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A comparison of contemporaneous airborne altimetry and ice-thickness measurements of Antarctic ice shelves 南极冰架同时期空中测高和冰厚测量的比较
IF 3.4 3区 地球科学 Q2 GEOGRAPHY, PHYSICAL Pub Date : 2023-08-03 DOI: 10.1017/jog.2023.49
Allison M. Chartrand, I. Howat
Estimates of ice shelf mass loss are typically based on surface height measurements, assuming hydrostatic equilibrium and estimated firn thickness. Recent investigations, however, challenge the assumption that ice shelves are freely floating, particularly in proximity to narrow structures such as basal channels and shear margins. We compare contemporaneous measurements of Antarctic ice shelf thickness, from ice-penetrating radar, to freeboard height, from laser altimetry, acquired during multiple airborne surveys. On average, the hydrostatic thickness differs from observed thickness by at least ~17 ± 98 m, but this difference varies well beyond the propagated error within and among ice shelves, and depends on the corrections applied. We find that uncertainty in firn thickness can account for most, but not all, of the imbalance. Overall, errors in hydrostatic thickness do not significantly impact estimated basal melt rates. Our results indicate that localized approaches to estimating ice shelf thickness and rates of change are not applicable at large scales, and vice versa, and point to the need for more abundant and accurate firn and ice thickness measurements to improve estimates and predictions of ice shelf mass loss.
冰架质量损失的估计通常基于表面高度测量,假设流体静力平衡和估计的冷杉厚度。然而,最近的调查挑战了冰架自由漂浮的假设,特别是在狭窄结构(如基底通道和剪切边缘)附近。我们比较了在多次航空调查中获得的南极冰架厚度的同期测量值,从探冰雷达到干舷高度,从激光测高。平均而言,静水压厚度与观测到的厚度相差至少~17±98 m,但这种差异远远超出了冰架内部和冰架之间的传播误差,并取决于所应用的校正。我们发现,冷杉厚度的不确定性可以解释这种不平衡的大部分,但不是全部。总体而言,静水压厚度的误差不会显著影响估计的基本熔体速率。我们的研究结果表明,估计冰架厚度和变化率的局部方法不适用于大尺度,反之亦然,并指出需要更丰富、更准确的firn和冰厚度测量,以改进对冰架质量损失的估计和预测。
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引用次数: 0
Ice-flow perturbation analysis: a method to estimate ice-sheet bed topography and conditions from surface datasets 冰流摄动分析:一种从地表数据集估计冰盖床地形和条件的方法
IF 3.4 3区 地球科学 Q2 GEOGRAPHY, PHYSICAL Pub Date : 2023-08-03 DOI: 10.1017/jog.2023.50
Helen Ockenden, R. Bingham, Andrew Curtis, D. Goldberg
One of the largest contributors to uncertainty in predictions of sea-level rise from ice-sheet models is a lack of knowledge about the bed topography beneath ice sheets. Bed topography maps are normally made by interpolating between linear radar surveys using methods that include kriging, mass conservation and flowline diffusion, all of which may miss influential mesoscale (2–30 km) bedforms. Previous works have explored an Ice-Flow Perturbation Analysis (IFPA) approach for estimating bed topography using the surface expression of these mesoscale bedforms. Using regions of Pine Island Glacier that have been intensively surveyed by ice-penetrating radar as test sites, and a refined IFPA methodology, we find that IFPA detects bedforms capable of influencing ice flow which are not represented in Bedmachine Antarctica and other interpolated bed products. We further explore the ability of IFPA to estimate relative bed slipperiness, finding higher slipperiness in the main trunk and tributaries. Alongside other methods which estimate ice thickness, bed topography maps from IFPA have the potential to constrain projections of future sea-level rise, especially where radar data are sparse.
在根据冰盖模型预测海平面上升时,造成不确定性的最大因素之一是缺乏对冰盖下床地形的了解。河床地形图通常是在线性雷达测量之间进行插值绘制的,使用的方法包括克里格法、质量守恒法和流线扩散法,所有这些方法都可能错过有影响的中尺度(2-30公里)河床。以前的工作已经探索了冰流摄动分析(IFPA)方法,利用这些中尺度床型的表面表达来估计床地形。利用冰透雷达密集调查的松岛冰川区域作为测试点,并使用改进的IFPA方法,我们发现IFPA检测到能够影响冰流的床型,而这些床型在Bedmachine南极洲和其他插值床型产品中没有体现出来。我们进一步探索了IFPA估算相对地层滑度的能力,发现主干流和支流的滑度较高。与其他估算冰厚的方法一样,IFPA的床地形图有可能限制对未来海平面上升的预测,特别是在雷达数据稀少的地方。
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引用次数: 0
JOG volume 69 issue 276 Cover and Back matter JOG卷69期276封面和封底
IF 3.4 3区 地球科学 Q2 GEOGRAPHY, PHYSICAL Pub Date : 2023-07-28 DOI: 10.1017/jog.2023.56
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引用次数: 0
JOG volume 69 issue 276 Cover and Front matter JOG第69卷第276期封面和封面
IF 3.4 3区 地球科学 Q2 GEOGRAPHY, PHYSICAL Pub Date : 2023-07-28 DOI: 10.1017/jog.2023.55
Lecture Theatre
s due Notification of acceptance Accommodations deadline Pre-registration deadline Papers due Deadline for full refund
s到期验收通知住宿截止日期预登记截止日期文件到期全额退款截止日期
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引用次数: 1
Numerical modelling of dense snow avalanches with a well-balanced scheme based on the 2D shallow water equations 基于二维浅水方程的良好平衡方案的密集雪崩数值模拟
IF 3.4 3区 地球科学 Q2 GEOGRAPHY, PHYSICAL Pub Date : 2023-07-25 DOI: 10.1017/jog.2023.48
M. Sanz-Ramos, E. Bladé, P. Oller, G. Furdada
A common technique for simulating non–Newtonian fluid dynamics, such as snow avalanches, is to solve the Shallow Water Equations (SWE), together with a rheological model describing the momentum dissipation by shear stresses. Friction and cohesion terms are commonly modelled using the Voellmy friction model and, recently, the Bartelt cohesion model. Here, an adaptation of the Roe scheme that ensures the balance between the flux and pressure gradients and the friction source term is presented. An upwind scheme was used for the discretisation of the SWE numerical fluxes and the non–velocity-dependent terms of the friction–cohesion model, whereas a centred scheme was used for the velocity-dependent source terms. The model was tested in analytically solvable settings, laboratory experiments and real cases. In all cases, the model performed well, avoiding numerical instabilities and achieving stable and consistent solution even for an avalanche stopping on a sloping terrain.
模拟非牛顿流体动力学(如雪崩)的常用技术是求解浅水方程(SWE),以及描述剪切应力的动量耗散的流变模型。摩擦和内聚项通常使用Voellmy摩擦模型和最近的Bartelt内聚模型来建模。本文对Roe格式进行了改进,以保证流量和压力梯度与摩擦源项之间的平衡。采用逆风格式对SWE数值通量和摩擦-内聚模型的非速度相关项进行离散化,而对速度相关源项采用中心格式。该模型在解析可解环境、实验室实验和实际案例中进行了测试。在所有情况下,该模型都表现良好,避免了数值不稳定性,即使在斜坡地形上停止雪崩也能获得稳定一致的解。
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引用次数: 2
A shallow approximation for ice streams sliding over strong beds 冰流在坚固床上滑动的浅层近似
IF 3.4 3区 地球科学 Q2 GEOGRAPHY, PHYSICAL Pub Date : 2023-07-25 DOI: 10.1017/jog.2023.47
K. Warburton, D. Hewitt, C. Meyer, J. Neufeld
Ice streams are regions of rapid ice sheet flow characterised by a high degree of sliding over a deforming bed. The shallow shelf approximation (SSA) provides a convenient way to obtain closed-form approximations of the velocity and flux in a rapidly sliding ice stream when the basal drag is much less than the driving stress. However, the validity of the SSA approximation breaks down when the magnitude of the basal drag increases. Here we find a more accurate expression for the velocity and flux in this transitional regime before vertical deformation fully dominates, in agreement with numerical results. The closed-form expressions we derive can be incorporated into wider modelling efforts to yield a better characterisation of ice stream dynamics, and inform the use of the SSA in large-scale simulations.
冰流是快速冰盖流动的区域,其特征是在变形床上高度滑动。当基础阻力远小于驱动应力时,浅冰架近似(SSA)提供了一种方便的方法来获得快速滑动冰流中速度和通量的闭合形式近似。然而,当基础阻力的大小增加时,SSA近似的有效性就会失效。在这里,我们发现了在垂直变形完全占主导地位之前,该过渡区的速度和通量的更准确表达式,与数值结果一致。我们推导出的闭合形式表达式可以被纳入更广泛的建模工作中,以更好地描述冰流动力学,并为SSA在大规模模拟中的使用提供信息。
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引用次数: 0
Changes in glacier albedo and the driving factors in the Western Nyainqentanglha Mountains from 2001 to 2020 2001年至2020年尼安春坦古拉山脉西部冰川反照率变化及其驱动因素
IF 3.4 3区 地球科学 Q2 GEOGRAPHY, PHYSICAL Pub Date : 2023-07-18 DOI: 10.1017/jog.2023.45
Shaoting Ren, L. Jia, M. Menenti, Jing Zhang
Abstract Glacier surface albedo dominates glacier energy balance, thus strongly affecting the glacier mass balance. Glaciers in the Western Nyainqentanglha Mountains (WNM) experienced large mass losses in the past two decades, but long-term changes of glacier albedo and its drivers are less understood. In this study, we retrieved glacier albedo with MODIS reflectance data to characterize the spatiotemporal variability of albedo from 2001 to 2020. Air temperature, rainfall, snowfall and deposition of light-absorbing impurities (LAIs) were evaluated as potential drivers of the observed variability in glacier albedo. The results showed that: (1) the glacier albedo experienced large inter-annual fluctuations, with the mean albedo being 0.552 ± 0.002 and a clear decreasing trend of 0.0443 ± 2 × 10−4 dec−1 in the WNM. The fastest decline was observed in autumn and in the vicinity of the equilibrium line altitude, indicating an extended melt season and an expansion of the ablation region to higher elevation; (2) local meteorology and LAIs deposition are the main drivers of glacier albedo change, but their effects on seasonal albedos are different due to different glacier processes. Both air temperature and the balance between liquid and solid precipitation affect summer and autumn albedos due to glacier ablation. Air temperature is the main driver of spring and winter albedos due to sublimation and metamorphism of snow, while snowfall carried by westerlies has limited influence on these two seasonal albedos due to less snowfall. LAIs mainly affect spring albedo due to high concentration coupled with the southerly wind in spring. These findings highlight the significance of changes in glacier albedo and the key role of local meteorology and LAIs deposition in determining such changes, which play an important role in glaciological and cryosphere processes.
冰川表面反照率主导着冰川能量平衡,从而强烈影响冰川质量平衡。在过去的二十年里,尼安春坦古拉山脉西部的冰川经历了巨大的质量损失,但冰川反照率及其驱动因素的长期变化却鲜为人知。在这项研究中,我们利用MODIS反射率数据检索了冰川反照率,以表征2001年至2020年反照率的时空变化。气温、降雨量、降雪量和吸光杂质的沉积被评估为观测到的冰川反照率变化的潜在驱动因素。结果表明:(1)冰川反照率经历了较大的年际波动,WNM的平均反照率为0.552±0.002,并有0.0443±2×10−4 dec−1的明显下降趋势。秋季和平衡线海拔附近的下降速度最快,表明融化季节延长,消融区域向更高海拔扩展;(2) 当地气象和LAIs沉积是冰川反照率变化的主要驱动因素,但由于冰川过程的不同,它们对季节反照率的影响不同。由于冰川消融,气温和液态和固态降水之间的平衡都会影响夏季和秋季的反照率。由于雪的升华和变质作用,气温是春季和冬季反照率的主要驱动因素,而西风带携带的降雪量较少,对这两个季节反照率影响有限。LAI主要影响春季反照率,因为春季的高浓度和南风。这些发现强调了冰川反照率变化的重要性,以及当地气象和LAI沉积在决定这种变化中的关键作用,这些变化在冰川学和冰冻圈过程中发挥着重要作用。
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引用次数: 0
Future projections for the Antarctic ice sheet until the year 2300 with a climate-index method 用气候指数法对南极冰盖到2300年的未来预测
IF 3.4 3区 地球科学 Q2 GEOGRAPHY, PHYSICAL Pub Date : 2023-07-11 DOI: 10.1017/jog.2023.41
R. Greve, C. Chambers, T. Obase, F. Saito, W. Chan, A. Abe‐Ouchi
As part of the Coupled Model Intercomparison Project Phase 6 (CMIP6), the Ice Sheet Model Intercomparison Project for CMIP6 (ISMIP6) was devised to assess the likely sea-level-rise contribution from the Earth's ice sheets. Here, we construct an ensemble of climate forcings for Antarctica until the year 2300 based on original ISMIP6 forcings until 2100, combined with climate indices from simulations with the MIROC4m climate model until 2300. We then use these forcings to run simulations for the Antarctic ice sheet with the SICOPOLIS model. For the unabated warming pathway RCP8.5/SSP5-8.5, the ice sheet suffers a severe mass loss, amounting to ~ 1.5 m SLE (sea-level equivalent) for the fourteen-experiment mean, and ~ 3.3 m SLE for the most sensitive experiment. Most of this loss originates from West Antarctica. For the reduced emissions pathway RCP2.6/SSP1-2.6, the loss is limited to a three-experiment mean of ~ 0.16 m SLE. The means are approximately two times larger than what was found in a previous study (Chambers and others, 2022, doi:10.1017/jog.2021.124) that assumed a sustained late-21st-century climate beyond 2100, demonstrating the importance of post-2100 climate trends on Antarctic mass changes in the 22nd and 23rd centuries.
作为耦合模式比对项目第6阶段(CMIP6)的一部分,CMIP6冰盖模式比对项目(ISMIP6)旨在评估地球冰盖可能对海平面上升的贡献。在此,我们基于原始的ISMIP6至2100年的强迫,结合MIROC4m至2300年气候模式模拟的气候指数,构建了南极洲至2300年的气候强迫集合。然后,我们利用这些强迫用SICOPOLIS模式对南极冰盖进行模拟。在不减弱的升温路径RCP8.5/SSP5-8.5中,冰盖遭受了严重的质量损失,14个实验的平均值为~ 1.5 m SLE(海平面当量),最敏感的实验为~ 3.3 m SLE。这种损失大部分来自南极洲西部。对于RCP2.6/SSP1-2.6的减排路径,损失限制在3个实验的平均值~ 0.16 m SLE。这一平均值比之前的研究(Chambers等人,2022,doi:10.1017/ joj .2021.124)中发现的平均值大约大两倍,该研究假设21世纪末的气候在2100年之后持续,证明了2100年后气候趋势对22世纪和23世纪南极质量变化的重要性。
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引用次数: 0
Effects of topography on dynamics and mass loss of lake-terminating glaciers in southern Patagonia 地形对巴塔哥尼亚南部湖泊冰川动力学和质量损失的影响
IF 3.4 3区 地球科学 Q2 GEOGRAPHY, PHYSICAL Pub Date : 2023-07-11 DOI: 10.1017/jog.2023.42
M. Minowa, Marius Schaefer, P. Skvarca
Calving glaciers are highly sensitive to bedrock geometry near their terminus. To understand the mechanisms controlling rapid calving glaciers’ mass loss, we measured the lake topography in front of four lake-terminating glaciers in the southern Patagonian icefield. Using remotely sensed surface elevation data, we calculated flotation height and surface slope and compared those with changes in ice-front position, surface speed and surface elevation. Rapid retreat accompanied by rapid flow acceleration and ice surface steepening was observed at Glaciar Upsala from 2008–2011, and at O'Higgins and Viedma glaciers from 2016–present. Surface lowering in the lower part of Glaciar Upsala reached 30 m a−1 and was 18 m a−1 and 12 m a−1 at O'Higgins and Viedma glaciers, respectively. Near- or super-buoyant conditions were observed prior to these events, leading to gradual flow acceleration due to low effective pressure and decoupling from the bed. The super-buoyant condition and gradual acceleration imply full-thickness buoyant calving, which causes the ice front to retreat from the shallow bedrock topography with substantial flow acceleration. We conclude that the buoyancy force plays an important role in the rapid mass loss of lake-terminating glaciers in southern Patagonia.
正在崩解的冰川对其终点附近的基岩几何形状高度敏感。为了了解控制冰川快速崩解的机制,我们测量了巴塔哥尼亚南部冰原四个湖泊终止冰川前的湖泊地形。利用遥感地表高程数据,计算浮力高度和地表坡度,对比冰锋位置、地表速度和地表高程的变化。2008年至2011年,乌普萨拉冰川和2016年至今的O'Higgins和Viedma冰川观测到快速退缩,同时观测到快速流动加速和冰面变陡。Upsala冰川下半部分的地表下降幅度为30 ma−1,O’higgins冰川和Viedma冰川的地表下降幅度分别为18 ma−1和12 ma−1。在此之前,观察到近浮力或超浮力条件,由于有效压力低且与床层分离,导致流动逐渐加速。超浮力条件和逐渐加速意味着全层浮力崩解,导致冰锋从浅层基岩地形后退,水流加速明显。我们认为,浮力在南巴塔哥尼亚终湖冰川的快速质量损失中起着重要作用。
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引用次数: 1
Mass-balance and ablation processes of a perennial polar ice patch on the northern coast of Ellesmere Island 埃尔斯米尔岛北海岸一个常年极地冰盖的质量平衡和消融过程
IF 3.4 3区 地球科学 Q2 GEOGRAPHY, PHYSICAL Pub Date : 2023-07-11 DOI: 10.1017/jog.2023.44
Gautier Davesne, David H. Fortier, F. Dominé, C. Kinnard
Ice patches have implications for landscape and ecosystem dynamics in polar deserts, however, the understanding of the driving factors that control their spatio-temporal variability is limited. This study aims to assess the seasonal and long-term evolution of ice patches on Ward Hunt Island (WHI; 83°N, Canadian High Arctic) based on field measurements of surface mass and energy balance. Results show that mass gains of the ice patch systems occur mostly through drifting snow, making them highly linked to the topography as well as the frequency and magnitude of wind events. Summer ablation is primarily driven by net radiation, but the short-term variability in melt rate is driven by sensible heat fluxes. The highest ablation rates occur during the passage of warm fronts that combine strong winds and mild temperatures. Conversely, foggy days reduce fluxes of solar radiation and sensible heat to the snow/ice surface, thereby suppressing ablation. Ice patches are less climate-sensitive than other cryospheric elements due to a feedback between snow accumulation and topography, however, summer ablation is strongly influenced by micrometeorology. Model projections of these factors suggest that conditions will become critical for preserving ice patches at WHI and along the northern coast of Ellesmere Island as early as in the next decades.
冰斑对极地沙漠景观和生态系统动态具有重要影响,但对控制其时空变化的驱动因素的认识有限。本研究旨在评估沃德亨特岛冰原的季节性和长期演变。83°N,加拿大高纬度北极),基于地面质量和能量平衡的实地测量。结果表明,冰原系统的质量增加主要是通过飘雪发生的,这使得它们与地形以及风事件的频率和强度密切相关。夏季消融主要是由净辐射驱动的,但融化速率的短期变率是由感热通量驱动的。在结合了强风和温和温度的暖锋经过时,发生了最高的消融率。相反,雾天减少太阳辐射通量和感热到雪/冰表面,从而抑制消融。由于积雪和地形之间的反馈作用,冰块对气候的敏感性低于其他冰冻圈要素,然而,夏季消融受微气象学的强烈影响。对这些因素的模型预测表明,最早在未来几十年,保护WHI和埃尔斯米尔岛北部海岸的冰原的条件将变得至关重要。
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引用次数: 0
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Journal of Glaciology
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