Rock-magnetic proxies of climate change in the loess-palaeosol sequences of the western Loess Plateau of China

Results of the first detailed study of the climate proxy record in the loess-palaeosol sequence at Xining-one of the few palaeoclimate sites in the currently arid western Loess Plateau of China-illustrate the importance of making many types of rock-magnetic measurements other than susceptibility. A multiparameter approach yielded confirmation that here, as elsewhere in the Loess Plateau, the susceptibility enhancement in palaeosols was caused primarily by ultrafine magnetite and maghaemite. Nevertheless, magnetic enhancement was caused not exclusively by changes in relative grain size, but also by variations in concentration and mineralogy of the magnetic fraction.
The effects of concentration variations were removed through normalization of susceptibility and anhysteretic remanence with saturation magnetization and saturation remanence, respectively. the resulting signal was ascribed more confidently to variation in magnetic grain size, which in turn was interpreted as a better proxy of pedogenesis than simple susceptibility. Variations in magnetic mineralogy were also determined to constrain interpretations further. the data were then used to discuss climate history at Xining. Finally, results from Xining were compared with other western sites and contrasted with eastern sites.
In summary: (1) data is presented from a new Loess Plateau site which also appears to yield a global climate signal; (2) a demonstration is made of a more rock-magnetically robust way to separate concentration, composition and grain-size controls on susceptibility and other magnetic parameters; and (3) models are provided for inter-regional comparisons of palaeoclimate proxy records.     

Effects of intraborehole flow on groundwater age distribution

Environmental tracers are used to estimate groundwater ages and travel times, but the strongly heterogeneous nature of many subsurface environments can cause mixing between waters of highly disparate ages, adding additional complexity to the age-estimation process. Mixing may be exacerbated by the presence of wells because long open intervals or long screens with openings at multiple depths can transport water and solutes rapidly over a large vertical distance. The effect of intraborehole flow on groundwater age was examined numerically using direct age transport simulation coupled with the Multi-Node Well Package of MODFLOW. Ages in a homogeneous, anisotropic aquifer reached a predevelopment steady state possessing strong depth dependence. A nonpumping multi-node well was then introduced in one of three locations within the system. In all three cases, vertical transport along the well resulted in substantial changes in age distributions within the system. After a pumping well was added near the nonpumping multi-node well, ages were further perturbed by a flow reversal in the nonpumping multi-node well. Results indicated that intraborehole flow can substantially alter groundwater ages, but the effects are highly dependent on local or regional flow conditions and may change with time.     

Stably stratified flows in meteorology

It is generally believed by those undertaking research in the fundamental aspects of geophysical fluid dynamics and meteorology that their results contribute to the improvements to numerical weather prediction and in practical weather forecasting. However, the techniques whereby the appropriate research results are selected and incorporated into the numerical models are not widely known, particularly the methods for representing the phenomena whose horizontal scale is less than that of the grid boxes.(say, 50 km). Some accounts of numerical weather prediction imply that the representation of subgrid-scale phenomena is formally similar to classical physics. In fact, atmospheric motions on these scales are not like molecular motions in an ideal gas, but show considerable structure, approximating to combinations of various idealized states. Great skill and experience in this specialized activity has been applied to deciding on these states, finding physical criteria for defining them and then modelling the relevant phenomena occurring on this scale. In this paper, we focus on a restricted range of phenomena associated with stably stratified flows, notably mountain waves, convection and clouds, and boundary layer phenomena. This category provides many examples of structures which need to be considered in detail to reconstruct the large-scale picture accurately, as well as in local forecasting.     

On mass transport in deep water waves

Summary Various formulations of the mass-transport problem are compared for progressive waves in deep water. In order to calculate the mass-transport velocity as a function of depth in the main body of the fluid, it is necessary to include the effect of viscous wave attenuation. It is shown that the usual assumptions of periodicity in distance and attenuation with time or periodicity in time and attenuation with distance, are both physically unsatisfactory. The first does not specify a unique solution, and the second is incompatible with the assumption of zero surface stress. A certain critical constant tangential wind stress will maintain strictly time-periodic deep water waves. The corresponding attenuation with distance is then calculated to order ³. A constant tangential stress greater or less than the critical causes waves, necessarily decaying with distance, to grow or decay with time.     

The opacity of some local Martian dust storms observed by the Viking IRTM

In this paper we analyze some Viking infrared thermal mapping (IRTM) measurements of local Martian dust storms observed in the southern tropical region of the planet between L_s=225 and 262°. The derived opacities of these storms show that in the most opaque regions of the cloud, the optical thickness may be ≈6. Away from the individual clouds, the opacity is ≈2, which is still about four times the background level of dustiness in the Martian atmosphere. We find considerable structure in the derived opacity which will create corresponding variations in the atmospheric heating, which in turn may have an important feedback upon the local winds.     

Influence of wind upon water quality in Liverpool Bay

Comprehensive distribution patterns of physical and chemical characteristics have been obtained from a series of cruises in Liverpool Bay. The marked feature of these distributions was their temporal variability, suggesting that the surface residual circulation is also temporally variable. The influence of wind stress upon the circulation pattern and hence water quality of this sea area is illustrated.