First Phase Monitoring Studies of Simulated Benthic Disturbance Delineating Movement of Fine Particles in the Central Indian Basin

Benthic disturbance due to future deep-sea polymetallic nodule mining would involve expensive sediment plume generation and resedimentation on the sea floor. In order to evaluate the effects of resedimentation on benthic environment, the Indian Deep-sea Environment Experiment (INDEX) was conducted in 1997, and pre-, and post-disturbance studies on grain size were carried out. The initial increase in clay content after the experiment, continued to increase further as measured in the first monitoring phase samples, 44 months later. Increase in clay-sized particles during monitoring-l (M-l) was highest within the simulated (disturbed) zone and to the north of it, which is attributed to the combined effects of disaggregation, abrasion, and powderization of sediments during transportation. Due to this fractionation (breaking up), the particles appear to have remained in suspension over a prolonged period of time after they were discharged in the water column 5 m above the seabed during INDEX. The travel effects of INDEX plume appears to be localized and confined within and around the disturbed zone (DZ) as resettlement of fine particles from the benthic plume was traced up to 2 km south and 12 to 18 km north of the DZ. The evidence does not suggest the existence of strong currents and benthic storms in the CIB     

Inter-relationship between Nuclei and Gross Characteristics of Manganese Nodules,Central Indian Ocean Basin

More than 200 samples of manganese nodules from the Central Indian Ocean Basin (CIOB) were studied for their different parameters. The study included various aspects such as morphology, texture, mineralogy, and composition of the nodules. The nuclei of the nodules were also examined along with the oxide layers. We attempt to correlate the nucleus (their type and abundance) with the nodule parameters such as their external morphology, chemical composition, and suitable location of formation, amongst others. We found various nucleating materials and these include rock fragments (fresh and altered), clay, pumice and sharks' teeth. In a majority of the cases, rock fragments are dominant in the core of the nodules and these conform to that of the seafloor basalts. The shape of the nuclei influences that of the nodules, especially during their initial period of growth. Irrespective of the kind of nuclei, todorokite is the main mineral of the nodules. The nodules of the CIOB were formed mostly due to hydrogenous accretion of ferromanganese oxides while diagenetic contribution of metals is less common.     

基于形态学重建算法的海底多金属结核覆盖率统计研究

为提高海底多金属结核覆盖率统计的精度,提出一种在图像处理后期填加形态学重建算法的优化方法。实验中,分别采用网格计数法、二值化图像处理法和形态学重建算法,对蛟龙号拍摄的海底多金属结核图像进行了覆盖率的统计和对比分析。实验结果表明:传统的网格计数法作为一种人工统计方法,工作量大、耗时费力且统计误差不稳定;二值化图像处理法统计效率和精度大大提高,但该方法无法如网格计数法般人为避免多金属结核表面被海底障碍物(软泥、砂砾等)覆盖带来的部分统计误差,使统计结果偏低;优化后的算法二值化阈值自动提取,遮盖区域得到填充,有效地弥补了其他两种方法的缺点,统计快速,准确率提高。     

数学地质方法在大洋多金属结核研究中的应用

回顾了一些数学地质的基本理论方法（即基础数学方法、多元统计、地质统计学、人工神经网络、分形理论）以及它们在大洋多金属结核研究中的应用状况，并探讨了其今后的主要应用方向。     

Ferromanganese Nodules and their Associated Sediments from the Central Indian Ocean Basin: Rare Earth Element Geochemistry

Abstract

The rare earth element (REE) distribution in nine deep-sea ferromanganese nodules and their associated siliceous sediments from the Central Indian Ocean Basin (CIOB) have been studied to elucidate the REE relationship among them. Total REE concentration varies from 398–928 ppm in the nodules and 137–235 ppm in the associated sediments, suggesting two- to four-fold enrichment in the nodules compared to associated sediments. REE of nodules and their associated sediments show a positive correlation, suggesting REE are supplied from a common source such as seawater. The positive correlation between REE of nodules and sediments from the CIOB is contrary to the competitive scavenging of REE between nodules and sediment in the equatorial Pacific Ocean. REEs in the nodules are carried by Fe, P, and Ti, whereas in the sediment they are carried by P and Mn phases. A similar REE fractionation pattern with middle REE enrichment over heavy and light REE in both the nodules and their associated sediment suggest fractionation is independent of REE abundance and their carrier phases.     

深海多金属结核生长模拟及宏观形貌研究

研究旨在提出深海多金属结核生长的数值模拟方法,以获取典型的结核宏观形貌,为后续结核输运过程的冲击碎裂仿真提供几何模型。根据已有的深海多金属结核采样研究结果,假定矿物沉积速率满足正态分布。将多阶段时变随机沉积模型嵌入ABAQUS UMESHMOTION子程序中,通过控制网格节点移动实现了结核多阶段随机生长模拟,给出了结核不同生长阶段的外形及截面特性模拟结果。分析了鱼骨、鲨鱼牙齿、板岩、鹅卵石等典型不同核心物质及矿物沉积速率变异性对结核生长过程的影响,确定了核心物质在海床淤泥中埋置深度对结核生长形态的影响。研究表明：基于网格节点移动的结核生长模拟技术可有效处理结核几何拓扑变化较小的生长过程,核心物质的初始形状及其在海床上的埋置深度是影响结核形貌的主要原因,而矿物沉积速率的变异性则主要影响结核表面的光滑度。     

Manganese nodule distribution in different topographic domains of the Central Indian Basin

Manganese nodule distribution is primarily influenced by seafloor topography. Nodule distribution at 479 locations vis‐à‐vis seabed topography is studied by superimposing sampling location on the topographic profile and assigning appropriate domain (hilltop, valley, slope, or plain) for the sampling location. Highest mean abundance is observed at the valleys (6.94 kg /m²), followed by hilltops, slopes, and least on plains. Frequency distributions are regular (Gaussian) on plains, whereas on valleys and hilltops they are irregular (Rayleigh type). Fe and Co content is highest in nodules from hilltops and lowest in those from plains. Conversely, Mn, Cu, and Ni content is highest on plains and least on valleys. Fe: Mn and Co: Mn are negatively correlated in all the domains. Mn and total metal content (Ni + Cu + Co) show direct relationship in all the domains. An inverse relation between nodule abundance and composition is found. Cluster analysis on chemical and abundance data shows two distinct groups in all domains. Abundance and Fe and Co content typically form one group, while all other elements form another group. Genesis of nodules depends on the availability of supply of transition elements to the abyssal environment, maintenance of nodules in the sediment‐water interface, and sedimentation rates.     

Polymetallic Nodule Mining, Waste Disposal, and Species Extinction at the Abyssal Seafloor

The size of individual mining blocks for polymetallic nodule extraction seems to be rather small, not more than 100 km² in the French mining claim. Even when adding an additional resedimentation zone to the directly impacted area, the size of the affected seabed would remain below 200 km². We assume that even rare species in the abyss inhabit larger areas and propose discussions of the International Seabed Authority and other stakeholders for the different subregions on mining strategies from the perspective of exploitation versus species extinction and conservation. Although impacts of waste disposal at the abyssal seafloor are different from those of nodule mining, the 200 km² concept may also be applied.     

Distribution of Grain Size and Clay Minerals in Sediments from the INDEX Area,Central Indian Basin

Abstract

The granulometry of 21 box core sediments from five selected sites in the Central Indian Basin (CIB) have been studied to understand the sediment size characteristics in the Pioneer area before the benthic disturbance experiment. The sediments are predominantly clayey silt. Statistical parameters were determined to understand the control and variations in the grain size. The mean grain size (M_zφ) ranged from 7.0 to 8.6 for the surface and from 6.6 to 8.6 for the subsurface sediments, indicating deposition of very fine fractions during the Neogene period. The sediments were poorly sorted as revealed from the higher ρ₁ values (2.7 to 2.9). Higher and negative values of skewness (SK₁) indicated a winnowing action of prevailing currents in the area. Average kurtosis (K_G) values for the surface (0.4 to 0.8) and subsurface (0.5 to 1.2) showed that sediments were very platykurtic and leptokurtic. Clay mineralogical studies showed that smectite had a wider range (from 6% to 55%) and decreased southward because of its terrigenous origin. The terrigenous influence of the sediments could be documented as far as 12°S. Smectite and kaolinite increased eastward and chlorite decreased southward. This observation positively correlated with the mean current direction in the area. However, the influence of Antarctic Bottom Water (AABW) in the area could be predicted from the southward increase in chlorite content.     

Distribution and Origin of Seamounts in the Central Indian Ocean Basin

Approximately 200 seamounts of different dimensions have been identified, from multibeam bathymetry maps of the Central Indian Ocean Basin (CIOB) (9°S to 16°S and 72°E to 80°E), of which 61% form eight chains that trend N-S. The seamounts are clustered above and below 12°S latitude. Area II (9°–12°S) shows a concentration of smaller seamounts (≤400 m height), and area I (12°–15°S) has a mixed population (including both less and more than 400 m height). Inspite of the differences in their height, the seamounts of these eight chains are morphologically (slope angle, flatness, basal width) corelatable. Furthermore, we suggest that height-width ratio could be useful in identifying the style of seamount eruption. The seamount chains in the CIOB probably originated from propagative fractures and were produced between 61 and 52 Ma (chrons A26 to A23) as a result of the interaction between the conjugate crusts of the Central Indian and Southeast Indian Ridges during the Indo-Eurasian collision event.     

Distribution and Origin of Seamounts in the Central Indian Ocean Basin

Approximately 200 seamounts of different dimensions have been identified, from multibeam bathymetry maps of the Central Indian Ocean Basin (CIOB) (9°S to 16°S and 72°E to 80°E), of which 61% form eight chains that trend N-S. The seamounts are clustered above and below 12°S latitude. Area II (9°-12°S) shows a concentration of smaller seamounts (≤400 m height), and area I (12°-15°S) has a mixed population (including both less and more than 400 m height). Inspite of the differences in their height, the seamounts of these eight chains are morphologically (slope angle, flatness, basal width) corelatable. Furthermore, we suggest that height-width ratio could be useful in identifying the style of seamount eruption. The seamount chains in the CIOB probably originated from propagative fractures and were produced between 61 and 52 Ma (chrons A26 to A23) as a result of the interaction between the conjugate crusts of the Central Indian and Southeast Indian Ridges during the Indo-Eurasian collision event.     

Monitoring the Impact of Simulated Deep-sea Mining in Central Indian Basin

Monitoring of deep-sea disturbances, naturai or man-made, has gained significance due to the associated sediment transport and for the ensuing alterations in environmental conditions. During the Indian Deep-sea Environment Experiment (INDEX), resuspension of deep-sea sediment in the Central Indian Basin (CIB) resulted in an increase and lateral movement of suspended particles, vertical mixing of sediments, changes in sedimentological, biochemical, and geochemical conditions and an overall reduction in benthic biomass. Monitoring the conditions 44 months after the experiment has shown a partial recovery of the benthic ecosystem, with indications of restoration and recolonization.     

雅浦海沟南缘铁锰结核矿物与地球化学特征及其成因研究

本文采用X射线衍射、全岩地球化学和电子探针等测试方法,对雅浦海沟南部附近海域获得的铁锰结核样品进行了显微构造、矿物和地球化学分析,并探讨了其成因。结果表明:铁锰结核的显微构造主要包括平行纹层构造、柱状构造、叠层状构造和同心环状构造;显微构造和探针结果显示铁锰结核在生长初期处于底部海洋动力比较强烈的环境,后期生长环境逐渐趋于稳定;铁锰结核的矿物组分以水羟锰矿、钠水锰矿、石英和钙十字石为主;样品中Fe、Mn元素含量较高且含量比较接近,Cu、Co、Ni和REE相对富集,REE分布模式整体比较平缓并都出现较强的Ce正异常和重稀土元素亏损现象;文中两块铁锰结核都为水成成因,成矿物质主要来自同期的海水沉淀,同时也受一定海底火山物质和陆源风尘物质的影响。     

Variability of the axial morphology and of the gravity structure along the Central Spreading Ridge (North Fiji Basin): evidence for contrasting thermal regimes

The Central Spreading Ridge (CSR) is located in the central part of the North Fiji Basin, a complex back-arc basin created 12 Ma ago between the Pacific and Indo-Australian plates. The 3.5 Ma old CSR is the best developed, for both structure and magmatism, of all the spreading centers identified in the basin, and may be one of the largest spreading systems of the west Pacific back-arc basins. It is more than 800 km long and 50–60 km wide, and has been intensively explored during the French-Japanese STARMER project (1987–1991).The CSR is segmented into three first order segments named, from north to south, N160°, N15° and N-S according to their orientation. This segmentation pattern is similar to that found at mid-ocean ridges. The calculated spreading rate is intermediate and ranges from 83 mm/yr at 20°30 S to 50 mm/yr at 17°S. In addition, there is a change in the axial ridge morphology and gravity structure between the northern and southern sections of the CSR. The axial morphology changes from a deep rift valley (N160° segment), to a dome split by an axial graben (N15° segment) and to a rectangular flat top high (N-S segment). The Mantle Bouguer Anomalies obtained on the northern part of the CSR (N160°/N15° segments) show bull's eye structures associated with mantle upwelling at the 16°50S triple junction and also in the middle of the segments. The Mantle Bouguer Anomalies of the southern part of the ridge (N-S segment) are more homogeneous and consistent with the observed smooth topography associated with axial isostatic compensation.At these intermediate spreading rates the contrast in bathymetry and gravity structure between the segments may reflect differences in heat supply. We suggest that the N160° and N15° segments are cold with respect to the hot N-S segment. We use a non-steady-state thermal model to test this hypothesis. In this model, the accretion is simulated as a nearly steady-state seafloor spreading upon which are superimposed periodic thermal inputs. With the measured spreading rate of 50 mm/yr, a cooling cycle of 200,000 yr develops a thermal state that permits to explain the axial morphology and gravity structure observed on the N160° segment. A spreading rate of 83 mm/yr and a cooling cycle of 120,000 yr would generate the optimal thermal structure to explain the characteristics of the N-S segment. The boundaries between the hot N-S segment and its cold bounding segments are the 18°10 S and 20°30 S propagating rifts. A heat propagation event along the N-S segment at the expense of the adjacent colder failing segments, can explain the sharp changes in the observed morphology and structure between the segments.     

Distribution of Deep-Sea Benthos in the Proposed Mining Area of Central Indian Basin

During the first stage of the project work on the Indian Deep-Sea Environment Experiment (INDEX), the abundance and distribution of deep-sea benthos were surveyed in the Central Indian Basin for the collection of baseline data. The deep-sea community of the sediment was characterized by a moderately high standing crop and diverse fauna. The macrofaunal component was dominated by polychaetes (100% prevalence) and peracarid crustaceans, whereas the meiofauna was dominated by nematodes and harpacticoid copepods. The results of this study conform to the general distribution reported elsewhere. The macrofaunal abundance showed an inverse relation to the abundance of polymetallic nodules. However, the relation between meiofaunal vertical distribution and the vertical profile of the total organic matter and total labile matter was positive.     

Distribution of Deep-Sea Benthos in the Proposed Mining Area of Central Indian Basin

Abstract

During the first stage of the project work on the Indian Deep-Sea Environment Experiment (INDEX), the abundance and distribution of deep-sea benthos were surveyed in the Central Indian Basin for the collection of baseline data. The deep-sea community of the sediment was characterized by a moderately high standing crop and diverse fauna. The macrofaunal component was dominated by polychaetes (100% prevalence) and peracarid crustaceans, whereas the meiofauna was dominated by nematodes and harpacticoid cope-pods. The results of this study conform to the general distribution reported elsewhere. The macrofaunal abundance showed an inverse relation to the abundance of polymetallic nodules. However, the relation between meiofaunal vertical distribution and the vertical profile of the total organic matter and total labile matter was positive.     

Distribution pattern and morphochemical relationships of manganese nodules from the Central Indian Basin

In the Central Indian Basin manganese nodule abundance was variable in all sediment types. Mean abundance varied from 1.5 in calcareous ooze to 10.2 kg/m² in terrigenous-siliceous ooze sediments. Nodule grade and growth rates are positively correlated only up to 10 mm/My (million years), and grade shows no distinct relationship with abundance. Relationships between the morphochemical characteristics of the nodules and host sediment types are subtle. Both hydrogenetic and diagenetic nodules (with smooth and rough surfaces respectively) occur on almost all sediments, but in variable proportions. Thus, the overall distribution pattern shows that small nodules (<4-cm diameters) of lower grade (average value Ni+Cu+Co=1.21%) with smooth surfaces are more common on red clay, terrigenous, and terrigenous-siliceous ooze transition-zone sediments. By contrast, large nodules (>4-cm diameters) of higher grade (average value Ni+Cu+Co=1.80%) with rough surfaces are more prevalent on siliceous ooze, siliceous ooze-red clay, and calcareous ooze-red clay transition-zone sediments. This implies an enhanced supply of trace metals from pore waters to rough-surface nodules during early diagenesis.     

Ferromanganese Nodules and their Associated Sediments from the Central Indian Ocean Basin: Rare Earth Element Geochemistry

The rare earth element (REE) distribution in nine deep-sea ferromanganese nodules and their associated siliceous sediments from the Central Indian Ocean Basin (CIOB) have been studied to elucidate the REE relationship among them. Total REE concentration varies from 398-928 ppm in the nodules and 137-235 ppm in the associated sediments, suggesting two- to four-fold enrichment in the nodules compared to associated sediments. REE of nodules and their associated sediments show a positive correlation, suggesting REE are supplied from a common source such as seawater. The positive correlation between REE of nodules and sediments from the CIOB is contrary to the competitive scavenging of REE between nodules and sediment in the equatorial Pacific Ocean. REEs in the nodules are carried by Fe, P, and Ti, whereas in the sediment they are carried by P and Mn phases. A similar REE fractionation pattern with middle REE enrichment over heavy and light REE in both the nodules and their associated sediment suggest fractionation is independent of REE abundance and their carrier phases.     

基于深海采矿过程的环境影响分析与管理对策建议

深海矿产开发所产生的环境影响是目前制约深海采矿的重要问题之一,了解开发全过程的环境影响和生态响应是商业化开采的前提。本文以多金属结核、富钴结壳和多金属硫化物三种具有代表性的深海固体矿产资源为例,分析了开发前赋存环境、开发过程中及开发后的环境影响。结果表明：①不同深海固体矿产资源的分布规律、深度以及生物特征等赋存环境存在较大差异,因采矿活动带来的赋存环境改变、对环境的影响以及采矿潜在影响区域、影响时长和恢复潜力也有所不同。②多金属结核开采的环境影响着重考虑了沉积物羽流的影响,结壳开采活动从沉积物扰动、外壳去除以及栖息地改变三个方面考虑环境影响,多金属硫化物开采的环境影响还要增加对有毒物质的释放以及栖息地移除两个方面的考虑。③深海采矿对底栖生物种群的数量和物种组成皆会造成不同程度的影响。最后,从持续跟进监测评估、充实数据、提升采矿技术与设备、顶层设计与决策管理、规则制定等方面提出了环境保护与可持续发展对策建议,为深海采矿的环境影响评价及规则制定提供参考。     

太平洋东马里亚纳海盆多金属结核成因及品位控制因素

本文选取东马里亚纳海盆与CC区中国多金属结核合同区西区的多金属结核样品,采用ICP-OES、ICP-MS以及XRD等测试方法对结核表层进行了地球化学与矿物学分析,并探讨了东马里亚纳海盆结核成因以及其主要成矿元素含量的控制因素。结果表明,结核具备水成型结核的主、微量元素特征,并受到成岩作用的影响。结核上下表层各元素含量差异明显,上表层Fe、Co、P等多数主量元素及∑REYs含量均高于下表层,而Mn、Cu、Ni等元素含量在下表层明显增加。根据结核矿物学以及海洋环境特征,并结合前人数据统计分析认为,东马里亚纳海盆结核样品中Mn、Ni、Cu、Co、Fe、Ce的品位主要受控于Mn矿物组成、底层海水溶解氧和表层海水初级生产力,La、Y等稀土元素品位还受到洋中脊热液活动的制约。