The critical role of climate and saprolite weathering in landscape evolution

Landscapes evolve in response to external forces, such as tectonics and climate, that influence surface processes of erosion and weathering. Internal feedbacks between erosion and weathering also play an integral role in regulating the landscapes response. Our understanding of these internal and external feedbacks is limited to a handful of field‐based studies, only a few of which have explicitly examined saprolite weathering. Here, we report rates of erosion and weathering in saprolite and soil to quantify how climate influences denudation, by focusing on an elevation transect in the western Sierra Nevada Mountains, California. We use an adapted mass balance approach and couple soil‐production rates from the cosmogenic radionuclide (CRN) ¹⁰Be with zirconium concentrations in rock, saprolite and soil. Our approach includes deep saprolite weathering and suggests that previous studies may have underestimated denudation rates across similar landscapes. Along the studied climate gradient, chemical weathering rates peak at middle elevations (1200–2000 m), averaging 112·3 ± 9·7 t km^–2 y^–1 compared to high and low elevation sites (46·8 ± 5·2 t km^?2 y^?1). Measured weathering rates follow similar patterns with climate as those of predicted silica fluxes, modeled using an Arrhenius temperature relationship and a linear relationship between flux and precipitation. Furthermore, chemical weathering and erosion are tightly correlated across our sites, and physical erosion rates increase with both saprolite weathering rates and intensity. Unexpectedly, saprolite and soil weathering intensities are inversely related, such that more weathered saprolites are overlain by weakly weathered soils. These data quantify exciting links between climate, weathering and erosion, and together suggest that climate controls chemical weathering via temperature and moisture control on chemical reaction rates. Our results also suggest that saprolite weathering reduces bedrock coherence, leading to faster rates of soil transport that, in turn, decrease material residence times in the soil column and limit soil weathering. Copyright © 2009 John Wiley & Sons, Ltd.     

Role of interannual equatorial forcing on the subsurface temperature dipole in the Bay of Bengal during IOD and ENSO events

Role of equatorial forcing on the thermocline variability in the Bay of Bengal (BoB) during positive and negative phases of the Indian Ocean Dipole (IOD) and El Niño Southern Oscillation (ENSO) was investigated using the Regional Ocean Modeling System (ROMS) simulations during 1988 to 2015. Two numerical experiments were carried out for (i) the Indian Ocean Model (IOM) with interannual open boundary conditions and (ii) the BoB Model (BoBM) with climatological boundary conditions. The first mode of Sea Surface Height Anomalies (SSHA) variability showed a west-east dipole nature in both IOM and altimetry observations around 11°N, which was absent in the BoBM. The vertical section of temperature along the same latitude showed a sharp subsurface temperature dipole with a core at ~ 100 m depth. The positive (negative) subsurface temperature anomalies were observed over the whole northeastern BoB during NIOD (PIOD) and LN (EN) composites due to stronger (weaker) second downwelling Kelvin Waves. During the negative phases of IOD and ENSO, the cyclonic eddy on the southwestern BoB strengthened due to intensified southward coastal current along the western BoB and local wind stress. The subsurface temperature dipole was at its peak during October–December (OND) with 1-month lag from IOD and was evident from the Argo observations and other reanalysis datasets as well. A new BoB dipole index (BDI) was defined as the normalized difference of 100-m temperature anomaly and found to be closely related to the frequency of cyclones and the surface chlorophyll-a concentration in the BoB.

     

Young circumnuclear disks in elliptical galaxies

By means of integral-field spectroscopy with the Multi-Pupil Field/Fiber Spectrograph of the Russian 6-m telescope we have studied the central parts of NGC 759 and NGC 83— regular (non-interacting, without strong nuclear activity) round red luminous (M _B =?20.8–?21.6) elliptical galaxies which are however known to possess molecular gas. In both galaxies we have found central stellar disks with the extension of 1–2 kpc along the radius which are evidently being formed just now.     

Noncircular outer disks in unbarred S0 galaxies: NGC 502 and NGC 5485

Highly noncircular outer stellar disks have been detected in two SA0 (unbarred) galaxies by comparing the spectroscopic data on the rotation of stars and the photometric data on the shape and orientation of isophotes. In NGC 502, the oval distortion of the disk is manifested in the shape of the inner and outer elliptical rings occupying wide radial zones between the bulge and the disk and at the outer disk edge; such a structure can be a consequence of the so-called “dry minor merger,” multiple cannibalization of gas-free satellites. In NGC 5485, the stellar kinematics is absolutely unrelated to the orientation of isophotes in the disk region, and for this galaxy the conclusion about its global triaxial structure is unavoidable.     

The thickness of stellar disks in early-type galaxies

We suggest and justify a new photometric method enabling the derivation of the relative thickness of a galactic disk from the two-dimensional surface-brightness distribution of the galaxy in the plane of the sky. The method is applied to images of 45 early-type (S0-Sb) galaxies with known radial exponential or piece-wise-exponential (with a flatter outer profile) surface-brightness distributions. The data were taken from the open SDSS archive. The statistics of the estimated relative thicknesses of the stellar disks of early-type galaxies show the following features. The disks of lenticular and spiral early-type galaxies have similar thickness. The presence of a bar results in only a slight increase of the thickness. However, there is a substantial difference between the thicknesses of disks with a single exponential brightness profile and exponential disks that represent the inner segments of Type III profiles (after Erwin); i.e., they have an outer exponential disk with a larger characteristic scale. The disks are significantly thicker in the former than in the latter case. This may provide evidence that a single exponential scale in a disk surface-brightness distribution forms due to viscosity effects acting over the entire period of star-formation evolution in the disk.     

Properties of stellar populations in isolated lenticular galaxies

We present the results of observations of a sample of isolated lenticular galaxies, performed at the SCORPIO and SCORPIO-2 spectrographs of the 6-meter BTA telescope of the SAO RAS in the long-slit mode. By direct spectra approximation, using the evolutionary synthesis models, we have measured the radial profiles of the rotation velocity as well as the dispersions of velocities, average age, and average metallicity of stars in 12 objects. The resulting average ages of the stellar population in bulges and discs fill an entire range of possible values from 1.5 to 15 Gyr which indicates the absence in the isolated lenticular galaxies, unlike in the members of groups and clusters, of a certain epoch when the structural components are formed: they could have been formed at a redshift of z > 2 as well as only several billion years ago. Unlike the S0 galaxies in a more dense environment, isolated galaxies typically have the same age of stars in the bulges and discs. The lenses and rings of increased stellar brightness, identified from the photometry of 7 of 11 galaxies, do not significantly differ from the stellar discs by the properties of stellar populations and velocity dispersion of stars. We draw a conclusion that the final arrangement of the morphological type of a lenticular galaxy in complete isolation is critically dependent on the possible modes of accretion of the cold external gas.     

Groundwater Quality assessment using Water Quality Index (WQI) in parts of Varanasi District,Uttar Pradesh,India

Either naturally occurring process or human activities may have a significant impact on the quality of sub-surface waters which further limit its use. Multivariate statistical techniques such as factor analysis (FA), cluster analysis (CA) were applied for the evaluation of spatial variations and the interpretation of ground water quality data around Bacheli and Kirandul area. The major anions, cations and heavy metals were determined for each of 20 samples collected in pre-monsoon seasons. Hydrochemical parameters like EC, pH, TDS, TH, TA, Na⁺, K⁺, Ca²⁺, Cl^-, F^-, SO₄^2-, As, Sb, Se, Pb, Cd, Zn, Cu were estimated in pre monsoon and post monsoon seasons. Different geochemical controls of the investigated parameters were also assessed. Factor 1 explains 33.47% of the total variance and indicates atmospheric controls and silicate mineral weathering process. Factor 2 explains 13.83% of total variance, indicating silicate mineral weathering process resulting in elevated pH. Generally, water types tend towards magnesium-bicarbonate-chloride.     

Probabilistic seismic hazard analysis of Tripura and Mizoram states

A probabilistic seismic hazard analysis for the states of Tripura and Mizoram in North East India is presented in this paper to evaluate the ground motion at bedrock level. Analyses were performed considering the available earthquake catalogs collected from different sources since 1731–2010 within a distance of 500 km from the political boundaries of the states. Earthquake data were declustered to remove the foreshocks and aftershocks in time and space window and then statistical analysis was carried out for data completeness. Based on seismicity, tectonic features and fault rupture mechanism, this region was divided into six major seismogenic zones and subsequently seismicity parameters (a and b) were calculated using Gutenberg–Richter (G–R) relationship. Faults data were extracted from SEISAT (Seismotectonic atlas of India, Geological Survey of India, New Delhi, 2000) published by Geological Survey of India and also from satellite images. The study area was divided into small grids of size 0.05° × 0.05° (approximately 5 km × 5 km), and the hazard parameters (rock level peak horizontal acceleration and spectral accelerations) were calculated at the center of each of these grid cells considering all the seismic sources within a radius of 500 km. Probabilistic seismic hazard analyses were carried out for Tripura and Mizoram states using the predictive ground motion equations given by Atkinson and Boore (Bull Seismol Soc Am 93:1703–1729, 2003) and Gupta (Soil Dyn Earthq Eng 30:368–377, 2010) for subduction belt. Attenuation relations were validated with the observed PGA values. Results are presented in the form of hazard curve, peak ground acceleration (PGA) and uniform hazard spectra for Agartala and Aizawl city (respective capital cities of Tripura and Mizoram states). Spatial variation of PGA at bedrock level with 2 and 10 % probability of exceedance in 50 years has been presented in the paper.     

Lenticular galaxies with ultraviolet rings

Based on GALEX (Galaxy Ultraviolet Explorer) data, we have compiled a list of lenticular galaxies with ultraviolet rings—radially localized star-forming regions. We have analyzed the optical structure of these galaxies using SDSS (Sloan Digital Sky Survey) surface photometry, measured the colors of the rings, and compared the radial localizations of the ring structures in the optical and ultraviolet spectral ranges. Possible scenarios for the formation of ring star-forming regions in lenticular galaxies having no other structural peculiarities and exhibiting a homogeneous old stellar population outside the rings are discussed.     

Optical and radar data comparison and integration: Kenya example

The purpose of this study was to evaluate the relative classification accuracies of four land covers/uses in Kenya using spaceborne quad polarization radar from the Japanese ALOS PALSAR system and optical Landsat Thematic Mapper data. Supervised signature extraction and classification (maximum likelihood) was used to classify the different land covers/uses followed by an accuracy assessment. The original four band radar had an overall accuracy of 77%. Variance texture was the most useful of four measures examined and did improve overall accuracy to 80% and improved the producer’s accuracy for urban by almost 25% over the original radar. Landsat provided a higher overall classification accuracy (86%) as compared to radar. The merger of Landsat with the radar texture did not increase overall accuracy but did improve the producer’s accuracy for urban indicated some advantages for sensor integration.