PGE distribution in deformed lherzolites of the Udachnaya kimberlite pipe (Yakutia)

The results of the first study of the PGE distribution in deformed lherzolites of the Udachnaya kimberlite pipe (Yakutia) are presented here. The complex character of evolution of the PGE composition in the Deformed lherzolites is assumed to be the result of silicate metasomatism. At the first stage, growth in the amount of clinopyroxene and garnet in the rock is accompanied by a decrease in the concentration of the compatible PGE (Os, Ir). During the final stage, the rock is enriched with incompatible PGE (Pt, Pd) and Re possible due to precipitation of submicron-sized particles of sulfides in the interstitial space of these mantle rocks.     

Antarctic sea-ice relationships with indices of the atmospheric circulation of the Southern Hemisphere

A link between the Antarctic sea-ice extent and low-frequency atmospheric variations, particularly ENSO, has been suggested by recent modeling and empirical studies. This question is examined here using a high-resolution (by week, by region) data base of Antarctic sea-ice extent for the 1973–1982 period. Although of relatively short duration by Northern Hemisphere standards, such a data base offers an opportunity rare in Southern Hemisphere climate studies. The seaice variations are examined in the context of longer-term indices of the large-scale atmospheric circulation. These are a Southern Oscillation Index (SOI) and an index of sea-level pressure (SLP) wavenumber one in the Southern Hemisphere extratropics. The indices are updated through 1982, and their associations with regional-scale pressure indices in the Australia-New Zealand sector are also examined. The 1973–1982 period is anomalous when compared with the period 1951–1972. Correlation analysis of the monthly sea ice and circulation index values reveals that much of the apparent link between the ice and the SOI suggested in previous studies arises from autocorrelations present in both data sets and the strong annual cycle of sea-ice extent. Removing these effects from the data and re-running the correlations reveals that most of the resulting significant associations between the ice and one or other of the circulation indices can probably be explained on the basis of chance. In order to reconcile these findings with previous studies that show some strong ice-circulation interactions on regional scales, only those months in which significant correlations occur between both largescale circulation indices and the sea ice are examined further. These occur preferentially in the Ross and Weddell sectors, which constitute the regions contributing most to the variability of Antarctic sea ice. The analysis suggests that the sea-ice-extent changes lag the SOI by several months but may precede changes in extratropical SLP wavenumber one. Confirmation of these tentative regional ice extent-circulation teleconnections necessarily awaits the forward extension of the high-resolution sea-ice data base beyond the 10 years available here.This paper is based on material presented at the Conference on Mechanisms of Interannual and Longer-Term Climatic Variations held at the University of Melbourne, Australia: December 8–12, 1986.     

Lessons Learned from 25 Years of Research at the MADE Site

Field studies at well‐instrumented research sites have provided extensive data sets and important insights essential for development and testing of transport theories and mathematical models. This paper provides an overview of over 25 years of research and lessons learned at one of such field research sites on the Columbus Air Force Base in Mississippi, commonly known as the Macrodispersion Experiment (MADE) site. Since the mid‐1980s, field data from the MADE site have been used extensively by researchers around the world to explore complex contaminant transport phenomena in highly heterogeneous porous media. Results from field investigations and modeling analyses suggested that connected networks of small‐scale preferential flow paths and relative flow barriers exert dominant control on solute transport processes. The classical advection‐dispersion model was shown to inadequately represent plume‐scale transport, while the dual‐domain mass transfer model was found to reproduce the primary observed plume characteristics. The MADE site has served as a valuable natural observatory for contaminant transport studies where new observations have led to better understanding and improved models have sprung out analysis of new data.     

Determination of the isotopic composition of molybdenum in the bottom sediments of freshwater basins

This paper presents the results of measurements of the Mo isotopic composition in the bottom sediments (BS) of freshwater basins. Mo isotopic ratios were measured using a multicollector inductively coupled plasma mass spectrometer (MC ICP MS). Efficient methods were used in this study for Mo separation from the elements of the sample matrix and correction for instrumental mass discrimination. This allowed us to achieve a high accuracy of 0.06, 0.08, and 0.14‰ (2 σ) for the measurement of ⁹⁷Mo/⁹⁵Mo, ⁹⁸Mo/⁹⁵Mo, and ¹⁰⁰Mo/⁹⁵Mo, respectively. The range of variations in Mo isotope ratios observed in the collected BS columns was ～2.2‰ in terms of δ⁹⁷Mo/⁹⁵Mo. The results obtained here suggest that geochemical processes occurring during Mo migration with land water can change the isotopic composition of Mo. It is pointed out that the potential use of Mo isotopic systematics for reconstructions of redox conditions in seawater over the geologic past requires the quantification of isotopic effects of Mo accompanying its migration on land and the extent of possible variations in the isotopic composition of Mo entering the ocean.     

Assessing climate change impacts on river hydrology – A case study in the Western Ghats of India

The objective of this study is to evaluate the hydrological impacts of climate change on rainfall, temperature and streamflow in a west flowing river originating in the Western Ghats of India. The long-term trend analysis for 110 yr of meteorological variables (rainfall and temperature) was carried out using the modified Mann–Kendall trend test and the magnitude of the trend was quantified using the Sen’s slope estimator. The Regional Climate Model (RCM), COordinated Regional climate Downscaling EXperiment (CORDEX) simulated daily weather data of baseline (1951–2005) and future RCP 4.5 scenarios (2006–2060) were used to run the hydrological model, Soil and Water Assessment Tool (SWAT), in order to evaluate the effect of climate change on rainfall, temperature and streamflow. Significant changes were observed with regard to rainfall, which have shown decreasing trend at the rate of 2.63 mm per year for the historical and 8.85 mm per year for RCP 4.5 future scenarios. The average temperature was found to be increasing at \(0.10\,^{\circ }\hbox {C}\) per decade for both historical and future scenarios. The impact of climate change on the annual streamflow yielded a decreasing trend at the rate of \(1.2\,\hbox {Mm}^{3}\) per year and 2.56 \(\hbox {Mm}^{3},\) respectively for the past and future scenarios. The present work also investigates the capability of SWAT to simulate the groundwater flow. The simulated results are compared with the recession limb of the hydrograph and were found to be reasonably accurate.     

Modes of climate variability as simulated by a coupled general circulation model. Part I: ENSO-like climate variability and its low-frequency modulation

The El Niño-Southern Oscillation (ENSO) is investigated in a multicentury integration conducted with the coupled general circulation model (CGCM) ECHAM3/LSG. The quasiperiodic interannual oscillations of the simulated equatorial Pacific climate system are due to subsurface temperature anomaly propagation and a positive atmosphere-ocean feedback. The gravest internal wave modes contribute to the generation of these anomalies. The simulated ENSO has a characteristic period of 5–8 years. Due to the coarse resolution of the ocean model the ENSO amplitude is underestimated by a factor of three as compared to observations. The model ENSO is associated with the typical atmospheric teleconnection patterns. Using wavelet statistics two characteristic interdecadal modulations of the ENSO variance are identified. The origins of a 22 and 35?y ENSO modulation as well as the characteristic ENSO response to greenhouse warming simulated by our model are discussed.