Particulate peptidoglycan in seawater determined by the silkworm larvae plasma (SLP) assay

Peptidoglycan (PG) is a biopolymer found exclusively in the cell wall of bacteria. Recent chemical analysis of particulate organic matter suggests that a major amount of the muramic acid, an amino sugar present only in PG, could not be accounted for in terms of bacterial cells (Benner and Kaiser, 2003); however, data on particulate PG is quite sparse. In the present study, conducted in 1996, the PG was examined at 5 sampling sites in the northwestern Pacific Ocean, and in natural seawater cultures. Particulate PG, which was concentrated using a 96-well filtration plate equipped with Durapore filters (pore size, 0.22 μm), was measured by the silkworm larvae plasma (SLP) assay. The PG concentration generally decreased with depth and correlated significantly with bacterial abundance throughout the entire water column. However, the ratio of particulate PG to bacterial abundance varied with depth. The average ratio was 0.61 ± 0.53 (average ± SD, n = 40) between 50 and 2000 m, which agreed with the bacterial cellular PG content from 0.63 to 1.1 fg cell⁻¹ obtained in seawater cultures. On the other hand, the ratios of PG to bacteria from the surface to 50 m (3.7 ± 2.6, n = 29) and below 2,000 m (2.1 ± 1.7, n = 7) were significantly higher than that between 50 and 2,000 m. These results may suggest that, in the surface and deep layers, a significant fraction of particulate PG was present in bacterial detritus, whereas this fraction was reduced in the middle layer.     

The application of isotopic and biogeochemical markers to the study of the biochemistry of organic matter in a macrotidal estuary, the Loire, France

The biogeochemistry of organic matter in a macrotidal estuary, the Loire, France, has been studied for two years during different seasons. Both particulate matter and sediment have been sampled in the riverine zone, in the maximum turbidity zone and in the ocean near the river mouth. Two techniques have been used: carbon isotopic ratio determination and analysis of lipid-marker signatures in the n-alkane, n-alkene and fatty acid series. For the period corresponding to the output of the maximum turbidity zone in the ocean, the complete change of organic matter, continental in nature in the inner estuary, pure marine in the outer estuary is well illustrated by the decrease of δ¹³C values and of carbon preference index of n-alkanes. Input sources of organic matter by continental plants, plankton and micro-organisms are discussed from biogeochemical-marker analyses data along with the processes of accumulation of particles and their evolution with the season. Some criteria for evidencing the nature of various organic-matter pools are assessed and compared in different chemical-marker series as follows: high molecular weight n-alkanes and fatty acids, perylene for continental imprints, polyunsaturated 18-, 20- and 22-carbon fatty acids, n-C₁₇, n-alkenes and squalene for algae imprints, branched iso and anteiso fatty acids, Δ11-C_18:1 for microbial imprints.     

Winter-spring phytoplankton blooms in Dabob Bay, Washington

Scientific investigations in Dabob Bay, Washington State, USA, have been extensive since the early 1960s, but phytoplankton blooms have been studied mostly with regard to chlorophyll concentrations and little is known about the phytoplankton species themselves. Here we provide information on the species present, their abundances during blooms, their contribution to organic carbon concentrations and the ability of some phytoplankton species to produce toxic aldehydes that may impact metazoan grazers.Multiple blooms of phytoplankton, dominated by diatoms, occurred in the late winter-early spring period, with depth-integrated chlorophyll levels ranging from <20 to 230 mg m⁻² and peaks in February and April. The major bloom species included Skeletonema costatum, Thalassiosira spp. and Chaetoceros spp; Phaeocystis cf. pouchetii occurred in 2002 and 2004. Other taxa or groups of organisms that were sometimes abundant included unidentified small flagellates <10 μm in size and unidentified heterotrophic dinoflagellates. Large diatoms usually comprised most of the cell carbon, but a large, heterotrophic dinoflagellate, identified only as Gyrodinium “tear” because of its shape, was a major contributor to the microplankton carbon when present even in small numbers. Five Thalassiosira species and S. costatum were found to produce polyunsaturated aldehydes (PUA) that are known to affect copepod reproduction and hatching success. Our findings are similar to the few previous studies in the last four decades that included phytoplankton species and suggest long-term similarities and relative stability in the phytoplankton species present and their timing in Dabob Bay.     

Fe(OH)_3胶体与铜离子作用的研究

使用切向流超滤系统得到粒度较均匀的Fe(OH)3胶体,进而对Fe(OH)3胶体粒子与Cu2 的作用进行了研究,并将实验结果与南沙群岛海区表层水中铜与胶体物质结合状况的调查数据进行了比较分析,得到如下结果:(1)在海水介质中,铜在Fe(OH)3胶体上结合的百分率(pH>5)随pH的升高而下降,随着Fe(OH)3胶体浓度的减小而下降?(2)在天然海水介质中,使铜在Fe(OH)3胶体上结合的百分率在50%-70%的有机物浓度为1.0mg·L-1,有机物浓度的增大使铜与无机胶体结合的百分率有下降的趋势?     

Sources and hydrothermal alteration of organic matter in Quaternary sediments: A synthesis of studies from the Central Gulf of California

Deep sea drilling in the Central Gulf of California, a young and active spreading centre, shows that the high heat flow typical of these regions causes extensive alteration of sediment organic matter, especially near sills and above magma chambers where hydrothermal activity is concentrated. Even on the nearby passive margin, where there are no sills, heat flow is moderately high and hydrocarbon generation has begun in immature sequences. Migrating light hydrocarbons are detected especially where hydrothermal activity is concentrated. Thermogenic methane is more widespread, though not in the passive margin bordering the spreading centre. Despite the incidence of hydrocarbon generation and migration, the amounts of hydrocarbons involved are relatively small and apparently do not lead to commercially significant accumulations of petroleum.The organic matter in these sediments is mostly marine because the Gulf of California generally has low runoff from land and highly productive surface waters. Turbidites rich in terrigenous organic material are locally abundant in the mainly pelagic section in the Guaymas Basin. The highest concentrations of organic matter are found in laminated diatomites deposited on the Guaymas passive margin within the oxygen minimum zone.     

夏、冬两季长江口及邻近海域悬浮物的分布特征及其沉积量

利用2001年7～8月 ,2002年1月两个航次的悬浮物浓度资料 ,并参考其它水文参数 ,简要分析长江口及邻近海域悬浮物的分布特征 :无论夏季还是冬季 ,长江入海悬浮物总是向东南方输运 ;冬季由于再悬浮作用显著 ,悬浮物浓度明显高于夏季 ,且南北分布范围也明显增大 ,垂向分布均匀。同时采用数值模拟的海流流速值和观测的悬浮物浓度值计算悬浮物的断面通量 ,并最终得计算区悬浮物夏、冬两季的沉积量 ,夏、冬季长江口及邻近海域悬浮物的沉积量分别为0.79×108t,1.44×108t。     

Quantum yield for the photochemical production of dissolved inorganic carbon in seawater

The direct photooxidation of coloured dissolved organic matter (CDOM) to dissolved inorganic carbon (DIC) may provide a significant sink for organic carbon in the ocean. To calculate the rate of this reaction on a global scale, it is essential to know its quantum yield, or photochemical efficiency. We have determined quantum yield spectra, φ(λ), (moles DIC/mole photons absorbed) for 14 samples of seawater from environments ranging from a turbid, eutrophic bay to the Gulf Stream. The spectra vary among locations, but can be represented quite well by three pooled spectra for zones defined by location and salinity: inshore φ(λ)=e^{−(6.66+0.0285(λ−290))}; coastal φ(λ)=e^{−(6.36+0.0140(λ−290))}; and open ocean φ(λ)=e^{−(5.53+0.00914(λ−290))}. Production efficiency increases offshore, which suggests that the most highly absorbing and quickly faded terrestrial chromophores are not those directly responsible for DIC photoproduction.     

Distributions of dissolved and particulate biogenic thiols in the subartic Pacific Ocean

Dissolved and particulate concentrations of the biogenic thiols cysteine (Cys), arginine–cysteine (Arg–Cys), glutamine–cysteine (Gln–Cys), γ-glutamate–cysteine (γ-Glu–Cys) and glutathione (GSH) were measured in the subartic Pacific Ocean in the summer of 2003 using high performance liquid chromatography (HPLC) with precolumn derivatization as reported in previous work. In this study, a preconcentration protocol for the derivatized thiols was utilized to extend detection limits of dissolved thiols to picomolar levels. The measured concentrations of particulate and dissolved thiols were uncoupled, with distinctive depth profiles and large differences in the particulate to dissolved ratios between individual compounds. Glutathione was the most abundant particulate thiol whereas the most abundant dissolved thiol was γ-Glu–Cys, with concentrations as high as 15 nM. Given the relatively small pool of intracellular γ-Glu–Cys and the very low dissolved concentrations of GSH, we hypothesize that glutathione released from cells is rapidly converted to the potentially degradation resistant γ-Glu–Cys outside the cell. The relatively high concentrations of other dissolved thiols compared to particulate concentrations implies both biological exudation and slow degradation rates. Some thiols appear to vary with changes in nutrient availability but this effect is difficult to decouple from changes in community structure inferred from pigment analyses. Dissolved thiol concentrations also exceed typical metal concentrations in the subartic Pacific, supporting previous arguments that they may be important in metal speciation.     

Complexation of mercury by dissolved organic matter in surface waters of Galveston Bay, Texas

The chemical speciation of dissolved mercury in surface waters of Galveston Bay was determined using the concentrations of mercury-complexing ligands and conditional stability constants of mercury-ligand complexes. Two classes of natural ligands associated with dissolved organic matter were determined by a competitive ligand exchange-solvent solvent extraction (CLE-SSE) method: a strong class (L_s), ranging from 19 to 93 pM with an average conditional stability constant (K_HgLs) of 10²⁸, and a weak class (L_w) ranging from 1.4 to 9.8 nM with an average K_HgLs of 10²³. The range of conditional stability constants between mercury and natural ligands suggested that sulfides and thiolates are important binding sites for dissolved mercury in estuarine waters. A positive correlation between the estuarine distribution of dissolved glutathione and that of mercury-complexing ligands supported this suggestion. Thermodynamic equilibrium modeling using stability constants for HgL, HgCl_x, Hg(OH)_x, and HgCl(OH) and concentrations of each ligand demonstrated that almost all of the dissolved mercury (> 99%) in Galveston Bay was complexed by natural ligands associated with dissolved organic matter. The importance of low concentrations of high-affinity ligands that may originate in the biological system (i.e., glutathione and phytochelatin) suggests that the greater portion of bulk dissolved organic matter may not be important for mercury complexation in estuarine surface waters.     

Eddy Diffusion Coefficients of Suspended Particulate Matter: Effects of Wind Energy Transfer and Stratification

Gross sedimentation rates (GSR) have been measured using sediment traps placed at nine different levels above the bed (0·3, 0·5, 0·8, 1·0, 2·0, 4·0, 6·0, 8·0 and 10·0 m). The sediment traps were deployed for 1·25 years and recovered 28 times during the study period. Low average GSR values of 5·5 g m^-2 day^-1 were obtained at 10·0 m, and high average GSR values of 114·8 g m^-2 day^-1 were obtained at 0·3 m. An expression for the eddy diffusion coefficient of suspended particulate matter (K_s), based on the measured GSR is given. The expression has been used for modelling of K_s at the different trap levels above the bed. High values (≈42 cm² s^-1) of K_s were obtained at the upper traps, whereas low values (≈2 cm² s^-1) were obtained near the bed. Comparison between level of turbulent energy in terms of shear stress at the boundaries of the water column, i.e. from the wind and the bed flow, showed that wind energy exceeded that of the bed flow by a factor 16. At 5·0 m K_s was positively correlated (r=0·66) to the eddy diffusion coefficient of momentum (K_m) derived from the wind energy transfer to the water, giving an average β of 0·5 for K_s =βK_m. The density difference between surface and bottom waters has been designated a parameter of stratification, and is discussed in relation to variations of K_s and K_m .