The influence of delta growth on paleo‐tidal flow: Fraser River delta,British Columbia—Part 3: Paleo‐tidal flows and delta growth

Abstract

Tidal flow patterns computed at various stages of the tide (high tide, falling tide, ebb tide, low tide, and flooding tide) and at different chronological stages (9000, 6000, 4500, 3000, and 2300 years B.P. and the present) using tidal numerical models were presented and interpreted in relation to sedimentary processes and the growth of the Fraser River delta during the past 9000 years. The overall tidal flows are least affected by the deltaic growth at high tide than at any other state of the tide. The net tidal flow with the overall northerly component has a sedimentary effect, in that there is an asymmetry in the transportation of silt and clay with more of these fine materials moved to the north of the delta than to the south. There is also independent seismic evidence for the existence of a tidal channel some 2000 B.P. between Point Roberts and the Fraser delta. This study attempted to link closely the sedimentary structure of the deltaic growth of the Fraser River with the physical oceanographic processes.     

Surface distribution of albacore tuna,Thunnus alalunga Bonnaterre,in relation to the Subtropical Convergence Zone east of New Zealand

Trolling surveys showed that albacore tuna are about equally abundant in subtropical and Subtropical Convergence Zone surface waters off the south‐east coast of New Zealand. Few albacore were located in Subantarctic Surface Water, indicating that the Subtropical Convergence Zone is the southern limit for albacore in this area.     

The impact of natural and anthropogenic forcings on climate and hydrology since 1550

A climate simulation of an ocean/atmosphere general circulation model driven with natural forcings alone (constant “pre-industrial” land-cover and well-mixed greenhouse gases, changing orbital, solar and volcanic forcing) has been carried out from 1492 to 2000. Another simulation driven with natural and anthropogenic forcings (changes in greenhouse gases, ozone, the direct and first indirect effect of anthropogenic sulphate aerosol and land-cover) from 1750 to 2000 has also been carried out. These simulations suggest that since 1550, in the absence of anthropogenic forcings, climate would have warmed by about 0.1 K. Simulated response is not in equilibrium with the external forcings suggesting that both climate sensitivity and the rate at which the ocean takes up heat determine the magnitude of the response to forcings since 1550. In the simulation with natural forcings climate sensitivity is similar to other simulations of HadCM3 driven with CO₂ alone. Climate sensitivity increases when anthropogenic forcings are included. The natural forcing used in our experiment increases decadal–centennial time-scale and large spatial scale climate variability, relative to internal variability, as diagnosed from a control simulation. Mean conditions in the natural simulation are cooler than in our control simulation reflecting the reduction in forcing. However, over certain regions there is significant warming, relative to control, due to an increase in forest cover. Comparing the simulation driven by anthropogenic and natural forcings with the natural-only simulation suggests that anthropogenic forcings have had a significant impact on, particularly tropical, climate since the early nineteenth century. Thus the entire instrumental temperature record may be “contaminated” by anthropogenic influences. Both the hydrological cycle and cryosphere are also affected by anthropogenic forcings. Changes in tree-cover appear to be responsible for some of the local and hydrological changes as well as an increase in northern hemisphere spring snow cover.

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The Australia telescope 20 GHz survey: hardware, observing strategy, and scanning survey catalog

The Australia Telescope 20 GHz (AT20G) survey is a large area (2?? sr), sensitive (40 mJy), high frequency (20 GHz) survey of the southern sky. The survey was conducted in two parts: an initial fast scanning survey, and a series of more accurate follow-up observations. The follow-up survey catalog has been presented by Murphy et al. (MNRAS 402:2403, 2010). In this paper we discuss the hardware setup and scanning survey strategy as well as the production of the scanning survey catalog.     

The effect of finite electrical and thermal conductivities on magnetic buoyancy in a rotating gas

A horizontal magnetic field if increasing in strength downwards can cause a horizontal layer of electrically conducting fluid to become unstable, a phenomenon known as ‘magnetic buoyancy’, and sometimes thought to have relevance to magnetic A stars, and to sunspot creation. Analyses that assume infinite thermal and electrical conductivities (and zero viscosity) predict that modes of zero horizontal wave-length, in the direction perpendidular to the field, are maximally unstable but are stabilised by even small Coriolis forces. It is shown here, however, that when proper allowance is made for the finite (though large) conductivities of the fluid the layer may experience a ‘conductive instability’ that grows on the ohmic time-scale and is maximally unstable to a mode of non-zero horizontal extent.     

The structure of the Moine and Dalradian Rocks in the Dalmally District of Argyllshire,Scotland

Two phases of deformation are described from the area. D1 is related to the first phase movements widely recognised in the Dalradian; D2 is related to more localised modifications of the D1 fold pattern. Four major D2 folds are recognised from the evidence of minor structures. Three of these, the Beinn Chuirn, the Ben Lui and the Ra Chreag Folds, had previously been considered as D1 structures, whilst the fourth, the Dalmally Fold, was unrecognised. These folds provide continuity between the southeast facing of the D1 folds of the Moine and Ballachulish Succession of Glen Orchy (Thomas and Treagus 1968) and the southeast facing of the D1 Jay Nappe (Shacketon 1958) in the Iltay Succession above. The D2 deformation reaches a climax at the junction between the two Successions, the Iltay Boundary Slide, which is now regarded as a D2 structure. The regional implications of these results are briefly considered.     

A Unified Approach to Mean Field Electrodynamics

Using the first order smoothing approximation and a novel technique (double Fourier transformation and expansion) a number of results, new and old, in the theory of mean field electrodynamics and magnetohydrodynamics are given a systematic and general derivation. They are cast into forms which bring into new prominence the role of the helicity spectrum in induction processes. The situations in which the results may be expected to be accurate are delineated. New expressions are given for the reduction in the mean electromotive force created by the LORENTZ forces acting on the microscale turbulence.     

Jointing and minor tectonics of the S. Crop of the South Wales Coalfield between Machen and Bridgend

Observations on joints, minor faults and mineral veins at 47 localities along the south and south east crop of the S. Wales Coalfield indicate the presence of a joint system comprised of up to 6 sets of fractures striking at 350°, 330°, 290°, 270°, 250° and 210°. The joint sets are parallel to minor faults of strike and dip-slip types, whilst minor thrust faults indicate an early phase of sub-horizontal compression. The joint system is thought to be of tectonic origin and developed early in the deformational history of the area in response to a N-S compression. Later, dilational episodes facilitated the infilling of mineral veins, with the W.N.W. trending set probably indicating the latest phase of dilation in the area. All structures are considered to be of Armorican age, whilst the marked similarity in the orientation of the joint system to that of the North Crop of the Coalfield suggests that the brittle deformation was relatively homogeneous on both flanks of the Coalfield.