Brief Communication: On the magnitude and frequency of Khurdopin glacier surge events

The return periods of Karakoram glacier surges are poorly quantified. Here, we present evidence of an historic surge of the Khurdopin Glacier that began in the mid-1970s and peaked in 1979. Measured surface displacements reached >5 km a⁻¹, two orders of magnitude faster than during quiescence. The Khurdopin Glacier next surged in the late 1990s, equating to a return period of 20 years. Surge evolution in the two events shows remarkable similarity suggesting a common trigger. Surge activity in the Karakoram needs to be better understood if accurate mass balance assessments of Hindu-Kush–Karakoram–Himalaya glaciers are to be made

Glacier dynamics over the last quarter of a century at Helheim, Kangerdlugssuaq and 14 other major Greenland outlet glaciers

The Greenland ice sheet is experiencing increasing rates of mass loss, the majority of which results from changes in discharge from tidewater glaciers. Both atmospheric and ocean drivers have been implicated in these dynamic changes, but understanding the nature of the response has been hampered by the lack of measurements of glacier flow rates predating the recent period of warming. Here, using Landsat-5 data from 1985 onwards, we extend back in time the record of surface velocities and ice-front position for 16 of Greenland's fastest-flowing tidewater glaciers, and compare these to more recent data from Landsat-7 and satellite-borne synthetic-aperture radar. Climate re-analysis data and sea surface temperatures from 1982 show that since 1995 most of Greenland and its surrounding oceans have experienced significant overall warming, and a switch to a warming trend. During the period from 1985 to 1995 when Greenland and the surrounding oceans were not warming, major tidewater outlet glaciers around Greenland, including Kangerdlugssuaq and Helheim, were dynamically stable. Since the mid-1990s, glacier discharge has consistently been both greater and more variable. Together, these observations support the hypothesis that recent dynamic change is a rapid response to climate forcing. Both air and ocean temperatures in this region are predicted to continue to warm, and will therefore likely drive further change in outlet glacier discharge

Effects of undercutting and sliding on calving: a global approach applied to Kronebreen, Svalbard

In this paper, we study the effects of basal friction, sub-aqueous undercutting and glacier geometry on the calving process by combining six different models in an offline-coupled workflow: a continuum–mechanical ice flow model (Elmer/Ice), a climatic mass balance model, a simple subglacial hydrology model, a plume model, an undercutting model and a discrete particle model to investigate fracture dynamics (Helsinki Discrete Element Model, HiDEM). We demonstrate the feasibility of reproducing the observed calving retreat at the front of Kronebreen, a tidewater glacier in Svalbard, during a melt season by using the output from the first five models as input to HiDEM. Basal sliding and glacier motion are addressed using Elmer/Ice, while calving is modelled by HiDEM. A hydrology model calculates subglacial drainage paths and indicates two main outlets with different discharges. Depending on the discharge, the plume model computes frontal melt rates, which are iteratively projected to the actual front of the glacier at subglacial discharge locations. This produces undercutting of different sizes, as melt is concentrated close to the surface for high discharge and is more diffuse for low discharge. By testing different configurations, we show that undercutting plays a key role in glacier retreat and is necessary to reproduce observed retreat in the vicinity of the discharge locations during the melting season. Calving rates are also influenced by basal friction, through its effects on near-terminus strain rates and ice velocity

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

Extrusion induced low-order starch matrices: enzymic hydrolysis and structure

Waxy, normal and highwaymen maize starches were extruded with water as sole plasticizer to achieve low-order starch matrices. Of the three starches, we found that only high-amylose extrudate showed lower digestion rate/extent than starches cooked in excess water. The ordered structure of high-amylose starches in cooked and extruded forms was similar, as judged by NMR, XRD and DSC techniques, but enzyme resistance was much greater for extruded forms. Size exclusion chromatography suggested that longer chains were involved in enzyme resistance. We propose that the local molecular density of packing of amylose chains can control the digestion kinetics rather than just crystallinity, with the principle being that density sufficient to either prevent/limit binding and/or slow down catalysis can be achieved by dense amorphous packing

Rapidly changing subglacial hydrological pathways at a tidewater glacier revealed through simultaneous observations of water pressure, supraglacial lakes, meltwater plumes and surface velocities

This work was funded by the Conoco Phillips-Lundin Northern Area Program through the CRIOS project (Calving Rates and Impact On Sea level, http://www.researchinsvalbard.no/project/7037). Penelope How is supported by a NERC PhD studentship.Subglacial hydrological processes at tidewater glaciers remain poorly understood due to the difficulty in obtaining direct measurements and lack of empirical verification for modelling approaches. Here, we investigate the subglacial hydrology of Kronebreen, a fast-flowing tidewater glacier in Svalbard during the 2014 melt season. We combine observations of borehole water pressure, supraglacial lake drainage, surface velocities and plume activity with modelled run-off and water routing to develop a conceptual model that thoroughly encapsulates subglacial drainage at a tidewater glacier. Simultaneous measurements suggest that an early-season episode of subglacial flushing took place during our observation period, and a stable efficient drainage system effectively transported subglacial water through the northern region of the glacier tongue. Drainage pathways through the central and southern regions of the glacier tongue were disrupted throughout the following melt season. Periodic plume activity at the terminus appears to be a signal for modulated subglacial pulsing, i.e. an internally driven storage and release of subglacial meltwater that operates independently of marine influences. This storage is a key control on ice flow in the 2014 melt season. Evidence from this work and previous studies strongly suggests that long-term changes in ice flow at Kronebreen are controlled by the location of efficient/inefficient drainage and the position of regions where water is stored and released.Publisher PDFPeer reviewe

Brief communication: Thwaites Glacier cavity evolution

Between 2014 and 2017, ocean melt eroded a large cavity beneath and along the western margin of the fast-flowing core of Thwaites Glacier. Here we show that from2017 to the end of 2020 the cavity persisted but did not ex-pand. This behaviour, of melt concentrated at the groundingline within confined sub-shelf cavities, fits with prior observations and modelling studies. We also show that acceleration and thinning of Thwaites Glacier grounded ice continued, with an increase in speed of 400 m a−1and a thinning rate of at least 1.5 m a−1, between 2012 and 2020

Systems Analysis of complex glaciological processes and application to calving of Amery Ice Shelf, East Antarctica

Calving is a complex process subject to several cooperating atmospheric, oceanographic and glaciological forcings that vary in space and time, and whose relative effects are challenging to separate. Statistical ‘Systems Analysis’ is commonly used in engineering and economics to extricate complex ‘force–response’ relationships. Here we apply Systems Analysis to the Amery rift system, East Antarctica. We develop a scalable ‘System Model’ driven by a coarsely-sampled dataset characteristic of glaciological observations in remote locations, and validate it using rift lengths observed in 2000–06 and 2012. In this initial demonstration, we forecast a detachment date of ∼2019 ± 5 years for the large tabular iceberg colloquially known as the ‘Loose Tooth’, for which relative humidity surprisingly emerges as the best statistical predictor. RACMO2 climate modelling reveals that relative humidity correlates best with surface albedo and snowmelt, both of which are intimately linked to firn compaction and ice shelf temperature and flow. We postulate that relative humidity can therefore serve as a proxy for internal stress, a known key control of ‘Loose Tooth’ calving. Although no physical causality is implied in Systems Analysis, postulates such as this can aid in setting priorities in studies of complex glaciological processes

Frailty exists in younger adults admitted as surgical emergency leading to adverse outcomes

Background: Frailty is prevalent in the older adult population (≥65 years of age) and results in adverse outcomes in the emergency general surgical population. Objective: To determine whether frailty exists in the younger adult emergency surgical population (<65 years) and what influence frailty may have on patient related outcomes. Design: Prospective observational cohort study. Setting: Emergency general surgical admissions. Participants: All patients ≥40 years divided into 2 groups: younger adults (40-64.9 years) and older adult comparative group (≥65). Measurements: Over a 6-month time frame the following data was collected: demographics; Scottish Index of Multiple Deprivation (SIMD); blood markers; multi-morbidities, polypharmacy and cognition. Frailty was assessed by completion of the Canadian Study of Health and Ageing (CSHA). Each patient was followed up for 90 days to allow determination of length of stay, re-admission and mortality. Results: 82 young adults were included and the prevalence of frailty was 16% (versus older adults 38%; p=0.001) and associated with: multi-morbidity; poly-pharmacy; cognitive impairment; and deprivation. Frailty in older adults was only significantly associated with increasing age. Conclusions: This novel study has found that frailty exists in 16% of younger adults admitted to emergency general surgical units, potentially leading to adverse short and long-term outcomes. Strategies need to be developed that identify and treat frailty in this vulnerable younger adult population

Tree-Ring Dates for the Maximum Little Ice Age Advance of Kaskawulsh Glacier, St. Elias Mountains, Canada

A dendroglaciological study at Kaskawulsh Glacier provides the first calendar dating of a Little Ice Age glacier advance in the northeast St. Elias Mountains of Yukon Territory. Ring series from white spruce trees, Picea glauca (Moench) Voss, that had been sheared, tilted, and killed by deposition of till at the glacier’s terminal moraine were cross-dated with a millennium-length ring-width chronology developed at a site near the south end of Kluane Lake, about 25 km north of the glacier forefield. Six cross-dated samples from two sites at Kaskawulsh Glacier suggest that the north lobe of the glacier reached its greatest Holocene extent in the mid-1750s. Additional limited data suggest that the east lobe may have reached its maximum extent somewhat earlier (ca. 1717). This chronology of Little Ice Age activity of Kaskawulsh Glacier is consistent with well-dated glacier chronologies from adjacent mountain ranges in coastal and interior Alaska. The results also demonstrate the potential to derive calendar dates from subfossil wood in the St. Elias Mountains that hitherto had been dated only with much lower precision, using radiocarbon techniques.L’étude dendroglaciologique du glacier Kaskawulsh fournit la première datation de calendrier de l’avancée glaciaire du petit âge glaciaire, dans le nord-est des montagnes St. Elias, territoire du Yukon. Les séries de cernes d’épinettes blanches, Picea glauca (Moench) Voss, qui avaient été abattues, inclinées et tuées par le dépôt de till à la moraine terminale du glacier, ont été contre-datées à l’aide d’une chronologie millénaire de largeur des cernes mise au point à un emplacement situé près du côté sud du lac Kluane, à environ 25 km au nord du front du glacier. Six échantillons contre-datés provenant de deux emplacements du glacier Kaskawulsh suggèrent que le lobe nord du glacier a atteint sa plus grande étendue holocène dans le milieu des années 1750. Par ailleurs, certaines données supplémentaires suggèrent que le lobe est pourrait avoir atteint son étendue maximale un peu plus tôt (vers 1717). Cette chronologie de l’activité du petit âge glaciaire du glacier Kaskawulsh coïncide avec les chronologies bien datées des chaînes de montagnes adjacentes, sur la côte et à l’intérieur de l’Alaska. Les résultats démontrent aussi la possibilité d’établir les dates de calendrier à partir de bois subfossile dans les montagnes St. Elias qui avait été daté avec beaucoup moins de précision jusqu’ici à l’aide de techniques de datation au carbone 14