Enrichment of Rare Earth Elements during magmatic and post-magmatic processes: a case study from the Loch Loyal Syenite Complex, northern Scotland

Concern about security of supply of critical elements used in new technologies, such as the Rare Earth Elements (REE), means that it is increasingly important to understand the processes by which they are enriched in crustal settings. High REE contents are found in syenite-dominated alkaline complexes intruded along the Moine Thrust Zone, a major collisional zone in north-west Scotland. The most northerly of these is the Loch Loyal Syenite Complex, which comprises three separate intrusions. One of these, the Cnoc nan Cuilean intrusion, contains two mappable zones: a Mixed Syenite Zone in which mafic melasyenite is mixed and mingled with leucosyenite and a Massive Leucosyenite Zone. Within the Mixed Syenite Zone, hydrothermal activity is evident in the form of narrow altered veins dominated by biotite and magnetite; these are poorly exposed and their lateral extent is uncertain. The REE mineral allanite is relatively abundant in the melasyenite and is extremely enriched in the biotite–magnetite veins, which have up to 2 % total rare earth oxides in bulk rock analyses. An overall model for development of this intrusion can be divided into three episodes: (1) generation of a Light Rare Earth Element (LREE)-enriched parental magma due to enrichment of the mantle source by subduction of pelagic carbonates; (2) early crystallisation of allanite in melasyenite, due to the saturation of the magma in the LREE; and (3) hydrothermal alteration, in three different episodes identified by petrography and mineral chemistry, generating the intense enrichment of REE in the biotite–magnetite veins. Dating of allanite and titanite in the biotite–magnetite veins gives ages of c. 426 Ma, overlapping with previously published crystallisation ages for zircon in the syenite.     

Mean flow-transient perturbation interaction in the Southern Hemisphere: a simulation using a variable-resolution GCM

The ability of an atmospheric general circulation model to reproduce fundamental features of the wintertime extratropical Southern Hemisphere (SH) circulation is evaluated with emphasis on the daily variability of the SH mean flow and the mean flow-transient perturbations interaction. Two 10-year simulations using a new version of the LMDZ GCM with a stretched grid scheme centered at 45 °S and forced by climatological SST are performed: a high (144Ꮡ) and low (64Ꭹ) horizontal resolution runs. The performance of both simulations was determined by comparing several simulated fields (zonal wind, temperature, kinetic energy, transient eddy momentum and heat fluxes, Eliassen-Palm fluxes, Eady growth rate and baroclinic conversion term) against the European Centre for Medium Range Weather Forecast reanalyses (ERA). High and low-resolution simulations are similar in many respects; in particular, both experiments reproduce the main patterns of the southern extratropical large-scale circulation satisfactorily. Increasing resolution does not improve universally some spurious aspects of the low resolution simulation (e.g. the cold bias in the high polar troposphere, the debilitated subtropical jet, the low baroclinic conversion rate). Those aspects present little sensitivity to the model resolution. The interaction between transient eddies and zonal mean flow are examined. The low-resolution experiment is able to qualitatively represent the acceleration/deceleration of the mean flow by transient perturbations, south/north of 30 °S with an accuracy similar to that of the high-resolution experiment. Although both experiments represent the baroclinic structure of the mean flow satisfactorily, the model underestimates some transient properties due to the underestimation of the baroclinic conversion term in middle latitudes. Such misrepresentation does not improve with increasing resolution and is related to the relatively weak meridional temperature gradient and the inadequate geographical distribution of the eddy heat fluxes. In particular, the eddy kinetic energy is always underestimated. Eddy kinetic energy does not improve convincingly with increasing resolution, suggesting that the adequate representation of the storm tracks is highly influenced by the physical parametrizations.     

On characteristics of wind direction fluctuations in the surface layer

It is shown that the ratio of standard deviation of lateral velocity to the friction velocity, /u _*, and therefore wind direction fluctuations, are sensitive to mesoscale terrain properties. Under neutral conditions, /u _* is almost 40% larger in rolling terrain than over a horizontal surface. In the lee of a low mountain, the fluctuations may be 2.5 times as strong as over horizontal terrain. In contrast, vertical velocity fluctuations are little influenced by mesoscale terrain features.Now with Air Weather Service, Offutt AFB, Omaha, Nebraska.     

Frequency distributions of transient regional climate change from perturbed physics ensembles of general circulation model simulations

Large ensembles of coupled atmosphere–ocean general circulation model (AOGCM) simulations are required to explore modelling uncertainty and make probabilistic predictions of future transient climate change at regional scales. These are not yet computationally feasible so we have developed a technique to emulate the response of such an ensemble by scaling equilibrium patterns of climate change derived from much cheaper “slab” model ensembles in which the atmospheric component of an AOGCM is coupled to a mixed-layer ocean. Climate feedback parameters are diagnosed for each member of a slab model ensemble and used to drive an energy balance model (EBM) to predict the time-dependent response of global surface temperature expected for different combinations of uncertain AOGCM parameters affecting atmospheric, land and sea-ice processes. The EBM projections are then used to scale normalised patterns of change derived for each slab member, and hence emulate the response of the relevant atmospheric model version when coupled to a dynamic ocean, in response to a 1% per annum increase in CO₂. The emulated responses are validated by comparison with predictions from a 17 member ensemble of AOGCM simulations, constructed from variants of HadCM3 using the same parameter combinations as 17 members of the slab model ensemble. Cross-validation permits estimation of the spatial and temporal dependence of emulation error, and also allows estimation of a correction field to correct discrepancies between the scaled equilibrium patterns and the transient response, reducing the emulation error. Emulated transient responses and their associated errors are obtained from the slab ensemble for 129 pseudo-HadCM3 versions containing multiple atmospheric parameter perturbations. These are combined to produce regional frequency distributions for the transient response of annual surface temperature change and boreal winter precipitation change. The technique can be extended to any surface climate variable demonstrating a scaleable, approximately linear response to forcing.     

Summer temperature variability across four urban neighborhoods in Knoxville,Tennessee, USA

The urban heat island (UHI) is a well-documented effect of urbanization on local climate, identified by higher temperatures compared to surrounding areas, especially at night and during the warm season. The details of a UHI are city-specific, and microclimates may even exist within a given city. Thus, investigating the spatiotemporal variability of a city’s UHI is an ongoing and critical research need. We deploy ten weather stations across Knoxville, Tennessee, to analyze the city’s UHI and its differential impacts across urban neighborhoods: two each in four neighborhoods, one in more dense tree cover and one in less dense tree cover, and one each in downtown Knoxville and Ijams Nature Center that serve as control locations. Three months of temperature data (beginning 2 July 2014) are analyzed using paired-sample t tests and a three-way analysis of variance. Major findings include the following: (1) Within a given neighborhood, tree cover helps negate daytime heat (resulting in up to 1.19 ^°C lower maximum temperature), but does not have as large of an influence on minimum temperature; (2) largest temperature differences between neighborhoods occur during the day (0.38–1.16 ^°C difference), but larger differences between neighborhoods and the downtown control occur at night (1.04–1.88 ^°C difference); (3) presiding weather (i.e., air mass type) has a significant, consistent impact on the temperature in a given city, and lacks the differential impacts found at a larger-scale in previous studies; (4) distance from city center does not impact temperature as much as land use factors. This is a preliminary step towards informing local planning with a scientific understanding of how mitigation strategies may help minimize the UHI and reduce the effects of extreme weather on public health and well-being.     

一堆气候模式的灵敏度分析

在本文中我们设计了一个只有垂直方向的一维气候模式。该模式可以用来研究大气中CO_2气体浓度从330增加到660ppm时地面温度的变化。同时我们将分析几个反馈机制对气候系统灵敏度的贡献,其中包括大气湿度反馈、云反馈和地面反射率反馈等机制。     

The problem of “naturally”-occurring drought

Naturally-occurring drought is defined here to be drought arising from the nonlinear interactions which are an inherent part of the dynamics of the climatic system. As such it has no specific excitation mechanism, in contrast to forced drought where sea surface temperature anomalies are frequently cited as an important precursor. The essential difference between these two types of drought is that the former is very local and isolated spatially, whereas the latter is widespread and coherent. Observations for Australia are used to illustrate these points. Results are given for a 10-year general circulation model integration which clearly simulated naturally occurring drought and highlighted its unique characteristics. Multi-annual time series for specific geographical regions in the model show that no differences in monthly mean values of relative humidity or zonal and meridional fluxes of moisture were apparent for years with or without drought. More detailed analysis indicated that rather small differences exist in atmospheric temperatures and absolute humidities between drought and nondrought years which are important factors in determining the onset of precipitation in the model.Overall the analysis emphasises the subtlety of the processes involved. These processes, however, were able to produce completely different precipitation histories from one year to the next at a given point. The smallness of the changes involved in the atmospheric processes indicates that the nonlinearities were able to modulate conditions at a given point within an existing synoptic system only slightly, rather than initiate a new climatic regime in drought years. The problem of naturally-occurring drought, of course, is that it is intrinsically unpredictable.     

A New Gastrioceras from Sinkiang

In the rich collection of fossils made in Sinkiang by Professor P.L.Yuan of the Tsinghua University,there are a few but very beautifulspecimens representing a new species of Gastrioceras.They were obtainedfrom Shihtsientan~1,a locality lying about 150 kilometers NNE of theChitai city~2 in northern Sinkiang.The writer takes the opportunity torecord sincere thanks to Professor P.L.Yuan for giving him the privilege     

Culm Plants from Northern Kuangtung

正 In February 1943 some valuable specimens of plant fossils were collected by the members of the Geological Survey of Kuangtung and Kuangsi from a coal series in     

High-frequency climatic oscillations during the last deglaciation as revealed by oxygen-isotope records of benthic organisms (Ammersee,southern Germany)

High-resolution oxygen-isotope records of benthic ostracods and molluscs from Ammersee, southern Germany, show high-frequency climatic changes during the last deglaciation and parallel in great detail published faunal and floral variations reconstructed from Norwegian Sea sediments and isotope variations in Greenland ice cores. The marine and the terrestrial records give evidence of a synchronous late glacial climatic development in Greenland, NW- and Mid-Europe. However,¹⁴C-ages of the supraregional climatic events and of two tephra layers in the marine sediments of the northeastern Atlantic Ocean are significantly older than the¹⁴C-ages of the corresponding horizons on land. These differences strongly suggest that major short-term events have affected the exchangeable carbon on earth during the dramatic environmental changes related to the deglaciation and in particular have affected the CO₂-distribution within the ocean and between ocean and atmosphere. Dating methods independent of climatic variations and of the global carbon budget should be given priority to refine the timescales of the marine and atmospheric processes during the last deglaciation.This is the fourth paper in a series of papers published in this issue on high-resolution paleolimnology. These papers were presented at the Sixth International Palaeolimnology Symposium held 19–21 April, 1993 at the Australian National University, Canberra, Australia. Dr. A. F. Lotter and Dr. M. Sturm served as guest editors for these papers.