Microalgal Communities of the Sea Ice, Ice-Covered and Ice-Free Waters of Wood Bay (Ross Sea, Antarctica) During the Austral Summer 1993 – 94     

Isabella Moro  Roberta Paccagnella  Carlo Barbante  Carlo Andreoli 《Marine Ecology》2000,21(3-4):233-245

Abstract. During the austral summer 1993 – 94, microalgal density and biomass were investigated in the sea ice, in the underlying water column, in the melt water and during the formation of the sea ice. Of the 96 taxa identified, 59 were diatoms and 32 were dinoflagellates. Among the remaining five species, Pseudopleurochloris antarctica  was very abundant both in the sea ice and in the ice-free waters. Cell densities and biomass of microalgae were higher in the bottom of the sea ice and during the formation of the ice than in the seawater, and diatoms were the dominant group at higher microalgal biomass. Among these, Entomoneis kufferathii , Chaetoceros dichaeta and Fragilariopsis species were the most common taxa.  相似文献   

New Compositional and Structural Constraints on the Smithsonian Microanalytical Reference Materials: Amphiboles from Kakanui and Arenal     

Yujie Liu  Wenqiang Yang  Chao Zhang  Zhian Bao  Shitou Wu  Renat R. Almeev  Filippo Ridolfi  Roberta Oberti 《Geostandards and Geoanalytical Research》2023,47(3):595-608

The amphiboles from Kakanui and Arenal are two natural minerals that have been used worldwide as microanalytical reference materials, but their compositions and crystal structures are still poorly constrained. In this paper, we report new data on H₂O and trace element mass fractions and single-crystal structural refinement of these two amphiboles. H₂O mass fractions of the Kakanui and Arenal amphiboles determined via Karl-Fischer titration are 0.92 ± 0.18 (2s) and 1.56 ± 0.22% m/m (2s), respectively; these values estimated based on crystal-structure refinement are 0.86 and 1.46% m/m, respectively. Trace element mass fractions measured via LA-ICP-MS in two laboratories are in good agreement, and spots from five fragments for both Kakanui and Arenal amphiboles are generally consistent within reproducibility precision (2s). Our measurements indicate a better homogeneity for the amphiboles from Kakanui than that from Arenal. According to the latest scheme for amphibole classification and nomenclature (Hawthorne et al. 2012), the sample from Arenal is a (partially dehydrogenated) pargasite, and that from Kakanui is a kaersutite. The significant amount of oxo-component and that ^CTi⁴⁺ content is strongly ordered at the M(1) site for both amphiboles indicate crystallisation under high fO₂ conditions.  相似文献   

Toward quantification of strain‐related mosaicity in shocked lunar and terrestrial plagioclase by in situ micro‐X‐ray diffraction          下载免费PDF全文

Annemarie E. Pickersgill  Roberta L. Flemming  Gordon R. Osinski 《Meteoritics & planetary science》2015,50(11):1851-1862

Studies of shock metamorphism of feldspar typically rely on qualitative petrographic observations, which, while providing invaluable information, can be difficult to interpret. Shocked feldspars, therefore, are now being studied in greater detail by various groups using a variety of modern techniques. We apply in situ micro‐X‐ray diffraction (μXRD) to shocked lunar and terrestrial plagioclase feldspar to contribute to the development of a quantitative scale of shock deformation for the feldspar group. Andesine and labradorite from the Mistastin Lake impact structure, Labrador, Canada, and anorthite from Earth's Moon, returned during the Apollo program, were examined using optical petrography and assigned to subgroups of the optical shock level classification system of Stöffler (1971). Two‐dimensional μXRD patterns from the same samples revealed increased peak broadening in the chi dimension (χ), due to strain‐related mosaicity, with increased optical signs of deformation. Measurement of the full width at half maximum along χ (FWHMχ) of these peaks provides a quantitative way to measure strain‐related mosaicity in plagioclase feldspar as a proxy for shock level.  相似文献   

A lithium isotopic study of sub-greenschist to greenschist facies metamorphism in an accretionary prism,New Zealand     

Lin Qiu  Roberta L. Rudnick  Jay J. Ague  William F. McDonough 《Earth and Planetary Science Letters》2011,301(1-2):213-221

To investigate the behavior of Li during low-grade metamorphism and fluid flux in an accretionary prism we measured the Li concentrations ([Li]) and isotopic compositions (δ⁷Li) of sub-greenschist and greenschist-facies Otago Schist composites, as well as cross-cutting quartz veins, which are interpreted to have precipitated from slab-derived fluids. The average [Li] of sub-greenschist facies composites (41 ± 13 μg/g, 2σ) is statistically distinct (97% confidence level, student t test) to that of greenschist facies composites (34 ± 9 μg/g, 2σ), which have experienced mass addition of silica in the form of quartz veins having [Li] between 0.4–2.3 μg/g. A linear regression of the correlation between [Li] and calculated mass additions suggests that the depletion of [Li] in greenschist facies composites is due to both dilution from the addition of the quartz veins, as well as metamorphic dehydration. The [Li] of both groups of composites correlates with their CIA (Chemical Index of Alteration) values (50–58), which are low, consistent with the inferred graywacke protolith of the Otago Schist. The δ⁷Li of sub-greenschist and greenschist facies composites are remarkably constant, with an average δ⁷Li of 0.2 ± 1.7 (2σ) and ?0.5 ± 1.9 (2σ), respectively, and comparable to that of the average upper continental crust. Thus, metamorphism has had no discernable effect on δ⁷Li in these samples. The Li isotopic signature of the schists is similar to that seen in pelitic sedimentary rocks and likely reflects the δ⁷Li of the protoliths. The surprisingly light δ⁷Li of the quartz veins (?2.8 to ?1.4) likely records kinetic fractionation associated with Li ingress into the veins from surrounding wallrock.An isotopic equilibrium fluid flow model indicates that: 1) if the [Li] of slab-derived fluids is less than a few μg/g, the δ⁷Li of the overlying lithologies (i.e., the schists) is not significantly influenced by the fluid flux, regardless of the δ⁷Li of the fluids, 2) the slab-derived fluids will have heavy δ⁷Li of > + 10 after reacting with the prism sediments during their ascent, and 3) the [Li] of the slab-derived fluids is likely in the range of 0 < [Li] ≤ 41(μg/g). Thus, isotopically heavy slab-derived fluids that traverse sediments in accretionary prisms may leave little trace in the rocks and their surface compositional characteristics will reflect the net result of their interaction with the sediments of the prism.  相似文献   

Shopping to save lives: Gender and environment theories meet ethical consumption     

Roberta Hawkins 《Geoforum》2012,43(4):750-759

Much of the current work in the field of ‘gender and environment’ has been developed around case studies of environmental roles, rights and responsibilities at the community or household scale in the South. This paper asserts that the theoretical insights developed through these case studies can be of great use when examining issues of gender and environment in the North, particularly when it comes to issues of ethical consumption. In this paper I examine the promotional discourses of two cause-related marketing (CRM) campaigns (where consumption of a CRM product triggers a donation to a development cause) using two such insights: (i) the mutual constitution of gendered subjectivities and environments and (ii) a gender and environment approach to questioning neoliberalization. This approach highlights the ways in which – through consumption – gender is constituted transnationally at the same time that it is constituted in relation to environments. This approach also emphasizes a series of questions about the neoliberal aspects of CRM campaigns that are usually hidden behind discourses of motherhood and responsibility. Overall, I argue that bringing gender and environment and ethical consumption research together allows us to advance both areas of study in critical and insightful ways.  相似文献   

Origins of non-equilibrium lithium isotopic fractionation in xenolithic peridotite minerals: Examples from Tanzania     

Sonja Aulbach  Roberta L. Rudnick 《Chemical Geology》2009,258(1-2):17-27

Olivine, clinopyroxene and orthopyroxene in variably metasomatised peridotite xenoliths from three lithospheric mantle sections beneath the East African Rift in Tanzania (Lashaine, Olmani, Labait) show systematic differences in their average Li concentrations (2.4 ppm, 2.0 ppm and 1.5 ppm, respectively) and intermineral isotopic fractionations, with olivine being heaviest (δ⁷Li = + 2.3 to + 13.9‰, average + 5.0‰), followed by orthopyroxene (? 4.1 to + 6.5‰, average + 0.8‰) and clinopyroxene (? 6.7 to + 4.1‰, average ? 1.6‰). These features are ascribed to the effects of kinetic Li isotope fractionation combined with different Li diffusivities in mantle minerals.Two main mechanisms likely generate diffusion-driven kinetic Li isotope fractionation in mantle xenoliths (1) Li diffusion from grain boundary melt into minerals during recent metasomatism or entrainment in the host magma and (2) subsolidus intermineral Li-redistribution. The latter can produce both isotopically light (Li-addition) and heavy (Li-loss) minerals and may occur in response to changes in pressure and/or temperature.Modelling shows that non-mantle-like δ⁷Li in clinopyroxene (< + 2‰), combined with apparent equilibrium olivine-clinopyroxene elemental partitioning in most peridotite xenoliths from all three Tanzanian localities probably reflects incipient Li addition during interaction with the host magma. Low δ⁷Li (< ? 3‰), combined with high Li concentrations (> 3 ppm) in some clinopyroxene may require very recent (minutes) Li ingress from a Li-rich melt (100s of ppm) having mantle-like δ⁷Li. This might happen during late fragmentation of some mantle xenoliths caused by a volatile- (and Li-) rich component exsolved from the host basalt. In contrast, high Li concentrations (> 2 ppm) and δ⁷Li (> 4‰) in olivine from many Labait and Olmani samples are attributed to an older, pre-entrainment enrichment event during which isotopic equilibrium was attained and whose signature was not corrupted during xenolith entrainment. Low Li concentrations and mantle-like isotopic composition of olivine from most Lashaine xenoliths indicate limited metasomatic Li addition.Thus, Li concentrations and isotope compositions of mantle peridotites worldwide may reflect two processes, with olivine mainly preserving a signature of depletion in refractory samples (low Li contents and δ⁷Li) or of older (precursory) melt addition in metasomatised samples (high Li contents and δ⁷Li), while non mantle-like, low δ⁷Li in almost all clinopyroxene can be due to Li ingress during transport in the host magma and/or slow cooling, if the samples were erupted in lavas. In Tanzania, the peridotites experienced rift-related heating prior to entrainment and were quenched upon eruption, so Li ingress is the most likely process responsible for the isotopically light clinopyroxene here.  相似文献   

Li and δLi in mudrocks from the British Caledonides: Metamorphism and source influences     

Lin Qiu  Roberta L. Rudnick  Richard J. Merriman 《Geochimica et cosmochimica acta》2009,73(24):7325-85

Mudrocks from three lower Paleozoic basins in the British Caledonides (southern Lake District, northern Lake District and Southern Uplands) were investigated to determine the influence of sub-greenschist facies metamorphism on Li and the factors that control Li in fine-grained terrigenous sedimentary rocks. Metamorphic grade, as determined by KI (Kübler index) does not correlate with Li content ([Li]) and δ⁷Li, indicating that sub-greenschist facies metamorphism has negligible effect on Li in these rocks. Collectively, the data for all three basins show a negative correlation between [Li] and δ⁷Li and a positive correlation between [Li] and the Chemical Index of Alteration (CIA), suggesting that provenance exerts the greatest control on Li in mudrocks. Samples from the northern Lake District, which were deposited in an extensional basin, have homogeneous REE patterns, similar to shale composites (PAAS), the highest CIA, Th/U and [Li] and the lowest δ⁷Li and ε_Nd, consistent with their derivation from a highly weathered, ancient continental source. By contrast, mudrocks from the Southern Uplands range to the lowest CIA, Th/U and [Li] and have the highest δ⁷Li and ε_Nd. These samples were deposited in a forearc basin on the southern margin of the Laurentian craton and contain volcanic detritus. Their REE patterns are the most variable, ranging from average shale-like patterns to less LREE-enriched patterns. The compositional heterogeneity within the Southern Uplands mudrocks is consistent with a mixed provenance that includes juvenile crustal materials (lower [Li], ε_Nd and Th/U, higher δ⁷Li), likely derived from the arc, as well as more highly weathered continental detritus. Mudrocks from the southern Lake District were deposited in a foreland basin, and exhibit geochemical characteristics intermediate between the northern Lake District and the Southern Uplands mudrocks, indicating their derivation from a mixed source. Our study shows that Li concentrations and δ⁷Li can provide additional information on the degree of weathering of the provenance of mudrocks.  相似文献   

Geochemistry of xenolithic eclogites from West Africa, part 2: origins of the high MgO eclogites   总被引：1，自引：0，他引：1  

Matthias G Barth  Roberta L Rudnick  Ingo Horn  William F McDonough  Michael J SpicuzzaJohn W Valley  Stephen E Haggerty 《Geochimica et cosmochimica acta》2002,66(24):4325-4345

Oxygen isotope, mineral trace element, and measured and reconstructed whole-rock compositions are reported for the high MgO eclogite xenolith suite (16 to 20 wt% MgO in the whole rock) from the Koidu Kimberlite complex, Sierra Leone. In contrast to the previously published data for low MgO eclogites (6 to 13 wt% MgO) from this area, high MgO eclogites equilibrated at higher temperatures (1080 to 1130°C vs. 890 to 930°C) have only mantlelike δ¹⁸O and show variable degrees of light rare earth element (REE) enrichment. Analyses of multiple mineral generations suggest that the heterogeneous REE patterns of the high MgO eclogites reflect variable degrees of metasomatic overprinting. High MgO and Al₂O₃ contents of the eclogites suggest a cumulate origin, either as high-pressure (2 to 3 GPa) garnet-pyroxene cumulates or low-pressure (<1 GPa) plagioclase-pyroxene-olivine cumulates. Trace element modeling suggests a low-P origin for eclogites with flat heavy REE patterns and a high-P origin for eclogites with fractionated heavy REE. Flat heavy REE patterns, the presence of Sr anomalies, and low to moderate transition element contents in the low-P group are consistent with a low-pressure origin as metamorphosed olivine gabbros and troctolites. These metagabbroic high MgO eclogites either could represent the basal section of subducted oceanic crust or foundered mafic lower continental crust. In the former case, the metagabbroic high MgO eclogites may be genetically related to the Koidu low MgO suite. Crystal fractionation trends suggest that the metapyroxenitic high MgO eclogites formed at lower pressures than their current estimated equilibrium pressures (>4 GPa).  相似文献   

Measurement of the activity of multixenobiotic resistance mechanism in the common carp Cyprinus carpio     

Smital T  Sauerborn R 《Marine environmental research》2002,54(3-5):449-453

The multixenobiotic resistance (MXR) mechanism, mediated by activity of the transmembrane P-glycoprotein, represents a basic biological defence system in aquatic organisms. Here we investigate the MXR transport activity in an aquatic vertebrate, the common carp (Cyprinus carpio). We measured the accumulation rate of a model MXR substrate, the fluorescent dye rhodamine B (RB), in gills, lateral muscles, liver and bile. Results obtained using this method showed a significant increase of RB accumulation in tissues of fish exposed for I h to 3 microM RB in the presence of the model MXR inhibitors cyclosporin A (CA, 5 microM) or verapamil (VER, 10 microM), when compared with specimens exposed without inhibitors. The highest increase in RB accumulation detected in the liver (VER 54%, CA 170%) indicates that among the tissues analysed within this study, liver is the most prominent candidate organ for the functional detection of MXR activity in C. carpio.  相似文献   

First record of Bonnemaisonia hamifera (Bonnemaisoniales,Rhodophyta) in the South Pacific,from the South Island of New Zealand     

David J. Garbary  Roberta D’Archino  Brendan Flack  Christopher D. Hepburn  Wendy A. Nelson  Daniel Pritchard 《新西兰海洋与淡水研究杂志》2020,54(2):167-176

ABSTRACT

The tetrasporophytic ‘Trailliella’ stage of the red algal genus Bonnemaisonia is reported for the first time from the Southern Hemisphere. Here we describe a bloom of the tetrasporophyte of B. hamifera from the mouth of the Waikouaiti River, Karitāne, South Island, where it occurred as thousands of free-floating tufts up to 1?cm wide in shallow water, accumulated in windrows on sand banks and beaches, and in the water column at depths of 10–12?m on the adjacent open coast. Gametophytic stages have not yet been found in New Zealand. The material collected to date is strictly vegetative, and reproduction occurs via fragmentation. The identity of the New Zealand samples as B. hamifera was confirmed by both morphology and rbcL sequencing. The abundance and floating dispersal of B. hamifera suggests that it is invasive and will become widely distributed in New Zealand.  相似文献