Reconstruction of Little Ice Age Events in the Canadian Rocky Mountains

The well-developed moraines of the Little Ice Age represent the most significant regional Holocene glacial event in the Canadian Rocky Mountains. The application of dating techniques (documentary sources, dendrochronology, lichenometry and radiocarbon dating) appropriate to this timeframe are briefly reviewed and summary data from 33 glaciers are presented. Three main periods of moraine development are recognised (i) 1500-1700 A.D., represented by small fragments of poorly dated moraines, (ii) early 1700's when about one-third of the glaciers show a maximum advance, (iii) mid-to-late-nineteenth century when major readvances built moraines close to or beyond (i) and (ii). In addition to these periods, 14C dates from overridden trees indicate a 12th/13th century glacial advance to within 400 and 1400 m of the Little Ice Age Maximum positions at Robson and Kiwa (Premier Range) Glaciers respectively. Prior to this advance a period of warmer conditions is inferred between ca. 700-1100 A.D. from the presence of large, 14C-dated snags at tree-line near the Athabasca Glacier, including a 1000 14C yr-old larch (probably Larix lyallii) about 90 km northwest of its present limit. Tree-line may have readvanced at the Athabasca site between ca. 1300-1700 A.D. but receded again during the eighteenth and nineteenth centuries. Future research should be directed towards using the relatively long tree-ring records (500-1000 yrs, with cross-dating) of this area for climatic reconstructions.Les moraines bien développées mises en place au cours du Petit Âge glaciaire sont les témoins les plus importants des glaciations holocènes dans les Rocheuses. On passe ici en revue les principales techniques de datation (sources de documentation, dendrochronologie, lichénométrie et datations au radiocarbone) appropriées à cette période et on présente les données résumées sur 33 glaciers. On a reconnu trois principales phases de développement des moraines caractérisées par: i) quelques tronçons de moraines imparfaitement datées entre 1500 et 1700 ap. J.-C. ; ii) une avancée maximale au début du XVIIIe s. pour environ le tiers des glaciers; iii) des récurrences majeures survenues de la deuxième moitié à la fin du XIXe s. qui ont rejoint sinon dépassé les positions atteintes en i) et ii). Certaines datations au radiocarbone à partir d'arbres ravagés démontrent qu'une avancée glaciaire aux XIIe et XIIIe s. s'est approchée, jusqu'à 400 et 1400 m respectivement, des positions atteintes à l'apogée du Petit Age glaciaire aux glaciers Robson et Kiwa. De grosses souches datées au 14C, situées à la limite des arbres près du glacier d'Athabaska, et notamment un mélèze vieux de 1000 ans (probablement Larix lyallii) trouvé à 90 km au nord-ouest de la limite actuelle des arbres, démontrent qu'un épisode plus chaud a prévalu entre 700 et 1100 ap. J.-C. La limite des arbres était probablement non loin de ce site vers 1300-1700 ap. J.-C, mais elle a de nouveau reculé au cours des XVIIIe et XIXe s. Les recherches sur les reconstitutions climatiques dans la région devront certainement tenir compte de cette longue série de données (500-1000 ans) sur les anneaux de croissance.Die gut entwickelten Morànen der "kleinen Eiszeit" sind das wichtigste régionale Eiszeit-Ereignis in den kanadischen Rocky Mountains wàhrend des Holozân. Die Anwendung von zu diesem Zeitrahmen passenden Datierungstechniken (dokumentarische Quellen, Dendrochronologie, Lichénométrie und Radiokarbondatierungen) werden kurz besprochen und zusammengefaBte Daten von 33 Gletschern werden vorgestellt. Drei Hauptperioden der Morànen-Entwicklung werden festgestellt : (i) 1500-1700 v.u.Z., charakterisiert durch kleine Fragmente ungenùgend datierter Morànen; (ii) eine Période des frùhen 17. Jahrhunderts, als etwa ein Drittel der Gletscher einen maximalen VorstoB aufweisen; (iii) mittleres bis spates 19. Jahrhundert, als HauptrùckvorstôBe zur Bildung von Morànen fùhrten, die denjenigen von (i) und (ii) glichen oder darùber hinausgingen. Zusâtzlich zu diesen Perioden zeigen 14C Daten von zerstôrten Bâumen einen EisvorstoB im 12./13. Jahrhundert, der sich bis auf 400 bzw. 1400 m den Maximal-Positionen der kleinen Eiszeit am Robson und Kiwagletscher nâherte. Vor diesem VorstoB wird auf eine Période wàrmerer Bedingungen geschlossen zwischen etwa 700-1100 v.u.Z., auf Grund des Vorkommens von auf 14C datierten groBen Baumstùmpfen an der Baumgrenze in der Nahe des Athabasca-Gletschers, einschlieBlich einer 1000 Jahre alten 14C Lârche (wahrscheinlich Larix lyallii), die etwa 90 km nordwestlich ihrer gegenwârtigen Grenze gefungen wurde. Die Baumgrenze ist môglicherweise zwischen 1300-1700 v.u.Z. bis zum Athabasca-Gebiet rùckvorgestoBen, dann aber wieder wàhrend des 18. und 19. Jahrhunderts zurùckgewichen. Zukùnftige Forschung ùber die klimatische Rekonstruktion sollte in diesem Gebiet auf die Nutzung der relativ langen Baumring-Belege gerichtet werden (500-1000 Jahre, mit Quer-Datierung)

Proxy Climatic Data from Tree Rings at Lake Louise, Alberta : A Preliminary Report

Preliminary results are presented of studies using oxygen isotopes and tree-ring densitometry to derive proxy climatic data from Picea engelmannii and Abies Iasiocarpa in the Canadian Rockies. Significant correlations occur between mean annual temperatures and δ18O determinations from five year groups of tree rings from three trees. However, unexplained anomalies in these relationships indicate that ring-width effects may reduce this correlation in some cases and that further exploratory work is necessary. Indexed chronologies for the period 1705-1980 were developed for 15 tree-ring variables derived by X-ray densitometry from 16 Picea cores. Principal components analysis was used to identify three groups of highly inter-correlated variables related to ring width, earlywood density and latewood characteristics. Each group responds differently to climatic controls increasing the potential for development of proxy climatic data over ring-width measures alone. Transfer function development is incomplete but preliminary results for summer temperature (June and July, R2 = 0,46) and December-March precipitation (R2 = 0,40) are presented as examples. Using these equations preliminary reconstructions for the period 1710-1980 are presented.On présente ici les résultats préliminaires d'études dont le but est d'obtenir des données climatiques par l'intermédiaire, chez Picea engelmannii et Abies lasiocarpa, dans les Rocheuses du Canada, des isotopes d'oxygène et de la densité des anneaux de croissance. On obtient des corrélations significatives entre les températures moyennes annuelles et les déterminations au δ18O sur les anneaux de croissance de trois arbres, par périodes de 5 ans. Toutefois, des anomalies encore inexpliquées révèlent que certaines caractéristiques de la largeur des anneaux pourraient, dans certains cas, réduire la corrélation. Il est donc nécessaire de poursuivre les recherches dans ce domaine. On a dressé des répertoires chronologiques, allant de 1705 à 1980. Ils tiennent compte de 15 variables provenant des anneaux de croissance et obtenues par densitométrie ra-diologique sur 16 noyaux de Picea. On a ensuite réparti les variables en trois groupes principaux en se fondant sur la largeur des anneaux, la densité du bois de printemps et les particularités du bois d'automne. Chaque groupe réagit différemment au climat, si bien que les données climatiques indirectes risquent d'être plus importantes que celles que fournissent les seules mesures de largeur des anneaux de croissance. L'élaboration de la fonction de transfert est incomplète, mais on donne, à titre d'exemple, les résultats préliminaires touchant les températures d'été de juin à juillet (R2 = 0,46) et les précipitations de décembre à mars (R2 = 0,40). À l'aide de ces équations on a pu effectuer des reconstitutions climatiques préliminaires pour la période allant de 1710 à 1980.Es werden vorlâufige Ergebnisse vorgestellt von Studien. die mittels Sauerstoff-lsotopen und der Dichte der Baumjahresringe indirekte klimatische Daten von Picea engelmannii und Abies Iasiocarpa in den kanadischen Rockies gewinnen. Es erscheinen signifikante Korrelationen zwischen durchschnittlichen Jahrestemperaturen und den δ18O Bestimmungen auf den Jahresringen von drei Bâu-men in fùnf Jahresgruppen. Jedoch weisen unerklàrte Anomalien in diesen Beziehungen darauf hin, daB Wirkungen der Ring-Breite dièse Korrelation in manchen Fallen reduzieren kann, und dafî weitere Forschungsarbeit notwendig ist. Fur die Zeit von 1705-1980 wurden chronologische Register entwickelt fur 15 Baum-Ring-Variablen. Dièse wurden durch Messung der Dichte von 16 Picea Kernen mittels Rôntgenaufnahmen gewonnen. Die Analyse der hauptsàchlichen Komponenten diente der Identifizierung von drei Gruppen von Variablen, die in intensiver Wechselbeziehung stehen, wobei man sich auf die Breite der Ringe, die Dichte des Frùhjahrsbaumwuchses und die Charakteristika des Herbstbaumwuchses bezog. Jede Gruppe reagiert anders auf klimatische Einflùsse, so daB die indirekt gewonnenen klimatischen Daten wichtiger sind, als die allein durch Messung der Ring-Weite gewonnenen. Die Ausarbeitung der Transferfunktion ist unvollstândig, aber vorlâufige Ergebnisse fur Sommertemperatur (Juni und JuIi, R2 = 0.46) und Dezember bis Màrz Niederschlag (R2 = 0.40) werden als Beispiel dargestellt. Mittels dieser Gleichungen werden vorlâufige Rekonstruktionen fur die Période von 1710 bis 1980 vorgestellt

The Paleoecological Record of 6 ka BP Climate in the Canadian Prairie Provinces

Synthesis of available paleoecological studies in the Prairie provinces of Canada indicates that although the peak in postglacial aridity that characterized early Holocene climate of the western foothills and plains had passed, conditions remained warmer and drier than present throughout the region ca. 6000 yr BP Compared to today, treeline elevations were higher and alpine glaciers were reduced in size in the Rocky Mountains, lake levels were lower over much of the Interior Plains, and the grassland and boreal forest ecozones extended north of their present positions. Forest fires were more prevalent ca. 6000 yr BP than they are today, aiding westward migration of jack pine (Pinus banksiana) through the boreal forest and increasing the area occupied by grassland in boreal and montane forest regions. Attempts to quantify the magnitude of 6 ka temperature and precipitation differences have produced variable results, but suggest that mean annual temperature was 0.50°C to 1.50°C higher than today (summer temperature may have been up to 3°C higher) and mean annual precipitation was reduced by 65 mm (or summer precipitation was reduced by 50 mm), compared to present. The nature and scale of these changes suggests that a vigorous zonal atmospheric circulation pattern, similar to that of the 1930s but shifted northward, prevailed at 6 ka.La synthèse des études paléoécologiques montrent qu'à 6 ka le maximum d'aridité, qui caractérisait l'Holocène inférieur, avait été atteint, mais le climat demeurait plus chaud et plus sec que maintenant dans toute la région. Les différentes limites des arbres étaient plus élevées qu'aujourd'hui et la superficie des glaciers alpins étaient plus petite, les niveaux lacustres étaient moins élevés dans la plus grande partie des plaines intérieures et les écozones des Prairies et de la forêt boréale s'étendaient plus au nord qu'aujourd'hui. Les feux de forêt étaient plus fréquents à 6 ka qu'actuellement, ce qui a favorisé la migration du pin gris (Pinus banksiana) vers l'ouest à travers la forêt boréale et accru la superficie de la prairie dans les zones de forêts boréale et alpine. Les essais faits dans le but de mesurer l'ampleur des différences de températures et de précipitations à 6 ka ont donné des résultats variables, mais montrent que la température était de 0,5 à 1,5°C plus élevé que maintenant (avec une température estivale jusqu'à 3°C plus élevée) et les précipitations annuelles moyennes étaient de 65 mm inférieures (avec des précipitations estivales de 50 mm inférieures) à maintenant. La nature et le degré des changements laissent croire qu'une forte circulation atmosphérique zonale, semblable à celle des années 1930, mais plus nordique, existait à 6 ka.Die Synthèse der verfùgbaren palâoôkologischen Studien in den Prârie-Provinzen Kanadas zeigt, daf3 das Klima in der ganzen Region um etwa 6000 Jahre v.u.Z. warmer und trockener als gegenwârtig blieb, wenn auch das Maximum an postglazialer Trockenheit, welches im frùhen Holozàn das Klima der westlichen Gebirgsauslâufer und Ebenen charakterisierte, vorùber war. Verglichen mit heute waren die Baumgrenzen hôher und die alpinen Gletscher in den Rocky Mountains kleiner, die Seehôhen waren niedriger im grôBten Teil der inneren Ebenen, und die Ôkozonen von Grasland und nôrdlichem WaId erstreckten sich weiter nôrdlich als heute. Waldbrânde traten um etwa 6000 v.u.Z. hâufiger als gegenwârtig auf und haben so die Westwàrtswanderung von Graukiefer (Pinus banksiana) durch den nôrdlichen WaId begùnstigt und die Graslandflàchen in den Gebieten des nôrdlichen und alpinen Waldes vergrôBert. Versuche, den Umfang der Unterschiede in Temperatur und Niederschlàgen um 6 ka zu bestimmen, ergaben wechselnde Ergebnissse, doch zeigen sie, daB die durchschnittliche jâhrliche Temperatur 0.5° C bis 1.50C hôher als gegenwârtig war (die Sommertemperatur dûrfte bis zu 3°C hôher gewesen sein) und die durchschnittlichen jâhrlichen Niederschlâge waren um 65 mm geringer (oder die Sommer-Niederschlàge waren um 50 mm geringer) verglichen mit heute. Die Natur und der Grad dieser Wechsel lassen vermuten, daB eine krâftige zonale atmosphàrische Strômung, àhnlich der von den 1930 iger Jahren aber nôrdlicher gelagert, um 6 ka vorherrschte

Basal crevasses in Larsen C Ice Shelf and implications for their global abundance

Basal crevasses extend upwards from the base of ice bodies and can penetrate more than halfway through the ice column under conditions found commonly on ice shelves. As a result, they may locally modify the exchange of mass and energy between ice shelf and ocean, and by altering the shelf's mechanical properties could play a fundamental role in ice shelf stability. Although early studies revealed that such features may be abundant on Antarctic ice shelves, their geometrical properties and spatial distribution has gained little attention. We investigate basal crevasses in Larsen C Ice Shelf using field radar survey, remote sensing and numerical modelling. We demonstrate that a group of features visible in MODIS imagery are the surface expressions of basal crevasses in the form of surface troughs, and find that basal crevasses can be generated as a result of stresses well downstream of the grounding line. We show that linear elastic fracture mechanics modelling is a good predictor of basal crevasse penetration height where stresses are predominantly tensile, and that measured surface trough depth does not always reflect this height, probably because of snow accumulation in the trough, marine ice accretion in the crevasse, or stress bridging from the surrounding ice. We conclude that all features visible in MODIS imagery of ice shelves and previously labelled simply as "crevasses", where they are not full thickness rifts, must be basal crevasse troughs, highlighting a fundamental structural property of many ice shelves that may have been previously overlooked

The Relationship Between Consumer Lending and Economic Growth

For centuries economists have attempted to explain what causes the ebb and flow of the economy. None thus far have been able to perfectly explain the nuances of the economy as a whole. In this paper, I explore the relationship between consumer lending volume and economic growth. Consumer lending is defined as credit card debt, motor vehicle loans, and student loans taken on by individuals. Mortgages are excluded from the data as they are considered significantly different from the other mentioned forms of consumer lending. Economic growth is defined as the change in Gross Domestic Product (GDP)/capita. I have selected four countries to examine: The United States of America (USA), The United Kingdom (UK), Australia, and Japan. I use multivariate regression analysis to determine the relationship between consumer lending and economic growth in the identified nations. My findings establish a statistically significant contemporaneous and lead-lag relationship between consumer lending and GDP/capita growth. The results for each nation researched vary drastically and are discussed in detail within the paper

Brief Communication: Newly developing rift in Larsen C Ice Shelf presents significant risk to stability

An established rift in the Larsen C Ice Shelf, formerly constrained by a suture zone containing marine ice, grew rapidly during 2014 and is likely in the near future to generate the largest calving event since the 1980s and result in a new minimum area for the ice shelf. Here we investigate the recent development of the rift, quantify the projected calving event and, using a numerical model, assess its likely impact on ice shelf stability. We find that the ice front is at risk of becoming unstable when the anticipated calving event occurs

Meltwater produced by wind–albedo interaction stored in an East Antarctic ice shelf

Surface melt and subsequent firn air depletion can ultimately lead to disintegration of Antarctic ice shelves1,2 causing grounded glaciers to accelerate3 and sea level to rise. In the Antarctic Peninsula, foehn winds enhance melting near the grounding line4, which in the recent past has led to the disintegration of the most northerly ice shelves5,6. Here, we provide observational and model evidence that this process also occurs over an East Antarctic ice shelf, where meltwaterinduced firn air depletion is found in the grounding zone. Unlike the Antarctic Peninsula, where foehn events originate from episodic interaction of the circumpolar westerlies with the topography, in coastal East Antarctica high temperatures are caused by persistent katabatic winds originating from the ice sheet’s interior. Katabatic winds warm and mix the air as it flows downward and cause widespread snow erosion, explaining >3 K higher near-surface temperatures in summer and surface melt doubling in the grounding zone compared with its surroundings. Additionally, these winds expose blue ice and firn with lower surface albedo, further enhancing melt. The in situ observation of supraglacial flow and englacial storage of meltwater suggests that ice-shelf grounding zones in East Antarctica, like their Antarctic Peninsula counterparts, are vulnerable to hydrofracturing7

Extensive retreat of Greenland tidewater glaciers 2000-2010

Overall mass loss from the Greenland ice sheet nearly doubled during the early 2000s resulting in an increased contribution to sea-level rise, with this step-change being mainly attributed to the widespread frontal retreat and accompanying dynamic thinning of tidewater glaciers. Changes in glacier calving-front positions are easily derived from remotely sensed imagery and provide a record of dynamic change. However, ice-sheet-wide studies of calving fronts have been either spatially or temporally limited. In this study multiple calving-front positions were derived for 199 Greenland marine-terminating outlet glaciers with width greater than 1 km using Landsat imagery for the 11-year period 2000–2010 in order to identify regional seasonal and inter-annual variations. During this period, outlet glaciers were characterized by sustained and substantial retreat summing to more than 267 km, with only 11 glaciers showing overall advance. In general, the pattern of mass loss detected by GRACE (Gravity Recovery and Climate Experiment) and other measurements is reflected in the calving record of Greenland glaciers. Our results suggest several regions in the south and east of the ice sheet likely share controls on their dynamic changes, but no simple single control is apparent

Spatiotemporal interpolation of elevation changes derived from satellite altimetry for Jakobshavn Isbræ, Greenland

Estimation of ice sheet mass balance from satellite altimetry requires interpolation of point-scale elevation change (dHdt) data over the area of interest. The largest dHdt values occur over narrow, fast-flowing outlet glaciers, where data coverage of current satellite altimetry is poorest. In those areas, straightforward interpolation of data is unlikely to reflect the true patterns of dHdt. Here, four interpolation methods are compared and evaluated over Jakobshavn Isbr, an outlet glacier for which widespread airborne validation data are available from NASAs Airborne Topographic Mapper (ATM). The four methods are ordinary kriging (OK), kriging with external drift (KED), where the spatial pattern of surface velocity is used as a proxy for that of dHdt, and their spatiotemporal equivalents (ST-OK and ST-KED)

Postfeminist stylistics, work femininities and coaching: a multimodal study of a website

The aim of this paper is to examine representations of work femininities on a British website offering coaching specifically aimed at women. It builds on and contributes to studies of postfeminist representations but with a specific focus on work femininities and coaching webpages. Although studies on postfeminist representation have analysed the way young women’s, embodied and sexualised femininities are depicted across a wide variety of mainstream media, there has not been a study that focuses on the representation of work femininities on coaching websites. My approach matter because feminist authors critique popular psychology and link it to postfeminism and neoliberalism but as yet studies have focused on self-help books and magazines and not new media. Furthermore, coaching websites are an important medium for circulating postfeminist work femininities and psychological advice, produced through the digital labour of women entrepreneurs. Through my analysis of one website, influenced by feminist social semiotic multimodality literature, the paper contributes to postfeminist theory and organisation studies by explaining how ‘postfeminist stylistics’ reproduce postfeminist tropes and depictions of relational and individualised entrepreneurial femininities visually and textually (Lewis, 2014)