Regional representation of glaciers in Chandra Basin region,western Himalaya,India

Hamtah and Chhota Shigri are two nearby, well monitored glaciers of western Himalaya, lying in the same climatic zone and driven by the same climatic conditions. In this study, topographical characteristics of both the glacier have been explored to understand the role of topography in controlling the glacier response. Further, their topographical characteristics and possible response towards climatic variations have been compared with each other and also with that of the other glaciers in the basin to find out the suitability of these two glaciers to be considered as representative of the region. Multi sensor and multi temporal remote sensing data have been used to carry out to fulfill the objectives. It is found that being in the same climatic zone, the mean accumulation area ratio of Chhota Shigri is 54% and Hamtah is 11% between 1980 and 2014. In comparison to Hamtah, Chhota Shigri glacier has a small upslope area, low compactness ratio indicating the ability of the glacier to receive direct precipitation and solar radiation. The analysis revealed that the Chhota Shigri glacier has a closer resemblance with the other glaciers in the region than Hamtah glacier. Also, the topographical settings of Chhota Shigri glacier are suitable for recording and reflecting year-to-year climatic variations.     

TBT contamination identified in Antarctic marine sediments

We report for the first time butyltin contamination of near-shore sediments at six sites in the Ross Sea, Antarctica. A very high concentration of 2290 microg Sn kg(-1) sediment was recorded in one sample. The most likely source is abrasion of antifouling paint from the hulls of ice-breakers, but this pattern of contamination is also possible following ship groundings. Antifoulant biocides, such as TBT, have not been considered or detected in Antarctica previously and represent a new challenge to environmental managers and custodians.     

Historical deposits of Alexandrium catenella resting cysts in the sediments of Queen Charlotte Sound,New Zealand

In 2011, a large repository of resting cysts of the toxic dinoflagellate Alexandrium catenella was discovered in the sediments of the Onapua/Opua inlet located off Tory Channel, Queen Charlotte Sound. The inlet is a potential source of infection for other areas, such as the major mussel-growing areas of Port Underwood and Pelorus Sound. This study aimed to establish whether the dinoflagellate was a new arrival in the Sounds or had existed unnoticed in this isolated embayment for some time. Alexandrium catenella cysts were identified to a depth of 20–21?cm within the sediment cores, corresponding to a date estimated by radioisotope (²¹⁰Pb and ¹³⁷Cs) and Pinus radiata pollen distribution to at least the mid 1970s. Over this time span, resident populations of A. catenella have not become established beyond the confines of Queen Charlotte Sound, suggesting it does not pose an imminent threat of doing so unless increasingly intense and prolonged blooms result in more widespread cyst dispersal.     

The Petrological and Geochemical Evolution of Ediacaran Rare-Metal Bearing A-type Granites from the Jabal Aja Complex, Northern Arabian Shield, Saudi Arabia

New fieldwork, mineralogical and geochemical data and interpretations are presented for the rare-metal bearing A-type granites of the Aja intrusive complex(AIC) in the northern segment of the Arabian Shield. This complex is characterized by discontinuous ring-shaped outcrops cut by later faulting. The A-type rocks of the AIC are late Neoproterozoic post-collisional granites, including alkali feldspar granite, alkaline granite and peralkaline granite. They represent the outer zones of the AIC, surrounding a core of older rocks including monzogranite, syenogranite and granophyre granite. The sharp contacts between A-type granites of the outer zone and the different granitic rocks of the inner zone suggest that the AIC was emplaced as different phases over a time interval, following complete crystallization of earlier batches. The A-type granites represent the late intrusive phases of the AIC, which were emplaced during tectonic extension, as shown by the emplacement of dykes synchronous with the granite emplacement and the presence of cataclastic features. The A-type granites consist of K-feldspars, quartz, albite, amphiboles and sodic pyroxene with a wide variety of accessory minerals, including Fe-Ti oxides, zircon, allanite, fluorite, monazite, titanite, apatite, columbite, xenotime and epidote. They are highly evolved(71.3–75.8 wt% SiO_2) and display the typical geochemical characteristics of post-collisional, within-plate granites. They are rare-metal granites enriched in total alkalis, Nb, Zr, Y, Ga, Ta, REE with low CaO, MgO, Ba, and Sr. Eu-negative anomalies(Eu/Eu* = 0.17–0.37) of the A-type granites reflect extreme magmatic fractionation and perhaps the effects of late fluid-rock interactions. The chemical characteristics indicate that the A-type granites of the AIC represent products of extreme fractional crystallization involving alkali feldspar, quartz and, to a lesser extent, ferromagnesian minerals. The parent magma was derived from the partial melting of a juvenile crustal protolith with a mantle contribution. Accumulation of residual volatile-rich melt and exsolved fluids in the late stage of the magma evolution produced pegmatite and quartz veins that cut the peripheries of the AIC. Post-magmatic alteration related to the final stages of the evolution of the A-type granitic magma, indicated by alterations of sodic amphibole and sodic pyroxene, hematitization and partial albitization.     

Late holocene human impact on lake basins in central mexico

Palaeolimnological investigations in the volcanic highlands of Central Mexico (19°N) have yielded clear evidence of environmental degradation associated with episodes of forest clearance and agricultural expansion during the last 3500 years. Preliminary results are presented from five lake basins situated at altitudes of 1700 to 2575 m a.s.l., along a gradient of decreasing aridity and temperature from north to south: Hoya San Nicolás de Parangueo (Guanajuato); La Piscina de Yuriria (Guanajuato); Pátzcuaro (Michoacán); Zacapu (Michoacán) and Upper Lerma (Estado de México). Samples from sediment cores and pits are being analyzed for loss-on-ignition, magnetic susceptibility (X and X_fd), major cations, total P, C/N, carbonate content, δ¹³C, δ¹⁸O, diatoms, pollen, and charcoal content. Evidence for disturbance is provided by increases in non-arboreal pollen types, especially maize (Zea mays), peaks of X, X_fd and charcoal; increased concentrations of elements associated with soil material such as Al, Fe, Ti, and P, and diatoms indicative of cultural eutrophication. Pátzcuaro, Hoya San Nicolás, Zacapu, and Upper Lerma show an initial phase of disturbance dating from ca. 3500 to 1400 yr B.P., reflecting the widespread adoption of maize cultivation during the Preclassic. A later, more intense phase is recorded in all the basins. In Hoya San Nicolás, La Piscina de Yuriria, Zacapu, and Pátzcuaro, which lay within, or on the margins of the Tarascan state, this episode dates from Postclassic to Hispanic times (<1100 yr B.P.). In contrast, disturbance in the Matlatzincan area (the Upper Lerma Basin) was apparently more continuous, culminating during the late Classic to early Postclassic (ca. 1400-700 yr B.P.).