Recent studies have shown that specific geochemical characteristics of sediments can be used to reconstruct past methane seepage events.In this work,the correlation between the Sr/Ca and Mg/Ca ratios of sediment sampl...Recent studies have shown that specific geochemical characteristics of sediments can be used to reconstruct past methane seepage events.In this work,the correlation between the Sr/Ca and Mg/Ca ratios of sediment samples is analyzed and the sulfate concentration profile in Site C14 from cold-seep sediments in the Qiongdongnan Basin in northern South China Sea is obtained.The results confirmed that,sulfate at 0–247 cm below sea floor(Unit I)is mainly consumed by organic matter sulfate reduction(OSR),while sulfate at 247–655 cm(UnitⅡ)is consumed by both the OSR and the anaerobic oxidation of methane(AOM).In addition,the bottom sediment layer is affected by weak methane seepage.The Mo and U enrichment factors also exhibit similar trends in their respective depth profiles.The responses of trace elements,including Co/Al,Ni/Al,Cr/Al and Zn/Al ratios to methane seepage allowed the study of depositional conditions and methane seepage events.Based on the results,it is speculated that the depositional conditions of UnitⅡchanged with depth from moderate conditions of sulfidic and oxic conditions to locally anoxic conditions,and finally to suboxic conditions due to methane fluid leakage.The stable isotope values of chromium-reducible sulfide produced by AOM and those of sulfide formed by OSR in the early diagenetic environment suffered serious depletion of 34S.This was probably due to weak methane leakage,which caused the slower upward diffusion and the effect of early diagenesis on the samples.It is necessary to consider the effects of depositional environments and diagenesis on these geochemical parameters.展开更多
Long-chain n-alkanols and n-alkanes in core sediments from the northern South China Sea(SCS)were measured to make a comparison during terrestrial vegetation reconstruction from~42 ka to~7 ka.The results showed that te...Long-chain n-alkanols and n-alkanes in core sediments from the northern South China Sea(SCS)were measured to make a comparison during terrestrial vegetation reconstruction from~42 ka to~7 ka.The results showed that terrestrial vegetation record from long-chain n-alkanes matched well with previous studies in nearby cores,showing that more C_(4)plants developed during the Last Glacial Maximum(LGM)and C_(3)plants dominated in the interglacial period.However,these scenarios were not revealed by terrestrial vegetation reconstruction using long-chain n-alkanols,which showed C_(3)plant expansion during the LGM.The discrepancy during the interglacial period could be attributed to the aerobic degradation of functionalized long-chain n-alkanols in the oxygen-rich bottom water,resulting in poor preservation of terrestrial vegetation signals.On the other hand,the different advantages of functionalized n-alkanols and non-functional n-alkanes to record local and distal vegetation signals,respectively,may offer a potential explanation for the contradiction during the LGM when the SCS was characterized by low-oxygen deep water.Nevertheless,large variations on n-alkyl lipid compositions in C_(3)/C_(4)plants could play a part in modulating sedimentary long-chain n-alkanols and n-alkanes toward different vegetation signals,thereby suggesting that caution must be taken in respect to the terrestrial vegetation reconstruction using long-chain n-alkanes and long-chain n-alkanols.展开更多
Anaerobic oxidation of methane(AOM) is an important biogeochemical process, which has important scientific significance for global climate change and atmospheric evolution. This research examined the δ^(34)S, terrige...Anaerobic oxidation of methane(AOM) is an important biogeochemical process, which has important scientific significance for global climate change and atmospheric evolution. This research examined the δ^(34)S, terrigenous clastic indices of TiO_(2) and Al_(2)O_(3), and times for formation of the Ba front at site SH1, site SH3 and site 973-4 in the South China Sea. Three different coupling mechanisms of deposition rate and methane flux were discovered. The different coupling mechanisms had different effects on the role of AOM. At site 973-4, a high deposition rate caused a rapid vertical downward migration of the sulphate–methane transition zone(SMTZ), and the higher input resulted in mineral dissolution. At site SH3, the deposition rate and methane flux were basically in balance,so the SMTZ and paleo-SMTZ were the most stable of any site, and these were in a slow process of migration. At site SH1, the methane flux dominated the coupled mode, so the movement of the SMTZ at site SH1 was consistent with the general understanding. Understanding the factors influencing the SMTZ is important for understanding the early diagenesis process.展开更多
基金The Program of Institution of South China Sea Ecology and Environmental Engineering,Chinese Academy of Sciences under contract No.ISEE2018YB03the Special Project for Marine Economy Development of Guangdong Province under contract No.GDME-2018D002+1 种基金the Evaluation and Detection Technology Laboratory for Marine Mineral Resources,Qingdao National Laboratory for Marine Science and Technology under contract No.KC201703the Youth Innovation Promotion Association CAS under contract No.201432
文摘Recent studies have shown that specific geochemical characteristics of sediments can be used to reconstruct past methane seepage events.In this work,the correlation between the Sr/Ca and Mg/Ca ratios of sediment samples is analyzed and the sulfate concentration profile in Site C14 from cold-seep sediments in the Qiongdongnan Basin in northern South China Sea is obtained.The results confirmed that,sulfate at 0–247 cm below sea floor(Unit I)is mainly consumed by organic matter sulfate reduction(OSR),while sulfate at 247–655 cm(UnitⅡ)is consumed by both the OSR and the anaerobic oxidation of methane(AOM).In addition,the bottom sediment layer is affected by weak methane seepage.The Mo and U enrichment factors also exhibit similar trends in their respective depth profiles.The responses of trace elements,including Co/Al,Ni/Al,Cr/Al and Zn/Al ratios to methane seepage allowed the study of depositional conditions and methane seepage events.Based on the results,it is speculated that the depositional conditions of UnitⅡchanged with depth from moderate conditions of sulfidic and oxic conditions to locally anoxic conditions,and finally to suboxic conditions due to methane fluid leakage.The stable isotope values of chromium-reducible sulfide produced by AOM and those of sulfide formed by OSR in the early diagenetic environment suffered serious depletion of 34S.This was probably due to weak methane leakage,which caused the slower upward diffusion and the effect of early diagenesis on the samples.It is necessary to consider the effects of depositional environments and diagenesis on these geochemical parameters.
基金The Key Special Project for Introduced Talents Team of Southern Marine Science and Engineering Guangdong Laboratory(Guangzhou)under contract No.GML2019ZD0104the Science and Technology Program of Guangzhou,China under contract No.201804010264+3 种基金the Guangdong MEPP Fund under contract No.GDOE[2019]A41the National Natural Science Foundation of China under contract No.41706059the Fund of Institution of South China Sea Ecology and Environmental Engineering,Chinese Academy of Sciences under contract No.ISEE2020YB05the State Key R&D Project under contract No.2016YFA0601104。
文摘Long-chain n-alkanols and n-alkanes in core sediments from the northern South China Sea(SCS)were measured to make a comparison during terrestrial vegetation reconstruction from~42 ka to~7 ka.The results showed that terrestrial vegetation record from long-chain n-alkanes matched well with previous studies in nearby cores,showing that more C_(4)plants developed during the Last Glacial Maximum(LGM)and C_(3)plants dominated in the interglacial period.However,these scenarios were not revealed by terrestrial vegetation reconstruction using long-chain n-alkanols,which showed C_(3)plant expansion during the LGM.The discrepancy during the interglacial period could be attributed to the aerobic degradation of functionalized long-chain n-alkanols in the oxygen-rich bottom water,resulting in poor preservation of terrestrial vegetation signals.On the other hand,the different advantages of functionalized n-alkanols and non-functional n-alkanes to record local and distal vegetation signals,respectively,may offer a potential explanation for the contradiction during the LGM when the SCS was characterized by low-oxygen deep water.Nevertheless,large variations on n-alkyl lipid compositions in C_(3)/C_(4)plants could play a part in modulating sedimentary long-chain n-alkanols and n-alkanes toward different vegetation signals,thereby suggesting that caution must be taken in respect to the terrestrial vegetation reconstruction using long-chain n-alkanes and long-chain n-alkanols.
基金The Guangdong Basic and Applied Basic Research Fund Project under contract No.2021A1515011509the Municipal Science and Technology Program of Guangzhou under contract No.201904010311the Special Project for Marine Economy Development of Guangdong Province under contract No.GDME-2018D002。
文摘Anaerobic oxidation of methane(AOM) is an important biogeochemical process, which has important scientific significance for global climate change and atmospheric evolution. This research examined the δ^(34)S, terrigenous clastic indices of TiO_(2) and Al_(2)O_(3), and times for formation of the Ba front at site SH1, site SH3 and site 973-4 in the South China Sea. Three different coupling mechanisms of deposition rate and methane flux were discovered. The different coupling mechanisms had different effects on the role of AOM. At site 973-4, a high deposition rate caused a rapid vertical downward migration of the sulphate–methane transition zone(SMTZ), and the higher input resulted in mineral dissolution. At site SH3, the deposition rate and methane flux were basically in balance,so the SMTZ and paleo-SMTZ were the most stable of any site, and these were in a slow process of migration. At site SH1, the methane flux dominated the coupled mode, so the movement of the SMTZ at site SH1 was consistent with the general understanding. Understanding the factors influencing the SMTZ is important for understanding the early diagenesis process.
