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1.
《Deep Sea Research Part I: Oceanographic Research Papers》2007,54(9):1571-1592
Seasonal and depth variations in alkenone flux and molecular and isotopic composition of sinking particles were examined using a 21-month time-series sediment trap experiment at a mooring station WCT-2 (39°N, 147°E) in the mid-latitude NW Pacific to assess the influences of seasonality, production depth, and degradation in the water column on the alkenone unsaturation index UK′37. Analysis of the underlying sediments was also conducted to evaluate the effects of alkenone degradation at the water–sediment interface on UK′37. Alkenone sinking flux and UK′37-based temperature showed strong seasonal variability. Alkenone fluxes were higher from spring to fall than they were from fall to spring. During periods of high alkenone flux, the UK′37-based temperatures were lower than the contemporary sea-surface temperatures (SSTs), suggesting alkenone production in a well-developed thermocline (shallower than 30 m). During low alkenone flux periods, the UK′37-based temperatures were nearly constant and were higher than the contemporary SSTs. The nearly constant carbon isotopic ratios of C37:2 and C38:2 alkenones suggest that alkenones produced in early fall were suspended in the surface water until sinking. The alkenone sinking flux decreased exponentially with increasing depth. The decreasing trend was enhanced during the periods of high alkenone flux, suggesting that fresh and labile particles sank from spring to fall, while old and stable particles sank from fall to spring. The UK′37-based temperature usually increased with increasing depth. The preservation efficiency of alkenones was ∼2.7–5.2% at the water–sediment interface. Despite the significant degradation of the alkenones, there was little difference in UK′37 levels between sinking particles and the surface sediment. 相似文献
2.
Osamu Seki Takeshi Nakatsuka Kimitaka Kawamura Sei-Ichi Saitoh Masaaki Wakatsuchi 《Marine Chemistry》2007,104(3-4):253-265
C37–C39 alkenones were measured in time-series sediment trap samples collected from August 1998 to June 2000 at two depths in the seasonal sea ice region of the western Sea of Okhotsk, off Sakhalin, in order to investigate alkenone production and water-column processes in the region. Measurable export fluxes of alkenones are ranged from < 0.1 to 5.8 μg/m2/day and clearly showed that the alkenone production was restricted to autumn. In 1998, maximum export flux of alkenones occurred in September when surface water column was well stratified with low nutrients in the surface mixing layer. In the next year, the maximum flux is observed in October. Comparison between alkenone temperature and satellite based sea surface temperature (SST) shows that the estimated alkenone temperatures in August 1998 were found to be 10 °C lower than the temporal satellite SST, suggesting that alkenones are produced in surface to subsurface thermocline layers during the period. Annual mean flux of alkenones is lower in the lower traps than that of the upper traps, suggesting rapid degradation of alkenones in water column, but the UK37′ value is not significantly altered. This study indicates that UK37′ values preserved in the surface sediments off Sakhalin reflect the seasonal temperature signal of near surface water, rather than annual mean surface temperature. 相似文献
3.
《Deep Sea Research Part I: Oceanographic Research Papers》2001,48(2):515-528
C37–39 alkenones and C36 alkenoates, biomarkers of haptophyte origin, were measured in a 10-month sediment trap times series from the Wilkinson Basin in the Gulf of Maine (GOM). Highest biomarker flux to the seabed was observed in summertime, the period when surface waters are stratified and a persistent, subsurface chlorophyll maximum (SCM) exists within the upper thermocline and at the base of the euphotic zone throughout the GOM. Comparison of biomarker content and composition of sediment trap particles and underlying surface sediments indicates significant loss (>50%) of signal due to the impact of early diagenesis. Despite such loss, however, C37 alkenone unsaturation patterns (U37K′) are not altered. Estimates of algal growth temperature made from analysis of U37K′ in these sedimentary materials correspond with water temperature measured at the SCM, identifying this biological oceanographic feature as a key site of alkenone export production to the GOM sediment record. Given the common occurrence of SCM in surface waters of the world ocean, particularly the expansive oligotrophic regions of the subtropical to temperate ocean, export of alkenones produced within such features is a potentially widespread biological oceanographic phenomenon which shapes the sediment record for these biomarkers. 相似文献
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Jennifer L. Mercer Meixun Zhao Steven M. Colman 《Estuarine, Coastal and Shelf Science》2005,63(4):675-682
Alkenone unsaturation indices (UK37 and UK′37) have long been used as proxies for surface water temperature in the open ocean. Recent studies have suggested that in other marine environments, variables other than temperature may affect both the production of alkenones and the values of the indices. Here, we present the results of a reconnaissance field study in which alkenones were extracted from particulate matter filtered from the water column in Chesapeake Bay during 2000 and 2001. A multivariate analysis shows a strong positive correlation between UK37 (and UK′37) values and temperature, and a significant negative correlation between UK37 (and UK′37) values and nitrate concentrations. However, temperature and nitrate concentrations also co-vary significantly. The temperature vs. UK37 relationships (UK37=0.018 (T)−0.162, R2=0.84, UK′37=0.013 (T)−0.04, R2=0.80) have lower slopes than the open-ocean equations of Prahl et al. [1988. Further evaluation of long-chain alkenones as indicators of paleoceanographic conditions. Geochimica et Cosmochimica Acta 52, 2303–2310] and Müller et al. [1998. Calibration of the alkenone paleotemperature index UK′37 based on core-tops from the eastern South Atlantic and the global ocean (60°N–60°S). Geochimica et Cosmochimica Acta 62, 1757–1772], but are similar to the relationships found in controlled studies with elevated nutrient levels and higher nitrate:phosphate (N:P) ratios. This implies that high nutrient levels in Chesapeake Bay have either lowered the UK37 vs. temperature slope, or nutrient levels are the main controller of the UK37 index. In addition, particularly high abundances (>5% of total C37 alkenones) of the tetra-unsaturated ketone, C37:4, were found when water temperatures reached 25 °C or higher, thus posing further questions about the controls on alkenone production as well as the biochemical roles of alkenones. 相似文献
6.
Sterol and alkenone compositions in suspended particle and surface sediment samples collected in the Northwestern Mediterranean Sea during the MEDFLUX program were used to evaluate the relative importance of biotic and abiotic degradation processes on marine organic matter. Alkenone concentrations decreased much more rapidly (~ 500 fold) between 5 and 800 m than Δ5-sterols (~ 100-fold) or POC (~ 100-fold). The diverse functional groups attached to the stable tetracyclic carbon skeleton of Δ5-sterols appeared to be useful for estimating the relative effects of biotic vs. abiotic (photooxidation and autoxidation) degradation. Products of abiotic degradation predominated over products of biotic degradation in suspended particles in the NW Mediterranean. For alkenones, the U37K′ index increased from 0.43 to 0.55 with increasing water depth, and a good correlation between variations of U37K′ and concentrations of specific Δ5-sterol autoxidation products points to selective autoxidation of alkenones in suspended particles. Stereomutated alkenones (with cis double bonds) were detected in the surface sediment, allowing us to estimate that stereomutation resulted in a + 0.05 increase in U37K′. Therefore, abiotic degradation may be another factor effect on alkenone-derived paleothermometry. 相似文献
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Shuqin Tao Lei Xing Xiaofan Luo Hao Wei Yanguang Liu Meixun Zhao 《Geo-Marine Letters》2012,32(1):61-71
The
\textU\textK￠37 {\text{U}}^{{{\text{K}}\prime}}_{{37}} index has been widely applied for sea surface temperature (SST) reconstruction in open ocean environments, but has inherently
limited applications at smaller, regional scales including some marginal seas where both historical and reconstructed SST
records are urgently needed for understanding regional climate evolution. We determined the spatial distribution of alkenone
contents in surface sediments from the southern Yellow Sea to assess the regional
\textU37\textK￠ {\text{U}}_{{{37}}}^{{{\text{K'}}}} —SST relationship for paleo-SST reconstructions. C37:2 and C37:3 alkenones were detected at all 36 sites covering most of the southern Yellow Sea. Alkenone content ranges from 17 to 1,063 ng/g,
with high values (ca. 400 to 1,000 ng/g) at deep water sites and a decreasing trend shoreward. For six samples at shallower
depths near the coast and further offshore, the values were too low for statistical evaluation. This spatial pattern of alkenone
contents is consistent with existing knowledge on the spatial distribution and productivity of alkenone-producing coccolithophorid
species in the region. There is a significant positive relationship (
\textU37\textK￠ = 0.059\textSST - 0.350 {\text{U}}_{{{37}}}^{{{\text{K'}}}} = 0.059{\text{SST}} - 0.350 , R = 0.912, n = 30) between the
\textU37\textK￠ {\text{U}}_{{{37}}}^{{{\text{K'}}}} values and satellite-derived annual mean SSTs (0 m) for the last 27 years, providing support for the application of a region-specific
\textU37\textK￠ {\text{U}}_{{{37}}}^{{{\text{K'}}}} index as paleothermometer in the southern Yellow Sea. However, the slope of the southern Yellow Sea calibration (0.059) is
considerably larger than that of the well-known global core-top calibration (0.033). This implies that global SST trends may
not adequately encompass regional SST patterns and/or that environmental factors other than temperature may gain importance
in explaining coccolithophore dynamics in marginal seas. 相似文献
9.
Stéphane Christodoulou Jean-Claude Marty Juan-Carlos Miquel John K. Volkman Jean-François Rontani 《Marine Chemistry》2009,113(1-2):25-40
Changes in phytoplankton composition and degradation of particulate organic matter (POM) in the northwestern Mediterranean Sea were studied using time-series sediment trap samples collected during the spring of 2003 at the DYFAMED station. Lipid biomarkers (pigments, fatty acids, sterols, acyclic isoprenoids, alkenones and n-alkanols) were used to identify the main contributors to the POM produced during two phytoplankton blooms, while the effects of photooxidation, autoxidation and biodegradation were differentiated using characteristic lipid degradation products. Traps collected material corresponding to pre-bloom, bloom and post-bloom periods. Pigment analyses in the integrated (0-200 m) water column samples indicated that diatoms dominated the initial stages of the bloom event, with smaller amounts of haptophytes and pelagophytes. During the second part of bloom event there was a switch to haptophyte dominance with significant contributions from diatoms and pelagophytes, and an increased contribution from cryptophytes. Fatty acid distributions in the trap samples reflected contributions from marine bacteria, phytoplankton and zooplankton. Photooxidation and autoxidation products of monounsaturated oleic, cis-vaccenic and palmitoleic acids were detected along with photooxidation products from the chlorophyll side-chain. The relatively good correlation between the variation of U37K′ index and specific phytol autoxidation product percentage allowed us to attribute the alterations of U37K′ observed during the pre-bloom period and in the deeper traps to the involvement of selective autoxidative degradation processes. A variety of sterol oxidation products formed by biohydrogenation, autoxidation and photooxidation were detected. Sterol degradation products appeared to be less suited than oxidation products of monounsaturated fatty acids for the precise monitoring of the degradation state of POM, but their stable functionalized cyclic structure constitutes a useful tool to estimate the part played by biotic and abiotic processes. In these waters, biotic degradation generally predominates, but abiotic degradation is not negligible and, as expected, the extent of biotic degradation increases with depth. To obtain a more complete picture of POM degradation, the use of a pool of lipid degradation products (i.e. from unsaturated fatty acids, the phytyl side-chain and sterols) should be employed. 相似文献
10.
Masaki Inagaki Masanobu Yamamoto Yaeko Igarashi Ken Ikehara 《Journal of Oceanography》2009,65(6):847-858
We investigated marine and terrestrial environmental changes at the northern Japan margin in the northwestern Pacific during
the last 23,000 years by analyzing biomarkers (alkenones, long-chain n-alkanes, long-chain n-fatty acids, and lignin-derived materials) in Core GH02-1030. The U
37K′-derived temperature in the last glacial maximum (LGM) centered at 21 ka was ∼10°C, which was 2°C lower than the core-top
temperature (∼12°C). This small temperature drop does not agree with pollen evidence of a large air temperature drop (more
than 4°C) in the Tokachi area. This disagreement might be attributed to a bias of U
37K′-derived temperature within 2.5°C by a seasonal shift in alkenone production. The U
37K′-derived temperature was significantly low during the last deglaciation. Because this cooling was significant in the Kuroshio-Oyashio
transition zone, the temperature drops are attributable to the southward displacement of the Kuroshio-Oyashio boundary. Abundant
lignin-derived materials, long-chain n-alkanes and long-chain n-fatty acids indicate a higher contribution of terrigenous organic matter from 17 to 12 ka. This phenomenon might have resulted
from an enhanced coastal erosion of terrestrial soils due to marine transgression and/or an efficient inflow of higher plant
debris to river waters from 17 to 12 ka. 相似文献
11.
A series of molecular organic markers were determined in surface sediments from the Gulf of Genoa (Ligurian Sea) in order to evaluate their potential for palaeo-environmental reconstructions. Allochthonous input can be characterized by the distributions of n-C29 and n-C31 alkanes, n-C26 and n-C28 alkanols and branched glycerol dialkyl glycerol tetraethers (GDGTs), whose concentrations are generally highest near the river mouths. In the open basin however, terrestrial n-alkanes and n-alkanols may have an additional, eolian source. Autochthonous input is represented by crenarchaeol and isoprenoid GDGTs. Their concentrations are highest in the open basin showing the preference of Thaumarchaeota for oligotrophic waters. Indications of a significant degradation of sterols and C37 alkenones exclude these lipids as reliable productivity proxies. Using terrestrial and aquatic lipids as end-members allows estimating the percentage of terrestrial organic matter between 20% and 58% in the coastal area decreasing to 1–30% in the deep basin. The spatial distribution of sea surface temperature (SST) estimates using the alkenone-based UK′37 index is very similar to the autumnal (November) mean satellite-based SST distribution. Conversely, TEXH86-derived SST estimates are close to winter SSTs in the coastal area and summer SSTs in the open basin. This pattern reflects presumably a shift in the main production of Thaumarchaeota from the coastal area in winter to the open basin in summer. This study represents a major prerequisite for the future application of lipid biomarkers on sediment cores from the Gulf of Genoa. 相似文献
12.
《Deep Sea Research Part I: Oceanographic Research Papers》2006,53(7):1224-1243
Recent studies have revealed that lateral transport and focusing of particles strongly influences the depositional patterns of organic matter in marine sediments. Transport can occur in the water column prior to initial deposition or following sediment re-suspension. In both cases, fine-grained particles and organic-rich aggregates are more susceptible to lateral transport than coarse-grained particles (e.g., foraminiferal tests) because of the slower sinking velocities of the former. This may lead to spatial and, in the case of redistribution of re-suspended sediments, temporal decoupling of organic matter from coarser sediment constituents. Prior studies from the Argentine Basin have yielded evidence that suspended particles are displaced significant distances (100–1000 km) northward and downslope by strong surface and/or bottom currents. These transport processes result in anomalously cold alkenone-derived sea-surface temperature (SST) estimates (up to 6 °C colder than measured SST) and in the presence of frustules of Antarctic diatom species in surface sediments from this area. Here we examine advective transport processes through combined measurements of compound-specific radiocarbon ages of marine phytoplankton-derived biomarkers (alkenones) from core tops and excess 230Th (230Thxs)-derived focusing factors for late Holocene sediments from the Argentine Basin. On the continental slope, we observe 230Thxs-based focusing factors of 1.4–3.2 at sites where alkenone-based SST estimates were 4–6 °C colder than measured values. In contrast, alkenone radiocarbon data suggest coeval deposition of marine biomarkers and planktic foraminifera, as alkenones in core tops were younger than, or similar in age to, foraminifera. We therefore infer that the transport processes leading to the lateral displacement of these sediment components are rapid, and hence probably occur in the upper water column (<1500 m). 相似文献
13.
采用高效液相色谱法为定性、定量手段,研究土霉素在牙鲆(Paralichthys olivaceus)体内的药代动力学过程,采用DAS(Drug and Statistics)药代动力学程序对数据进行分析.结果表明,牙鲆单剂量口服土霉素后(200 mg/kg),血药经时过程符合二室模型,主要动力学参数如下:吸收半衰期(T(1/2)a)为10.043 h,单剂量给药后牙鲆体内出现最高质量分数的时间(Tmax)为4.000 h,单剂量给药后牙鲆体内最高血药质量分数(Cmax)为0.54 mg/L,药时曲线下总面积(CAU0-72)为17.15 (mg*h)/L,吸收速率常数(Ka)为0.223,消除速率常数(k)为0.476 h-1.牙鲆肌肉中土霉素的经时过程符合一级吸收一室模型,主要动力学参数:T(1/2)a为74.893 h,Tmax为4.000 h,Cmax为3.58 mg/L,CAU0-72为148.56 (mg*h)/L,Ka为0.731,k为2.991 h-1.牙鲆肝脏中土霉素的经时过程符合一级吸收一室模型,主要动力学参数:T(1/2)a为31.376 h,Tmax为4.000 h,Cmax为13.78 mg/L,CAU0-72为494.14 (mg*h)/L,Ka为0.876,k为4.940 h-1. 相似文献
14.
《Coastal Engineering》2005,52(1):25-42
The performance of the standard k–ε, Wilcox high-Reynolds-number k–ω, Wilcox low-Reynolds-number k–ω and Smagorinsky's subgrid scale (SGS) turbulence models is examined against the flow around a circular cylinder 0.37 diameter above a rigid wall. The governing equations are solved using finite difference method in a non-orthogonal boundary-fitted curvilinear coordinate system. A mesh dependence study for the four turbulence models is carried out on computational meshes with different densities. In addition, the performance of the k–ω models with either wall function or no-slip boundary condition on the cylinder surface is examined on the finest mesh. It is found that the SGS model over-predicts the shedding of vortices from the cylinder and is sensitive to the computational mesh and the model constant Cs used. The standard k–ε and the Wilcox k–ω models predict the mean velocity field quite well but generally under-predict the velocity and hydrodynamic force oscillations using wall functions on the cylinder surface. It is also found that the Wilcox k–ω models with the no-slip boundary condition on the cylinder surface give better predictions on the shedding of vortices than their counterparts using the wall function boundary condition. 相似文献
15.
The geochemistry, origin and charge history of oils from the Yuqi area of Tarim Basin have been investigated, through GC, GC-MS and fluid inclusion microthermometry analysis. The Yuqi oils accumulated mainly in three intervals: (1) in the Lower-Middle Ordovician Yingshan Formation (O1-2y) carbonate reservoirs; (2) in the overlying Upper Triassic Halahatang Formation (T3h); and (3) in the Lower Cretaceous Yageliemu Formation (K1y) sandstones. Oils from different reservoirs have distinct physical properties, varying from extra-heavy (O1-2y), heavy (T3h), to light oils (T3h and K1y). However, their geochemical compositions show a high degree of similarity, which indicates that they derive from the same source rock. Abundant tricyclic terpanes, gammacerane, dibenzothiophene and C21C22steranes, together with a low level of diasteranes, indicate an anoxic marine source rock for oils in the Yuqi area. Oil-oil correlation shows that Yuqi oils derive from the same source bed as Tahe oils. The co-occurrence of intact n-alkanes and 25-norhopanes in all the samples supports the proposition that there is a mixture of an early filled severely biodegraded oil and a late filled fresh oil.In this study, charge history is examined on the basis of integration of fluid inclusion homogenization temperature data with 1D burial-thermal history models. Two episodes of oil charging are identified in the O1-2y reservoir (well YQX1-1) at around 436-420 Ma (Middle-Late Silurian) and 10-3 Ma (Miocene to Pliocene), respectively. For the samples from the T3h and K1y intervals, only one episode of oil charge is indicated by the homogenization temperatures of coexisting aqueous inclusions with an inferred timing around 10-3 Ma. The T3h heavy oil reservoir is assumed to be a secondary hydrocarbon pool, which accumulated by re-migration and re-distribution of hydrocarbons from O1-2y hydrocarbon pools. The few early biodegraded oils in the K1y light oils were probably picked up along the migration pathway during the late fresh oil charging. 相似文献
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Capillary gas chromatography (GC) and gas chromatography-mass spectrometry (GC-MS) have been used to examine the aliphatic hydrocarbon fraction of specimens of the mussel, Mytilus edulis, collected from the legs of a North Sea oil-production platform. In addition to an unresolved complex mixture (UCM) of fossil fuel pollutant hydrocarbons (ca. 64 μg g?1 dry weight average), the fraction was dominated by large amounts (ca. 21 μgg?1 dry weight) of C31 and C33n-alkenes with 2, 3 and 4 double bonds. These alkenes have also been identified in the ubiquitous marine alga, Emiliania huxleyi, and in some species of fish taken from the North Sea. The close correspondence in the composition data suggest that, in the mussel, these alkenes arise from a biogenic dietary source, most probably from Emiliania huxleyi. This contention is supported by the identification in the mussel of unusual C37, C38 and C39 unsaturated straight-chain ketones which have recently been shown to be biosynthesised by Emiliania. 相似文献
18.
Wind-wave spectra measured in a wind-flume are analyzed according to the hypothesis of local equilibrium. The gross relation between the wave height and the frequency is reexamined to yield the basic validity of the 3/2-power law of Toba orE～? in the range of 0.4≦?≦1, where? is the wave-wind parameter defined by?=ω p u */g; ω p denotes the peak frequency of the wind-wave spectra,u * the friction velocity andg the gravitational acceleration. Noticeable deviation is found, however, for?<0.4 or?>1. In particular, the data for large? suggest the existence of an upper limit of the wave nonlinearityE at about 5×10?2, whereE=Eω p 4 /g2 withE the total power of the wind wave spectrum. Then, the spectral form is investigated in detail. As? decreases, the normalized spectrum becomes more gradual as a whole, but its forward (low frequency) part tends to show a steeper profile. In the high frequency region ( \(\tilde \omega \) >2.6), the spectrum is found to have a functional form likeu * 2 ω ?3, which differs from the usualω-dependence asω ?5 orω ?4. It suggests weak dependence of the high-frequency spectra on the gravitational accelerationg and on the peak frequencyω p ; spectral density at high frequencies may be saturated, so that its magnitude may be dominated by the frequencyω, the friction velocityu *, the surface tension and the viscosity. 相似文献
19.
CFD simulations of the effects of fouling and antifouling 总被引：1，自引：0，他引：1
Yee Shin Khor 《Ocean Engineering》2011,38(10):1065-1079
Biofouling is a global problem in the marine industry though its effects on lift and drag are rarely discussed. This paper seeks to employ Computational Fluid Dynamics (CFD) method to quantify the effects of this problem based on the obtained flow field information. The simulation is carried out on a NACA 4424 airfoil and Defence Research Establishment Atlantic (DREA) Submarine Hull. Different levels of fouling are studied with quantified fouling height and density. As an extension, the effects of two common antifouling methods, i.e. tin-free Self-Polishing Copolymer (SPC) and Foul Release on the drag of NACA 4424 foil and the submarine hull is investigated. For NACA 4424 airfoil, fouling reduces lift-drag ratio (CL/CD) by up to 80% in maximum and therefore result in the significant increase in fuel consumption. Predicted flow data shows this is related to the increased flow separation region caused by the fouling. It is found that pressure gradient gradually increases from the smallest fouling height to the largest but does not vary that much for fouling of varying densities. The general trend of CL/CD varies with angle of attack agrees well with others experimental data. Computed results also show good agreement with experimental data for the DREA bare hull. As to antifouling, Foul Release, despite being 30% more expensive than SPC, exhibits 10-40% higher CL/CD as compared to SPC for NACA foil and submarine hull. 相似文献