古海洋生产力与氧化还原指标——元素地球化学综述

海洋表层初级生产力大小以及水体氧化还原条件是古海洋和古气候研究的重要内容,而元素地球化学是研究初级生产力以及氧化还原条件最常用的手段。主量元素Fe和Si是限制生物的营养元素,痕量金属元素Cu、Ni和Zn是微营养元素,而营养条件是沉积生产力的限制因素,因此这些元素的含量能反映初级生产力大小。Ba和Mo是随有机质一起沉淀下来的,与水体的有机碳通量有关,也是古生产力大小的指标。对氧化还原敏感的痕量金属元素含量(如Cr、V和U)以及元素比值(如V/(V+Ni)、V/Cr、Ni/Co、U/Th和V/Sc)常用来重构水体的氧化还原条件。     

沉积物－水界面的生物地球化学作用

沉积物－水界面是天然水体在物理、化学和生物特征等方面差异性最显著和负责水体和沉积物之间物质输送和交换的重要边界环境。对沉积物－水界面生物地球化学的定义、研究方法和它在水体微量物质循环中所起的作用、物质迁移方式、典型氧化还原敏感性元素转化反应（Ｃ、Ｏ、Ｎ）、界面扩散通量和表面扩散亚层的意义和估算等进行了讨论。     

水体内藻类的生物地球化学

藻类对水体内生命元素的转化及其分布、迁移的影响．是目前水体内藻类生物地球化学研究的重点内容。藻通过光合作用和生物矿化，控制着C、N、Si、P、S、Ca等元素在水体内的循环；驱动着C和S在水体和大气之间的交换，进而影响大气中的C和S。藻生物积累及其对环境变化的及时反馈，使藻类成为地球化学环境变化的生物指示物。本文对水体内藻类的生物地球化学进行了综述。     

沉积物-水界面的生物地球化学作用

沉积物－水界面是天然水体在物理、化学和生物特征等方面差异性最显著和负责水体和沉积物之间物质输送和交换的重要边界环境。对沉积物－水界面生物地球化学的定义、研究方法和它在水体微量物质循环中所起的作用、物质迁移方式、典型氧化还原敏感性元素转化反应（Ｃ、Ｏ、Ｎ）、界面扩散通量和表面扩散亚层的意义和估算等进行了讨论。      

广东三水盆地古近系(土布)心组地球化学特征及其所指示的氧化还原条件

古近系心组红岗段是广东三水盆地的主要生油层,以一套黑—灰黑色页岩沉积为主,其富含有机质、纹层理发育良好的岩层与相对贫有机质、含微体生物化石的微扰动层交替出现。根据纹层状页岩与生物扰动页岩的C-S-Fe关系以及对氧化还原条件敏感的痕量元素(Mo、U、V、Co、Ni、Pb和Cu)地球化学记录,对这两种不同岩相的地球化学特征及其所反映的水体氧化还原条件进行了分析。纹层状页岩的TOC、S含量和DOPT值均较高,TOC-S、TOC-DOPT显示较弱的相关性;而生物扰动页岩的TOC、S含量和DOPT值相对较低,TOC-S、TOC-DOPT相关性显著。痕量元素在两种岩相中的分布也有差别,各元素在纹层状页岩中的丰度均高于生物扰动页岩,尤其是Mo和U具有较高的丰度水平、且在不同岩相中显示明显差别。黑色页岩中的C-S-Fe关系和痕量元素(特别是Mo和U)分布反映了心组红岗段沉积时期湖盆水体的氧化还原条件变化。生物扰动页岩沉积期间,底部水体主要为氧化环境,间歇性出现贫氧条件,硫酸盐还原作用发生于沉积物/水界面及其以下沉积物中。纹层状页岩形成于缺氧的底部水体条件下,水体和沉积物中均可含H2S,为有机质保存以及对氧化还原条件敏感的痕量元素的富集提供了有利条件。     

新疆北部中二叠统烃源岩有机质与沉积环境的关系

依据地表剖面烃源岩地球化学分析资料,结合部分井下样品分析数据对新疆北部准噶尔、吐哈及伊犁盆地中二叠统碳酸盐岩类、泥岩类烃源岩的元素地球化学和有机地球化学特征进行了系统分析.研究认为烃源岩的轻稀土元素富集程度较高,重稀土元素相对较低,Ce/Ce*具有较明显的正异常,反映出烃源岩的沉积环境总体为还原环境.多项地球化学分析证实,沉积水体的元素地球化学特征及古盐度等环境条件与烃源岩有机相关系密切.研究结果表明,烃源岩的植烷优势主要是在还原条件的沉积环境下释放出大量的植烷所致,伽马腊烷、β-胡萝卜烷等生物标志化合物的检出表征诸盆地烃源岩沉积时具有一定的盐度条件.还原程度高的沉积相带是原始有机质沉积的良好场所,沉积有机质能及时沉积、保存,烃源岩大多有机质丰度高、类型好;反之,则明显变差.     

有机生物地球化学与晚新生代古全球变化研究

有机生物地球化学在古全球变化研究中的应用越来越受到重视。在古海洋学领域,表层海水温度、海洋初级生产力的大小及其种群结构的变化对全球碳循环的影响、海底甲烷释放等关键性科学问题都需要有机生物地球化学积极参与。有机生物地球化学也能在陆地古生态系统中植被的演变、C3与C4植物的消长变化、湖泊水体环境的变化等方面作出独特的贡献。文中简要评述了上述内容的研究现状。     

海洋沉积物中氧化还原敏感元素对水体环境缺氧状况的指示作用

近年来由于人为污染水体富营养化加剧,缺氧区面积不断增大,利用沉积物中氧化还原敏感元素反演水体缺氧情况已经发展成为海洋化学领域的热点研究方向。本文详细阐述了氧化还原敏感元素的富集机制,并总结了利用沉积物中氧化还原敏感元素在不同氧化还原条件下的富集程度反映海水缺氧程度和底质氧化还原状况的一系列指标,如Re/Mo、Cd/U、Th/U、V/Sc、V/(V+Ni)值,U—Mo共变模型,δ~(98/95)Mo,多指标微/痕量元素模型以及氧化还原敏感元素-有机质共变模型等。沉积物中Re、Mo含量、Re/Mo值、自生Mo/U值、Th/U值对上层水体缺氧和氧化条件区分良好,可定量指征上层水体的缺氧情况。沉积物中Re含量近似于1 ng/g(地壳值),Mo含量1μg/g(地壳值),Re/Mo值接近0.3×10~(-3),Mo—U富集系数比为(0.1～0.3)×现代海水,Th/U值2,可指示氧化环境;Re含量在10～30 ng/g,Mo含量近似于1μg/g,Re/Mo值10×10~(-3)～30×10~(-3),Mo—U富集系数比1×现代海水,Th/U值在0～2范围内,可指示缺氧环境;Re含量30 ng/g,Mo富集达到20～40μg/g,Re/Mo值接近0.7×10~(-3)(海水中Re/Mo值),Mo—U富集系数比为(3～10)×现代海水,可指示极度缺氧的硫化环境。Mo_(EF)—U_(EF)交会对数坐标图、氧化还原敏感元素-有机质共变模型指标可定性分析上层水体的缺氧情况;V/(V+Ni)值对于次氧化沉积物指示效果不佳;Cd/U值在次缺氧条件下的变化机制复杂,还需进一步研究。生物扰动、成岩作用、人为污染、水体局限、高有机碳通量、Fe、Mn氧化物循环等因素通过影响氧化还原敏感元素在沉积物中的富集与迁移,从而影响氧化还原敏感元素指标的应用,应剔除有机质吸附与陆源输入等非自生部分的影响,结合各种指标互相印证,综合判别水体氧化还原状态。     

松辽盆地北部白垩纪青山口组黑色页岩元素地球化学特征及沉积古环境恢复

对松辽盆地北部青山口组118块页岩样品进行有机碳和元素地球化学测试,运用一系列判别古气候、古盐度、古生产力和古氧化还原条件的地化指标,恢复青山口组黑色页岩的沉积环境,探讨富有机质页岩成因机制。青山口组沉积期为温暖半湿润亚热带气候,古气温>15℃,水体为陆相微咸水—半咸水环境,盐度5‰～10‰。青山口组底部发育厚度约30 m的富有机质页岩,TOC最高达到9.39%,自下而上有机碳含量逐渐变低。富有机质页岩Cu、Ni、Mo和Zn含量高,发育大量胶磷矿、藻席,表明青山口组早期湖盆生产力达到峰值,为有机质富集提供物质基础。U元素含量以及V/（V+Ni）、V/Sc比值较高,表明青山口组早期水体为强还原环境,为富有机质页岩保存提供有利条件。中-晚期随着湖盆收缩、水体变浅,还原环境遭到破坏,有机碳含量降低。TOC与古生产力及氧化还原指标呈正相关关系,表明有机质含量的变化主要受控于湖盆生产力和氧化还原环境。古海侵事件带来丰富营养物质,极大提高了湖盆生产力,保证有机质大量供应;同时海侵造成盐度分层,使底部水体的强还原环境不受破坏,促进了有机质的保存。松辽盆地青山口组在白垩纪全球缺氧事件影响下形成了面积约5×10⁴ km²的黑色页岩,是页岩油勘探的重要目标。     

江汉平原浅层含水层中土著硫酸盐还原菌对砷迁移释放的影响

硫酸盐还原菌是厌氧环境中参与砷形态转化的重要微生物种群,其介导的生物地球化学循环过程对铁氧化物表面吸附态砷迁移转化的影响亟待深入研究.选取江汉平原典型高砷含水层原位沉积物分离纯化出一株严格厌氧硫酸盐还原菌Desulfovibrio JH-S1,对其进行砷和铁还原能力鉴定,并通过模拟培养实验探究硫酸盐还原菌参与下的铁矿物相转化对吸附态砷迁移的影响.Desulfovibrio JH-S1具有Fe(III)还原能力,无硫和有硫体系中Fe(III)均能被还原,但在硫酸盐充足条件下铁还原量显著增加;该菌株不具备As(V)还原能力,但添加硫酸盐的培养体系中As(V)去除率可达96%以上.Desulfovibrio JH-S1能够还原硫酸盐从而促进载砷的水铁矿还原转化为纤铁矿,并导致吸附的砷释放.江汉平原高砷含水层土著硫酸盐还原菌兼具硫酸盐/铁还原功能,参与了高砷含水层系统中砷-铁-硫耦合循环,对高砷地下水的形成具有重要作用.      

The Distribution of Trace Elements-Organic Ligands in Seawater and Factors Influencing Their Complexation

Organic metal-binding ligands represent an essential role in the bioavailability of trace elements since they govern the species and sizes of those elements in seawater. The distribution and properties of organic ligands in seawater as well as the factors influencing their complexation abilities were summarized in this paper. Most organic ligands exist in the low molecular weight fraction, and their concentration nearshore is often higher than that of open ocean while the vertical distribution varies in different areas. The complexation of trace elements and organic ligands is influenced by several factors such as molecular weight of organic ligands, salinity, pH, biological activities and redox conditions. Ligand with a lower molecular weight usually represents stronger complexation ability, whereas the opposite seems to be true sometimes due to the specific affinity between some elements and ligands. Increasing salinity lowers the electrostatic repulsion among adjacent functional groups of ligands and thus decreases their complexing rate, yet increasing pH promotes the ionization of organic ligands and results in the formation of more complexes. The utilization of phytoplankton and degradation of microorganism release more low molecular weight organic ligands while more high molecular weight ligands are released from marine organisms under heavy metal stress. Therefore, sufficient significance should be attached to characterizing the structure and molecular weight of organic ligands and exploring the interaction between trace elements and organic ligands and the influence of related marine factors on their behaviors, which will certainly help us to understand the global biogeochemical cycles and ecological significance of trace elements.     

Metal–organic matter interaction: Ecological roles of ligands in oceanic DOM

The ecological roles of dissolved organic matter (DOM) in seawater have not been well understood. One definite function of DOM stems from its complexation ability with trace metals under the conditions of seawater. A chemical complexation model of the marine system was introduced in order to clarify the ecological roles of strong organic ligands in DOM related to the acquisition of bioactive metals (Cu, Fe and Zn) by phytoplankton, assuming that two types of strong organic ligands coexist in oceanic DOM and complexes with bioactive metals. The results reveal that the weaker organic ligand, rather than the stronger one, plays a significant role in the reduction of Cu toxicity for phytoplankton growth. It is suggested that the presence of reactions with Cu that are competitive to the strong organic ligand causes extremely low Fe concentrations in seawater and leads to Fe deficiency for phytoplankton growth. Therefore, it is concluded that the strong ligands in DOM play a chemical role in controlling free ion concentration levels of bioactive metals in the marine environment.     

Modeling on adsorption–desorption of trace metals to suspended particle matter in the Changjiang Estuary

The uptake and release of trace metals (Cu, Ni, Zn, Cd, and Co) in estuaries are studied using river and sea end-member waters and suspended particulate matter (SPM) collected from the Changjiang Estuary, China. The kinetics of adsorption and desorption were studied in terms of environmental factors (pH, SPM loading, and salinity) and metal concentrations. The uptake of the metals studied onto SPM occurred mostly within 10 h and reached an asymptotic value within 40 h in the Changjiang Estuary. As low pH river water flows into the high pH seawater and the water become more alkaline as it approaches to the seaside of estuary, metals adsorb more on SPM in higher pH water, thus, particulate phase transport of metal become increasingly important in the seaward side of the estuary. The percentage of adsorption recovery and the distribution coefficients for trace metals remained to be relatively invariable and a significant reduction only occurred in very high concentrations of metals (>0.1 mg L⁻¹). The general effect of salinity on metal behavior was to decrease the degree of adsorption of Cu, Zn, Cd, Co, and Ni onto SPM but to increase their adsorption equilibrium pH. The adsorption–desorption kinetics of trace metals were further investigated using Kurbatov adsorption model. The model appears to be most useful for the metals showing the conservative behavior during mixing of river and seawater in the estuary. Our work demonstrates that dissolved concentration of trace metals in estuary can be modeled based on the metal concentration in SPM, pH and salinity using a Kurbatov adsorption model assuming the natural SPM as a simple surfaced molecule.     

New operational method of testing colloid complexation with metals in natural waters

A dialysis procedure was used to assess the distribution coefficients of ∼50 major and trace elements (TEs) between colloidal (1 kDa–0.22 μm) and truly dissolved (<1 kDa) phases in Fe- and organic-rich boreal surface waters. These measurements allowed quantification of both TE partitioning coefficients and the proportion of colloidal forms as a function of solution pH (from 3 to 8). Two groups of elements can be distinguished according to their behaviour during dialysis: (i) elements which are strongly associated with colloids and exhibit significant increases of relative proportion of colloidal forms with pH increase (Al, Ba, Cd, Co, Cr, Cu, Fe, Ga, Hf, Mn, Ni, Pb, rare earth elements (REEs), Sr, Th, U, Y, Zn, Zr and dissolved organic C) and (ii) elements that are weakly associated with colloids and whose distribution coefficients between colloidal and truly dissolved phases are not significantly affected by solution pH (As, B, Ca, Cs, Ge, K, Li, Mg, Mo, Na, Nb, Rb, Sb, Si, Sn, Ti, V). Element speciation was assessed using the Visual MINTEQ computer code with an implemented NICA-Donnan humic ion binding model and database. The model reproduces quantitatively the pH-dependence of colloidal form proportion for alkaline-earth (Ba, Ca, Mg, Sr) and most divalent metals (Co, Cd, Mn, Ni, Pb, Zn) implying that the complexation of these metals with low molecular weight organic matter (<1 kDa fraction) is negligible. In contrast, model prediction of colloidal proportion (fraction of 1 kDa–0.22 μm) of Cu²⁺ and all trivalent and tetravalent metals is much higher than that measured in the experiment. This difference may be explained by (i) the presence of strong metal-binding organic ligands in the <1 kDa fraction whose stability constants are several orders of magnitude higher than those of colloidal humic and fulvic acids and/or (ii) coprecipitation of TE with Fe(Al) oxy(hydr)oxides in the colloidal fraction, whose dissolution and aggregation controls the pH-dependent pattern of TE partitioning. Quantitative modeling of metal – organic ligand complexation and empirical distribution coefficients corroborate the existence of two colloidal pools, formerly reported in boreal surface waters: “classic” fulvic or humic acids binding divalent transition metals and alkaline-earth elements and large-size organo-ferric colloids transporting insoluble trivalent and tetravalent elements.     

Salinization in coastal aquifers of arid zones: an example from Santo Domingo,Baja California Sur,Mexico

Groundwater quality in the Santo Domingo Irrigation District area in Baja California Sur, Mexico, indicates the presence of various salinization processes, (1) the geological matter of marine origin comprising the aquifer material suffers diagenetic effects due to its interaction with groundwater of low salinity, (2) the effects of intensive agriculture practices produce effluents that infiltrate to the saturated zone, and (3) the extraction of groundwater causes modifications in the natural flow system induces lateral flow of seawater from the coast line. However, groundwater management has been carried out with the belief that the latter is the main source of salinization. This has resulted in a policy of installing wells increasingly far from the coast, which is not solving the problem. Irrigation-return and seawater that remains in the geological units have been identified as major sources of salinization. Controls should be imposed when installing wells in contact with clayey units that form the base of the aquifer. Extracted groundwater consists of a mixture of (1) groundwater of relatively low salinity that circulates in the aquifer and (2) an extreme member with salinity different to seawater contained mainly in formations that have low permeability, which limits the aquifer underneath. The geochemistry of carbonates and cation-exchange reactions (both direct and reverse) control the concentration of Ca, Mg, Na, and HCO₃, as well as pH values. The concentrations of dissolved trace elements (F, Li, Ba, Sr) suggest that the extreme saline member is different from the average seawater composition. A distinction between the salinization caused by farming practices and that blamed on seawater is defined by the use of NO₃.     

海洋胶体与痕量金属的相互作用

痕量金属的胶体结合态是海洋中金属的一种相当普遍的存在形式。胶体与痕量金属之间的相互作用影响着痕量金属在海水中的形态、迁移、生物可利用性及其归宿。总结了海洋胶体态金属的存在及其显著性,概述了胶体对金属在河口混合过程中行为的影响,并简要讨论了胶体在海水中痕量金属的固液相分配中的作用。     

Geochemical factors controlling free Cu ion concentrations in river water

Copper speciation was determined monthly at seven sites on four rivers in southern New England to understand which geochemical factors control free metal ion concentrations in river water. Samples were conventionally filtered (<0.45 μm) and then ultrafiltered (3.000 molecular weight cut-off) to determine Cu speciation in the truly dissolved size fraction. Differential pulse anodic stripping voltammetry (DPASV) was used to quantify natural organic complexation and cathodic stripping square wave voltammetry (CSSWV) to measure directly both Cu sulfide complexes and total EDTA concentrations. The results showed both dissolved organic matter (DOM) and sulfide complexation dominate Cu speciation and control the concentrations of free ion. Free Cu²⁺ was calculated to be in the subnanomolar range for the majority of the year. Only in the winter months, when concentrations of DOM and metal sulfides complexes were at a minimum were free metal ions directly measurable by DPASV at low nanomolar concentrations. The extent of sulfide complexation appears to be dominated by the size of headwater marshes (upstream sampling sites) and by the amount of sewage treatment plant effluent (downstream sites). DOM complexation was related to the organic matter composition and followed model organic ligands. Indirect evidence suggests variations in river water pH and Ca²⁺ (metal competition) has only a minor role in Cu complexation. Measured concentrations of total EDTA suggest this synthetic ligand can control Cu speciation in some highly developed watersheds; however, competition from Ni (and possibly Fe) limits the extent of this complexation.     

Geochemistry and mineralogy of marine and non-marine Namurian black shales from the Tansley Borehole, Derbyshire

The Namurian black shales studied have a good palaeontological control. Pyrite, illite and organic matter are higher in the marine shales, and siderite and kaolinite are higher in the non-marine shales. The distribution of the diagenetic iron minerals is attributed to anionic activities controlled by salinity. The same control could account for the observed clay-mineral distribution by differential flocculation. The major element geochemistry closely reflects the above mineral variation. Mn and Zr are higher in the non-marine shales due to siderite and zircon respectively. Co, Cr, Rb, Y and Ba are not significantly different and a detrital source, mainly clay minerals, is suggested. In the marine shales the elements Pb, Cu, V, Ni, Sr and Zn are significantly higher. Using a discriminant function analysis the palaeosalinity groups are separated and the contribution of each element to the separation is calculated. The present element locations are thought, from correlation analysis, to be pyrite and organic matter. By analogy with experimental work and modern environments, the element enrichment is mainly attributed to reactions involving organic matter and oxyhydroxide material in environments in which salinity and slow rates of sedimentation were important factors. The element enrichment cannot be related directly to seawater concentrations, unlike some black shales, and the accumulation rates for Pb and Cu are thought to be unusually high.     

Sorption of Trace Elements on Mineral Surfaces: Modern Perspectives from Spectroscopic Studies,and Comments on Sorption in the Marine Environment

The partitioning (or sorption) of trace elements from aqueous solutions onto mineral surfaces and natural organic matter (NOM) has played a major role in determining the trace element content of natural waters. This review examines sorption processes on mineral surfaces for nine trace elements (Cr, Co, Ni, Cu, Zn, Sr, Cd, Hg, Pb), focusing on the results of modern x-ray spectroscopic studies. Such studies provide unique information on the structure and composition of sorption products, including their mode of attachment to mineral surfaces or functional groups in NOM under in situ conditions (i.e., with aqueous solution present at 25°C). The types of chemical reactions (acid-base, ligand exchange, redox, dissolution/reprecipitation) that can occur at mineral-aqueous solution interfaces are also reviewed, and some of the factors that affect the reactivity of mineral surfaces are discussed, including changes in the geometric and electronic structures of mineral surfaces when they first react with aqueous solutions and constraints on the bonding of adions to surface functional groups imposed by Pauling bond valence sums. A summary of electrical double layer (EDL) theory is presented, including the results of several recent x-ray spectroscopic and parameter regression studies of the EDL for metal-(oxyhydr) oxide-aqueous solution interfaces. The effects of common inorganic and organic complexants on the sorption of trace metal cations at mineral-solution interfaces are considered, in the context of spectroscopic studies where possible. The results of sorption studies of trace metal cations on NOM, common bacteria, and marine biomass are reviewed, and the effects of coatings of NOM and microbial biofilms on cation uptake on mineral surfaces are discussed, based on macroscopic and spectroscopic data. The objective here is to assess the relative importance of inorganic versus organic sorption processes in aquatic systems. The paper concludes with a discussion of the effects of water composition on trace element removal mechanisms, with the aim of providing an understanding of the effects of the high salinity of seawater on trace element sorption processes. The information presented in this review indicates that sorption processes on mineral, NOM, and microbial and algal surfaces, including true adsorption and precipitation, are highly effective at removing trace elements from natural waters and generally supports Krauskopf's (1956) conclusion that such processes are likely responsible for the present trace element concentrations in seawater.     

冀北-辽西地区洪水庄期海洋氧化还原环境的不均一性

洪水庄组沉积时期的海洋氧化还原条件及其对有机质保存的影响目前仍有较大的争议.通过对辽西地区洪水庄组页岩的稀土和微量元素进行分析,探究了该时期海洋氧化还原条件.研究区稀土元素丰度较高,分布范围为167.57×10-6~316.95×10-6.稀土元素分布具有典型的海水特征,轻稀土较为亏损而重稀土相对富集.Ce负异常较为明显,基本不具有Eu异常,Y/Ho比值较低.微量元素（V、Cr、Ni、Co、Th和U）及其比值基本分布在一个较宽的范围内,说明该时期海洋具有不均一氧化的特征.稀土和微量元素指标均指示该时期海洋部分氧化和部分还原的特征,且部分地区属于硫化环境.综合华北北部其他地区洪水庄组氧化还原指标表明,该时期的海洋含氧量在空间上具有明显的不均一性,还原性较强的环境基本处于TOC较高的区域,与该区域的高生产力和丰富的营养元素有较好的关联性.