Marine and terrigenous lipids in coastal sediments from the Peru upwelling region at 15°S: Sterols and triterpene alcohols

The distributions of free 4-desmethyl sterols in sediments from the Peru coastal zone at 15°S have been determined. Major free sterols in the surface sediments include cholesterol, which is mainly derived from zooplankton, and two C₂₈ sterols: 24-methylcholesta-5,24(28)-dien-3β-ol and 24-methylcholesta-5,22E-dien-3β-ol both of which are derived fro diatoms. Their concentrations decrease by almost an order of magnitude in the top 20 cm of sediment depth, indicating that free sterols are rapidly degraded in this sedimentary environment. Lipids from higher plants were also detected: long chain fatty acids and alcohols and various triterpenoid alcohols, including taraxerol, lupeol and α- and β-amyrin. The concentrations of most terrigenous lipids varied by less than a factor of 3 over the same depth, and these changes were not correlated with changes in the concentrations of total organic carbon. Below 3 cm, lipids from higher plants predominated in the extractable lipid distributions due to the more rapid degradation of marine lipids. We postulate that there are significant marine sources of the higher plant sterols 24-ethylcholesterol, 24-ethylcholesta-5,22E-dien-3β-ol and 24-methylcholesterol in these sediments. A high proportion of many of the terrigenous lipids in these sediments are probably transported into the coastal zone by rivers, rather than from the atmosphere, and then redistributed by bottom currents.     

南海北部油气缓释环境沉积物脂类化合物组成特征

认识沉积环境有机碳留存状况是阐述油气形成过程中有机碳早期成岩的关键内容。以南海珠江口盆地及其邻近海域为背景,通过研究表层沉积物中脂类化合物的形态组成,认识脂类有机碳的来源和留存状态,阐述特征脂类分子的早期成岩特征。结果表明,研究区域表层沉积物有机碳含量为0.22%～0.66%,有机碳稳定同位素分布在-20.88‰～-22.93‰之间,表现为显著的海源特征。沉积物中共检测出21种脂肪酸、6种脂肪醇、8种甾醇和植醇;总脂肪酸、脂肪醇、甾醇和植醇含量分别为12.57～40.27μg/g、5.35～8.98μg/g、0.15～3.75μg/g和0.01～3.99μg/g干重,总体表现为靠近珠江口和台湾海峡略高。脂类化合物的存在形态以游离态(FR)和碱性水解态(BH)为主,酸性水解态(AH)贡献较低;其中植醇和甾醇呈现显著的BH优势,植醇中未检出AH组分的贡献。脂类化合物主要来自于海洋现场生产,海洋微藻和细菌的相对贡献率分别为21.18%～33.78%和11.02%～15.64%,陆源高等植物贡献低于5%。来源于硫酸盐还原菌的支链脂肪酸在靠近珠江口海域高达1.79～2.62μg/g,占总脂肪酸的5.14%～6.50%,并与硫酸盐还原过程相关的古菌分布相一致。     

Temperature and Salinity Effects on Alkenone Ratios Measured in Surface Sediments from the Indian Ocean

We compare alkenone unsaturation ratios measured on recent sediments from the Indian Ocean (20°N–45°S) with modern sea oceanographic parameters. For each of the core sites we estimated average seasonal cycles of sea surface temperature (SST) and salinity, which we then weighted with the seasonal productivity cycle derived from chlorophyll satellite imagery. The unsaturation index (U₃₇^K′) ranges from 0.2 to 1 and correlates with water temperature but not with salinity. TheU₃₇^K′versus SST relationship for Indian Ocean sediments (U₃₇^K′= 0.033 SST + 0.05) is similar to what has been observed for core tops from the Pacific and Atlantic oceans and the Black Sea. A global compilation for core tops givesU₃₇^K′= 0.031 T + 0.084 (R= 0.98), which is close to a previously reported calibration based on particulate organic matter from the water column. For temperatures between 24° and 29°C, however, the slope seems to decrease to about 0.02U₃₇^K′unit/°C. For Indian Ocean core tops, the ratios of total C₃₇alkenones/total C₃₈alkenones and the slope of theU₃₇^K′-SST relationship are similar to those previously observed for cultures ofEmiliania huxleyibut different from those previously published forGephyrocapsa oceanica.EitherE. huxleyiis a major producer of alkenones in the Indian Ocean or strains ofG. oceanicaliving in the northern Indian Ocean behave differently from the one cultured. In contrast with coccolithophorid assemblages, the ratios of C₃₇alkenones to total C₃₈alkenones lack clear geographic pattern in the Indian Ocean.     

Occurrence of Different Forms and Implications of Compound Specific Sterols in Continental Sediments of the Northeast South China Sea

The South China Sea(SCS) is one of the most productive and accumulative marginal shelves of organic carbon in the world. To expound the transformation and preservation of organic carbon in the Northeast SCS, where abundant oil and gas resources have been reported, compound specific sterols in free(FR), base hydrolytic(BH), and acid hydrolytic(AH) forms were analyzed in surface and columnar sediments in May, 2016. The results showed that the total contents of sterols detected ranged from 0.15 to 3.74 ppm dry weight in the surface sediments, and gradually decreased from 3.41 to0.17 ppm dry weight from surface to deep sediments, in which cholesterol(27~(△5)) was the most abundant component. Sterols mainly existed in the BH form(54.51%-74.20%), followed by the FR form(25.50%-45.49%) and then the AH form(0-3.77%) in turn, in the surface sediments. BH and FR sterols accounted for 0-49.08% and 50.92%-100% in the columnar sediments, while AH sterols were undetectable. The contents of specific sterols indicated that, the primary source of marine organic carbon was about 5 times as much as that from terrestrial input. More and more FR sterols transformed into BH sterols with increasing sedimentary depth, and BH sterols absolutely dominated in sediment depths under 25 cm. The forms of Sterols C27 were maintained at a relative consistence state, but Sterols C28 to C30 degraded gradually during the sedimentation process. It was suggested that the stability of sterols, based on the chemical structures, might be the primary factor controlling their degradation and preservation in deeper sediments. These results would help to understand the organic carbon(OC) transformation in a hydrate formation area in a marginal sea.     

Short-term changes in C and N distribution in soil particle size fractions induced by agricultural practices in a cultivated volcanic soil from Mexico

The purpose of this study was to assess the effect of agricultural practices on the characteristics of soil organic carbon (SOC). The study area is located in the Central Volcanic Belt (Michoacán) in Mexico. The soil is an Acrisol, acidic and rich in clays and sesquioxides. Experimental plots were treated with four different agronomic management systems between 2002 and 2003: traditional, improved traditional, organic and fallow. Each treatment was replicated twice. Samples were taken at depths of 0–10 and 10–20 cm and were subjected to a physical fractionation process by way of particle size. SOC was fractionated into fulvic acids, humic acids and humin. After two years of cultivation, the SOC content increased significantly with the organic management (2.2 mg g⁻¹ at 0–10 cm and 5.8 mg g⁻¹ at 10–20 cm). The C content of the soil fine particle fraction increased with the traditional and organic managements. The organic C and N contents of the silt + clay particle-size fraction were mainly concentrated as humin, indicating that this SOM should be stable and have a low risk of mineralization. The humin C content only decreased significantly under the traditional and fallow treatments. The N content of the humin fraction decreased significantly under the traditional management system (from 69% to 54%), indicating the low sustainability of this soil management. The C/N ratio of the soil increased significantly under all treatments, but mainly under the traditional and organic treatments (from 12.1 and 12.8 to 13.7 and 14.0, respectively). This indicates a decrease in humus quality. In addition, the C/N of the humin increased significantly (from 13.3 and 12.7 to 19.2 and 16.0, respectively).     

Presence of Hippidion at two sites of western Argentina: Diet composition and contribution to the study of the extinction of Pleistocene megafauna

The composition of Hippidion diet, and possible changes that could relate to its extinction, were evaluated in the Argentinean-Chilean Central Andes, a Neotropical environment characterized by arid to semiarid conditions (Andean hot and cold deserts). Microhistological analyses were made on feces of Hippidion found at Los Morrillos (31°43′S–68°42′W, 3000 m a.s.l.) and Gruta del Indio (34°35′S, 68°22′W, 660 m a.s.l.). At Gruta del Indio the diet of Hippidion was based mainly on woody species. At Los Morrillos, it was based on herbaceous species.This flexibility in diet composition could be a relative adaptive advantage allowing a longer permanence of this species in comparison to others recorded in the region (such as Megatheriumand Mylodon). Nevertheless, this advantage was not enough to guarantee its survival during the Holocene. Extinction could have been affected by diverse agents, such as growing aridification of the area, increasing competition with other species (mainly Lama guanicoe), and human presence, along with a relatively low population density (as expected from the limited presence of Hippidion at the archaeological and palaeontological sites of South America. At Gruta del Indio significant changes in the diet of Hippidion corresponding to different intervals of the period 31,000–9000 ¹⁴C BP are not evident. Given this evidence for similar diets for Hippidion throughout the late Quaternary, other factors need to be considered to explain the extinction of this horse.     

The influence of tectonically derived relief and climate on the extent of the last Glaciation east of the Patagonian ice fields (Argentina, Chile)

Two large ice fields between 46°30′ and 51°30′S cover the Patagonian Andes. The North and South Patagonian Ice Fields are separated by the transandine depth line at 47°45′ to 48°15′S. Canal and Río Baker run through this depression. The two ice fields are generally considered relics of a continuous ice cap, which covered the entire Patagonian Andes from 39° to 52°S and extended far into the eastern foreland of the Andes. This assumption is not correct for the 200-km-long section of the Andes between Lago Pueyrredón (Lago Cochrane in Chile) (47°15′S) and Lago San Martín (Lago O'Higgins in Chile) (48°45′S). The lack of a continuous ice cap extending far into the east is caused by the transandine depth line, playing a crucial role in the fluvial erosion and the glacial scouring of this tectonic zone. This depression formed a river system (e.g. Río Baker, Río Bravo and Río Mayer) that drains towards the west. Reconstruction of the maximum glacial advance of the last ice age shows that the eastern outlet glaciers of the two ice fields between Lago San Martín and Lago Pueyrredón did not drain towards the east, but rather followed the general gradient of the transandine depth line. In this area the eastern flank of the Andes between Monte San Lorenzo (3770 m) and Sa. de Sangra (2155 m) supported valley glaciers, which were independent of the expanding ice fields. Only a few valley glaciers advanced towards the Patagonian Meseta. The terminal moraines of these glaciers were erroneously interpreted as the eastern edge of a continuous ice cap. North of 47°30′S the outlet glaciers of the NPI advanced 200 km during the LGM and the late glacial advances nearly reached to 71°W. In contrast, south of 49°S glacier expansion was comparatively less: The LGM is situated only 85–115 km east of the present margins of the large outlet glaciers (O'Higgins, Viedma, and Upsala), and no late glacial advance reached 72°W. These considerable differences of glacier expansion were influenced by the northward migration of the westerly precipitation belt during glacial cycles. There is tentative evidence that the glaciers advanced three times in the period from 14 000 to 9 500 ¹⁴C years BP.     

The geochemical significance in early sedimentation of geolipids obtained by saponification of lacustrine sediments

Significant quantities of solvent-inextractable geolipids, obtained by saponification of solvent extracted sediments, were found in various sedimentary samples including soils, river inlet sediment and lake sediments from Lake Suwa.The carbon isotopic composition ($\text{δ}{}^{13}\text{C}$) of extractable and inextractable geolipids from the same sediment sample were similar. Moreover, the carbon number distributions of sterols in the two geolipid fractions from the same sediment were also similar.Whereas the ratios of both lipids and sterols to total organic carbon for the extractable geolipids in the lake sediments decreased with depth, the former ratio for inextractable giolipids tends to increase with depth and the latter remains fairly constant. On the other hand, the stanol to stenol ratio of the extractable fraction increased with depth but that of the inextractable fraction was lower than that of the extractable fraction and was fairly constant irrespective of sediment depth.The transformation of extractable sterols into inextractable ones was not observed during incubation for 1200 days of sterols with Suwa sediments.Thus, the following conclusions were made: (1) the extractable and inextractable geolipids have similar origins, (2) some constituents of the latter may be protected from chemical or microbiological degradation and transformation in the sediments, and (3) the transformation of some constituents of the former into the inextractable ones virtually does not occur after incorporation into Suwa sediments.These results suggest that some constituents of the inextractable geolipid fraction may provide fundamental information on early diagenetic alteration of geolipids in lake sediments and on the relatively recent paleoenvironment.     

Expansion of Magellanic Moorland during the late Pleistocene: Palynological evidence from northern Isla de Chiloé, Chile

The late Quaternary vegetation of northern Isla de Chiloé is inferred from palynological analysis of a section in the Río Negro drainage (42°03′S, 73°50′W). At ca. 30,500 yr B.P., maxima of Astelia and Donatia occurred, suggesting wetland development. From that time until ca. 27,000 yr B.P., steppe indicators such as Compositae/Gramineae dominated, suggesting drier conditions. After 27,000 yr B.P., the moorland shrub Dacrydium gradually increased, reaching a maximum by 18,000 yr B.P. At this time Astelia increased again, suggesting development of cushion bog during cold and wet conditions. The glacial-postglacial transition is characterized by a marked change from peaty sediments to clays, a decrease in the cushion bog flora, and the prevalence of Gramineae/ Compositae and swamp taxa. This vegetation prevailed until ca.7000 yr B.P. when forest taxa became dominant. The floristic pattern inferred from the pollen spectra of the Rio Negro section suggests that the late Pleistocene vegetation of Chiloé resembled modern Magellanic Moorland vegetation (52°–56°lat S). Based on climatic conditions presently associated with Magellanic Moorland, its occurrence in Chiloé at low elevations during the late Pleistocene implies a decrease in average temperature of at least 4°C and an increase in annual precipitation of at least 1500 mm.     

Natural-abundance radiocarbon as a tracer of assimilation of petroleum carbon by bacteria in salt marsh sediments

The natural abundance of radiocarbon (¹⁴C) provides unique insight into the source and cycling of sedimentary organic matter. Radiocarbon analysis of bacterial phospholipid lipid fatty acids (PLFAs) in salt-marsh sediments of southeast Georgia (USA)—one heavily contaminated by petroleum residues—was used to assess the fate of petroleum-derived carbon in sediments and incorporation of fossil carbon into microbial biomass. PLFAs that are common components of eubacterial cell membranes (e.g., branched C₁₅ and C₁₇, 10-methyl-C₁₆) were depleted in ¹⁴C in the contaminated sediment (mean Δ¹⁴C value of +25 ± 19‰ for bacterial PLFAs) relative to PLFAs in uncontaminated “control” sediment (Δ¹⁴C = +101 ± 12‰). We suggest that the ¹⁴C-depletion in bacterial PLFAs at the contaminated site results from microbial metabolism of petroleum and subsequent incorporation of petroleum-derived carbon into bacterial membrane lipids. A mass balance calculation indicates that 6-10% of the carbon in bacterial PLFAs at the oiled site could derive from petroleum residues. These results demonstrate that even weathered petroleum may contain components of sufficient lability to be a carbon source for biomass production by marsh sediment microorganisms. Furthermore, a small but significant fraction of fossil carbon is assimilated even in the presence of a much larger pool of presumably more-labile and faster-cycling carbon substrates.     

Complex geometry and segmentation of the surface rupture associated with the 14 November 2001 great Kunlun earthquake, northern Tibet, China

The 14 November 2001 Kunlun, China, earthquake with a moment magnitude (M_w) 7.8 occurred along the Kusai Lake–Kunlun Pass fault of the Kunlun fault system. We document the spatial distribution and geometry of surface rupture zone produced by this earthquake, based on high-resolution satellite (Landsat ETM, ASTER, SPOT and IKONOS) images combined with field measurements. Our results show that the surface rupture zone can be divided into five segments according to the geometry of surface rupture, including the Sun Lake, Buka Daban–Hongshui River, Kusai Lake, Hubei Peak and Kunlun Pass segments from west to east. These segments, each 55 to 130 km long, are separated by step-overs. The Sun Lake segment extends about 65 km with a strike of N45° 75°W (between 90°05′E 90°50′E) along the previously unrecognized West Sun Lake fault. A gap of about 30 km long exists between the Sun Lake and Buka Daban Peak where no obvious surface ruptures can be observed either from the satellite images or field observations. The Buka Daban–Hongshui River, Kusai Lake, Hubei Peak and Kunlun Pass segments run about 365 km striking N75° 85°W along the southern slope of the Kunlun Mountains (between 91°07′E 94°58′E). This segmentation of the surface rupture is well correlated with the pattern of slip distribution measured in the field. Detailed mapping suggest that these five first-order segments can be further separated into over 20 second-order segments with a length of 10–30 km, linked by smaller scale step-overs or bends.Our result also shows that the total coseismic surface rupture length produced by the 2001 Kunlun earthquake is about 430 km (excluding the 30-km-long gap), which is the longest coseismic surface rupture for an intracontinental earthquake ever recorded.Finally, we suggest a multiple bilateral rupture propagation model that shows the rupture process of the 2001 M_w 7.8 earthquake is complex. It consists of westward and eastward rupture propagations and interaction of these bilateral rupture processes.     

Diagenesis of organic matter in suspended particles and sediments in the Cariaco Trench

Suspended particulate materials and bottom sediments from the Cariaco Trench were analysed for lipid content to investigate the diagenesis of organic matter in an anoxic water column and sediment. Distributions of fatty acids, sterols, and the acyclic isoprenoid hydrocarbons, lycopane and 2,6,10,15,19-pentamethyleicosane, support the hypothesis that alteration of organic matter usually attributed to sedimentary diagenesis occurs in the water column. Typical indicators of diagenetic processes, including preferential loss of unsaturated fatty acids, increased abundances of branched fatty acids, stenol-to-stanol conversion, and abundant acyclic isoprenoids, were observed in the water column across the oxic/anoxic interface in the Cariaco Trench. Lipid distributions in the sediment were remarkably uniform with depth. We conclude that organic material delivered to the sediment has been extensively altered in the water column, but that which is buried is preserved without much additional alteration.     

Influence of HCl/HF treatment on organic matter in aquifer sediments: A Rock-Eval pyrolysis study

Rock–Eval pyrolysis is increasingly used for the routine characterization of natural organic matter in soils and sediments. In this work the bulk composition of sedimentary organic matter (SOM) in sandy aquifer sediments is studied, as well as purified samples (isolation of SOM) by HCl/HF treatment. This treatment is necessary to avoid detection limit problems for samples with low SOM contents, but the results presented here indicate that this treatment influences the organic geochemistry of the aquifer sediment samples. The FID and CO₂/CO pyrograms show a shift of 10–40 °C of the major peak to a lower temperature. Organic matter alteration or removal of components containing O-bearing groups may explain this. It is also suggested that destruction of the mineral matrix may lead to the reduced retention of the material. For the change of the CO₂/CO pyrograms of the RC fraction only organic matter alteration seems to be likely. Concentrated organic matter samples may also accelerate the release of exothermic energy and influence the pyrograms. Results indicate that the organic matter concentration in the sample influences the measured total organic matter (TOM) content and the T_max of the FID pyrogram, while the sample loading (absolute organic matter amount) up to 80 mg in the Rock–Eval apparatus does not. The FID pyrograms can be deconvoluted into four subpeaks, which allows comparison of samples at various depths. Rock–Eval pyrolysis may only be routinely applied to characterize SOM in aquifer sediments when such systematic and analytical phenomena are taken into account.     

Spatial relationships between natural seismicity and faults, southeastern Ontario and north-central New York state

A statistical analysis was carried out to investigate spatial associations between natural seismicity and faults in southeastern Ontario and north-central New York State (between 73°18′ and 77°00′W and 43°30′ and 45°18′N). The study area is situated to the west of the seismically active St. Lawrence fault zone, and to the east of the Lake Ontario basin where recently documented geological and geophysical evidence points to possible neotectonic faulting. The weights of evidence method was used to judge the spatial associations between seismic events and populations of faults in eight arbitrarily defined orientation groups. Spatial analysis of data sets for seismic events in the periods 1930–1970 and post-1970 suggest stronger spatial associations between earthquake epicentres and faults with strikes that lie in the NW–SE quadrants, and weaker spatial associations of epicentres with faults that have strikes in the NE–SW quadrants. The strongest spatial associations were determined for groups of faults with strikes between 101° and 146°. The results suggest that faults striking broadly NW–SE, at high angles to the regional maximum horizontal compressive stress, are statistically more likely to be spatially associated with seismic events than faults striking broadly NE–SW. If the positive spatial associations can be interpreted as indicating genetic relationships between earthquakes and mapped faults, then the results may suggest that, as a population, NW–SE trending faults are more likely to be seismically active than NE–SW striking faults. Detailed geological studies of faults in the study area would be required to determine possible neotectonic displacements and the kinematics of the displacements.     

Evolution of Isotopic Carbon Dioxide–Water Systems in Lithogenesis: Communication 1. Sedimentogenesis and Diagenesis

Isotope-geochemical features of the formation of carbon and oxygen isotopic compositions in sedimentary and diagenetic carbonates are considered. Isotopic criteria for the identification of early diagenesis zone are proposed. The transition from sedimentogenesis to diagenesis (upper boundary of the early diagenesis zone) is accompanied by the alteration of carbon isotopic composition in the HCO^– _{3(hydrosphere)}–HCO^– _{3(pore water of sediment)}system. The lower boundary of early diagenesis zone is registered by the alteration of oxygen isotopic composition in the pore water of sediments and authigenic carbonates.     

Sandstone diagenesis in the Pattani Basin (Gulf of Thailand): history of water-rock interaction and comparison with the Gulf of Mexico

In the Pattani Basin, a failed-rift basin, extensive water-rock interaction has occurred between subquartzose alluvial sandstones of Miocene age and their pore fluids. Diagenetic rates and pathways have been strongly influenced by high geothermal gradients, high CO₂ fugacities, and low pore water salinities. Depositional pore water was fresh to brackish, depending on the depositional environment of the sediments. Chloride concentrations in modern formation water are believed primarily to reflect the proportions of river and sea water in the depositional environment. However, the concentration of other important solutes and the isotopic composition of the formation waters can not be explained by roportional mixing of these two end-member waters. Dissolution of detrital plagioclase (An = 3) and K- feldspar are reactions of major significance that are reflected chemically in the Na/Cl and K/Cl ratios of the formation water. Despite the high temperature of the sandstones (120–200°C), diagenetic albite does not occur. Geochemical calculations indicate the formation water is undersaturated with respect to both orthoclase and albite. This style of feldspar diagenesis differs significantly from that of sandstones of similar composition in other basins, and has probably influenced other aspects of silicate diagenesis.Important authigenic minerals are: 1. locally abundant calcite cement (δ¹³C= −12.8, δ¹⁸O= −17.3 PDB), an early diagenetic phase that formed at about 60°C; 2. pore-filling kaolinite (δ¹⁸O= 9.9, δD= −83.5SMOW) that was closely associated with feldspar dissolution and formed over a range of temperatures; and 3. fibrous pore-lining and pore-bridging illite (δ¹⁸O = 9.8, δD = − 86.7 SMOW, the last significant cement, formed at temperatures of 120 to 150°C. Potassium/argon dates on illite indicate that sandstone diagenesis took place during a period of rapid sedimentation in the first two-thirds of the burial history.Comparison of Pattani Basin diagenesis with diagenesis of sandstones of similar age in other sedimentary basins demonstrates that chemical diagenesis, relative to mechanical compaction, has been especially rapid in the Pattani Basin. This reflects the effect of high temperatures on reaction rates. The net effect is a high average rate of porosity loss with burial (11% km).     

Allochthonous versus autochthonous naturally occurring organic matter in the Anllóns river bed sediments (Spain)

Despite of the importance of the aquatic ecosystems as organic matter pools within the global carbon cycle, specific studies in river sediments are still insufficient. This study was carried out in an Atlantic basin where nine sites were selected in the lowest middle stretch of the River. The analyses include total organic carbon, C/N ratios, humus composition (humic, fulvic and humin), A2/A4 and A4/A6 ratios, biologically active organic matter (BAOM), water soluble organic matter (WSOC) and coloured water soluble organic carbon (CWSOC). The results suggested a predominance of allochthonous sources to the organic matter, highly influenced by the land uses together with the river hydrodynamics, namely urban and forest at sites 1, 2 and 9, and agricultural at sites 7 and 8. The 38% of the total organic matter was humic and fulvic acids. The biologically active organic matter, which may act as a proxy of microbial activity, showed a mean value of 0.9% of the total organic matter, showing the lowest values at sites with the highest organic matter total, soluble or coloured. This coloured organic matter represented an average of 3.60% of the total organic matter, and showed the highest visible light absorption at those sites more affected by human activities, close to centres of population (1, 2 and 9). This coloured fraction showed also a high degree of photostability. C/N ratios were less effective to discriminate between allochthonous or autochthonous sources, whereas A4/A6 ratios were effective to estimate variations of autochthonous sources, as it measures the variations of phytopigments of the river bed sediments.     

Temperature induced decoupling of enzymatic hydrolysis and carbon remineralization in long-term incubations of Arctic and temperate sediments

Extracellular enzymatic hydrolysis of high-molecular weight organic matter is the initial step in sedimentary organic carbon degradation and is often regarded as the rate-limiting step. Temperature effects on enzyme activities may therefore exert an indirect control on carbon mineralization. We explored the temperature sensitivity of enzymatic hydrolysis and its connection to subsequent steps in anoxic organic carbon degradation in long-term incubations of sediments from the Arctic and the North Sea. These sediments were incubated under anaerobic conditions for 24 months at temperatures of 0, 10, and 20 °C. The short-term temperature response of the active microbial community was tested in temperature gradient block incubations. The temperature optimum of extracellular enzymatic hydrolysis, as measured with a polysaccharide (chondroitin sulfate), differed between Arctic and temperate habitats by about 8-13 °C in fresh sediments and in sediments incubated for 24 months. In both Arctic and temperate sediments, the temperature response of chondroitin sulfate hydrolysis was initially similar to that of sulfate reduction. After 24 months, however, hydrolysis outpaced sulfate reduction rates, as demonstrated by increased concentrations of dissolved organic carbon (DOC) and total dissolved carbohydrates. This effect was stronger at higher incubation temperatures, particularly in the Arctic sediments. In all experiments, concentrations of volatile fatty acids (VFA) were low, indicating tight coupling between VFA production and consumption. Together, these data indicate that long-term incubation at elevated temperatures led to increased decoupling of hydrolytic DOC production relative to fermentation. Temperature increases in marine sedimentary environments may thus significantly affect the downstream carbon mineralization and lead to the increased formation of refractory DOC.     

The characteristics and source of laminated mud at Lake Barrine, Northeast Australia

In a small (1 km²) crater lake in the Australian upland tropics (17°15′S, 145°38′E, 721 m a.s.l.), laminated mud has accumulated throughout the past 5 ka. It is limited to a central region below 50–67 m of water where it is protected by a monimolimnion. The contents of the laminae (e.g., total lake products, organic detritus, diatoms, pollen grains, vivianite crystals) distinguish two contrasting types, namely detritus-rich and detritus-poor. Judged against radiocarbon dates over long sequences, these couplets are not annual. Gravimetric, mineralogical and chemical observations on the mud, and on suspended organic and inorganic matter caught through several periods, indicate some diagenetic changes across the mud–water interface. Diatom analyses do not assist in relating mud type to source or period of origin. The most likely mechanism of lamination is that continuous deposition of clay, with small and varied detrital accompaniment, is periodically enhanced by greater detrital input. This occurs in some, but not all, periods of winter isothermy when ground temperatures fall to zero and below on several consecutive nights. This leads to the stirring of sediments in water shallower than 50 m and their relocation in the deeper meromictic zone. Fine variations in, e.g., diatom content, partly independent of lamination type, probably contain a wealth of detail about the lake’s environmental history.     

河西猪野泽沉积物有机地化指标之间的关系及古环境意义

探讨了河西走廊石羊河终端湖泊--猪野泽晚冰期以来沉积物总有机碳(TOC)、碳氮比(C/N)、有机碳同位素(δ13C)三种有机地球化学指标之间的关系及古环境意义.结果表明:猪野泽QTH01剖面沉积物TOC指标主要代表湖泊及流域的植被初级生产力;C/N值受到周围区域表土C/N值和沉积物成岩过程的双重影响,总体较低,并不能直...