Analysis Of Interstitial Water Research Articles

Environmental Factors and Metal Mobilisation in Alluvial Sediments—Minas Gerais, Brazil

In areas contaminated by potentially toxic elements (PTEs), knowledge of processes of metal mobilisation is the basis for the choice of appropriate remediation methodologies. The mobilisation of metals is a function of several factors, and the response to these factors must be well known during the planning of remediation strategies. The activity of an ore metallurgical plant in South-East Brazil resulted in major contamination by several heavy metals. Reversing the contamination’s negative impact required geochemical assessment of the area, including the physicochemical characterisation, quantification, and delimitation of PTEs, and the rating of the solubilisation/mobilisation capacity of these elements. The definition of spatial patterns for PTEs’ distribution allowed the construction of contamination risk maps which work as a tool for the mitigation and control of the contamination plume. The chemical analysis of interstitial water and selective and sequential extraction methodologies showed that elements that occur in the environment in critical concentrations (Zn, Cd, Pb, As) are mostly associated with easily mobilised forms (soluble, exchangeable cations, associated with Mn oxides). Given the great mobility of the contamination plume, any process of removal of contaminated material becomes unfeasible, thus the strategy of remediation for the stream and associated alluvial deposits must be based on methods of in situ decontamination.

India National Gas Hydrate Program Expedition-02: Operational and technical summary

Abstract The India National Gas Hydrate Program is being steered by the government of India's Ministry of Petroleum and Natural Gas (MoPNG) with participation of Directorate General of Hydrocarbons (DGH), Oil and Natural Gas Corporation Limited (ONGC), and the National Oil Companies and Research Institutes of India. The India National Gas Hydrate Program Expedition 01 (NGHP-01) established the presence of gas hydrate in the Krishna Godavari (KG) and Mahanadi Basins and in the offshore area of the Andaman Sea Basin. However, the gas hydrates discovered during NGHP-01 were mainly distributed as fracture-filling material in fine-grained clay-rich sediments. The India National Gas Hydrate Program Expedition 02 (NGHP-02) was carried out with an objective to discover gas hydrate in sand-rich sediment along the eastern offshore margin of India. ONGC planned and executed NGHP-02 on the behalf of the MoPNG. NGHP-02 started on March 3, 2015 and was completed on July 28, 2015 (total 147 days) using the Japanese scientific Drilling Vessel Chikyu (D/V Chikyu). During NGHP-02, 42 holes at 25 sites were drilled, cored, and/or surveyed with downhole logging tools. These sites were located in four areas along the eastern margin of India and formally named Area A (Mahanadi Basin, three sites), Area B (northern part of the KG-Basin, twelve sites), Area C (central part of the KG-Basin, six sites), and Area E (southern part to the KG-Basin, four sites). All 25 sites established during NGHP-02 were first drilled and logged with logging-while-drilling (LWD) tools and an additional 17 holes were then drilled and/or cored with conventional coring tools (HPCS/ESCS) or pressure coring tools (PCTB). Wireline logging was conducted in 10 holes and formation tests using a dual packer Modular Formation Dynamics Tester (MDT) tool were carried out in two holes. The onboard science team used the laboratory facilities on the D/V Chikyu to examine and analyse the physical properties, geochemistry, and sedimentology of all the cores collected during the expedition. Core samples were also analysed in additional post-expedition shore-based studies conducted in numerous domestic and international gas hydrate research laboratories. The NGHP-02 sediment cores were archived at the National Gas Hydrate Core Repository in Mumbai (India), which is associated with the ONGC Gas Hydrate Research and Technology Centre (GHRTC). The necessary data for characterizing the occurrence of gas hydrate, such as interstitial water chlorinities, core-derived gas chemistry, physical and sedimentological properties, thermal images of the recovered cores, pressure core and downhole measured logging data (LWD and/or conventional wireline log data), were obtained from most of the drill sites established during NGHP-02. Almost all the drill sites yielded evidence for the occurrence of gas hydrate; however, the inferred in situ concentration of gas hydrate varied substantially from site to site. For the most part, the interpretation of downhole logging data, core thermal images, interstitial water analyses, and pressure core images from the sites established during NGHP-02 indicate that the occurrence of concentrated gas hydrate is mostly associated with coarser grained (sand-rich) sediments. This paper presents the operational and technical summary of NGHP-02.

Origin of low-chloride fluid in sediments from the eastern continental margin of India, results from the National Gas Hydrate Program Expedition 02

Abstract National Gas Hydrate Program Expedition 02 was conducted in 2015 by D/V Chikyu in the western Bay of Bengal, India. Analyses of interstitial water in sediment from four drilling sites along the eastern and western transect in the Krishna–Godavari Basin show that dissolved chloride (Cl−) concentrations decreased with depth from seawater values (>550 mM) near the sediment surface to 300–400 mM at 350–400 m below seafloor (mbsf), suggesting the upward advection of low-Cl– fluid. Excursions of Cl− concentrations toward low values in gas hydrate zones were attributed to the presence of fresh water released by dissociation of gas hydrate during core recovery. At Sites in the western transect, Cl− concentrations below the gas hydrate reservoir (around 280 mbsf) were ca. 60 mM and ca. 45 mM lower than those from above the reservoir, and δ18O and δD values were 1–2‰ and 0.7–1.3‰ higher than those from above the reservoir, respectively. These results suggest that a fraction of migrating low-Cl– fluid is trapped in the gas hydrate zone, causing decreases of δ18O and δD in the residual water due to isotopic fractionation during gas hydrate formation. From mass-balance calculations, we estimated that 10–20% of the advected fluid is trapped at the gas hydrate zone. At all sites, the δ18O and δD values below the gas hydrate zone, representing relatively unaltered low-Cl– fluid, were 0.5–1‰ higher and ca. 13–15‰ lower than those of seawater, respectively. This trend is consistent with water derived from the dehydration of clay minerals, which generally occurs in deeply buried sediments. The contribution of clay mineral dehydration is relatively large at the western transect compared to that in the eastern transect. Our results imply that fluid advection contributes to the accumulation of gas hydrate in the study area.

日本海の表層型ガスハイドレート胚胎域でみられる間隙水の化学組成・溶存ガス組成の時系列変化とガス湧出強度の変動：オスモサンプラーによる長期連続サンプリングの応用

日本海の表層型ガスハイドレート胚胎域でみられる間隙水の化学組成・溶存ガス組成の時系列変化とガス湧出強度の変動：オスモサンプラーによる長期連続サンプリングの応用

Pore Water Collection, Analysis and Evolution: The Need for Standardization.

Investigating the ecological impacts of contaminants released into the environment requires integration of multiple lines of evidence. Collection and analysis of interstitial water is an often-used line of evidence for developing benthic exposure estimates in aquatic ecosystems. It is a well-established principle that chemical and toxicity data on interstitial water samples should represent in-situ conditions; i.e., sample integrity must be maintained throughout the sample collection process to avoid alteration of the in-situ geochemical conditions. Unfortunately, collection and processing of pore water is not standardized to address possible geochemical transformations introduced by atmospheric exposure. Furthermore, there are no suitable benchmarks (ecological or human health) against which to evaluate adverse effects from chemicals in pore water; i.e., empirical data is lacking on the toxicity of inorganic contaminants in sediment interstitial water. It is clear that pore water data is best evaluated by considering the bioavailability of trace elements and the partitioning of contaminants between the aqueous and solid phases. It is also evident that there is a need for sediment researchers and regulatory agencies to collaborate in developing a standardized approach for sediment/pore water collection and data evaluation. Without such guidelines, the number of different pore water collection and extraction techniques will continue to expand, and investigators will continue to evaluate potentially questionable data by comparison to inappropriate criteria.

Geologic implications of gas hydrates in the offshore of India: Results of the National Gas Hydrate Program Expedition 01

The Indian National Gas Hydrate Program Expedition 01 (NGHP-01) is designed to study the occurrence of gas hydrate along the passive continental margin of the Indian Peninsula and in the Andaman convergent margin, with special emphasis on understanding the geologic and geochemical controls on the occurrence of gas hydrate in these two diverse settings. The NGHP-01 expedition established the presence of gas hydrates in the Krishna–Godavari and Mahanadi Basins, and the Andaman Sea. The expedition discovered in the Krishna–Godavari Basin one of the thickest gas hydrate accumulations ever documented, in the Andaman Sea one of the thickest and deepest gas hydrate stability zones in the world, and established the existence of a fully developed gas hydrate petroleum system in all three basins.The primary goal of NGHP-01 was to conduct scientific ocean drilling/coring, logging, and analytical activities to assess the geologic occurrence, regional context, and characteristics of gas hydrate deposits along the continental margins of India. This was done in order to meet the long-term goal of exploiting gas hydrate as a potential energy resource in a cost effective and safe manner. During its 113.5-day voyage, the D/V JOIDES Resolution cored and/or drilled 39 holes at 21 sites (1 site in Kerala–Konkan, 15 sites in Krishna–Godavari, 4 sites in Mahanadi, and 1 site in the Andaman deep offshore area), penetrated more than 9250 m of sedimentary section, and recovered nearly 2850 m of core. Twelve holes were logged with logging-while-drilling (LWD) tools and an additional 13 holes were wireline logged. The science team utilized extensive on-board laboratory facilities to examine and prepare preliminary reports on the physical properties, geochemistry, and sedimentology of all the data collected prior to the end of the expedition. Samples were also analyzed in additional post-expedition shore-based studies conducted in leading laboratories around the world.One of the specific objectives of this expedition was to test gas hydrate formation models and constrain model parameters, especially those that account for the formation of concentrated gas hydrate accumulations. The necessary data for characterizing the occurrence of in situ gas hydrate, such as interstitial water chlorinities, core-derived gas chemistry, physical and sedimentological properties, thermal images of the recovered cores, and downhole measured logging data (LWD and/or conventional wireline log data), were obtained from most of the drill sites established during NGHP-01. Almost all of the drill sites yielded evidence for the occurrence of gas hydrate; however, the inferred in situ concentration of gas hydrate varied substantially from site to site. For the most part, the interpretation of downhole logging data, core thermal images, interstitial water analyses, and pressure core images from the sites drilled during NGHP-01 indicate that the occurrence of concentrated gas hydrate is mostly associated with the presence of fractures in the sediments, and in some limited cases, by coarser grained (mostly sand-rich) sediments.

Fast Measurement of Dissolved Inorganic Carbon Concentration for Small-Volume Interstitial Water by Acid Extraction and Nondispersive Infrared Gas Analysis

We developed a system for measuring the total dissolved inorganic carbon (DIC) concentrations in interstitial water and hydrothermal fluid, which are hard to obtain in large volumes. The system requires a sample volume of only 500 μL, and it takes only 150 s per one sample. The detection limit of this system was estimated to be 66.6 μmol/kg with repeated analysis of CO(2)-free ultrapure water (n = 9). The precision of this nondispersive infrared (NDIR) system was ±3.1% of the relative standard deviations (2σ) by repeated CRM batch 104 (n = 10). This result is much larger than the required precision for oceanographic studies, but is comparable to a previous result of interstitial water analysis. An on-site trial showed a significant DIC enrichment in interstitial water of hydrothermally altered sediment, and is considered to occur by the mixing of hydrothermal fluid. This procedure will achieve carbon dioxide flux calculations from hydrothermal activities, and will bring a more accurate feature on the global carbon cycle.

IODP Expedition 331: Strong and Expansive Subseafloor Hydrothermal Activities in the Okinawa Trough

Integrated Ocean Drilling Program (IODP) Expedition 331 drilled into the Iheya North hydrothermal system in the middle Okinawa Trough in order to investigate active subseafloor microbial ecosystems and their physical and chemical settings. We drilled five sites during Expedition 331 using special guide bases at three holes for reentry, casing, and capping, including installation of a steel mesh platform with valve controls for postcruise sampling of fluids. At Site C0016, drilling at the base of the North Big Chimney (NBC) mound yielded low recovery, but core included the first Kuroko-type black ore ever recovered from the modern subseafloor. The other four sites yielded interbedded hemipelagic and strongly pumiceous volcaniclastic sediment, along with volcanogenic breccias that are variably hydrothermally altered and mineralized. At most sites, analyses of interstitial water and headspace gas yielded complex patterns with depth and lateral distance of only a few meters. Documented processes included formation of brines and vapor-rich fluids by phase separation and segregation, uptake of Mg and Na by alteration minerals in exchange for Ca, leaching of K at high temperature and uptake at low temperature, anhydrite precipitation, potential microbial oxidation of organic matter and anaerobic oxidation of methane utilizing sulfate, and methanogenesis. Shipboard analyses have found evidence for microbial activity in sediments within the upper 10–30 m below seafloor (mbsf) where temperatures were relatively low, but little evidence in the deeper hydrothermally altered zones and hydrothermal fluid regime. doi:10.2204/iodp.sd.13.03.2011

IODP Expedition 331: Strong and Expansive Subseafloor Hydrothermal Activities in the Okinawa Trough

Integrated Ocean Drilling Program (IODP) Expedition 331 drilled into the Iheya North hydrothermal system in the middle Okinawa Trough in order to investigate active subseafloor microbial ecosystems and their physical and chemical settings. We drilled five sites during Expedition 331 using special guide bases at three holes for reentry, casing, and capping, including installation of a steel mesh platform with valve controls for postcruise sampling of fluids. At Site C0016, drilling at the base of the North Big Chimney (NBC) mound yielded low recovery, but core included the first Kuroko-type black ore ever recovered from the modern subseafloor. The other four sites yielded interbedded hemipelagic and strongly pumiceous volcaniclastic sediment, along with volcanogenic breccias that are variably hydrothermally altered and mineralized. At most sites, analyses of interstitial water and headspace gas yielded complex patterns with depth and lateral distance of only a few meters. Documented processes included formation of brines and vapor-rich fluids by phase separation and segregation, uptake of Mg and Na by alteration minerals in exchange for Ca, leaching of K at high temperature and uptake at low temperature, anhydrite precipitation, potential microbial oxidation of organic matter and anaerobic oxidation of methane utilizing sulfate, and methanogenesis. Shipboard analyses have found evidence for microbial activity in sediments within the upper 10–30 m below seafloor (mbsf) where temperatures were relatively low, but little evidence in the deeper hydrothermally altered zones and hydrothermal fluid regime. <br><br> doi:<a href="http://dx.doi.org/10.2204/iodp.sd.13.03.2011" target="_blank">10.2204/iodp.sd.13.03.2011</a>

科学掘削船「ちきゅう」船上でのキャビティリングダウン分光式マスを用いた間隙水の酸素・水素同位体比分析とその有効性

科学掘削船「ちきゅう」船上でのキャビティリングダウン分光式マスを用いた間隙水の酸素・水素同位体比分析とその有効性

Determination of Interstitial Water Chemistry and Porosity in Consolidated Aquifer Materials by Diffusion Equilibrium-Exchange

Diffusion equilibrium exchange (DEE) is presented as a novel, practical alternative to centrifugation for the recovery and chemical analysis of interstitial water in contaminated core samples from consolidated rocks and aquifers. The methodology is suitable for sampling organic and inorganic compounds, including redox sensitive species such as SO4(2-), NO3-, NO2-, Mn(II), Fe(II), and sulfide (HS-). DEE also permits analyte extraction from kilogram quantities of core, which avoids extended centrifugation or sample amalgamation and provides analyte masses appropriate for stable isotope analysis. The procedure involves simple and rapid on-site sectioning of representative core samples, which are preserved in the field by storage in airtight bottles filled with deoxygenated deionized water containing a conservative tracer (Br-). Equilibration times for individual solutes can be estimated in advance to reduce the need for time-series analysis; for an effective diffusion coefficient of 2.5 x 10(-10) m2 s(-1) (Br- in chalk rock) equilibration was >90% completed after 30 h, consistent with the predicted equilibration time. The DEE method presented minimizes sampling errors from temperature changes, oxidation of reduced chemical species, and loss of volatile compounds, which can occur with other interstitial water sampling techniques. It also gives superior resolution of in situ solute distributions and geochemical processes in consolidated sediments than centrifugation and can provide estimates of aquifer porosity in core samples. Laboratory experiments using chalk rock core and simulated extraction procedures confirm the superior performance of the DEE method over centrifugation for a range of solutes. The method has been used to generate detailed interstitial water profiles of electron acceptor and contaminant concentrations along the flow path of a petroleum hydrocarbon plume in the U.K. Upper Chalk aquifer as part of a natural attenuation assessment.

Delineating and quantifying ground water discharge zones using streambed temperatures.

Streambed temperature mapping, hydraulic testing using minipiezometers, and geochemical analyses of interstitial water of the streambed were used to delineate the pattern of ground water discharge in a sandy streambed and to develop a flux-based conceptual model for ground water/surface water interactions. A new and simple empirical method was used to relate fluxes obtained from minipiezometer data to streambed temperatures. The relationship allowed flux to be calculated at locations where only streambed temperature measurements were made. Slug testing and potentiomanometer measurements at 34 piezometers indicated ground water discharge ranged from 0.03 to 446 L/m2/day (and possibly as high as 7060 L/m2/day) along a 60 m long by 11 to 14 m wide reach of river. Complex but similar plan-view patterns of flux were calculated for both summer and winter using hundreds of streambed temperatures measured on a 1 by 2 m grid. The reach was dominated by ground water discharge and 5% to 7% of the area accounted for approximately 20% to 24% of the total discharge. < 12% of the total area consisted of recharge zones or no-discharge zones. A conceptual model for ground water/surface water interactions consisting of five different behaviors was developed based on the magnitude and direction of flux across the surface of the streambed. The behaviors include short-circuit discharge (e.g., high-flow springs), high discharge (e.g., preferential flowpaths), low to moderate discharge, no discharge (e.g., horizontal hyporheic or ground water flow), and recharge. Geological variations at depth played a key role in determining which type of flow behavior occurred in the streambed.

Effectiveness of bioremediation of crude oil contaminated subantarctic intertidal sediment: the microbial response.

A field study was initiated in February 1996 in a remote sandy beach of The Grande Terre (Kerguelen Archipelago, 69 degrees 42 degrees E, 49 degrees 19 degrees S) with the objective of determining the long-term effects of some bioremediation agents on the biodegradation rate and the toxicity of oil residues under severe subantarctic conditions. A series of 10 experimental plots were settled firmly into sediment. Each plot received 2L of Arabian light crude oil and some of them were treated with bioremediation agents: slow release fertilizer Inipol EAP-22 (Elf Atochem) or fish composts. Plots were sampled on a regular basis over a 3-year period. A two-order of magnitude increase of saprophytic and hydrocarbon-utilizing microorganisms occurred during the first month of the experiment in all treated enclosures, but no clear differences appeared between the plots. Very high microbial populations were present during the experiment. Biodegradation within treated spots was faster than within the untreated ones and appeared almost complete after 6 months as indicated by the degradation index of aliphatic hydrocarbons within all plots. The analysis of interstitial water collected below the oily residues presented no toxicity. However, a high toxicity signal, using Microtox solid phase, appeared for all oiled sand samples with a noticeable reduction with time even if the toxicity signal remained present and strong after 311 days of oil exposition. As a conclusion, it is clear that the microbial response was rapid and efficient in spite of the severe weather conditions, and the rate of degradation was improved in presence of bioremediation agents. However, the remaining residues had a relatively high toxicity.

Radionuclide concentrations in underground waters of Mururoa and Fangataufa Atolls

In 1997 an expedition to Mururoa and Fangataufa Atolls was carried out to sample underground waters from cavity-chimneys and carbonate monitoring wells. The aim of this study was to determine the prevailing concentration and distribution status of radionuclides. Elemental analysis of interstitial waters was carried out in the water fraction as well as in particles collected at 11 underground monitoring wells. 238Pu, 239,240Pu, 241Am, 137Cs, 90Sr, 3H, 125Sb, 155Eu and 60Co were analyzed in both fractions by alpha-, beta- and gamma-spectrometry. Measurements showed that at 60% of the sites, pH and Eh seemed to be related to tidal cycles; in contrast HTO was constant during the sampling time. Interstitial waters from carbonates and transition zones shared similar chemical composition that were not different from that of the surrounding seawater. Waters collected from basalt cavities left after nuclear tests, (Aristee and Ceto) have a different chemical signature characterized by a deficiency in Mg, K and SO 4 as well as enrichment in Sr, Si, Al and Cl compared to the rest of the stations. Radionuclide concentrations present in both, water and particulate fractions, were significantly higher at Ceto and Aristee than at any other monitoring wells, except for Fuseau and Mitre monitoring wells (Fangataufa) where values similar to Ceto were found (e.g. 239,240Pu: >20 mBq g −1). Considering that Pu isotopes showed high K d values compared to non-sorbing radionuclides such as 3H, 90Sr and 137Cs it is very unlikely that migration from cavities to monitoring wells accounts for the concentration of Pu isotopes and Am at Fuseau 30 and Mitre 27. Perhaps the contact of lagoon waters with the well before sealing could be a possible source of the transuranics found at these sites. The 238Pu/ 239,240Pu ratios measured in the particles were similar to that of the lagoon (0.38), thus supporting this hypothesis. The fact that transuranics were found only in the particle fraction, in the water (colloids included) these radionuclides were below detection limits, may be accounted for the conspicuous quantity of iron oxy-hydroxides present in the particulate fraction that under the appropriate redox conditions may be interacting selectively with elements in solution (scavenging) resulting in the enhanced transuranic signal. While transuranics have been found in places of their origin, radionuclides with low K d values ( 3H, 90Sr, 137Cs) have already been transported to monitoring wells, as well as to the atolls' lagoons and the open ocean.

Metal pollution by old lead-zinc mines in Urumea river valley (Basque Country, Spain). Soil, biota and sediment

Soil, aquatic biota (moss: Brachythecium rivulare; aquatic macrophytes: Juncus effusus, Potamogeton crispus; fish: Salmo trutta fario, Anguilla anguilla, Phoxinus phoxinus, Chelon labrosus) and sediment samples from the Urumea river valley were analysed for metals by acid digestion and atomic absorption spectroscopy. The sediments show the presence of metal pollution (Cd: 2.5–24 mg kg-1; Pb: 125–1,150 mg kg-1; Zn: 125–2,500 mg kg-1) because mining and industrial wastes. A selective retention of dense minerals in dam sediments contributes to the load of metal, but interstitial water analysis (Cd: ), but they are used, indistinctly, for farming and pasture.

Analysis of interstitial water during culture of Hydrilla verticillata with controlled release fertilizers

The dioecious strain of hydrilla ( Hydrilla verticillata (L.f.) Royle) was cultured outdoors with fertilizer placed as a layer in a sand rooting medium. Plant dry weight averaged 77 g per culture container after 12 weeks of summer growth and was more than three times that for plants cultured for the same length of time during the following winter season. Concentrations of nitrate, ammonia-nitrogen, and phosphate-phosphorus in interstitial water after 12 weeks of hydrilla growth were 90, 88, and 47% lower, respectively, than in containers without plants. However, potassium in interstitial water was 61% higher after 12 weeks of plant growth as compared to containers without plants suggesting hydrilla was transporting this nutrient from the upper ambient pond water to the root zone. Results for the winter season were similar but differences in nutrient concentrations between containers with and without plants were not as great as during the summer season.

Interstitial water chemistry of sediments of the Costa Rica Accretionary Complex off the Nicoya Peninsula

Interstitial water analyses from numerous piston, gravity, and Alvin push cores show that fluid flow at the Costa Rica Accretionary Prism is spatially limited and can only be detected by visually directed cores in zones of biogenic activity. Most of the sites cored show evidence for normal diagenetic processes in rapidly deposited, organic carbon‐rich sediments, with little evidence for fluid advection. However, in visually directed Alvin push cores, obtained from black sulfidic sediments characterized by the presence of Calyptogena clams or tubeworms, evidence for fluids advected upward from greater depth horizons is shown. These zones are associated with a large mudvolcano on the prism and with the zoes of Out Of Sequence Thrusts. As changes from sea water concentrations are still relatively small, substantial mixing with sea water must have occurred during this upward fluid movement.

A back-extraction procedure for the dithiocarbamate solvent extraction method. Rapid determination of metals in seawater matrices

A ligand exchange liquid/liquid extraction method using dithiocarbamate complexes is elaborated for the graphite furnace atomic absorption spectrometry (GF-AAS) of seawater and marine interstitial water. Palladium is used for the exchange. This metal ensures a rapid and quantitative back-extraction. It simultaneously works as matrix modifier in the GF-AAS analysis. The proposed method is evaluated in the analysis of lead, copper, nickel, and cadmium in CASS-II marine reference seawater and samples from the North Sea. A microanalytical variant of the method is applied in marine interstitial water analysis down to sample volumes of 500 μl.

Early diagenetic influences on iron transformations in a freshwater lake sediment

Iron transformations in a calcium carbonate rich fresh-water sediment were studied by analyzing the relevant constituents of both interstitial water and solid matter. Analysis of interstitial water shows that the observed redox sequence NO − 3 NH + 4 , MnO 2 Mn(II) , FeOOH/Fe(II), SO 2− 4 S(−II) is roughly in agreement with that predicted by the Gibbs Free Energy for the corresponding reactions. In contrast to marine sediments, these redox transitions occur in the uppermost sediments, i.e., at depths of 0–4 cm. Deeper in the sedimentary sequence, the depth profile for dissolved iron exhibits a steady non-linear increase up to 400 μmol dm −3. In this anoxic zone, according to thermodynamic predictions, iron (II)-minerals such as iron sulfide, siderite, and vivianite should precipitate while Fe(III) oxides should be completely dissolved. However, microscopic analysis showed that Fe(III) oxides were present throughout the studied sediment. Furthermore, scanning electron microscope/energy dispersive spectroscopy analysis suggests the presence of iron sulfide could be verified but not that of siderite or vivianite. These observations indicate kinetic control of iron transformations. We have investigated the importance of kinetic control of iron distribution in anoxic sediments using a diagenetic model for dissolved iron(II). A rough estimate of time scales for dissolution and precipitation rates was made by imposing limiting boundary conditions. Using the calculated rate constant, we established that more than 1000 years would be required for the complete dissolution of Fe(III) oxides, which is agreement with our observations and experimental data from the literature. Calculated precipitation rates of Fe(II) for a given mineral phase such as siderite yield a maximum value of 3 μg (FeCO 3) g −1 (dry sediment) yr −1. Such low rates would explain the absence of siderite and vivianite. Finally, it can be inferred from the Mn T Fe T ratio in the sediments that this ratio depends on the redox conditions of the sediment-water interface at the time of deposition. Thus, this ratio can be used as “paleo-redox indicator” in lacustrine sediments.

A note on the geochemistry procedures and the geochemical data base of the Ocean Drilling Program

We present a brief description of routine and special geochemical analyses, including methodology and instrumentation, performed onboard R.V. JOIDES Resolution SEDCO/BP 471 during drilling campaigns of the Ocean Drilling Program. The organic geochemical program is centered on hydrocarbon monitoring and produces data on organic matter abundance, composition, and maturity. Specialized equipment is available for examining interstitial gas composition and concentration, and lipid composition of solvent extracts. Interstitial water analyses measure major dissolved ions and nutrients. The structure and content of the ODP data base that incorporates these new data and those from 96 DSDP legs contains at present results of more than 95,000 analyses, mainly of carbonate and organic carbon content. Data base structure enables specific searches and relational sorting, which makes regional or temporal searches possible.