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Knowledge of the strength of sediments overlying sub-seafloor gas-hydrate deposits is crucial for predicting borehole and seafloor stability during hydrate extraction. Ideally, sediment strength should be determined along a continuous downhole profile from the seafloor to the hydrate reservoir, but few such profiles have been obtained. In this study we used cores retrieved at Site NGHP-02-23 in the Krishna–Godavari Basin in unconfined penetration tests on split cores and in triaxial deformation experiments on hydrate-free sediment samples. Although penetrometer tests identified relatively low strength (70–250 kPa) likely due to hydrate dissociation in the hydrate-bearing interval 90–300 m below seafloor (mbsf), sediment strength exceeded 350 kPa in the intervals 140–170 and 250–270 mbsf, each of which lies just above a zone of high gas-hydrate concentration. The average stress ratio of triaxial strength at 4% axial strain to effective mean stress (qe=4%/p’) of hydrate-free silts was about 0.67 throughout the Hole. An exception to this trend was in fine sands from 280 mbsf in the deeper gas-hydrate zone, where the stress ratios were greater than 1.0. The stress ratios of hydrate-bearing sediments in the deeper gas-hydrate zone that were reported from the pressure-core measurements were far greater than those of any hydrate-free sediments for a given effective mean stress. The high-strength intervals in silty sediments we identified by the penetration tests could be associated with zones of high hydrate concentration. Because high-strength layers in fine-grained silty sediments commonly exhibit lower permeability than sandy layers (potential hydrate-host), they may act as seals that assist the precipitation of hydrate below them.

We estimate the rate of upward pore fluid flow and chlorinity (Cl−) concentrations at depth through a joint analysis of Cl− concentration and temperature versus depth profiles obtained from gas hydrate related test sites drilled and cored in the Krishna-Godavari Basin off the eastern coast of India. Cl−, measured on conventional core samples, decreases with depth at all sites but some of the Cl−profiles show a prominent convex shape, whereas in situ temperature profiles, obtained by the Advanced Piston Coring Temperature probe, are mostly linear at all sites established during the National Gas Hydrate Program 02 Expedition (NGHP-02). Assuming a one-dimensional, time-dependent model for the advection of pore fluid including the sedimentation effect and depth-dependent diffusivity, we estimate darcy velocity and the Cl− concentrations at depth. The best-fit darcy velocity of 1.2–1.6 × 10−11 m/s was estimated for the sites along the crest of the regional anticlinal structure in the NGHP-02 Area B, which was significantly faster than those on the flanks of the anticline. Because the thermal diffusion coefficient is much larger than the chloride ion diffusion coefficient, estimated darcy velocities are not great enough to generate nonlinear temperature profiles with depth, which is consistent with observed linear thermal profiles.

Physical properties like porosity and density are important parameters for size estimations of fossil fuel reservoir in host sediments and rocks. X-ray CT based imaging and subsequent analysis of the images by using various techniques for estimations of these properties of host rocks and sediments has been attempted. However, most of those techniques tend to be biased and subjective due to complications in image processing. Here we describe a new procedure for estimating porosity and density without processing the XCT images, but using the raw data that are used for producing the images. In this study, large-size cylindrical core samples (up to 150 cm long and 6.6 cm diameter) were imaged in a matter of minutes by using a medical XCT scanner soon after their recovery from seafloor onboard drillship in order to record as realistic as possible condition of hydrate-bearing sediments. Despite some uncertainty in relative volumes of solid, liquid and gas phases at voxel level, the results obtained by this rapid and non-destructive procedure are in good agreement with those obtained by time- and sample-consuming conventional methods of physical property measurements.

Gas hydrate-bearing layers are normally identified by a seismic imaged bottom simulating reflectors (BSR) or by downhole log responses because of their high acoustic velocity and electric resistivity compared to surrounding formations. These gas hydrate characteristics can also result in contrasting in-situ formation compressive strengths. Here, we describe gas hydrate-bearing layers based on equivalent strength (EST), which relates to in-situ compressive strength, in five exploration boreholes drilled during the Indian National Gas Hydrate Program Expedition 02 (NGHP-02). For Site NGHP-02-23, a representative site for those that were established during NGHP-02, the EST evaluated from drilling parameters shows a constant trend of ∼2 MPa, with some strong peak values in the 0–271.4 m-below-seafloor (mbsf) interval, and a sudden increase up to 4 MPa above the BSR depth (271.4–290.0 mbsf). Below the BSR, the EST stays at ∼2 MPa to the bottom of the hole (378 mbsf). Comparing the EST with logging data and a core sample description suggests that the EST depth profiles reflect the formation lithology and gas hydrate content. The EST increases in sand-rich and gas hydrate-bearing zone. In the lower gas hydrate layers in particular, the EST curve shows the same approximate trend with that of P-wave velocity and resistivity measured during downhole logging. Similar relationships between EST, hydrate layer, and log responses are confirmed in other four sites drilled nearby in NGHP-02 Area B. These results suggest that the EST, as a proxy for in-situ formation strength, can indicate the location and extent of the gas hydrate as well as borehole logging. Although the EST was calculated after drilling, utilizing the recorded surface drilling parameters (weight on bit, top drive torque, RPM and rate of penetration) in this study, the EST can be acquired during drilling using real-time drilling parameters. In addition, the EST only requires drilling performance data without any additional tools or measurements, making it a simple and economical tool for the exploration of gas hydrates.

The existence of overpressure in shallow sediments, which is often constrained by hydraulic properties, influences the gas-hydrate formation process and gas production. Porosity, permeability, and grain size measurements in laboratory experiments were conducted on core samples from gas-hydrate-bearing regions offshore from the Krishna-Godavari Basin, eastern India. Porosity was found to decrease with increasing effective stress; this is explained by the exponential decay curve along which porosity decreases from 65 % at 0 MPa to 40 % at 10 MPa. Permeability and the corresponding hydraulic diffusivity decrease from 10−17 to less than 10−18 m2 and from 10−7 to 10−8 m2/s at 0.5 and 5 MPa, respectively. Grain sizes were larger and the sand fraction more scattered in channel-filled sediment sites compared to slope sediment sites. The preconsolidation stresses evaluated from consolidation curves indicate the absence of overpressure at shallow depths. In contrast, a comparison of ship-board measurements and standard compaction curves suggested that measured porosity was higher than the predicted porosity at greater depths. These porosity anomalies are interpreted as a sign of overpressure that approaches near lithostatic values at greater depths in slope sediment sites. A one-dimensional sedimentation model recreated overpressure profiles similar to those predicted by porosity gaps, under the assumption of large basial fluid influx or lower permeability than that derived from laboratory data. The modeling results suggest that near-hydrostatic pressure at shallow depths and significant overpressure at greater depths proposed by the porosity gap method is explained by the non-linearity of transport properties. The relatively small overpressure generation in channel-filled sites compared with slope sites can be explained by the higher permeability due to coarser grain size and larger sand fraction and by the smaller basal influx. On the contrary, considerably large basal influx associated with clay mineral dehydration and methane gas supply from deep sediments was expected to promote overpressure at slope sites, which is confirmed by Cl− concentration-depth profiles.

金沢大学理工研究域地球社会基盤学系, Detailed reconstruction of Indian summer monsoons is necessary to better understand the late Quaternary climate history of the Bay of Bengal and Indian peninsula. We established a chronostratigraphy for a sediment core from Hole 19B in the western Bay of Bengal, extending to approximately 80kyr BP and examined major and trace element compositions and clay mineral components of the sediments. Higher δ 18 O values, lower TiO 2 contents, and weaker weathering in the sediment source area during marine isotope stages (MIS) 2 and 4 compared to MIS 1, 3, and 5 are explained by increased Indian summer monsoonal precipitation and river discharge around the western Bay of Bengal. Clay mineral and chemical components indicate a felsic sediment source, suggesting the Precambrian gneissic complex of the eastern Indian peninsula as the dominant sediment source at this site since 80kyr. Trace element ratios (Cr/Th, Th/Sc, Th/Co, La/Cr, and Eu/Eu*) indicate increased sediment contributions from mafic rocks during MIS 2 and 4. We interpret these results as reflecting the changing influences of the eastern and western branches of the Indian summer monsoon and a greater decrease in rainfall in the eastern and northeastern parts of the Indian peninsula than in the western part during MIS 2 and 4. © 2018. American Geophysical Union. All Rights Reserved.

Gas hydrates have been reported to exist in marine sediments from various parts of the world ocean. The hydrates start decomposing soon after recovery of the sediments through coring operations due...

In order to understand settling process of particles in high sedimentation area, one mooring of sediment trap was deployed right above the IMAGES coring site in the northwestern North Pacific. In spite of two large maxima of settling particle fluxes in June–July 2002 and October–early January 2003, organic matter (OM) and carbonate showed higher peaks in June–July while lithogenics showed a large peak in October–early January with degraded OM (low aspartic acid/beta-alanine (Asp/Bala) and glutamic acid/gamma-aminobutyric (Glu/Gaba) ratios). Fresh OM production peaked in June–July 2002 and April–May 2003. Thus a large export production occurred in spring–early summer (April–June). Alkenone production was enhanced mainly in June–July. The mean alkenone SST of the settling particles was rather consistent with the observed annual mean SST and alkenone SST determined from the surface sediments. On the other hand, the maximum lithogenic flux along with the degradation of OM indicated that a significant amount of resuspended matter contaminated the bottom sediments. Based upon idealized model, the current and settling speeds make fractionation by size and density of resuspended particles during the settling process. Accumulation rates of lithogenics were ~ 5 times those in the sediment traps, which indicate large contribution of resuspended particles to settling particles especially during October–early January, when the Tsugaru current showed high current speed. These observations call our attention to carefully reconstruct paleo-environments based upon lithogenics and several other proxies such as biogenic silica, which would be biased for example in the record of IMAGES core at Site Shimokita located on the gentle continental slope.

Siliceous ooze was reacted with NaCl solution at temperatures of 100-250°C to evaluate the effect of the mineralogical and chemical properties of host sediments on the thermal stability of amino acids (AAs). Results were compared with those previously reported from calcareous ooze. The siliceous ooze preserved more AAs than did the calcareous ooze, and the solution with the siliceous ooze preserved the AAs for a longer time than did the solution with the calcareous ooze. When siliceous ooze was reacted under hydrothermal conditions, the AAs were released easily and were more stable in alkaline solution than in the NaCl solution. Solubility of silica was greater in alkaline solution than in NaCl solution, and an excess of hydroxyl ion and/or carbonate species in the alkaline solution underwent exchange more frequently with AAs in the siliceous ooze than in the NaCl solution. The thermal stability of neutral AAs was enhanced significantly in alkaline solution at temperatures higher than 200°C. When montmorillonite and saponite were heated in NaCl solution with a known amount of AAs at 250°C, some AA concentrations increased, probably due to negatively charged AAs binding to cations in the clay minerals. The results suggest that the AAs are dissolved into the solution from the sediments primary via ion exchange, and that polymerization of silica that included AAs in its framework stabilized AAs in siliceous ooze.

Hydrothermal systems have been suggested as being favourable environments for the origin and evolution of life on the primitive Earth. To test this hypothesis, it is necessary to investigate under hydrothermal conditions the behaviour of biomolecules such as amino acids (AAs), a major component of organisms. In contrast to submarine hydrothermal systems, hot springs in the Rift Valley in eastern Africa on the thick continental crust often have a high pH (alkaline conditions) as a result of enrichment via Na 2 CO 3 and volatile gases. We reacted siliceous ooze with an aqueous solution of NaCl and Na 2 CO 3 at elevated temperature (100–300 °C) to evaluate the thermal stability of the AAs under alkaline hydrothermal conditions. The AAs in the sediment in peptide form were released to the liquid phase and decomposed through hydrolysis of peptide bonds. Comparison of the results with those from similar experiments using the same sediment sample under neutral conditions reveals that the rates of decomposition of the AAs are significantly inhibited under alkaline conditions. Moreover, AAs remained in both the solid and liquid phases even after heating at 300 °C for 240 h. Our results indicate that AAs are more thermally stable in alkaline solution, indicating that these hydrothermal conditions are more favourable for the evolution of primitive life on the thick continental crust. They also imply that alkaline hydrothermal systems on other planets might be plausible places for extraterrestrial life.

Four year-long time-series sediment trap experiments were conducted along the equatorial Pacific Ocean in order to understand the biogeochemistry of particulate organic matter (POM) on the basis of amino acid (AA) and hexosamine (HA) compositions of the settling particles. Total mass flux in the study area varied over 4 orders of magnitude without a common seasonality among all trap sites. Planktonic blooms were apparent in terms of total mass and AA fluxes at the easternmost end of the Nino-4 region. AA fluxes closely followed the total mass flux profiles, suggesting that increased particle flux delivered a greater amount of labile OM to the deep ocean. A labile OM index (LI)-based classification showed that during the El Nino conditions in 2002, the eastern side of the equatorial Pacific transported relatively more labile OM than the western equatorial Pacific. An overall change in AA and HA composition of settling particles could be revealed with the help of discriminant analysis, suggesting that settling particles during El Nino were compositionally different from those settling during La Nina condition in the equatorial Pacific.

Arsenic resistance and removal was evaluated in nine bacterial strains of marine and non-marine origins. Of the strains tested, Marinomonas communis exhibited the second-highest arsenic resistance with median effective concentration (EC(50)) value of 510 mg As l(-1), and was capable of removing arsenic from culture medium amended with arsenate. Arsenic accumulation in cells amounted to 2290 microg As g(-1) (dry weight) when incubated on medium containing 5 mg As l(-1) of arsenate. More than half of the arsenic removed was related to metabolic activity: 45% of the arsenic was incorporated into the cytosol fraction and 10% was found in the lipid-bound fraction of the membrane, with the remaining arsenic considered to be adsorbed onto the cell surface. Potential arsenic resistance and removal were also examined in six marine and non-marine environmental water samples. Of the total bacterial colony counts, 28-100% of bacteria showed arsenic resistance. Some of the bacterial consortia, especially those from seawater enriched with arsenate, exhibited higher accumulated levels of arsenic than M. communis under the same condition. These results showed that arsenic resistant and/or accumulating bacteria are widespread in the aquatic environment, and that arsenic-accumulating bacteria such as M. communis are potential candidates for bioremediation of arsenic contaminated water.

The composition of total hydrolysable amino acids (THAAs) in a skeleton of the coral Porites australiensis, collected from Ishigaki Island, Japan, was examined in order to determine whether amino acids (AA) can be used as biomarkers of past changes in coral physiology (metabolism). Micro-samples, corresponding to a time resolution of 1 month, were collected along the growth axis of the coral. Of the 20 AAs analyzed, aspartic acid (Asp) was the most abundant, and its mole concentration relative to the sum of all other AAs (mole%Asp) showed a clear seasonal pattern of low content during winters and high during summers. A growth disturbance in the coral skeleton during 1988–1990, shown by X-ray scans and oxygen and carbon stable isotope data, was marked by a high mole%Asp ratio. Variability in carbon isotope data has often been attributed to metabolic effects, or changes in the isotopic composition of seawater, or both. The changes in mole%Asp shown here suggest that metabolic effects are mainly responsible for sharp changes in carbon isotope profiles during periods of growth disturbance.

Particulate amino acid (AA) content of a 41.85 m long IMAGES core (MD01-2379), collected in 560 m water depth offshore from Northwest Australia, was analyzed to study organic matter (OM) degradation and preservation through glacial–interglacial intervals. A comparison of stable oxygen isotope (δ18O) records of the planktonic foraminifera Globigerinoides ruber with the SPECMAP δ18O profile, suggests a core bottom age of about 486 ky, and an average sedimentation rate of about 9.4 cm ky− 1. Total hydrolysable amino acid (THAA) concentrations are the lowest (240 μg g− 1) in the deeper part of the core, and the highest (1820 μg g− 1) at about 80 cm below the core top. The glacial–interglacial fluctuations in THAA are clearly visible in the upper half of the core, but less prominent in the lower half. An exponential decrease in THAA with increasing depth implies that AAs are decomposed/recycled even after their rapid decomposition at the water/sediment interface. Depth distribution profiles of organic carbon (OC), total nitrogen and THAA indicate long term degradation of OM in deeply buried sediments. An equation has been defined to correct for the loss of OC due to this degradation. Corrected values of OC concentration are significantly higher than those actually measured. We suggest that these corrected values more accurately reflect the OC initially deposited on the sea floor. Thus, primary productivity estimates based on the ‘corrected’ OC content and its interpretation in the light of logarithmic degradation/preservation of labile OM have potential to improve current estimation of paleoproductivity and its fluctuation with glacial–interglacial variations.

Oxidation and reduction processes can influence extent of leaching of elements from solid waste. Three samples of municipal solid waste combustion fly ash were subjected to oxidizing and reducing conditions in order to evaluate leaching of elements in the Milli-Q water and fly ash (liquid to solid ratio, 100) mixtures. Although the oxidizing and reducing conditions were applied for 6 hours only, elements like Cs, Li, Mg, Sb, Tl and V leached more under oxidizing condition than under reducing condition in the case of all three ash samples. Cadmium, Pb and Zn leached more from all samples under reducing condition than under oxidizing condition. Leaching of other elements like Al, Ba, Cr, Cu, Ni and Rb was inconsistent with oxidizing or reducing conditions and varied from sample to sample, suggesting that factors other than redox may be more important in controlling leaching of these elements. Strong acid neutralization capacity of the fly ash samples let the pH vary within a narrow range, and thus severely limited the extent of leaching during the course of the experiment. Lead and Zn were the most sensitive while K and Na were the least sensitive to changes in redox conditions.

As an essential component of living organisms amino acids (AAs) and their distributions are important for quantifying the extent of the biosphere. Calcareous sediments were heated with NaCl solution in an airtight vessel at elevated temperature (100–300 °C) to estimate the thermal stability of the AAs in seafloor hydrothermal systems. The concentration of total hydrolysable amino acids (THAAs) decreased with time and temperature as AAs were lost from the solid to the liquid phase and decomposed. Consequently, THAAs in the liquid phase increased at 100 and 120 °C and during first 24 h at 150 °C and 9 h at 200 °C, and then started to decrease gradually. No AAs could be detected in the liquid phase after 240 h reaction at 250 and 300 °C. The proportions of decomposed AAs at 100, 150, 200 and 300 °C were 23.5%, 62.7%, 90.1% and 99.7%, respectively. The upper temperature limit for the stable presence of AAs probably lay between 150 and 200 °C. Our results demonstrate that AAs cannot be synthesized or survive in hot hydrothermal waters at temperatures higher than 250 °C, unless a solid phase such as clay minerals protects them significantly, and that a temperature of about 150 °C is optimal for the survival of microorganisms in natural submarine hydrothermal systems.

Municipal solid waste combustion leads to concentration of various metals in the solid residue (fly ash) remaining after combustion. These metals pose serious environmental hazard and require proper handling and monitoring in order to control their harmful effects. Leachability of some metals from fly ash was examined in fly ash and Milli-Q water mixture (liquid-to-solid ratio, 100) under various temperature and pH conditions in the laboratory. The leaching experiments conducted for 24 hours showed that pH was generally more important than temperature in controlling the amount of metals leached out of the fly ash. However, at a given pH, rise in temperature led to different degree of (usually one to two fold) enhanced or reduced leaching of metals. Owing to amphoteric nature of oxides of Al, Cr, Pb and Zn, these metals often yielded typical pattern of increase and decrease in their concentrations with change in pH. The extent of leaching of Cr and Pb in our experiments suggests that decrease of pH to acidic range in the case of Pb and to neutral to acidic range for Cr over a long period of storage of fly ash at solid waste dumping site may facilitate leaching of these metals from fly ash, leading to contamination of groundwater to the level that exceeds beyond the level permitted by the environmental laws.

Terrestrial core samples of semi-permafrost sediment were analyzed for total free amino acids (TFAA). The TFAA content ranged from 12.0 to 462.0 nmol/g of sediment, and generally consisted of protein amino acids as the most abundant component of TFAA. The depth profiles in terms of the content drastically decreased with the depth, followed by the vertical distribution patterns of total hydrolyzed amino acids (THAA) within the same sediment. The abundance of THAA was 14 to 327 times larger than that of TFAA. Plots of TFAA versus THAA values yielded a straight line, as defined by the equation THAA = 10.1 x TFAA^1.4 (R^2 = 0.86) based on the least-squares method. The molar ratio of β-alanine and γ-aminobutyric acid did not increase with the depth via diagenesis, as was the case in the THAA fraction. On the other hand, the molar ratio of basic amino acids such as histidine and ornithine gradually decreased with increasing depth. The present study determined that the major organic matter content in the sediment consisted not of free, but bound amino acid analogs.

Oxygen and carbon isotope values of single benthic foraminiferal tests in a core from the Shatsky Rise, NW Pacific Ocean, show greater intra-horizon variance during the Holocene than during the Last Glacial Maximum (LGM). This greater variance is caused by the introduction of glacial specimens some 20 cm upward from their original deposition layer due to bioturbation. In contrast, foraminiferal populations belonging to glacial layers do not include Holocene specimens. The difference in direction of bioturbation greatly modifies climate information in horizons formed during and after deglacial events. After omitting glacial specimens from Holocene sediments, the glacial–interglacial difference in δ18O suggests that Pacific deep-water temperature changed by 2.4–3.8°C at the most. The δ13C values suggest that nutrient concentration was higher during the LGM than the Holocene. The glacial deep North Pacific Ocean apparently was influenced by cold deep waters of southern origin.

Core sediment samples collected from the Hess Rise, North Pacific, were analyzed for 20 common amino acids (AA) and two hexosamines (HA) to understand the relation between glacial–interglacial variations and deposition/preservation of sedimentary organic matter (OM). The sediments are predominantly carbonaceous (carbonates 35–80%). AA-based parameters—aspartic acid/glycine ratio and serine+threonine relative mole content—suggest that calcareous plankton was the major source of OM in these sediments. This inference is supported by the similarity in distribution patterns of AA and HA contents with that of organic carbon. Low values of AA/HA and glucosamine/galactosamine ratios (average 4.4 and 1.1, respectively) imply that much of the planktonic OM was replaced by microbial OM. The relative molar concentration of two nonprotein AA (β-alanine and γ-aminobutyric acid) varied with age of sediments; i.e., they were less abundant in recent sediments and more abundant in the oldest sediments. This trend is an indicator of extremely slow but continuous enzymatic degradation of proteinaceous OM within the sediments. So far, bulk OM has been believed to be one of the best proxies for estimation of primary productivity. However, it may be an underestimate, even for the late Quaternary sediments. Comparison of AA and HA content variations with SPECMAP stack revealed their enhanced deposition and preservation during glacial periods relative to interglacial periods. This, in turn, affected not only the planktonic production in surface waters but also the benthic community, including bacteria on the seafloor.

Time-series data from sediment trap moorings intermittently deployed during 1991–1999 show that the fluxes of biogenic material (carbonate, opal and organic matter, including amino acids) and other related parameters are temporally and spatially distinct across the Western Pacific Warm Pool (WPWP). These variations resulted from the El Nino and La Nina conditions, which alternately prevailed over the equatorial Pacific Ocean during the mooring deployments. The westernmost WPWP (a hemipelagic region) recorded relatively high average total mass and amino acid fluxes during the El Nino event. This was in sharp contrast to the eastern part of the WPWP (oligotrophic and weak upwelling regions) which recorded higher flux values during the La Nina event. Settling particulate organic matter was rich in labile components (amino acids) during La Nina throughout the study area. Relative molar ratios of aspartic acid to β-alanine together with relative molar content of non-protein amino acids β-alanine and γ-aminobutyric acid) suggested that organic matter degradation was more intense during La Nina relative to that during El Nino in the WPWP. This study clearly shows that during an El Nino event the well documented decrease in export flux in the easternmost equatorial Pacific is accompanied by a significant increase in export flux in the westernmost equatorial Pacific Ocean.

Sediment trap moorings deployed along the equator at three distinct oceanographic zones within the western Pacific Ocean during 1991–93, 1994–95, and 1999 provided data on total mass and amino acid fluxes and composition of particulate organic matter (POM) sinking in this part of the Pacific. An intercomparison of annual averages of various parameters revealed discrete patterns in flux and composition of POM under the El Nino (1991–93, 1994–95) and La Nina (1999) conditions that prevailed over the equatorial Pacific during the sampling periods. In the hemipelagic zone of the far western equatorial Pacific, where terrestrial deposition of particles larger than 5 μm accounts for >25% of the total sediment, average total mass and amino acid fluxes were relatively higher during El Nino than during La Nina. However, at the oligotrophic warm pool and upwelling sites, total mass and amino acid fluxes were higher during La Nina. Influence of ENSO-related changes in the sinking particle flux was much clearer in the hemipelagic zone compared to that in the warm pool. Average values of biogeochemical parameters such as glucosamine/galactosamine and amino acids/hexosamines, and bulk parameters like amino acid carbon and nitrogen contents relative to organic carbon and total nitrogen (THAA-C% and THAA-N%, respectively), and organic carbon normalised amino acid concentrations indicated that sinking POM was more labile during La Nina at all the sites. The ratios Aspartic acid/β-alanine, Glutamic acid/γ-aminobutyric acid, and relative concentration of non-protein amino acids (β-alanine+γ-aminobutyric acid) suggested that POM degradation was more intense during La Nina than during El Nino conditions at all sites. >

The distribution and nature of sedimentary organic matter (OM) have been examined in sediment cores collected from the lower reaches, including estuary, of the Godavari River in order to understand sedimentation patterns, sources, and diagenesis of OM. The samples were analyzed for organic carbon (Corg), total nitrogen, amino acids and hexosamines. The observed irregular trends in Corg distribution with depth indicate the unstable nature of bed sediment in the lower reaches of the river. Yet, in the lower estuarine region, regular trends in Corg distribution with depth reflect the deposition of sediment. The atomic ratio of Corg and total nitrogen (C/N; 10.5–16.1) also supported this observation. The distribution of amino acids and diagenetic indicators (β-ala+γ-aba mol.%, AA/HA and Glc-NH2/Gal-NH2) in individual cores revealed the post-depositional changes in the OM. In the core sediment from the lower reaches, there was no clear cut trend in amino acid content with depth. In the estuarine region, however, amino acid content was very low (50.5 and 186.5 μg g−1) in the upper layers compared to that in the lower layers (558.5 and 1099.3 μg g−1). Reactivity index (range 0.3–3.7) revealed that OM in the upper few centimeters, especially in the lower estuarine region, was more reactive relative to that in the deeper layers.

Sinking matter collected by sediment traps, which were deployed in the equatorial Pacific Ocean at 175°E for about 11 months during 1992–1993, were analyzed for their flux and labile components in terms of amino acids and hexosamines. The samples provided a temporal resolution of 15 days and were collected from 1357 (shallow trap) and 4363 m (deep trap) depths where sea floor depth was 4880 m. Particle flux along with major components (carbonate, organic matter, biogenic opal and lithogenic material) and amino acid parameters showed distinct temporal variations, which were more pronounced in the shallow trap relative to deep trap. A coupling between the fluxes in the shallow and deep traps was more evident during the period of maximum particle flux, which seems to be connected with the short reappearance of non-El Nino conditions in equatorial Pacific during the 1991–1993 El Nino event. The biogeochemical indicators C/N, Asp/Bala, Glu/Gaba, Bala+Gaba mol%, THAA-C% and THAA-N% implied that the increase in sinking flux was associated with upwelling and enhanced surface production. Degradation of sinking particulate organic matter between the shallow and deep traps was also evident. Occasionally higher mass and major component fluxes in the deep trap relative to the shallow trap are attributed to contribution of resuspended particulates from sea floor (nepheloid layer) or to laterally advected particulates from nearby areas. Carbonate and opal composition of the sinking flux showed a predominance of calcareous plankton; however, Asp/Gly mol ratio and Ser+Thr mol% indicated enhanced occurrence of diatoms during the periods of higher flux.

The dissolved fluoride (F−) in the Lower Ganges-Brahmaputra-Meghna (GBM) river system, Bengal basin, Bangladesh, was studied during 1991–1993 to determine its distribution and source in the basin, and its annual flux to the Bay of Bengal. The concentration of dissolved F− varied between 2 and 11 μmol l−1 with statistically significant variations both spatially and temporally in the basin. Such variations are attributable to the geology of the individual subbasins (Ganges, Brahmaputra and Meghna), dilution by rainwater during monsoon and groundwater contribution to the river systems during dry season. Correlation coefficients among F− and major cations and anions suggest diverse inorganic processes responsible for regulating the concentration of F− in these river systems. However, fluorite seems to be one of the major sources of dissolved F−. The concentration of F− in the Lower GBM river system is low compared to the rivers draining Deccan Plateau and arid regions of the subcontinent, for example, Yamuna and its tributaries. However, it is within the range of most of the other Peninsular and Himalayan rivers. The GBM system contributes about 115×103 tonnes year−1 of dissolved F− into the Bay of Bengal, and thus accounts for about 3% of the global F− flux to the oceans annually.

Based on skeletal oxygen and carbon isotope analyses, we found a remarkable decrease in skeletal linear extension rate of a Porites colony during the bleaching event of 1998 around the Ryukyu Islands. Water temperature in the summer of 1998 was recorded as the highest for at least last 50 years in the region. This colony, growing in a channel of fringing reef in Ishigaki Island, has experienced complete bleaching, as evidenced from direct observations of discoloration of the colony. Growth increment between the summer of 1997 and winter of 1997–98 is about 7 mm long while the corresponding increment between the summer of 1998 and winter of 1998–99 is only 2 mm long. Since the surface colonization by algae and excavating sponges cannot be recognized by visual inspection of X-radiographs, the slow growth might have been caused by the temporal perturbations in coral-algal symbiotic system, which inhibits calcification. The shift of skeletal carbon isotope ratios toward negative during bleaching also suggests the decrease of photosynthetic activity of symbiotic algae. Presumably, high temperature during the summer of 1998 could have led to massive decrease in carbonate production by coral reefs around the Ryukyu Islands through a large-scale coral bleaching event.

The Bengal basin is one of the geologically youngest and tectonically active drainage regimes of the world which includes the total Lower Ganges–Brahmaputra–Meghna (GBM) river system, one of the highest sediment dispersal systems in the world. The sediment load in this system comprises exclusively fine sand, silt and clay. River bed sediments, and suspended matter from stations situated uniformly all over the basin, have been analyzed in order to understand the spatial distribution and biogeochemical processing of the C, N and P in the system. Among the Ganges, Brahmaputra and Meghna subbasins, variations in total phosphorus (TP) and nitrogen (TN) contents in the bulk and

R-mode factor analysis of the recently acquired data on water and sediment chemistry has been performed. Basic chemical parameters have been merged together which aid in interpreting a few empirical geochemical factors controlling the chemical nature of water and sediments of the Gomti River, a major Himalayan tributary of the Ganges drainage basin. Water chemistry seems to be controlled by three factors: bicarbonate, rainfall and silicate and phosphate factors. Sediment chemistry is largely controlled by the following four factors: clay, adsorption/desorption, Fe-Mn hydroxide and mercury factors. These factors show spatial and temporal variability in terms of their R-scores.

The Godavari River, the third largest river of India,has been sampled for Particulate Inorganic and OrganicCarbon (PIC, POC), Particulate Nitrogen (PN), andParticulate Amino Acids (PAA, including 2 hexosamines(HA)). During the dry season Particulate OrganicMatter (POM) in the upper reaches is relatively freshand autochthonous, in the lower reaches it is degradedand inorganic suspended matter content is higher here.In the wet season (wet monsoon) heavy rains cause abasin-wide flushing of humus from entire catchmentarea consequently POM in the river is mainly degradedand allochthonous. Annual transport of the GodavariRiver amounts to 2.81 × 10 6 ton POC, 0.29 × 10 6ton PN and 0.10 × 10 6 tonParticulate Amino Acid Nitrogen. These amounts rank theGodavari River to one of the most important organic carbontransporting rivers in the world.

Water and sediment samples collected from the Gomti River, a tributary of the Ganges River system, during the postmonsoon season have been analyzed to estimate major elemental chemistry. Water chemistry of the River Gomti shows almost monotonous spatial distribution of various chemical species, especially because of uniform presence of alluvium Dun gravels throughout the basin. The river annually transports 0.34×106 tonnes of total suspended material (TSM) and 3.0×106 tonnes of total dissolved solids (TDS), 69 percent of which is accounted for by bicarbonate ions only. Samples collected downstream of the city of Lucknow show the influence of anthropogenic loadings for a considerable distance in the river water. Na+, Cl−, and SO4 2− concentrations build up downstream. The bed sediment chemistry is dominated by Si (36 percent), reflecting a high percentage of detrital quartz, which makes up about 74 percent of the mineralogy of the bed sediments in the River Gomti. The average Kjeldahl nitrogen concentration (234 μg/g) indicates indirectly the amount of organic matter in the sediments. The Hg concentration in sediments has been found to be higher (average 904 ppb) than the background value. The suspended sediments are well sorted, very finely skewed, and extremely leptokurtic, indicating a low energy condition of flow in the Gomti River. The influence of chemical loads in the Gomti has been found to be small or nonexistent on the Ganges River, perhaps because the water discharge of the Gomti (1.57 percent) to the Ganges is quite low.

The effects of waste ash leachates on soil microorganism were evaluated along with a chemical characterization of ash leachates. Thirty fly ash samples and cyclone ash samples obtained from the incineration of municipal solid waste, plastic waste, and construction waste were used. Twenty-one and 22 samples inhibited N transformation activity of soil microorganism and growth of Bacillus subtilis, respectively. On the other hand, 11 and 18 samples stimulated bacterial activity and growth, respectively, at low concentrations. Generally, cyclone ash contained a smaller amount of toxic metals than fly ash. Our results suggest that cyclone ash can be further studied for reuse, perhaps as a soil amendment. Pb was found to be highly accumulated in B. subtilis cells, and should be carefully monitored when waste ash is reused in the environment.

Settling particles collected by sediment traps deployed intermittently for about 1 year at various locations in the Pacific Ocean showed spatial, sporadic and sometimes seasonal variations in flux and labile composition of the particles. The samples from the western Pacific warm pool (WPWP) provided clear evidence of El Nino–Southern Oscillation (ENSO)-related changes in the composition of particulate labile components (amino acids (AA) and hexosamines (HAs)) and in the flux of settling particles. The particle flux in the western WPWP was higher during El Nino, whereas in the eastern WPWP it was higher during La Nina. Settling particles in the WPWP were more labile during a La Nina event than during El Nino. On the other hand, settling particles collected from the Tasman Sea during La Nina showed the highest concentration of AAs, HAs and particulate organic carbon-normalised AAs, which is consistent with higher primary productivity in this part of the Pacific Ocean. Settling particles at deeper depths in the ocean are more deficient in labile components than those at shallow depths because of ongoing microbial decomposition of organic matter. Occasionally higher particle fluxes were also observed at deeper depths relative to those at shallow depths, probably as a result of lateral advection and re-suspension of highly degraded particulate organic matter in the deep ocean.

Settling particles collected by sediment traps deployed for about one year (1993–94) at four sites along 175°E longitude in the central North Pacific have been analyzed for amino acids (AA) and amino sugars (or hexosamines, HA). These compounds account for about 12.5–27.9% of particulate organic carbon flux to the deep ocean. Biogeochemical indicator parameters varied in the range comparable with similar studies conducted in other oceanic sites. Correlations between non-protein AA (β-alanine and γ-aminobutyric acid) and flux parameters indicate repackaging of settling particulate organic matter (POM) around intermediate water depth (below 1500 m) at all trap sites. Mean values of indicator parameters in the shallow trap differ significantly (Student's t -test; p < 0.03) from those in deep traps at the same site. Latitudinal trends in POM flux and its labile composition suggest that relatively fresh POM is being deposited at a higher rate in the subarctic area of the Pacific. However, this trend is not so clear in deep traps, probably due to the influence of bioactive transport and deposition of laterally advected particles in these traps. Total and particulate organic carbon fluxes normalized to primary productivity estimates show a sharp rise in efficiency of the biological pump towards the subarctic area, which is responsible for enhanced fluxes of particles with a high labile content to the deep ocean in this part of the Pacific. DOI: 10.1034/j.1600-0889.2003.01428.x

Settling particles collected by sediment traps deployed for approximately 1 year in the Coral Sea and Tasman Sea were analysed to understand the biogeochemical processes controlling the cycling and flux of particulate organic matter (POM) in the south-west Pacific. Samples were analysed for 20 amino acids (AA) and two hexosamines (HA) and the data were interpreted together with already published data on opal (biogenic silica), organic carbon and total nitrogen contents. Mean fluxes of labile carbon and nitrogen at one site were significantly different (P < 0.04, t-test; n = 14–18) from those at other sites. The southernmost trap recorded the highest concentrations of AA, HA and organic carbon normalized AA. At a site in the south, POM was more degraded in the deep trap than in the shallow trap. Occasionally, higher fluxes were also recorded at the deep trap relative to the shallow trap. The C/Natomic ratio coupled with AA- and HA-based parameters clearly suggested contribution of POM through resuspension as well as lateral advection at the more southern site, whereas a strong influence of zooplankton on total mass flux was revealed at the northern site during the period August–September 1995. It is evident from the data that higher flux of particles having higher labile contents (AA and HA) is more prevalent in the Tasman Sea than in the Coral Sea.