Biogenic-silica accumulation in the Ross Sea and the importance of Antarctic continental-shelf deposits in the marine silica budget

Thirty-five box cores were collected from the continental shelf in the Ross Sea during cruises in January and February, 1983. Pb-210 and Pu-239, 240 geochronologies coupled with biogenic-silica measurements were used to calculate accumulation rates of biogenic silica. Sediment in the southern Ross Sea accumulates at rates ranging from ≤0.6 to 2.7 mm/y, with the highest values occurring in the southwestern Ross Sea. Biogenic-silica content in surface sediments ranges from 2% (by weight) in Sulzberger Bay and the eastern Ross Sea to 41% in the southwestern Ross Sea. Biogenic-silica accumulation in the southwestern Ross Sea averages 2.7 × 10⁻² g/cm²/y and is comparable to accumulation rates in high-productivity, upwelling environments from low-latitude continental margins (e.g., Gulf of California, coast of Peru). The total rate of biogenic-silica accumulation in the southern Ross Sea is approximately 0.2 × 10¹⁴ g/y, with most of the accumulation occurring in basins (500–1000 m water depth). If biogenic-silica accumulation in the southern Ross Sea continental shelf is typical of other basins on the Antarctic continental shelf, as much as 1.2 × 10¹⁴ g/y of silica could be accumulating in these deposits. Biogenic-silica accumulation on the Antarctic continental shelf may account for as much as a fourth of the dissolved silica supplied to the world ocean by rivers and hydrothermal vents.     

Till in the marine environment

Till is of common occurrence in the marine environment and can be both subglacial and proglacial in origin. Former glacial margins are often represented by till tongues, that are interbedded with stratified glaciomarine sediment, and the relationship is readily mappable using seismic reflection techniques. It is inferred that within individual till tongues, sediment-gravity flow deposits form transitional contacts with till of subglacial origin, but these contacts cannot be distinguished on seismic profiles. These unstratified, gravity-induced deposits formed in close proximity to the glacial source at the grounding line are considered to be secondary tills (flow-till complex) in terms of the INQUA classification of tills. Till-tongue successions and till deltas are large, ice-marginal depocentres associated with floating front ice-margins, and appear to be closely related in origin. Tabular and hummocky moraines of the mid-Norwegian Shelf also are considered to be products of floating-front margins and represent a large proportion of the retreat tills formed during ice recession. Seismostratigraphic evidence for channelisation in ice-marginal deposits appears to provide a means of distinguishing between former tidewater and floating-front margins.     

Metal-organic complexation in the marine environment

We discuss the voltammetric methods that are used to assess metal-organic complexation in seawater. These consist of titration methods using anodic stripping voltammetry (ASV) and cathodic stripping voltammetry competitive ligand experiments (CSV-CLE). These approaches and a kinetic approach using CSV-CLE give similar information on the amount of excess ligand to metal in a sample and the conditional metal ligand stability constant for the excess ligand bound to the metal. CSV-CLE data using different ligands to measure Fe(III) organic complexes are similar. All these methods give conditional stability constants for which the side reaction coefficient for the metal can be corrected but not that for the ligand. Another approach, pseudovoltammetry, provides information on the actual metal-ligand complex(es) in a sample by doing ASV experiments where the deposition potential is varied more negatively in order to destroy the metal-ligand complex. This latter approach gives concentration information on each actual ligand bound to the metal as well as the thermodynamic stability constant of each complex in solution when compared to known metal-ligand complexes. In this case the side reaction coefficients for the metal and ligand are corrected. Thus, this method may not give identical information to the titration methods because the excess ligand in the sample may not be identical to some of the actual ligands binding the metal in the sample.     

Biological uptake and accumulation of silica on the Amazon continental shelf

Water column and seabed samples were obtained from 92 stations on the Amazon continental shelf during October of 1979. Uptake of silica near and southeast of the river mouth began at a salinity of 8%. and accounted for 17% of the riverine silica flux to this region. Uptake northwest of the river mouth began at a salinity of 20%. and resulted in 33% removal of the riverine silica flux. Examination of filtered suspended solids revealed abundant diatoms in the surface waters, including Coscinodiscus. Skeletonema, Synedra. and Thalassiosira. The biological uptake of silica appears to be dependent on three factors: turbidity, turbulence, and nutrient availability. There was no evidence of abiological removal of silica in the Amazon estuary. 75 to 88% of the silica removed from surface waters by diatoms dissolves prior to accumulation in the seabed. Based on the mean biogenic silica content of shelf sediment (0.25%) and estimates of rates of sediment accumulation, the biogenic silica accumulation rate on the shelf is 2 × 10¹² g/yr, which represents only 4% of the dissolved silica supplied by the Amazon River. Biological uptake of silica in estuarine surface waters may not accurately reflect permanent removal of biogenic silica to the seabed because of dissolution which occurs in bottom waters and near the sediment-water interface.     

Metal–organic complexation in the marine environment

We discuss the voltammetric methods that are used to assess metal–organic complexation in seawater. These consist of titration methods using anodic stripping voltammetry (ASV) and cathodic stripping voltammetry competitive ligand experiments (CSV-CLE). These approaches and a kinetic approach using CSV-CLE give similar information on the amount of excess ligand to metal in a sample and the conditional metal ligand stability constant for the excess ligand bound to the metal. CSV-CLE data using different ligands to measure Fe(III) organic complexes are similar. All these methods give conditional stability constants for which the side reaction coefficient for the metal can be corrected but not that for the ligand. Another approach, pseudovoltammetry, provides information on the actual metal–ligand complex(es) in a sample by doing ASV experiments where the deposition potential is varied more negatively in order to destroy the metal–ligand complex. This latter approach gives concentration information on each actual ligand bound to the metal as well as the thermodynamic stability constant of each complex in solution when compared to known metal–ligand complexes. In this case the side reaction coefficients for the metal and ligand are corrected. Thus, this method may not give identical information to the titration methods because the excess ligand in the sample may not be identical to some of the actual ligands binding the metal in the sample.     

白垩纪中期海相富有机碳沉积的地球生物学背景

白垩纪中期(约125～88Ma)海相富有机碳沉积广泛发育于全球各主要洋盆和沉降区,是许多大油田的重要烃源岩。文中从地球生物学的角度探讨了当时海相富有机碳沉积的地质背景和主控因素,认为在白垩纪中期全球事件频发的特殊背景下,保存条件(大洋缺氧)和生产力的提高共同控制了有机质的富集。大洋缺氧不但加快了海洋生物的灭绝和更替,使有机质大量堆积,而且促进了营养元素(P、N、Fe等)的再生和厌氧自养型海洋微生物(如蓝细菌、绿硫细菌和古菌类等)的极度繁盛,提高了生产力水平;而高的生产力又反过来加剧了海洋的缺氧。新的研究成果(Os同位素证据)表明,白垩纪大规模海底火山作用引发了持续的温室效应和海水循环的静滞、紊乱以及弱上升流发育,进而导致生产力的提高和大洋缺氧事件(OAE)的发生,最终造成有机质的广泛堆积和保存。     

Comparative analysis of pelagic Pleistocene silica accumulation in the Pacific and Indian Oceans

The methodical principles of the analysis of biogenic silica accumulation in the pelagic zones of the Pacific and Indian oceans are considered. Two quantitative approaches of lithological analysis are compared: method of absolute mass by A.D. Arkhangel’skii and volumetric method by A.B. Ronov. It is established that the concept of “two oceans” (“ice” and “non-ice”) may be applied to both the oceans. Differences in the evolution of the silica accumulation rate in the Pleistocene between high- and low-latitude oceans are revealed.     

Two-dimensional modeling of the accumulation of carbonate deposits in marine environments

A program is developed for modeling the accumulation of deep-water, shallow-sea, reef and fragmentary carbonate deposits in marine environments. The formation of the Maldives carbonate platform is modeled using the developed program. The comparison of the modeling results and the geological cross-section demonstrates that the algorithms allow the construction of geological cross-sections in sufficient detail.     

The Ocean after christopher columbus — thoughts about society and the marine environment

The objective of this paper is to consider the Columbus’ enterprise from the point of view of the evolution of the involvement of society in the marine environment. Recently Columbus has been regarded as a protagonist of the Renaissance because he was able to produce interaction between the willingness to discover new geographical frontiers, the use of knowledge for developing political strategies, the search for riches, the conquest of extra-Mediterranean and extra-European areas. This approach sustained both the palaeo- and neo-industrial stages in which the ocean environment as a whole was involved in conquest-oriented and resource-use strategies. Both Enlightenment and Positivism were the natural prolongation of Columbus’ approaches and those of the Renaissance. Changes occurred in the seventies: (i) the general system-based approach, jointly with the growing attention to the ocean ecosystem, have led to approaches in which sea uses and the natural context are regarded as interacting systems; (ii) in particular, the ocean ecosystem has been increasingly regarded in a no deterministic way; (iii) United Nations’ policy has encouraged policies based on the duoenvironment anddevelopment. As a final result, in terms of cultural values, the post-Columbus era has initiated just as the quincentenary of his enterprise is being celebrated.     

Nutrient exchange between subtropical lagoons and the marine environment

The tidal exchange of ammonia-nitrogen, nitrate-nitrogen, total nitrogen, total phosphorus, and total organic carbon between coastal lagoons and the marine environment were determined. Constituent measurements were made in Huizache-Caimanero Lagoon in Northwest Mexico over 24-h sampling periods during both dry and wet seasons. The exchange of these nutrients was also compared to exchanges in estuarine marshes of other latitudes. High exchange rates were found to be associated to extreme climatic events.     

Sandy gravel accumulation in a fluvial environment

Particle size, pebble shape, pebble fabric, discharge and flow velocity data are used to introduce a model of sandy gravel formation in Welsh gravel-bed rivers. The development of contact-imbrication of the typically very bladed and very platy cobbles and larger pebbles subsequently acts to significantly affect the depositional modes and patterns of small pebbles and sand particles. An important distinction is drawn between sand deposition, which can occur at or below the bed surface, and pebble and cobble deposition, which is merely a surface phenomenon.     

大鹏湾海洋地质环境与地质灾害综合分析

广州海洋地质调查局在大鹏湾深圳海域开展了海洋地质环境与地质灾害综合调查研究。笔者根据调查所取得的海水化学、海底表层沉积物和海底工程地质条件(包括潜在地质灾害)等方面的资料，结合实测的海底地形地貌背景，对大鹏湾海域的海洋地质环境进行了单因子评价和多因子综合评价，认为大鹏湾的海洋地质环境总体呈良好状况，并对大鹏湾的海洋开发工程建设提出了有益建议。     

Carbohydrate sources in a coastal marine environment

Individual neutral sugars in sediments, sediment trap materials and major biological sources of a coastal marine environment (Dabob Bay, Washington State) were analyzed by capillary gas chromatography of equilibrated isomeric mixtures. Plankton, bacteria, and vascular plant tissues of different types yielded reproducible and biochemically consistent compositional patterns. These patterns, when expressed in simple parameters, allowed distinctions between marine and terrestrial carbohydrate sources as well as among the major different types of vascular plant tissues. Plankton and bacteria, due to their compositional diversity, were not further distinguishable by carbohydrate compositions alone. Carbohydrate compositions of Dabob Bay sediments and sediment trap materials, interpreted using source-indicator parameters, indicate a predominantly marine origin with increased relative input of terrestrially-derived carbohydrates in winter periods of low phytoplankton productivity. Both plankton and grasses are indicated as major carbohydrate sources during spring. Glucose yield enhancement factors, determined by comparative acid pretreatments, confirm the general predominance of α-cellulose-poor marine polysaccharides and increased levels of α-cellulose-rich vascular plant remains in winter sediment trap samples.     

活动论构造古地理与中国大型叠合盆地海相油气聚集研究

20世纪60年代板块学说的诞生为活动论构造古地理研究提供了理论基础并推动了这一领域的发展。20世纪90年代该领域有关地质历史中洋、陆重建、古地理和古气候成果已被石油地质家用于全球石油聚集和分布规律研究。在中国,王鸿祯先生是对活动论构造古地理领域做出重要贡献的先驱。文中阐述了笔者对他的概念体系和学术思想的理解和应用。当前中国能源战略研究中大型叠合盆地古生界和早中生界海相油气已被证实为我国今后油气资源接替的重要领域之一,这就更需要用活动论构造古地理的思想和方法重建地质历史过程中盆地及烃源岩的形成环境,以预测大型油气系统的分布。     

近33ka以来辽河口沉积环境演变与生物硅记录

沉积物岩心记录着沉积环境的演变过程,其中生物硅(BSi)记录能反映硅质生物的生产力时间和空间变化,2012年5月在下辽河平原西南缘得到了ZK2钻孔柱状样,通过对其沉积物原位密度、生物硅、碳埋藏、粒度、AMS~(14)C和OSL测年、有孔虫鉴定、孢粉鉴定,将ZK2孔的沉积环境主要划分为上三角洲平原相沉积、海洋主导的沉积、湖相沉积、河道沉积4个沉积单元,其相应的生物硅(BSiO_2)浓度分布依次为(2.85±0.23)%、(1.55±0.10)%、(1.96±0.10)%、(0.92±0.05)%,并且生物硅的波动与颗粒有机碳浓度的波动同步。特别是在17~25 cal ka BP冰期形成的湖沼沉积出现较大的颗粒无机碳(PIC)浓度的波动,推测与当时干冷气候条件下CaCO_3过饱和从湖水中沉淀析出有关。钻孔沉积物生物硅浓度记录对格陵兰冰芯~(18)O同位素值的响应存在大约300 a的滞后现象。     

海陆交互相下粘性土的性状研究

长江口北侧海陆交互相沉积粘性土具有粘粒与粉粒交替形成的互层层理结构特征及粉粒含量高的粒度成分特征。且表现出物理性质指标与力学性质指标互不吻合的工程特性。运用多元统计理论中主成分分析原理,分析了海陆交互相沉积粘性土常规物理性质指标反映其工程特性的能力。研究结果表明：将亚砂土隶属于粘性土范畴是不科学的,同时运用液性指数判别其物理稠度状态及推断其工程特性的方法存在不尽合理之处。     

Gypsum-organic interactions in the marine environment: sorption of fatty acids and hydrocarbons

Free fatty acids make up the bulk (50–84% wt/wt) of lipid materials recovered from artificial gypsum precipitates and crystals collected from sea salt evaporation pans. Both the fatty acids and hydrocarbons associated with artificial gypsum tend to be of longer mean chain length than organic materials dissolved in the mother liquor. Increased specific adsorption of n-fatty acids at Ca²⁺ sites on gypsum surfaces is positively correlated with alkyl chain length. Neutral lipids were not significantly enriched in either type of gypsum precipitates. The fatty acids associated with gypsum from sea salt evaporation pans are branched fatty acids in contrast to the predominantly normal acids associated with artificial gypsum samples. Differences in the two adsorbed acid distributions are attributed to the unique lipids of hypersaline biota.     

The impact of aluminium sacrificial anodes on the marine environment: A case study

Cathodic protection using Al sacrificial anodes is a method of corrosion control that is often applied to submerged metallic structures. This technique leads to the progressive dissolution of the sacrificial anode and the metal(s) constituting the anode are inevitably released into the surrounding aquatic environment with potentially detrimental effects. The chemistry of sediments and waters from a French harbour where Al sacrificial anodes are deployed is examined in this study. In order to assess the potential influence of Al dissolution from the anode on the aquatic environment, total Al concentrations in water and sediment were determined and corresponding Al enrichment factors were calculated. Single and sequential extractions were also undertaken in order to evaluate the mobility of Al in the sediments. Results showed that whilst anodic dissolution does not significantly increase the concentration of Al in the water, both enrichment and an increase in the mobility of Al were evident in sediments sampled from the vicinity of the sacrificial anodes.     

中国海相碳酸盐岩层系油气贫化与次生成藏

我国海相层系经过多期构造运动的叠加,油气地质条件除受"先天条件"的影响外,"后天因素"的影响更加突出,表现在现今油气成藏虽仍以海相烃源为主,但油气成藏与油气主要生烃高峰多已不匹配; 油气相态多已发生变化,如四川盆地从含油盆地转为含气盆地; 油气富集过程受构造影响而发生了改变,油气藏规模因此发生了变化,表现出油气藏的破坏规模缩小,或随断层的切割,油气发生泄露,向上运聚到浅层形成次生油气藏,导致油气贫化。因此,具有多期成藏、多期改造、相态转化及晚期就位的特点。现今海相层系发现的油气藏实际上已经是经过"变位、变相"的残留及次生油气藏。针对这一特性,在海相层系油气勘探中更应注意后期油气藏演化所带来的特殊性,进一步深化整体保存环境对油气藏形成、保持的影响。