Luminescence chronology of river adjustment and incision of Quaternary sediments in the alluvial plain of the Sabarmati River, north Gujarat, India

River adjustment and incision in the Sabarmati basin, Gujarat, India have been examined at a site near Mahudi. Towards this, the morphostratigraphy and depositional chronometry of the middle alluvial plains were investigated. The upper fluvial sequence, along with the overlying aeolian sand and riverbed scroll plains, provide clues to the evolution of the present Sabarmati River. Sedimentological analyses of the upper fluvial sequence indicate its deposition by a meandering river system during what is believed to be a persistent wetter phase. Luminescence chronology bracketed this sequence to between 54 and 30 ka, which corresponds to Oxygen Isotope Stage-3, during which the SW monsoon was enhanced. The overlying aeolian sand has been dated to 12 ka, indicating that dune accretion occurred simultaneously with the strengthening of the SW monsoon during the Early Holocene. Adjustment of the Sabarmati along a N–S transect is placed around 12 ka and the incision is bracketed between 12 and 4.5 ka. River adjustment could have been tectonic; however, the incision was facilitated by the availability of continuous flow in the river caused by the SW monsoon. The basin experienced two tectonic events at about 3 and 0.3 ka, as demonstrated by the morphology of the scroll plains.     

Horizontal and vertical zones of influence for root systems of four Mojave Desert shrubs

Horizontal and vertical zones of influence for root systems of four Mojave Desert shrubs were characterized using ³²P as a nutrient tracer. Larrea tridentata's horizontal zone of influence was sparse near the plant's stem base, with a maximum probability of accessing ³²P (P_max) of 41%. However, its horizontal zone of influence extended beyond 5 m, and the distance from the stem base at which the probability of accessing ³²P was half P_max (L₅₀3 m) was significantly greater than the other three shrubs. Ambrosia dumosa's zone of influence was dense near the plant's stem base (P_max78%), but was rare at distances >2 m (L₅₀1 m). Zones of influence for Lycium andersonii and Lycium pallidum were intermediate between those of L. tridentata and A. dumosa. For vertical zones of influence, L. tridentata was more likely to obtain ³²P from 5 m soil depths than A. dumosa, but L. pallidum was not significantly different from either A. dumosa or L. tridentata. Horizontal zones of influence did not change with treatments that altered soil water and nitrogen availability, but vertical zones of influence increased with a flood irrigation treatment that increased water availability to 5 m soil depth. These differences among species likely reflect compromises between their shoot growth strategies and their need to acquire spatially and temporally limited soil resources, especially through competitive interactions.     

A regional model for studies of atmosphere-ice-ocean interaction in the western Arctic

Summary Asa step in the development of a fully coupled regional model of the atmosphere-ice-ocean system, atmospheric and sea ice models have been adapted to a western Arctic domain centered on the Bering Strait. Lateral boundary conditions derived from operational analyses drive the models through simulations on grids having horizontal resolutions of 21 km and 7 km. Sensitivities to the presence of sea ice are large after only 48 hours, by which time the surface temperatures in the Bering and Chukchi Seas are 10–15°C higher without sea ice than with sea ice. The temperatures, in turn, modify the fields of sea level pressure, surface wind and precipitation. By influencing the surface wind stress through the static static stability, the surface state feeds back to the surface momentum exchange, ice/ocean transport, and the rate of formation of new ice. The results also show a resolution-dependence of the surface winds, precipitation rates and new ice formation rates, particularly in areas in which the coastal configuration and topography are spatially complex. The experiments will be augmented by the implementation of an ocean model on the same grids.With 12 Figures     

On the relationships between impact crater diameters and projectile kinetic energy

By reforming a series of expressions derived by Öpik (1969), we have shown explicitly the dependence of impact crater diameter on projectile kinetic energy. Comparisons between this reformed version of Öpik's theory and the models of Gault (1973) and Oberbeck and Aoyagi (1972) have demonstrated good agreement between experiment and theory over seventeen orders of magnitude of projectile kinetic energy.     

Non-linear and finite-amplitude thermal convection in a heterogeneous terrestrial planet

Summary. Equations governing non-linear and finite-amplitude convection in a heterogeneous planetary interior are developed. Using spherical harmonic expressions of variables, together with Green's function of Laplacian operator in a spherical coordinate, the equations are reduced to one-dimensional integro-differential equations and their numerical solutions are obtained by a finite-difference scheme. The theory is then applied to several lunar models and the following conclusions are obtained.
(1) The mean temperatures and velocities of convecting zones of variable viscosity models are higher than those of constant viscosity ones. This is due to the development of lithospheres with 400–500 km thicknesses in the former models, which reduce heat loss considerably.
(2) Molten regions are continuous shells in variable viscosity models whereas they become discontinuous and localized in a constant viscosity model. The continuous molten shells decrease lateral variations of temperature significantly and tend to stabilize convection.
(3) Lateral variations of viscosity have negligible effects on the thermal evolution of the models considered.     

Linear and planar structure in ordered multivariate data as applied to progressive demagnetization of palaeomagnetic remanence

Summary. Consider a sequence of, say, 10 to 20 vector observations in three-dimensional space. It is suspected that a few subsets of consecutive observations are made up of collinear points. The purpose of this paper is to construct a statistically based algorithm to find such linear segments and to assess their accuracy. A similar assessment is made for coplanar sets of points.
This algorithm is applied here to palaeomagnetic data and is claimed to be superior to previous methods of palaeomagnetic analysis in terms of completeness and balance of analysis, treatment of measurement errors and other sources of scatter, criteria for identification of linear and planar sets of points, and statistical rigour. Stability spectra, with statistically based confidence limits, are obtained as a by-product.     

Convergent solutions of the inviscid solar wind equations

Formal solutions of the inviscid solar wind equations as power series in the inverse one seventh power and in the inverse one fifth power of the distance from the sun are shown to be convergent.