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 the representation of Arctic and Antarctic sea ice in models participating in the 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 Reference Experiments version 2, CORE-II). To understand why, we study the sea ice concentration budget and its relations to surface heat and momentum fluxes as well as the connections between the simulated ice drift and the ice concentration, the ice thickness and the wind stress in a subset of three models (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 surface fluxes 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 by both 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 Weddell Sea (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 improved surface wind stress in OMIP2 giving better winter Antarctic ice concentration and the Arctic ice drift magnitude simulations near the ice edge. The ice velocity direction simulations in the Beaufort Gyre and the Pacific and Atlantic sectors of the Southern Ocean in OMIP2 are also improved owing to surface wind stress changes. This study provides clues on how improved atmospheric reanalysis products influence sea ice simulations. Our findings suggest that attention should be paid to the radiation fluxes and winds in atmospheric reanalyses in polar regions.
{"title":"Impact of atmospheric forcing uncertainties on Arctic and Antarctic sea ice simulations in CMIP6 OMIP models","authors":"Xia Lin, F. Massonnet, T. Fichefet, M. Vancoppenolle","doi":"10.5194/tc-17-1935-2023","DOIUrl":"https://doi.org/10.5194/tc-17-1935-2023","url":null,"abstract":"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 the\u0000representation of Arctic and Antarctic sea ice in models participating in\u0000the 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 Reference\u0000Experiments version 2, CORE-II). To understand why, we study the sea ice\u0000concentration budget and its relations to surface heat and momentum fluxes as well as the connections between the simulated ice drift and the ice\u0000concentration, the ice thickness and the wind stress in a subset of three\u0000models (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 surface\u0000fluxes and the tendencies of ice concentrations attributed to dynamic and thermodynamic processes required for the ice concentration budget analysis.\u0000The sea ice simulations of two other models (EC-Earth3 and MIROC6) forced by\u0000both 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 Weddell\u0000Sea (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 improved\u0000surface wind stress in OMIP2 giving better winter Antarctic ice\u0000concentration and the Arctic ice drift magnitude simulations near the ice\u0000edge. The ice velocity direction simulations in the Beaufort Gyre and the Pacific and Atlantic sectors of the Southern Ocean in OMIP2 are also\u0000improved owing to surface wind stress changes. This study provides clues on\u0000how improved atmospheric reanalysis products influence sea ice simulations.\u0000Our findings suggest that attention should be paid to the radiation fluxes\u0000and winds in atmospheric reanalyses in polar regions.\u0000","PeriodicalId":56315,"journal":{"name":"Cryosphere","volume":null,"pages":null},"PeriodicalIF":5.2,"publicationDate":"2023-05-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45760971","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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.
{"title":"A model of the weathering crust and microbial activity on an ice-sheet surface","authors":"Tilly Woods, I. Hewitt","doi":"10.5194/tc-17-1967-2023","DOIUrl":"https://doi.org/10.5194/tc-17-1967-2023","url":null,"abstract":"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.\u0000","PeriodicalId":56315,"journal":{"name":"Cryosphere","volume":null,"pages":null},"PeriodicalIF":5.2,"publicationDate":"2023-05-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43586756","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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。
{"title":"European heat waves 2022: contribution to extreme glacier melt in Switzerland inferred from automated ablation readings","authors":"Aaron Cremona, M. Huss, J. Landmann, Joël Borner, D. Farinotti","doi":"10.5194/tc-17-1895-2023","DOIUrl":"https://doi.org/10.5194/tc-17-1895-2023","url":null,"abstract":"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.\u0000","PeriodicalId":56315,"journal":{"name":"Cryosphere","volume":null,"pages":null},"PeriodicalIF":5.2,"publicationDate":"2023-05-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45867956","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Abstract. Trends in March mean snow water equivalent (SWE) in the Northern Hemisphere are attributed to changes in three main factors: total precipitation (P), fraction of precipitation as snowfall (F), and fraction of accumulated snowfall remaining on the ground (G). This trend attribution is repeated for two reanalyses (ERA5-Land from March 1951 to 2022 and MERRA2 – Modern-Era Retrospective analysis for Research and Applications, Version 2 – from 1981 to 2022) and simulations by 22 climate models from the 6th phase of the Coupled Model Intercomparison Project (CMIP6). The results reveal a decrease in SWE in most of the Northern Hemisphere, as decreases in F and G dominate over mostly positive trends in P. However, there is spatial variability in both the magnitude and sign of these trends. There is substantial variation between the individual CMIP6 models, but the agreement between the CMIP6 multi-model mean and ERA5-Land is reasonable for both the area means and the geographical distribution of the trends from 1951 to 2022, with a spatial correlation of 0.51 for the total SWE trend. The agreement for the trends from 1981 to 2022 is worse, probably partly due to internal climate variability but also due to the overestimation of the recent warming in the CMIP6 models. Over this shorter period for which ERA5-Land can be compared with MERRA2, there are also marked trend differences between these two reanalyses. However, the SWE decreases associated with reduced snowfall fraction (F) are more consistent between the different data sets than the trends resulting from changes in P and G.
{"title":"Changes in March mean snow water equivalent since the mid-20th century and the contributing factors in reanalyses and CMIP6 climate models","authors":"J. Räisänen","doi":"10.5194/tc-17-1913-2023","DOIUrl":"https://doi.org/10.5194/tc-17-1913-2023","url":null,"abstract":"Abstract. Trends in March mean snow water equivalent (SWE) in the\u0000Northern Hemisphere are attributed to changes in three main factors: total\u0000precipitation (P), fraction of precipitation as snowfall (F), and fraction of\u0000accumulated snowfall remaining on the ground (G). This trend attribution is\u0000repeated for two reanalyses (ERA5-Land from March 1951 to 2022 and MERRA2 – Modern-Era\u0000Retrospective analysis for Research and Applications, Version 2 –\u0000from 1981 to 2022) and simulations by 22 climate models from the 6th phase\u0000of the Coupled Model Intercomparison Project (CMIP6). The results reveal a\u0000decrease in SWE in most of the Northern Hemisphere, as decreases in F and G\u0000dominate over mostly positive trends in P. However, there is spatial\u0000variability in both the magnitude and sign of these trends. There is\u0000substantial variation between the individual CMIP6 models, but the agreement\u0000between the CMIP6 multi-model mean and ERA5-Land is reasonable for both the\u0000area means and the geographical distribution of the trends from 1951 to\u00002022, with a spatial correlation of 0.51 for the total SWE trend. The\u0000agreement for the trends from 1981 to 2022 is worse, probably partly due to\u0000internal climate variability but also due to the overestimation of the\u0000recent warming in the CMIP6 models. Over this shorter period for which\u0000ERA5-Land can be compared with MERRA2, there are also marked trend\u0000differences between these two reanalyses. However, the SWE decreases\u0000associated with reduced snowfall fraction (F) are more consistent between the\u0000different data sets than the trends resulting from changes in P and G.\u0000","PeriodicalId":56315,"journal":{"name":"Cryosphere","volume":null,"pages":null},"PeriodicalIF":5.2,"publicationDate":"2023-05-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48743863","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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.
{"title":"Modelling the evolution of Arctic multiyear sea ice over 2000–2018","authors":"H. Regan, P. Rampal, Einar Örn Ólason, Guillaume Boutin, A. Korosov","doi":"10.5194/tc-17-1873-2023","DOIUrl":"https://doi.org/10.5194/tc-17-1873-2023","url":null,"abstract":"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.\u0000Notably, 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.\u0000","PeriodicalId":56315,"journal":{"name":"Cryosphere","volume":null,"pages":null},"PeriodicalIF":5.2,"publicationDate":"2023-05-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44764534","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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 significant change to its floating margins and has been identified as vulnerable to future climate warming. Inflow of warm Atlantic Intermediate Water (AIW) from the continental shelf has been observed in the vicinity of the Nioghalvfjerdsfjorden (79∘ N) Glacier calving front, but AIW penetration deep into the ice shelf cavity has not been observed directly. Here, we report temperature and salinity measurements from profiles in an epishelf lake, which provide the first direct evidence of AIW proximal to the grounding line of 79∘ N Glacier, over 50 km from the calving front. We also report evidence for partial un-grounding of the margin of 79∘ N Glacier taking place at the western end of the epishelf lake. Comparison of our measurements to those close to the calving front shows that AIW transits the cavity to reach the grounding line within a few months. The observations provide support for modelling studies that infer AIW-driven basal melt proximal to the grounding line and demonstrate that offshore oceanographic changes can be rapidly transmitted throughout the sub-ice-shelf cavity, with implications for near-future stability of the ice stream.
{"title":"Direct measurement of warm Atlantic Intermediate Water close to the grounding line of Nioghalvfjerdsfjorden (79° N) Glacier, northeast Greenland","authors":"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","doi":"10.5194/tc-17-1821-2023","DOIUrl":"https://doi.org/10.5194/tc-17-1821-2023","url":null,"abstract":"Abstract. The Northeast Greenland Ice Stream has recently seen significant\u0000change to its floating margins and has been identified as vulnerable to\u0000future climate warming. Inflow of warm Atlantic Intermediate Water (AIW)\u0000from the continental shelf has been observed in the vicinity of the\u0000Nioghalvfjerdsfjorden (79∘ N) Glacier calving front, but AIW\u0000penetration deep into the ice shelf cavity has not been observed directly.\u0000Here, we report temperature and salinity measurements from profiles in an\u0000epishelf lake, which provide the first direct evidence of AIW proximal to\u0000the grounding line of 79∘ N Glacier, over 50 km from the calving\u0000front. We also report evidence for partial un-grounding of the margin of\u000079∘ N Glacier taking place at the western end of the epishelf\u0000lake. Comparison of our measurements to those close to the calving front\u0000shows that AIW transits the cavity to reach the grounding line within a few\u0000months. The observations provide support for modelling studies that infer\u0000AIW-driven basal melt proximal to the grounding line and demonstrate that\u0000offshore oceanographic changes can be rapidly transmitted throughout the\u0000sub-ice-shelf cavity, with implications for near-future stability of the ice\u0000stream.\u0000","PeriodicalId":56315,"journal":{"name":"Cryosphere","volume":null,"pages":null},"PeriodicalIF":5.2,"publicationDate":"2023-05-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41825382","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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.
{"title":"Impact of tides on calving patterns at Kronebreen, Svalbard – insights from three-dimensional ice dynamical modelling","authors":"Felicity A. Holmes, E. V. van Dongen, R. Noormets, M. Pętlicki, N. Kirchner","doi":"10.5194/tc-17-1853-2023","DOIUrl":"https://doi.org/10.5194/tc-17-1853-2023","url":null,"abstract":"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.\u0000","PeriodicalId":56315,"journal":{"name":"Cryosphere","volume":null,"pages":null},"PeriodicalIF":5.2,"publicationDate":"2023-05-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47318054","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
K. Chan, C. Grima, A. Rutishauser, D. Young, R. Culberg, D. Blankenship
Abstract. Melting and refreezing processes in the firn of the Devon Ice Cap control meltwater infiltration and runoff across the ice cap, but their full spatial extent and effect on near-surface structure is difficult to measure with surface-based traverses or existing satellite remote sensing. Here, we derive the coherent component of the near-surface return from airborne 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 of dual-frequency airborne ice-penetrating radar to characterize the spatial and vertical near-surface structure of the Devon Ice Cap by leveraging differences in range resolution of the radar systems. Comparison with reflectivities using a thin layer reflectivity model, informed by surface-based radar and firn core measurements, indicates that the coherent component is sensitive to the near-surface firn structure composed of quasi-specular ice and firn layers, limited by the bandwidth-constrained radar range resolution. Our results suggest that average ice slab thickness throughout the Devon Ice Cap percolation zone ranges from 4.2 to 5.6 m. This implies conditions that can enable lateral meltwater runoff and potentially contribute to the total surface runoff routed through supraglacial rivers down glacier. Together with the incoherent component of the surface return previously studied, our dual-frequency approach provides an alternative method for characterizing bulk firn properties, particularly where high-resolution radar data are not available.
{"title":"Spatial characterization of near-surface structure and meltwater runoff conditions across the Devon Ice Cap from dual-frequency radar reflectivity","authors":"K. Chan, C. Grima, A. Rutishauser, D. Young, R. Culberg, D. Blankenship","doi":"10.5194/tc-17-1839-2023","DOIUrl":"https://doi.org/10.5194/tc-17-1839-2023","url":null,"abstract":"Abstract. Melting and refreezing processes in the firn of the Devon Ice\u0000Cap control meltwater infiltration and runoff across the ice cap, but their\u0000full spatial extent and effect on near-surface structure is difficult to\u0000measure with surface-based traverses or existing satellite remote sensing.\u0000Here, we derive the coherent component of the near-surface return from\u0000airborne ice-penetrating radar surveys over the Devon Ice Cap, Canadian Arctic,\u0000to characterize firn containing centimeter- to meter-thick ice layers (i.e.,\u0000ice slabs) formed from refrozen meltwater in firn. We assess the use of\u0000dual-frequency airborne ice-penetrating radar to characterize the spatial\u0000and vertical near-surface structure of the Devon Ice Cap by leveraging\u0000differences in range resolution of the radar systems. Comparison with\u0000reflectivities using a thin layer reflectivity model, informed by\u0000surface-based radar and firn core measurements, indicates that the coherent\u0000component is sensitive to the near-surface firn structure composed of\u0000quasi-specular ice and firn layers, limited by the bandwidth-constrained\u0000radar range resolution. Our results suggest that average ice slab thickness\u0000throughout the Devon Ice Cap percolation zone ranges from 4.2 to 5.6 m. This\u0000implies conditions that can enable lateral meltwater runoff and potentially\u0000contribute to the total surface runoff routed through supraglacial rivers\u0000down glacier. Together with the incoherent component of the surface return\u0000previously studied, our dual-frequency approach provides an alternative\u0000method for characterizing bulk firn properties, particularly where high-resolution radar data are not available.\u0000","PeriodicalId":56315,"journal":{"name":"Cryosphere","volume":null,"pages":null},"PeriodicalIF":5.2,"publicationDate":"2023-05-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47507462","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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.
{"title":"Permafrost degradation at two monitored palsa mires in north-west Finland","authors":"Mariana Verdonen, Alexander Störmer, E. Lotsari, Pasi Korpelainen, Benjamin Burkhard, A. Colpaert, T. Kumpula","doi":"10.5194/tc-17-1803-2023","DOIUrl":"https://doi.org/10.5194/tc-17-1803-2023","url":null,"abstract":"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.\u0000","PeriodicalId":56315,"journal":{"name":"Cryosphere","volume":null,"pages":null},"PeriodicalIF":5.2,"publicationDate":"2023-05-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47117187","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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.
{"title":"Reversible ice sheet thinning in the Amundsen Sea Embayment during the Late Holocene","authors":"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","doi":"10.5194/tc-17-1787-2023","DOIUrl":"https://doi.org/10.5194/tc-17-1787-2023","url":null,"abstract":"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.\u0000","PeriodicalId":56315,"journal":{"name":"Cryosphere","volume":null,"pages":null},"PeriodicalIF":5.2,"publicationDate":"2023-04-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44455782","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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