Factors controlling specific sediment yield in the upper Indus River basin,northern Pakistan

Estimates of sediment yield are essential in water resources analysis, modelling and engineering, in investigations of continental denudation rates, and in studies of drainage basin response to changes in climate and land use. The availability of high resolution, global environmental datasets offers an opportunity to examine the relationships between specific sediment yield (SY_sp) and drainage basin attributes in a geographical information system (GIS) environment. This study examines SY_sp at 14 long‐term gauging stations within the upper Indus River basin. Twenty‐nine environmental variables were derived from global datasets, the majority with a 1 × 1 km resolution. The SY_sp ranges from 194 to 1302 t km^?2 yr^?1 for sub‐basins ranging from 567 to 212 447 km². The high degree of scatter in SY_sp is greatly reduced when the stations are divided into three groups: upper, glacierized sub‐basins; lower, monsoon sub‐basins; and the main Indus River. Percentage snow/ice cover (LC_s) emerges as the single major land cover control for SY_sp in the high mountainous upper Indus River basin. A regression model with percentage snow/ice cover (LC_s) as the single independent variable explains 73·4% of the variance in SY_sp for the whole Indus basin. A combination of percentage snow/ice cover (LC_s), relief and climate variables explains 98·5% of the variance for the upper, glacierized sub‐basins. For the lower monsoon region, a regression model with only mean annual precipitation (P) explains 99·4% of the variance. Along the main Indus River, a regression model including just basin relief (R) explains 92·4% of the variance in SY_sp. Based on the R²_adj and P‐value statistics, the variables used are capable of explaining the majority of variance in the upper Indus River basin. Copyright © 2007 John Wiley & Sons, Ltd.     

Jurassic granitoid magmatism in the Dinaride Neotethys: geochronological constraints from detrital minerals

Three independent single‐grain geochronometers applied to detrital minerals from Central Dinaride sediments constrain the timing of felsic magmatism that associated the Jurassic evolution of the Neotethys. The Lower Cretaceous clastic wedge of the Bosnian Flysch, sourced from the Dinaride ophiolitic thrust complex, yields magmatic monazite and zircon grains with dominant age components of 164 ± 3 and 152 ± 10 Ma respectively. A unique tephra horizon within the Adriatic Carbonate Platform was dated at 148 ± 11 Ma by apatite fission track analysis. These consistent results suggest that leucocractic melt generation in the Central Dinaride segment of the Neotethys culminated in Middle to Late Jurassic times, coeval with and slightly post‐dating subophiolitic sole metamorphism. Growth of magmatic monazite and explosive volcanism call for supra‐subduction‐zone processes at the convergent Neotethyan margin. New compilation of geochronological data demonstrates that such Jurassic felsic rocks are widespread in the entire Dinaride–Hellenide orogen.     

Frequency and intensity of high-altitude floods over the last 3.5 ka in northwestern French Alps (Lake Anterne)

In central Western Europe, several studies have shown that colder Holocene periods, such as the Little Ice Age, also correspond to wet periods. However, in mountain areas which are highly sensitive to erosion processes and where precipitation events can be localized, past evolution of hydrological activity might be more complicated. To assess these past hydrological changes, a paleolimnological approach was applied on a 13.4-m-long sediment core taken in alpine Lake Anterne (2063 m asl) and representing the last 3.5 ka. Lake sedimentation is mainly composed of flood deposits triggered by precipitation events. Sedimentological and geochemical analyses show that floods were more frequent during cold periods while high-intensity flood events occurred preferentially during warmer periods. In mild temperature conditions, both flood patterns are present. This underlines the complex relationship between flood hazards and climatic change in mountain areas. During the warmer and/or dryer times of the end of Iron Age and the Roman Period, both the frequency and intensity of floods increased. This is interpreted as an effect of human-induced clearing for grazing activities and reveals that anthropogenic interferences must be taken into account when reconstructing climatic signals from natural archives.     

Mixing processes in hydrothermal spring systems and implications for interpreting geochemical data: a case study in the Cappadocia region of Turkey

Mixing is a dominant hydrogeological process in the hydrothermal spring system in the Cappadocia region of Turkey. All springs emerge along faults, which have the potential to transmit waters rapidly from great depths. However, mixing with shallow meteoric waters within the flow system results in uncertainty in the interpretation of geochemical results. The chemical compositions of cold and warm springs and geothermal waters are varied, but overall there is a trend from Ca–HCO₃ dominated to Na–Cl dominated. There is little difference in the seasonal ionic compositions of the hot springs, suggesting the waters are sourced from a well-mixed reservoir. Based on δ¹⁸O and δ²H concentrations, all waters are of meteoric origin with evidence of temperature equilibration with carbonate rocks and evaporation. Seasonal isotopic variability indicates that only a small proportion of late spring and summer precipitation forms recharge and that fresh meteoric waters move rapidly into the flow system and mix with thermal waters at depth. ³H and percent modern carbon (pmC) values reflect progressively longer groundwater pathways from cold to geothermal waters; however, mixing processes and the very high dissolved inorganic carbon (DIC) of the water samples preclude the use of either isotope to gain any insight on actual groundwater ages.     

http://www.sciencedirect.com/science/article/pii/S1674987114000218

Fluid infiltration into retrograde granulites of the Southern Marginal Zone(Limpopo high grade terrain)is exemplified by hydration reactions.shear zone hosted metasomatism,and lode gold mineralisation.Hydration reactions include the breakdown of cordierite and orthopyroxene to gedrite kyanite,and anthophyllite,respectively.Metamorphic petrology,fluid inclusions,and field data indicate that a low H_2O-activity carbon-saturated CO_2-rich and a saline aqueous fluid infiltrated the Southern Marginal Zone during exhumation.The formation of anthophyllite after orthopyroxene eslablished a regional retrograde anthophyllite-in isograd and occurred at P-T conditions of- 6 kbar and 610 C,which fixes the minimum mole fraction of II.0 in the CO_2-rich fluid phase at- 0.1.The maximum H_2O mole fraction is hxed by the lower temperature limit(~800℃) for partial melting at ~0.3.C-O-H fluid calculations show that the CO_2-rich fluid had an oxygen fugacity that was 0.6 log10 units higher than that of the fayalite-magnetitequartz buffer and that the CO_2/(CO_2+CH_4) mole ratio of this fluid was 1.The presence of dominantly relatively low density CO_2-rich fluid inclusions in the hydrated granulites indicates that the fluid pressure was less than the lithostatic pressure.This can be explained by strike slip faulting and/or an increase of the rock permeability caused by hydration reactions.     

Mineral chemical and geochronological constraints on the age and provenance of the eastern Circum-Rhodope Belt low-grade metasedimentary rocks, NE Greece

In north-eastern Greece the mid-greenschist facies Makri Unit and the anchizonal Melia Formation belong to the eastern Circum-Rhodope Belt that forms the uppermost tectonostratigraphic unit of the Rhodope metamorphic nappe pile. The two metasedimentary successions had different source areas, although they now lie in close proximity in the Rhodope Massif. The U-Pb isotopic ages of detrital zircons from a metasandstone of the Makri Unit analysed using LA-SF-ICP-MS and SHRIMP-II gave age clusters at ca. 310-290 Ma and at ca. 240 Ma for magmatic zircons, which may have been derived from Carboniferous-Permian basement rocks of the Thracia Terrane (Lower Tectonic Unit of the Rhodope Massif) that subsequently underwent Triassic rifting. The youngest detrital zircon grains found so far indicate that the metasedimentary succession of the Makri Unit, or at least parts of it, cannot be older than Late Triassic. By contrast, clastic sedimentary rocks of the Melia Formation contain the primary detrital mineral assemblage of epidote, zoisite, garnet, and phengitic mica, which is absent in the Makri Unit, and clearly points to metamorphic rocks being the major source for these sediments. U-Pb analyses of detrital zircons gave a prominent age cluster at ca. 315-285 Ma for magmatic zircons. Inherited cores indicate the involvement of Pan-African and Late Ordovician-Early Silurian crustal sources during Late Carboniferous-Early Permian igneous event(s). Moreover, U-Pb detrital zircon geochronology indicates that the Melia Formation cannot be older than latest Middle Jurassic. We suggest that the Melia Formation was deposited in front of a metamorphic nappe pile with Rhodopean affinities in Tithonian or Cretaceous times. Both the Makri Unit and the Melia Formation have been tectonically juxtaposed from different sources to their present location during Balkan and Alpine orogenic processes.     

Leaf wax n-alkane δD values of field-grown barley reflect leaf water δD values at the time of leaf formation

Leaf wax n-alkanes from barley (Hordeum vulgare) from a field in Switzerland exhibited changes in δD values on the order of 20‰ over a growing season, while source water (soil water) and leaf water varied by 40‰. Additionally the seasonal variability in δD values of leaf wax n-alkanes of different barley leaves can only be found across different leaf generations (i.e. leaves that were produced at different times during the growing season) while n-alkane δD values did not vary significantly within a leaf generation. Interestingly, δD values of n-alkanes correlated best with the δD values of leaf water at midday of the sampling day but showed no significant correlation with soil water (e.g. precipitation) δD values. These results provide empirical evidence that leaf wax δD values record leaf water enrichment, and therefore integrate the isotopic effects of precipitation and evapotranspiration. Our results show that leaf wax n-alkane δD values from grasses are ‘locked in’ early during leaf development and hence record the environmental drivers of leaf water enrichment, such as vapor pressure deficit (VPD). Our data have important implications for the interpretation of paleorecords of leaf wax δD. We suggest that leaf wax n-alkane δD values from sedimentary records could be used to estimate changes in the degree of leaf water enrichment and hence VPD.     

Low‐temperature phase decomposition in iron‐nickel metal of the Portales Valley meteorite

Abstract— The Portales Valley meteorite provides an opportunity to investigate and compare the microstructure in Fe‐Ni metal of the metallic particles in the chondritic portion and in the metal veins. The low‐temperature phase decomposition of Fe‐Ni metal was investigated using scanning electron microscopy, transmission electron microscopy, and atomic force microscopy. The microstructure is formed as the Portales Valley meteorite cooled from high temperatures and includes the outer taenite rim, the cloudy zone, clear taenite, and martensite. Martensite in turn decomposes into a fine admixture of fcc rods in a bcc matrix. The width of the island phase of the cloudy zone in the metal particles of the chondritic portion and the metal veins can be used to estimate a low‐temperature cooling rate. The microstructural evidence indicates that the chondritic portions and the metal veins in the Portales Valley meteorite cooled together as a mixture with a cooling rate of roughly 6.5 K/Ma.     

Understanding the cost of establishing marine protected areas

While the recurrent cost of managing marine protected areas (MPAs) has been documented and estimated, there has been virtually no attempt to quantify the cost of establishing MPAs in the first place. This lack of attention is likely the result of the complexity of the process, involving often uncoordinated efforts of a multitude of governmental and non-governmental entities over a protracted period of time with no clear start and end-point. Using information gathered from a representative subset of MPAs worldwide, this paper presents the first attempt to identify and describe the various components, and explore potential predictors of the total funds spent in the course of establishment. The thirteen MPAs studied vary in size (from <1 to >360,000 km²), location (including near- and offshore in both developed and developing countries), objectives and degree of protection. Variation in MPA start-up costs is shown to be most significantly related to both MPA size and the duration of the establishment phase. Development of a method to estimate the potential cost of establishing proposed MPAs should play a crucial role in the conservation planning process.     

Autonomous video camera system for monitoring impacts to benthic habitats from demersal fishing gear, including longlines

Studies of the interactions of demersal fishing gear with the benthic environment are needed in order to manage conservation of benthic habitats. There has been limited direct assessment of these interactions through deployment of cameras on commercial fishing gear especially on demersal longlines. A compact, autonomous deep-sea video system was designed and constructed by the Australian Antarctic Division (AAD) for deployment on commercial fishing gear to observe interactions with benthos in the Southern Ocean finfish fisheries (targeting toothfish, Dissostichus spp). The Benthic Impacts Camera System (BICS) is capable of withstanding depths to 2500 m, has been successfully fitted to both longline and demersal trawl fishing gear, and is suitable for routine deployment by non-experts such as fisheries observers or crew. The system is entirely autonomous, robust, compact, easy to operate, and has minimal effect on the performance of the fishing gear it is attached to. To date, the system has successfully captured footage that demonstrates the interactions between demersal fishing gear and the benthos during routine commercial operations. It provides the first footage demonstrating the nature of the interaction between demersal longlines and benthic habitats in the Southern Ocean, as well as showing potential as a tool for rapidly assessing habitat types and presence of mobile biota such as krill (Euphausia superba).