Bivalve shell fossils,cemented by authigenic carbonates,are widely spread in the Haima cold seep,Qiongdongnan Basin of the South China Sea(SCS).In this study,we examined an element profile of Gigantidas platifrons in ...Bivalve shell fossils,cemented by authigenic carbonates,are widely spread in the Haima cold seep,Qiongdongnan Basin of the South China Sea(SCS).In this study,we examined an element profile of Gigantidas platifrons in the Haima cold seeps at a water depth of 1381 m.Based on the scanning electron microscope(SEM)analyses,the prismatic layer and nacreous layer were identified,which are characterized by prismatic structure and stratified structure,respectively.In addition,the profile can be subdivided into two parts:altered and unaltered zones.Laser inductively coupled plasma mass spectrometry(LA-ICP-MS)mapping shows that the element concentrations of the altered zones were influenced by the authigenic carbonate rocks,whereas the element concentrations of unaltered zones remain stable.In-situ X-ray diffraction(XRD)analyses show that the mineral constituent of the prismatic layer is mainly composed of aragonite.Along with the growth profile,Mg/Ca ratios of unaltered zones have minor variations,ranging 0.72-0.97 mmol/mol(mean=0.87 mmol/mol),with estimated temperatures of 3.8-4.1℃,indicating that the temperature of the surrounding seawater remains constant and agree with the measured data of 3.9℃which was conducted by a conductivity-temperature-depth system(CTD).The minor variations of Ba/Ca ratios(0.01-0.06 mmol/mol;mean=0.04 mmol/mol)indicate a relatively stabilized salinity of the surrounding seawater.S/Ca ratios show large variations of 0.04-4.15 mmol/mol(mean=1.37 mmol/mol).S/Ca ratios have regular variations which generally correspond to the variations of the Mg/Ca ratios,highlighting that the S/Ca ratios of bivalve shells show the potential to reflect the growth rate of the Gigantides.However,further studies should be carried out on the understanding of the links between the S/Ca ratios and seepage intensity of cold-seep fluids.展开更多
Methane(CH4)is a powerful greenhouse gas and its largest reservoir on Earth is held in marine sediments.CH4 in marine sediments is mainly stored in gas-hydrate reservoirs and deep sedimentary strata along continental ...Methane(CH4)is a powerful greenhouse gas and its largest reservoir on Earth is held in marine sediments.CH4 in marine sediments is mainly stored in gas-hydrate reservoirs and deep sedimentary strata along continental margins,where large amounts of deep-sourced CH4 ascend to different degrees toward the seafloor.However,the amount of deep-sourced CH4 and its role in subseafloor carbon and sulfur cycling remains poorly constrained.We analyzed sulfate(SO_(4)^(2-))profiles of 157 sites along with previous published 85 sites to determine the regional distribution and amount of SO_(4)^(2-) reduction for an area of 1.23×10^(5) km^(2) of the northern South China Sea.Then we compared these obtained results with estimates based on sedimentation rates from the same area.Significantly higher regional SO_(4)^(2-) flux estimates based on SO_(4)^(2-) profiles(4.26×10^(-3)Tmol a^(-1)),compared to lower estimates based on sedimentation rates(1.23×10^(-3)Tmol a^(-1)),reflect abundant ascending deep-sourced CH4.The difference of the regional SO_(4)^(2-) flux estimates(3.03×10^(-3)Tmol a^(-1))represents the amount of SO_(4)^(2-) reduced by CH_(4) through the anaerobic oxidation of CH_(4)(AOM).Deep-sourced CH_(4) contributes 71%to total SO_(4)^(2-) consumption in the study area,largely exceeding SO_(4)^(2-) consumption by organoclastic sulfate reduction.Our findings substantiate that deep-sourced CH4 governs subseafloor carbon and sulfur cycling to a previously underrated extent,fueling extensive chemosynthesis-based ecosystems along continental slope and rise.展开更多
基金Supported by the Key Research and Development Project of Guangdong Province(No.2020B1111510001)the National Natural Science Foundation of China(No.U2244224)+1 种基金the PI Project of Southern Marine Science and Engineering Guangdong Laboratory(Guangzhou)(No.GML2020GD0802)the Guangdong Special Support Team Program(No.2019BT02H594)。
文摘Bivalve shell fossils,cemented by authigenic carbonates,are widely spread in the Haima cold seep,Qiongdongnan Basin of the South China Sea(SCS).In this study,we examined an element profile of Gigantidas platifrons in the Haima cold seeps at a water depth of 1381 m.Based on the scanning electron microscope(SEM)analyses,the prismatic layer and nacreous layer were identified,which are characterized by prismatic structure and stratified structure,respectively.In addition,the profile can be subdivided into two parts:altered and unaltered zones.Laser inductively coupled plasma mass spectrometry(LA-ICP-MS)mapping shows that the element concentrations of the altered zones were influenced by the authigenic carbonate rocks,whereas the element concentrations of unaltered zones remain stable.In-situ X-ray diffraction(XRD)analyses show that the mineral constituent of the prismatic layer is mainly composed of aragonite.Along with the growth profile,Mg/Ca ratios of unaltered zones have minor variations,ranging 0.72-0.97 mmol/mol(mean=0.87 mmol/mol),with estimated temperatures of 3.8-4.1℃,indicating that the temperature of the surrounding seawater remains constant and agree with the measured data of 3.9℃which was conducted by a conductivity-temperature-depth system(CTD).The minor variations of Ba/Ca ratios(0.01-0.06 mmol/mol;mean=0.04 mmol/mol)indicate a relatively stabilized salinity of the surrounding seawater.S/Ca ratios show large variations of 0.04-4.15 mmol/mol(mean=1.37 mmol/mol).S/Ca ratios have regular variations which generally correspond to the variations of the Mg/Ca ratios,highlighting that the S/Ca ratios of bivalve shells show the potential to reflect the growth rate of the Gigantides.However,further studies should be carried out on the understanding of the links between the S/Ca ratios and seepage intensity of cold-seep fluids.
基金supported by the National Natural Science Foundation of China(41730528,42225603,and 42176056)the Shanghai Pujiang Program(Grant No 21PJ1404700)。
文摘Methane(CH4)is a powerful greenhouse gas and its largest reservoir on Earth is held in marine sediments.CH4 in marine sediments is mainly stored in gas-hydrate reservoirs and deep sedimentary strata along continental margins,where large amounts of deep-sourced CH4 ascend to different degrees toward the seafloor.However,the amount of deep-sourced CH4 and its role in subseafloor carbon and sulfur cycling remains poorly constrained.We analyzed sulfate(SO_(4)^(2-))profiles of 157 sites along with previous published 85 sites to determine the regional distribution and amount of SO_(4)^(2-) reduction for an area of 1.23×10^(5) km^(2) of the northern South China Sea.Then we compared these obtained results with estimates based on sedimentation rates from the same area.Significantly higher regional SO_(4)^(2-) flux estimates based on SO_(4)^(2-) profiles(4.26×10^(-3)Tmol a^(-1)),compared to lower estimates based on sedimentation rates(1.23×10^(-3)Tmol a^(-1)),reflect abundant ascending deep-sourced CH4.The difference of the regional SO_(4)^(2-) flux estimates(3.03×10^(-3)Tmol a^(-1))represents the amount of SO_(4)^(2-) reduced by CH_(4) through the anaerobic oxidation of CH_(4)(AOM).Deep-sourced CH_(4) contributes 71%to total SO_(4)^(2-) consumption in the study area,largely exceeding SO_(4)^(2-) consumption by organoclastic sulfate reduction.Our findings substantiate that deep-sourced CH4 governs subseafloor carbon and sulfur cycling to a previously underrated extent,fueling extensive chemosynthesis-based ecosystems along continental slope and rise.
基金partially supported by the National Natural Science Foundation of China(41730528 and 41773091)Key Special Project for Introduced Talents Team of Southern Marine Science and Engineering Guangdong Laboratory(Guangzhou)(GML2019ZD0506)。
