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11121. 题目: Correction for the siderite effect on Rock-Eval parameters: Application to the sediments of Lake Barombi (southwest Cameroon)
文章编号: N18060133
期刊: Organic Geochemistry
作者: David Sebag, Yannick Garcin, Thierry Adatte, Pierre Deschamps, Guillemette Ménot, Eric P. Verrecchia
更新时间: 2018-06-01
摘要: Originally developed for use in the petroleum industry, Rock-Eval pyrolysis is a technique commonly applied to lake sediments to infer paleoenvironmental reconstructions. The standard Rock-Eval parameters provide information on the amount of total organic and inorganic carbon (TOC and MinC, respectively), and are usually interpreted as proxies for the source (aquatic or terrestrial) of the primary production of organic matter (Hydrogen Index vs Oxygen Index). Although this method usually provides valuable evidence, the common presence of siderite in tropical lake sediments can alter the primary signal of the sedimentary organic matter (SOM). Indeed, the CO2 and CO released by the pyrolysis of siderite are integral to the calculation of the SOM-related standard Rock-Eval parameters. In this study, we analyze sediments from a core collected in the Lake Barombi (southwest Cameroon) and describe the impact of siderite on standard Rock-Eval parameters. We propose a workflow that allows standard Rock-Eval parameters to be corrected, based on the analysis of thermograms. The proposed corrections provide siderite-effect-free parameters, accurately reflecting the changes in sedimentary organic matter composition.

11122. 题目: Determination and geochemical implication of multiple series of long-chain oxygen-bearing compounds trapped in kerogen in the Lucaogou Formation, Santanghu Basin, NW China
文章编号: N18060132
期刊: Organic Geochemistry
作者: Bin Cheng, Jianbing Xu, Yungan Liang, Qian Deng, Yankuan Tian, Zewen Liao
更新时间: 2018-06-01
摘要: Studies of occluded oxygen-bearing compounds inside kerogen are scarce, although such studies are important in understanding early-stage transformation of organic matter. A relatively low-maturity kerogen from the late Permian mudstone of the Lucaogou Formation of the Santanghu Basin, northwestern China, was successively extracted with n-hexane, acetone and dichloromethane to release the adsorbed components, and the extracted kerogen was treated with a mild oxidation reagent H2O2 to release the occluded components. Gas chromatography–mass spectrometry analysis of the adsorbed and occluded components revealed a suite of oxygen-bearing compounds, including n-alkan-2-ones, n-aldehydes and fatty acid methyl esters. The n-alkan-2-ones were mainly detected in the adsorbed fraction and n-aldehydes in the occluded component. Comparison of the long-chain oxygen-bearing compound distributions and their individual stable carbon isotope characteristics both suggest that the oxygen-bearing compounds released by H2O2 treatment were occluded in the kerogen. The shorter-chain (C15 to C19) occluded n-aldehydes reflected similar isotopic distribution trends to the adsorbed n-alkan-2-ones, and the δ13C values of the mid-length (C21 to C25) occluded n-aldehydes were much closer to the adsorbed n-alkanes. Bacterially mediated methylation and decarbonylation of the n-aldehydes during kerogen formation may be important source(s) of n-alkan-2-ones and n-alkanes, respectively. The mid-chain ketones mainly originated from hydrothermal alteration of n-alkanes after kerogen formation. Uplift of the Lucaogou Formation in the Yuejingou section allowed surface-enhanced aerobic reactions.

11123. 题目: Effect of simulated diagenesis on the compositions, chemical stability and sorption properties of natural and engineered organic matter with different mineral contents
文章编号: N18060131
期刊: Organic Geochemistry
作者: Lanfang Han, Ziying Wang, Marco Keiluweit, Yan Yang, Ke Sun, Zheyun Zhang, Baoshan Xing
更新时间: 2018-06-01
摘要: Despite the abundance of diagenetically derived organic materials in the environment, the effects of diagenesis on the structure and some of the associated properties (e.g., stability and sorption behavior) of organic matter (OM) remain unclear. Here, subcritical water treatment, suggested previously to mimic the diagenesis process, was chosen to further investigate the impact of diagenesis on OM compositions, stability and sorption of selected hydrophobic organic compounds. Humic acids and biochars were selected as representatives of natural and engineered OM, respectively. To examine the impact of mineral constituents on the diagenesis of OM, de-ashed samples, as well as samples amended with minerals (kaolinite, calcite and calcium dihydrogen phosphate), were included in the diagenesis treatment system. Comparison of OM composition before and after treatment indicated that simulated diagenesis resulted in lower bulk polarity, higher surface polarity and aromaticity and greater microporosity. Thermal analysis and chemical oxidation suggested that as a result of the increase in aromaticity and decrease in O/C ratio of OM, the resistance of OM to thermal and chemical oxidation was enhanced after simulated diagenesis. Moreover, our diagenesis treatment of OM induced stronger sorption nonlinearity and higher sorption capacity, for phenanthrene. Additionally, minerals protected the structure of OM from being changed by simulated diagenesis. Consequently, with regard to the susceptibility of OM to oxidative decay, the presence of minerals mitigated the increase in chemical stability imparted by simulated diagenesis but, on the other hand, protected OM from degradation.

11124. 题目: Geochemical characterization of lacustrine and marine oils from off-shore Brazilian sedimentary basins using negative-ion electrospray Fourier transform ion cyclotron resonance mass spectrometry (ESI FTICR-MS)
文章编号: N18060130
期刊: Organic Geochemistry
作者: Ygor dos Santos Rocha, Rosana Cardoso Lopes Pereira, Jo?o Graciano Mendon?a Filho
更新时间: 2018-06-01
摘要: Lacustrine and marine crude oils from different off-shore Brazilian basins were analyzed using a 7.2 Tesla LTQ FTICR-MS instrument. The samples were analyzed via electrospray ionization in the negative ion mode focusing on the polar compounds, i.e., nitrogen-, sulfur-, and oxygen-containing (NSO) compounds. We also employed a combination of other geochemical methods, such as GC-FID and GC-MS analyses, to characterize and assess the depositional environments of the different oil families. The results indicate that lacustrine oils tend to be enriched in Nx compounds, while marine oils show preference for Ox compounds. The dominant heteroatomic classes in crude oils are N1, followed by O1, O2, and N1O1 with remarkable differences in their distributions between marine and lacustrine, strongly suggesting the control by the kerogen type of the heteroatomic compounds found in these crude oils. Considerable differences in the DBE distribution of the main classes analyzed between the crude oils allowed an efficient geochemical characterization regarding their origin. The use of negative ESI FTICR-MS as a geochemistry tool can provide additional information beyond that obtained with currently employed geochemical methods, resulting in the full comprehension of crude oil composition.

11125. 题目: Influence of vegetation type on n-alkane composition and hydrogen isotope values from a high latitude ombrotrophic bog
文章编号: N18060129
期刊: Organic Geochemistry
作者: Nicholas L. Balascio, William J. D'Andrea, R. Scott Anderson, Stephen Wickler
更新时间: 2018-06-01
摘要: The composition and hydrogen isotope values of leaf wax components can be powerful tools in reconstructing past climate and environments. However, interpretation of past environmental conditions from such components in sediments is complicated by species-specific influences and there is a need to better understand how vegetation type affects leaf wax composition and isotope ratios in modern environments. In this study we analyzed leaf wax (n-alkane) distributions and hydrogen isotope values of plants from a high latitude ombrotrophic bog in northern Norway. The isotopic analysis of surface water was also conducted on samples from 15 lakes along a ca. 150 km transect to contextualize the bog water isotopic composition and constrain fractionation factors among n-alkane homologues. We identified 14 different plant types growing on the bog surface, including mosses, graminoids and other herbs, sub-shrubs and a tree. n-Alkanes from the leaves of the modern plants had average chain lengths from 25 to 30.5, with a variety of distributions, and with the dominant compound of longer chain lengths (C27, C29, or C31). δD values of n-C25 to n-C33 for the vegetation samples ranged from -197‰ to -116‰, with an average of -162‰. The data also revealed that the δD values for the homologues for half of the vegetation types had ranges that were ≥20‰. Using the average isotopic value of bog water samples, -60‰, we calculated apparent fractionation factors that ranged from -66‰ to -134‰ (avg. -108 ± 22‰), similar to other sites across Europe and to a global data compilation. Our results demonstrate the range of species-specific influences on leaf wax composition and isotopic values at this site and presumably other ombrotrophic bog environments, and provide a dataset to help evaluate the influence of vegetation type on regional sedimentary leaf wax records.

11126. 题目: Modelling leaf wax n-alkane inputs to soils along a latitudinal transect across Australia
文章编号: N18060128
期刊: Organic Geochemistry
作者: S. Howard, F.A. McInerney, S. Caddy-Retalic, P.A. Hall, J.W. Andrae
更新时间: 2018-06-01
摘要: Leaf wax n-alkanes provide a valuable palaeoecological proxy, but their interpretation requires an understanding of the scale of temporal and spatial integration in soils. Leaf wax n-alkanes are continually deposited into soils directly from local plants as well as from more distant plants via wind or water transport. In addition, n-alkanes can persist in soils for thousands of years, and tend to decrease in age with shallower depth. To explore whether the uppermost soils reflect recent leaf fall inputs we compared surface soils and modern vegetation from 20 sites along a transect across Australia. At each site, the three most dominant plant species and a soil sample from the top 3 cm were analysed for n-alkane concentration, average chain length (ACL), proportional abundance of C33 and C29 (Norm33) and carbon preference index (CPI). Chain length distributions differ between trees and grasses, with a higher proportion of C29 in trees and C33 in grasses. Norm33 in soils correlates with proportional grass to tree cover across the transect. To model n-alkane inputs for each site, we calculated a predicted ACL, Norm33 and CPI using the dominant plants at that site, weighted by proportional species cover and n-alkane concentration. Predicted ACL, Norm33 and CPI inputs were generally higher than the soils, demonstrating that recent and local inputs do not dominate soil n-alkanes at our study sites. Thus, n-alkane distributions in surface soils do not correlate with local, current vegetation, but do correlate with proportional grass and tree cover, suggesting they provide a faithful record of large scale ecosystem structure.

11127. 题目: n-Alkan-2-one biomarkers as a proxy for palaeoclimate reconstruction in the Mfabeni fen, South Africa
文章编号: N18060127
期刊: Organic Geochemistry
作者: Andrea Baker, Joyanto Routh, Alakendra N. Roychoudhury
更新时间: 2018-06-01
摘要: The sub-tropical Mfabeni fen is the only continuous coastal peat deposit that documents glacial and interglacial palaeoenvironmental conditions since the late Pleistocene (ca. 47 cal kyr BP) in southern Africa. Published bulk geochemical, biomarker and leaf wax δ13C data, along with palynology and stratigraphic studies of the Mfabeni peat sequence, render it an ideal record for testing new palaeoreconstruction proxies. In this study, we aimed to establish the proxy potential of n-alkan-2-one (n-ket) compounds by tracing their source/origin and post-depositional diagenetic change, and if they preserve or not a robust palaeoenvironment signal that complements our understanding of palaeoclimatic variations. In the Mfabeni archive the most likely source for n-kets is via microbial decarboxylation of n + 1-alkanoic acids (n-FAs) and, to a lesser degree, oxidation of same chain length n-alkanes (n-alks). The n-ket average chain length (ACLket) and n-C23 and C25ket/precursor ratios displayed a statistical significant negative relationship with the n-alk aquatic plant proxy (Paq), suggesting the source of n-kets to be submerged aquatic plants during waterlogged conditions that suppressed microbial activity during the ensuing anoxic conditions. Both the mid-chain and long chain n-ket/precursor ratios displayed predominant water level fluctuation controls, with temperature as a secondary regulator. By comparing the n-ket data with published environmental and climate reconstructions from the same core, and with geomorphology and palynological studies of the Mfabeni basin, we conclude that the n-kets show promise as a palaeoclimate proxy and can be used in conjunction with other biomarker proxies to reconstruct ancient hydrological changes in sub-tropical peatlands.

11128. 题目: On the changes of polycyclic aromatic compounds in waterflooded oil and their implications for geochemical interpretation
文章编号: N18060126
期刊: Organic Geochemistry
作者: Xiangchun Chang, Yue Wang, Yaohui Xu, Jing Cui, Tao Wang
更新时间: 2018-06-01
摘要: Qudi oilfield had been producing for over twenty years and became waterflooded ten years ago. Samples from nine producing wells drilled recently in the Qudi oilfield were collected during the three recovery stages spanning an eight month interval of waterflooding and were analyzed for changes in their polycyclic aromatic compounds (PACs). The results indicate that most of waterflooded oils are characterized by increased tricyclic, tetracyclic, pentacyclic and triaromatic steroids concentrations. The irregular changes in parameters based on two or fewer alkyl-substituted naphthalenes (MNR, ENR, DBR, DNR-1) implies a different depletion order for the PACs because the abundances of the compounds are controlled by the predominance of water washing and biodegradation over a certain time. The increase in DBTs and DBFs with water washing reflects their strong resistance to biodegradation. Lower aqueous solubility and strong resistance to biodegradation are possibly responsible for the mainly unchanged values of the three or more alkylnaphthalene-related parameters (TNR-1, TDE-1, TDE-3, TBR and TeBR), tricyclic aromatics (MPI-1 and PP-1), tetracyclic aromatics (MCI, MCI2, 2-MC/1-MC, and BaA/(BaA + Chry)), triaromatic steroids parameters (C26-TAS/C28-TAS, C27-TAS/C28-TAS, C28-TAS 20S/(20R + 20S), and TA(I)/TA(I + II)), and heterocyclic aromatic parameters (4-MDBT/DBT, 4-MDBT/1-MDBT, and 4,6-DMDBT/(1,4 + 1,6)-DMDBT), confirming their validity for geochemical interpretation even after extensive water washing. However, pentacyclic aromatic parameters (BeP/Pe, (BeP + BaP)/Pe, BF/Pe, and BF/BeP), which are theoretically expected to be unaffected, change significantly with the advance of the waterflooding process, implying a complex alteration mechanism that needs further investigation.

11129. 题目: Organic matter in sediments of a tropical and upwelling influenced region of the Brazilian continental margin (Campos Basin, Rio de Janeiro)
文章编号: N18060125
期刊: Organic Geochemistry
作者: Lívia G.M.S. Cordeiro, Angela L.R. Wagener, Renato S. Carreira
更新时间: 2018-06-01
摘要: Lipid biomarkers [fatty acids (FAs), sterols and alcohols] and carbon stable isotopes (δ13C values) in surface sediments from 9 cross shelf transects (25–3000 m water depth) from the Campos Basin, SE Brazilian continental margin were analyzed. The aim was to investigate the link between the prevailing regional specific oceanographic conditions (upwelling events, intrusion of cold and nutrient-rich water, low river input) and the nature and distribution of organic matter (OM) in the basin. A general predominance of OM from autochthonous processes, but with a relevant spatial gradient in the quality and quantity of the sedimentary OM, was observed. On the shelf (<150 m), concentrations of lipids were usually low, except in areas influenced by upwelling, but the presence of labile compounds suggested the occurrence of fresh OM in the sediment. The export of continental OM was observed only in shelf sediments near the Paraíba do Sul River. The upper and middle slope (400–1300 m) exhibited the highest concentrations of total organic carbon (TOC) and lipids, but lipid biomarkers suggested the presence of OM with a high degree of bacterial degradation. This may result from the export of material from shallow areas, possibly due to the action of eddies and meandering of the Brazil Current and bottom currents in the region. On the lower slope (1900–3000 m), only the more recalcitrant compounds were above detection limit. The presence of labile lipids in high amount in the shelf and slope suggests the presence of OM with a high potential for supplying the food requirements of heterotrophic organisms in the sediment, which may in turn have a major influence on the ecology of benthic communities.

11130. 题目: Patterns of change in permanganate oxidizable soil organic matter from semiarid drylands reflected by absorbance spectroscopy and Fourier transform ion cyclotron resonance mass spectrometry
文章编号: N18060124
期刊: Organic Geochemistry
作者: Carlos M. Romero, Richard E. Engel, Juliana D'Andrilli, Chengci Chen, Catherine Zabinski, Perry R. Miller, Roseann Wallander
更新时间: 2018-06-01
摘要: Organic matter (OM) oxidized by slightly alkaline KMnO4, termed permanganate-oxidizable carbon (POXC), has recently emerged as a standardized indicator of active, labile carbon within soil quality frameworks. Yet, qualitative information on POXC, particularly in semiarid drylands, is very scarce. The aim of this study was to characterize POXC within three long-term field experiments in Montana, USA: (i) across a wide range of edaphic (e.g., % clay) and management conditions (e.g., cropping intensity) (n = 148); and (ii) to identify the molecular composition of soil OM before and after KMnO4 treatment using electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI FT-ICR MS). The content of POXC was significantly greater under perennial (382–685 mg/kg) or annual cropping (404–607 mg/kg) than fallow-wheat (359–543 mg/kg) systems. Soil OM changes, however, were equally or better expressed when considering soil organic carbon (SOC) concentration. The occurrence of POXC paralleled SOC (R = 0.87; P < 0.001) and total nitrogen (TN) (R = 0.82; P < 0.001) concentrations, regardless of soil textural differences. The ESI FT-ICR MS analyses of aqueous soil extracts indicated that the KMnO4 reaction oxidized dissolved OM of diverse molecular character. OM molecular composition after KMnO4 treatment was enriched by strongly reduced chemical constituents (O/C < 0.4) at greater condensed aromaticity (AI > 0.67) and hydrogen saturation (aliphatic composition; H/C > 1.5) across all heterogeneous groups (CcHhNnOoSs). Although POXC is a rapid assay widely used for characterizing soil OM dynamics, it may not provide a clear advantage over SOC concentration in semiarid drylands. The view of POXC as a merely labile, simple biodegradable OM fraction needs to be reconsidered.

11131. 题目: Production and turnover of microbial organic matter in surface intertidal sediments
文章编号: N18060123
期刊: Organic Geochemistry
作者: Weichao Wu, Travis Meador, Kai-Uwe Hinrichs
更新时间: 2018-06-01
摘要: Benthic microorganisms play a significant role in the remineralization of sedimentary organic matter (OM). In order to constrain the growth rate, turnover and carbon metabolism of microbial communities in anoxic sandy sediments, we quantified the rate of inorganic carbon (IC) assimilation and of lipid production via a recently developed dual isotope-labelling assay that can differentiate autotrophic vs. heterotrophic production in a 22 cm sediment core from the Janssand tidal flat (Wadden Sea, Germany). Despite an extremely low concentration of total organic carbon (TOC) in the majority of samples (<0.3%), the concentration of total fatty acids (TFAs) was in the range 4.5 to 28.4 μg/mg TOC, suggestive of a high contribution of fresh microbial and algal biomass to the TOC pool. This was corroborated by a production rate of microbial FAs, which ranged from 0.3 to 4.7 μg TFAs/gdw/yr (where dw = dry wt) and the mean turnover time of microbial FAs was 6 ± 5 yr. The enhanced production rate of iso- and anteiso-branched FAs was consistent with the presence of an active population of sulfate reducing Deltaproteobacteria. The assimilation rate of IC into bacterial lipids was relatively low (0.16 ± 0.07 μg C/gdw/yr) in OM-lean sandy sediments (i.e. upper 17 cm), such that the IC assimilation to lipid production ratio values was typically <0.3, indicating that heterotrophic bacteria were dominant and dark IC fixation played a minor role at the study site. The measured rates of FA production converted to an anaerobic heterotrophic C demand of 0.4–1.8 g C/gdw/d, assuming a bacterial growth efficiency of 10%. Such high biomass proportion, production rate and C demand suggested that dissolved OM must play a vital role in sustaining the active heterotrophic microbial populations in these sandy sediments.

11132. 题目: Wax lipids in fresh and charred anatomical parts of the Celtis australis tree: Insights on paleofire interpretation
文章编号: N18060122
期刊: Organic Geochemistry
作者: Margarita Jambrina-Enríquez, Antonio V. Herrera-Herrera, Carolina Mallol
更新时间: 2018-06-01
摘要: Leaf waxes have been assumed to be the dominant source of wax delivered to sediment. However, wooden branches and twigs have not been widely considered in this context and could be a potential source of wax lipids in fire places or combustion structures. Black sedimentary layers are the main material of open-air archaeological combustion structures and represent either carbonized fuel (wood) or the charred ground beneath the fire (mainly leaves) and it is difficult to discern between the two sources. To identify different plant parts as components of combustion residues, fresh and charred leaves, branches and twigs (bark and xylem) of the Celtis australis tree were analyzed for aliphatic and aromatic hydrocarbons and fatty acid concentrations, as well as the carbon isotopic composition of n-alkanes (δ13Calkane). Charred biomass was produced under limited oxygen conditions at 150, 250 (3 and 5 h), 350 and 450 °C for 1h. The n-alkyl profiles in different parts of C. australis are sufficiently distinct to allow their identification as components of combustion structures under low combustion temperature conditions. Average chain lengths and carbon preference index ratios decrease with increasing temperature and vary among plant parts. The δ13Calkane values remained slightly unaltered until 350 °C and changed by 3–4‰ at 450 °C. Our results provide new information on the molecular and isotopic changes that occur upon burning different plant parts, which in turn show potential for good preservation of organic matter in archaeological black layers and for positive identification of burned leaf and wood residues in them.
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11133. 题目: What is the meaning of Hydrogen-to-Carbon ratio determined in Archean organic matter?
文章编号: N18060121
期刊: Organic Geochemistry
作者: Frédéric Delarue, Sylvie Derenne, Kenichiro Sugitani, Fran?ois Baudin, Frances Westall, Barbara Kremer, Romain Tartèse, Adriana Gonzalez, Fran?ois Robert
更新时间: 2018-06-01
摘要: The search for hydrocarbon molecular biomarkers in Archean metasediments is of prime importance for deciphering the early evolution of life. Suitable criteria are required to identify promising targets for further molecular biomarkers. Possible criteria include the Hydrogen-to-Carbon (H/C) atomic ratio used as a proxy of the aliphatic content of the kerogen matrix. However, H/C ratio values exhibit large variation in Archean kerogens and their significance remains poorly understood. In this study, we thus investigate the significance of the H/C ratios of Archean kerogens by combining elemental analyses, Nanoscale Secondary Ion Mass Spectrometry (NanoSIMS), Rock-Eval pyrolysis and Raman spectroscopy. First, NanoSIMS investigations show the H/C ratio of kerogen can be compromised by residual minerals. In addition, Rock-Eval pyrolysis underlines the fact that thermal cracking of Archean kerogens does not just release hydrocarbon covalently linked to the macromolecular network but also a complex mixture of organic pools distinguished by their thermal maturity. Therefore, the H/C ratio alone cannot be used to probe the preservation of aliphatic compounds bound to kerogen since it can be biased by the presence of (i) residual bitumen, as well as (ii) refractory organic matter in secondary hydrothermal veins whose syngenecity is debatable. Rock-Eval pyrolysis then provides a useful and complementary method to check the significance of H/C atomic ratio as a proxy for hydrocarbon preservation in Archean kerogens.

11134. 题目: Inter-molecular variations of fatty acid δD in algae and submerged plants from the north-eastern Tibetan Plateau
文章编号: N18060120
期刊: Organic Geochemistry
作者: Hu Liu, Hong Yang, Yunning Cao, Qin Leng, Weiguo Liu
更新时间: 2018-06-01
摘要: Hydrogen isotopic compositions (δD) of fatty acids (FAs) in lake sediments have been widely used in palaeoenvironmental reconstruction, but investigations on FA δD values in algae and submerged plants from natural lakes are still limited, greatly hampering the application and interpretation of their δD values in lacustrine environments. Here, we systematically investigated δD values of short-chain (C14–C18), mid-chain (C20–C24), and long-chain (C26–C30) FAs in four algae and submerged macrophytes, two algal genera Chara and Cladophora and two angiosperm genera Potamogeton and Ruppia, that commonly occur in six lakes on the north-eastern Tibetan Plateau. We obtained the following results: (i) C20–C30 FAs in each algal and submerged plant sample have similar variation patterns in δD values, suggesting that δD values of C20–C30 FAs have consistent responses to their source water δD. In C4-like taxa (Potamogeton, Ruppia, and Chara), the C16 and C26 FAs have minor differences in their δD values, while in the C3-like Cladophora, δD values of C16 FAs are significantly more negative (avg. –48 ± 7‰) than that of the C26 FAs. We propose that different photosynthetic mechanisms in these algae and submerged plants account for the different inter-molecular δD variations between C16 and C26 FAs; (ii) δD values of C26 FAs in the carbonate-coated alga Chara are significantly correlated with the δ18O values of carbonate encrustations – such a co-variance suggests that in addition to lake water, other factors may also influence both lipid synthesis and carbonate encrustation building up in Chara, leading to a significantly positive apparent hydrogen isotope fractionation factors (εFA-W) between C26 FAs of Chara and lake water; (iii) δD values of C26 FAs from Potamogeton, Ruppia and Cladophora are correlated well with lake water δD values (R 2 = 0.84, p < 0.001, n = 19), suggesting that the δD values of long-chain FAs potentially record δD variations of lake water with the apparent hydrogen isotope fractionation factors (εFA-W) of C26 FAs ranging from -153‰ to -134‰. Our results highlight the impact of different photosynthetic pathways on the inter-molecular difference of FA δD values in algae and submerged plants and illustrate both the potential and the challenge of applying their FA δD values as a palaeo-hydrology proxy.

11135. 题目: Impact of CO2 on the elemental composition of the particulate and dissolved organic matter of marine diatoms emerged after nitrate depletion
文章编号: N18060119
期刊: Limnology and Oceanography
作者: Koji Sugie, Takeshi Yoshimura, Masahide Wakita
更新时间: 2018-06-01
摘要: Although the dissolved inorganic carbon concentration, pH, and nutrient regimes of seawater dramatically change in coastal regions, the synergistic effects of changes in the CO2 and nutrient levels on the elemental dynamics of the particulate and dissolved organic matters (DOMs) produced by diatoms are rarely investigated. Here, we investigated the impacts of four different CO2 levels (180, 380, 600, and 1000 μatm partial pressure of CO2 : pCO2) on the allocation of carbon, nitrogen, phosphorus, and silicon between the particulate matter (PM) and DOM in two cosmopolitan coastal diatoms, Chaetoceros affinis and Ditylum brightwellii, under nutrient‐replete and nitrate‐depleted conditions. Under nutrient‐replete conditions, the specific growth rates of both species were positively correlated with pCO2 levels. The elemental compositions of the exponentially growing diatoms were stable under the different pCO2 conditions. After nitrate depletion, the particulate organic carbon to particulate nitrogen ratio and biogenic silica content per unit biomass in both species were positively correlated with the pCO2 value. Factors affecting the pCO2 dependent change in elemental composition were the variations in the partitioning of organic carbon between PM and DOM in C. affinis, and the physiological uncoupling of intracellular carbon and nitrogen and the intracellular silicon and nitrogen, as well as resting spore formation in D. brightwellii. Under high‐CO2 conditions, the faster growth rates of both diatom species could lead to their dominance in a phytoplankton community; their blooms could modify the first‐order processes in the biogeochemical cycling of bioelements after nitrate depletion.

11136. 题目: Light may have triggered a period of net heterotrophy in Lake Superior
文章编号: N18060118
期刊: Limnology and Oceanography
作者: Soren Brothers, Paul Sibley
更新时间: 2018-06-01
摘要: Recent studies of Lake Superior, the Earth's largest freshwater lake by surface area, describe it as net heterotrophic (primary production < community respiration), making it a net source of carbon dioxide (CO2) to the atmosphere. This conclusion is largely based on measurements made between 1998 and 2001. We present a long‐term (1968–2016) analysis of ice‐free (April–November) surface oxygen (O2) saturation data collected by monitoring agencies. These data indicate that Lake Superior's surface waters are typically supersaturated with dissolved O2 from May to September (May–September mean is 103.5% ± 0.6%; pooled mean from April, October, and November is 97.6% ± 1.1%, standard error of the mean). However, these data also support prior studies which describe a state of net heterotrophy from 1998 to 2001. We investigated potential triggers for a transient heterotrophic period and discuss the sources of organic carbon necessary to fuel net heterotrophy in a large oligotrophic lake. We conclude that net heterotrophy likely resulted from an increase in light period and penetration driven by declines in cloud cover, increases in water clarity, and a reduction of winter ice cover following the 1997–1998 El Ni o. Together, these could have depleted a pre‐existing pool of dissolved organic carbon (DOC) via photomineralization and/or photochemical degradation. Our results indicate that Lake Superior is typically net autotrophic (calculated annual CO2 influx = 0.4 Tg C). These results highlight how water clarity and aquatic DOC pools may interact to induce net metabolic shifts in large oligotrophic aquatic ecosystems

11137. 题目: Shallow ponds are biogeochemically distinct habitats in salt marsh ecosystems
文章编号: N18060117
期刊: Limnology and Oceanography
作者: Amanda C. Spivak, Kelsey M. Gosselin, Sean P. Sylva
更新时间: 2018-06-01
摘要: Runaway expansion of shallow ponds can catalyze the conversion of vegetated marshes into open water environments. Predicting how this transition affects ecosystem functioning is difficult because little is known about pond biogeochemistry. We characterized sediment organic matter sources and transformations in three ponds with different plant communities, over alternating periods of tidal isolation and flushing, during summer and fall, using a combination of stable isotopes, lipid biomarkers, and benthic fluxes. Sediment respiration rates (1.66 ± 0.09 mmol C m-2 d-1 to 28.53 ± 7.76 mmol C m-2 d-1) were comparable to shallow estuaries and driven by sulfate reduction. Rates varied across ponds, reflecting differences in summertime Ruppia maritima and macroalgae abundances, but were similar between seasons. Interactions between aboveground plant and sediment bacterial communities translated into distinct biogeochemical processes across the three ponds. Tidal isolation and summer weather intensified plant and bacterial community effects on pond carbon dynamics, resulting in algal biomass and lipid δ13C values that were 3–12‰ enriched, compared to nearby habitats. Surface sediment organic matter mainly derived from pond microalgae and was compositionally distinct from tidal creeks and marshes. Surprisingly, sediment bacteria were not tightly coupled to benthic microalgae but decomposed multiple carbon sources in surface sediments and became increasingly reliant on buried peat at deeper horizons. Pond development over time could largely be explained by sediment respiration and the simultaneous accretion of the surrounding marsh platform. The role of decomposition in pond expansion is consistent with previous assessments based on whole‐pond metabolism rates. Consequently, future pond expansion could alter ecosystem biogeochemistry and reduce carbon storage.

11138. 题目: Spatiotemporal transformation of dissolved organic matter along an alpine stream flowpath on the Qinghai-Tibetan Plateau: importance of source and permafrost degradation
文章编号: N18060116
期刊: Biogeosciences
作者: Yinghui Wang, Robert G. M. Spencer, David Podgorski, Anne Kellerman, Harunur Rashid, Phoebe Zito, Wenjie Xiao, Dandan Wei, Yuanhe Yang, and Yunping Xu
更新时间: 2018-06-01
摘要: The Qinghai-Tibetan Plateau (QTP) accounts for approximately 70% of global alpine permafrost and is an area sensitive to climate change. The thawing and mobilization of ice and organic carbon-rich permafrost impact hydrologic conditions and biogeochemical processes on the QTP. Despite numerous studies of Arctic permafrost, there are no reports to date for the molecular-level in-stream processing of permafrost-derived dissolved organic matter (DOM) on the QTP. In this study, we examine temporal and spatial changes of chemical composition of DOM and 14C age of dissolved organic carbon (DOC) along an alpine stream (3850–3207m above sea level) by Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS), accelerator mass spectrometry (AMS) and UV-visible spectroscopy. Compared to downstream sites, the DOM at the headstream exhibited older radiocarbon (14C-DOC) age, higher mean molecular weight, higher aromaticity and fewer polyunsaturated components. At the molecular level, 6409 and 1345 formulas were identified as unique to the active layer (AL) leachate and permafrost layer (PL) leachate, respectively. Comparing permafrost leachates to the downstream site, 59% of AL-specific formulas and 90% of PL-specific formulas were degraded, likely a result of rapid instream degradation of permafrost-derived DOM. From peak discharge in the summer to low flow in late autumn, the DOC concentration at the headstream site decreased from 13.9 to 10.2mg/L, while the 14C-DOC age increased from 745 to 1560 years before present (BP), reflecting an increase in relative contribution of deep permafrost carbon due to the effect of changing hydrological conditions over the course of the summer on DOM source (AL vs. PL). Our study thus demonstrates that hydrological conditions impact the mobilization of permafrost carbon in an alpine fluvial network, the signature of which is quickly lost through in-stream metabolism.

11139. 题目: Evidence of high N2 fixation rates in productive waters of the temperate Northeast Atlantic
文章编号: N18060115
期刊: Biogeosciences
作者: Debany Fonseca-Batista, Xuefeng Li, Virginie Riou, Valérie Michotey, Forian Deman, Fran?ois Fripiat, Sophie Guasco, Natacha Brion, Nolwenn Lemaitre, Manon Tonnard, Morgane Gallinari, Hélène Planquette, Frédéric Planchon, Géraldine Sarthou, Marc Elskens, Lei Chou, and Frank Dehairs
更新时间: 2018-06-01
摘要: Diazotrophic activity and primary production (PP) were investigated along two transects (Belgica BG2014/14 and GEOVIDE cruises) off the western Iberian Margin and the Bay of Biscay (38.8–46.5°N; 8.0–19.7°W) in May 2014 close to the end of the spring bloom. We report substantial N2 fixation activities, reaching up to 65nmolNL-1d-1 and 1533 molNm-2d-1 close to the Iberian Margin between 38.8°N and 40.7°N. Similar figures in the basin have only been reported in the temperate and tropical western North Atlantic waters with coastal, shelf or mesohaline characteristics, as opposed to the mostly open ocean conditions studied here. In agreement with previous studies, the qualitative assessment of nifH gene diversity (encoding the nitrogenase enzyme that fixes N2) suggested a predominance of heterotrophic diazotrophs, and the absence of filamentous cyanobacteria. At the sites where N2 fixation activity was highest sequences affiliated to UCYN-A1, obligate symbiont of eukaryotic prymnesiophyte algae, were recovered. The remaining phylotypes were non-cyanobacterial diazotrophs, known to live in association with suspended particles and zooplankton (i.e., Bacteroidetes, Firmicutes and Proteobacteria). Outside the area of exceptional activity, N2 fixation in the open ocean and at shelf-influenced sites was also relatively high, ranging from 81 to 384 molNm-2d-1, but was undetectable in the central Bay of Biscay. We propose that the unexpectedly high heterotrophic N2 fixation activity recorded at the time of our study was sustained by the availability of phytoplankton derived organic matter (dissolved and/or particulate) resulting from the ongoing to post spring bloom. We pose that this organic material not only sustained bacterial production, but also provided sufficient nutrients essential for the nitrogenase activity (e.g., phosphorus). Dissolved Fe was supplied through atmospheric dust deposition during the month preceding our study and through advection of surface waters from the subtropical region and the shelf area. Our findings stress the need for a more detailed monitoring of the spatial and temporal distribution of oceanic N2 fixation in productive waters of the temperate North Atlantic to better constrain the basin-scale nitrogen input to the ocean inventory.

11140. 题目: Dissolved and colloidal copper in the tropical South Pacific
文章编号: N18060114
期刊: Geochimica et Cosmochimica Acta
作者: Saeed Roshan, Jingfeng Wu
更新时间: 2018-06-01
摘要: Copper (Cu) as a bioactive trace metal in the ocean has widely been studied in the context of chemical speciation. However, this trace metal is extremely understudied in the context of physical speciation (i.e., size- or molecular weight-partitioning), which may help in characterizing dissolved Cu species. In this study, we determine total dissolved Cu (<0.2 μm) distribution and its physical speciation along the US GEOTRACES 2013 cruise, a 4300-km east-west transect in the tropical South Pacific. The distribution of dissolved Cu is rather uniform horizontally and exhibits a linear increase with depth from surface to 2500–3000 m, below which it varies less significantly both vertically and horizontally. Dissolved Cu shows a strong correlation with silicate (SiO4 4-) in the upper 1500 m, which is in agreement with previous studies in other regions. This correlation is weaker but with higher slope at depths below 1500 m, which supports the sedimentary source hypothesis. Although hydrothermal activity at the East Pacific Rise (EPR) does not show a readily evident impact on the dissolved Cu distribution, high-quality data at 2300–2800 m allow for diagnosing a subtle westward decrease in the background-subtracted dissolved Cu component. This component of dissolved Cu poorly correlates with mantle-derived 3He (R2 = 0.41), indicating a possible hydrothermal source for dissolved Cu, in contrast to previous studies. For the first time in a major basin, we also determined the physical speciation of dissolved Cu, which shows that Cu species lighter than 10 kDa (Da = 1 g mol-1) dominate the pool of dissolved Cu (<0.2 μm) below 1000 m with a contribution of 61 ± 6% (fraction of total dissolved). 39 ± 6% of dissolved Cu at depths below 1000 m, thus, occurs in the pool of colloidal matter (10 kDa–0.2 μm). Moreover, using a suite of molecular weight cutoffs indicate that Cu species are distributed between two distinct molecular weight classes: the lighter than 5 kDa and heavier than 300 kDa classes, which form 53 ± 6% and 37 ± 7% of dissolved Cu at 2200–2800 m, respectively. The Cu species with molecular weight between 5 kDa and 300 kDa contribute only to 10 ± 12% of the pool at 2200–2800 m. These results offer new insights into structure, reactivity and bioavailability of oceanic Cu compounds. As an organic-dominating metal, Cu physical speciation may also shed light on size-reactivity spectrum of dissolved organic matter (DOM) in the deep ocean.

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