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A model of the weathering crust and microbial activity on an ice-sheet surface 冰盖表面风化壳和微生物活动的模型
IF 5.2 2区 地球科学 Q1 GEOGRAPHY, PHYSICAL Pub Date : 2023-05-10 DOI: 10.5194/tc-17-1967-2023
Tilly Woods, I. Hewitt
Abstract. Shortwave radiation penetrating beneath an ice-sheet surface can cause internal melting and the formation of a near-surface porous layer known as the weathering crust, a dynamic hydrological system that provides home to impurities and microbial life. We develop a mathematical model, incorporating thermodynamics and population dynamics, for the evolution of such layers. The model accounts for conservation of mass and energy, for internal and surface-absorbed radiation, and for logistic growth of a microbial species mediated by nutrients that are sourced from the melting ice. It also accounts for potential melt–albedo and microbe–albedo feedbacks, through the dependence of the absorption coefficient on the porosity or microbial concentration. We investigate one-dimensional steadily melting solutions of the model, which give rise to predictions for the weathering crust depth, water content, melt rate, and microbial abundance, depending on a number of parameters. In particular, we examine how these quantities depend on the forcing energy fluxes, finding that the relative amounts of shortwave (surface-penetrating) radiation and other heat fluxes are particularly important in determining the structure of the weathering crust. The results explain why weathering crusts form and disappear under different forcing conditions and suggest a range of possible changes in behaviour in response to climate change.
摘要穿透冰盖表面下的短波辐射会导致内部融化,并形成一个被称为风化壳的近表面多孔层,这是一个动态的水文系统,为杂质和微生物生命提供了家园。我们开发了一个数学模型,结合热力学和种群动力学,为这些层的演变。该模型考虑了质量和能量守恒,内部和表面吸收的辐射,以及由来自融化冰的营养物质介导的微生物物种的逻辑生长。它还考虑了潜在的熔融反照率和微生物反照率反馈,通过吸收系数对孔隙度或微生物浓度的依赖。我们研究了模型的一维稳定融化解,根据一些参数对风化壳深度、含水量、融化速率和微生物丰度进行了预测。特别是,我们研究了这些量如何依赖于强迫能量通量,发现短波(表面穿透)辐射和其他热通量的相对量在确定风化壳的结构方面特别重要。这些结果解释了为什么风化壳在不同的强迫条件下形成和消失,并提出了一系列可能的行为变化,以响应气候变化。
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引用次数: 1
Impact of atmospheric forcing uncertainties on Arctic and Antarctic sea ice simulations in CMIP6 OMIP models CMIP6 OMIP模型中大气强迫不确定性对北极和南极海冰模拟的影响
IF 5.2 2区 地球科学 Q1 GEOGRAPHY, PHYSICAL Pub Date : 2023-05-10 DOI: 10.5194/tc-17-1935-2023
Xia Lin, F. Massonnet, T. Fichefet, M. Vancoppenolle
Abstract. Atmospheric reanalyses are valuable datasets for driving ocean–sea ice general circulation models and for proposing multidecadal reconstructions of the ocean–sea ice system in polar regions. However, these reanalyses exhibit biases in these regions. It was previously found that therepresentation of Arctic and Antarctic sea ice in models participating inthe Ocean Model Intercomparison Project Phase 2 (OMIP2, using the updated Japanese 55-year atmospheric reanalysis, JRA55-do) was significantly more realistic than in OMIP1 (forced by the atmospheric state from the Coordinated Ocean-ice ReferenceExperiments version 2, CORE-II). To understand why, we study the sea iceconcentration budget and its relations to surface heat and momentum fluxes as well as the connections between the simulated ice drift and the iceconcentration, the ice thickness and the wind stress in a subset of threemodels (CMCC-CM2-SR5, MRI-ESM2-0 and NorESM2-LM). These three models are representative of the ensemble and are the only ones to provide the surfacefluxes and the tendencies of ice concentrations attributed to dynamic and thermodynamic processes required for the ice concentration budget analysis.The sea ice simulations of two other models (EC-Earth3 and MIROC6) forced byboth CORE-II and JRA55-do reanalysis are also included in the analysis. It is found that negative summer biases in high-ice-concentration regions and positive biases in the Canadian Arctic Archipelago (CAA) and central WeddellSea (CWS) regions are reduced from OMIP1 to OMIP2 due to surface heat flux changes. Net shortwave radiation fluxes provide key improvements in the Arctic interior, CAA and CWS regions. There is also an influence of improvedsurface wind stress in OMIP2 giving better winter Antarctic iceconcentration and the Arctic ice drift magnitude simulations near the iceedge. The ice velocity direction simulations in the Beaufort Gyre and the Pacific and Atlantic sectors of the Southern Ocean in OMIP2 are alsoimproved owing to surface wind stress changes. This study provides clues onhow improved atmospheric reanalysis products influence sea ice simulations.Our findings suggest that attention should be paid to the radiation fluxesand winds in atmospheric reanalyses in polar regions.
摘要大气再分析是驱动海洋-海冰环流模型和提出极地海洋-海冰系统数十年重建的宝贵数据集。然而,这些重新分析在这些地区显示出偏见。先前发现,参与海洋模式相互比较项目第二阶段(OMIP2,使用最新的日本55年大气再分析,JRA55do)的模型中北极和南极海冰的呈现明显比OMIP1(由协调海冰参考实验第二版CORE-II的大气状态所迫)更现实。为了理解原因,我们在三个模型(CMCC-CM2-SR5、MRI-ESM2-0和NorESM2-LM)的子集中研究了海冰浓度预算及其与表面热量和动量通量的关系,以及模拟冰漂移与冰浓度、冰厚度和风应力之间的联系。这三个模型是集合的代表,是唯一提供冰浓度预算分析所需的动态和热力学过程所导致的冰浓度的表面通量和趋势的模型。CORE-II和JRA55对另外两个模型(EC-Earth3和MIROC6)的海冰模拟也包括在分析中。研究发现,由于地表热通量的变化,高冰浓度地区的夏季负偏差和加拿大北极群岛(CAA)和威德尔海中部(CWS)地区的正偏差从OMIP1减少到OMIP2。净短波辐射通量为北极内陆、CAA和CWS地区提供了关键改善。OMIP2的表面风应力改善也有影响,使冬季南极的冰浓度和冰缘附近的北极冰漂移幅度模拟更好。由于表面风应力的变化,OMIP2中波弗特Gyre以及南大洋太平洋和大西洋部分的冰速度方向模拟也得到了改进。这项研究为改进的大气再分析产品如何影响海冰模拟提供了线索。我们的研究结果表明,在极地大气再分析中应注意辐射通量和风。
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引用次数: 2
European heat waves 2022: contribution to extreme glacier melt in Switzerland inferred from automated ablation readings 2022年欧洲热浪:根据自动消融读数推断瑞士极端冰川融化的原因
IF 5.2 2区 地球科学 Q1 GEOGRAPHY, PHYSICAL Pub Date : 2023-05-09 DOI: 10.5194/tc-17-1895-2023
Aaron Cremona, M. Huss, J. Landmann, Joël Borner, D. Farinotti
Abstract. Accelerating glacier melt rates were observed during the last decades. Substantial ice loss occurs particularly during heat waves that are expected to intensify in the future. Because measuring and modelling glacier mass balance on a daily scale remains challenging, short-term mass balance variations, including extreme melt events, are poorly captured. Here, we present a novel approach based on computer-vision techniques for automatically determining daily mass balance variations at the local scale. The approach is based on the automated recognition of colour-taped ablation stakes from camera images and is tested and validated at six stations installed on three Alpine glaciers during the summers of 2019–2022. Our approach produces daily mass balance with an uncertainty of ±0.81 cm w.e. d−1, which is about half of the accuracy obtained from visual readouts. The automatically retrieved daily mass balances at the six sites were compared to average daily mass balances over the last decade derived from seasonal in situ observations to detect and assess extreme melt events. This allows analysing the impact that the summer heat waves which occurred in 2022 had on glacier melt. Our results indicate 23 d with extreme melt, showing a strong correspondence between the heat wave periods and extreme melt events. The combination of below-average winter snowfall and a suite of summer heat waves led to unprecedented glacier mass loss. The Switzerland-wide glacier storage change during the 25 d of heat waves in 2022 is estimated as 1.27 ± 0.10 km3 of water, corresponding to 35 % of the overall glacier mass loss during that summer. The same 25 d of heat waves caused a glacier mass loss that corresponds to 56 % of the average mass loss experienced over the entire melt season during the summers 2010–2020, demonstrating the relevance of heat waves for seasonal melt.
摘要在过去的几十年里,人们观察到冰川融化速度在加快。特别是在预计未来会加剧的热浪期间,会发生大量的冰损失。由于在日常尺度上测量和模拟冰川物质平衡仍然具有挑战性,短期的物质平衡变化,包括极端的融化事件,很难被捕捉到。在这里,我们提出了一种基于计算机视觉技术的新方法,用于自动确定局部尺度上的每日质量平衡变化。该方法基于对相机图像中彩色胶带消融桩的自动识别,并于2019-2022年夏季在三个阿尔卑斯冰川上安装的六个站点进行了测试和验证。我们的方法产生的每日质量平衡的不确定度为±0.81 cm w.e。d−1,大约是视觉读数准确度的一半。将6个站点自动获取的每日质量平衡与过去10年的平均每日质量平衡进行比较,这些平衡是由季节性现场观测得出的,以检测和评估极端融化事件。这样就可以分析2022年夏季热浪对冰川融化的影响。结果表明,23 d为极端融化期,热浪周期与极端融化事件具有较强的对应关系。低于平均水平的冬季降雪量和一系列夏季热浪的结合导致了前所未有的冰川质量损失。据估计,2022年热浪出现的25 d期间,瑞士全境的冰川储水量变化为1.27±0.10 km3,相当于该夏季冰川总损失量的35%。同样25天的热浪造成的冰川质量损失相当于2010-2020年夏季整个融化季节平均质量损失的56%,这表明热浪与季节性融化的相关性。
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引用次数: 4
Changes in March mean snow water equivalent since the mid-20th century and the contributing factors in reanalyses and CMIP6 climate models 自20世纪中期以来3月平均雪水当量的变化以及再分析和CMIP6气候模式中的促成因素
IF 5.2 2区 地球科学 Q1 GEOGRAPHY, PHYSICAL Pub Date : 2023-05-09 DOI: 10.5194/tc-17-1913-2023
J. Räisänen
Abstract. Trends in March mean snow water equivalent (SWE) in theNorthern Hemisphere are attributed to changes in three main factors: totalprecipitation (P), fraction of precipitation as snowfall (F), and fraction ofaccumulated snowfall remaining on the ground (G). This trend attribution isrepeated for two reanalyses (ERA5-Land from March 1951 to 2022 and MERRA2 – Modern-EraRetrospective analysis for Research and Applications, Version 2 –from 1981 to 2022) and simulations by 22 climate models from the 6th phaseof the Coupled Model Intercomparison Project (CMIP6). The results reveal adecrease in SWE in most of the Northern Hemisphere, as decreases in F and Gdominate over mostly positive trends in P. However, there is spatialvariability in both the magnitude and sign of these trends. There issubstantial variation between the individual CMIP6 models, but the agreementbetween the CMIP6 multi-model mean and ERA5-Land is reasonable for both thearea means and the geographical distribution of the trends from 1951 to2022, with a spatial correlation of 0.51 for the total SWE trend. Theagreement for the trends from 1981 to 2022 is worse, probably partly due tointernal climate variability but also due to the overestimation of therecent warming in the CMIP6 models. Over this shorter period for whichERA5-Land can be compared with MERRA2, there are also marked trenddifferences between these two reanalyses. However, the SWE decreasesassociated with reduced snowfall fraction (F) are more consistent between thedifferent data sets than the trends resulting from changes in P and G.
摘要北半球3月份平均雪水当量(SWE)的趋势归因于三个主要因素的变化:总降水量(P)、降水量作为降雪量的分数(F)和地面累积降雪量的百分比(G)。这一趋势归因适用于两次重新分析(1951年3月至2022年的ERA5 Land和MERRA2——现代Era研究和应用回顾分析,第2版——1981年至2022年),以及耦合模型相互比较项目(CMIP6)第六阶段的22个气候模型的模拟。结果显示,北半球大部分地区的SWE增加,因为F和G的减少超过了P的大部分积极趋势。然而,这些趋势的幅度和符号都存在空间变异性。个别CMIP6模型之间存在实质性差异,但CMIP6多模型平均值和ERA5 Land之间的一致性对于1951年至2022年趋势的面积平均值和地理分布都是合理的,总SWE趋势的空间相关性为0.51。对1981年至2022年趋势的一致性更差,部分原因可能是内部气候变化,但也可能是CMIP6模型高估了局部变暖。在ERA5 Land可以与MERRA2进行比较的较短时间内,这两次重新分析之间也存在显著的趋势差异。然而,与P和G的变化趋势相比,不同数据集之间与降雪量减少(F)相关的SWE减少更为一致。
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引用次数: 1
Modelling the evolution of Arctic multiyear sea ice over 2000–2018 模拟2000-2018年北极多年海冰的演变
IF 5.2 2区 地球科学 Q1 GEOGRAPHY, PHYSICAL Pub Date : 2023-05-08 DOI: 10.5194/tc-17-1873-2023
H. Regan, P. Rampal, Einar Örn Ólason, Guillaume Boutin, A. Korosov
Abstract. Multiyear sea ice (MYI) cover in the Arctic has been monitored for decades using increasingly sophisticated remote sensing techniques, and these have documented a significant decline in MYI over time. However, such techniques are unable to differentiate between the processes affecting the evolution of the MYI. Further, estimating the thickness and thus the volume of MYI remains challenging. In this study we employ a sea ice–ocean model to investigate the changes to MYI over the period 2000–2018. We exploit the Lagrangian framework of the sea ice model to introduce a new method of tracking MYI area and volume which is based on identifying MYI during freeze onset each autumn. The model is found to successfully reproduce the spatial distribution and evolution of observed MYI extent. We discuss the balance of the processes (melt, ridging, export, and replenishment) linked to the general decline in MYI cover. The model suggests that rather than one process dominating the losses, there is an episodic imbalance between the different sources and sinks of MYI. We identify those key to the significant observed declines in 2007 and 2012; while melt and replenishment are important in 2012, sea ice dynamics play a significant role in 2007.Notably, the model suggests that in years such as 2007, convergence of the ice, through ridging, can result in large reductions in MYI area without a corresponding loss of MYI volume. This highlights the benefit of using models alongside satellite observations to aid interpretation of the observed MYI evolution in the Arctic.
摘要几十年来,人们一直在使用越来越复杂的遥感技术监测北极的多年海冰覆盖情况,这些技术记录了多年海冰覆盖率随时间的推移显著下降。然而,这种技术无法区分影响MYI进化的过程。此外,估计MYI的厚度和体积仍然具有挑战性。在这项研究中,我们使用海冰-海洋模型来调查2000-2008年期间MYI的变化。我们利用海冰模型的拉格朗日框架,引入了一种新的跟踪MYI面积和体积的方法,该方法基于识别每年秋季结冰期间的MYI。该模型成功地再现了观测到的MYI范围的空间分布和演化。我们讨论了与MYI覆盖率普遍下降相关的过程平衡(融化、隆起、出口和补充)。该模型表明,MYI的不同来源和汇之间存在偶发性失衡,而不是一个过程主导损失。我们确定了2007年和2012年出现显著下降的关键因素;虽然融化和补给在2012年很重要,但海冰动力学在2007年发挥了重要作用。值得注意的是,该模型表明,在2007年等年份,通过隆起,冰的汇聚可以导致多年平均气温面积的大幅减少,而不会造成多年平均气温量的相应损失。这突出了在卫星观测的同时使用模型来帮助解释观测到的北极MYI演变的好处。
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引用次数: 1
Direct measurement of warm Atlantic Intermediate Water close to the grounding line of Nioghalvfjerdsfjorden (79° N) Glacier, northeast Greenland Nioghalvfjerdsfjorden接地线附近温暖的大西洋中间水的直接测量(79° N) 格陵兰东北部冰川
IF 5.2 2区 地球科学 Q1 GEOGRAPHY, PHYSICAL Pub Date : 2023-05-05 DOI: 10.5194/tc-17-1821-2023
M. J. Bentley, James A. Smith, S. Jamieson, M. Lindeman, B. Rea, A. Humbert, T. Lane, C. Darvill, J. Lloyd, F. Straneo, V. Helm, D. Roberts
Abstract. The Northeast Greenland Ice Stream has recently seen significantchange to its floating margins and has been identified as vulnerable tofuture climate warming. Inflow of warm Atlantic Intermediate Water (AIW)from the continental shelf has been observed in the vicinity of theNioghalvfjerdsfjorden (79∘ N) Glacier calving front, but AIWpenetration deep into the ice shelf cavity has not been observed directly.Here, we report temperature and salinity measurements from profiles in anepishelf lake, which provide the first direct evidence of AIW proximal tothe grounding line of 79∘ N Glacier, over 50 km from the calvingfront. We also report evidence for partial un-grounding of the margin of79∘ N Glacier taking place at the western end of the epishelflake. Comparison of our measurements to those close to the calving frontshows that AIW transits the cavity to reach the grounding line within a fewmonths. The observations provide support for modelling studies that inferAIW-driven basal melt proximal to the grounding line and demonstrate thatoffshore oceanographic changes can be rapidly transmitted throughout thesub-ice-shelf cavity, with implications for near-future stability of the icestream.
摘要格陵兰东北冰流的漂浮边缘最近发生了重大变化,并被确定为易受未来气候变暖的影响。在Nioghalvfjerdsfjorden(79∘ N) 冰川崩解前沿,但尚未直接观察到AIW深入冰架空腔。在这里,我们报告了从阿涅皮舍尔夫湖剖面中测量的温度和盐度,这提供了接近79∘地线的AIW的第一个直接证据 N冰川,超过50 距离卡尔文前线公里。我们还报告了79∘的边缘部分不接地的证据 N冰川发生在epishelflake的西端。我们的测量结果与靠近产裂前沿的测量结果的比较表明,AIW在几个月内穿过空腔到达接地线。这些观测结果为模型研究提供了支持,这些研究推断了接地线附近由海浪驱动的基底融化,并证明近海海洋变化可以迅速传递到整个冰架下洞穴,这对冰流近期的稳定性有影响。
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引用次数: 5
Impact of tides on calving patterns at Kronebreen, Svalbard – insights from three-dimensional ice dynamical modelling 斯瓦尔巴群岛克罗内布林的潮汐对产犊模式的影响——来自三维冰动力模型的见解
IF 5.2 2区 地球科学 Q1 GEOGRAPHY, PHYSICAL Pub Date : 2023-05-05 DOI: 10.5194/tc-17-1853-2023
Felicity A. Holmes, E. V. van Dongen, R. Noormets, M. Pętlicki, N. Kirchner
Abstract. Understanding calving processes and their controls is of importance for reducing uncertainty in sea level rise estimates. The impact of tidal fluctuations and frontal melt on calving patterns has been researched through both modelling and observational studies but remains uncertain and may vary from glacier to glacier. In this study, we isolate various different impacts of tidal fluctuations on a glacier terminus to understand their influence on the timing of calving events in a model of Kronebreen, Svalbard, for the duration of 1 month. In addition, we impose a simplified frontal melt parameterisation onto the calving front in order to allow for an undercut to develop over the course of the simulations. We find that calving events show a tidal signal when there is a small or no undercut, but, after a critical point, undercut-driven calving becomes dominant and drowns out the tidal signal. However, the relationship is complex, and large calving events show a tidal signal even with a large modelled undercut. The modelled undercut sizes are then compared to observational profiles, showing that undercuts of up to ca. 25 m are plausible but with a more complex geometry being evident in observations than that captured in the model. These findings highlight the complex interactions occurring at the calving front of Kronebreen and suggest further observational data and modelling work is needed to fully understand the hierarchy of controls on calving.
摘要了解崩解过程及其控制对于减少海平面上升估计的不确定性至关重要。潮汐波动和锋面融化对崩解模式的影响已经通过建模和观测研究进行了研究,但仍不确定,可能因冰川而异。在这项研究中,我们分离了潮汐波动对冰川终点的各种不同影响,以了解它们对斯瓦尔巴群岛Kronebreen模型中1个月内崩解事件时间的影响。此外,我们将简化的前缘熔体参数化应用于崩解前缘,以便在模拟过程中形成底切。我们发现,当存在小的或没有底切时,崩解事件显示出潮汐信号,但在临界点之后,底切驱动的崩解成为主导并淹没潮汐信号。然而,这种关系是复杂的,即使有大的模拟底切,大型崩解事件也会显示出潮汐信号。然后将建模的底切尺寸与观测剖面进行比较,表明底切高达ca.25 m是合理的,但在观测中比在模型中捕捉到的几何结构更复杂。这些发现突出了Kronebreen崩解前沿发生的复杂相互作用,并表明需要进一步的观测数据和建模工作来充分了解控制崩解的层次。
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引用次数: 3
Spatial characterization of near-surface structure and meltwater runoff conditions across the Devon Ice Cap from dual-frequency radar reflectivity 基于双频雷达反射率的德文冰帽近地表结构和融水径流条件的空间特征
IF 5.2 2区 地球科学 Q1 GEOGRAPHY, PHYSICAL Pub Date : 2023-05-05 DOI: 10.5194/tc-17-1839-2023
K. Chan, C. Grima, A. Rutishauser, D. Young, R. Culberg, D. Blankenship
Abstract. Melting and refreezing processes in the firn of the Devon IceCap control meltwater infiltration and runoff across the ice cap, but theirfull spatial extent and effect on near-surface structure is difficult tomeasure with surface-based traverses or existing satellite remote sensing.Here, we derive the coherent component of the near-surface return fromairborne ice-penetrating radar surveys over the Devon Ice Cap, Canadian Arctic,to characterize firn containing centimeter- to meter-thick ice layers (i.e.,ice slabs) formed from refrozen meltwater in firn. We assess the use ofdual-frequency airborne ice-penetrating radar to characterize the spatialand vertical near-surface structure of the Devon Ice Cap by leveragingdifferences in range resolution of the radar systems. Comparison withreflectivities using a thin layer reflectivity model, informed bysurface-based radar and firn core measurements, indicates that the coherentcomponent is sensitive to the near-surface firn structure composed ofquasi-specular ice and firn layers, limited by the bandwidth-constrainedradar range resolution. Our results suggest that average ice slab thicknessthroughout the Devon Ice Cap percolation zone ranges from 4.2 to 5.6 m. Thisimplies conditions that can enable lateral meltwater runoff and potentiallycontribute to the total surface runoff routed through supraglacial riversdown glacier. Together with the incoherent component of the surface returnpreviously studied, our dual-frequency approach provides an alternativemethod for characterizing bulk firn properties, particularly where high-resolution radar data are not available.
摘要德文郡冰冠上部的融化和再冻结过程控制着整个冰冠的融水入渗和径流,但它们的全部空间范围和对近地表结构的影响很难用地面穿越或现有的卫星遥感来测量。在这里,我们从加拿大北极德文冰帽的机载破冰雷达调查中获得近地表返回的相干分量,以表征含有厘米至米厚冰层(即冰块)的雪,这些冰层是由雪中的融水重新冻结形成的。我们评估了双频机载破冰雷达的使用,利用雷达系统的距离分辨率差异来表征德文冰盖的空间和垂直近地表结构。与基于地面雷达和冰芯测量的薄层反射率模型的反射率比较表明,受带宽限制的雷达距离分辨率限制,相干分量对由准镜面冰层和冰芯层组成的近地表冰芯结构很敏感。我们的研究结果表明,整个德文冰帽渗透带的平均冰盖厚度在4.2 - 5.6 m之间。这意味着有条件使侧向融水径流成为可能,并有可能促成通过冰川上河流而下的总地表径流。与之前研究的表面回波的非相干成分一起,我们的双频方法为表征大块岩石特性提供了一种替代方法,特别是在没有高分辨率雷达数据的情况下。
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引用次数: 0
Permafrost degradation at two monitored palsa mires in north-west Finland 芬兰西北部两个监测的palsa沼泽的永久冻土退化
IF 5.2 2区 地球科学 Q1 GEOGRAPHY, PHYSICAL Pub Date : 2023-05-03 DOI: 10.5194/tc-17-1803-2023
Mariana Verdonen, Alexander Störmer, E. Lotsari, Pasi Korpelainen, Benjamin Burkhard, A. Colpaert, T. Kumpula
Abstract. Palsas and peat plateaus are expected to disappear from many regions, including Finnish Lapland. However, detailed long-term monitoring data of the degradation process on palsas are scarce. Here, we present the results of the aerial photography time series analysis (1959–2021), annual real-time kinematic (RTK) GNSS and active layer monitoring (2007–2021), and annual unoccupied aerial system surveys (2016–2021) at two palsa sites (Peera and Laassaniemi, 68∘ N) located in north-west Finland. We analysed temporal trends of palsa degradation and their relation to climate using linear regression. At both sites, the decrease in palsa area by −77 % to −90 % since 1959 and height by −16 % to −49 % since 2007 indicate substantial permafrost degradation throughout the study periods. The area loss rates are mainly connected to winter air temperature changes at Peera and winter precipitation changes at Laassaniemi. The active layer thickness (ALT) has varied annually between 2007 and 2021 with no significant trend and is related mainly to the number of very warm days during summer, autumn rainfall of previous year, and snow depths at Peera. At Laassaniemi, the ALT is weakly related to climate and has been decreasing in the middle part of the palsa during the past 8 years despite the continuous decrease in palsa volume. Our findings imply that the ALT in the inner parts of palsas do not necessarily reflect the overall permafrost conditions and underline the importance of surface position monitoring alongside the active layer measurements. The results also showed a negative relationship between the ALT and snow cover onset, indicating the complexity of climate–permafrost feedbacks in palsa mires.
摘要包括芬兰拉普兰在内的许多地区预计将会消失沼泽和泥炭高原。然而,关于palsas降解过程的详细的长期监测数据很少。在这里,我们展示了位于芬兰西北部的两个palsa站点(Peera和Laassaniemi, 68°N)的航空摄影时间序列分析(1959-2021)、年度实时运动学(RTK) GNSS和有源层监测(2007-2021)和年度无人航空系统调查(2016-2021)的结果。利用线性回归分析了棕丛退化的时间趋势及其与气候的关系。在这两个地点,自1959年以来,palsa面积减少了- 77%至- 90%,高度自2007年以来减少了- 16%至- 49%,这表明在整个研究期间,永久冻土发生了实质性的退化。面积损失率主要与Peera的冬季气温变化和Laassaniemi的冬季降水变化有关。活动层厚度(ALT)在2007 - 2021年间呈逐年变化趋势,主要与夏季极暖日数、往年秋季降雨量和Peera积雪深度有关。在Laassaniemi,尽管palsa体积持续减少,但palsa中部的ALT与气候的相关性较弱,近8年来一直呈下降趋势。我们的研究结果表明,palsas内部的ALT不一定反映总体永久冻土条件,并强调了地表位置监测与活动层测量的重要性。ALT与积雪的发生呈负相关,说明黄土高原气候-冻土反馈的复杂性。
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引用次数: 2
Reversible ice sheet thinning in the Amundsen Sea Embayment during the Late Holocene 全新世晚期阿蒙森海堤的可逆冰盖变薄
IF 5.2 2区 地球科学 Q1 GEOGRAPHY, PHYSICAL Pub Date : 2023-04-28 DOI: 10.5194/tc-17-1787-2023
G. Balco, N. Brown, K. Nichols, R. Venturelli, Jonathan Adams, S. Braddock, S. Campbell, B. Goehring, Joanne S. Johnson, D. Rood, K. Wilcken, B. Hall, J. Woodward
Abstract. Cosmogenic-nuclide concentrations in subglacial bedrock cores show that the West Antarctic Ice Sheet (WAIS) at a site between Thwaites and Pope glaciers was at least 35 m thinner than present in the past several thousand years and then subsequently thickened. This is important because of concern that present thinning and grounding line retreat at these and nearby glaciers in the Amundsen Sea Embayment may irreversibly lead to deglaciation of significant portions of the WAIS, with decimeter- to meter-scale sea level rise within decades to centuries. A past episode of ice sheet thinning that took place in a similar, although not identical, climate was not irreversible. We propose that the past thinning–thickening cycle was due to a glacioisostatic rebound feedback, similar to that invoked as a possible stabilizing mechanism for current grounding line retreat, in which isostatic uplift caused by Early Holocene thinning led to relative sea level fall favoring grounding line advance.
摘要冰下基岩岩芯中的宇宙成因核素浓度表明,位于斯维特冰川和波普冰川之间的南极西部冰盖(WAIS)至少为35 m比过去几千年的现在更薄,然后变厚。这一点很重要,因为人们担心,目前阿蒙森海堤中这些冰川和附近冰川的变薄和接地线退缩可能会不可逆转地导致WAIS的大部分冰川消融,在几十年到几个世纪内,海平面将以分米到米的比例上升。过去发生在类似但不完全相同的气候中的冰盖变薄事件并非不可逆转。我们认为,过去的变薄-增厚周期是由于冰川均衡反弹反馈,类似于被称为当前接地线后退的可能稳定机制,其中全新世早期变薄引起的均衡抬升导致相对海平面下降,有利于接地线前进。
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引用次数: 2
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Cryosphere
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