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Characterising ice slabs in firn using seismic full waveform inversion, a sensitivity study 利用地震全波形反演的灵敏度研究在firn中表征冰板
IF 3.4 3区 地球科学 Q2 GEOGRAPHY, PHYSICAL Pub Date : 2023-05-25 DOI: 10.1017/jog.2023.30
E. Pearce, A. Booth, S. Rost, P. Sava, T. Konuk, A. Brisbourne, B. Hubbard, I. Jones
The density structure of firn has implications for hydrological and climate modelling, and ice-shelf stability. The structure of firn can be evaluated from depth models of seismic velocity, widely obtained with Herglotz–Wiechert inversion (HWI), an approach that considers the slowness of refracted seismic arrivals. However, HWI is strictly appropriate only for steady-state firn profiles and the inversion accuracy can be compromised where firn contains ice layers. In these cases, full waveform inversion (FWI) may yield more success than HWI. FWI extends HWI capabilities by considering the full seismic waveform and incorporates reflected arrivals. Using synthetic firn density profiles, assuming both steady- and non-steady-state accumulation, we show that FWI outperforms HWI for detecting ice slab boundaries (5–80 m thick, 5–80 m deep) and velocity anomalies within firn. FWI can detect slabs thicker than one wavelength (here, 20 m, assuming a maximum frequency of 60 Hz) but requires the starting velocity model to be accurate to ±2.5%. We recommend for field practice that the shallowest layers of velocity models are constrained with ground-truth data. Nonetheless, FWI shows advantages over established methods, and should be considered when the characterisation of firn ice slabs is the goal of the seismic survey.
冷杉的密度结构对水文和气候建模以及冰架稳定性有影响。firn的结构可以从地震速度的深度模型中进行评估,该模型通过Herglotz–Wiechert反演(HWI)广泛获得,该方法考虑了折射地震到达的缓慢性。然而,HWI仅严格适用于稳态firn剖面,并且在firn包含冰层的情况下,反演精度可能会受到影响。在这些情况下,全波形反演(FWI)可能比HWI更成功。FWI通过考虑完整的地震波形扩展了HWI能力,并结合了反射到达。使用合成的firn密度剖面,假设稳态和非稳态积累,我们表明FWI在探测冰板边界(5–80 m厚,5–80米深)和firn内的速度异常方面优于HWI。FWI可以检测到厚度超过一个波长(此处为20 m,假设最大频率为60 Hz)的板块,但要求起始速度模型的精度为±2.5%。我们建议现场实践中,速度模型的最浅层受地面实况数据的约束。尽管如此,FWI显示出优于现有方法的优势,当地震勘测的目标是描述firn冰板时,应考虑FWI。
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引用次数: 1
JOG volume 69 issue 275 Cover and Front matter JOG第69卷第275期封面和封面问题
IF 3.4 3区 地球科学 Q2 GEOGRAPHY, PHYSICAL Pub Date : 2023-05-23 DOI: 10.1017/jog.2023.31
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引用次数: 0
JOG volume 69 issue 275 Cover and Back matter JOG卷69期275封面和封底
IF 3.4 3区 地球科学 Q2 GEOGRAPHY, PHYSICAL Pub Date : 2023-05-23 DOI: 10.1017/jog.2023.32
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引用次数: 0
Automated prediction of wet-snow avalanche activity in the Swiss Alps 瑞士阿尔卑斯山湿雪崩活动的自动预测
IF 3.4 3区 地球科学 Q2 GEOGRAPHY, PHYSICAL Pub Date : 2023-05-18 DOI: 10.1017/jog.2023.24
M. Hendrick, F. Techel, M. Volpi, Tasko Olevski, Cristina Pérez-Guillén, A. Herwijnen, J. Schweizer
Wet-snow avalanches are triggered by the infiltration of liquid water which weakens the snowpack. Wet-snow avalanches are among the most destructive avalanches, yet their release mechanism is not sufficiently understood for a process-based prediction model. Therefore, we followed a data-driven approach and developed a random forest model, depending on slope aspect, to predict the local wet-snow avalanche activity at the locations of 124 automated weather stations distributed throughout the Swiss Alps. The input variables were the snow and weather data recorded by the stations over the past 20 years. The target variable was based on manual observations over the same 20-year period. To filter out erroneous reports, we defined the days with wet-snow avalanches in a stringent manner, selecting only the most extreme active or inactive days, which reduced the size of the dataset but increased the reliability of the target variable. The model was trained with weather variables and variables computed from simulated snow stratigraphy in 38 $^circ$ slopes facing the 4 cardinal directions. While model development and validation were done in nowcast mode, we also studied model performance in 24-hour forecast mode by using input variables computed from a numerical weather prediction (NWP) model. Overall, the performance was good in both nowcast and forecast mode (f1-score around 0.8). To assess model performance beyond the stringent definition of wet-snow avalanche days, we compared model predictions to wet-snow avalanche activity over the entire Swiss Alps, based on the raw data over 8 winters. We obtained a Spearman correlation coefficient of 0.71. Hence, our model represents a step toward the application of support tools in operational wet-snow avalanche forecasting.
湿雪雪崩是由液态水的渗透引发的,液态水会削弱积雪。湿雪雪崩是最具破坏性的雪崩之一,但其释放机制对于基于过程的预测模型来说还不够了解。因此,我们采用数据驱动的方法,根据坡度,开发了一个随机森林模型,以预测分布在瑞士阿尔卑斯山各地的124个自动气象站所在地的当地湿雪崩活动。输入变量是过去20年中气象站记录的雪和天气数据。目标变量基于20年期间的人工观测。为了过滤错误的报告,我们以严格的方式定义了湿雪雪崩的天数,只选择最极端的活动或非活动天数,这减少了数据集的大小,但提高了目标变量的可靠性。该模型使用天气变量和模拟雪地层中面向4个主要方向的38$^circ$斜坡中计算的变量进行训练。虽然模型的开发和验证是在nowcast模式下进行的,但我们也通过使用数值天气预报(NWP)模型计算的输入变量来研究24小时预报模式下的模型性能。总的来说,在nowcast和预测模式下的性能都很好(f1得分约为0.8)。为了评估超出湿雪崩天数严格定义的模型性能,我们根据8个冬天的原始数据,将模型预测与整个瑞士阿尔卑斯山的湿雪崩活动进行了比较。我们得到的斯皮尔曼相关系数为0.71。因此,我们的模型代表着支持工具在湿雪崩预报中的应用迈出了一步。
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引用次数: 3
Snow and avalanche climates in the French Alps using avalanche problem frequencies 使用雪崩问题频率的法国阿尔卑斯山的雪和雪崩气候
IF 3.4 3区 地球科学 Q2 GEOGRAPHY, PHYSICAL Pub Date : 2023-05-18 DOI: 10.1017/jog.2023.23
B. Reuter, P. Hagenmuller, N. Eckert
Avalanches result from an interaction of weather and terrain, where past weather and internal snow cover processes play important roles. So far, climatology was mainly based on weather data, as regional snow instability information, such as avalanche activity, is scarce on climatological time scales. We present a new approach to create a snow avalanche climatology from simulations of avalanche problem types based on snow cover simulations of reanalysis data and a cluster analysis. Analyzing the winters between 1958 and 2020 in the French Alps, wet-snow situations dominated natural release. Dry-snow situations with non-persistent and persistent weak layers occurred each on at least one third of the days. Four typical patterns of avalanche problem types were identified. They follow the main orography with more new snow situations in the northern regions and more cases of persistent weak layers in inner-Alpine regions. In the front-ranges and in southern regions wet-snow situations occurred early in winter – typical for coastal snow climates. Agreement with the standard snow climate classification and the geography of the French Alps suggests that mountain regions with similar conditions can now be outlined. This method for snow avalanche climatology will inform avalanche forecasting and facilitate climate change impact studies.
雪崩是天气和地形相互作用的结果,其中过去的天气和内部积雪过程起着重要作用。到目前为止,气候学主要基于天气数据,因为在气候时间尺度上,雪崩活动等区域积雪不稳定信息很少。我们提出了一种基于再分析数据的积雪模拟和聚类分析的雪崩问题类型模拟来创建雪崩气候学的新方法。分析1958年至2020年法国阿尔卑斯山的冬季,湿雪情况占自然释放的主导地位。非持续性和持续性弱层的干雪情况至少在三分之一的天发生。确定了雪崩问题类型的四种典型模式。它们遵循主要地形,在北部地区有更多的新雪情况,在阿尔卑斯内部地区有更多持续薄弱的层。在前沿山脉和南部地区,冬季早期出现了湿雪,这是典型的沿海雪气候。与标准雪气候分类和法国阿尔卑斯山脉地理的一致表明,现在可以概述具有类似条件的山区。这种雪崩气候学方法将为雪崩预报提供信息,并促进气候变化影响研究。
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引用次数: 0
Firn aquifer water discharges into crevasses across Southeast Greenland 冷杉含水层的水排入格陵兰岛东南部的决口
IF 3.4 3区 地球科学 Q2 GEOGRAPHY, PHYSICAL Pub Date : 2023-05-17 DOI: 10.1017/jog.2023.25
Eric Cicero, K. Poinar, R. Jones-Ivey, A. Petty, Jeanette M. Sperhac, A. Patra, J. Briner
In Southeast Greenland, summer melt and high winter snowfall rates give rise to firn aquifers: vast stores of meltwater buried beneath the ice-sheet surface. Previous detailed studies of a single Greenland firn aquifer site suggest that the water drains into crevasses, but this is not known at a regional scale. We develop and use a tool in Ghub, an online gateway of shared datasets, tools and supercomputing resources for glaciology, to identify crevasses from elevation data collected by NASA's Airborne Topographic Mapper across 29000 km2 of Southeast Greenland. We find crevasses within 3 km of the previously mapped downglacier boundary of the firn aquifer at 20 of 25 flightline crossings. Our data suggest that crevasses widen until they reach the downglacier boundary of the firn aquifer, implying that crevasses collect firn-aquifer water, but we did not find this trend with statistical significance. The median crevasse width, 27 meters, implies an aspect ratio consistent with the crevasses reaching the bed. Our results support the idea that most water in Southeast Greenland firn aquifers drains through crevasses. Less common fates are discharge at the ice-sheet surface (3 of 25 sites) and refreezing at the aquifer bottom (1 of 25 sites).
在格陵兰岛东南部,夏季的融化和冬季的高降雪率导致了冷杉蓄水层的形成:大量的融水埋在冰盖表面下。先前对格陵兰冷杉含水层的详细研究表明,这些水会排入决口,但这在区域范围内尚不清楚。我们在Ghub中开发并使用了一个工具,该工具是冰川学共享数据集、工具和超级计算资源的在线门户,用于根据美国国家航空航天局的机载地形测绘仪收集的格陵兰东南部29000平方公里的高程数据来识别裂缝。我们在25个航线交叉点中的20个发现了距离先前绘制的firn含水层冰川下边界3公里以内的决口。我们的数据表明,决口变宽,直到到达冷杉含水层的冰川下边界,这意味着决口收集了冷杉含水层水,但我们没有发现这种具有统计意义的趋势。裂缝宽度中值为27米,意味着与到达河床的裂缝的纵横比一致。我们的研究结果支持了这样一种观点,即格陵兰东南部冷杉含水层的大部分水都是通过决口排出的。不太常见的命运是在冰盖表面排放(25个地点中的3个)和在含水层底部重新冻结(25个位置中的1个)。
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引用次数: 0
Basal debris of the NEEM ice core, Greenland: a window into sub-ice-sheet geology, basal ice processes and ice-sheet oscillations 格陵兰NEEM冰芯的基底碎屑:亚冰盖地质、基底冰过程和冰盖振荡的窗口
IF 3.4 3区 地球科学 Q2 GEOGRAPHY, PHYSICAL Pub Date : 2023-05-17 DOI: 10.1017/jog.2022.122
P. Blard, M. Protin, J. Tison, F. Fripiat, D. Dahl-Jensen, J. Steffensen, W. Mahaney, P. Bierman, A. Christ, L. Corbett, V. Debaille, T. Rigaudier, P. Claeys
Abstract We present new data from the debris-rich basal ice layers of the NEEM ice core (NW Greenland). Using mineralogical observations, SEM imagery, geochemical data from silicates (meteoric 10Be, εNd, 87Sr/86Sr) and organic material (C/N, δ13C), we characterize the source material, succession of previous glaciations and deglaciations and the paleoecological conditions during ice-free episodes. Meteoric 10Be data and grain features indicate that the ice sheet interacted with paleosols and eroded fresh bedrock, leading to mixing in these debris-rich ice layers. Our analysis also identifies four successive stages in NW Greenland: (1) initial preglacial conditions, (2) glacial advance 1, (3) glacial retreat and interglacial conditions and (4) glacial advance 2 (current ice-sheet development). C/N and δ13C data suggest that deglacial environments favored the development of tundra and taiga ecosystems. These two successive glacial fluctuations observed at NEEM are consistent with those identified from the Camp Century core basal sediments over the last 3 Ma. Further inland, GRIP and GISP2 summit sites have remained glaciated more continuously than the western margin, with less intense ice-substratum interactions than those observed at NEEM.
我们提出了来自NEEM冰芯(格陵兰岛西北部)富含碎屑的基底冰层的新数据。利用矿物学观测、扫描电镜图像、硅酸盐地球化学资料(大气10Be、εNd、87Sr/86Sr)和有机质资料(C/N、δ13C),表征了冰期的物源、冰期和脱冰期的演替和无冰期的古生态条件。大气10Be数据和颗粒特征表明,冰盖与古土壤和侵蚀的新基岩相互作用,导致这些富含碎屑的冰层混合在一起。我们的分析还确定了西北格陵兰岛的四个连续阶段:(1)初始冰川期,(2)冰川推进1期,(3)冰川后退和间冰期,(4)冰川推进2期(当前冰盖发育)。C/N和δ13C数据表明,去冰环境有利于冻土带和针叶林生态系统的发育。在NEEM观测到的这两次连续的冰川波动与在近3 Ma的世纪营岩心基底沉积物中发现的冰川波动一致。在更内陆的地方,GRIP和GISP2峰顶的冰川持续时间比西部边缘更长,冰-基底相互作用的强度比NEEM观测到的要小。
{"title":"Basal debris of the NEEM ice core, Greenland: a window into sub-ice-sheet geology, basal ice processes and ice-sheet oscillations","authors":"P. Blard, M. Protin, J. Tison, F. Fripiat, D. Dahl-Jensen, J. Steffensen, W. Mahaney, P. Bierman, A. Christ, L. Corbett, V. Debaille, T. Rigaudier, P. Claeys","doi":"10.1017/jog.2022.122","DOIUrl":"https://doi.org/10.1017/jog.2022.122","url":null,"abstract":"Abstract We present new data from the debris-rich basal ice layers of the NEEM ice core (NW Greenland). Using mineralogical observations, SEM imagery, geochemical data from silicates (meteoric 10Be, εNd, 87Sr/86Sr) and organic material (C/N, δ13C), we characterize the source material, succession of previous glaciations and deglaciations and the paleoecological conditions during ice-free episodes. Meteoric 10Be data and grain features indicate that the ice sheet interacted with paleosols and eroded fresh bedrock, leading to mixing in these debris-rich ice layers. Our analysis also identifies four successive stages in NW Greenland: (1) initial preglacial conditions, (2) glacial advance 1, (3) glacial retreat and interglacial conditions and (4) glacial advance 2 (current ice-sheet development). C/N and δ13C data suggest that deglacial environments favored the development of tundra and taiga ecosystems. These two successive glacial fluctuations observed at NEEM are consistent with those identified from the Camp Century core basal sediments over the last 3 Ma. Further inland, GRIP and GISP2 summit sites have remained glaciated more continuously than the western margin, with less intense ice-substratum interactions than those observed at NEEM.","PeriodicalId":15981,"journal":{"name":"Journal of Glaciology","volume":"69 1","pages":"1011 - 1029"},"PeriodicalIF":3.4,"publicationDate":"2023-05-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48297398","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 0
Robust reconstruction of glacier beds using transient 2D assimilation with Stokes 利用Stokes瞬态二维同化对冰川床进行鲁棒重建
IF 3.4 3区 地球科学 Q2 GEOGRAPHY, PHYSICAL Pub Date : 2023-05-12 DOI: 10.1017/jog.2023.26
Samuel J. Cook, F. Gillet-Chaulet, J. Fürst
Initialising model glaciers such that they match well with their real counterparts and are thus able to make more accurate predictions is an ongoing challenge in glacier modelling. We set out a data-assimilation approach using an ensemble Kalman filter in a 2D flowline example that provides one possible solution to this problem. We show that our approach is valid across a range of parameters and scenarios, including deliberately data-deficient or inaccurate ones, and leads to robust retrieval of the glacier bed. We also provide some suggestions for how best to use data assimilation within a mountain-glacier context.
初始化冰川模型,使其与真实冰川匹配,从而能够做出更准确的预测,这是冰川建模中的一个持续挑战。我们在二维流线示例中使用集合卡尔曼滤波器提出了一种数据同化方法,为该问题提供了一种可能的解决方案。我们表明,我们的方法在一系列参数和场景中都是有效的,包括故意数据不足或不准确的参数和场景,并导致对冰川床的稳健检索。我们还就如何在山区冰川背景下最好地使用数据同化提供了一些建议。
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引用次数: 0
The first cultivation of the glacier ice alga Ancylonema alaskanum (Zygnematophyceae, Streptophyta): differences in morphology and photophysiology of field vs laboratory strain cells 冰川冰藻alaskanum (zynematophyceae,链藻目)的首次培养:野外与实验室菌株细胞形态和光生理的差异
IF 3.4 3区 地球科学 Q2 GEOGRAPHY, PHYSICAL Pub Date : 2023-05-10 DOI: 10.1017/jog.2023.22
D. Remias, Lenka Procházková
Abstract Melting glacier surfaces are unique ecosystems for specialized microbes, frequently harbouring blooms of microalgae with pigments contributing to the darkening of ice surfaces, reducing albedo and enhancing melt rates. The main cause of this phenomenon is algae of the genus Ancylonema. Prior investigation depended on field-collected material because these algae resisted cultivation. To enhance research on how these algae dominate melting ice, we established a strain of Ancylonema alaskanum from an alpine glacier and exposed to temperatures around the freezing point at irradiations of ~10% of full sunlight. The morphology of the culture changed, with the cells becoming longer and turning green by losing their brownish pigmentation, indicating that these dark phenols are crucial for survival in the cryosphere. Photophysiological comparisons of strain and glacial material showed adaptation of the photosynthetic apparatus to prevailing conditions. This laboratorial strain opens possibilities for a wide range of comparative ‘omics’ research.
摘要融化的冰川表面是专门微生物的独特生态系统,经常含有大量微藻,这些微藻的色素会导致冰川表面变暗,降低反照率,提高融化速率。造成这种现象的主要原因是Ancylonema属的藻类。之前的调查依赖于现场收集的材料,因为这些藻类抗拒种植。为了加强对这些藻类如何主导融化的冰的研究,我们从高山冰川中建立了一株阿拉斯加Ancylonema菌株,并在约10%的全阳光照射下暴露在冰点附近的温度下。培养物的形态发生了变化,细胞变得更长,并因失去褐色色素而变绿,这表明这些深色酚类物质对在冰冻圈中的生存至关重要。菌株和冰川物质的光生理学比较表明,光合装置对主要条件的适应。这种实验室菌株为广泛的比较“组学”研究开辟了可能性。
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引用次数: 3
Ice aprons on steep high-alpine slopes: insights from the Mont-Blanc massif, Western Alps 陡峭的高山斜坡上的冰围裙:从西阿尔卑斯勃朗峰地块的视角
IF 3.4 3区 地球科学 Q2 GEOGRAPHY, PHYSICAL Pub Date : 2023-05-09 DOI: 10.1017/jog.2023.15
L. Ravanel, G. Guillet, S. Kaushik, S. Preunkert, E. Malet, F. Magnin, E. Trouvé, M. Montagnat, Yajing Yan, P. Deline
Ice aprons are defined as very small ice bodies covering steep rock slopes. They have only been the subject of increased scientific interest for a few years, despite the fact that they are a condition for mountaineering and obvious elements in the high-alpine landscapes. However, very little is known about their distribution, evolution and physical characteristics. In this paper, we review the existing knowledge on ice aprons, which have almost exclusively been investigated in the Mont-Blanc massif, Western Alps. We supplement this review with novel results from recent surveys of ice aprons. We used a wide array of methodologies, from remote sensing (multi-source imagery) to in situ (stakes and thermal monitoring) and laboratory (radiocarbon dating and texture analysis) glaciological investigations. In the Mont-Blanc massif, ice aprons occupy 4.2 km2 within the alpine permafrost zone. Temperature measured at the ice–rock interface is indeed largely negative. Thinness of ice aprons coupled with the cold context implies a quasi-stationary shear regime without basal Sliding. Only ice at the surface can possibly melt in warm periods. After a shrinking period from the end of the Little Ice Age to the mid-to-late-1960s, ice aprons experienced a short period of expansion, followed by an accelerated shrinkage since the beginning of the 21st century. This shrinkage now favours rockfall triggering and poses a serious threat to a glaciological heritage since ice aprons host several-thousand-year-old ice. Finally, we synthesize this information to assess the existing definition of ice aprons, and propose some future research directions.
冰围裙被定义为覆盖在陡峭岩石斜坡上的非常小的冰体。尽管它们是登山活动的条件,也是高高山景观中明显的元素,但近年来,它们才成为科学兴趣日益增加的主题。然而,人们对它们的分布、演化和物理特征知之甚少。在本文中,我们回顾了现有的关于冰围裙的知识,这些知识几乎都是在西阿尔卑斯勃朗峰地块进行的。我们用最近对冰围裙调查的新结果来补充这一综述。我们使用了广泛的方法,从遥感(多源图像)到现场(木桩和热监测)和实验室(放射性碳定年和质地分析)冰川学调查。在勃朗峰地块,冰圈在高山永久冻土带内占地4.2平方公里。在冰-岩界面测得的温度确实在很大程度上是负值。冰圈的厚度与寒冷环境的耦合意味着一个没有基底滑动的准静止剪切状态。只有表面的冰可能在温暖时期融化。在小冰期结束至20世纪60年代中后期的收缩期之后,冰圈经历了短暂的扩张期,随后自21世纪初开始加速收缩。这种收缩现在有利于引发岩崩,并对冰川学遗产构成严重威胁,因为冰围裙承载着数千年前的冰。最后,综合这些信息对现有的冰围裙定义进行了评价,并提出了未来的研究方向。
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引用次数: 1
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Journal of Glaciology
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