Sea ice volume and age: Sensitivity to physical parameterizations and thickness resolution in the CICE sea ice model

New dynamics parameterizations in Version 5 of the Los Alamos Sea Ice Model, CICE, feature an anisotropic rheology and variable drag coefficients. This study investigates their effect on Arctic sea ice volume and age simulations, along with the effects of several pre-existing model options: a parameter that represents the mean cumulative area of ice participating in ridging, the resolution of the ice thickness distribution, and the resolution of the vertical temperature and salinity profiles.By increasing shear stress between floes, the anisotropic rheology slows the ice motion, producing a thicker, older ice pack. The inclusion of variable drag coefficients, which depend on modeled roughness elements such as deformed ice and melt pond edges, leads to thinner ice and a more realistic simulation of sea ice age. Several feedback processes act to enhance differences among the runs. Notably, if less open water is produced mechanically through ice deformational processes, the simulated ice thins relative to runs with more mechanically produced open water. Thermodynamic processes can have opposing effects on ice age and volume; for instance, growth of new ice increases the volume while decreasing the age of the pack. Therefore, age data provides additional information useful for differentiating among process parameterization effects and sensitivities to other model parameters.Resolution of thicker ice types is crucial for proper modeling of sea ice volume, because the volume of ice in the thicker ice categories determines the total ice volume. Model thickness categories tend to focus resolution for thinner ice; this paper demonstrates that 5 ice thickness categories are not enough to accurately resolve the ice thickness distribution for simulations of ice volume.     

A 2000-yr reconstruction of air temperature in the Great Basin of the United States with specific reference to the Medieval Climatic Anomaly

A sediment core representing the past two millennia was recovered from Stella Lake in the Snake Range of the central Great Basin in Nevada. The core was analyzed for sub-fossil chironomids and sediment organic content. A quantitative reconstruction of mean July air temperature (MJAT) was developed using a regional training set and a chironomid-based WA-PLS inference model (r²_jack = 0.55, RMSEP = 0.9°C). The chironomid-based MJAT reconstruction suggests that the interval between AD 900 and AD 1300, corresponding to the Medieval Climate Anomaly (MCA), was characterized by MJAT elevated 1.0°C above the subsequent Little Ice Age (LIA), but likely not as warm as recent conditions. Comparison of the Stella Lake temperature reconstruction to previously published paleoclimate records from this region indicates that the temperature fluctuations inferred to have occurred at Stella Lake between AD 900 and AD 1300 correspond to regional records documenting hydroclimate variability during the MCA interval. The Stella Lake record provides evidence that elevated summer temperature contributed to the increased aridity that characterized the western United States during the MCA.     

A 7000-year record of environmental change,including early farming impact,based on lake-sediment geochemistry and pollen data from County Sligo,western Ireland

Detailed, chronologically tightly constrained, lake-sediment-based geochemical and pollen records have enabled local changes in soil erosion, woodland cover and composition, and prehistoric farming impact to be reconstructed in considerable detail. The profile opens shortly after 7800 BC when tall canopy trees were well-established and presumably in equilibrium with their environment. A distinct perturbation that involved an increase in pine and birch, a decrease in oak and a minor opening-up of the woodland is regarded as the local expression of the 8.2 ka climate anomaly. Lack of response in the geochemical erosional indicators is interpreted as evidence for drier conditions. A short-lived, over-compensation in climate recovery followed the 8.2 ka event. Neolithic farming impact is clearly expressed in both the pollen and geochemical data. Both datasets indicate that Neolithic impact was concentrated in the early Neolithic (3715–3440 BC). In the interval 3000–2700 BC there appears to have been a break in farming activity. The pollen data suggest substantially increased farming impact (both arable and pastoral) in the Bronze Age, with maximum farming and woodland clearances taking place in the late Bronze Age (1155–935 BC). These developments are poorly expressed in the geochemical record, possibly due to within-lake changes.     

全球过去千年典型暖期温度空间格局重建

利用过去两千年全球变化研究网络(PAGES 2k network)最新公布的501条代用记录,重建了全球过去千年全年平均温度空间格局的演化特征,对比分析了中世纪暖期及其最暖100年与20世纪现代暖期、中世纪暖期和小冰期最暖30年与20世纪最近30年的年平均温度空间模态异同.结果显示,在世纪尺度上,现代暖期与历史上中世纪暖期的温度异常空间格局大致相同,变化幅度也在大部分区域相当,但从年代际尺度上,最近30年的升温比过去千年中世纪暖期和小冰期两个典型时期都明显.值得一提的是北大西洋中高纬度海温变化与上述特征并不相同,在年代际和世纪尺度上小冰期和中世纪暖期海温均高于20世纪.可能原因是大西洋经圈翻转环流在中世纪暖期、小冰期和20世纪现代暖期等3个特征时段对太阳辐射、火山活动和温室气体等外强迫的响应不同.     

ENVIRONMENTAL CHANGE AND ITS IMPACTS ON HUMAN SETTLF, MENT IN THE CHANGJIANG RIVER DELTA IN NEOLITHIC AGE

Dating data, altitude of Neolithic sites, climatic changes from sedimentary records and previous research results were collected and analyzed to detect possible connections between climatic changes and human activities in the Changjiang River Delta in the Neolithic Age. The results indicated that hydrological changes greatly impacted the human activities in the study region. Low-lying geomorphology made the floods and sea level changes become the important factors affecting human activities, especially the altitude change of human settlements. People usually moved to higher places during the periods characterized by high sea level and frequent floods to escape the negative influences from water body expansion, which resulted in cultural hiatus in certain profiles. However, some higher-altitude settlements were not the results of climatic changes but the results of social factors, such as religious ceremony and social status. Therefore, further research will be necessary for the degree and types of impacts of climatic changes on human activities in the study area at that time.     

Moraine development at a small High‐Arctic valley glacier: Rieperbreen,Svalbard

Ice‐cored lateral and frontal moraine complexes, formed at the margin of the small, land‐based Rieperbreen glacier, central Svalbard, have been investigated through field observations and interpretations of aerial photographs (1936, 1961 and 1990). The main focus has been on the stratigraphical and dynamic development of these moraines as well as the disintegration processes. The glacier has been wasting down since the ‘Little Ice Age’ (LIA) maximum, and between 1936 and 1990 the glacier surface was lowered by 50–60 m and the front retreated by approximately 900 m. As the glacier wasted, three moraine ridges developed at the front, mainly as melting out of sediments from debris‐rich foliation and debris‐bands formed when the glacier was polythermal, probably during the LIA maximum. The disintegration of the moraines is dominated by wastage of buried ice, sediment gravity‐flows, meltwater activity and some frost weathering. A transverse glacier profile with a northward sloping surface has developed owing to the higher insolation along the south‐facing ice margin. This asymmetric geometry also strongly affects the supraglacial drainage pattern. Lateral moraines have formed along both sides of the glacier, although the insolation aspect of the glacier has resulted in the development of a moraine 60 m high along its northern margin. Copyright © 2001 John Wiley & Sons, Ltd.     

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.     

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.     

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…