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1.
利用孔隙水化学和稳定同位素化学等方法分析珠江口红树林湿地沉积层孔隙水硫酸根(SO_4~(2-))、游离甲烷气体(CH_4)、总溶解无机碳(DIC)以及δ13CDIC的垂直剖面分布特征.结果显示,孔隙水SO_4~(2-)浓度自表至底呈线性梯度减小,至硫酸盐-甲烷界面(SMI)附近,硫酸盐几乎全部消耗,而CH_4浓度急剧增大,KC1、KC3、KC4、K17和K10等5个站位SMI深度分别为20、50、70、80、50 cm,SMI深度由红树林湿地林间向光滩逐渐增大.同时,孔隙水DIC浓度在该深度明显升高,沉积物发生强烈的甲烷厌氧氧化(AOM)作用.在AOM过程中,由于12CH_4氧化速率较13CH_4快,故引起沉积物孔隙水δ13CDIC偏轻.沉积层中的有机质含量及其活性高低是制约沉积物SMI分布深浅的关键因素,高含量的活性有机质可加速孔隙水SO_4~(2-)再矿化过程的消耗,使得通过AOM作用的SO_4~(2-)消耗通量相应增大.在微生物作用下,部分活性有机质被大量消耗,致使进入沉积物SO_4~(2-)还原带的活性有机质数量相应减少,从而引起部分SO_4~(2-)转为与CH_4发生反应促进AOM作用.  相似文献   

2.
程俊  王淑红  黄怡  颜文 《海洋科学》2019,43(5):110-122
综述了天然气水合物赋存区甲烷渗漏活动的地球化学响应指标的研究进展,分析了应用单一指标识别甲烷渗漏活动各自所存在的问题,包括浅表层沉积物孔隙水中CH_4、SO_4~(2–)、Cl~–等离子浓度随深度的变化;浅层沉积物全岩W_(TOC)(W表示质量分数,TOC表示总有机碳)和W_(TS)(TS表示总硫)之间的相关性及比值;自生碳酸盐岩δ~(13)C和δ~(18)O;自生矿物重晶石、黄铁矿、自生石膏的δ~(34)S;有孔虫壳体和生物标志化合物的δ~(13)C等。结果表明孔隙水中的CH_4、SO4_~(2–)浓度及溶解无机碳的碳同位素组成可以用来识别目前正在发生的甲烷渗漏活动;而沉积物中的WTS、自生矿物的δ~(34)S、钡含量及其异常峰值和生物标志化合物的δ~(13)C等指标的联合使用可以更真实准确地反映地质历史时期天然气水合物赋存区的甲烷渗漏活动。因此,在实际研究过程中,可将孔隙水和沉积物两种介质的多种指标相结合。随着非传统稳定同位素(Fe、Ca、Mg等)和沉积物氧化还原敏感元素(Mo、V、U等)等研究的发展,甲烷渗漏活动地球化学响应指标的研究也将得到拓展,而多种地球化学指标的联合使用将为天然气水合物勘探及其形成分解过程识别研究提供重要的科学依据。  相似文献   

3.
在2011年7月利用35SO2-4培养示踪法测定九龙江河口两个站位(A站位位于咸淡混合区,盐度3~5;B站位位于海相区,盐度20~25)沉积柱中硫酸盐还原速率的垂直分布。结果显示A站位沉积柱中硫酸盐还原速率变化范围为54~2 345nmol/(cm3·d),从表层到底部先增大后减小,最大值出现在20cm深度附近;B站位硫酸盐还原速率在24~987nmol/(cm3·d)之间,分别在10cm和78cm深度附近出现两个峰值,分别为876nmol/(cm3·d)和987nmol/(cm3·d)。综合分析两个站位孔隙水中SO2-4、甲烷浓度和沉积物中总有机碳、温度和氧化还原电位的垂直变化趋势与其硫酸盐还原速率的分布规律,表明A站位沉积物中硫酸盐还原以有机矿化为主;B站位受到有机质矿化和甲烷厌氧氧化的共同作用;两个站位硫酸盐还原速率及垂直分布趋势受孔隙水中SO2-4浓度、有机质活性和温度的共同影响;根据各个层位硫酸盐还原速率估算两个站位硫酸盐还原通量(以硫计)分别为527.9mmol/(m2·d)和357.1mmol/(m2·d),表明硫酸盐还原是九龙江河口有机质厌氧矿化的重要路径。  相似文献   

4.
对珠江口淇澳岛海岸带3个站位(QA-11,QA-9和QA-14)的沉积物中不同形态的还原硫(酸可挥发性硫,黄铁矿和有机硫)、总有机碳(TOC)和孔隙水中SO42-,甲烷浓度进行了测定,并且利用稳态扩散模型计算其中2个站位(QA-9和QA-14)硫酸盐还原通量[1.74和1.14 mmol/(m2.d)]和甲烷厌氧氧化通量[0.34和0.29 mmol/(m2.d)]。研究结果表明由于潮间带沉积物受到SO42-供给的限制,因此位于潮间带的QA-11站位硫酸盐还原带较浅(约16 cm);在潮下带的QA-9和QA-14站位,随离海岸距离和水深的增加,硫酸盐还原通量呈现减小的趋势,并且硫酸还原逐渐受到可利用活性有机质的限制;甲烷厌氧氧化对硫酸盐还原的贡献表现出增加的趋势,由19.2%增加至25.5%。三个站位沉积物中按不同形态还原硫含量由大到小列出,它们是有机硫(OS)、黄铁矿(DS)、酸可挥发性硫(AVS)。沉积物中AVS的空间分布与硫酸盐还原通量有正相关性。QA-11和QA-14站位的黄铁矿与AVS硫的含量比值大于3,分别为7.9和3.6,表明两个站位的黄铁矿形成可能受硫酸盐还原作用的控制;QA-9站位黄铁矿与AVS硫的含量比值为2.2,暗示AVS向黄铁矿转化受到可利用活性铁的限制。  相似文献   

5.
2009年8月份采用静态箱法对珠江口淇澳岛湿地甲烷通量日变化进行测定,结果表明甲烷排放通量在当日23∶00和翌日早晨9∶00出现两个高峰值,分别为40.07和50.99mg·m-2·h-1;在当日17∶00和翌日凌晨5∶00出现两极小值,分别为1.13和1.57mg·m-2·h-1,同步观测孔隙水中SO2-4、Cl-浓度和沉积物表层温度和采样点潮位变化,发现湿地甲烷排放通量与孔隙水中SO2-4浓度和潮位存在显著负相关性,因此,潮汐所导致孔隙水中SO2-4浓度和上覆水深度改变,可能是控制珠江口淇澳岛潮间带湿地甲烷日排放通量变化的两个关键因素。同时计算采样点甲烷日排放净通量达到962.7mg·m-2·d-1,表明夏季珠江口淇澳岛湿地是大气甲烷的源区。柱状沉积物孔隙水中甲烷浓度范围为0.52~5.18mmol·dm-3,其最大值出现在9cm深度,同时测试沉积物中总有机碳(TOC)、温度、氧化还原电位和孔隙水中SO2-4的浓度,结果表明高的甲烷浓度主要是由于沉积物中高的TOC含量和孔隙水中低的SO2-4浓度所导致。  相似文献   

6.
在天然气水合物发育区海底沉积物中甲烷厌氧氧化作用(AOM)是碳循环的重要组成部分。通过定量计算表层沉积物中甲烷迁移转化通量,可以更准确评估甲烷来源碳对沉积物碳库和海洋深部碳库影响。本文利用反应―运移模型对采集于南海神狐水合物发育区两个站位(SH-W19-PC、SH-W23-PC)采集的孔隙水SO_4~(2-)、溶解无机碳(DIC)、Ca~(2+)剖面进行拟合,同时对DIC碳同位素进行分析,确定近海底沉积物中的碳循环。研究显示两个站位孔隙水中SO_4~(2-)和Ca~(2+)浓度在剖面上随深度呈线性减少,DIC浓度随深度逐渐增加,其δ~(13)C_(DIC)值随深度逐渐降低至约-25‰,表明两个站位存在一定程度的AOM。模拟计算两个站位沉积物孔隙水溶解甲烷向上的通量分别为25.9和18.4 mmol·m~(-2) a~(-1),AOM作用产生的DIC分别占其总DIC量的70.7%和60%。由沉积物向海水中释放的DIC通量占DIC汇的约60%。因此,在天然气水合物发育区向海底渗漏甲烷大部分以DIC的形式进入上覆海水,这些具有极负碳同位素值的甲烷来源的DIC可能对局部深海碳库产生一定的影响。  相似文献   

7.
孟宪伟  张俊  夏鹏 《海洋学报》2014,36(2):33-39
深海,特别是天然气水合物区的沉积物-孔隙水体系中,Ba循环受到孔隙水中的硫酸盐(SO24-)和甲烷(CH4)之间的氧化还原反应的强烈制约。沉积物中"Ba峰"的存在体现了SO2-4亏损的长时间累积效应,并与海平面变化制约下的天然气水合物分解有关。南海北部陆坡ODP1146站钻孔上部深度185m沉积物中发育了4个"Ba峰",其中发育于深度约58m的"Ba峰"(F3)与当前SO2-4-CH4反应界面(SMI)深度一致,推断其他3个"Ba峰"(F1、F2和F4)对应的SMI深度分别约为24m、46m和84m。"Ba峰"最大峰值与沉积物Cl通量减小和冰期-间冰期转换带的对应性表明:在冰期,海平面大幅度降低诱发的浅水区(如东沙群岛附近)天然气水合物的分解持续释放了低盐度、高浓度CH4流体,其中部分流体迁移至ODP1146站所在的陆坡区沉积物中,导致了间隙水中SO2-4的持续亏损和自生Ba的长时间累积,结果在冰期-间冰期转换阶段形成显著的"Ba峰";同时,部分逸散于大气中的CH4加快了冰期的结束。在距今约50万年的冰期-间冰期旋回制约下的海平面周期性变化过程中,南海北部浅水区天然气水合物分解释放的低盐度和高浓度CH4流体也间歇地迁移至深水陆坡沉积区,导致了多个"Ba峰"的形成和沉积埋藏。"Ba峰"可以用于评价历史时期南海北部陆坡天然气水合物分解释放甲烷通量的变化。  相似文献   

8.
对南海北部陆坡东沙海域、神狐海域及西沙海槽甲烷渗漏环境和无甲烷渗漏环境87个浅表层沉积物中的底栖有孔虫Uvigerinaspp.进行碳同位素分析研究,结果表明,东沙海域δ13C值为-0.52‰~-5.68‰,平均值为-1.41‰,出现明显的负偏移;神狐海域δ13C值介于-0.36‰~-1.10‰,平均值为-0.75‰,未见明显的δ13C值负偏移;西沙海槽δ13C值介于-0.01%~-0.89‰,平均值为-0.45‰;对Uvigerinaspp.碳同位素组成与沉积物有机碳(TOC)、甲烷(CH4)间的关系进行探讨,发现δ13C负偏移主要出现在甲烷渗漏环境,发生在末次盛冰期,与溶解无机碳负偏移以及沉积物全样的δ13C值负偏移层位相吻合,有可能作为富甲烷环境的替代指标。  相似文献   

9.
沉积物释放是海洋环境中甲烷(CH_4)的重要来源。通过2013年7月和8月两个航次,对东、黄海泥质区沉积物中CH_4浓度的垂直分布和沉积物-水界面通量进行了研究。结果表明,除个别站位外,黄海沉积物(50 cm以浅)中CH_4的浓度变化范围在0.2～1.0μmol/L之间,长江口及浙闽沿岸附近的沉积物中CH_4浓度则要更高(1.0～2.0μmol/L),而东海东部海域沉积物中CH_4浓度波动范围为0.2～3.0μmol/L。总体来说,东、黄海沉积物中CH_4浓度偏低,这可能与观测到的高浓度硫酸盐(20 mmol/L)有关。通过整柱密室培养实验估算出东、黄海沉积物-水界面CH_4释放速率在0.64～2.12μmol/(m2·d)之间,东、黄海沉积物CH_4释放总量为6.7×108 mol/yr;但采用菲克定律估算的CH_4扩散通量则要比现场培养的结果低2～5倍,表明不同的方法在估算沉积物-水界面CH_4通量上还具有一定的不确定性。  相似文献   

10.
杭州湾海底沉积物中蕴藏着大量的浅层生物气,作为温室气体CH4的重要载体,研究其甲烷厌氧氧化(AOM)及相关碳循环过程,对正确评估浅层生物气的生态环境效应具有重要的科学意义。通过对YS6孔柱状沉积物孔隙水、顶空气等地球化学参数的测试分析,基于质量平衡和碳同位素质量平衡原理,利用"箱式模型"定量研究了硫酸盐—甲烷转换带(SMTZ)内的碳循环过程。结果表明:SMTZ位于海底约6～8 mbsf沉积层,其内部碳循环过程除了包含有机质的硫酸盐还原(OSR)、AOM和碳酸盐沉淀(CP)反应外,还隐藏存在"AOM生成的溶解无机碳(DIC)"产甲烷反应(CR),反应速率分别为9.14、7.42、4.36、2.72 mmol·m~(-2)·a~(-1),而有机质降解产甲烷反应(ME)未发生。各反应对SMTZ内孔隙水DIC的补充贡献率为OSRAOMME,而对DIC的消耗贡献率CPCR。深部含甲烷沉积层向上扩散而来的CH4并不是驱动SMTZ内部SO42-还原的唯一电子供体,CR和OSR反应亦是导致进入SMTZ内硫酸盐扩散通量大于甲烷的重要因素,且SMTZ下边缘沉积层出现明显的13CH4亏损亦与CR反应有关。本研究认为,定量评估海底沉积物中AOM作用的相对强弱时,SMTZ内可能存在的"隐藏的"产甲烷作用(如CR、ME等)不能忽视。  相似文献   

11.
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(Unit II) 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 Unit II changed 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 34 S. 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.  相似文献   

12.
南海北部琼东南盆地海底存在着巨型麻坑, 现有研究多认为其形成主要与海底流体渗漏有关。目前对琼东南盆地深海沉积物地球化学特征及麻坑区的生物地球化学过程等尚不清楚。文章选取南海北部琼东南盆地C14、C19两个站位岩心样品, 进行了总硫(TS)、总碳(TC)、总有机碳(TOC)、铬还原性硫化物(CRS)及其δ34SCRS值测试, 并结合总氮/总碳(TN/TOC)比值和已发表的孔隙水中SO42-浓度等进行了地球化学特征分析。研究表明: C14站位以3.91m bsf (below seafloor)为界, 上下分别存在有机质参与的硫酸盐还原反应(OSR)和甲烷厌氧氧化作用(AOM)驱动的硫酸盐还原反应(SR); 3.91m bsf以上的部位沉积物的TS、TC含量均低于3.91m bsf以下部位, 且沉积物孔隙水中SO42-浓度由3.91m bsf以上的缓慢凹型减少变成3.91m bsf以下的线性减少, 说明该处成为沉积物中地球化学特征分界的明显标志; 在3.91m bsf以下, 受到甲烷渗漏的影响。C19站位沉积物中TS与TC含量由浅到深逐渐增加, 但与TN/TOC比值变化呈现几乎相反趋势, 即整个岩心以OSR为主, 并呈现出有机质早期成岩阶段的沉积现象。C14和C19两个站位柱状沉积物的δ34SCRS值变化范围分别为-50.2‰~-46.9‰和-50.1‰~-42.0‰ (V-CDT标准), 均显示出了较为偏负的硫同位素值, 表明研究区主要的生物化学过程是在相对开放体系下硫酸盐还原作用的结果, 综合说明该研究区麻坑的甲烷流体已经喷发, 目前可能处于衰退期, 甚至已经不活跃, 该结果与前人的认识基本一致。  相似文献   

13.
Authigenic barite nodules associated with modestly 13C-depleted calcium carbonate concretions and 34S-enriched pyrite at the bottom of the Upper Devonian Hanover Shale of western New York provide evidence of sulfate reduction coupled with anaerobic oxidation of methane (AOM). The methane, much of it biogenic in origin, may have diffused upward from Middle Devonian Marcellus Shale and perhaps the Upper Ordovician Utica Shale. Strong 34S enrichment and high δ34S/δ18O values of the barite nodules reflect: (1) substantial kinetic fractionation induced by microbial sulfate reduction perhaps intensified by a low seawater sulfate recharge rate and (2) upward delivery of Ba2+- and CH4- bearing pore fluid sourced within underlying sulfate-depleted deposits. However, the association of authigenic calcium carbonate and barite in the same stratigraphic interval, especially the presence of barite overgrowths on carbonate concretions, is not consistent with what is known of AOM-related mineralization of a sediment column passing downward through the sulfate–methane transition (SMT). The documented early formation of authigenic carbonate followed by barite observed relations may reflect a diminished rate of methanogenesis and/or CH4 supply. The tempered methane flux would have induced the SMT to descend the sediment column enabling barite to form within the same stratigraphic horizon that 13C-depleted calcium carbonate had most recently precipitated. Diminished methane flux may have been caused by burial-related passage of the organic-rich Marcellus Shale below the depth of peak biogenic methane generation and its replacement at that depth interval by organic-lean deposits of the upper part of the Hamilton Group. Subsidence of the SMT would have increased the preservation potential of authigenic barite. However, continued survival of the labile barite as it eventually moved through the SMT suggests that the underlying sulfate-depleted zone was strongly enriched in Ba2+.  相似文献   

14.
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_2O_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.  相似文献   

15.
The geochemical cycling of barium was investigated in sediments of pockmarks of the northern Congo Fan, characterized by surface and subsurface gas hydrates, chemosynthetic fauna, and authigenic carbonates. Two gravity cores retrieved from the so-called Hydrate Hole and Worm Hole pockmarks were examined using high-resolution pore-water and solid-phase analyses. The results indicate that, although gas hydrates in the study area are stable with respect to pressure and temperature, they are and have been subject to dissolution due to methane-undersaturated pore waters. The process significantly driving dissolution is the anaerobic oxidation of methane (AOM) above the shallowest hydrate-bearing sediment layer. It is suggested that episodic seep events temporarily increase the upward flux of methane, and induce hydrate formation close to the sediment surface. AOM establishes at a sediment depth where the upward flux of methane from the uppermost hydrate layer counterbalances the downward flux of seawater sulfate. After seepage ceases, AOM continues to consume methane at the sulfate/methane transition (SMT) above the hydrates, thereby driving the progressive dissolution of the hydrates “from above”. As a result the SMT migrates downward, leaving behind enrichments of authigenic barite and carbonates that typically precipitate at this biogeochemical reaction front. Calculation of the time needed to produce the observed solid-phase barium enrichments above the present-day depths of the SMT served to track the net downward migration of the SMT and to estimate the total time of hydrate dissolution in the recovered sediments. Methane fluxes were higher, and the SMT was located closer to the sediment surface in the past at both sites. Active seepage and hydrate formation are inferred to have occurred only a few thousands of years ago at the Hydrate Hole site. By contrast, AOM-driven hydrate dissolution as a consequence of an overall net decrease in upward methane flux seems to have persisted for a considerably longer time at the Worm Hole site, amounting to a few tens of thousands of years.  相似文献   

16.
通过提取黄河、辽河和鸭绿江表层沉积物中的碎屑矿物角闪石,对单矿物采用电子探针,对群体角闪石采用ICP-MS和ICP-AES分析其常量元素及微量元素组成。结果表明:角闪石单矿物主成分在一定范围内有较大变化,都具有高Si、Ca、Mg和低Na、K的特征;3条河流的角闪石晶体化学都归属钙角闪石组,半数以上矿物种为镁角闪石;角闪石群体矿物化学显示黄河角闪石的稀土元素浓度明显高于黄土和黄河全岩沉积物,而且重稀土比轻稀土更富集,说明角闪石是黄河和黄土沉积物稀土元素的主要载体之一,角闪石含量变化会对全岩样品稀土元素含量造成重要影响。微量元素特征显示新旧黄河样品间差别很小,与其同一来源物质的事实相符。虽然黄河、辽河和鸭绿江河流样品角闪石主成分相近,但微量元素方面(元素含量、元素含量对比值及特征值)显示较明显不同,样品间多种数值指标相对偏差在20%以上,可作为物源识别的判别标志,如微量元素Ba、Li、Rb、Cs、Ta、Tl、Pb、La、Ce、Pr、Nd等含量的差异,元素对比值c(La)/c(Y)、c(Sr)/c(Rb)、c(Zn)/c(Cu)、c(Gd)/c(Cd)、c(Li)/c(Be)、c(Rb)/c(Cs)、c(Sr)/c(Ba)、c(Hf)/c(Ta)、c(Pb)/c(Bi)等的差异;特征值∑c(REE)、Σc(LREE)、∑c(HREE)、∑c(LREE)/∑c(HREE)、[c(La)/c(Lu)]N、[c(La)/c(Yb)]N、[c(La)/c(Sm)]N等的差异。  相似文献   

17.
Cold seeps are pervasive along the continental margin worldwide,and are recognized as hotspots for elemental cycling pathway on Earth.In this study,analyses of pore water geochemical compositions of one-400 cm piston core(S3) and the application of a mass balance model are conducted to assess methane-associated biogeochemical reactions and uncover the relationship of methane in shallow sediment with gas hydrate reservoir at the Makran accretionary wedge off Pakistan.The results revealed that approximately 77% of sulfate is consumed by the predominant biogeochemical process of anaerobic oxidation of methane.However,the estimated sulfate-methane interface depth is-400 cm below sea floor with the methane diffusive flux of 0.039 mol/(m~2·a),suggesting the activity of methane seepage.Based on the δ~(13)C_(DIC) mass balance model combined with the contribution proportion of different dissolved inorganic carbon sources,this study calculated the δ~(13)C of the exogenous methane to be-57.9‰,indicating that the exogenous methane may be a mixture source,including thermogenic and biogenic methane.The study of pore water geochemistry at Makran accretionary wedge off Pakistan may have considerable implications for understanding the specific details on the dynamics of methane in cold seeps and provide important evidence for the potential occurrence of subsurface gas hydrate in this area.  相似文献   

18.
We studied specific lipid biomarkers of archaea and bacteria, that are associated with the anaerobic oxidation of methane (AOM) in a cold seep environment as well as the origin of sedimentary organic matter on the continental slope off NE Sakhalin in the Sea of Okhotsk. The organic geochemical parameters demonstrated that most of the sedimentary organic matter containing hydrate layers could be derived from marine phytoplankton and bacteria, except for a station (LV39-29H) which was remarkably affected by terrestrial vascular plant. Specific methanotrophic archaea biomarkers was vertically detected in hydrate-bearing cores (LV39-40H), coinciding with the negative excursion of the δ13Corg at core depths of 90–100 cm below the seafloor. These results suggest that methane provided from gas hydrates are already available substrates for microbes thriving in this sediment depth. In addition, the stable isotope mass balance method revealed that approximately 2.77–3.41% of the total organic carbon (or 0.036–0.044% dry weight sediment) was generated by the activity of the AOM consortium in the corresponding depth of core LV39-40H. On the other hand, the heavier δ13C values of archaeol in the gas hydrate stability zone may allow ongoing methanogenesis in deeper sediment depth.  相似文献   

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