The history of the Tissint meteorite,from its crystallization on Mars to its exposure in space: New geochemical,isotopic, and cosmogenic nuclide data

The Tissint meteorite fell on July 18, 2011 in Morocco and was quickly recovered, allowing the investigation of a new unaltered sample from Mars. We report new high‐field strength and highly siderophile element (HSE) data, Sr‐Nd‐Hf‐W‐Os isotope analyses, and data for cosmogenic nuclides in order to examine the history of the Tissint meteorite, from its source composition and crystallization to its irradiation history. We present high‐field strength element compositions that are typical for depleted Martian basalts (0.174 ppm Nb, 17.4 ppm Zr, 0.7352 ppm Hf, and 0.0444 ppm W), and, together with an extended literature data set for shergottites, help to reevaluate Mars’ tectonic evolution in comparison to that of the early Earth. HSE contents (0.07 ppb Re, 0.92 ppb Os, 2.55 ppb Ir, and 7.87 ppb Pt) vary significantly in comparison to literature data, reflecting significant sample inhomogeneity. Isotope data for Os and W (¹⁸⁷Os/¹⁸⁸Os = 0.1289 ± 15 and an ε¹⁸²W = +1.41 ± 0.46) are both indistinguishable from literature data. An internal Lu‐Hf isochron for Tissint defines a crystallization age of 665 ± 74 Ma. Considering only Sm‐Nd and Lu‐Hf chronometry, we obtain, using our and literature values, a best estimate for the age of Tissint of 582 ± 18 Ma (MSWD = 3.2). Cosmogenic radionuclides analyzed in the Tissint meteorite are typical for a recent fall. Tissint's pre‐atmospheric radius was estimated to be 22 ± 2 cm, resulting in an estimated total mass of 130 ± 40 kg. Our cosmic‐ray exposure age of 0.9 ± 0.2 Ma is consistent with earlier estimations and exposure ages for other shergottites in general.     

Diapycnal mixing by meso-scale eddies

The mean available potential energy released by baroclinic instability into the meso-scale eddy field has to be dissipated in some way and Tandon and Garrett [Tandon, A., Garrett, C., 1996. On a recent parameterization of mesoscale eddies. J. Phys. Oceanogr. 26 (3), 406–416] suggested that this dissipation could ultimately involve irreversible mixing of buoyancy by molecular processes at the small-scale end of the turbulence cascade. We revisit this idea and argue that the presence of dissipation within the thermocline automatically requires that a component of the eddy flux associated with meso-scale eddies must be associated with irreversible mixing of buoyancy within the thermocline. We offer a parameterisation of the implied diapycnal diffusivity based on (i) the dissipation rate for eddy kinetic energy given by the meso-scale eddy closure of Eden and Greatbatch [Eden, C., Greatbatch, R.J., 2008. Towards a meso-scale eddy closure. Ocean Modell. 20, 223–239.] and (ii) a fixed mixing efficiency. The implied eddy-induced diapycnal diffusivity (κ) is implemented in a coarse resolution model of the North Atlantic. In contrast to the vertical diffusivity given by a standard vertical mixing scheme, large lateral inhomogeneities can be found for κ in the interior of the ocean. In general, κ is large, i.e. up to o(10) cm²/s, near the western boundaries and almost vanishing in the interior of the ocean.     

Estimating the potential predictability of Australian surface maximum and minimum temperature

A study is made of the potential predictability of seasonal means in Australian surface maximum and minimum temperature using monthly data from December 1950 to November 2000. Because the usual assumption of stationarity cannot be applied to the observations at all stations and for all seasons, a modification to an existing methodology is proposed. Here, we show that, to a first order, monthly mean variances within a season can be modeled by a linear relationship, and inter-monthly correlations can be assumed to be stationary. The intraseasonal component of variability can then be estimated using monthly data. Removing the intraseasonal variance from the total interannual variance allows an estimate of the potential predictability to be made. Surface maximum and minimum temperature has high potential predictability over most of northern Australia in the four main seasons. However, there is high potential predictability only in some of the four seasons for the centre and south of Australia. Surface minimum temperature is generally more potentially predictable than surface maximum temperature. The spatial and temporal patterns of potential predictability are generally consistent with published patterns of hindcast skill from a statistical forecast scheme. A comparison between the intraseasonal variance of Australian surface maximum and minimum temperature estimated using the stationary variance assumption and the linear assumptions showed qualitatively and quantitatively similar patterns of distribution.     

Geochemical constraints on the petrogenesis of arc picrites and basalts,New Georgia Group,Solomon Islands

Island arc picrites are restricted to a few localities including the Lesser Antilles, Japan, Vanuatu and the Solomon Islands. The picrite occurrences appear to be linked to the subduction of young, hot oceanic crust and anomalous geotherms. At the Solomon arc, the Australian plate is presently subducted beneath the Pacific plate. A particular feature of the Solomon arc is the subduction of a spreading center (Woodlark Ridge). In the Solomon Islands, picrites only occur in the New Georgia archipelago, located above or close to the subducting Woodlark Ridge. These picrites contain between 12 and 30 wt% MgO, the associated primitive basalts show MgO contents from 11.5 to 13.6 wt%. Linear trends defined by Cr, Ni and other trace elements vs. MgO indicate that the picritic bulk compositions originate from mixing between a basaltic-picritic melt and a Mg- and Cr-rich endmember, rather than from fractional crystallization of extremely Mg-rich magmas. Major and trace element modeling identify mantle wedge peridotite as the most likely mixing endmember. Trace element abundances in the Solomon arc picrites indicate a mantle source enrichment by subduction components and a large depletion of Nb and Ta that is typical for island arc volcanic rocks. Most incompatible trace element patterns of the New Georgia picrites and basalts are parallel, supporting a cogenetic evolution of these rocks by mixing processes. ⁸⁷Sr/⁸⁶Sr and Nd values in the basalts and picrites range from 0.7033 to 0.7043 and +5.8 to +8.0, respectively. These values partially overlap with compositions of the Indian MORB field. Alternatively, subducted sediment and fluids from altered MORB may have displaced the Sr isotope composition to more radiogenic ⁸⁷Sr/⁸⁶Sr. Hf values range from +12.2 to +14.6 and show in combination with Nd that the picrites were most likely generated within the Indian mantle domain.This revised version was published online September 2004 with a correction to Table 2.     

Highly depleted Hadean mantle reservoirs in the sources of early Archean arc-like rocks, Isua supracrustal belt, southern West Greenland

Growing evidence from the accessible geological record reveals that crust-mantle differentiation on Earth started as early as 4.4 Ga. In order to assess the extent of early Archean mantle depletion, we obtained ¹⁷⁶Lu-¹⁷⁶Hf, ¹⁴⁷Sm-¹⁴³Nd, and high field strength element (HFSE) concentration data for the least altered, well characterized boninite-like metabasalts and associated metasedimentary rocks from the Isua supracrustal belt (southern West Greenland). The metasediments exhibit initial εHf₍₃₇₂₀₎ values from −0.7 to +1.5 and initial εNd₍₃₇₂₀₎ values from +1.6 to +2.1. Initial εHf₍₃₇₂₀₎ values of the least altered boninite-like metabasalts span a range from +3.5 to +12.9 and initial εNd₍₃₇₂₀₎ values from −0.3 to +3.2. These initial Hf-isotope ratios display coherent trends with SiO₂, Al₂O₃/TiO₂ and other relatively immobile elements, indicating contamination via assimilation of enriched components, most likely sediments derived from the earliest crust in the region. This model is also consistent with previously reported initial γOs₍₃₇₂₀₎ values for some of the samples. In addition to the positive εHf₍₃₇₂₀₎ values, the least disturbed samples exhibit positive εNd₍₃₇₂₀₎ values and a co-variation of εHf₍₃₇₂₀₎ and εΝd₍₃₇₂₀₎ values. Based on these observations, it is argued, that the most depleted samples with initial εHf₍₃₇₂₀₎ values of up to +12.9 and high ¹⁷⁶Lu/¹⁷⁷Hf of ∼0.05 to ∼0.09 tap a highly depleted mantle source with a long term depletion history in the garnet stability field. High precision high field strength element (HFSE) data obtained for the Isua samples confirm the contamination trend. Even the most primitive samples display negative Nb-Ta anomalies and elevated Nb/Ta, indicating a subduction zone setting and overprint of the depleted mantle sources by felsic melts generated by partial melting of eclogite. Collectively, the data for boninite-like metabasalts support the presence of strongly depleted mantle reservoirs as previously inferred from Hf isotope data for Hadean zircons and combined ¹⁴²Nd-¹⁴³Nd isotope data for early Archean rocks.     

Optical Design of Multilayer Achromatic Waveplate by Simulated Annealing Algorithm

We applied a Monte Carlo method-simulated annealing algorithm-to carry out the design of multilayer achromatic waveplate. We present solutions for three-, six-and ten-layer achromatic waveplates. The optimized retardance settings are found to be 89°51'39"±0°33'37" and 89°54'46"±0°22'4" for the six-and ten-layer waveplates, respectively, for a wavelength range from 1000nm to 1800nm. The polarimetric properties of multilayer waveplates are investigated based on several numerical experiments. In contrast to previously proposed three-layer achromatic waveplate, the fast axes of the new six-and ten-layer achromatic waveplate remain at fixed angles, independent of the wavelength. Two applications of multilayer achromatic waveplate are discussed, the general-purpose phase shifter and the birefringent filter in the Infrared Imaging Magnetograph (IRIM) system of the Big Bear Solar Observatory (BBSO). We also checked an experimental method to measure the retardance of waveplates.     

Improvement of hydrodynamic forecasting of Danish waters: impact of low-frequency North Atlantic barotropic variations

The Danish Maritime Safety Administration (DaMSA) provides forecast of elevations, currents, and other parameters to the maritime society. Accurate and reliable predictions are important to help navigate Danish waters in a safe manner, and the forecasts are routinely used by the Vessel Traffic Services in the Great Belt and the Sound. The DaMSA model setup includes three nested models, with coarse resolution in the North Atlantic and increasing to 600 m in the Belt Sea and South West Baltic. Observations of some special events in late 2009 drew attention to a possible relation between Atlantic-scale surge events and small-scale currents in the Danish Straits. During the special event with large-scale surge, the observed southward moving current in the Danish Straits was 0.5–2.0 m/s for several days, while the operational model showed a much smaller response. As a consequence, the entire DaMSA model complex was revised during 2010. Multi-annual reruns have showed that with the updated model, the explained variance of the current increases from 67% to 88%.     

Comparison of approaches for the characterization of contamination at rural megasites

The present work focuses on approaches for the characterization of subsurface contamination, which need to be reliable and cost-effective, particularly for extended and remote areas aimed at being redeveloped. Requirements are discussed with respect to specific conditions at megasites, in order to enable site valorization. In a case study, two approaches are compared, comprising (1) conventional site investigation based on historical surveys and concentration measurements at monitoring wells installed in areas suspected of being polluted and (2) the use of direct push (DP) methods covering the complete area. The DP investigation provided information on the contamination distribution and yielded also important information on hydraulic conditions. Statistical analysis of the results applying indicator kriging revealed that the conventional approach is markedly risky when decision-making relies solely on historical and sparse data. The DP campaign remarkably reduced the uncertainty concerning the estimated occurrence of polluted groundwater at the whole site. Furthermore, monitoring measurements are analyzed showing the possible importance of temporal variability. Taking economical consideration into account, DP-based groundwater screening is recommended to obtain either first or complementary information on the entire site. Based on these data, also locations for a long-term monitoring could be selected if temporal variability is assumed relevant.     

Can CDM monitoring requirements be reduced while maintaining environmental integrity?

Monitoring, reporting, and verification (MRV) requirements in the Clean Development Mechanism (CDM) are perceived to be of high quality, but also complex and stringent. Only one-third of the registered projects successfully managed initial verification and already received carbon credits. The time required to achieve first issuance remains high despite considerable improvements in other CDM project cycle steps. This leads to the question of whether MRV provisions in the CDM represent barriers that could be lowered while ensuring the CDM's integrity. The CDM requirements are compared with the MRV provisions of the EU Emission Trading System (EU ETS). The comparison shows that CDM–MRV provisions are often stricter and less flexible compared to similar provisions in the EU ETS. Due to structural differences between the EU ETS and the CDM, some different MRV approaches are justified and reflect the CDM's disparate objectives and complexity. It is found that some CDM provisions result in barriers which seem avoidable and do not contribute to the CDM's environmental integrity. Recommendations are made for CDM-specific improvements and general structural changes to improve cost-efficiency and reduce uncertainty with relevance to policy developments around future market mechanisms.     

An integrative hierarchical monitoring approach applied at a natural analogue site to monitor CO2 degassing areas

This paper introduces an integrative hierarchical monitoring concept allowing for the detection and assessment of possible leakages from geological storage formations into the shallow subsurface or atmosphere. The concept introduced in this paper combines various investigation methods working at different scales and with varying resolutions. This approach will allow large spatial areas to be consistently covered, to enable efficient monitoring. Experience gained from the adoption of these tools for naturally occurring CO₂ deposits (analogue sites) is helpful for the evaluation and adoption of the methods to the requirements of storage projects.