南海北部陆坡冷泉区和非冷泉区地球化学特征对甲烷渗漏活动的响应

南海北部陆坡冷泉区和非冷泉区地球化学特征对甲烷渗漏活动的响应目录一 引言 引言（一）选题依据与研究目的在冷泉进入人类视野的30年中，全世界范围内发现了各种油气渗漏点这些地点已经成为了解甲烷渗透和相关生物地球化学过程变化的模型系统。目前，中国南海的冷泉研究，多集中于单个区域，或者单一地研究冷泉碳酸盐岩、沉积物或沉积物孔隙水的地球化学特征，少有对南海多个冷泉活动区、各种沉积特征综合的对比研究。因此针对以上存在的问题，结合已有的研究条件，本文测试了南海北部陆坡F站位冷泉区、海马冷泉区和九龙峡谷非冷泉区的沉积物和沉积物孔隙水地球化学特征，对比研究冷泉区和非冷泉区、冷泉活动在不同时间尺度上的沉积特征。（二）全球冷泉分布大陆边缘斜坡海底之下有着丰富的甲烷贮藏，以固态天然气水合物、溶解于海水或气体的形式存在ADDINCSL_CITATION{"citationItems":[{"id":"ITEM-1","itemData":{"ISSN":"0029-8182","author":[{"dropping-particle":"","family":"Gross","given":"MG","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"Oceanus","id":"ITEM-1","issue":"3","issued":{"date-parts":[["1984"]]},"page":"2-6","title":"Introduction:Deep-seahotspringsandcoldseeps","type":"article-journal","volume":"27"},"uris":["/documents/?uuid=82685057-5d9e-3bfd-bc92-3d9f10af69e5"]}],"mendeley":{"formattedCitation":"(Gross,1984)","plainTextFormattedCitation":"(Gross,1984)","previouslyFormattedCitation":"(Gross,1984)"},"properties":{"noteIndex":0},"schema":"/citation-style-language/schema/raw/master/csl-citation.json"}(Gross,1984)。在重力和构造应力的作用下产生甲烷通道，海底之下的以甲烷等有机质为主要成分的流体从通道中泄漏进海水，被称为冷泉ADDINCSL_CITATION{"citationItems":[{"id":"ITEM-1","itemData":{"DOI":"10.1038/ngeo1926","ISSN":"17520894","abstract":"Theleakageofcold,methane-richfluidsfromsubsurfacereservoirstotheseaflooratspecificsitesoncontinentalslopes,termedcoldseeps,sustainssomeoftherichestecosystemsontheseabed.Theseseep-fuelledcommunitiesutilizearoundtwoordersofmagnitudemoreoxygenperunitareathannon-seepseafloorcommunities.Muchoftheoxygenisconsumedbymicrobesandanimal–microbesymbiosesthatusemethaneasanenergysource.Theproportionofmethaneconsumedvarieswithfluidflowrate,rangingfrom80%inseepswithslowfluidflowtolessthan20%inseepswherefluidflowishigh.Assumingthepresenceofafewtensofthousandsofactivecoldseepsystemsoncontinentalslopesworldwide,weestimatethatthetotaleffluxofmethanetotheoverlyingoceancouldreach0.02Gtofcarbonannually.Asmuchmoremethaneislostfromcontinentalslopes,beitthroughemissiontothehydrosphereorconsumptionbymicrobes,thancanbeproduced,wesuggestthatasubstantialfractionofthemethanethatfuelsseepecosystemsissourcedfromdeepcarbonburiedkilometresundertheseafloor.","author":[{"dropping-particle":"","family":"Boetius","given":"Antje","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Wenzhöfer","given":"Frank","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"NatureGeoscience","id":"ITEM-1","issue":"9","issued":{"date-parts":[["2013"]]},"page":"725-734","publisher":"NaturePublishingGroup","title":"Seaflooroxygenconsumptionfuelledbymethanefromcoldseeps","type":"article-journal","volume":"6"},"uris":["/documents/?uuid=1f4f7131-4375-40f7-bc05-09b03b57d0da"]}],"mendeley":{"formattedCitation":"(BoetiusandWenzhöfer,2013)","plainTextFormattedCitation":"(BoetiusandWenzhöfer,2013)","previouslyFormattedCitation":"(BoetiusandWenzhöfer,2013)"},"properties":{"noteIndex":0},"schema":"/citation-style-language/schema/raw/master/csl-citation.json"}(BoetiusandWenzhöfer,2013)。冷泉流体的温度通常低于周围海水温度不知道出处。冷泉渗漏会在海底产生一系列物理、化学、生物地质作用，同时促进不需要光合作用、通过化能合成作用自养生存的生物群落发育，形成独特的冷泉系统ADDINCSL_CITATION{"citationItems":[{"id":"ITEM-1","itemData":{"DOI":"10.1126/science.226.4677.965","ISSN":"00368075","abstract":"DensebiologicalcommunitiesoflargeepifaunaltaxasimilartothosefoundalongridgecrestventsattheEastPacificRisewerediscoveredintheabyssalGulfofMexico.TheseassemblagesoccuronapassivecontinentalmarginatthebaseoftheFloridaEscarpment,theinterfacebetweentherelativelyimpermeablehemipelagicclaysofthedistalMississippiFanandthejointedCretaceouslimestoneoftheFloridaPlatform.Thefaunaapparentlyisnourishedbysulfiderichhypersalinewatersseepingoutatnearambienttemperaturesontotheseafloor.","author":[{"dropping-particle":"","family":"Paull","given":"C.K.","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Hecker","given":"B.","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Commeau","given":"R.","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Freeman-Lynde","given":"R.P.","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Neumann","given":"C.","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Corso","given":"W.P.","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Golubic","given":"S.","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Hook","given":"J.E.","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Sikes","given":"E.","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Curray","given":"J.","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"Science","id":"ITEM-1","issued":{"date-parts":[["1984"]]},"title":"BiologicalcommunitiesattheFloridaEscarpmentresemblehydrothermalventtaxa","type":"article-journal"},"uris":["/documents/?uuid=2939db7e-4339-35ef-9297-e53a897d2767"]}],"mendeley":{"formattedCitation":"(Paull<i>etal.</i>,1984)","plainTextFormattedCitation":"(Paulletal.,1984)","previouslyFormattedCitation":"(Paull<i>etal.</i>,1984)"},"properties":{"noteIndex":0},"schema":"/citation-style-language/schema/raw/master/csl-citation.json"}(Paulletal.,1984)。不知道出处继20世纪70年代阿尔文号深海考察船在东太平洋隆海底直接观察到海底热液之后，冷泉于1983年在墨西哥湾3200m的海底最早发现ADDINCSL_CITATION{"citationItems":[{"id":"ITEM-1","itemData":{"DOI":"10.1126/science.226.4677.965","ISSN":"00368075","abstract":"DensebiologicalcommunitiesoflargeepifaunaltaxasimilartothosefoundalongridgecrestventsattheEastPacificRisewerediscoveredintheabyssalGulfofMexico.TheseassemblagesoccuronapassivecontinentalmarginatthebaseoftheFloridaEscarpment,theinterfacebetweentherelativelyimpermeablehemipelagicclaysofthedistalMississippiFanandthejointedCretaceouslimestoneoftheFloridaPlatform.Thefaunaapparentlyisnourishedbysulfiderichhypersalinewatersseepingoutatnearambienttemperaturesontotheseafloor.","author":[{"dropping-particle":"","family":"Paull","given":"C.K.","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Hecker","given":"B.","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Commeau","given":"R.","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Freeman-Lynde","given":"R.P.","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Neumann","given":"C.","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Corso","given":"W.P.","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Golubic","given":"S.","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Hook","given":"J.E.","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Sikes","given":"E.","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Curray","given":"J.","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"Science","id":"ITEM-1","issued":{"date-parts":[["1984"]]},"title":"BiologicalcommunitiesattheFloridaEscarpmentresemblehydrothermalventtaxa","type":"article-journal"},"uris":["/documents/?uuid=2939db7e-4339-35ef-9297-e53a897d2767"]}],"mendeley":{"formattedCitation":"(Paull<i>etal.</i>,1984)","plainTextFormattedCitation":"(Paulletal.,1984)","previouslyFormattedCitation":"(Paull<i>etal.</i>,1984)"},"properties":{"noteIndex":0},"schema":"/citation-style-language/schema/raw/master/csl-citation.json"}(Paulletal.,1984)。之后，冷泉在世界范围内陆续发现，是近30年以来全球海洋地质调查所取得的最重要的科学成就之一。冷泉一般呈线状分布，广泛发育于板块活动活跃的主动大陆边缘或沉积物重力加载作用下和与垂直方向差异压实作用相关的被动大陆边缘，因为这些区域的地壳形变和压实作用有利于形成甲烷通道，便于冷泉流体排出海底ADDINCSL_CITATION{"citationItems":[{"id":"ITEM-1","itemData":{"DOI":"10.1038/ngeo1926","ISSN":"17520894","abstract":"Theleakageofcold,methane-richfluidsfromsubsurfacereservoirstotheseaflooratspecificsitesoncontinentalslopes,termedcoldseeps,sustainssomeoftherichestecosystemsontheseabed.Theseseep-fuelledcommunitiesutilizearoundtwoordersofmagnitudemoreoxygenperunitareathannon-seepseafloorcommunities.Muchoftheoxygenisconsumedbymicrobesandanimal–microbesymbiosesthatusemethaneasanenergysource.Theproportionofmethaneconsumedvarieswithfluidflowrate,rangingfrom80%inseepswithslowfluidflowtolessthan20%inseepswherefluidflowishigh.Assumingthepresenceofafewtensofthousandsofactivecoldseepsystemsoncontinentalslopesworldwide,weestimatethatthetotaleffluxofmethanetotheoverlyingoceancouldreach0.02Gtofcarbonannually.Asmuchmoremethaneislostfromcontinentalslopes,beitthroughemissiontothehydrosphereorconsumptionbymicrobes,thancanbeproduced,wesuggestthatasubstantialfractionofthemethanethatfuelsseepecosystemsissourcedfromdeepcarbonburiedkilometresundertheseafloor.","author":[{"dropping-particle":"","family":"Boetius","given":"Antje","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Wenzhöfer","given":"Frank","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"NatureGeoscience","id":"ITEM-1","issue":"9","issued":{"date-parts":[["2013"]]},"page":"725-734","publisher":"NaturePublishingGroup","title":"Seaflooroxygenconsumptionfuelledbymethanefromcoldseeps","type":"article-journal","volume":"6"},"uris":["/documents/?uuid=1f4f7131-4375-40f7-bc05-09b03b57d0da"]}],"mendeley":{"formattedCitation":"(BoetiusandWenzhöfer,2013)","plainTextFormattedCitation":"(BoetiusandWenzhöfer,2013)","previouslyFormattedCitation":"(BoetiusandWenzhöfer,2013)"},"properties":{"noteIndex":0},"schema":"/citation-style-language/schema/raw/master/csl-citation.json"}(BoetiusandWenzhöfer,2013)（图1）。冷泉从热带海域到南极下冰架都有分布，目前已知最浅的冷泉发育区圣巴巴拉海峡水深为15mADDINCSL_CITATION{"citationItems":[{"id":"ITEM-1","itemData":{"DOI":"10.1357/002224087788326894","ISSN":"00222402","abstract":"PreviousstudiesoftheIslaVistapetroleumseepintheSantaBarbaraChannelfoundmuchhigherabundancesofmacrofaunaandconcentrationsofadenosinetriphosphate(ATP)insedimentsnearpetroleumseepagecomparedtothosefromnonseepareas.Tofurtherassessthepossibleeffectofpetroleumonorganismsatthebaseofbenthicfoodwebs,populationabundancesofmeiobenthosandtheirsuspectedmicrobialfood(bacteriaanddiatoms)weremeasuredbiweeklyforoneyearatthreestationswithdifferingpetroleumexposure.Determinationsofsuspendedparticulatematterandtheabundanceandgutcontentsofjuvenilefisheswerealsomadeatseepandnonseepstations.(DBO)","author":[{"dropping-particle":"","family":"Montagna","given":"PaulA.","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Bauer","given":"JamesE.","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Toal","given":"Jon","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Hardin","given":"Dane","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Spies","given":"RobertB.","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"JournalofMarineResearch","id":"ITEM-1","issue":"3","issued":{"date-parts":[["1987","5","19"]]},"page":"761-789","publisher":"JournalofMarineResearch/Yale","title":"Temporalvariabilityandtherelationshipbetweenbenthicmeiofaunalandmicrobialpopulationsofanaturalcoastalpetroleumseep","type":"article-journal","volume":"45"},"uris":["/documents/?uuid=5e15c643-6b8e-353a-a2c8-934fd18ae193"]}],"mendeley":{"formattedCitation":"(Montagna<i>etal.</i>,1987)","plainTextFormattedCitation":"(Montagnaetal.,1987)","previouslyFormattedCitation":"(Montagna<i>etal.</i>,1987)"},"properties":{"noteIndex":0},"schema":"/citation-style-language/schema/raw/master/csl-citation.json"}(Montagnaetal.,1987)，最深的冷泉发育区为水深9345米的Kurile海沟待引文。古冷泉，级冷泉活动的地质记录，也越来越多地被发现和报道，活动时代主要在晚中生代和新生代。待引文由于冷泉常与天然气水合物、全球气候变化和极端环境生命起源等问题紧密联系，因此长期以来引起科学各界的广泛关注。

图1.1全球冷泉。具有水合物-变质带-微生物-碳酸盐特征的渗漏部位；主动大陆边缘（蓝色），被动大陆边缘包括地下水渗漏（橙色）；转换断层边缘（绿色）。ADDINCSL_CITATION{"citationItems":[{"id":"ITEM-1","itemData":{"DOI":"10.1007/s00531-014-1010-0","ISBN":"0053101410100","author":[{"dropping-particle":"","family":"Suess","given":"Erwin","non-dropping-particle":"","parse-names":false,"suffix":""}],"id":"ITEM-1","issued":{"date-parts":[["2014"]]},"page":"1889-1916","title":"Marinecoldseepsandtheirmanifestations:geologicalcontrol,biogeochemicalcriteriaandenvironmentalconditions","type":"article-journal"},"uris":["/documents/?uuid=22ffe03f-41df-470b-8645-3e3fcb6a61bc"]}],"mendeley":{"formattedCitation":"(Suess,2014)","plainTextFormattedCitation":"(Suess,2014)","previouslyFormattedCitation":"(Suess,2014)"},"properties":{"noteIndex":0},"schema":"/citation-style-language/schema/raw/master/csl-citation.json"}(Suess,2014)（二）冷泉中甲烷的来源冷泉流体的最主要成分为甲烷，甲烷的来源可分为有机成因和无机成因。有机成因的甲烷主要为生物有机质降解形成，无机成因的甲烷主要为蛇纹石化形成或地球形成过程中形成保存在地球内部ADDINCSL_CITATION{"citationItems":[{"id":"ITEM-1","itemData":{"DOI":"10.1007/978-1-4684-2757-8_8","abstract":"Methanehasbeendetectedinseveralcoresofrapidlydeposited({>}50m/my)deepseasediments.Othergases,suchascarbondioxideandethane,arecommonlypresentbutonlyinminorandtraceamounts,respectively.ThemethaneoriginatespredominantlyfrombacterialreductionofC02,asindicatedbycomplimentarychangeswithdepthintheamountandisotopiccompositionofredox-linkedporewaterconstituents:sulfate-bicarbonateandbicarbonate-methane.Presently,noprecisedeterminationexistsoftheamountofgaspresentunderinsituconditionsindeepseasediments.UsingC13/C12isotoperatiosofthedissolvedbicarbonateandmethane,andemployingkineticcalculationsbasedonRayleighdistillationequa-tions,theamountsofmethanegeneratedbyreductionofcarbondi-oxidebyhydrogenhasbeenestimated.Theamountscalculatedsuggestthataminimumof20mmolCH4/kginterstitialwaterisformed.Amethaneconcentrationof20mmol/kgapproachestheamountre-quiredfortheformationofgashydratesunderpressure-temperatureconditionscorrespondingtoawatercolumnofabout500meters,withatemperatureof5°Catthesediment-waterinterface.Depthofsta-bilityofthegashydratewithinthesedimentisdirectlypropor-tionalto:hydrostaticpressure,orheightofthewatercolumnabovethesediment,temperatureatthesedimentsurface,thegeothermalgradient,andconcentrationofmethane.Underaverageoceaniccon-ditions,gashydratescouldbestableinsedimentundera3kmwatercolumntodepthsofapproximately600meters,ifsufficientmethaneispresent.","author":[{"dropping-particle":"","family":"Claypool","given":"GeorgeE.","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"Kaplan","given":"I.R.","non-dropping-particle":"","parse-names":false,"suffix":""}],"container-title":"NaturalGasesinMarineSediments","id":"ITEM-1","issued":{"date-parts":[["2012"]]},"title":"TheOriginandDistributionofMethaneinMarineSediments","type":"chapter"},"uris":["/documents/?uuid=aaefd384-06b3-3ac4-b644-45a6792bde12"]},{"id":"ITEM-2","itemData":{"author":[{"dropping-particle":"","family":"王先彬","given":"","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"欧阳自远","given":"","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"卓胜广","given":"","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"张明峰","given":"","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"郑国东","given":"","non-dropping-particle":"","parse-names":false,"suffix":""},{"dropping-particle":"","family":"王永莉","given":"","non-dropping-particle":"","parse-names":false,"suffix":""}],"id":"ITEM-2","issued":{"date-parts":[["2014"]]},"title":"蛇纹石化作用、非生物成因有机化合物与深部生命.pdf","type":"article"},"uris":["/documents/?uuid=080e9c3b-91bc-4fbe-b8ab-2af2b8fa1854"]}],"mendeley":{"formattedCitation":"(ClaypoolandKaplan,2012;王先彬<i>etal.</i>,2014)","plainTextFormattedCitation":"(ClaypoolandKaplan,2012;王先彬etal.,2014)","previouslyFormattedCitation":"(ClaypoolandKaplan,2012;王先彬<i>etal.</i>,2014)"},"properties":{"noteIndex":0},"schema":"/citation-style-language/schema/raw/master/csl-citation.json"}(ClaypoolandKaplan,2012;王先彬etal.,2014)。（三）冷泉系统主要的生物地球化学过程在正常海洋沉积环境中，海底沉积物中的有机质在埋藏过程中被O2、NO3-、Mn4+、Fe3+和SO42-等电子受体氧化，在沉积物-底层水界面以下形成氧还原带、硝酸盐还原带、锰还原带、铁还原带、硫酸盐还原带和产甲烷带（图2）由于海水中的硫酸根离子浓度远高于其他电子受体的浓度，因此硫酸盐还原作用是早期成岩作用中的主要过程，硫酸盐还原作用消耗的有机碳占沉积物中总有机碳的50%以上（Canfieldetal.，1993;Jorgensenetal.，1982）还没引。在滨海沉积环境中，沉积物沉积速率较高，陆源物质充足，铁锰氧化物和氢氧化物含量高，各反应带都较为发育，硫酸盐还原带深度较浅（Daleetal.，2006）没引；；在上升流发育区，有机质含量很高，为相对缺氧环境，各种受体浓度增加，硫酸盐还原反应速率大，硫酸盐还原带深度较浅；在陆坡沉积环境种，初级生产力和沉积速率较低，缺少陆源物质，铁锰氧化物和氢氧化物含量较低，硫酸盐还原反应速率较低，硫

还没引没引图1.2海洋沉积物中各种氧化还原反应及各种物质的矿化带分布示意图（胡钰，2015）。酸盐还原带深度较深（表1）。硫酸盐还原作用主要通过有机质还原硫酸盐和缺氧条件下甲烷还原硫酸盐，即甲烷缺氧氧化作用（Anaerobicoxidationofmethane，简称AOM）完成，两种作用的反应方程式分别为：2CH2O+SO42-2HCO3-+H2S（1.1）CH4+SO42-HCO3-+HS-+H2O（1.2）硫酸盐驱动的甲烷缺氧氧化作用是由甲烷氧化古菌和硫酸盐还原菌共同完成的。甲烷氧化古菌简称为ANME。ANME与产甲烷菌的关系非常密切，最近的研究结果表明，AOM作用可能是产甲烷过程中酶的逆转录（Nauhausetal.，2005）没引。目前人们对于甲烷氧化古菌和硫酸盐还原菌在AOM反应中直接的相互作用以及其中的中间体仍然知之甚少。海洋沉积物是生产甲烷非常重要的来源，但大气中只有2%的甲烷来自海洋，绝大多数来自陆地，如湿地或水稻田发生的产甲烷作用。这主要是因为来自深海的甲烷在向上运移到海表的过程中，有85%以上的甲烷被硫酸盐还原甲烷缺氧氧化作用所消耗，因此AOM作用能有效的减少具有温室效应的甲烷排放到大气中，对调节大气甲烷浓度和遏制全球气候的快速变暖具有非常重要的意义（Nauhausetal.，2005）没引。没引没引正常海洋沉积环境，沉积物深部埋藏的有机质含量较低时，如开放的大洋盆地环境中，产甲烷作用较弱，向上扩散的甲烷浓度很低，因此硫酸盐主要被有机质还原，沉积物孔隙水中的硫酸盐浓度在沉积物—水界面以下随深度缓慢降低最后趋于稳定；而有机质含量较高时，如海岸带和陆坡等环境，地层中产甲烷菌产生的甲烷在向上扩散时会与海水中向下扩散的硫酸盐发生甲烷缺氧氧化作用，也就是说硫酸盐主要通过甲烷厌氧氧化作用消耗，沉积物孔隙水中的硫酸盐浓度下降速度与深度呈正比关系（图3）（Borowskietal.，1996，1999;Michaelisetal.，2002）没引。在水合物发育区，由于水合物分解产生的甲烷气体在向上运移时会与海水中向下扩散的硫酸盐发生缺氧氧化作用，沉积物孔隙水中的硫酸盐浓度随深度下降趋势在剖面上也呈直线下降；甲烷浓度在产甲烷带达到饱和保持不变，甲烷向上扩散，浓度随深度变浅呈直线减少；在硫酸盐—甲烷转换带（sulfatemethanetransitionzone，简称SMTZ）附近，硫酸盐和甲烷含量最低，甲烷缺氧氧化作用和硫酸盐还原作用最强（Borowskietal.，1996;1999）。没引图1.3不同沉积环境下：1正常深海沉积物；2高有机质含量沉积物，如海岸带；3天然气水合物发育区沉积物，甲烷气体的来源和甲烷厌氧氧化作用，POC代表颗粒有机碳，SAT代表甲烷饱和浓度，修改自Haeckel，2015

图1.4冷泉沉积物孔隙水中发生的主要生物地球化学过程及相关的早期成岩作用过程示意图(参考Rodriguezetal.(2000)).在SMTZ的下边界，硫酸盐浓度几乎为0，而甲烷浓度则迅速增加。在水合物发育区，甲烷扩散到SMTZ附近，发生强烈的甲烷缺氧氧化作用，导致SMTZ较浅，SMTZ界面之上的孔隙水中硫酸根大量被消耗。SMTZ在一定程度上能指示深部的甲烷通量，较浅的SMTZ通常指示高通量的甲烷，因此能指示下伏的天然气水合物藏（图4）（Borowskietal.，1996;Hensenetal.，2003）没有引。根据前任研究，在全球范围内，一般水合物发育区的SMTZ深度都小于50米，平均深度在20米左右；而在没有水合物藏的大洋和大陆边缘SMTZ深度一般大于50米，部分大于100米（Borowskietal.，1996）没有引。在我国南海已探明的水合物发育区，SMTZ深度一般小于15米，有的甚至小于5米。通过对南海东沙海域两个水合物有利区域：九龙甲烷礁和―海洋四号‖高速沉积体的表层沉积物孔隙水的地球化学研究发现，东沙海域水合物有利区域的SMTZ一般小于8米，通过硫酸盐浓度梯度计算得出的甲烷通量为3.8×10-3~5.9×10-3mmol/（cm2.a），类似于国际上已发现水合物区域的甲烷通量水平，暗示该海域深部可能存在天然气水合物藏（陆红峰等，2005，2006；邬黛黛等，2009a，2013；吴时国等，2004）。

没有引没有引图1.6甲烷通量与SMTZ界面深度的关系（Borowskietal.，1996）海洋沉积根据来源和组成的不同一般可以分为三种类型：（1）成岩沉积物（lithogenoussediments），主要由陆源碎屑及火山物质组成；（2）生物成因沉积物（biogenoussediments）；（3）自生沉积物（authigenicsediments）。冷泉沉积物基本也是由这三类物质组成，但与正常海洋沉积物相比生物成因和自生沉积所占的比例很高，因此也是研究的重点。冷泉活动强烈时，冷泉生物及自生沉积物发育，研究冷泉相关的科学问题完全可以依赖冷泉生物（如管状蠕虫类、贻贝类及蛤类等）及自生沉积岩（如冷泉碳酸盐岩及重晶石）进行。但当冷泉活动相对较弱或微弱时，冷泉生物并不发育，形成的自生沉积物含量低并散布在沉积物中，从而增加了研究的难度。尽管如此，冷泉沉积物中的地球化学研究则可以在某种程度上克服了上述困难。目前，冷泉沉积物中总的无机碳含量（TIC）、铬还原性硫的含量（chromiumreduciblesulfur;CRS）及它们各自的同位素值δ13CTIC和δ34SCRS经常被用来识别古代的硫酸盐-甲烷转换带（SMTZ），古代SMTZ界面附近由于AOM和SR作用导致TIC和CRS含量异常高、δ13CTIC偏负、δ34SCRS大幅偏正，代表了一次古代的甲烷渗漏事件（Limetal.,2011;Peketietal.,2012;Borowskietal.,2013）。此外，古代SMTZ界面有时可以发育Ba的异常富集（即“Ba峰”）及氧化还原敏感元素Mo的富集现象（Torresetal.,1996;Dickens,2001;Kastenetal.,2012;Peketietal.,2012;Satoetal.,2012）。上述指标均可以有效地被用于研究古代的甲烷渗漏事件及活动特征。在记录古代甲烷渗漏事件方面，沉积物中所含的底栖有孔虫壳体的13C值可以用指示古代甲烷渗漏事件，同时结合各种定年手段（如浮游有孔虫14C定年），来探讨古代甲烷渗漏发生的时间及触发机制等（Weferetal.,1994;Rathburnetal.,2003;Martin,etal.,2007,2010;Fontanier,etal.,2014;Consolaroetal.,2015）。正常情况下，沉积物一般具有较好的沉积序列，在定年的基础上获得时间框架，结合沉积物中记录的古海洋学信息，有望能够更好地用于研究古冷泉形成时的环境、探索地质历史时期中甲烷渗漏事件的触发机制、过程及影响。综上所述，冷泉系统中的冷泉生物、流体、自生矿物及沉积物均能够记录下AOＭ信号，是了解和研究冷泉环境中的生物地球化学过程、探索冷泉形成的机制和演过等的重要载体。研究冷泉环境中正在进行的生物地球化学过程及相关的机制，冷泉流体（孔隙水）及部分活的冷泉生物是理想的载体。然而，探索过去的冷泉活动及特征，则只能依靠冷泉自生沉积岩（主要是碳酸盐岩和重晶石）、沉积物及少部分可以保存的生物壳体。作为冷泉流体强烈渗漏作用的产物，冷泉碳酸盐岩和重晶石能够很好地记录古代冷泉流体的特征，结合定年数据能够揭示古代冷泉流体的演化和控制因素。但与冷泉沉积物相比，还是缺乏连续的时间记录。同时，冷泉沉积物记录的古海洋学信息也能提供冷泉的形成和演化的诸多信息。因此，为了更全面、深入地了解冷泉系统的形成、演化及所涉及到的生物地球化学过程，有必要对冷泉系统中的各种产物（冷泉生物、流体、自生矿物及沉积物）进行综合的研究和对比分析。胡玉-没改过胡玉-没改过（四）冷泉系统生物群落除了硫酸盐还原细菌和甲烷缺氧氧化古菌等微生物外，在海底冷泉区常发育肉眼可见的白色的或橙色的细菌席（Fischeretal.,2012；图1-3）。同时，冷泉系统还孕育有大量化能自养型的生物群落，常见管状蠕虫类、贻贝类及蛤（Macdonaldetal.,1990；图1-3）。某些种属的管状蠕虫生长长度可达3m、寿命可长达几百年(Fisheretal.,1997;Bergquistetal.,2000)。最近研究表明某些管状蠕虫的根部能改造周围沉积物的地球化学特征（Cordesetal.,2003；Dattaguptaet.,2008），并且相应的地球化学特征能记录在冷泉碳酸盐岩中（Fengetal.,2010c,2013a）。冷泉环境中贻贝主要依靠嗜甲烷的或者嗜硫化氢的细菌共生体获取营养而生存(e.g.Paulletal.,1985;Childressetal.,1986;Cordesetal.,2009;Duperron,2010)。不同的细菌共生体所需要的含碳和含硫的种类和同位素特征又各不相同(Fisher,1990;Conwayetal.,1994;VetterandFry,1998;Yamanakaetal.,2000)，因此，自养型生物中的碳和硫的稳定同位素组成能够用来揭示冷泉生物的生活方式(e.g.Childressetal.,1986;Levin,2005;Macavoyetal.,2008;Beckeretal.,2010,2013,2014;Rodriguesetal.,2013).。最近的研究表明利用贻贝的软组织中碳、氮和硫稳定同位素能够有效地示踪冷泉环境中的生物地球化学过程（Fengetal.,2015）。因此，冷泉环境中对冷泉生物进行地球化学研究不仅有助于探索冷泉生物的生活习性和方式，而且有希望用于示踪冷泉环境中的生物地球化学过程插图。没改过插图没改过地质背景（一）地理位置南海位于太平洋板块、欧亚板块和印度洋板块交汇处，是西太平洋上最大的边缘海之一（图2-1）。南海的水团主要通过巴士海峡和马六甲海峡分别与太平洋和印度洋相连。南海是我国最大的边缘海，面积约350×104km2，平均水深1212米，马尼拉海沟南端为最深处5567米。研究区主要位于南海北部陆坡水合物发育区。由于各种海山、陡崖和海槽的广泛发育，南海北部大陆坡地形非常复杂。大陆坡水深150~3500米之间，很多新生代的含油气盆地发育，如莺歌海盆地、琼东南盆地、台西南盆地和北部湾盆地等，被认为是洋盆二次扩张作用的结果（张光学等，2002；王宏斌等，2003）。

图2.1南海地理位置图（李牛，2015）（二）构造背景南海兼具主动大陆边缘和被动大陆边缘的特征，可能由三次大规模的构造运动塑造了如今的构造格局。南海第一次大规模的海底扩张运动主要发生在中生代末期-新生代早期。太平洋版块对华南微板块的俯冲结束，华南微板块开始向北部运动，区域应力场从原先的挤压变为松弛，并且在华南微板块前缘形成了NE向的地堑式断陷盆地，由此拉开了南海陆源扩张的序幕。华南微板块在古新世-始新世向南漂移并伴随顺时针的转动。中-晚始新世，华南微板块向南运动，在其东南边缘出现北东-南西向的挤压应力场，使早期的地堑式断陷盆地开始沿东南方向扩张。同时，大陆地壳持续拉张减薄，盆地不断切割加深，基性岩浆冒出，形成南海海洋地壳和慢速扩张洋中脊，形成了原始南海。南海的第二次扩张活动的开始在大约32~17百万年，即中渐新世-早中新世，此时沿NWW方向挤压的太平洋板块和由南向北运动的华南微板块使南海形成东两向的扩张轴，西沙海槽在此时期形成。南海的第三次扩张活动在中中新世-上新世，构造运动主要以垂向为主，并伴随着大范围的沉降活动。在太平洋板块的挤压作用之下，南海洋壳消减于吕宋岛弧的仰冲之下。现代南海的构造格局在上新世之后基本形成（刘昭蜀等，2002）。（三）沉积环境特征南海北部陆坡的沉积环境随着ODP184航次的实施得到了非常广泛的研究。南海北部陆坡的物源主要是来自珠江、台湾海峡、巴士海峡和吕宋的大陆陆源碎屑。南海的三次扩张运动，从大陆输入了大量的陆源碎屑，沉积速率较高。而且青藏高原的快速隆升也为南海北部陆坡带来了丰富的陆源物质。莺歌海盆地在上新世的沉积速率，最高可达40cm/ka，而琼东南盆地最高为60cm/ka；ODP1144站位，位于东沙群岛陆坡区的沉积速率为48cm/ka（Bühringetal.，2004），晚中新世的1143站位，位于南部陆坡区，沉积速率为11.4cm/ka（吴必豪等，2003）。一般认为水合物发育需要的沉积速率为3~30cm/ka（Kvenvold，1985）。而且ODP深海钻探的结果也表明，0.5~100cm/ka的沉积速率利于水合物的发育。由此可见，南海的沉积速率具有发育水合物的条件。而且南海发育巨厚的新生代沉积盆地，厚度达到2~11km，有机质丰富，包含大量的甲烷等烃类资源。南海北部陆坡沉积物中的有机碳含量为0.46%~1.95%，超过了水合物发育所需要的沉积物中有机碳含量0.5%的下限（Kvenvold，1985），而且深海钻探表明南海北部陆坡多个站位深部富含生物成因甲烷和热解成因甲烷。因此南海北部陆坡这些高沉积速率、高有机质含量的地层以及各种等深流、重力流沉积和断裂构造的发育为天然气水合物的发育和冷泉流体的运移提供了良好的条件。南海北部陆坡是我国开展水合物调查研究的重点海域，已通过地球物理、地球化学等方法圈定数个水合物远景区域，并于2007年和2013年在神狐海域和珠江口盆地钻获水合物实物样品（Zhangetal.,2007；Zhangetal.,2014）。此外，通过近20年的调查研究结果还发现了大量与海底冷泉渗漏有关的冷泉碳酸盐岩和冷泉生物，如蛤和贻贝。在琼东南盆地、西沙海槽、神狐海域、东沙海域及台西南盆地等40多个站位采集到冷泉碳酸盐岩样品和/或冷泉生物样品（图2-2）。通过德国“太阳号”在东沙东北海域海底发现目前已知最大面积的冷泉碳酸盐岩礁——九龙甲烷礁，引起国内及国际同行的广泛关注。因此，南海北部陆坡是我国水合物勘探重点区域和研究冷泉生物地球化学过程和冷泉生物图2-2南海北部陆坡目前已知的冷泉碳酸盐岩发现点（冯东，内部资料）的天然实验室。图2.2南海北部陆坡目前已知的冷泉碳酸盐岩发现点（冯东，内部资料）

采样和测试方法(一)研究样品（二）样品的前处理首先，将采集得到的样品切割为50-100cm的长度，中间切开，进行拍照和样品描述，并用密封袋包好以后放入4℃的冷柜中保存。然后在中科院地化所边缘海地质重点实验室对样品进行切割和拍照描述。每隔2cm一个样品，样品经冷冻干燥后用玛瑙碾钵手工碎样，进一步的粒度、化学和同位素分析在中科院地化所、中科院广州地化所和中科院南海海洋研究所等地进行。（三）分析方法1.TOC、TIC、N和总S分析沉积物中的TOC、TIC、N和总S采用ThermoScientificFlashSmart元素分析仪进行测试。选取120~150mg样品，加入过量2mol/L的HCl除去碳酸钙，再用超纯水进行多次稀释，直到样品为中性，然后冷冻干燥24小时以上。采用未经HCl处理的样品测试总硫、总氮和总碳的含量，经HCl处理后的样品测试TOC的含量，TIC为总碳和TOC者之间的差值，仪器的精度和准确度均优于1%。2.孔隙水阴、阳离子浓度分析孔隙水中阴离子（SO42−）和阳离子（Mg2+和Ca2+）浓度用戴安公司DionexICS-900型离子色谱仪在中科院广州地球化学研究所完成。SO42−浓度用超纯水稀释500倍后上机测试，Mg2+和Ca2+浓度则用超纯水稀释200倍后上机测试。AS23型色谱分离柱（用于阴离子）和CS12A型色谱分离柱（用于阳离子）用来进行各种离子的分离。测试阴离子浓度用4.5mMNa2CO3/0.8mMNaHCO3混合液作为为淋洗液，25mMH2SO4为再生液，进样体积为50μL，流速设定为1ml/min。测试阳离子浓度时用11mMH2SO4作为淋洗液，自动电解水为再生液，进样体积为50μL，流速设定为1ml/min。通过用标准水体进行检测和质量控制，阴阳离子的标准偏差均小于2%。

C、N、S元素含量和阴阳离子浓度特征（一）C、N、S结果分析1.F站位沉积物SiteFPC1总硫含量总体在0.15%~0.45%之间，略高于正常氧化环境海相沉积物的值（Berneretal.,1980）。含量在0.44%~0.66%之间，总体在0.5%左右，有随深度增加TOC含量减小的趋势。TIC总体含量偏高，在0.79%~1.67%之间，大致与TOC含量变化相反。C/N原子比值在3~5之间，显示沉积物中陆源和海源有机质输入通量的变化(Meyers,1994)放到讨论说。放到讨论说SiteFPC2总硫含量在0.4%~0.7%之间，高于正常氧化环境海相沉积物的值（Berneretal.,1980）。TOC含量在0.3%~0.7%之间，并随深度逐渐减小。TIC含量在0.5%~0.7%之间，基本保持在0.6%左右变化很小。C/N原子比值在1~4之间，与TOC含量变化趋势一致。SiteFPC3总硫含量在0.60%~0.80%之间，远高于正常氧化环境下的海洋沉积物中总硫含量。TOC含量在0.44%~0.68%之间，并随深度缓慢增加。TIC含量在0.33%~0.77%之间，并随深度缓慢增加。C/N含量在3~5之间。SiteFPC4总硫含量在0.11%~0.61%之间，上段含量较低，为正常水平，下段含量突然增加至0.3%以上。TOC含量在0.48%~0.66%之间。TIC含量在0.53%~0.90%之间，与TOC含量变化呈反相关。C/N含量在3~5之间。

图4.1F站位沉积物TS、TOC、TIC含量和C/N比值剖面上随深度变化图样品点深度(cm)TN(%)TS(%)TOC(%)TIC(%)C/NSiteFPC11.000.160.150.641.213.953.000.150.170.551.283.665.000.140.240.660.794.567.000.140.290.501.083.4511.000.160.450.601.443.7413.000.140.380.591.674.2815.000.140.350.571.334.1117.000.140.320.441.463.07SiteFPC21.000.150.480.450.533.053.000.170.540.630.633.715.000.130.580.520.543.857.000.150.600.440.652.999.000.140.530.490.643.4711.000.160.690.310.611.89SiteFPC31.000.140.650.580.374.103.000.150.750.630.334.155.000.120.780.500.524.027.000.110.780.460.544.039.000.120.740.440.573.5811.000.120.700.570.414.9113.000.130.660.560.444.1815.000.140.650.610.344.3017.000.150.670.550.413.7619.000.140.720.680.354.7521.000.140.680.680.394.7523.000.150.680.560.773.8325.000.140.700.630.524.3527.000.140.680.610.624.3229.000.150.600.670.604.63SiteFPC41.000.140.160.510.903.693.000.150.110.660.564.325.000.140.110.480.703.387.000.140.110.490.773.509.000.140.150.580.534.2511.000.140.370.500.703.5713.000.130.590.630.504.8615.000.140.610.430.733.1317.000.130.500.500.663.9919.000.120.470.580.564.83表4.1F站位沉积物TN、TS、TOC、TIC含量和C/N比值2海马冷泉区Haiyang4PC1沉积物总硫含量在0.32%~0.72%之间，含量随深度增加明显。TOC含量在0.6%~0.8%之间，含量随深度缓慢减小。TIC含量在0.31%~0.41%之间，变化不明显。C/N含量在4~6之间。Haiyang4PC2沉积物总硫含量在0.08%~0.31%之间，含量变化不明显。TOC含量在0.09%~0.14%之间，含量随