On Nonlocal Energy Transfer via Zonal Flow in the Dimits Shift

The two-dimensional Terry-Horton equation is shown to exhibit the Dimits shift when suitably modified to capture both the nonlinear enhancement of zonal/drift-wave interactions and the existence of residual Rosenbluth-Hinton states. This phenomenon persists through numerous simplifications of the equation, including a quasilinear approximation as well as a four-mode truncation. It is shown that the use of an appropriate adiabatic electron response, for which the electrons are not affected by the flux-averaged potential, results in an $\boldsymbol{E}\boldsymbol{\times}\boldsymbol{B}$ nonlinearity that can efficiently transfer energy nonlocally to length scales on the order of the sound radius. The size of the shift for the nonlinear system is heuristically calculated and found to be in excellent agreement with numerical solutions. The existence of the Dimits shift for this system is then understood as an ability of the unstable primary modes to efficiently couple to stable modes at smaller scales, and the shift ends when these stable modes eventually destabilize as the density gradient is increased. This nonlocal mechanism of energy transfer is argued to be generically important even for more physically complete systems.Comment: 28 pages, 7 figures, 4 movie

The Sangamonian Stage and the Laurentide Ice Sheet

This review of the most recent studies (up to June 1986) dealing with the Sangamonian in some key areas clearly indicates that, as yet, there is no definitive answer to the question : "When did the ice which eventually became the Laurentide Ice Sheet begin to accumulate?" In most areas the stratigraphic record simply identifies a probable interglacial period; the record yields no information on when ice growth may have started following that warm climatic interval. However the deltaic glacial lake sediments of the Scarborough Formation in the Toronto area and the Bécancour Till in the Trois-Rivières area are thought to possibly date from the Sangamonian (marine isotope sub-stages 5d-b). The Adam Till in the James Bay Lowland may be correlative. In Atlantic Canada, mostly in Cape Breton Island, plant fossils suggest a mid-Sangamonian climate roughly comparable to that which prevailed 11-12 ka ago. On Baffin Island a marine transgression of mid-Sangamonian age is thought to result from important ice accumulation in the area. These stratigraphic interpretations suggest significant glacier expansion in several areas of the North American continent during part of the Sangamonian Stage. Whether or not any of this ice survived a warmer climate period near the end of the Sangamonian to become part of the Laurentide Ice Sheet is a matter of speculation.La présente revue des travaux sur le Sangamonien (jusqu'à juin 1986) effectués dans des régions clés démontre qu'il n'y a pas encore de réponse satisfaisante à la question suivante: « À quel moment la glace, qui allait devenir la calotte glaciaire laurentidienne, a-t-elle commencer à s'accumuler? » Dans la plupart des régions, la séquence stratigraphique ne fait que signaler l'existence probable d'une période interglaciaire, sans toutefois permettre de déterminer le moment où la glace a commencé à s'accumuler après l'intervalle climatique chaud. Il existe toutefois quelques indices. Les sédiments d'un delta glaciolacustres de la Formation de Scarborough, dans la région de Toronto, et le Till de Bécancour, dans la région de Trois-Rivières, datent probablement du Sangamonien (sous-phases isotopiques marines 5d-b). Le Till d'Adam, dans les basses terres de la baie James, leur est probablement corrélatif. Dans les régions atlantiques du Canada, en particulier à l'île du Cap-Breton, des restes de plantes indiquent que le climat au cours du Sangamonien moyen aurait été très semblable à celui de la période de 11 000 à 12 000 ans BP. À l'île de Baffin, une transgression marine qui a eu lieu au Sangamonien moyen aurait pu être le résultat d'une importante accumulation de glace dans la région. Ces diverses interprétations régionales témoignent d'une importante croissance des glaciers dans plusieurs régions du continent nord-américain au cours du Sangamonien. On ne peut toutefois pas préciser si ces accumulations de glace ont survécu à la période plus chaude qui a prévalu à la fin du Sangamonien pour ensuite s'intégrer à la calotte glaciaire laurentidienne.Dieser Überblick über die neuesten Studien (bis Juni 1986) zur sangamonischen Zeit in einigen Schlüsselgebieten zeigt deutlich, dap es bis heute keine endgültige Antwort auf die Frage gibt: "Wann begann sich das Eis anzuhäufen, das schlieBlich zur laurentischen Eisdecke wurde?" In den meisten Gebieten zeugen die stratigraphischen Spuren von einem wahrscheinlichen interglazialen Zeitabschnitt; die Spuren geben keine Auskunft darüber, wann der Eiswuchs nach diesem warmen klimatischen Zwischenspiel begonnen haben mag. Die Sedimente der deltaförmigen EisSeen der ScarboroughFormation in der Gegend von Toronto und die Bécancour-Grundmoräne in der Gegend von Trois-Rivières stammen vermutlich beide aus der sangamonischen Phase (Meeres-lsotopische Unterstadien 5d-b). Die AdamGrundmoräne im James-Bay-Tiefland hängt damit möglicherweise zusammen. In OstKanada, vor allem auf der Cap-Breton-Insel, legen Pflanzen-Fossilien nahe, daB dort ein Klima der mittleren sangamonischen Phase herrschte, das dem von vor 11 bis 12 ka ungefähr glich. Auf der Baffinlnsel halt man die UferBewegung in der sangamonischen Zeit fur die Auswirkung groBer Eisanhäufung in der Gegend. Diëse Deutungen der Stratigraphie legen eine umfangreiche GletscherAusdehnung in mehreren Gegenden des nordamerikanischen Kontinents während eines Teils der sangamonischen Zeit nahe. Ob Teile dieses Eises eine wärmere Phase gegen Ende der sangamonischen Zeit überdauerten, um ein Teil der laurentischen Eisdecke zu werden, Oder ob dies nient der Fall war, bleibt often

An Introduction to the Continental Record of the Laurentide Ice Sheet

The record of the Laurentide Ice Sheet is not well preserved in terrestrial deposits. Sediment sequences are incomplete and few record events older than the last ice retreat. Furthermore, in the absence of absolute dating methods for deposits older than the limit of radiocarbon dating, units are generally assigned a chronostratigraphic position by "counting from the top". As a result age estimates of many units can differ significantly between authors.Les dépôts abandonnés par la calotte laurentidienne relatent bien imparfaitement son évolution. Les séquences sédimentaires sont incomplètes et peu d'entre elles sont antérieures au retrait des derniers glaciers. De plus, en l'absence de méthodes de datation absolue des dépôts au-delà des limites du radiocarbone, la position chronostratigraphique d'un sédiment est généralement déterminée en comptant les unités de haut en bas. Conséquemment, les estimations de l'âge des unités varient de façon importante d'un auteur à l'autre

Glass transitions in 1, 2, 3, and 4 dimensional binary Lennard-Jones systems

We investigate the calorimetric liquid-glass transition by performing simulations of a binary Lennard-Jones mixture in one through four dimensions. Starting at a high temperature, the systems are cooled to T=0 and heated back to the ergodic liquid state at constant rates. Glass transitions are observed in two, three and four dimensions as a hysteresis between the cooling and heating curves. This hysteresis appears in the energy and pressure diagrams, and the scanning-rate dependence of the area and height of the hysteresis can be described by power laws. The one dimensional system does not experience a glass transition but its specific heat curve resembles the shape of the $D\geq 2$ results in the supercooled liquid regime above the glass transition. As $D$ increases, the radial distribution functions reflect reduced geometric constraints. Nearest-neighbor distances become smaller with increasing $D$ due to interactions between nearest and next-nearest neighbors. Simulation data for the glasses are compared with crystal and melting data obtained with a Lennard-Jones system with only one type of particle and we find that with increasing $D$ crystallization becomes increasingly more difficult.Comment: 26 pages, 13 figure

Mitotic Regulation of Protein Kinase CK2

Protein kinase CK2 is a serine/threonine kinase with a multitude of substrates and roles in many cellular processes, including mitosis. CK2 is constitutively active, yet we hypothesize that CK2 is indeed regulated in mitosis through subtle means, enabling CK2 to perform its functions unique to cell division. Our aims were to examine the roles of mitotic phosphorylation, subcellular localization, and interplay with mitotic kinases in the regulation of CK2 activity. We first examined the role of four highly conserved mitotic phosphorylation sites located in the unique C-terminus of CK2α. Phosphospecific antibodies generated against the sites show that CK2α phosphorylation is temporally regulated and occurs during prophase and metaphase during normal mitotic progression. Proper phosphorylation of CK2α is required for proper mitotic progression, as stable cell lines expressing phosphorylation site mutants of CK2α display severe mitotic defects. We next examined the impact of these phosphorylation events on the subcellular localization of CK2. We show that CK2α, but not CK2α’, localizes to the mitotic spindle. Localization of CK2α to the mitotic spindle is phosphodependent, and requires the peptidyl-prolyl isomerase Pin1. These results are a rare example of functional divergence between the two catalytic isoforms of CK2, and suggest that the role of CK2α phosphorylation during mitosis is to promote localization of CK2 to the mitotic spindle. Finally, we examined the possibility that CK2 activity during mitosis is regulated through hierarchal phosphorylation events, wherein CK2 would phosphorylate proteins only after priming phosphorylation events catalyzed by other mitotic kinases, particularly Cdk1. As this phenomenon has never been systematically investigated, we have investigated the consensus requirements for CK2 primed phosphorylation, and in particular Cdk/CK2 hierarchical phosphorylation. A genome-wide search for potential mitotic substrates matching the consensus sequence suggests that Cdk1/CK2 hierarchical phosphorylation may indeed contribute to mitotic signaling, particularly on the mitotic spindle. Taken together, our results confirm the importance of CK2 in mitotic cell division, and highlight several examples of subtle regulation of CK2, through phosphorylation, subcellular localization, and interplay with other protein kinases. This helps explain how CK2, a constitutively active kinase, can participate in tightly regulated cellular processes like mitosis

Late Wisconsinan Morphosedimentary Sequences of the Lower Coppermine River Valley, Nunavut and Northwest Territories

A series of late Wisconsinan sedimentary sequences occupy parts of the Coppermine River valley, and are grouped into five morphosedimentary zones representing four environments at the time of last ice retreat: glacial, paraglacial, lacustrine and marine. The sequences commonly interfinger, and document episodic deposition in time-transgressive environments related to ice frontal positions. Glacial and paraglacial sediments are, in part, reworked in a glaciolacustrine environment extending from delta topsets of bouldery gravel to bottomset rhythmites of silt-clay. The glacial-lake rhythmites formed the matrix of a later sequence of debris-flow events, which emplaced a wedge of massive diamicton in the postglacial marine sediments. This sedimentary sequence, composed of a chaotic mass of heterogeneous material that is intimately mixed, and is accumulated in the form of a semi-fluid body in a marine environment, is possibly the best exposed Quaternary olistostrome. A general overview of the Quaternary history of the area east of Great Bear Lake and north of Point Lake shows: a) deglaciation proceeded by large-scale downwasting with no discernable readvance pulses, b) that the Coppermine River valley between Point Lake and Rocky Defile Rapids was ice-free by 10 250 14C years BP, and, c) that earth-shaping processes were intensely active for a short period at the time of deglaciation; since then the landscape has been mostly quiescent.SOMMAIREDes séquences sédimentaires de la fin du Wisconsinien qui occupent des sections de la vallée de la rivière Coppermine définissent cinq zones morphosédimentaires représentant quatre environnements différents du retrait glaciaire, soit les milieux glaciaire, paraglaciaire, lacustre et marin.  Ces séquences qui s’interdigitent souvent, documentent des épisodes sédimentaires de milieux qui varient avec le temps et les changements de position du front glaciaire.  Les sédiments glaciaires et paraglaciaires sont en partie remaniés dans des milieux glaciolacustres allant des lit topset deltaïques de gravier à blocs jusqu’à des rythmites de limon-argile.  Les rythmites glacio-lacustres constituent la matrice d’une séquence subséquente de lave torrentielle, qui a déposé un énorme prisme de diamictons dans les sédiments marins postglaciaires.  Cette séquence sédimentaire, composée d’une masse chaotique de matériaux hétérogènes intimement mélangés accumulée sous forme semi-fluide en milieu marin, est peut-être le meilleur affleurement d’olistostrome quaternaire. Un coup d’œil sur l’histoire du Quaternaire de la région à l’est du Grand lac de l’Ours et au nord du lac Point, montre : a) que la déglaciation s’est déroulée par fonte du glacier sans réavancée discernable, b) que la vallée de la rivière Coppermine entre le lac Point et les rapides de Rocky Defile  était libre de glace vers 10 250 14C BP, et c) que les mécanismes d’érosion ont été intenses pendant une courte période au moment de la déglaciation; depuis lors, le paysage est demeuré relativement statique

Morphodynamics of Cold High Latitude Semiarid Regions: The Example of Ellef Ringnes Island, Nunavut

In this paper we use the example of Ellef Ringnes Island, Nunavut, to examine active geomorphic processes in a high latitude semiarid region. The spectacular landscape of Ellef Ringnes Island is principally the result of fluvial erosion controlled by geological structure. The nival regime concentrates flow in a brief late-spring period which provides strong erosive capabilities for rivers in spite of low annual precipitation. Other processes related to the cold environment produce a variety of minor landforms such as patterned ground, mud flows associated with ground ice, and solifluction lobes.Dans cet article, nous utilisons l’île Ellef Ringnes, au Nunavut, comme exemple en vue d’identifier les processus actifs pour cette région semi-aride de haute latitude. L’érosion fluviale contrôlée par la structure géologique est à l’origine du relief spectaculaire de l’île Ellef Ringnes. Le régime nival, qui concentre les débits sur une courte période à la fin du printemps, est caractérisé par une forte capacité érosive des cours d’eau en dépit des faibles précipitations annuelles. D’autres processus reliés aux milieux froids produisent une variété de formes mineures telles que les sols à figures géométriques, les coulées de boue associées à la présence de glace dans le sol et les lobes de solifluxion

Les formes d’effondrement et le mode de déglaciation de la région du lac Qingaluk, Territoires-du-Nord-Ouest, Canada

Les formes et les sédiments glaciaires de la vallée de la rivière Qingaluk illustrent la complexité du recul du front du glacier du Keewatin, au Wisconsinien supérieur, à l'ouest de la vallée de la rivière Coppermine dans les Territoires-du-Nord-Ouest. Dans cette région à relief modéré (300 m), des retraits mineurs du front glaciaire (2-5 km) ont provoqué des changements importants dans le sens d'écoulement des eaux de fonte et ont modifié les environnements sédimentaires dans la vallée. La sédimentation rapide en bordure du front glaciaire fut responsable de l'ensevelissement de blocs de glace. De nombreuses formes d'affaissement ont résulté de la fonte de ceux-ci après que l'activité des eaux fluvio-glaciaires eut cessé. Ces formes, de même que les crêtes morainiques, peuvent être utilisées pour déterminer des positions successives du front glaciaire. Quatre de ces positions, associées à un haut niveau du lac glaciaire Coppermine (phase Kamut), ont été définies dans la région du lac Qingaluk. Ces positions frontales permettent d'expliquer des inversions du sens de l'écoulement des rivières et du relief dans les dépôts fluvio-glaciaires, ainsi que des étagements de terrasses dans l'exutoire de la phase Kamut du lac glaciaire Coppermine.Glacial and glaciofluvial sediments and associated landforms in the Qingaluk River valley illustrate the complexity of glacial retreat in the Coppermine River Valley region, N.W.T. In this area of moderate relief (300 m), minor retreat (2-5 km) of the ice front led to dramatic changes in melt-water flow patterns and in sedimentary environments within the valley. Near the ice-front, dead-ice blocks were buried by rapid deposition of coarse sediments from meltwater streams. Subsequent melting of these buried ice masses, after meltwater activity had ceased, created typical collapse landforms. These, along with moraine ridges, can be used to define the former ice margins. Four such positions have been recognized in the Qingaluk Lake region. The last of these held up a high-level Glacial Lake Coppermine (Kamut Phase). The sequence of déglaciation explains the reversals in river flow direction, the inverted relief in outwash, and the terracing along the outlet of the Kamut Phase of Glacial Lake Coppermine

An ensemble approach to assess hydrological models’ contribution to uncertainties in the analysis of climate change impact on water resources

Over the recent years, several research efforts investigated the impact of climate change on water resources for different regions of the world. The projection of future river flows is affected by different sources of uncertainty in the hydro-climatic modelling chain. One of the aims of the QBic3 5 project (Que´bec-Bavarian International Collaboration on Climate Change) is to assess the contribution to uncertainty of hydrological models by using an ensemble of hydrological models presenting a diversity of structural complexity (i.e. lumped, semi distributed and distributed models). The study investigates two humid, mid-latitude catchments with natural flow conditions; one located in 10 Southern Que´bec (Canada) and one in Southern Bavaria (Germany). Daily flow is simulated with four different hydrological models, forced by outputs from regional climate models driven by a given number of GCMs’ members over a reference (1971–2000) and a future (2041–2070) periods. The results show that the choice of the hydrological model does strongly affect the climate change response of selected hydrological indicators, especially those related to low flows. Indicators related to high flows seem less sensitive on the choice of the hydrological model. Therefore, the computationally less demanding models (usually simple, lumped and conceptual) give a significant level of trust for high and overall mean flows

On the need for bias correction in regional climate scenarios to assess climate change impacts on river runoff

In climate change impact research, the assessment of future river runoff as well as the catchment scale water balance is impeded by different sources of modeling uncertainty. Some research has already been done in order to quantify the uncertainty of climate 5 projections originating from the climate models and the downscaling techniques as well as from the internal variability evaluated from climate model member ensembles. Yet, the use of hydrological models adds another layer of incertitude. Within the QBic3 project (Qu´ebec-Bavaria International Collaboration on Climate Change) the relative contributions to the overall uncertainty from the whole model chain (from global climate 10 models to water management models) are investigated using an ensemble of multiple climate and hydrological models. Although there are many options to downscale global climate projections to the regional scale, recent impact studies tend to use Regional Climate Models (RCMs). One reason for that is that the physical coherence between atmospheric and land-surface 15 variables is preserved. The coherence between temperature and precipitation is of particular interest in hydrology. However, the regional climate model outputs often are biased compared to the observed climatology of a given region. Therefore, biases in those outputs are often corrected to reproduce historic runoff conditions from hydrological models using them, even if those corrections alter the relationship between temperature and precipitation. So, as bias correction may affect the consistency between RCM output variables, the use of correction techniques and even the use of (biased) climate model data itself is sometimes disputed among scientists. For those reasons, the effect of bias correction on simulated runoff regimes and the relative change in selected runoff indicators is explored. If it affects the conclusion of climate change analysis in 25 hydrology, we should consider it as a source of uncertainty. If not, the application of bias correction methods is either unnecessary in hydro-climatic projections, or safe to use as it does not alter the change signal of river runoff. The results of the present paper highlight the analysis of daily runoff simulated with four different hydrological models in two natural-flow catchments, driven by different regional climate models for a reference and a future period. As expected, bias correction of climate model outputs is important for the reproduction of the runoff regime of the 5 past regardless of the hydrological model used. Then again, its impact on the relative change of flow indicators between reference and future period is weak for most indicators with the exception of the timing of the spring flood peak. Still, our results indicate that the impact of bias correction on runoff indicators increases with bias in the climate simulations