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1.
The intricately nanopatterned siliceous frustules of diatoms are formed under the control of template organic molecules, some of which are tightly incorporated into the frustule during formation. Long chain polyamines (LCPAs) attract dissolved silicic acid species, enhance silica precipitation and play a role in frustule nanopattern formation. LCPAs thus play a central biogeochemical role, linking the cycling of organic matter with the cycling of silicic acid in the photic zone of the upper ocean. Their distribution and molecular diversity in the environment are as yet unknown. We used high performance liquid chromatography electrospray ionization–mass spectrometry (HPLC–ESI–MSn) to investigate the distribution and molecular diversity of aliphatic LCPAs extracted from the frustules of diatoms in mixed marine plankton communities collected within the euphotic zone of the northeastern Pacific coast, Bering Sea, and Puget Sound estuary. An astonishing variety of over 100 natural LCPAS with complex distribution patterns was found in each sample. Structural variation included degree of methylation, overall chain length, presence of secondary amine functionalities, incorporation of quaternary ammonium and occurrence of sulfonated derivatives. Putrescine-based LCPAs with various degrees of methylation and N-methyl propylamine repeat units were ubiquitous. Although some LCPA species overlapped between samples, there were regional differences in composition and structural characteristics. The structural variety of LCPAs employed by diatoms to produce their nanopatterned silicified exoskeleton could inform biomimetic studies of silica precipitation.  相似文献   

2.
Diatomite associated with the Kolubara Coal Basin was studied to better understand early stage silica diagenesis of shallow water deposits. The Kolubara Basin consists of Neogene siliciclastic rocks, diatomite, marlstone and rare carbonates. Palaeozoic metamorphic and Mesozoic sedimentary and igneous basement rocks are transgressively overlain by Upper Miocene sandstone, siltstone, shale and mudstone. This Upper Miocene section is transgressively overlain by the Pontian section, which contains diatomite and coal beds. White and grey diatomite forms beds 0.7-2.2 m thick that are continuous over an area of about 2 km2. Siliceous rocks vary in composition from diatomite (81-89 per cent SiO2) to diatom-bearing shale (58-60 per cent SiO2). Siliceous deposits are laminated in places, with the laminae defined by variations in clay minerals, organic matter and diatoms. Diatomite shows only incipient diagenesis characterized by the fragmentation of diatom frustules, the minor to moderate corrosion of frustules and the formation of minor amounts of opal-A' (X-ray amorphous inorganic opal) cement. The low degree of diagenesis results from the young age of the deposits, low burial temperatures and possibly also from the presence of abundant organic matter and the dissolution of kaolinite. The presence of only weak diagenesis is also reflected by the characteristically poor consolidation of the rocks and low rank of the associated coal.  相似文献   

3.
Life cycle variations in the morphological and behavioral traits of modern pennate diatoms are known for a wide variety of genera and it is assumed that patterns of asexual and sexual reproduction (e.g. size reduction and auxosporulation) have remained essentially unchanged since their origin. We show here that many characteristics of modern pennate diatoms and the communities they inhabit can indeed be recognized in remarkably well-preserved, non-marine fossil material from the Cretaceous (∼70 Ma) Huepac Chert in NW Mexico. Besides the incremental size reduction of the siliceous frustules in species including Fragilaria tarahumara, we also demonstrate the spatial arrangement and distribution of these cells in in situ microalgal communities, and present evidence for local production of dense exopolymeric substances, cell division, and possibly auxospores. This is the first time that such life cycle stages are reported for non-marine fossil diatoms.  相似文献   

4.
This work reports on a concerted study of diatom-water interfaces for two marine planktonic (Thalassiosira weissflogii= TW, Skeletonema costatum= SC) and two freshwater periphytic species (Achnanthidium minutissimum= AMIN, Navicula minima= NMIN). Proton surface adsorption was measured at 25°C, pH of 3 to 11 and ionic strength of 0.001 to 1.0 M via potentiometric titration using a limited residence time reactor. Electrophoretic mobility of living cells and their frustules was measured as a function of pH and ionic strength. Information on the chemical composition and molecular structure of diatoms surfaces was obtained using FT-IR (in situ attenuated total reflectance) and X-ray Photoelectron Spectroscopy (XPS). The surface area of living cells and their frustules in aqueous solutions was quantified using Small Angle X-ray Scattering Spectroscopy (SAXS).These observations allowed us to identify the nature and to determine the concentration of the major surface functional groups (carboxyl, amine and silanol) responsible for the amphoteric behavior of cell surfaces in aqueous solutions. Taking into account the relative proportion of surface sites inferred from XPS and FT-IR measurements, a surface complexation model of diatom-solution interfaces was generated on the basis of surface titration results. The cell-normalized ratios of the three major surface sites {>COOH}: {>NH3}: {>SiOH} are 1:1:0.1, 1:10:0, 1:1:0.4 and 1:1:0.3 for TW, SC, AMIN and NMIN, respectively. The total amount of proton/hydroxyl active surface sites for investigated species ranges from 1 (NMIN) to 9 (SC) mmol/g dry weight. Normalization of these site densities to the area of siliceous skeleton yields values between 0.3 (NMIN) and 0.9 mmol/m2 (SC) which are an order of magnitude higher than corresponding values for organic-free frustules or amorphous silica. This suggests that the amphoteric properties and possibly the affinity for metal adsorption of diatom cultures are essentially controlled by the 3-D organic layers covering the silica frustule.  相似文献   

5.
硅藻氧同位素已日益成为陆相古气候重建的一种重要手段。文章在简述这一领域已取得的基本认识基础上,着重介绍了近年来的重要进展。主要进展包括: 1)在硅藻的分离纯化方面,规范了重液分离法和新的重力差异流体分离法;2)完善了分步氟化法,创生了高温碳还原法的氧同位素制取技术;3)通过实验培养和天然湖泊监测实验,证实了硅藻氧同位素与温度的分馏平衡关系;4)湖泊硅藻氧同位素可以反映古温度、气候干旱事件和大气降水来源变化。同时,对目前硅藻氧同位素在湖泊沉积古气候研究中存在的主要问题作了讨论和展望。  相似文献   

6.
The lipid content of sea ice samples collected in 2011 and 2012 from Resolute Passage in the Canadian Arctic Archipelago was measured and compared with related samples obtained from the Amundsen Gulf in 2008. The highly branched isoprenoid (HBI) sea ice biomarker, IP25, was found in sea ice samples from each study, consistent with its formation by diatoms during the spring bloom. Our analysis also revealed the occurrence of a number of sterols in Arctic sea ice and these were rigorously identified and quantified for the first time. Concentrations of IP25 and sterols exhibited some variability between sampling studies, with somewhat higher values in samples from Resolute in 2012 than for the other two datasets, consistent with a general increase in biomass; however, major differences in biomarker concentration between sampling studies were not observed. An estimate of the proportion of Arctic sea ice diatoms that produce IP25 (ca. 1–5%) was obtained by comparison of the concentration of IP25 in the samples with those in laboratory cultures of known HBI-producing diatoms and cell enumeration in selected sea ice samples. The estimate is similar to the proportion of Haslea spp. in the same samples, providing further support to the suggestion that at least some species of the Haslea genus may be responsible for the biosynthesis of IP25 and related HBI diatom lipids in Arctic sea ice and that IP25 is made by a relatively small proportion of sea ice diatoms. In contrast, median sterol/IP25 values were all substantially higher than those in cultures of HBI-producing diatoms, suggesting that sterols are made by the majority of sea ice diatoms. The sterol/IP25 ratio was quite variable between locations and samples, likely as a result of differences in diatom assemblage; however, a comparison of individual and median sterol/IP25 values in sea ice with those from surface sediments from different Arctic regions demonstrated that sterols from sea ice diatoms may, in some cases, have a significant impact on the sedimentary budget. This should be considered carefully for quantitative estimates of palaeo sea ice reconstruction using methods such as the PIP25 index, which are based on the relative concentrations of IP25 and sterols in Arctic marine sediment cores.  相似文献   

7.
Previous attempts to evaluate ocean P mass balance and residence time have utilized sequential extraction techniques to isolate and analyze P associated with Fe and Mn oxides and oxyhydroxides, authigenic minerals, detrital, and organic phases. However, in many oceanographic settings, diatoms are the primary producers, and the traditional sequential extraction protocol does not result in complete dissolution of diatom frustules and may not liberate all of the opal intrinsic P associated with the frustules themselves. By adding an opal dissolution step to the end of the extraction protocol, additional P was liberated from the sediments, suggesting that there is an opal-associated P fraction that likely contributes to total reactive P concentrations. In opal-rich sediments, the opal-associated P fraction averages as much as 50-60% of extractable P, and total reactive P concentrations are often more than double when the opal-associated P fraction is included. The presence of opal-intrinsic P potentially has significant implications for ocean P mass balance and residence time of P in the oceans. For example, P burial has possibly been underestimated in settings dominated by diatoms. Additionally, consideration of a significant sedimentary opal-P component suggests that the residence time of P in the oceans may be even shorter than currently suspected.  相似文献   

8.
Long chain 1,14-diols have been reported in diatoms of the genus Proboscia and applied as specific biomarker lipids for such algae. We report here the presence of saturated C28, C30 and C32 1,14-diols in a culture of the marine heterokont alga Apedinella radians (Class Dictyochophyceae, order Pedinellales). Apedinella species occur globally, although predominantly in estuarine waters, so the finding has potential implications for the use of long chain 1,14-diols as biomarkers of Proboscia diatoms and as an indicator of upwelling.  相似文献   

9.
In estuarine ecosystems, microphytobenthos resuspended by tidal currents often represents a large part of the food supply available to bivalves which feed selectively. This study investigated the feeding behavior of the Pacific oysterCrassostrea gigas (Thunberg) relative to a natural microphytobenthic assemblage and the effect on the structure of this assemblage. Oysters were fed only benthic microalgae collected on the intertidal mud flats of Bourgneuf Bay (France) at a suspended particulate matter concentration above the threshold of pseudofeces production. All species in the assemblage were endemic diatoms characteritic of tidal mud flat environments. Four dominant ones, which were all solitary cells with spear-shaped frustules [Navicula ammophila (Grunow),Navicula rostellata (Kützing),Plagiotropis lepidoptera (Kuntze), andStaurophora amphioxys (Mann)] represented more than 95% of the 16 species involved. Analysis of feeding processes showed that the retention of the four main diatoms was not significantly different, but that two species, the smallest (N. ammophila [22×4 μm]) and the largest (P. lepidoptera [60×15 μm]), were preferentially ingested. The study of post-ingestive selection revealed that these two species were also preferentially digeted, i.e., preferentially directed into the digestive diverticulum, when they passed through the gut ofC. gigas. Cell size and shape did not appear to account for pre-ingestive and post-ingestive selection. The composition of the assemblage was significantly modified by oyster filtration, although the retention rates of the four main species were not significantly different. The composition of microalgae in pseudofeces and feces as a result of pre-ingestive and post-ingestive selection differed from that in seawater.  相似文献   

10.
We have investigated the transfer of oxygen isotope signals of diatomaceous silica (δ18Odiatom) from the epilimnion (0-7 m) through the hypolimnion to the lake bottom (∼20 m) in freshwater Lake Holzmaar, Germany. Sediment-traps were deployed in 2001 at depths of 7 and 16 m to harvest fresh diatoms every 28 days. The 7 m trap collected diatoms from the epilimnion being the main zone of primary production, while the 16 m trap collected material already settled through the hypolimnion. Also a bottom sediment sample was taken containing diatom frustules from approximately the last 25 years. The δ18Odiatom values of the 7 m trap varied from 29.4‰ in spring/autumn to 26.2‰ in summer according to the temperature dependence of oxygen isotope fractionation and represent the initial isotope signal in this study. Remarkably, despite the short settling distance δ18Odiatom values of the 7 and the 16 m trap were identical only during spring and autumn seasons while from April to September δ18Odiatom values of the 16 m trap were roughly ∼1.5‰ enriched in 18O compared to those of the 7 m trap. Isotopic exchange with the isotopically lighter water of the hypolimnion would shift the δ18Odiatom value to lower values during settling from 7 to 16 m excluding this process as a cause for the deviation. Dissolution of opal during settling with intact organic coatings of the diatom cells and near neutral pH of the water should only cause a minor enrichment of the 16 m values. Nevertheless, opal from the bottom sediment was found to be 2.5‰ enriched in 18O compared to the weighted average of the opal from the 7 m trap. Thus, resuspension of bottom material must have contributed to the intermediate δ18Odiatom signal of the 16 m trap during summer. Dissolution experiments allowed further investigation of the cause for the remarkably enriched δ18Odiatom value of the bottom sediment. Experiments with different fresh diatomaceous materials show an increase of opaline 18O at high pH values which is remarkably reduced when organic coatings of the cells still exist or at near neutral pH. In contrast, high pH conditions do not affect the δ18Odiatom values of sub-fossil and even fossil opal. IR analyses show that the 18O enrichment of the sedimentary silica is associated with a decrease in Si-OH groups and the formation of Si-O-Si linkages. This indicates a silica dehydroxylation process as cause for the isotopic enrichment of the bottom sediment. Silica dissolution and dehydroxylation clearly induce a maturation process of the diatom oxygen isotope signal presumably following an exponential behaviour with a rapid initial phase of signal alteration. The dynamics of this process is of particular importance for the quantitative interpretation of sedimentary δ18Odiatom values in terms of palaeothermometry.  相似文献   

11.
Carbon isotope ratio (δ13Corg) values of organic matter in lake sediments are commonly used to reconstruct environmental change, but the factors which influence change are varied and complex. Here we report δ13C values for sediments from Erlongwan maar lake in northeast China. In this record, changes in δ13C cannot be explained by simple changes in aquatic productivity. Instead, values were likely influenced by differences in the ratio between planktonic and benthic algae, as indicated by the remains of diatoms. This is because the variation of δ13Corg in algae from different habitats is controlled by the thickness of the diffusive boundary layer, which is dependent on the turbulence of the water. Compared with benthic algae, which grow in relatively still water, pelagic algae are exposed to greater water movement. This is known to dramatically reduce the thickness of the boundary layer and was found to cause even more severe δ13C depletion. In Erlongwan maar lake, low values were linked to the dominance of planktonic diatoms during the period commonly known as the Medieval Warm Period. Values gradually increased with the onset of the Little Ice Age, which we interpret as being driven by an increase in the proportion of benthic taxa, due to effect of the colder climate. The increase in planktonic diatoms at the end of the Little Ice Age, linked to higher temperature and a reduction in ice cover, resulted in a further decline in δ13Corg.  相似文献   

12.
Foraminifera and diatoms preserved in salt-marsh sediments have been used to produce high-resolution records of Holocene relative sea-level (RSL) change. To determine which of these microfossil groups is most appropriate for this purpose we investigated their relative utility from salt marshes in North Carolina, USA. Regional-scale transfer functions were developed using foraminifera, diatoms and a combination of both (multi-proxy) from three salt marshes (Oregon Inlet, Currituck Barrier Island and Pea Island). We evaluated each approach on the basis of transfer-function performance. Foraminifera, diatoms and multi-proxy-based transfer functions all demonstrated a strong relationship between observed and predicted elevations (r2jack > 0.74 and RMSEP < 0.05 m), suggesting that they have equal utility. Application of the transfer functions to a fossil core from Salvo to reconstruct former sea levels enabled us to consider relative utility in light of ‘paleo-performance’. Fossil foraminifera had strong modern analogues, whilst diatoms had poor modern analogues making them unreliable. This result reflects the high diversity and site-specific distribution of modern diatoms. Consequently, we used foraminifera to reconstruct RSL change for the period since ∼ AD 1800 using a 210Pb- and 14C-based chronology, and we were able to reconcile this with tide-gauge records.  相似文献   

13.
The presence of the C30 sterol gorgosterol (22,23-methylene-23,24-dimethylcholest-5-en-3ß-ol) and its analogues in some marine and freshwater environments is generally associated with invertebrate animals or dinoflagellates since there have been no reports of them in other microalgal classes. Here we show that two unialgal cultures of different species of the marine diatom Delphineis contain gorgosterol in addition to sterols more commonly found in diatoms. Our findings suggest that some reports of gorgosterol in seawater and marine sediments may well have an origin, at least in part, from diatoms.  相似文献   

14.
The goal of this study was to develop a method for extracting quantitative annual records of diatoms and other microfossils from sediments that are resistant to existing varve-counting methods because of their variable, complex, or indistinct laminations. Very linely laminated organic sediments from a deep diamictic lake in central Minnesota, USA were collected by freeze-core, dehydrated by solvent exchange, embedded with epoxy, and petrographically thin-sectioned. Diatom frustules and pollen grains were counted in contiguous 400 pm microscope fields-of-view and used to construct a sediment chronology. The concentration of diatoms in the sediment was cyclic and lowest in sediment deposited during summer. The concentration of pollen in the sediment was also cyclic and sediment deposited during the summer contained the highest concentrations of pollen and the highest percentages of ragweed ( Ambrosia spp.) pollen. The sediment chronology that was produced accurately records the onset of regional (c. 1850) and watershed ( c . 1880) development, a historic tornadic storm complex (1894), and individual drought years (1932, 1934 & 1935) within the 1930's drought.  相似文献   

15.
Historical changes in bioavailable Zn concentrations of the surface waters of Lake Geneva were assessed by analyzing the zinc content of fossil diatoms. The measured ratios of Zn to Si in the opal ((Zn/Si)opal) were consistent with both data obtained for cultured freshwater diatoms that were representative of lake Geneva and with field data. Reconstructed variations suggested that increased Zn uptake by phytoplankton occurred in the period from 1960–1980 resulting from an increased loading of Zn to the lake. Nonetheless, observed concentrations were sufficiently low that no adverse effects were expected on the pelagic community. The data presented here suggest that (Zn/Si)opal records may become a valuable tool to assess past changes in bioavailable Zn concentrations in freshwater systems.  相似文献   

16.
For the first time a biological source for the long-chain alkyl 1,14-diols and 12-hydroxy methyl alkanoates, lipids widely occurring in the marine water column and sediments, has been identified. Cultures of Proboscia indica and Proboscia alata, rhizosolenoid diatoms belonging to the widespread diatom genus Proboscia, contain C28, C28:1, C30, and C30:1 alkyl 1,14-diols, and C27 and C29 12-hydroxy methyl alkanoates as major neutral lipids. These components form a substantial fraction of lipid fractions from sediment traps or sediments, especially in areas with an elevated primary production such as upwelling regions. Examination of literature data reveals that as much as 20 to 35% of the total lipid flux in the Arabian Sea is derived from Proboscia diatoms during the start of the upwelling season. Their rapid transfer to the water-sediment interface may explain why corresponding 1,14-keto-ols, inferred oxidation products of diols, are hardly formed. These interpretations are supported by compound-specific carbon isotopic analysis of long-chain keto-ols and diols in surface sediments of the Arabian Sea. The data indicate that long-chain alkyl 1,14-diols and 12-hydroxy methyl alkanoates can be applied as indicators for high-nutrient conditions in the photic zone.  相似文献   

17.
A diatomite, about 60 m thick, of late Palaeocene-early Eocene age crops out in northern Jutland, Denmark. The diatomite is locally termed ‘Moler’. Frustules of marine diatoms constitute c. 65% (by weight) of the diatomite, and clay minerals, chiefly montmorillonite, make up the remainder. Slight variations in the relative supply of diatom frustules and clay minerals are preserved undisturbed in laminated diatomite, while lamination is partly destroyed by burrowing organisms in weakly laminated diatomite and obliterated by total bioturbation in structureless diatomite; these three facies alternate throughout the sequence. The presence or absence of infaunal burrowing organisms is interpreted as a record of the content of dissolved oxygen in the water above the sediment-water interface and hence of the position of the redox potential discontinuity. Interspaced in the diatomite are 179 identifiable layers of volcanic ash. These ash layers provide a means of precise lateral correlation. They show that levels of laminated diatomite may be followed throughout the basin and therefore that changes between anoxic and oxic conditions occurred simultaneously across the area. The laminated diatomites may consequently be interpreted as representing short-term anoxic events, of which twelve have been recognized.  相似文献   

18.
This is a summary of new oxygen isotope record of diatoms from Lake Kotokel sediments, with implications for responses of the lake system and its environment to global change over the past 46 kyr. Fossil diatoms in all samples are free from visible contamination signatures and contain no more than 2.5% Al2O3, which ensures reliable reconstructions. The 518O values in diatoms vary between + 23.7 and + 31.2%c over the record. The results present mainly diatom assemblages of summer blooming periods, except for the time span between 36 and 32 kyr, when the isotopic signal records mainly a shift from summer to spring blooming conditions. Possible water temperature changes only partly explain the changes in the isotopic record. The observed isotopic patterns are produced mainly by isotope changes in lake water in response to variations in air temperature, hydrology, and atmospheric circulation in the region. During Marine Isotope Stage (MIS) 2 (Last Glacial maximum), high 518Odiatom resulted from rapid evaporation and low fluvial inputs. The high 518Odiatom values of about + 29 to + 30%c during the first half of MIS 1 (Holocene interglacial) suggest an increased share of summer rainfalls associated with southern/southeastern air transport. The 518Odiatom decrease to + 24%c during the second half of MIS 1 is due to the overall hemispheric cooling and increased moisture supply to the area by the Atlantic air masses. The record of Lake Kotokel sediments provides an example of complex interplay among several climatic/environmental controls of 518Odiatom during the Late Pleistocene and the Holocene.  相似文献   

19.
The occurrence of a novel C25 highly branched isoprenoid (HBI) mono-unsaturated hydrocarbon in Arctic marine sediments from the Fram Strait is described. The structure was determined following synthesis from a closely related diene and NMR spectroscopic analysis. The position of the double bond was confirmed by oxidation (RuO4) and comparison of the mass spectrum of the resulting C19 ketone with that of an authentic sample synthesised previously. The same C19 ketone was also present following oxidation of the Fram Strait sediment extracts. The source of the novel HBI monoene biomarker is not known, but is believed to be certain marine diatoms on the basis of structural similarities with other HBIs from such sources. It does not, however, appear to be biosynthesised by Arctic sea ice diatoms, unlike its regio isomer, IP25, an established proxy for Arctic sea ice. Alternatively, it may represent a diagenetic product of the sea ice diatom biomarker IP25; this seems unlikely, however, on the basis of their respective structures. Since the new HBI monoene and IP25 possess similar gas chromatographic and mass spectral properties, but probably have contrasting sources, we suggest that future paleo sea ice reconstruction studies based on the occurrence of IP25 should pay further attention to the rigorous assignment of this biomarker in marine sediment extracts. Some suggestions for achieving this, based on analytical purification and mass spectrometric measurements, are provided.  相似文献   

20.
The composition and distribution of diatom algae inhabiting estuaries and coasts of the subtropical Americas are poorly documented, especially relative to the central role diatoms play in coastal food webs and to their potential utility as sentinels of environmental change in these threatened ecosystems. Here, we document the distribution of diatoms among the diverse habitat types and long environmental gradients represented by the shallow topographic relief of the South Florida, USA, coastline. A total of 592 species were encountered from 38 freshwater, mangrove, and marine locations in the Everglades wetland and Florida Bay during two seasonal collections, with the highest diversity occurring at sites of high salinity and low water column organic carbon concentration (WTOC). Freshwater, mangrove, and estuarine assemblages were compositionally distinct, but seasonal differences were only detected in mangrove and estuarine sites where solute concentration differed greatly between wet and dry seasons. Epiphytic, planktonic, and sediment assemblages were compositionally similar, implying a high degree of mixing along the shallow, tidal, and storm-prone coast. The relationships between diatom taxa and salinity, water total phosphorus (WTP), water total nitrogen (WTN), and WTOC concentrations were determined and incorporated into weighted averaging partial least squares regression models. Salinity was the most influential variable, resulting in a highly predictive model (r apparent2 = 0.97, r jackknife2 = 0.95) that can be used in the future to infer changes in coastal freshwater delivery or sea-level rise in South Florida and compositionally similar environments. Models predicting WTN (r apparent2 = 0.75, r jackknife2 = 0.46), WTP (r apparent2 = 0.75, r jackknife2 = 0.49), and WTOC (r apparent2 = 0.79, r jackknife2 = 0.57) were also strong, suggesting that diatoms can provide reliable inferences of changes in solute delivery to the coastal ecosystem.  相似文献   

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