Manganese and iron distributions off central California influenced by upwelling and shelf width

In July 2002, a combination of underway mapping and discrete profiles revealed significant along-shore variability in the concentrations of manganese and iron in the vicinity of Monterey Bay, California. Both metals had lower concentrations in surface waters south of Monterey Bay, where the shelf is about 2.5 km wide, than north of Monterey Bay, where the shelf is about 10 km wide. During non-upwelling conditions over the northern broad shelf, dissolvable iron concentrations measured underway in surface waters reached 3.5 nmol L⁻¹ and dissolved manganese reached 25 nmol L⁻¹. In contrast, during non-upwelling conditions over the southern narrow shelf, dissolvable iron concentrations in surface waters were less than 1 nmol L⁻¹ and dissolved manganese concentrations were less than 5 nmol L⁻¹. A pair of vertical profiles at 1000 m water depth collected during an upwelling event showed dissolved manganese concentrations of 10 decreasing to 2 nmol L⁻¹, and dissolvable iron concentrations of 12–20 nmol L⁻¹ in the upper 100 m in the north, compared to 3.5–2 nmol L⁻¹ Mn and 0.6 nmol L⁻¹ Fe in the upper 100 m in the south, suggesting the effect of shelf width influences the chemistry of waters beyond the shelf.These observations are consistent with current understanding of the mechanism of iron supply to coastal upwelling systems: Iron from shelf sediments, predominantly associated with particles greater than 20 μm, is brought to the surface during upwelling conditions. We hypothesize that manganese oxides are brought to the surface with upwelling and are then reduced to dissolved manganese, perhaps by photoreduction, following a lag after upwelling.Greater phytoplankton biomass, primary productivity, and nutrient drawdown were observed over the broad shelf, consistent with the greater supply of iron. Incubation experiments conducted 20 km offshore in both regions, during a period of wind relaxation, confirm the potential of these sites to become limited by iron. There was no additional growth response when copper, manganese or cobalt was added in addition to iron. The growth response of surface water incubated with bottom sediment (4 nmol L⁻¹ dissolvable Fe) was slightly greater than in control incubations, but less than in the presence of 4 nmol L⁻¹ dissolved iron. This may indicate that dissolvable iron is not as bioavailable as dissolved iron, although the influence of additional inhibitory elements in the sediment cannot be ruled out.     

Multi-indicator conductivity transfer functions for Quaternary palaeoclimate reconstruction

Diatoms (Bacillariophyceae; single-celled algae) and ostracods (Ostracoda; shelled microcrustacea) are known for their sensitivity to salinity. In palaeolimnology, the potential has yet to be tested for quantifying past salinity, lake level, and by inference, climate change, by application of multiple-indicator transfer functions. We used weighted averaging techniques to derive diatom (n = 91; r ²  = 0.92) and ostracod (n = 53; r ²  = 0.83) conductivity transfer functions from modern diatom, ostracod and water chemistry data collected in lakes of central, western and northern Turkey. Diatoms were better represented across the full gradient than ostracods, at intermediate levels of conductivity in particular, but both transfer functions were statistically robust. Because transfer functions are not infallible, we further tested the strength and simplicity of salinity response and the potential for identifying characteristic associations of diatom and ostracod taxa in different parts of the salinity gradient, to improve palaeoclimate reconstruction. We identified a subset of 51 samples that contained both diatoms and ostracods, collected at the same time from the same habitat. We used Two-Way Indicator Species Analysis of a combined diatom-ostracod data set, transformed to achieve numerical equivalence, to explore distributions in more detail. A clear ecological threshold was apparent at ~3 g l⁻¹ salinity, rather than at 5 g l⁻¹, the boundary used by some workers, equating to the oligosaline-mesosaline boundary. Other salinity boundaries were poorly defined, indicating lack of a simple, well-defined salinity response. We did, however, define characteristic associations of taxa, to facilitate the distinction to be drawn between a hydrologically open, fresh lake and an oligosaline lake, in palaeoenvironmental reconstruction. Over the rest of the salinity gradient, we highlighted the potential for the multi-proxy approach to strengthen ostracod-based reconstruction in particular, to overcome the problem of broad apparent tolerance ranges in common halophilic taxa such as Limnocythere inopinata, which often dominate in low-diversity fossil assemblages. The combination of multi-proxy quantitative reconstruction, complemented by qualitative understanding of ecological responses generated by the analysis, remains a powerful tool in Quaternary palaeoclimate research.     

Magma plumbing beneath Anak Krakatau volcano, Indonesia: evidence for multiple magma storage regions

Understanding magma plumbing is essential for predicting the behaviour of explosive volcanoes. We investigate magma plumbing at the highly active Anak Krakatau volcano (Indonesia), situated on the rim of the 1883 Krakatau caldera by employing a suite of thermobarometric models. These include clinopyroxene-melt thermobarometry, plagioclase-melt thermobarometry, clinopyroxene composition barometry and olivine-melt thermometry. Petrological studies have previously identified shallow magma storage in the region of 2–8 km beneath Krakatau, while existing seismic evidence points towards mid- to deep-crustal storage zone(s), at 9 and 22 km, respectively. Our results show that clinopyroxene in Anak Krakatau lavas crystallized at a depth of 7–12 km, while plagioclase records both shallow crustal (3–7 km) and sub-Moho (23–28 km) levels of crystallization. These magma storage regions coincide with well-constrained major lithological boundaries in the crust, implying that magma ascent and storage at Anak Krakatau is strongly controlled by crustal properties. A tandem seismic tomography survey independently identified a separate upper crustal (<7 km) and a lower to mid-crustal magma storage region (>7 km). Both petrological and seismic methods are sensitive in detecting magma bodies in the crust, but suffer from various limitations. Combined geophysical and petrological surveys, in turn, offer increased potential for a comprehensive characterization of magma plumbing at active volcanic complexes.     

Institutional power-geometries: enduring and shifting work relations in cleansing depots

Institutions are objects of study that raise questions about the relationship between continuity and change. Employment is changing and for this reason it presents an opportunity to explore how it is that paid work might be thought of as an institutional ‘space’ that is made up of enduring and shifting power relations. This paper views institutions through a lens of ‘power-geometries’, that is, as complex webs of relations of domination and subordination (Massey, D., 1992. New Left Review 196, 65–84). The paper illustrates these power-geometries by exploring employment in local authority cleansing depots in South East England. I concentrate on how the inequity of employment relations enables the institutionalisation of work practices. Employment relations were found to have shifted to different degrees according to the particular geographies and histories of labour markets, employer strategies, local politics and worker solidarities. Despite these variations the asymmetry of employment relations is seen to have endured. I conclude by arguing that whilst power-geometries are not fixed, when ‘institutionalised’ they are not easily changed during ‘everyday’ interaction.     

低温绿泥石成分温度计Fe/(Fe+Mg)校正的必要性问题

绿泥石是沉积岩、低级变质岩和水热蚀变岩中的常见矿物,基于四次配位Al含量的绿泥石成分温度计是确定古成岩或变质温度的最主要的手段之一。介绍了四种应用最为广泛的绿泥石成分温度计的原理,并从离子替代规律和比较研究的角度着重讨论了近年来关于绿泥石成分温度计校正的必要性。研究表明,在铝饱和的条件下,根据绿泥石中的Fe/(Fe Mg)值对绿泥石温度计进行校正并不能使计算值与实际值更为接近,而且从晶体化学的角度看,全岩的Fe/(Fe Mg)主要影响的是绿泥石中六次配位Fe与Mg的占位,而且偶合置换(Si4 )Ⅳ(Mg2 )Ⅵ—(Al3 )Ⅳ(Al3 )Ⅵ和(Si4 )Ⅳ(Fe2 )Ⅵ—(Al3 )Ⅳ(Al3 )Ⅵ共同控制着四次配位Al的占位。所以在铝饱和的岩石体系中可不必进行Fe/(Fe Mg)值的校正。     

The effect of organic materials on the mobility and toxicity of metals in contaminated soils

Organic materials such as compost are often proposed as suitable materials for the remediation of contaminated brownfield sites intended for soft end-use. In addition to vitalising the soil, they are also believed to immobilise metals thereby breaking contaminant-receptor pathways and reducing the ecotoxicity of the contaminants. However, some research has demonstrated contradictory effects between composts on metal immobilisation. In the present study, four different composts and a liming product containing organic matter (LimeX70) were tested to examine both their metal retention and toxicity reduction capabilities on three different metal contaminated soils. Leaching tests, a plant growth test with Greek cress (Lepidium sativum), an earthworm (Eisenia fetida) survival and condition test and a bacterial toxicity test using Vibrio fischeri were carried out. The leaching test results showed that spent mushroom compost caused an increase in metal concentration in the leachates, while LimeX70 caused a decrease. The variation in behaviour between different amendments for each soil was high, so a generic conclusion could not be drawn. Toxicity tests showed significant reduction of metal bioavailability and toxicity for Greek cress, earthworms and bacteria. The results also suggest that more research should be undertaken to understand the mechanisms involved in metal complexation using different types of organic matter, in order to optimise the use of organic materials like compost for soil remediation.     

Between-Population Differences in Multi-stressor Tolerance During Embryo Development in the American Horseshoe Crab, <Emphasis Type="Italic">Limulus polyphemus</Emphasis>

The American horseshoe crab, Limulus polyphemus, is found along the Atlantic and Gulf of Mexico coasts in genetically isolated populations. Eggs are laid in shoreline beaches that expose developing embryos to combinations of environmental stressors. Whether populations of L. polyphemus differ in multi-stressor tolerance had never been tested. We assessed the multi-stressor tolerance of L. polyphemus embryos from a population in Delaware Bay (DE) and determined whether these differed from the multi-stressor tolerance of embryos from a more southerly Florida Gulf Coast (FGC) population. We monitored the field sediment temperatures and determined multi-stressor tolerance of DE embryos, then compared these to published data for FGC embryos. For multi-stressor tolerance, we assessed development success of embryos in 2-week exposures to 36 full-factorial combinations of temperature (20, 25, 30, 35 °C), salinity (5, 15, and 34 ppt), and ambient O₂ (5, 13, and 21% O₂), followed by 2 weeks in recovery conditions. Sediment temperatures in the DE site ranged from 9.5 to 46 °C, with extended periods exceeding 35 °C. Development success was similar between the DE and FGC populations in 14 of 26 multi-stressor combinations. The DE embryos were generally more successful in conditions that included high temperature or moderate hyposalinity, whereas the FGC embryos were generally more successful in conditions that included extreme hyposalinity. This suggests that although multi-stressor tolerances are generally similar between the two populations, specific differences exist that correlate more with differences in nest microenvironment than latitude.     

Caledonian eclogite-facies metamorphism of Early Proterozoic protoliths from the North-East Greenland Eclogite Province

High-pressure metamorphic assemblages occur in mafic, ultramafic and a few intermediate rocks in a gneiss complex that covers an area of approximately 400 × 100 km in the North-East Greenland Caledonides. Detailed petrologic and geochronologic studies were carried out on three samples in order to clarify the P-T-t evolution of this eclogite province. Geothermobarometry yields temperature estimates of 700–800 °C and pressure estimates of at least 1.5 GPa from an eclogite sensu stricto and as high as 2.35 GPa for a garnet websterite. The eclogite defines a garnet-clinopyroxene-amphibole-whole rock Sm-Nd isochron age of 405 ± 24 Ma (MSWD 0.9). Isofacial garnet websterites define garnet-clinopyroxene-orthopyroxene-amphibole-whole rock-(biotite) ages of 439 ± 8 Ma (MSWD =2.1) for a coarse-grained sample and 370 ± 12 Ma (MSWD=0.6) for a finer-grained variety. Overgrowths on zircons from the fine-grained pyroxenite and the eclogite give a pooled ²⁰⁶Pb/²³⁸U SHRIMP age of 377 ± 7 Ma (n=4). Significantly younger Rb-Sr biotite ages of 357 ± 8, 330 ± 6 and 326 ± 6 agree with young Rb-Sr, K-Ar and ⁴⁰Ar/³⁹Ar mineral ages from the gneiss complex and indicate slow cooling of the eclogitic rocks. High-pressure metamorphism may have been at least 439 Ma old (Siluro-Ordovician) with cooling through amphibolite-facies conditions in the Devonian and continued crustal thinning and exhumation well into the Carboniferous. Sm-Nd whole rock model ages indicate the eclogite protoliths are Early Proterozoic in age, while ²⁰⁷Pb/²⁰⁶Pb SHRIMP ages of 1889 ± 18 and 1981 ± 8 from anhedral zircon cores probably reflect Proterozoic metasomatism. The samples have negative ɛ_Nd values (−5 to −16) and elevated ⁸⁷Sr/⁸⁶Sr ratios (0.708–0.715), consistent with field evidence that the eclogite protoliths were an integral part of the continental crust long before Caledonian metamorphism. The presence of a large Caledonian eclogite terrane in Greenland requires modification of current tectonic models that postulate subduction of Baltica beneath Laurentia during the Caledonian orogeny. Received: 9 October 1996 / Accepted: 7 July 1997