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1.
选自长江口F2-F5站住的4个表层沉积物及其粒度分级（1～8Ф）样品,经过孢粉相和热解检测,探讨有机质特征及其在碳循环中的命运。未分级样品的孢粉相主要由木质组织、丝炭和黑团块组成,显示陆地输入有机质的贡献巨大。样品分级后,孢粉相面貌发生显著变化。细粒的8函中无定形为主,其他粒级（2～7Ф）中主要由结构有机质组成。细粒的...  相似文献   

2.
To assess settling particulate organic matter (POM) seasonality and its availability to the benthic community, settling particulate matter was studied in terms of mass fluxes and main biogeochemical characteristics (including organic carbon (OC), nitrogen, and stable carbon and nitrogen isotopic values) at two Lake Superior offshore sites over the course of a year. Fourier transform infrared spectroscopy (FTIR) and hydrolysis, extraction, and derivatization were used to provide further compositional information. Carbon and nitrogen content, isotopic and wet chemical data, and FTIR spectra show that summer particulate material is mainly autochthonous, with higher proportions of amide and carbohydrate. FTIR shows that spring particulate material contains relatively high proportions of clay minerals, indicating major sources from sediment resuspension and/or spring runoff. Distinct amino acid distributions at the two sites, revealed by principal component analysis (PCA) based on amino acid mol% composition, possibly result from differences in OM sources and the degree of degradation occurring at the two sites. Carbohydrate (PCHO), total hydrolyzable amino acid (THAA) and FTIR data suggest that the nutritional value of bulk POM to benthic heterotrophs should be lower in spring than summer-fall, although both periods exhibited high sinking fluxes of total mass and OC. Due to sediment resuspension events and an oxic water column, organic matter eventually buried in Lake Superior’s sediments has probably experienced extensive alteration due to several cycles through the water column and the bacterially-active sediment-water interface.  相似文献   

3.
Molar organic carbon to total nitrogen to organic phosphorus (OC:TN:OP) ratios are used in tandem with carbon isotopic values to constrain sources of organic matter (OM) to marine sediments in a tropical coastal embayment. Analysis of end-members specific to the study site indicates that the bulk OM pool cannot be modeled as a simple mixture of two end-members (terrestrial vs. marine OM), but rather reflects a more complex, multicomponent mixture. Mangrove, coral reef ecosystems, and bacterial biomass contribute OM to tropical coastal marine sediments that is compositionally distinct from traditional marine and terrestrial end-members and thus preclude the application of a classical two end-member mixing model of the sort that has been used traditionally in sediments from temperate environments. A survey of elemental ratios and carbon isotopic values of potential OM end-members reported in the literature, as well as depth profiles before and after whole-core incubation experiments conducted as part of this study, were used to evaluate the strength of OC:TN versus OC:OP ratios as OM source indices. Our study suggests that OC:TN ratios are a weaker indicator of OM source than OC:OP ratios, because: (1) the more restricted dynamic range of OC:TN ratios prevents clear distinction of terrestrial-from marine-derived OM, and (2) post-depositional changes in OC:TN ratios occur during diagenesis, obscuring the source signature of initially deposited OM. The fidelity of OM indices during early diagenesis underscores the importance of quantifying OP in sediments to assess sedimentary OM source.  相似文献   

4.
Density fractionation, X-ray photoelectron spectroscopy (XPS) and amino acid analyses were used to evaluate the physical form of preserved organic carbon (OC) in sediments from transects in the north east Pacific Ocean off the Mexican (Mazatlan) and Washington coasts. Low density (i.e. mineral-free) organic material dominated the OC in sediments with very short oxygen exposure times (OET <1 yr; total wt% OC 7.9-9.3, ∼70% in ρ < 1.9 fractions). Quantities of low density OC decreased with increasing OET, suggesting that organic-rich debris was oxygen-sensitive. As OET increased from years to decades, OC was found predominately in the form of organic-mineral aggregates (58-77% of total OC was in the 1.9-2.2 ρ mesodensity fraction). Aggregated OC then decreased in abundance as a function of OET, suggesting that long-term oxygen exposure leads to destruction of organic-mineral aggregates. At OET values of centuries to millennia, the dominant forms of organic matter were OC sorbed to mineral surfaces (∼50% of total) and OC locked within biogenic diatom frustules (∼22% of total). These two physical forms of OC in marine sediments may provide the best long-term protection for OC.  相似文献   

5.
Mineral-associated organic matter (OM) represents a large reservoir of organic carbon (OC) in natural environments. The factors controlling the extent of the mineral-mediated OC stabilization, however, are poorly understood. The protection of OM against biodegradation upon sorption to mineral phases is assumed to result from the formation of strong bonds that limit desorption. To test this, we studied the biodegradation of OM bound to goethite (α-FeOOH), pyrophyllite, and vermiculite via specific mechanisms as estimated from OC uptake in different background electrolytes and operationally defined as ‘ligand exchange’, ‘Ca2+ bridging’, and ‘van der Waals forces’. Organic matter extracted from an Oa forest floor horizon under Norway spruce (Picea abies (L.) Karst) was reacted with minerals at dissolved OC concentrations of ∼5-130 mg/L at pH 4. Goethite retained up to 30.1 mg OC/g predominantly by ‘ligand exchange’; pyrophyllite sorbed maximally 12.5 mg OC/g, largely via ‘van der Waals forces’ and ‘Ca2+ bridging’, while sorption of OM to vermiculite was 7.3 mg OC/g, mainly due to the formation of ‘Ca2+ bridges’. Aromatic OM components were selectively sorbed by all minerals (goethite ? phyllosilicates). The sorption of OM was strongly hysteretic with the desorption into 0.01 M NaCl being larger for OM held by ‘Ca2+ bridges’ and ‘van der Waals forces’ than by ‘ligand exchange’. Incubation experiments under aerobic conditions (initial pH 4; 90 days) revealed that OM mainly bound to minerals by ‘ligand exchange’ was more resistant against mineralization than OM held by non-columbic interactions (‘van der Waals forces’). Calcium bridges enhanced the stability of sorbed OM, especially for vermiculite, but less than the binding via ‘ligand exchange’. Combined evidence suggests that the extent and rate of mineralization of mineral-associated OM are governed by desorption. The intrinsic stability of sorbed OM as related to the presence of resistant, lignin-derived aromatic components appears less decisive for the sorptive stabilization of OM than the involved binding mechanisms. In a given environment, the type of minerals present and the solution chemistry determine the operating binding mechanisms, thereby the extent of OM sorption and desorption, and thus ultimately the bioavailability of mineral-associated OM.  相似文献   

6.
Sorptive stabilization of organic matter in soils by hydrous iron oxides   总被引：5，自引：0，他引：5  
Strong correlations between iron oxides (FeOx) and organic matter (OM) in soils have implied the importance of the former in stabilizing the latter. One mechanism thought to be important in this stabilization is sorption. We tested this possibility by reductively dissolving FeOx in a wide variety of soils and measuring the organic carbon (OC) that was solubilized. The OC dissolved from non-FeOx phases via anion exchange was corrected for by parallel control extractions. The resultant pool, reductively soluble OC, made up a minor amount of total soil OC in all but one of these soils, indicating that simple sorption reactions do not stabilize the bulk of soil OC in most mineral soils. OC:Fe ratios in the extracts from 2/3 of these soils were less than 0.22 (wt/wt), consistent with a sorbed state for this OC and showing that OC sorption by FeOx in these soils is limited by the amount of FeOx. The remaining soils had low pH and high OM concentrations; their higher OC:Fe ratios indicate inclusion of precipitated organo-Fe complexes in the extracts, which are likely only partially extracted by our method. The high volumetric ratios of OM to FeOx found in correlations between them from the literature are inconsistent with a dominant sorption control and point instead to stabilization to other mechanisms such as organo-Fe complexes or ternary associations among FeOx, OM and other minerals.  相似文献   

7.
Inherent chemical recalcitrance and association of organic matter (OM) with minerals are mechanisms responsible for the long term preservation of OM in soils. The structural characteristics of OM are also believed to control specific interactions between OM and soil minerals. However, the extent of the relationship between recalcitrance and mineral protection and the specificity of these chemically driven interactions are not clearly understood at the molecular level. To measure chemical patterns of OM sequestration in sand-, silt-, clay-size and light fractions, we analyzed three soils, which mainly differed in carbon content and overlying vegetation, but have similar clay mineralogy, using biomarker analysis and nuclear magnetic resonance (NMR). Despite differences in environmental controls, long chain aliphatic compounds generally accumulated in the fine fractions of all soils. This accumulation is likely due to the strong interaction between recalcitrant forms of OM and soil minerals. For example, polymethylene and >C20 organic acids accumulated in fine fractions, while lignin-derived phenols were protected from oxidation in silt-size fractions. Diffusion edited solution state 1H NMR suggested that contributions from microbial-derived OM was greater in finer fractions, which is likely due to the accumulation of microbial-derived compounds or higher microbial activity in clay micro-sites. Our data suggest that, for these Prairie soils, the specific structure of OM and not environmental factors is responsible for long term preservation of OM in mineral fractions. Further research is necessary to understand the interplay between these preservation mechanisms such that the long term fate of OM can be further elucidated.  相似文献   

8.
To examine the biogeochemistry of amino acids (AAs) in the sediment of Lake Taihu, surface sediments (0–3 cm) and deeper sediments (18–21 cm) were collected at 21 sites from different ecotype zones of the lake. AAs were extracted from the sediments, and the total hydrolyzable amino acids (THAA) were determined by high-performance liquid chromatography instrument. The THAA contents in Taihu sediment were much lower than that in marine sediments, ranging from 6.84 to 38.24 μmol g−1 in surface sediments and from 2.91 to 18.75 μmol g−1 in deeper sediments in Taihu, respectively. AAs were a major fraction of the organic matter (OM) and organic nitrogen in Taihu sediments. The AAs on average contributed 8.2% of organic carbon (OC) and 25.0% of total nitrogen (TN) from surface sediments, and 5.9% of OC and 20.5% of TN in deeper sediments, respectively. AA composition provided very useful information about the degradation of OM. Glycine (Gly) and lysine (Lys) were the predominant forms of AAs in the sediments, irrespective of lake regions, followed by alanine, glutamic acid, serine (Ser), and aspartic acid (Asp). The high concentrations of Gly, Lys, and Ser suggested that these forms of AAs were relatively refractory during OM degradation in sediments. The relationship between the Asp/Gly ratio and Ser + Thr [mol%] indicated that OM in surface sediment was relatively fresher than that in deeper sediments. The AAs-based degradation index (DI) gave a similar conclusion. The composition and DI of AAs in surface sediments are markedly different across different zones in Taihu. The percentages of AAs to organic carbon (AA-C%) and total nitrogen (AA-N%) were higher in phytoplankton-dominated zones than those in macrophyte-dominated zones. These results suggest that DI could provide useful information about the degradation of OM in shallow lakes such as Taihu.  相似文献   

9.
Newly vegetated sites provide opportunities to enlighten organic matter (OM) transformation mechanisms in soils and sediments at very early stages of development which, in turn, is relevant to better understand general ecosystem functioning. Mine acid soils and sediments in the Lusatian open cast lignite mining district (Germany) contains a high concentration of fossil carbon (lignite) in ad mixture with recent OM from the local vegetation, both contributing to the humified OM pool. In this study, analytical pyrolysis (Py–GC–MS) was used to monitor the different C sources (lignite or plant derived) in developing mine tailing soils and sediments and their degree of degradation in contrasting environments. Representative vegetation and the organic carbon (OC) rich soil/sediment fraction (humus fraction) were sampled at two depths (0–5 and 5–10 cm) in three plots along a transect covering an upland forest soil, a partially submerged sediment at the land–water interface and a constantly submerged sediment. The analysis of plant (lipds, isoprenoids, methoxyphenols and carbohydrates) and possible lignite (alkyl napththalenes, alkyl benzenes and PAHs) biomarkers released after pyrolysis supports previous findings in the area using other proxies. It was possible to discern OM sources in soil/sediment humus fractions, both from the substrate (lignite) as well as from the prevailing vegetation of the area. Environmental conditions in the submerged sediment seem to favour OM protection and the accumulation of decomposing plant material, whereas more intense OM degradation seems to prevail in the land–water interface areas characterized by fluctuating water level. In addition, a well resolved series of organic sulfur compounds (OSCS) found in the submerged sediments of rehabilitated acid lakes, indicates the possible occurrence of particular mechanisms of C preservation in this extreme anoxic S rich environment, i.e. via sulphur “quenching” with plant derived lipids during early diagenesis.  相似文献   

10.
粘土矿物保存海洋沉积有机质研究进展及其碳循环意义   总被引：3，自引：0，他引：3  
海洋沉积物吸附有机质的量和有机质循环周期与粘土矿物类型和吸附方式密切相关,并在全球碳循环中扮演着不同的角色。粘土吸附有机质有物理吸附和化学吸附之分,前者主要存在于粘土的微孔隙中,参与年、十年或百年尺度的循环;后者主要存在于粘土矿物层间和外表面,稳定性较好,有机质易于保存,可参与百万年或更长时间的循环,这种不同时间尺度内的碳循环,将会改写海洋沉积物有机碳“源”、“汇”的关系。不同类型粘土矿物的性质存在差异,决定了吸附有机质量的多寡,蒙脱石的吸附量远大于伊利石的吸附量,这可能是造成全球不同海域中有机碳“源”、“汇”变化的原因。海洋沉积物处于水圈、生物圈和岩石圈的交汇地带,有机碳的差异和变化,都会对全球碳循环及气候变化产生重要的影响。  相似文献   

11.
Burial of organic carbon (OC) in ocean sediments acts as the ultimate long-term sink for both terrestrial and marine carbon, however, the mechanisms controlling the preservation of this carbon are poorly understood. To better understand these mechanisms, we applied solid-state 13C nuclear magnetic resonance (NMR) spectroscopy, along with elemental, stable carbon isotopic (δ13C) and lignin phenol analyses, to size and density fractions of sediments influenced by either mixed terrestrial and marine OC inputs (Washington Coast slope) or dominantly marine inputs (Mexican Margin). Elemental, isotopic and lignin analyses all reveal that within the Washington Coast sediment, the OC mixes linearly between nitrogen-poor and 13C-depleted, lignin-rich OC in the large and light fractions and nitrogen-rich and 13C-enriched, lignin-poor OC in the small and dense fractions, suggesting that this sediment contains a two-component mixture of terrestrial vascular plant- and marine-derived OC. The integral areas of each of seven NMR spectral regions in the different samples trend linearly when plotted versus δ13C signature, with most R2 values of 0.78 or greater, demonstrating that the NMR spectra of the two sources of carbon also mix linearly between the two endmembers. The terrestrial endmember in this sediment appears to be dominated by lignin and black carbon whereas the source of the marine endmember is less clear from the NMR spectra. In contrast, all of the analyses indicate that OC in the Mexican Margin sediment fractions is homogenous and derives almost exclusively from marine sources. It appears that selective preservation of (bio)chemically recalcitrant lignin and black carbon is the primary mechanism of preservation of terrestrial OC, whereas mineral-protection is the dominant mechanism preserving marine OC in the Washington coast sediment. There is little evidence showing that either preservation mechanism functions in the Mexican Margin sediments.  相似文献   

12.
The copper (Cu) distributions and speciation in the surface sediment collected from Nansi Lake (NL) (China) were investigated by chemical and physical fractionation methods. Sediment was first fractionated into four grain size fractions (< 63, 78–163, 163–280, and > 280 μm) in wet condition. Each fraction was then further divided into two density sub-fractions (low and heavy) by flotation in sodium-polytungstate solution (ρ = 2.0 g/cm3). In addition, a three-stage extraction procedure following the European Communities Bureau of Reference (BCR) protocol was applied to study the speciation distribution of Cu among grain size fractions. It was found that the speciation distributions of Cu among different grain size fractions were quite close to each other, although the total Cu concentrations were different in the individual fractions. Moreover, Cu mainly occurred in the coarser, low density, OC-rich fractions. Extractable Cu, which was dominated by reducible and oxidizable parts, occupied almost 80% of the total Cu concentration. Total Cu concentrations in grain size fractions and density sub-fractions ranged from 29.6 to 72.9 and from 21.4 to 156 mg/kg dw, respectively. It was noted that low-density fractions had 4–7 times higher Cu concentrations and 5–12 times higher organic carbon (OC) content than those in high-density fractions. The results demonstrated that OC was a main factor influencing Cu distributions in either grain size or density fractionated sediment. This study suggests that the role of the Cu-rich fraction should be considered when conducting the remediation of Cu contamination in NL.  相似文献   

13.
The particulate organic matter in < 63 µm surface sediments from the Mackenzie River and its main tributaries was studied using Rock-Eval pyrolysis and organic petrology. The organic matter in the sediments is dominated by refractory residual organic carbon (RC) of mainly terrigenous nature, as indicated by abundant inertinite, vitrinite, and type III kerogen. Sediments from the tributaries contained significantly more algal-derived organic matter than from the main channel of the river, highlighting the importance of low-energy system dynamics in the tributaries, which allows modest algal production, more accumulation, and better preservation of autochthonous organic matter. This is particularly true for tributaries fed by lacustrine systems, which showed the highest S1 and S2 fractions, and consequently higher total particulate organic carbon (POC) in the basin. Organic petrology of the sediment samples confirms abundant liptinitic materials (i.e., fat-rich structured algae, spores and pollen, cuticles, and resins). Forest fire and coal deposits are also confirmed to contribute to the basin. Assuming that suspended and fine surfacial sediments have a similar OC composition, the Mackenzie River is estimated to deliver a total POC flux of 1.1 Mt C/yr to its delta, of which 85% is residual carbon with liptinitic OC (S1 + S2) and S3 accounting for another 9% and 6%, respectively.  相似文献   

14.
The interaction of organic compounds with the mineral phase is considered as one stabilization mechanism for organic carbon (OC) in soils. The objective of this study is to assess the role of mineral surfaces for the long-term stabilization of OC in arable soils, with special emphasis on iron oxides. Soil samples were taken from two contrasting treatment types, i.e. fertilized plots and C-depleted plots, in long-term agroecosystem experiments. The soil organic carbon pool of the C-depleted plots is considered to show a lower contribution of labile compounds and consequently to be relatively enriched in refractory compounds compared with the fertilized counterparts. In fractions <6 μm, OC was studied in relation to total mineral surface area, surface area contributed by oxides and silicates, and the content and type of iron oxides (dithionite and oxalate extractable iron, Fed and Feo). In two sandy soils, OC contents were linearly related to total mineral surface area and the content of the two iron oxide fractions (Fed and Feo). The surface area developed by the silicates was low and thus the surface area contribution from oxides was dominant in fractions <6 μm. In contrast to the sandy soils, in a loamy soil OC was not correlated with surface area or the iron oxide content. However, the different soils agreed with respect to the behavior of C in density fractions: losses of OC occurred mainly from the light fraction (2 g cm−3), whereas C in the heavy fraction (>2 g cm−3) proved to be stable. For the sandy soils, mineral surface area appears to control the storage of OC in fine fractions. Given the dominant surface area contribution from oxides, OC storage here primarily depends on the oxides. The C-depleted plots in particular show that surface area controls the accumulation of refractory C. The interaction of organic compounds with the mineral phase, mainly with the surface of oxides, seems to be a major mechanism for the long-term stabilization of OC in these sandy soils. An interaction with minerals seems to be important for stabilizing OC also in the loamy soil, although this is not reflected by a proportional relation between OC and surface area across the fractions.  相似文献   

15.
Sources of organic matter (OM) and lipids were assessed and factors affecting OM degradation were studied for two sediment cores representing distinct depositional regimes (i.e., the oscillating oxic to suboxic/anoxic western basin and oxic Zaka Bay) for eutrophic Lake Bled, NW Slovenia. Lower surface organic carbon (OC) concentration was determined in the western basin than for Zaka Bay sediments (5.1 vs. 5.4 wt% dry sediment, respectively), but one order of magnitude greater total lipid concentration was observed in the former. Also, there was a higher proportion of autochthonous OM in the western basin (77% vs. 66%) on the basis of atomic C/N ratios. Lipid-based origin assessment suggested a similar contribution of autochthonous OM in the western basin (64–77%), but a lower one in Zaka Bay (<50%). It seems that redox potential is the main factor governing OM degradation in the western basin. In contrast, a contribution from more refractory terrestrial OM, via the surface inflow in Zaka Bay, and higher sedimentation rates may surpass redox effects in Zaka Bay. Overall, oxygen may play a more important role in degradation of the more labile pool (i.e., lipids) than bulk OM. Higher apparent degradation rate constants (k′) for lipids also suggested a greater lability than for OC, while respective k′ values were higher in the oxic than anoxic environment.  相似文献   

16.
近年来的研究证明,中新生代未熟—低熟海相富有机质泥质烃源岩中有机质是通过溶解在水中的分子规模的碳有机质以化学吸附的形式被吸附到矿物表面上和蒙脱石结构层内。然而,对于高熟海相泥质烃源岩中有机质的赋存状态却少有报道。通过对塔里木盆地下寒统底部高熟海相泥质烃源岩的有机碳含量、矿物表面积、扫描电镜和透射电镜的综合分析,得到了其有机质以细小的颗粒状保存于沉积物颗粒之间的结论。同时,通过高熟海相烃源岩与现代未熟海相烃源岩有机质赋存状态的对比,提出了值得进一步研究的有关科学问题。  相似文献   

17.
Three sediment cores were taken from the Pearl River estuary and adjacent northern South China Sea (SCS). These sediment cores span the time interval 1900–2000 AD. The stratigraphy of the concentration, the ratio of total organic carbon (TOC) to total nitrogen (TN) and stable isotope (δ13Corg) of organic carbon (OC) from three high-resolution sediment cores were analyzed. The stratigraphic profiles of OC concentration, TOC/TN ratios and δ13Corg for the near past 100 yrs indicate that terrestrial organic matter decreases from 68.3% to 27.4% of the TOC in the Pearl River estuary, while Dapeng Bay (offshore east of Hong Kong) apparently had throughout little terrestrial organic matter input. The highest deposited OC occurs at the Humen River mouth and the OC concentrations are higher in the outer estuary than in the inner shelf of the northern SCS. The deposited OC at the River mouth increased with time, which could be caused by the high precipitation of land-derived organic matter and the high input of terrestrial organic matter, which is likely related to the rapid urbanization and industrial development in the Pearl River Delta since the 1970s. The OC concentrations did not exhibit an obvious increase with time in most areas of the Pear River estuary and adjacent inner shelf of the SCS, but the algal-derived OC concentration inferred from the δ13Corg values increased with time especially from 1980 to 2000 in the outer Pearl River estuary and Dapeng Bay. This increase is presumably caused by enhanced primary marine productivity supported by higher anthropogenic nutrient inputs.  相似文献   

18.
More and more evidence indicates that organic matter (OM) in immature organicrich sediments and sedimentary rocks is chemically adsorbed onto the outer surfaces of minerals and into interlayer (inner) surfaces of smectitic clay minerals in the form of amorphous molecular-scale carbon. But there have been few reports about the occurrence of highly mature OM in marine black shales ( petroleum source rocks ). The occurrence of highly mature OM in the black shales of basal Cambrian from northern Tarim Basin is studied in this paper. Based on the comprehensive analyses of total organic carbon contents (TOC) , maximum thermolysis tempera tures ( Tmax ) of OM, mineral surface areas (MSA) ,and scanning electronic microscopic (SEM) and transmission electronic microscopic (TEM) observations of the black shales, it is concluded that the highly mature OM in the marine black shales of the basal Cambrian from northern Tarim Basin occurs in particulates ranging in size from 1 to 5 μm in diameter. Through the contrast of the occurrence of the highly mature OM in the black shales with that of the immature ones in modern marine continental margin sediments, some scientific problems are proposed, which are worth to study further in detail.  相似文献   

19.
Long-term carbon cycling and climate change are strongly dependent on organic carbon (OC) burial in marine sediments. Radiocarbon (14C) has been widely used to constrain the sources, sinks, and processing of sedimentary OC. To elucidate the dominant controls on the radiocarbon content of total organic carbon (14CTOC) accumulating in surface sediments we construct a box model that predicts 14CTOC in the sediment mixed layer (measured as fraction modern, Fm). Our model defines three distinct OC pools (“degradable,” “semi-labile,” and “refractory”) and assumes that 14CTOC flux to sediments is exclusively derived from surface ocean primary productivity, and hence follows a “generic” surface ocean dissolved inorganic carbon (DIC) bomb curve. Model predictions are compared to a set of 75 surface sediment samples, which span a wide geographic range and reflect diverse water column and depositional conditions, and for which sedimentation rate and mixed-layer depth are well characterized. Our model overestimates the Fm value for a majority (65%) of these sites, especially at shallow water depths and for sites characterized by depleted δ13CTOC values. The model is most sensitive to sedimentation rate and mixed-layer depth. Therefore, slight changes to these parameters can lead to a match between modeled and measured Fm values at many sites. Yet, in some cases, we find that measured Fm values cannot be simulated without large and unrealistic changes to sedimentation rate and mixed-layer depth. These results point to sources of pre-aged OC to surface sediments and implicate soil-derived terrestrial OC, reworked marine OC, and/or anthropogenic carbon as important components of the organic matter present in surface sediments. This approach provides a valuable framework within which to explore controls on sedimentary organic matter composition and carbon burial over a range of spatial and temporal scales.  相似文献   

20.
Soil organic matter is known to contain a stable fraction with an old radiocarbon age. Size and stabilisation processes leading to the formation of this old soil carbon pool are still unclear. Our study aims to differentiate old organic matter from young and labile carbon compounds in two acid forest soils (dystric cambisol, haplic podzol). To identify such fractions soil samples were exposed to oxidation with Na2S2O8 and to dissolution by hydrofluoric acid (HF). A negative correlation between 14C activity and carbon release after dissolution of the mineral matrix by HF indicates a strong association of stabilised carbon compounds with the mineral phase. A negative correlation between the 14C activity and the relative proportion of carbon resistant to oxidation by Na2S2O8 shows that young carbon is removed preferentially by this treatment. The fraction remaining after oxidation represents a certain stabilised, long residence time carbon pool. This old fraction comprises between 1 and 30% of the total soil organic carbon in the surface horizons, but reaches up to 80% in the sub-surface horizons. Old OC is mainly stabilised by organo-mineral associations with clay minerals and/or iron oxides, whereas intercalation in clay minerals was not found to be important.  相似文献   

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