF2 is a novel strain ofA. ferrooxidans, and that phenotypic differences among the strains ofA. ferrooxidans are closely correlated with their genetic polymorphisms.
