Glacial imprints of the Okanogan Lobe,southern margin of the Cordilleran Ice Sheet

The glacial geomorphology of the Waterville Plateau (ca. 55 km²) provides information on the dynamics of the Okanogan Lobe, southern sector of the Cordilleran Ice Sheet in north‐central Washington. The Okanogan Lobe had a profound influence on the landscape. It diverted meltwater and floodwater along the ice front contributing to the Channeled Scabland features during the late Wisconsin (Fraser Glaciation). The glacial imprint may record surge behaviour of the former Okanogan Lobe based on a comparison with other glacial landsystems. Conditions that may have promoted instability include regional topographic constraints, ice marginal lakes and dynamics of the subglacial hydrological system, which probably included a subglacial reservoir. The ice‐surface morphology and estimated driving stresses (17–26 kPa) implied from ice thickness and surface slope reconstructed in the terminal area also suggest fast basal flow characteristics. This work identifies the location of a fast flowing ice corridor and this probably affected the stability and mass balance of the south‐central portion of the Cordilleran Ice Sheet. Evidence for fast ice flow is lacking in the main Okanogan River Valley, probably because it was destroyed during deglaciation by various glacial and fluvial processes. The only signature of fast ice flow left is the imprint on the Waterville Plateau. Copyright © 2004 John Wiley & Sons, Ltd.     

Volcanic eruption frequency over the last 45 ky as recorded in Epica-Dome C ice core (East Antarctica) and its relationship with climatic changes

The sulphate glacio-chemical profiles constitute a reliable proxy marker for reconstruction of past volcanic history, assuming a reliable method to distinguish sulphate spikes and to evaluate the flux of individual events is set up. The resulting volcanic event profile is used to reconstruct past event frequencies, and to investigate possible links between volcanism and climatic changes. Volcanic event signatures are useful also in comparing time scales from ice cores drilled at different locations. In this paper, a new method to pick out volcanic signals is proposed. It improves on methods based on the calculation of a threshold using a general mean value plus a multiple of the standard deviation by adding: (1) quantification of nonvolcanic sulphate contributions; (2) sulphate fluxes, instead of concentrations, accounting for accumulation rate changes; (3) data treatment using a log-normal statistic, instead of a Gaussian-type distribution, to take into account the real sulphate distribution; (4) a smoothed curve (weighted fitting) to better understand the residual variability of the sulphate background.This method is used to detect volcanic events throughout the 45 ky time span of the EDC96 ice core, drilled at Dome C on the East Antarctic plateau. A total of 283 volcanic signatures are recovered, with a mean of 6.3 events per millennium. The temporal event frequencies indicate that the last 2000 years were probably characterized by the highest volcanic activity in the period covered by the core and that there is no clear link between number of events recorded and climatic changes.     

Bayesian analysis of De distributions in optical dating: Towards a robust method for dealing with outliers

In optical dating, especially single-grain dating, various patterns of distributions in equivalent dose (D_e) are usually observed and analysed using different statistical models. None of these methods, however, is designed to deal with outliers that do not form part of the population of grains associated with the event of interest (the ‘target population’), despite outliers being commonly present in single-grain D_e distributions. In this paper, we present a Bayesian method for detecting D_e outliers and making allowance for them when estimating the D_e value of the target population. We test this so-called Bayesian outlier model (BOM) using data sets obtained for individual grains of quartz from sediments deposited in a variety of settings, and in simulations. We find that the BOM is suitable for single-grain D_e distributions containing outliers that, for a variety of reasons, do not form part of the target population. For example, D_e outliers may be associated with grains that have undesirable luminescence properties (e.g., thermal instability, high rates of anomalous fading) or with contaminant grains incorporated into a sample when collected in the field or prepared in the laboratory. Grains that have much larger or smaller D_e values than the target population, due to factors such as insufficient bleaching, beta-dose heterogeneity or post-depositional disturbance, may also be identified as outliers using the BOM, enabling these values to be weighted appropriately for final D_e and age determination.     

Testing a proposed new chronology for the Jasmund Glacitectonic Complex (SW Baltic Sea): No indication of incipient deformation during MIS 3

Weichselian advances of the Scandinavian Ice Sheet have generated several glacitectonically deformed structures in the southwestern Baltic Sea area. One example is the 100 km² large Jasmund Glacitectonic Complex (JGC), which was formed proglacially and consists of two subparallel-orientated sets of composite ridges that represent a northern and southern structural complex. The two-part morphological structure of the JGC suggests a formation by two ice advances, one approaching from NE and one from SE direction. So far, this divided structure has been assumed to have been formed by short-time ice-front oscillations during an MIS 2 ice advance. However, based on their recently published ice dynamic model for MIS 3 and the available age data from Jasmund, lüthgens et al. (2020) propose a chronological reinterpretation of the JGC development, according to which two distinct ice advances during early and late MIS 3 formed the JGC. In order to test this novel stratigraphical model for the JGC formation, five OSL samples were taken from fluvial and lacustrine deposits at a key section near Glowe (NW Jasmund). The investigated succession is divided into pre-kinematic sediments, deposited before the glacitectonic deformation, and post-kinematic sediments, deposited after the deformation. Our results show that the youngest dated pre-tectonic sediment has a burial age between ∼40 and 34 ka, which rules out a glacitectonic deformation during an early MIS 3 ice advance (∼60–50 ka). In addition, by reviewing the existing age data set, a development of the JGC during an early and late MIS 3 advance of the SIS must be rejected. Instead, our data confirm the genesis of the JGC during MIS 2.     

Stained Glass and Climate Change: How are they Connected?

As expressions of regional architecture, sacred (Christian) Gothic structures often possess several adaptations to their prevailing climate regime. The late medieval (Gothic) period in northern Europe is also, according to the evidence presented here, marked by a transition from warm and sunny to cooler and cloudier conditions. It is within the context of this climate change that we consider one of the most important features in Gothic churches—interior daylighting—during the transitional period (the thirteenth to the end of the fifteenth centuries) between the Medieval Warm Period (MWP) and the Little Ice Age (LIA). This paper seeks to determine whether increasingly cloudy conditions over northern continental Europe, in part due to a shift in North Atlantic Oscillation (NAO) phase, may have influenced the use of more white glass in the fourteenth century. To the best of our knowledge, this is the first time an extensive daylighting dataset has been collected in medieval sacred interiors. From an analysis of these illuminance and luminance data collected in European churches and cathedrals, we find that high-translucency glazing is associated with limited lighting gains compared to full-colour programs under sunny conditions but substantial lighting improvements (up to an order of magnitude) for cloudy conditions. Additionally, we find that backlighting from direct sunlight produces significant obscuration of some of the iconographical glass when interiors are dominated by high-translucency glazing, further suggesting that these interiors are not ideal for sunny conditions.

[Traduit par la rédaction] Étant donné que les cathédrales gothiques (chrétiennes) sont des expressions de l'architecture régionale, plusieurs adaptations au climat de l’époque y ont souvent été apportées. À la fin du Moyen Âge (période du gothique), le climat chaud et ensoleillé en Europe du nord continentale a fait place à un climat plus froid et plus nuageux, d'après les preuves que nous présentons ici. C'est donc dans la perspective de ce changement climatique que nous nous penchons sur l'un des éléments les plus importants de l'architecture des églises gothique, l’éclairage naturel intérieur, durant la transition (du XIII^e siècle à la fin du XV^e siècle) entre la période chaude médiévale (MWP) et le petit âge glaciaire (LIA). Dans le présent article, nous voulons notamment évaluer si l'utilisation de plus en plus fréquente du vitrail blanc au XIV^e siècle s'expliquerait par les conditions plus nuageuses en Europe du nord continentale, attribuables en partie à un changement dans l'indice d‘oscillation nord-atlantique (NAO). À notre connaissance, c'est la première fois qu'une série élaborée de données a été recueillie sur l’éclairage à l'intérieur des cathédrales gothiques. L'analyse des données sur l’éclairement lumineux et la luminance lumineuse dans les églises et les cathédrales d'Europe nous permet de constater que le verre très translucide présente peu d'avantages comparativement au verre plein coloré dans des conditions ensoleillées, mais qu'il améliore considérablement l’éclairage dans des conditions nuageuses (jusqu’à 10 fois). De plus, nous constatons que l’éclairage en contre-jour produit par l'ensoleillement direct obscurcit une partie des pièces de verre ornées d'icônes lorsque le verre très translucide domine à l'intérieur, ce qui confirme une fois de plus qu'il ne s'agit pas d'un aménagement idéal pour les conditions ensoleillées.     

中国小冰期气候研究综述

通过对小冰期研究文献进行综述,并对已发表的小冰期温度和降水数据进行综合对比分析,探讨小冰期时期中国气候特征的区域性.结果表明,小冰期在中国地区不同区域代用指标记录中均存在,但是小冰期的起讫及持续时间具有区域差异性,温湿配置也不尽相同.小冰期的起始时间主要呈现出由西向东推移的趋势,即青藏高原最早,华北地区次之而东部地区最晚.温湿配置的差异主要体现在东部季风区小冰期时期总体上是冷干的气候环境,而西部地区气候变化则呈现冷湿的气候特征.     

Subglacial bedform geomorphology of the Irish Ice Sheet reveals major configuration changes during growth and decay

The belated realisation that ribbed (Rogen) moraines form such an integral part of Irish geomorphology, and the piecemeal approach to previous drumlin mapping, is probably responsible for the highly contrasting views of palaeoflow patterns of the Irish Ice Sheet. Using a high resolution (25 m) digital elevation model we present morphological maps of a large part (100 × 100 km) of the so‐called ‘Drumlin Belt’ of north central Ireland. The landforms comprise mostly ribbed moraine much larger than found elsewhere (up to 16 km in length), which in places are superimposed on each other. Contrary to most prior assessments we find the bedform record to contain numerous and overlapping episodes of bed formation (ribbed moraine, drumlins and crag‐and‐tails) that provide a palimpsest record of changing flow geometries. These demonstrate an ice sheet with a centre of mass and flow geometry that changed during growth and decay. Using distinctive flow patterns and relative age relationships between them we reconstruct ice sheet evolution into four phases during a single glacial cycle. In phase 1 (early in the glacial cycle), Scottish and local ice coalesced to form a northeast‐centred Irish Ice Sheet. As it grew its centre of mass migrated southwards, culminating in a major N–S divide positioned down the east of Ireland (phase 2, ca. Last Glacial Maximum). During retreat, the centre of mass migrated at least 120 km northwards and became established in northwest Ireland and at this point a dramatic bedforming event produced one of the world's largest and most contiguous ribbed moraine fields (phase 3). Final deglaciation is thought to be by fragmentation into many topographically controlled minor ice‐caps (phase 4). Rather than any dramatic or unexpected behaviour, the reconstructed phases indicate a relatively predictable pattern of ice sheet growth and decay with changes in centres of mass, and does not require major readvances or ice‐stream events. Copyright © 2001 John Wiley & Sons, Ltd.     

Water in the upper martian surface at mid- and low-latitudes: presence, state, and consequences

Sublimation of water ice is more effective than evaporation of sorption water at the same temperature. Therefore, water in the form of ice must, over geologic time-scales, have left the upper martian surface (m-scale) at mid- and low-latitudes, leaving sorption water as a possible physical form of stable subsurface water. Adsorption water is “liquid-like” at these temperatures (in the sense of a 2D-liquid). This property is the reason for the specific importance of physisorbed water under martian conditions. It is shown that unfrozen adsorption water can cause numerous physical, chemical, and possibly also biological processes in the upper martian surface and may be responsible for a number of its properties.     

THE SAND WEDGE AND MIRABILITE OFTHE LAST ICE AGE AND THEIR PALEOCLIMATICSIGNIFICANCE IN HEXI CORRIDOR

Sand wedge is formed under the conditions of coldclimate, and is an important basis for reconstructingpaleoenvironment (LI et al., 1990; WANG, 1991 ). Ithas been reported constantly over the last 20 years inthe Qinghai-Xizang (Tibet) Plateau (GUO, 1979; CUl,1983; XU et al., 1984; LIANG et al.,, 1984; PAN etal., 199 ) and North China (YANG et al., 1983; DONGet al., 1985) and Northeast China (GUO et al.,1981 ). We also found fossil sand wedge groups formedin the end of the Late P…     

Hydrological character and sea-current structure in the front of Amery Ice Shelf

Hydrological character and Sea-current profiles structure are studied andanalyzed in sea-area of the front of Amery Ice Shelf,Prydz Bay with LADCP,CTDdata.These LADCP,CTD data were acquired during the 19th Chinese Antarctic Sci-entific Expedition.Results of this study agree with that,there exist four differentkinds of water masses in the area of the front of Amery Ice Shelf in the summer of Ant-arctica.Current distribution presents a semi-circumfluence which flows in at the eastand flows out in the west.Moreover,clockwise and anti-clockwise vortices werefound in upper layer and mid-layer in the Prydz Bay.Western areas of these anti-clockwise vortices are positions of inflows from Prydz Bay to Amery Ice Shelf.Thesource of these inflows is the coastal westward current originated in the east of PrydzBay.All these characteristics come down to the pattern of circumfluence,ice meltrate under Ice Shelf,scale of Ice Shelf water production and form of water exchangesbetween area of Ice Shelf and area of Prydz Bay.