Dissolution–precipitation processes governing the carbonation and silicification of the serpentinite sole of the New Caledonia ophiolite

The weathering of mantle peridotite tectonically exposed to the atmosphere leads commonly to natural carbonation processes. Extensive cryptocrystalline magnesite veins and stock-work are widespread in the serpentinite sole of the New Caledonia ophiolite. Silica is systematically associated with magnesite. It is commonly admitted that Mg and Si are released during the laterization of overlying peridotites. Thus, the occurrence of these veins is generally attributed to a per descensum mechanism that involves the infiltration of meteoric waters enriched in dissolved atmospheric CO₂. In this study, we investigate serpentinite carbonation processes, and related silicification, based on a detailed petrographic and crystal chemical study of serpentinites. The relationships between serpentine and alteration products are described using an original method for the analysis of micro-X-ray fluorescence images performed at the centimeter scale. Our investigations highlight a carbonation mechanism, together with precipitation of amorphous silica and sepiolite, based on a dissolution–precipitation process. In contrast with the per descensum Mg/Si-enrichment model that is mainly concentrated in rock fractures, dissolution–precipitation process is much more pervasive. Thus, although the texture of rocks remains relatively preserved, this process extends more widely into the rock and may represent a major part of total carbonation of the ophiolite.     

Sequential melting and fractional crystallization: Granites from Guarda-Sabugal area, central Portugal

Seven distinct phases of Variscan two-mica granite are recognized in the Guarda-Sabugal area. They intruded the Cambrian schist-metagraywacke complex, crystallized in the middle crust, and are syn- to late-D3 (309.2 ± 1.8 Ma), late-D3 (304–300 Ma) and late- to post-D3 (299 ± 3 Ma; ID-TIMS ages on zircon and monazite). Two of the granites, G2 and G5, are close in age and have similar Sr, Nd and O isotope characteristics but contrasting whole rock and mineral features and formed by sequential increasing degree of partial melting of a common metasedimentary protolith. During sequential melting Ti, total Fe, Mg, Ca, Zr, Zn, Sr, Ba and REE contents and (La/Yb)_N increase and Si and Rb contents decrease, plagioclase becomes richer in anorthite and biotite and muscovite richer in Ti and Mg. Each of these granites evolved subsequently by fractional crystallization of quartz, K-feldspar, plagioclase, biotite and ilmenite, defining separate series G2–G3–G7 and G5–G6 containing late Sn-bearing differentiates. Two other granites G1 and G4 represent distinct pulses of magma with individual fractionation trends for major and trace elements and distinct (⁸⁷Sr/⁸⁶Sr)₃₀₀, ?Nd₃₀₀ and δ¹⁸O values.     

Precise orbit determination for the GRACE mission using only GPS data

The GRACE (gravity recovery and climate experiment) satellites, launched in March 2002, are each equipped with a BlackJack GPS onboard receiver for precise orbit determination and gravity field recovery. Since launch, there have been significant improvements in the background force models used for satellite orbit determination, most notably the model for the geopotential. This has resulted in significant improvements to orbit accuracy for very low altitude satellites. The purpose of this paper is to investigate how well the orbits of the GRACE satellites (about 470 km in altitude) can currently be determined using only GPS data and based on the current models and methods. The orbit accuracy is assessed using a number of tests, which include analysis of orbit fits, orbit overlaps, orbit connecting points, satellite Laser ranging residuals and K-band ranging (KBR) residuals. We show that 1-cm radial orbit accuracy for the GRACE satellites has probably been achieved. These precise GRACE orbits can be used for such purposes as improving gravity recovery from the GRACE KBR data and for atmospheric profiling, and they demonstrate the quality of the background force models being used.     

Can marine fisheries and aquaculture meet fish demand from a growing human population in a changing climate?

Expansion in the world's human population and economic development will increase future demand for fish products. As global fisheries yield is constrained by ecosystems productivity and management effectiveness, per capita fish consumption can only be maintained or increased if aquaculture makes an increasing contribution to the volume and stability of global fish supplies. Here, we use predictions of changes in global and regional climate (according to IPCC emissions scenario A1B), marine ecosystem and fisheries production estimates from high resolution regional models, human population size estimates from United Nations prospects, fishmeal and oil price estimations, and projections of the technological development in aquaculture feed technology, to investigate the feasibility of sustaining current and increased per capita fish consumption rates in 2050. We conclude that meeting current and larger consumption rates is feasible, despite a growing population and the impacts of climate change on potential fisheries production, but only if fish resources are managed sustainably and the animal feeds industry reduces its reliance on wild fish. Ineffective fisheries management and rising fishmeal prices driven by greater demand could, however, compromise future aquaculture production and the availability of fish products.     

Shear wave propagation along infinite slopes: A theoretically based numerical study

In this paper, the seismic response of ‘infinitely’ long slopes is numerically analysed via the formulation of a 1D analytical/numerical model, in which the soil mechanical behaviour is assumed to be elasto‐perfectly viscoplastic and simple shear (SS) kinematical constraints are imposed. In order to simplify the problem, a theoretically based procedure to set up a fully 1D shear constitutive model is defined, within which the mechanical response of a multiaxial relationship is condensed. The use of a 1D shear constitutive model is aimed at reducing the number of unknowns and, therefore, the computational costs. In particular, the case of the Mohr–Coulomb yield criterion is considered, while an enhanced Taylor–Galerkin finite element algorithm is employed to simulate the seismic wave propagation within the soil stratum. The proposed ‘condensation’/calibration procedure captures both the ‘pseudo’‐hardening pre‐failure behaviour and the influence of dilation on the occurrence of strain‐localization, which characterize, under SS conditions, the static response of virgin perfectly plastic soils. The effectiveness of the conceived method is shown with reference to freshly deposited deposits, while, in the case of highly overconsolidated strata, some difficulties arise because of the brittle behaviour induced both by unloading and non‐associativeness. Copyright © 2011 John Wiley & Sons, Ltd.     

Process length variation of the cyst of the dinoflagellate Protoceratium reticulatum in the North Pacific and Baltic‐Skagerrak region: calibration as an annual density proxy and first evidence of pseudo‐cryptic speciation

Process length variation of cysts of the dinoflagellate Protoceratium reticulatum (Claparède et Lachmann) Bütschli in surface sediments from the North Pacific was investigated. The average process length showed a significant inverse relation to annual seawater density: σ_{t annual} = ?0.8674 × average process length + 1029.3 (R² = 0.84), with a standard error of 0.78 kg m^?3. A sediment trap study from Effingham Inlet in British Columbia revealed the same relationship between average process length and local seawater density variations. In the Baltic–Skagerrak region, the average process length variation was related significantly to annual seawater density: σ_{t annual} = 3.5457 × average process length ? 993.28 (R² = 0.86), with a standard error of 3.09 kg m^?3. These calibrations cannot be reconciled, which accentuates the regional character of the calibrations. This can be related to variations in molecular data (small subunit, long subunit and internal transcribed spacer sequences), which show the presence of several genotypes and the occurrence of pseudo‐cryptic speciation within this species. Copyright © 2012 John Wiley & Sons, Ltd.     

Strato-mesospheric ozone and IMF sector boundary

Summary We find no effect of the interplanetary magnetic field(IMF) sector boundary crossing in ozone at altitudes ranging from the middle stratosphere(10 hPa) to the lower mesosphere(0.4 hPa) at middle latitudes(40°–60° N), based on winter data over the period of December 1979–December 1982.

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Резюме Мы не нaшлu нuкaко о эффекma nересеченuя секmорноŭ рaнuцы межnлaнеmно о мa нumно о nоля в озоне в облaсmu высоm меж?rt;у сре?rt;неŭ сmрamосфероŭ(10 Пa) u нuжнеŭ мезосфероŭ(0,4 Пa) нa сре?rt;нuх шuроmaх(40°–60° с.ш.), nрuменяя зuмнuе ?rt;aнные зa nерuо?rt; ?rt;екaбрь 1979 – ?rt;екaбрь 1982 .

     

Ontogenic shifts in predatory roles involving two invasive species

The red swamp crayfish, Procambarus clarkii, and the eastern mosquitofish, Gambusia holbrooki have been introduced worldwide, but the interactions between these invasive species are not well known. The effects of crayfish presence, crayfish size and water depth on the consumption of G. holbrooki by P. clarkii were analyzed, as were the effects of mosquitofish presence and water depth on the consumption of recently hatched crayfish (RHC) by mosquitofish. To better understand this subject we conducted aquaria and open air mesocosm experiments simulating a rice field section. Aquarium experiments showed that P. clarkii consumes G. holbrooki and that G. holbrooki consumes RHC. Adult crayfish size did not significantly affect the consumption of mosquitofish and water depth had no effect on the consumption of G. holbrooki by P. clarkii and vice versa. In the outdoor mesocosm experiments P. clarkii caused no statistically significant effect on G. holbrooki numbers or biomass when compared with controls without crayfish. In spite of this, the analysis of crayfish stomach contents clearly demonstrated that several G. holbrooki individuals were consumed, indicating that crayfish can profit from the presence of G. holbrooki. Results from our study suggest that in shallow pools there are strong interactions between the two invasive species since adult crayfish predate mosquitofish and mosquitofish predate recently hatched crayfish. Therefore, there are bidirectional trophic interactions between these invasive species which change depending on their relative size. We believe that these interactions should become more relevant in confined areas such as small shallow pools formed during the late summer and autumn.     

NO2 total column evolution during the 1989 spring at Antarctica Peninsula

Ground-based visible differential absorption spectrometry during twilight has been used for NO₂ total column observations at the Antarctica Peninsula, Marambio Base (64S, 56W), during the austral spring of 1989 (9 September to 25 November).Results show moderate NO₂ vertical column levels of 1.5 to 2.5×10¹⁵ molec cm^-2 in the morning and 2 to 3×10¹⁵ molec cm^-2 in the evening until middle October, highly modulated by planetary wave activity. From that date until the end of the period, a steady increase occurs which is associated with the rising of lower stratosphere temperature as the vortex weakens, reaching values of 5×10¹⁵ molec cm^-2 in late November, with small a.m.-p.m. differences. NO₂ is found to be positively correlated to both total ozone and 50 hPa temperature during the entire spring. However, when analyzing the departures from linear trends, a highly negative correlation has been observed from day 301 onwards.