Re-interpretation of zircon date in a carbonatite dyke at the Bayan Obo giant REE-Fe-Nb deposit,China

Recent ce-valuation of the dating of the carbonatite dykes associated with the REE-Re-Nb giant deposit at Bayan Obo has     

Further Characterisation of the 91500 Zircon Crystal

This paper reports the results from a second characterisation of the 91500 zircon, including data from electron probe microanalysis, laser ablation inductively coupled plasma-mass spectrometry (LA-ICP-MS), secondary ion mass spectrometry (SIMS) and laser fluorination analyses. The focus of this initiative was to establish the suitability of this large single zircon crystal for calibrating in situ analyses of the rare earth elements and oxygen isotopes, as well as to provide working values for key geochemical systems. In addition to extensive testing of the chemical and structural homogeneity of this sample, the occurrence of banding in 91500 in both backscattered electron and cathodoluminescence images is described in detail. Blind intercomparison data reported by both LA-ICP-MS and SIMS laboratories indicate that only small systematic differences exist between the data sets provided by these two techniques. Furthermore, the use of NIST SRM 610 glass as the calibrant for SIMS analyses was found to introduce little or no systematic error into the results for zircon. Based on both laser fluorination and SIMS data, zircon 91500 seems to be very well suited for calibrating in situ oxygen isotopic analyses.     

A brief overview of the ACEP project: Ecosystem Processes in the KwaZulu-Natal Bight§

This introductory paper lays the basis for this supplementary issue by briefly presenting the state of knowledge on the KwaZulu-Natal (KZN) Bight at the start of this multi-disciplinary, multi-institutional, ship-based research project that ran from 2009 to 2013. The rationale and aims of the project are also described. The project was a major component of the South African Department of Science and Technology’s African Coelacanth Ecosystem Programme (ACEP), which has been prominent in supporting research on the east coast of South Africa and the wider South-West Indian Ocean. Pivotal to this was the RS Algoa, which was made available for two 30-day surveys (winter and summer) in the KZN Bight by the Department of Environmental Affairs. Although some aspects of the bight ecology are known, much of the research is dated and fragmented, and required refreshing and consolidation in order to produce a platform upon which the understanding of the region’s ecosystem functioning could be established. Much of the oceanographic knowledge is also dated, with no dedicated surveys and significant measurements undertaken since 1989. The overarching theme of the KZN Bight project was to examine the relative importance of sources of nutrients to the central KZN coast and how these are taken up and recycled in the ecosystem, and to describe aspects of the benthic biodiversity, which is poorly described in much of this region. An ambitious project, its accessibility to a ship-based research platform and the diverse scientific skills of the participating scientists allowed considerable success, as reflected in the papers that follow.     

On the mechanisms behind salinity anomaly signals of the northern North Atlantic

Hydrographic time series from the northern North Atlantic throughout the 20th century show oscillations in temperature and salinity at more or less regular intervals. The Great Salinity Anomalies described during the 1970s [Dickson, R.R., Meincke, J., Malmberg, S.-A., Lee, A.J., 1988. The “Great Salinity Anomaly” in the North Atlantic, 1968-1982. Progress in Oceanography 20, 103-151.], during the 1980s [Belkin, I.M., Levitus, S., Antonov, J., Malmberg, S.-A., 1998. “Great Salinity Anomalies” in the North Atlantic. Progress in Oceanography 41, 1-68.], and during the 1990s [Belkin, I.M., 2004. Propagation of the “Great Salinity Anomaly” of the 1990s around the northern North Atlantic. Geophysical Research Letters 31(8), L08306, doi:10.1029/2003GL019334.] have distinct amplitudes, and all three of them were interpreted as low salinity anomalies propagating downstream through the anti-clockwise circulation system of the northern North Atlantic Ocean. Further inspection of time series from the Northeast Atlantic and the Northwest Atlantic over the past century shows, however, several other distinct negative anomalies of lesser amplitudes. Additionally, a number of high salinity anomalies can be identified. The present paper analyses further the propagation of the negative and positive anomalies and links them together. It is shown that they have varying speeds of propagation, and that the varying speeds are correlated across the North Atlantic. We propose that varying volume fluxes in and out of the Arctic Basin is the causal mechanism behind the anomaly signals, and that the North Atlantic Oscillation (NAO) partly has influence on the flux variations described. Periods of large decadal-scale amplitudes of the NAO coincide with periods of large decadal-scale oscillation in the marine climate.     

Latitudinal changes in siphonophore assemblages across the Atlantic sector of the Southern Ocean

Siphonophores are commonly considered to be useful indicators of water masses and water-mass movement, but their employment as such across the wider Southern Ocean has not so far been attempted. We redress this here using archived samples, collected during January–February 1993 along a transect from Cape Town to the South African National Antarctic Expedition (SANAE) base in Antarctica, and compare the patterns generated with those determined from a prior analysis of whole assemblages at lower taxonomic resolution. Twenty-one species were identified from 18 of the original 53 samples collected, and two distinct assemblages were confirmed as separated by the Sub-Antarctic Front. That to the south was characterised by low diversity and high abundance and was dominated by cold-water specialists, whereas that to the north comprised a larger number of subtropical and temperate species at low abundance. Assemblage structure was strongly influenced by the mixed layer depth, sea surface salinity and chlorophyll a concentration, as well as mesozooplankton biomass. Congruence with the whole-assemblage study was high, indicating that this taxon can be suitably employed as a proxy in studies such as this. The study emphasises the value of archived plankton samples and makes a plea for better curation.     

ENVISAT Radar Altimeter Tracker Bias

In the past, errors in the determination of the orbit were dominant in radar altimeter missions, but technical advances have improved the orbit accuracy and hence, other sources of error have become more important. Sea-state bias is now the main source of error and can be divided into three sea-state dependent errors: skewness, electromagnetic bias, and tracker bias. We estimated the magnitude of the third term, by retracking ocean waveforms from ENVISAT RA-2. The retracking algorithm used is based on Maximum Likelihood Estimation. Tracker bias shows a seasonal and geographical dependence related to the distribution of significant wave height (SWH) and time origin differences. We estimated a mean value of 0.13 ± 0.07 %SWH. Temporal and regional dependent errors are introduced when using a linear retracker processing approach.     

The influence of Hudson Bay runoff and ice‐melt on the salinity of the inner Newfoundland Shelf

Abstract

The present study examines sources of the interannual variability in salinity on the Newfoundland continental shelf observed in a 40‐year time series from an oceanographic station known as Station 27. Specifically, we investigate, through lag‐correlation analysis, the a priori hypotheses that the salinity anomalies at Station 27 are determined by freshwater runoff anomalies from Hudson and Ungava bays and by ice‐melt anomalies in Hudson Bay and on the Labrador Shelf. Interannual variations of summer runoff into Hudson Bay were significantly negatively correlated with salinity anomalies on the Newfoundland Shelf with a lag (9 months) that is consistent with expected travel times based on known current velocities in Hudson Bay and along the Labrador Shelf. Sea‐ice extent over the Labrador and northern Newfoundland shelves was significantly negatively correlated with salinity at a lag of 3 to 4 months, corresponding to the time of minimum salinity at Station 27. It appears that ice‐melt over the Labrador‐northern Newfoundland Shelf is primarily responsible for the seasonal salinity minimum over the Newfoundland Shelf. Interannual variability in runoff into Ungava Bay and ice‐melt in Hudson Bay were not correlated with interannual salinity variations on the Newfoundland Shelf.     

新疆哈密香山西铜镍-钛铁矿床系同源岩浆分异演化产物——矿相学、锆石U-Pb年代学及岩石地球化学证据

香山西岩体是东天山地区发现的唯一的一个铜镍-钛铁复合型含矿岩体,前人对香山西铜镍-钛铁矿床成因认识一直存在争议。本次通过矿相学研究结合电子探针分析,在香山西铜镍矿石中发现了铜镍硫化物与钛铁氧化物共生的现象,并首次测定了香山西钛铁辉长岩的SIMS锆石U-Pb年龄为278.6±1.8Ma(MSWD=1.2),与前人测得香山中岩体角闪辉长岩的锆石U-Pb年龄基本一致,证实了香山西铜镍矿与钛铁矿为共生关系,两者空间上渐变过渡。岩石地球化学研究表明,香山岩体(包括钛铁辉长岩)为同源岩浆经结晶分异作用形成的一套镁铁-超镁铁质岩体,具有拉斑玄武质岩浆分异演化趋势,并且经历了与地壳物质的混染。与中段和东段岩石相比,香山西辉长岩类具有相对高的REE、SiO₂(平均48.99%)、K₂O+Na₂O(平均3.43%)、TiO₂(平均1.26%)和明显低的Mg^#值(平均62.4),表现出分异演化程度高于中段和东段。经反演得出香山岩体原始岩浆含MgO约10%,FeO约9%,TiO₂约1.14%,与同一成矿带内其它含铜镍矿岩体原始岩浆成份相近,应为 普通的拉斑玄武质岩浆。因此,香山西钛铁矿床的形成机制可能是由普通的拉斑玄武质岩浆,经历了较高程度的分异演化导致钛铁氧化物在残余岩浆中逐步富集,岩浆在上升侵位过程中与地壳物质的混染,不仅促使了岩浆中硫化物的饱和,同时提高了岩浆体系的氧逸度,进而促使了钛铁氧化物结晶沉淀。对香山西钛铁矿床成因研究的启示意义在于,除我国攀西地区高钛的玄武质岩浆外,普通的拉斑玄武质岩浆,在有利的分异演化条件下(如初始低氧逸度、相对高度的分异演化、后期与地壳物质混染)也有可能形成大型钛铁矿床。     

The surface brightness and colour–magnitude relations for Fornax cluster galaxies

We present BVI photometry of 190 galaxies in the central 4 ×3 deg² region of the Fornax cluster observed with the Michigan Curtis Schmidt Telescope. Results from the Fornax Cluster Spectroscopic Survey (FCSS) and the Flair-II Fornax Surveys have been used to confirm the membership status of galaxies in the Fornax Cluster Catalogue (FCC). In our catalogue of 213 member galaxies, 92 (43 per cent) have confirmed radial velocities.
In this paper, we investigate the surface brightness–magnitude relation for Fornax cluster galaxies. Particular attention is given to the sample of cluster dwarfs and the newly discovered ultracompact dwarf galaxies (UCDs) from the FCSS. We examine the reliability of the surface brightness–magnitude relation as a method for determining cluster membership and find that at surface brightnesses fainter than 22 mag arcsec⁻², it fails in its ability to distinguish between cluster members and barely resolved background galaxies. Cluster members exhibit a strong surface brightness–magnitude relation. Both elliptical (E) galaxies and dwarf elliptical (dE) galaxies increase in surface brightness as luminosity decreases. The UCDs lie off the locus of the relation.
  B − V   and   V − I   colours are determined for a sample of 113 cluster galaxies and the colour–magnitude relation is explored for each morphological type. The UCDs lie off the locus of the colour–magnitude relation. Their mean   V − I   colours (∼1.09) are similar to those of globular clusters associated with NGC 1399. The location of the UCDs on both surface brightness and colour–magnitude plots supports the 'galaxy threshing' model for infalling nucleated dwarf elliptical (dE, N) galaxies.