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1.
Marine sediments harbor an enormous quantity of microorganisms, including a multitude of novel species. The habitable zone of the marine sediment column begins at the sediment-water interface and probably extends to depths of several thousands of meters. Studies of the microbial diversity in this ecosystem have mostly relied on molecular biological techniques. We used a complementary method - analysis of intact polar membrane lipids - to characterize the in-situ microbial community in sediments covering a wide range of environmental conditions from Peru Margin, Equatorial Pacific, Hydrate Ridge, and Juan de Fuca Ridge. Bacterial and eukaryotic phospholipids were only detected in surface sediments from the Peru Margin. In contrast, deeply buried sediments, independent of their geographic location, were dominated by archaeal diether and tetraether lipids with various polar head groups and core lipids. We compared ring distributions of archaeal tetraether lipids derived from polar glycosidic precursors with those that are present as core lipids. The distributions of these related compound pools were distinct, suggestive of different archaeal sources, i.e., the polar compounds derive from sedimentary communities and the core lipids are fossil remnants from planktonic communities with possible admixtures of decayed sedimentary archaea. This in-situ production of distinct archaeal lipid populations potentially affects applications of the TEX86 paleotemperature proxy as demonstrated by offsets in reconstructed temperatures between both pools. We evaluated how varying cell and lipid stabilities will influence the sedimentary pool by using a box-model. The results are consistent with (i) a requirement of continuous inputs of freshly synthesized lipids in subsurface sediments for explaining the observed distribution of intact polar lipids, and (ii) decreasing lipid inputs with increasing burial depth. 相似文献
2.
Angela F. Dickens Jeffrey A. Baldock Stuart G. Wakeham Yves Gélinas 《Geochimica et cosmochimica acta》2006,70(3):666-686
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
3.
Alkane and PAH biomarkers as tracers of terrigenous organic carbon in Arctic Ocean sediments 总被引：2，自引：0，他引：2
Mark B. Yunker Robie W. Macdonald Lloyd R. Snowdon Brian R. Fowler 《Organic Geochemistry》2011,42(9):1109-1146
We present the first sedimentary biomarker study encompassing the entire Arctic Ocean. A large data set of organic markers for terrigenous, petroleum and combustion inputs [alkanes, hopanes and steranes, parent and alkyl polycyclic aromatic hydrocarbons (PAHs)] is examined for patterns in space and time using principal components analysis (PCA) and partial least squares (PLS). Biomarker patterns reveal the central Arctic Ocean basin sediments to be compositionally distinct from those of the Mackenzie River/Beaufort Sea and Barents Sea, but similar to those of the Laptev Sea. PAH distributions reflected in PAH ratios and PCA projections demonstrate that Arctic Ocean sediment is dominated by natural inputs to the extent that anthropogenic combustion PAHs are not significant. We find only modest changes between the glacial and post-glacial sediments for atmospherically transported hydrocarbon biomarkers, while particle associated biomarkers were captured strongly at basin edges during the glacial period, and much more evenly transported across basins during the post-glacial period. The orders of magnitude decreases in particle associated petrogenic alkanes and PAHs in central basins during glacial times, coupled with the uniformity of most petrogenic biomarker parameters for most basin and shelf locations, reflect a massive reduction in ice transport that makes the margins the most likely source of petrogenic material for the Pleistocene/Holocene central Arctic basins. The proximity of large coal deposits of various maturity levels along the Lena River, the overlap in PAH and biomarker composition of the Laptev Sea and surficial sediments from the central Arctic Ocean and the location of the Laptev Sea at the origin of the main Transpolar Drift all point to eroded coals from the Lena River/Laptev Sea as the likely source of petrogenic hydrocarbons to the central Arctic Ocean. The ubiquitous presence of allochthonous coal in Arctic Ocean surface sediments provides a major constraint on the use of petrogenic biomarkers to infer the presence of subsurface petroleum reserves. 相似文献
4.
Tracing the inputs of bacterial organic carbon to marine systems has been constrained by the lack of distinguishing geochemical tracers and limited contribution in sediments compared to other sources of organic matter. Bacteriohopanepolyols (BHPs) provide a direct means to identify bacterial inputs which also reflect potential bacterial groups and their activities in aquatic systems. We applied recent analytical approaches to identify and quantify bacterial derived carbon contributions to surface sediments from the western Arctic Ocean using BHPs. The abundance and distribution of BHPs resemble trends of water column primary production and suggest active heterotrophic recycling of in situ production with some component of long term preservation. BHPs proposed as terrestrial derived signatures (i.e. adenosylhopanes) were also abundant in western Arctic sediments and reflect offshore trends of other terrigenous lipid signatures with a fraction representing their degradative products. Analysis of BHPs in organic rich peat and surface sediments from two Arctic rivers showed the highest inputs of adenosylhopanes, implying active bacterial recycling of recalcitrant terrigenous material. BHPs observed in western Arctic surface sediments reveal significant contributions of bacteria associated with organic carbon from multiple sources. 相似文献
5.
Cynthia T. Schramm 《Quaternary Research》1985,24(2):204-218
The distribution of radiolarian assemblages identified by Q-mode factor analysis of radiolarian microfossils in surface sediments from low latitudes in the Pacific Ocean reflects their associations with surface water masses. Downcore fluctuations of these radiolarian assemblages at two sites, RC10-65 and V19–29, indicate changes in circulation in the eastern equatorial Pacific during the past 500,000 yr. Surface-water radiolarian assemblages characteristic of zonal flow have dominated siliceous sedimentation in the eastern equatorial Pacific, except during times of intense upwelling which can occur along the coast of Peru and in the Equatorial Undercurrent. Fluctuations in the importance of this upwelling have not been consistent with glacial/interglacial changes in ice volume throughout the late Quaternary. Intensification of upwelling in the equatorial divergence, however, has consistently coincided with increases in ice volume in the past 500,000 yr. The times at which changes in the nature of the relationship between upwelling and ice volume occur (approximately 240,000 and 380,000 yr B.P.) roughly coincide with times of observed changes in other proxy indicators of oceanographic conditions in the Pacific and Indian oceans. 相似文献
6.
Seawater samples were collected from four locations in the Equatorial Pacific Ocean during the MR02-K06 cruise of the R/V Mirai and analyzed for dissolved rare earth elements (REEs) using inductively coupled plasma mass spectrometry. According to variations
of REE concentrations and Yb/La ratios, the results show that the river input of the Papua New Guinea islands may affect the
compositions of REEs in the Equatorial Pacific surface water. The Yb/La values and the REE concentrations in the waters deeper
than 3,000 m in the western South Pacific and the Equatorial Pacific Oceans, which represent the characteristics of Antarctic
Bottom Water (AABW), demonstrate similar variation trend with depth. This result also indicates that the REEs which originated
from the South Pacific Ocean have entered the North Pacific Ocean across the equator with AABW intrusion. 相似文献
7.
Thorarinn S. Arnarson 《Geochimica et cosmochimica acta》2007,71(14):3545-3556
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
8.
PATRICK MEISTER† STEFANO M. BERNASCONI IVANO W. AIELLO‡ CRISÓGONO VASCONCELOS JUDITH A. MCKENZIE 《Sedimentology》2009,56(5):1552-1568
The occurrence of early diagenetic Ca‐rhodochrosite [(Mn,Ca)CO3] is reported in association with ‘griotte’‐type nodular limestones from basinal settings in the geological record; however, without the comparison of analogous modern examples, the controls on precipitation remain speculative. Here the findings of four layers of primary Ca‐rich rhodochrosite recovered from a modern deep‐sea setting in the Eastern Equatorial Pacific, from bioturbated sediments 300 m below sea floor, are reported (Ocean Drilling Program, Leg 201, Site 1226). The mineralogy is similar to cements in burrows recovered during Deep Sea Drilling Project Leg 68 at Eastern Equatorial Pacific Site 503 and from Ca‐rhodochrosite laminae in sediments of the central Baltic Sea. Petrographic relationships and constant oxygen isotopic compositions in the Ca‐rhodochrosite around 5‰ at all depths indicate a shallow burial depth of formation. The onset of 1‰ heavier oxygen isotope composition of Ca‐rhodochrosite at Site 503, about 30 m below the Pliocene/Pleistocene boundary, further suggests that precipitation occurs in the range of 30 m below sea floor. The approximate depth of formation allowed an approximate empirical fractionation factor for marine Ca‐rhodochrosite to be constrained that strongly differs from previously published theoretical values. Based on the approximate precipitation depth, authigenic Ca‐rhodochrosite forms within the SO42?‐reduction zone. Moderately negative δ13C values (around ?3‰) and total organic carbon lower than 2 wt% indicate a relatively low contribution of CO32? from organic C mineralization within the expanded redox zonation in the Eastern Equatorial Pacific. It is suggested that the alkalinity is increased by a rise in pH at focused sites of Mn‐reduction coupled with S2? oxidation. High concentrations of Mn‐oxide can accumulate in layers or burrows because of Mn‐cycling in suboxic sediments as suggested for the Baltic Sea Ca‐rhodochrosites. This study demonstrates how early diagenetic precipitates document biogeochemical processes from past diagenetic systems. 相似文献
9.
The absolute concentrations of minor and trace elements vary considerably in plankton. However, normalization of elemental abundances versus the minor elements Fe, Al and Zn (instead of the commonly used normalization versus seawater concentrations) demonstrates that these elements show remarkably constant proportions vis à vis each other. Thus, Ti, Fe, Al, Mn, V, and Zr occur in marine lower organisms in the same proportions as in the average shale, whereas Ba, Cr, Cu, Ni, Cd, Pb, Zn and B are enriched relative to the shale abundances, as are also Ca, Mg, Na, K, and Sr. These patterns appear to suggest that marine plankton are rich in lithogenic matter, but this is probably not the normal case.Contrary to the uniformity of plankton, sediments from the Pacific vary considerably in composition. Under the Equatorial high-productivity region the sediments show striking similarities with a mixture of average shale and average plankton mass, as could be expected, whereas sediments from the East Pacific Rise differ considerably from such mixtures. An iron—manganese phase (of deep-seated origin?), mixed with biological matter, on the other hand, yields model sediments with remarkable similarities to the East Pacific Rise deposits. It is therefore likely that biological processes account for a considerable fraction of some elements such as Cu, Ni, Zn and Ba also in the East Pacific Rise metalliferous sediments. 相似文献
10.
中国东北古亚洲与古太平洋构造域演化与转换 总被引：6，自引：0，他引：6
现今分布于中朝、塔里木古陆与西伯利亚古陆之间的古亚洲构造域,既存在于前中生代,也存在于中新生代.古亚洲构造域不能等同于古亚洲洋及其构造域.作为古亚洲构造域一部分的古亚洲洋开始于晚寒武世-奥陶纪,结束于中三叠世.古太平洋及其构造域形成于晚古生代,印支期后,成为滨太平洋构造域.在晚三叠世-侏罗纪时期与古亚洲构造域并存,形成两个构造域的板内造山带、局部盆山构造和东北高原.早白垩世形成以滨太平洋构造域为主体的北北东向盆山体系. 相似文献
11.
The sequestration of terrestrial organic carbon in Arctic Ocean sediments: A comparison of methods and implications for regional carbon budgets 总被引：1，自引：0，他引：1
A variety of approaches have previously been developed to estimate the fraction of terrestrial or marine organic carbon present in aquatic sediments. The task of quantifying each component is especially important for the Arctic due to the regions’ sensitivity to global climate change and the potential for enhanced terrestrial organic carbon inputs with continued Arctic warming to alter carbon sequestration. Yet it is unclear how each approach compares in defining organic carbon sources in sediments as well as their impact on regional or pan-Arctic carbon budgets. Here, we investigated multiple methods: (1) two end-member mixing models utilizing bulk stable carbon isotopes; (2) the relationship between long-chain n-alkanes and organic carbon (ALKOC); (3) principal components analysis (PCA) combined with scaling of a large suite of lipid biomarkers; and (4) ratios of branched and isoprenoid glycerol dialkyl glycerol tetraether lipids (the BIT index) to calculate the fraction of terrestrial organic matter components preserved in Arctic marine sediments.Estimated terrestrial organic carbon content among approaches showed considerable variation for identical sediment samples. For a majority of the samples, the BIT index resulted in the lowest estimates for terrestrial organic carbon, corroborating recent suggestions that this proxy may represent a distinct fraction of terrestrial organic matter; i.e., peat or soil organic matter, as opposed to markers such as n-alkanes or long-chain fatty acids which measure higher plant wax inputs. Because of the patchy inputs of n-alkanes to this region from coastal erosion in the western Arctic, the ALKOC approach was not as effective as when applied to river-dominated margins found in the eastern Arctic. The difficulties in constraining a marine δ13C end-member limit the applicability of stable isotope mixing models in polar regions. Estimates of terrestrial organic carbon using the lipid-based PCA method and the bulk δ13C mixing model approach varied drastically at each site, suggesting that organic matter fractions such as amino acids or carbohydrates may affect bulk organic matter composition in a manner that is not captured in the lipid-based analysis. Overall, terrestrial organic matter inputs to the Chukchi and western Beaufort Seas using the average of the methods at each site ranged from 11% to 44%, indicating that land-derived organic matter plays a substantial role in carbon dynamics in the western Arctic Ocean. 相似文献
12.
Ocean drilling has revealed the existence of vast microbial populations in the deep subseafloor, but to date little is known about their metabolic activities. To better understand the biogeochemical processes in the deep biosphere, we investigate the stable carbon isotope chemistry of acetate and other carbon-bearing metabolites in sediment pore-waters. Acetate is a key metabolite in the cycling of carbon in anoxic sediments. Its stable carbon isotopic composition provides information on the metabolic processes dominating acetate turnover in situ. This study reports our findings for a methane-rich site at the northern Cascadia Margin (NE Pacific) where Expedition 311 of the Integrated Ocean Drilling Program (IODP) sampled the upper 190 m of sediment. At Site U1329, δ13C values of acetate span a wide range from −46.0‰ to −11.0‰ vs. VPDB and change systematically with sediment depth. In contrast, δ13C values of both the bulk dissolved organic carbon (DOC) (−21.6 ± 1.3‰ vs. VPDB) and the low-molecular-weight compound lactate (−20.9 ± 1.8‰ vs. VPDB) show little variability. These species are interpreted to represent the carbon isotopic composition of fermentation products. Relative to DOC, acetate is up to 23.1‰ depleted and up to 9.1‰ enriched in 13C. Broadly, 13C-depletions of acetate relative to DOC indicate flux of carbon from acetogenesis into the acetate pool while 13C-enrichments of pore-water acetate relative to DOC suggest consumption of acetate by acetoclastic methanogenesis. Isotopic relationships between acetate and lactate or DOC provide new information on the carbon flow and the presence and activity of specific functional microbial communities in distinct biogeochemical horizons of the sediment. In particular, they suggest that acetogenic CO2-reduction can coexist with methanogenic CO2-reduction, a notion contrary to the hypothesis that hydrogen levels are controlled by the thermodynamically most favorable electron-accepting process. Further, the isotopic relationship suggests a relative increase in acetate flow to acetoclastic methanogenesis with depth although its contribution to total methanogenesis is probably small. Our study demonstrates how the stable carbon isotope biogeochemistry of acetate can be used to identify pathways of microbial carbon turnover in subsurface environments. Our observations also raise new questions regarding the factors controlling acetate turnover in marine sediments. 相似文献
13.
《Organic Geochemistry》1987,11(2):91-101
Nuclear magnetic resonance (NMR) techniques have been applied to the structural characterization of humic substances isolated from an organic-rich sediment in Loch Thurnaig, northwest Scotland. Both the sedimentary humic acid (SHA) and sedimentary fulvic acid (SFA) fractions from Loch Thurnaig contained substantial quantities of carboxylic and alkyl carbon with a small contribution (26 and 22% respectively) of aromatic/olefinic carbon atoms. The latter structures were shown by dipolar dephasing 13C NMR to be largely non-protonated. Differences in the alkyl structures of the two fractions were noted, with the SHA containing a larger amount of branched chain aliphatic material. As branched chain compounds are more resistant to microbial degradation than straight chain compounds, this may indicate that SHA is the older, more refractory fraction of the sedimentary organic matter, although it is possible that the results reflect different algal precursor material. The fraction of aromatic carbon was higher in the SHA than in the SFA as is generally found for humic and fulvic acids isolated from the same source. The low aromaticities and highly branched aliphatic structures show that the sedimentary humic substances from the loch resemble dissolved marine humic substances rather than their terrestrial counterparts. 相似文献
14.
14MaB.P.澳大利亚板块对赤道太平洋影响的数值模拟 总被引：2，自引：0，他引：2
文章利用美国NASA的GISS海气耦合模式,研究了14MaB.P.时期与现代情景下的澳大利亚板块不同位置对赤道太平洋的影响。结果表明:14MaB.P.澳大利亚板块位置较现代偏南时,海洋次表层南赤道海水穿过印度尼西亚通道直接进入印度洋,注入赤道潜流的南赤道海水减少,使得赤道潜流主要来源于北赤道海水,造成赤道太平洋海温比现在冷,其中以赤道西太平洋海温降低幅度最大。而在海洋近表层赤道中东太平洋地区,由于进入海洋的净能量增加和西向风应力加强的共同作用,使得14MaB.P.时海温较之现代情景下要低0.2℃左右。此外,14MaB.P.澳大利亚板块较现代偏南时,赤道太平洋地区的降水量少于现代。 相似文献
15.
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
16.
为了探究煤系石墨形成过程中结构演化及不同石墨化程度无烟煤和石墨的热反应行为,选取湖南新化系列变质程度无烟煤和煤系石墨为研究对象,通过X射线衍射（XRD）和高分辨率透射电子显微镜（HRTEM）对其结构进行表征,并结合程序控制升温法（TPO）分析不同变质程度无烟煤和煤系石墨的热反应行为。结果表明,随变质程度的增加,碳结构由无烟煤中的无定形态转变成石墨的三维有序C原子点阵。系列石墨化煤是由多种有序度不同的碳结构相组成,体现了其结构非均质性,碳结构相含量及分布随变质程度而逐渐变化,石墨化程度最高的煤系石墨中主要为石墨微晶集合体,但依旧含有结构缺陷。无烟煤和煤系石墨中碳结构的多相性和不均匀分布是影响其热反应行为的重要原因。 相似文献
17.
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。 相似文献
18.
19.
The provenance of organic matter in surface sediments from the northern Gulf of Mexico was investigated by analyzing the compositions of lipid biomarkers (n-alkanes, fatty acids, sterols) liberated after a series of chemical treatments designed to remove different organo-mineral matrix associations (i.e. freely extractable, base-hydrolyzable, unhydrolyzable). Bulk analyses of the organic matter (carbon content, carbon:nitrogen ratios, stable and radiocarbon isotopic analyses) were also performed on the intact sediments and their non-hydrolyzable, demineralized residue. We found recognizable lipids from distinct sources, including terrestrial vascular plants, bacteria and marine algae and zooplankton, within each of the isolated fractions. Based on the lipid signatures and bulk compositions, the organic matter within the unhydrolyzable fractions appeared to be the most diagenetically altered, was the oldest in age, and had the highest abundance of terrigenous lipids. In contrast, the base-hydrolyzable fraction was the most diagentically unaltered, had the youngest ages and was most enriched in N and marine lipids. Our results indicate that fresh, autochthonous organic matter is the most important contributor to base-hydrolyzable lipids, whereas highly altered allochthonous sources appear to be predominant source of unhydrolyzable lipids in the surface sediments from the Atchafalaya River shelf. Overall, the lipid biomarker signatures of intact sediments were biased towards the autochthonous source because many of the organic compounds indicative of degraded, terrigenous sources were protected from extraction and saponification by organo-mineral matrices. It is only after these protective matrices were removed by treatment with HCl and HF that these compounds became evident. 相似文献
20.
David R. Griffith William R. Martin Timothy I. Eglinton 《Geochimica et cosmochimica acta》2010,74(23):6788-6800
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