Tidal influence on Rutford Ice Stream, West Antarctica: observations of surface flow and basal processes from closely-spaced GPS and passive seismic stations

High-resolution surface velocity measurements and passive seismic observations from Rutford Ice Stream, West Antarctica, 40 km upstream from the grounding line are presented. These measurements indicate a complex relationship between the ocean tides and currents, basal conditions and ice-stream flow. Both the mean basal seismicity and the velocity of the ice stream are modulated by the tides. Seismic activity increases twice during each semi-diurnal tidal cycle. The tidal analysis shows the largest velocity variation is at the fortnightly period, with smaller variations superimposed at diurnal and semi-diurnal frequencies. The general pattern of the observed velocity is two velocity peaks during each semi-diurnal tidal cycle, but sometimes three peaks are observed. This pattern of two or three peaks is more regular during spring tides, when the largest-amplitude velocity variations are observed, than during neap tides. This is the first time that velocity and level of seismicity are shown to correlate and respond to tidal forcing as far as 40 km upstream from the grounding line of a large ice stream

Teacher Education in the Field of Reading

For too long a pervasive idea in the field of teacher education has been that primary teachers only, and more especiaHy those primary teachers who are concerned with the education of the very young, have the sole responsibility for teaching the students who are moving through our educational institutions how to read. The beginning and the end of the process of learning to read effectively have been left almost entirely in the hands of the primary teacher, who, up until recently, has experienced only minimal courses in the field of reading as part of his pre-service training. One of the main purposes of this paper will be to attempt to dispel this limited and educationally naive idea; more than lip service must be given to the truism that the development of the individual\u27s ability to read is a continuous process

Anteroventral thalamic nucleus: lesion effects on memory and cortico-limbic electrophysiology

Damage to the anterior thalamic nuclei (ATN) is associated with severe memory impairment in humans. What is unclear is how this damage affects electrophysiological activity within an extended hippocampal circuit for memory, of which the ATN is a key component. The current study provides a novel comparison of the electrophysiological activity of rats with lesions to the ATN and intact rats using two electrophysiological measures. These measure are peak power generated by each structure of interest, and the amount of signal amplitude covariance shared by structures, known as coherence. Data were recorded from four key neural memory structures (prefrontal cortex, hippocampus, retrosplenial cortex, and subiculum) during a behavioural paradigm in which rats were presented with novel or previously visited (repeat) arms in a radial arm maze. The current study found decreases in peak power within the sham group when entering repeat arms verses novel. There was also significantly reduced power in rats with ATN lesions compared to shams in the right hippocampus when entering novel arms, and in the right hippocampus and subiculum when entering repeat arms. While there were no significant between group differences in coherence, there was a reduction in coherence in shams when entering novel verses repeat arms in all structures analysed. Overall findings suggest that an intact ATN may play a regulatory role in electrophysiological activity across the extended hippocampal memory system

Magnetic effect on CO(2) solubility in seawater: A possible link between geomagnetic field variations and climate

Correlations between geomagnetic-field and climate parameters have beensuggested repeatedly, but possible links are controversially discussed.Here we test if weak (Earth-strength) magnetic fields can affectclimatically relevant properties of seawater. We found the solubility ofair in seawater to be by 15\% lower under reduced magnetic-field (20 muT) compared to normal field conditions (50 mu T). The magnetic-fieldeffect on CO(2) solubility is twice as large, from which we surmise thatgeomagnetic field variations modulate the carbon exchange betweenatmosphere and ocean. A 1\% reduction in magnetic dipole moment mayrelease up to ten times more CO(2) from the surface ocean than isemitted by subaerial volcanism. This figure is dwarfed in front ofanthropogenic CO(2) emissions

Descending Post-commissural Fornix Lesions Produce Impaired Spatial Working Memory in a 12-arm Maze

Memory is supported in the brain by a distributed neural network, comprised of cortical, limbic and brainstem structures and fibre pathways. The descending component of the post-commissural fornix (dPCFx) conveys hippocampal efferents to the mammillary bodies (MB), and so presents as a critical pathway along the hippocampal-MB-anterior thalamic axis, structures all crucial to memory function. However, two previous studies have reported surprisingly mild, if any, effect of selective dPCFx lesions on spatial memory in an 8-arm radial arm maze (RAM). To examine the impact of dPCFx lesions on electrophysiological activity in the anterior thalamus, dorsal hippocampus and prefrontal cortex, and in an effort to substantially increase task difficulty, we trained rats postoperatively in a 12-arm RAM. We found that dPCFx lesions produced a severe RAM impairment, showing that the RAM can elicit spatial working memory deficits after dPCFx lesions when task demands are high and suggesting that the dPCFx may indeed play an important mnemonic role

Tides and the flow of Rutford Ice Stream, West Antarctica

[1] Surface speeds of Rutford Ice Stream, West Antarctica, are known to vary by around 10–20% (depending on location) with a fortnightly periodicity corresponding to a springneap tidal cycle. The reasons for these periodic variations in flow are unclear. Here the possible role of tidal stress transmission upstream of the grounding line in affecting rates of basal motion is investigated. It is found that nonlinear rheological effects within the till, when coupled with transmission of tidal stresses within the ice that are linearly related to tidal amplitude, can give rise to the type of periodic oscillations in flow observed. This nonlinear interaction between tidal forcing and till deformation increases the mean ice flux across the grounding line by a few percent above what might be expected in the absence of tidal forcing. Periodic velocity fluctuations of this type have not been observed on other ice streams. However, modeling suggests that this may be due to lack of data and that such flow variations are likely to be common features of active ice streams draining into the Ronne Ice Shelf, as well as of other ice streams subjected to similar tidal forcing

Apparent correlation of palaeomagnetic intensity and climatic records in deep-sea sediments

Most reports of a correlation between Pleistocene climate and geomagnetic field intensity rely strongly on the assumption that sediment natural remanent magnetic (NRM) intensity provides a record of geomagnetic field strength and is not sensitive to local changes in properties of the sediment. Critical assessment of relevant data presented here and elsewhere from deep-sea sediment cores shows that a pronounced dependence of NRM intensity on sediment composition can occur which implies that this assumption is unlikely to be generally valid. As sediment composition often reflects varying depositional conditions induced by climatic change, the significance of correlations proposed between Pleistocene palaeomagnetism and climatic indicators in deep-sea sediments may be less dramatic than sometimes supposed

Constraints on Cosmic Neutrino Fluxes from the ANITA Experiment

We report new limits on cosmic neutrino fluxes from the test flight of the Antarctic Impulsive Transient Antenna (ANITA) experiment, which completed an 18.4 day flight of a prototype long-duration balloon payload, called ANITA-lite, in early 2004. We search for impulsive events that could be associated with ultra-high energy neutrino interactions in the ice, and derive limits that constrain several models for ultra-high energy neutrino fluxes. We rule out the long-standing Z-burst model as the source for the ultra-high energy cosmic rays.Comment: 4 pages, 3 figures, accepted to PR