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1.
Chromophoric dissolved organic matter (CDOM) is an important component in the aquatic environment and plays a key role in light attenuation and in carbon biogeochemical cycles. We examined CDOM production in each of two laboratory experiments in which phytoplankton and macrophyte degradation were monitored using absorption and excitation–emission matrix fluorescence spectroscopy (EEMs). During the incubation period, CDOM was produced from phytoplankton and macrophytes, and partly decomposed by microorganisms. The absorption spectra of the phytoplankton derived and the macrophyte derived CDOM were distinct and characterized by peaks and shoulders in the UV bands. Production of CDOM absorption at 350 nm, a(350), was 0.0125 m2/g per unit of chlorophyll a from phytoplankton CDOM from 0–3 d. Meanwhile a(350) production was 2.708 × 10−4 m2/g per unit of wet biomass from macrophytes CDOM from 1–7 d. Despite the high production of CDOM by phytoplankton and macrophytes, extrapolation of these values to the field indicated that about 15% of total CDOM was produced from phytoplankton during algal blooms in Meiliang Bay in summer and about 8% of total CDOM was produced from macrophytes in the macrophyte dominated littorals. The mean value of the spectral slope (S) describing the exponential decrease of the absorption spectrum, which was strongly correlated to an optical index of molecular size, for the phytoplankton derived CDOM was 10.26 ± 2.05 μm−1, which was significantly lower than the mean S of 14.47 ± 2.88 μm−1 for the macrophyte derived CDOM (t-test, p < 0.001). The mean value of the spectral slope ratio (SR) for the phytoplankton derived CDOM was 1.79 ± 0.52, which was significantly higher than that of 0.35 ± 0.58 for the macrophyte derived CDOM (t-test, p < 0.001). Three fluorescent components were validated in parallel factor analysis (PARAFAC) models calculated separately for phytoplankton derived and macrophyte derived CDOM, each CDOM source resulting in distinct excitation and emission maxima for each component. The significant differences in CDOM absorption spectra, S, SR and PARAFAC fluorescence component characteristics, all showed that phytoplankton derived CDOM was compositionally distinct from macrophyte derived CDOM. Overall both sources were important to the CDOM pool in the shallow temperate lake.  相似文献   

2.
梅梁湾、大太湖夏季和冬季CDOM特征及可能来源分析   总被引：26，自引：0，他引：26       下载免费PDF全文
基于2004年夏季水华暴发期和冬季在梅梁湾及大太湖各2次采样,分析了夏季、冬季CDOM的特征及其可能的来源,发现夏季CDOM吸收系数、叶绿素a浓度均明显高于冬季,DOC浓度、CDOM吸收系数a(355)的变化范围分别为5.17～12.42 mg/L、2.57～6.77 m-1,最大值均出现在冬季(12月15日)的直湖港入湖口.CDOM吸收系数与DOC浓度、定标后的荧光值一般都存在显著正相关,但夏季由于受浮游植物降解的影响,与DOC浓度和荧光的相关性明显低于冬季.表征CDOM组成和来源的参数比吸收系数、M值、S值存在显著的季节差异,夏季吸收系数a*(355)值明显要大于冬季,而S值、M值则要小于冬季.夏季水华暴发时CDOM吸收系数与叶绿素a浓度空间分布较为一致,吸收系数与叶绿素a浓度存在正相关,浮游植物降解产物可能是水体中CDOM的重要来源;相反,冬季CDOM吸收系数呈现从梁溪河入湖口、湾内往湾口递减的趋势,其来源可能主要以陆源为主,受入湖河流的影响较大.  相似文献   

3.
We investigated spatial and temporal changes in spectral irradiance, phytoplankton community composition, and primary productivity in North Inlet Estuary, South Carolina, USA. High concentrations of colored dissolved organic matter (CDOM) were responsible for up to 84 % of the attenuation of photosynthetically available radiation (PAR). Green-yellow wavelengths were the predominant colors of light available at the two sampling sites: Clam Bank Creek and Oyster Landing. Vertical attenuation coefficients of PAR were 0.7–2.1 m?1 with corresponding euphotic zone depths of 1.5–6.7 m. Phytoplankton biomass (as chlorophyll a [chl a]) varied seasonally with a summer maximum of 16 μg chl a l?1 and a winter minimum of 1.4 μg chl a l?1. The phytoplankton community consisted mainly of diatoms, prasinophytes, cryptophytes and haptophytes, with diatoms and prasinophytes accounting for up to 67 % of total chl a. Changes in phytoplankton community composition showed strongest correlations with temperature. Light-saturated chl a-specific rates of photosynthesis and daily primary productivity varied with season and ranged from 1.6 to 14 mg C (mg chl a) ?1?h?1 (32–803 mg C m?3?day?1). Calculated daily rates added up to an annual carbon fixation rate of 84 g C m?3?year?1. Overall, changes in phytoplankton community composition and primary productivity in North Inlet showed a strong dependence on temperature, with PAR and spectral irradiance playing a relatively minor role due to short residence times, strong tidal forcing and vertical mixing.  相似文献   

4.
Willow Slough, a seasonally irrigated agricultural watershed in the Sacramento River valley, California, was sampled weekly in 2006 in order to investigate seasonal concentrations and compositions of dissolved organic carbon (DOC). Average DOC concentrations nearly doubled from winter baseflow (2.75 mg L−1) to summer irrigation (5.14 mg L−1), while a concomitant increase in carbon-normalized vanillyl phenols (0.11 mg 100 mg OC−1 increasing to 0.31 mg 100 mg OC−1, on average) indicates that this additional carbon is likely vascular plant-derived. A strong linear relationship between lignin concentration and total suspended sediments (r2 = 0.79) demonstrates that agricultural management practices that mobilize sediments will likely have a direct and significant impact on DOC composition. The original source of vascular plant-derived DOC to Willow Slough appears to be the same throughout the year as evidenced by similar syringyl to vanillyl and cinnamyl to vanillyl ratios. However, differing diagenetic pathways during winter baseflow as compared to the rest of the year are evident in acid to aldehyde ratios of both vanillyl and syringyl phenols. The chromophoric dissolved organic matter (CDOM) absorption coefficient at 350 nm showed a strong correlation with lignin concentration (r2 = 0.83). Other CDOM measurements related to aromaticity and molecular weight also showed correlations with carbon-normalized yields (e.g. specific UV absorbance at 254 nm (r2 = 0.57) and spectral slope (r2 = 0.54)). Our overall findings suggest that irrigated agricultural watersheds like Willow Slough can potentially have a significant impact on mainstem DOC concentration and composition when scaled to the entire watershed of the main tributary.  相似文献   

5.
Lake Erie is biologically the most active lake among the Great Lakes of North America, experiencing seasonal harmful algal blooms (HABs). The early detection of HABs in the Western Basin of Lake Erie (WBLE) requires a more efficient and accurate monitoring tool. Remote sensing is an efficient tool with high spatial and temporal coverage that can allow accurate and timely detection of the HABs. The WBLE is heavily influenced by the surrounding terrestrial ecosystem via rivers such as the Sandusky River and the Maumee River. As a result, the optical properties of the WBLE are influenced by multiple color producing agents (CPAs) such as phytoplankton, colored dissolved organic matter (CDOM), organic detritus, and terrigenous inorganic particles. The diversity of the CPAs and their non-linear interactions makes these waters optically complex, and the task of optical remote sensing for retrieving estimates of CPAs more challenging. Chlorophyll a, which is the primary light harvesting pigment in all phytoplankton, is used as a proxy for algal biomass. In this study, several published remote sensing algorithms and band ratio models were applied to the reflectance data from the full resolution MERIS sensor to remotely estimate chlorophyll a concentrations in the WBLE. Efficiency of the sensor and the algorithms performance were tested through a least squares regression and residual analysis. The results indicate that, among the suite of existing bio-optical models, the Simis semi-analytical algorithm provided the best model results for measures of algal biomass in the optically complex WBLE with R 2 of 0.65, RMSE 0.85 μg/l, (n = 71, P < 0.05). The superior results of this model in detecting chlorophyll a are attributed to several factors including optimizing spectral regions that are less sensitive to CDOM and the incorporation of correction factors such as absorption effects due to pure water (a w), backscatter (b b) from suspended matter and interference due to phycocyanin (δ), a major accessory pigment in the WBLE.  相似文献   

6.
The Mattaponi River is part of the York River estuary in Chesapeake Bay. Our objective was to identify the organic matter (OM) sources fueling the lower food web in the tidal freshwater and oligohaline portions of the Mattaponi using the stable isotopes of carbon (C) and nitrogen (N). Over 3 years (2002–2004), we measured zooplankton densities and C and N stable isotope ratios during the spring zooplankton bloom. The river was characterized by a May–June zooplankton bloom numerically dominated by the calanoid copepod Eurytemora affinis and cladocera Bosmina freyi. Cluster analysis of the stable isotope data identified four distinct signatures within the lower food web: freshwater riverine, brackish water, benthic, and terrestrial. The stable isotope signatures of pelagic zooplankton, including E. affinis and B. freyi, were consistent with reliance on a mix of autochthonous and allochthonous OM, including OM derived from vascular plants and humic-rich sediments, whereas macroinvertebrates consistently utilized allochthonous OM. Based on a dual-isotope mixing model, reliance on autochthonous OM by pelagic zooplankton ranged from 20% to 95% of production, declining exponentially with increasing river discharge. The results imply that discharge plays an important role in regulating the energy sources utilized by pelagic zooplankton in the upper estuary. We hypothesize that this is so because during high discharge, particulate organic C loading to the upper estuary increased and phytoplankton biomass decreased, thereby decreasing phytoplankton availability to the food web.  相似文献   

7.
Surface water optical characteristics, nutrients, and planktonic chlorophyll a concentrations were analyzed in the Cape Fear River (CFR) plume over a 2-year period. CFR discharge during the dry year (109 ± 105 m3s−1) was only 25% of the wet year discharge (429 ± 337 m3s−1). Partitioning the contributions of phytoplankton pigments, non-pigmented particles, and colored dissolved organic matter (CDOM) to the absorption of photosynthetically active radiation (PAR) indicated that CDOM was the dominant contributor to PAR absorption. Particulate absorption was relatively greater during the dry year. Pigment absorption was minor and varied little among stations or between years. Chlorophyll a concentrations were reduced at the most plume-influenced stations during the wet year, despite lower turbidity and higher nitrate concentrations. Ammonium and orthophosphate concentrations were not different between years. CDOM absorption [a CDOM (412)] ranged from 0.05 to 8.25 m−1 with highest values occurring near the CFR mouth. Our results suggest that for coastal ecosystems with significant blackwater river inputs, CDOM may exert a major limiting influence over near-shore primary production.  相似文献   

8.
The parameter S1 + S2 (genetic potential) of Rock-Eval analysis is widely used as an evaluation of the genetic potential for the source rocks. Oligocene–Miocene saline lacustrine source rocks in the western Qaidam basin have low total organic C contents (TOC), most around 0.5% with a few exceptions >1.0%. Mineral matrix effects are substantial for source rocks with low TOC, resulting in relatively low S1 and S2 peaks. Based on the results of confined pyrolyses (sealed Au capsules) on 6 Oligocene–Miocene source rocks from the western Qaidam basin, with TOC ranging between 0.48% and 2.22%, the relationship between the S1 + S2 parameter and the maximum amount of extracted bitumen or saturated and aromatic hydrocarbons (SA) after the confined pyrolysis has been established as follows: bitumen (mg/g rock) = 1.4924 × (S1 + S2) + 0.3201 (r = 0.987), or SA (saturates + aromatics) (mg/g rock) = 0.7083 × (S1 + S2) + 0.4045 (r = 0.992). Based on these formulas, the amounts of hydrocarbons generated from source rocks can be reasonably estimated. The typical crude oils with low biomarker maturities in this region appear substantially different to the pyrolysates of these six rocks at 180–300 °C but comparable to the pyrolysates at 320 °C and higher temperatures based on molecular parameters. This result, in combination with the physical and gross compositions of the crude oils, suggests that the majority of these crude oils were generated from the source rocks during the main oil-generative stage, possibly at a maturity higher than Ro 0.74%.  相似文献   

9.
We investigated spatial and temporal relationships between spectral irradiance and phytoplankton community composition in the blackwater-influenced estuary Winyah Bay, South Carolina. Upstream, high concentrations of chromophoric dissolved organic matter (CDOM) absorbed blue wavelengths, resulting in a predominantly red light field. Green light prevailed downstream near the lower-CDOM coastal ocean, and phytoplankton community composition was distinct from upstream and mid-estuarine communities. Diatoms were abundant throughout the estuary in January, August, and October, cryptophytes dominated in July, and chlorophytes were abundant in December 2006. Only diatoms and chlorophytes showed significant covariation with the spectral attenuation coefficient (k(λ)): Chlorophytes showed positive relationships with k(442) (blue light) while diatoms were negatively correlated with k(442) and k(490) (violet to blue). Phytoplankton community composition in Winyah Bay appears to be driven by strong horizontal flow rather than gradients in spectral irradiance, but results indicate that water color is likely to play a greater role in blackwater-influenced estuaries with longer residence times.  相似文献   

10.
We have determined Cr diffusion coefficients (D) in orthopyroxene parallel to the a-, b-, and c-axial directions as a function temperature at f(O2) corresponding to those of the wüstite-iron (WI) buffer. Diffusion is found to be significantly anisotropic with D(//c) > D(//b) > D(//a), conforming to an earlier theoretical prediction. Increase of f(O2) from WI buffer conditions to 4.5 log unit above the buffer at 950 and 1050 °C leads to decrease of D(Cr) by a factor of two to three, possibly suggesting significant contribution from an interstitial diffusion mechanism. We have used the diffusion data to calculate the closure temperatures (Tc) of the Mn-Cr decay system in orthopyroxene as a function of initial temperature (T0), grain size (a) and cooling rate for spherical and plane sheet geometries. We also present graphical relations that permit retrieval of cooling rates from knowledge of the resetting of Mn-Cr ages in orthopyroxene during cooling, T0 and a. Application of these relations to the Mn-Cr age data of the cumulate eucrite Serra de Magé yields a Tc of 830-980 °C, and cooling rates of 2-27 °C/Myr at Tc and ∼1-13 °C/Myr at 500 °C. It is shown that the cooling of Serra de Magé to the closure temperature of the Mn-Cr system took place at its original site in the parent body, and thus implies a thickness for the eucrite crust in the commonly accepted HED parent body, Vesta, of greater than 30 km. This thickness of the eucrite crust is compatible only with a model of relatively olivine-poor bulk mineralogy in which olivine constitutes 19.7% of the total asteroidal mass.  相似文献   

11.
An investigation and remediation of instability along upstream cut slopes for an earthfill dam in differentially weathered rock in southern Turkey is described. The major instability problem was a 45-m high and 200-m long previously cut slope next to the main axis of the dam, above the diversion tunnels and water outlet structures. The slope was first designed and excavated in 1986 based on the temporary berm approach. Rising water level in the reservoir would change the shear strength parameters and the pore-water pressure in the slope; thus, probable deep failure would damage the entrance of the diversion tunnels and water outlet structures, as well as the earthfill embankment of the dam. In June 1996, the slope face was re-excavated and protected against wave erosion by placement of a layer of rock riprap over a layer of bedding and a filter material. A strong earthquake (MS = 6.2) occurred during a period of rapid drawdown in 27 June 1998. The slope remained stable, although numerous tension cracks developed in Quaternary terrace deposits near the reservoir area.  相似文献   

12.
Coastal upwelling in the northern California Current varies seasonally, with downwelling in winter and upwelling in summer, resulting in pronounced variability in hydrography, nutrients, phytoplankton biomass, and species composition. Winter was characterized by moderate concentrations of nitrate and silicate (averages of 10 and 18 μM, respectively) and low concentrations of chlorophyll a (Chl a). During the upwelling season, concentrations of the same nutrients ranged from near 0 μM to approximately 27 and 43 μM and Chl a 0.5?<?x?<?15 μg L?1. During autumn, upwelling weakened and nutrient concentrations were reduced, but large phytoplankton blooms continued to occur. Variations in hydrography, nutrients, and phytoplankton also occurred within the upwelling season due to alternation of the winds between northerly (active upwelling) and southerly (relaxation of upwelling), on a 5- to 10-day time scale. Eleven blooms were observed, most of which occurred near the end of active upwelling events and during relaxation of upwelling. Nonmetric multidimensional scaling ordination of species composition of the microplankton revealed four distinct communities: a winter community, early upwelling and late upwelling season communities, and an autumn community. Diatoms (Asterionellopsis glacialis, Eucampia zodiacus, and several Chaetoceros, Thalassiosira, and Pseudo-nitzschia species) dominated early in the upwelling season, averaging 80 % of the phytoplankton biomass, and dinoflagellates dominated near the end of the upwelling season, averaging 68 % of the phytoplankton biomass. Dinoflagellates formed two monospecific blooms—Prorocentrum gracile in late summer and Akashiwo sanguinea in autumn. Changes in community composition were correlated with bottom temperature and salinity (representing seasonal variability) and sea surface salinity (representing within-season event-scale variability in upwelling).  相似文献   

13.
The composition, productivity, and standing crop of net (>20 μm) and nano-(<20 μm) phytoplankton of Peconic Bay, Long Island, New York was examined from June 1978 through May 1979. Nanoplankton, primarily small solitary flagellates, chlorophytes, and diatoms, dominated from May through September accounting for 88.5% of the productivity and 88.1% of the standing crop (measured as chlorophyll a). An apparent net plankton bloom began in December and continued through March. The dominant organism through most of the winter bloom was the chain-forming diatom Skeletonema costatum (Grev.) Cl. Net plankton at this time represented 66.4% of the standing crop. For both size fractions, productivity/chlorophyll a (g C per g chl a per d, integrated through the euphotic zone) was a function of light energy over the year with the exception of a few sampling dates during the post-winter bloom period. Assimilation numbers (g C per g chl a per h at saturating light intensities) were a function of temperature between 0 and 20°C. Nitrogen deficiency did not appear to be a factor in regulating phytoplankton growth rate through the euphotic zone, as ratios of 14C assimilation for dark bottles enriched with NH3 and with no enrichment exhibited no relationship to environmental dissolved inorganic nitrogen concentrations. Zooplankton grazing pressure appeared to have been an important factor in regulating the upper limit of phytoplankton biomass and in influencing size fraction dominance. Dominance of one phytoplankton size fraction over the other on any given date was not based on physiological differences between the two groups since both fractions were composed of the same species. Apparent net phytoplankton blooms (in terms of productivity and chlorophyll a) were artifacts of increased chain lengths of nanoplankton diatoms such as Skeletonema costatum, and to a lesser extent, Thalassiosira nordenskioldii Cl. and Detonula confervacea (Cl.) Gran, rather than to the dominance of large, solitary cells.  相似文献   

14.
The 13C/12C ratio of carbon compounds is used to identify sources and sinks in the global carbon cycle. However, the relatively enriched 13C content observed for marine organic carbon remains enigmatic. The majority of oceanic carbon is fixed by algae and cyanobacteria via the Calvin-Benson-Bassham cycle, yet isotopic discrimination by the CO2 fixation enzyme, RubisCO (ribulose 1,5-bisphosphate carboxylase/oxygenase), has only been measured for a single marine cyanobacterium. Different forms of RubisCO occur in different phytoplankton species (overall amino acid identity varying by as much as ∼75%) and thus may vary in the degree to which they fractionate carbon. Here we measured isotope discrimination by RubisCO from the coccolithophore Emiliania huxleyi, a cosmopolitan species used as a marine algal model.E. huxleyi RubisCO discriminated substantially less (ε = 11.1‰) against 13CO2 than other RubisCO enzymes (18-29‰), despite having Michaelis-Menten kinetic parameters (KCO2 = 72 μM; Vmax = 0.66 μmol min−1 mg−1 protein) similar to those measured for RubisCO enzymes from different organisms. If widespread, decreased isotope discrimination of 13C by phytoplankton RubisCO may be a major factor influencing the enriched 13C content of marine organic carbon. This finding emphasizes the necessity of (a) determining ε values for RubisCOs of other marine phytoplankton and (b) re-evaluation of δ13C values from physiological, environmental, and geological studies.  相似文献   

15.
This paper describes the results of 10 years of water quality monitoring in the Indian River Lagoon Florida, with special emphasis on the relationships between trends in climatic conditions and the distribution, composition, and abundance of the phytoplankton community. The Indian River Lagoon, which spans 220 km of Florida’s east coast, is a region of particular concern because of the rapid rate of human development throughout the region and the hydrologically restricted character of the lagoon, which heightens the potential for algal bloom. Water sampling was carried out on a monthly to twice-monthly basis at six sites located in the northern and central lagoon. The 10-year study included both extended periods of below and above average rainfall. A number of ecologically distinct regions exist within the lagoon, which differ considerably in water exchange properties and watershed inputs. The northern lagoon is characterized by longer water residence times, lower phosphorus concentrations, higher nitrogen concentrations, and more stable salinity conditions than the central lagoon. Mean phytoplankton biovolumes were substantially higher at the sites in the northern lagoon than at the sites in the central lagoon, and algal blooms were more common and intense in the former region. Inter-annual patterns of phytoplankton biovolume were also different in the northern and central lagoon. In the northern lagoon, phytoplankton biovolumes were lowest during the drought period, from the autumn of 1998 to the spring of 2001. By contrast, algal bloom events in the central lagoon were not only less frequent but were not tied to periods of high rainfall. The most widespread and common bloom formers were the potentially toxic dinoflagellate Pyrodinium bahamense var. bahamense and two centric diatoms, Dactyliosolen fragilissimus and Cerataulina pelagica. Many of the biovolume peaks observed over the study period were attributable to these three species. The results of time series modeling of phytoplankton dynamics further highlighted the disparities between the two regions of the lagoon in terms of the suite of parameters that best predict the observed trends in the biomass of phytoplankton. Overall, the outcome of this initial modeling effort in the Indian River Lagoon suggests that time series approaches can help define the factors that influence phytoplankton dynamics.  相似文献   

16.
In order to use lithium isotopes as tracers of silicate weathering, it is of primary importance to determine the processes responsible for Li isotope fractionation and to constrain the isotope fractionation factors caused by each process as a function of environmental parameters (e.g. temperature, pH). The aim of this study is to assess Li isotope fractionation during the dissolution of basalt and particularly during leaching of Li into solution by diffusion or ion exchange. To this end, we performed dissolution experiments on a Li-enriched synthetic basaltic glass at low ratios of mineral surface area/volume of solution (S/V), over short timescales, at various temperatures (50 and 90 °C) and pH (3, 7, and 10). Analyses of the Li isotope composition of the resulting solutions show that the leachates are enriched in 6Li (δ7Li = +4.9 to +10.5‰) compared to the fresh basaltic glass (δ7Li = +10.3 ± 0.4‰). The δ7Li value of the leachate is lower during the early stages of the leaching process, increasing to values close to the fresh basaltic glass as leaching progresses. These low δ7Li values can be explained in terms of diffusion-driven isotope fractionation. In order to quantify the fractionation caused by diffusion, we have developed a model that couples Li diffusion with dissolution of the glassy silicate network. This model calculates the ratio of the diffusion coefficients of both isotopes (a = D7/D6), as well as its dependence on temperature, pH, and S/V. a is mainly dependent on temperature, which can be explained by a small difference in activation energy (0.10 ± 0.02 kJ/mol) between 6Li+ and 7Li+. This temperature dependence reveals that Li isotope fractionation during diffusion is low at low temperatures (T < 20 °C), but can be significant at high temperatures. However, concerning hydrothermal fluids (T > 120 °C), the dissolution rate of basaltic glass is also high and masks the effects of diffusion. These results indicate that the high δ7Li values of river waters, in particular in basaltic catchments, and the fractionated values of hydrothermal fluids are mainly controlled by precipitation of secondary phases.  相似文献   

17.
Here we present the first set of metal-silicate partitioning data for Cs, which we use to examine whether the primitive mantle depletion of Cs can be attributed to core segregation. Our experiments independently varied pressure from 5 to 15 GPa, temperature from 1900 to 2400 °C, metallic sulfur content from pure Fe to pure FeS, silicate melt polymerization, expressed as a ratio of non-bridging oxygens to tetrahedrally coordinated cations (nbo/t) from 1.26 to 3.1, and fO2 from two to four log units below the iron-wüstite buffer. The most important controls on the partitioning behavior of alkalis were the metallic sulfur content, expressed as XS, and the nbo/t of the silicate liquid. Normalization of XS to 0.5 yielded the following expressions for D-values as a function of nbo/t: log DNa = −2.0 + 0.44 × (nbo/t), log DK = −2.4 + 0.67 × ( nbo/t), and log DCs = −3.2 + 1.17 × (nbo/t). Normalization of nbo/t to 2.7 resulted in the following equations for D-values as a function of S content: log DNa = −4.1 + 6.4 × XS, log DK = −7.7 + 13.9 × XS, and log DCs = −12.1 + 23.3 × XS.There appears to be a negative pressure effect up to 15 GPa, but it should be noted that this trend was not present before normalization, and is based on only two measurements. There is a positive trend in cesium’s metal-silicate partition coefficient with increasing temperature. DCs exhibits the largest change and increased by a factor of three over 500 °C. The effect of oxygen fugacity has not been precisely determined but in general, lowering fO2 by two log units resulted in a rise in all D-values of approximately an order of magnitude. In general, the sensitivity of partition coefficients to changing parameters increased with atomic number.The highest D-value for Cs observed in this study is 0.345, which was obtained at nbo/t of 2.7 and a metal phase of pure FeS. This metallic composition has far more S than has been suggested for any credible core-forming metal. We therefore conclude that the depletion of Cs in Earth’s mantle is either caused by radically different behavior of Cs at pressures higher than 15 GPa or is not related to core formation. Even so, we have shown that a planet with a sufficient S inventory may incorporate significant amounts of alkali elements into its core.  相似文献   

18.
We investigated whether climate change results in long-term changes in phytoplankton biomass and phenology in a turbid eutrophic coastal plain estuary. Changes in annual mean chlorophyll a (chla) concentrations were studied for the period 1978–2006 in the eutrophic and turbid macro-tidal Western Scheldt estuary. Three stations were investigated: WS1, at the mouth of the estuary; station WS6, halfway up the estuary; and station WS11, near the Dutch–Belgian border near the upstream end of the estuary. No significant long-term changes in yearly averaged chla concentrations were observed in WS1 and WS6, but in WS11 the phytoplankton biomass decreased considerably. This is most likely due to an increase in grazing pressure as a result of an improvement in the dissolved oxygen concentrations. Spectral analyses revealed a possible periodicity of 7 years in the mean chla which was related to periodicity in river discharge. We also observed strong phenological responses in the timing of the spring/summer bloom which were related to a well-documented increase in the temperature in the estuary. The fulcrum, the center of gravity or the day at which 50% of the cumulative chla was reached during the year, advanced by 1–2 days/year. A similar trend was observed for the month in which the maximum bloom was observed, with the exception of station WS1. All stations showed an earlier initiation of the bloom, whereas the day at which the phytoplankton bloom was terminated also moved forward in time excepted for WS11. As a result, the bloom length decreased at station WS1, remained the same at station WS6, and increased at WS11. This complicated pattern in bloom phenology demonstrates the complex nature of ecosystem functioning in estuaries.  相似文献   

19.
Cadmium isotopic composition in the ocean   总被引：1，自引：0，他引：1  
The oceanic cycle of cadmium is still poorly understood, despite its importance for phytoplankton growth and paleoceanographic applications. As for other elements that are biologically recycled, variations in isotopic composition may bring unique insights. This article presents (i) a protocol for the measurement of cadmium isotopic composition (Cd IC) in seawater and in phytoplankton cells; (ii) the first Cd IC data in seawater, from two full depth stations, in the northwest Pacific and the northwest Mediterranean Sea; (iii) the first Cd IC data in phytoplankton cells, cultured in vitro. The Cd IC variation range in seawater found at these stations is not greater than 1.5 εCd/amu units, only slightly larger than the mean uncertainty of measurement (0.8 εCd/amu). Nevertheless, systematic variations of the Cd IC and concentration in the upper 300 m of the northwest Pacific suggest the occurrence of Cd isotopic fractionation by phytoplankton uptake, with a fractionation factor of 1.6 ± 1.4 εCd/amu units. This result is supported by the culture experiment data suggesting that freshwater phytoplankton (Chlamydomonas reinhardtii and Chlorella sp.) preferentially take up light Cd isotopes, with a fractionation factor of 3.4 ± 1.4 εCd/amu units. Systematic variations of the Cd IC and hydrographic data between 300 and 700 m in the northwest Pacific have been tentatively attributed to the mixing of the mesothermal (temperature maximum) water (εCd/amu = −0.9 ± 0.8) with the North Pacific Intermediate Water (εCd/amu = 0.5 ± 0.8). In contrast, no significant Cd IC variation is found in the northwest Mediterranean Sea. This observation was attributed to the small surface Cd depletion by phytoplankton uptake and the similar Cd IC of the different water masses found at this site. Overall, these data suggest that (i) phytoplankton uptake fractionates Cd isotopic composition to a measurable degree (fractionation factors of 1.6 and 3.4 εCd/amu units, for the in situ and culture experiment data, respectively), (ii) an open ocean profile of Cd IC shows upper water column variations consistent with preferential uptake and regeneration of light Cd isotopes, and (iii) different water masses may have different Cd IC. This isotopic system could therefore provide information on phytoplankton Cd uptake and on water mass trajectories and mixing in some areas of the ocean. However, the very small Cd IC variations found in this study indicate that applications of Cd isotopic composition to reveal aspects of the present or past Cd oceanic cycle will be very challenging and may require further analytical improvements. Better precision could possibly be obtained with larger seawater samples, a better chemical separation of tin and a more accurate mass bias correction through the use of the double spiking technique.  相似文献   

20.
The sodium solubility in silicate melts in the CaO-MgO-SiO2 (CMS) system at 1400 °C has been measured by using a closed thermochemical reactor designed to control alkali metal activity. In this reactor, Na(g) evaporation from a Na2O-xSiO2 melt imposes an alkali metal vapor pressure in equilibrium with the molten silicate samples. Because of equilibrium conditions in the reactor, the activity of sodium-metal oxide in the molten samples is the same as that of the source, i.e., aNa2O(sample) = aNa2O(source). This design also allows to determine the sodium oxide activity coefficient in the samples. Thirty-three different CMS compositions were studied. The results show that the amount of sodium entering from the gas phase (i.e., Na2O solubility) is strongly sensitive to silica content of the melt and, to a lesser extent, the relative amounts of CaO and MgO. Despite the large range of tested melt compositions (0 < CaO and MgO < 40; 40 < SiO2 < 100; in wt%), we found that Na2O solubility is conveniently modeled as a linear function of the optical basicity (Λ) calculated on a Na-free basis melt composition. In our experiments, γNa2O(sample) ranges from 7 × 10−7 to 5 × 10−6, indicating a strongly non-ideal behavior of Na2O solubility in the studied CMS melts (γNa2O(sample) ? 1). In addition to showing the effect of sodium on phase relationships in the CMS system, this Na2O solubility study brings valuable new constraints on how melt structure controls the solubility of Na in the CMS silicate melts. Our results suggest that Na2O addition causes depolymerization of the melt by preferential breaking of Si-O-Si bonds of the most polymerized tetrahedral sites, mainly Q4.  相似文献   

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