The Effects of the Laurentide Ice Sheet on North American Climate during the Last Glacial Maximum

A climate model, consisting of an atmospheric general circulation model coupled with a simple model of the oceanic mixed layer, is used to investigate the effects of the continental ice distribution of the last glacial maximum (LGM) on North American climate. This model has previously been used to simulate the LGM climate, producing temperature changes reasonably in agreement with paleoclimatic data. The LGM distribution of continental ice according to the maximum reconstruction of HUGHES et al. (1981) is used as input to the model. In response to the incorporation of the expanded continental ice of the LGM, the model produces major changes in the climate of North America. The ice sheet exerts an orographic effect on the tropospheric flow, resulting in a splitting of the midlatitude westerlies in all seasons but summer. Winter temperatures are greatly reduced over a wide region south of the Laurentide ice sheet, although summer cooling is less extensive. An area of reduced soil moisture develops in the interior of North America just south of the ice margin. At the same time, precipitation increases in a belt extending from the extreme southeastern portion of the ice sheet eastward into the North Atlantic. Some of these findings are similar to paleoclimatic inferences based on geological evidence.Un modèle climatique, composé d'un modèle de circulation atmosphérique général associé à un modèle simple de la couche océanique mixte, a servi à étudier l'influence de la répartition des glaciers continentaux sur le climat de l'Amérique du Nord au dernier pléniglaciaire. Ce modèle avait déjà servi pour simuler le climat au dernier pléniglaciaire; il a montré des changements de températures concordant assez bien avec les données paléoclimatiques. La répartition des glaces continentales pendant le pléniglaciaire selon l'hypothèse d'extension maximale de HUGHES et al. (1981) a servi à la modélisation. En réponse à l'incorporation des données de cette hypothèse, le modèle fait voir des changements majeurs dans le climat de l'Amérique du Nord. La présence de la calotte glaciaire fait ressortir l'influence de l'orographie sur le flux troposphérique qui se concrétise par une séparation des vents d'ouest aux latitudes moyennes durant toutes les saisons, sauf l'été. Les températures hivernales s'abaissent substantiellement dans une vaste région située au sud de la calotte laurentidienne, bien que le refroidissement soit moindre durant l'été. Une zone sèche se développe immédiatement au sud de la marge glaciaire. Au même moment, les précipitations augmentent dans la région qui s'étend de l'extrémité sud-est de la calotte glaciaire jusque dans l'Atlantique Nord, à l'est. Certains de ces résultats sur la nature du paléoclimat sont similaires aux déductions que les données géologiques ont inspirées.Um die Auswirkungen der kontinentalen Eisverbreitung im jüngsten glazialen Maximum auf das nordamerikanische Klima zu erforschen, wird ein Klima-Modell benutzt. das aus einem Modell der Hauptluftströmung in Verbindung mit einem einfachen Modell der gemischten ozeanischen Schicht besteht. Frùher wurde dieses Modell benutzt, um das Klima im jüngsten glazialen Maximum zu simulieren. Die Ergebnisse haben Temperaturschwankungen ergeben, die einigermapen genau mit den paleoklimatischen Daten übereinstimmten. Ausgegangen wurde bei dem Modell von der Verteilung des kontinentalen Eises im jüngsten glazialen Maximum entsprechend der Maximum-Rekonstruktion von HUGHES et al. (1981). AIs Antwort auf die Einverleibung des ausgedehnten kontinentalen Eises im jüngsten glazialen Maximum produziert das Modell bedeutende Veränderungen im nordamerikanischen Klima. Die Eisdecke übt eine orographische Wirkung auf die troposphärische Luftströmung aus, was zu einer Aufsplitterung der westlichen Winde mittlerer Breite in alien Jahreszeiten auBer im Sommer führt. Die Winter-Temperaturen sinken stark in einem weiten Gebiet südlich der laurentischen Eisdecke, während die sommerliche Abkühlung weniger stark ausfällt. Im Innern Nordamerikas südlich der Eisgrenze entwickelt sich ein Gebiet verringerter Bodenfeuchtigkeit. Gleichzeitig nehmen die Niederschläge innerhalb eines Gürtels zu, der von dem äupersten südöstlichen Teil der Eisdecke ostwärts in den Nordatlantik reicht. Einige dieser Ergebnisse decken sich mit paleoklimatischen Folgerungen, die sich auf geologische Nachweise stützen

Smart climate hydropower tool: A machine-learning seasonal forecasting climate service to support cost–benefit analysis of reservoir management

This study proposes a climate service named Smart Climate Hydropower Tool (SCHT) and designed as a hybrid forecast system for supporting decision-making in a context of hydropower production. SCHT is technically designed to make use of information from state-of-art seasonal forecasts provided by the Copernicus Climate Data Store (CDS) combined with a range of different machine learning algorithms to perform the seasonal forecast of the accumulated inflow discharges to the reservoir of hydropower plants. The machine learning algorithms considered include support vector regression, Gaussian processes, long short-term memory, non-linear autoregressive neural networks with exogenous inputs, and a deep-learning neural networks model. Each machine learning model is trained over past decades datasets of recorded data, and forecast performances are validated and evaluated using separate test sets with reference to the historical average of discharge values and simpler multiparametric regressions. Final results are presented to the users through a user-friendly web interface developed from a tied connection with end-users in an effective co-design process. Methods are tested for forecasting the accumulated seasonal river discharges up to six months in advance for two catchments in Colombia, South America. Results indicate that the machine learning algorithms that make use of a complex and/or recurrent architecture can better simulate the temporal dynamic behaviour of the accumulated river discharge inflow to both case study reservoirs, thus rendering SCHT a useful tool in providing information for water resource managers in better planning the allocation of water resources for different users and for hydropower plant managers when negotiating power purchase contracts in competitive energy markets

Measuring vertebrate telomeres: applications and limitations

Telomeres are short tandem repeated sequences of DNA found at the ends of eukaryotic chromosomes that function in stabilizing chromosomal end integrity. In vivo studies of somatic tissue of mammals and birds have shown a correlation between telomere length and organismal age within species, and correlations between telomere shortening rate and lifespan among species. This result presents the tantalizing possibility that telomere length could be used to provide much needed information on age, ageing and survival in natural populations where longitudinal studies are lacking. Here we review methods available for measuring telomere length and discuss the potential uses and limitations of telomeres as age and ageing estimators in the fields of vertebrate ecology, evolution and conservation

TSPAN5 Enriched Microdomains Provide a Platform for Dendritic Spine Maturation through Neuroligin-1 Clustering

Tetraspanins are a class of evolutionarily conserved transmembrane proteins with 33 members identified in mammals that have the ability to organize specific membrane domains, named tetraspanin-enriched microdomains (TEMs). Despite the relative abundance of different tetraspanins in the CNS, few studies have explored their role at synapses. Here, we investigate the function of TSPAN5, a member of the tetraspanin superfamily for which mRNA transcripts are found at high levels in the mouse brain. We demonstrate that TSPAN5 is localized in dendritic spines of pyramidal excitatory neurons and that TSPAN5 knockdown induces a dramatic decrease in spine number because of defects in the spine maturation process. Moreover, we show that TSPAN5 interacts with the postsynaptic adhesion molecule neuroligin-1, promoting its correct surface clustering. We propose that membrane compartmentalization by tetraspanins represents an additional mechanism for regulating excitatory synapses

Heparin prevents Zika virus induced-cytopathic effects in human neural progenitor cells

The recent Zika virus (ZIKV) outbreak, which mainly affected Brazil and neighbouring states, demonstrated the paucity of information concerning the epidemiology of several flaviruses, but also highlighted the lack of available agents with which to treat such emerging diseases. Here, we show that heparin, a widely used anticoagulant, while exerting a modest inhibitory effect on Zika Virus replication, fully prevents virus-induced cell death of human neural progenitor cells (NPCs)

Differential Roles for L-Type Calcium Channel Subtypes in Alcohol Dependence

It has previously been shown that the inhibition of L-type calcium channels (LTCCs) decreases alcohol consumption, although the contribution of the central LTCC subtypes Cav1.2 and Cav1.3 remains unknown. Here, we determined changes in Cav1.2 (Cacna1c) and Cav1.3 (Cacna1d) mRNA and protein expression in alcohol-dependent rats during protracted abstinence and naive controls using in situ hybridization and western blot analysis. Functional validation was obtained by electrophysiological recordings of calcium currents in dissociated hippocampal pyramidal neurons. We then measured alcohol self-administration and cue-induced reinstatement of alcohol seeking in dependent and nondependent rats after intracerebroventricular (i.c.v.) injection of the LTCC antagonist verapamil, as well as in mice with an inducible knockout (KO) of Cav1.2 in Ca2+/calmodulin-dependent protein kinase parallel to alpha (CaMKII alpha)-expressing neurons. Our results show that Cacna1c mRNA concentration was increased in the amygdala and hippocampus of alcohol-dependent rats after 21 days of abstinence, with no changes in Cacna1d mRNA. This was associated with increased Cav1.2 protein concentration and L-type calcium current amplitudes. Further analysis of Cacna1c mRNA in the CA1, basolateral amygdala (BLA), and central amygdala (CeA) revealed a dynamic regulation over time during the development of alcohol dependence. The inhibition of central LTCCs via i. c. v. administration of verapamil prevented cue-induced reinstatement of alcohol seeking in alcohol-dependent rats. Further studies in conditional Cav1.2-KO mice showed a lack of dependence-induced increase of alcohol-seeking behavior. Together, our data indicate that central Cav1.2 channels, rather than Cav1.3, mediate alcohol-seeking behavior. This finding may be of interest for the development of new antirelapse medications

PRRT2 controls neuronal excitability by negatively modulating Na+ channel 1.2/1.6 activity

Proline-rich transmembrane protein 2 (PRRT2) is the causative gene for a heterogeneous group of familial paroxysmal neurological disorders that include seizures with onset in the first year of life (benign familial infantile seizures), paroxysmal kinesigenic dyskinesia or a combination of both. Most of the PRRT2 mutations are loss-of-function leading to haploinsufficiency and 80% of the patients carry the same frameshift mutation (c.649dupC; p.Arg217Profs*8), which leads to a premature stop codon. To model the disease and dissect the physiological role of PRRT2, we studied the phenotype of neurons differentiated from induced pluripotent stem cells from previously described heterozygous and homozygous siblings carrying the c.649dupC mutation. Singlecell patch-clamp experiments on induced pluripotent stem cell-derived neurons from homozygous patients showed increased Na+ currents that were fully rescued by expression of wild-type PRRT2. Closely similar electrophysiological features were observed in primary neurons obtained from the recently characterized PRRT2 knockout mouse. This phenotype was associated with an increased length of the axon initial segment and with markedly augmented spontaneous and evoked firing and bursting activities evaluated, at the network level, by multi-electrode array electrophysiology. Using HEK-293 cells stably expressing Nav channel subtypes, we demonstrated that the expression of PRRT2 decreases the membrane exposure and Na+ current of Nav1.2/Nav1.6, but not Nav1.1, channels. Moreover, PRRT2 directly interacted with Nav1.2/Nav1.6 channels and induced a negative shift in the voltage-dependence of inactivation and a slow-down in the recovery from inactivation. In addition, by co-immunoprecipitation assays, we showed that the PRRT2-Nav interaction also occurs in brain tissue. The study demonstrates that the lack of PRRT2 leads to a hyperactivity of voltage-dependent Na+ channels in homozygous PRRT2 knockout human and mouse neurons and that, in addition to the reported synaptic functions, PRRT2 is an important negative modulator of Nav1.2 and Nav1.6 channels. Given the predominant paroxysmal character of PRRT2-linked diseases, the disturbance in cellular excitability by lack of negative modulation of Na+ channels appears as the key pathogenetic mechanism

Using the past to constrain the future: how the palaeorecord can improve estimates of global warming

Climate sensitivity is defined as the change in global mean equilibrium temperature after a doubling of atmospheric CO2 concentration and provides a simple measure of global warming. An early estimate of climate sensitivity, 1.5-4.5{\deg}C, has changed little subsequently, including the latest assessment by the Intergovernmental Panel on Climate Change. The persistence of such large uncertainties in this simple measure casts doubt on our understanding of the mechanisms of climate change and our ability to predict the response of the climate system to future perturbations. This has motivated continued attempts to constrain the range with climate data, alone or in conjunction with models. The majority of studies use data from the instrumental period (post-1850) but recent work has made use of information about the large climate changes experienced in the geological past. In this review, we first outline approaches that estimate climate sensitivity using instrumental climate observations and then summarise attempts to use the record of climate change on geological timescales. We examine the limitations of these studies and suggest ways in which the power of the palaeoclimate record could be better used to reduce uncertainties in our predictions of climate sensitivity.Comment: The final, definitive version of this paper has been published in Progress in Physical Geography, 31(5), 2007 by SAGE Publications Ltd, All rights reserved. \c{opyright} 2007 Edwards, Crucifix and Harriso