F. Paolo, A. Gardner, C. Greene, J. Nilsson, M. Schodlok, N. Schlegel, H. Fricker
Abstract. Antarctica's floating ice shelves modulate discharge of grounded ice into the ocean by providing a backstress. Ice shelf thinning and grounding line retreat have reduced this backstress, driving rapid drawdown of key unstable areas of the Antarctic Ice Sheet, leading to sea-level rise. If ice shelf loss continues, it may initiate irreversible glacier retreat through the marine ice sheet instability. Identification of areas undergoing significant change requires knowledge of spatial and temporal patterns in recent ice shelf loss. We used 26 years (1992–2017) of satellite-derived Antarctic ice shelf thickness, flow, and basal melt rates to construct a time-dependent dataset of ice shelf thickness and basal melt on a 3 km grid every 3 months. We used a novel data fusion approach, state-of-the-art satellite-derived velocities, and a new surface mass balance model. Our data revealed an overall pattern of thinning all around Antarctica, with a thinning slowdown starting around 2008 widespread across the Amundsen, Bellingshausen, and Wilkes sectors. We attribute this slowdown partly to modulation in external ocean forcing, altered in West Antarctica by negative feedbacks between ice shelf thinning rates and grounded ice flow, and sub-ice-shelf cavity geometry and basal melting. In agreement with earlier studies, the highest rates of ice shelf thinning are found for those ice shelves located in the Amundsen and Bellingshausen sectors. Our study reveals that over the 1992–2017 observational period the Amundsen and Bellingshausen ice shelves experienced a slight reduction in rates of basal melting, suggesting that high rates of thinning are largely a response to changes in ocean conditions that predate our satellite altimetry record, with shorter-term variability only resulting in small deviations from the long-term trend. Our work demonstrates that causal inference drawn from ice shelf thinning and basal melt rates must take into account complex feedbacks between thinning and ice advection and between ice shelf draft and basal melt rates.
{"title":"Widespread slowdown in thinning rates of West Antarctic ice shelves","authors":"F. Paolo, A. Gardner, C. Greene, J. Nilsson, M. Schodlok, N. Schlegel, H. Fricker","doi":"10.5194/tc-17-3409-2023","DOIUrl":"https://doi.org/10.5194/tc-17-3409-2023","url":null,"abstract":"Abstract. Antarctica's floating ice shelves modulate discharge of\u0000grounded ice into the ocean by providing a backstress. Ice shelf thinning\u0000and grounding line retreat have reduced this backstress, driving rapid\u0000drawdown of key unstable areas of the Antarctic Ice Sheet, leading to sea-level rise. If ice shelf loss continues, it may initiate irreversible\u0000glacier retreat through the marine ice sheet instability. Identification of\u0000areas undergoing significant change requires knowledge of spatial and\u0000temporal patterns in recent ice shelf loss. We used 26 years (1992–2017)\u0000of satellite-derived Antarctic ice shelf thickness, flow, and basal melt\u0000rates to construct a time-dependent dataset of ice shelf thickness and basal\u0000melt on a 3 km grid every 3 months. We used a novel data fusion approach,\u0000state-of-the-art satellite-derived velocities, and a new surface mass\u0000balance model. Our data revealed an overall pattern of thinning all around\u0000Antarctica, with a thinning slowdown starting around 2008 widespread across\u0000the Amundsen, Bellingshausen, and Wilkes sectors. We attribute this slowdown\u0000partly to modulation in external ocean forcing, altered in West Antarctica\u0000by negative feedbacks between ice shelf thinning rates and grounded ice\u0000flow, and sub-ice-shelf cavity geometry and basal melting. In agreement with\u0000earlier studies, the highest rates of ice shelf thinning are found for those ice\u0000shelves located in the Amundsen and Bellingshausen sectors. Our study\u0000reveals that over the 1992–2017 observational period the Amundsen and\u0000Bellingshausen ice shelves experienced a slight reduction in rates of basal\u0000melting, suggesting that high rates of thinning are largely a response to\u0000changes in ocean conditions that predate our satellite altimetry record,\u0000with shorter-term variability only resulting in small deviations from the\u0000long-term trend. Our work demonstrates that causal inference drawn from ice\u0000shelf thinning and basal melt rates must take into account complex feedbacks\u0000between thinning and ice advection and between ice shelf draft and basal\u0000melt rates.\u0000","PeriodicalId":56315,"journal":{"name":"Cryosphere","volume":" ","pages":""},"PeriodicalIF":5.2,"publicationDate":"2023-08-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45393516","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}
Leon J. Bührle, M. Marty, Lucie A. Eberhard, A. Stoffel, Elisabeth D. Hafner, Y. Bühler
Abstract. Information on snow depth and its spatial distribution is important for numerous applications, including natural hazard management, snow water equivalent estimation for hydropower, the study of the distribution and evolution of flora and fauna, and the validation of snow hydrological models. Due to its heterogeneity and complexity, specific remote sensing tools are required to accurately map the snow depth distribution in Alpine terrain. To cover large areas (>100 km2), airborne laser scanning (ALS) or aerial photogrammetry with large-format cameras is needed. While both systems require piloted aircraft for data acquisition, ALS is typically more expensive than photogrammetry but yields better results in forested terrain. While photogrammetry is slightly cheaper, it is limited due to its dependency on favourable acquisition conditions (weather, light conditions). In this study, we present photogrammetrically processed high-spatial-resolution (0.5 m) annual snow depth maps, recorded during the peak of winter over a 5-year period under different acquisition conditions over a study area around Davos, Switzerland. Compared to previously carried out studies, using the Vexcel UltraCam Eagle Mark 3 (M3) sensor improves the average ground sampling distance to 0.1 m at similar flight altitudes above ground. This allows for very detailed snow depth maps in open areas, calculated by subtracting a snow-off digital terrain model (DTM, acquired with ALS) from the snow-on digital surface models (DSMs) processed from the airborne imagery. Despite challenging acquisition conditions during the recording of the UltraCam images (clouds, shaded areas and fresh snow), 99 % of unforested areas were successfully photogrammetrically reconstructed. We applied masks (high vegetation, settlements, water, glaciers) to increase the reliability of the snow depth calculations. An extensive accuracy assessment was carried out using check points, the comparison to DSMs derived from unpiloted aerial systems and the comparison of snow-free DSM pixels to the ALS DTM. The results show a root mean square error of approximately 0.25 m for the UltraCam X and 0.15 m for the successor, the UltraCam Eagle M3. We developed a consistent and reliable photogrammetric workflow for accurate snow depth distribution mapping over large regions, capable of analysing snow distribution in complex terrain. This enables more detailed investigations on seasonal snow dynamics and can be used for numerous applications related to snow depth distribution, as well as serving as a ground reference for new modelling approaches and satellite-based snow depth mapping.
{"title":"Spatially continuous snow depth mapping by aeroplane photogrammetry for annual peak of winter from 2017 to 2021 in open areas","authors":"Leon J. Bührle, M. Marty, Lucie A. Eberhard, A. Stoffel, Elisabeth D. Hafner, Y. Bühler","doi":"10.5194/tc-17-3383-2023","DOIUrl":"https://doi.org/10.5194/tc-17-3383-2023","url":null,"abstract":"Abstract. Information on snow depth and its spatial distribution is important for\u0000numerous applications, including natural hazard management, snow water\u0000equivalent estimation for hydropower, the study of the distribution and\u0000evolution of flora and fauna, and the validation of snow hydrological\u0000models. Due to its heterogeneity and complexity, specific remote sensing\u0000tools are required to accurately map the snow depth distribution in Alpine\u0000terrain. To cover large areas (>100 km2),\u0000airborne laser scanning (ALS) or aerial photogrammetry with large-format\u0000cameras is needed. While both systems require piloted aircraft for data\u0000acquisition, ALS is typically more expensive than photogrammetry but yields\u0000better results in forested terrain. While photogrammetry is slightly\u0000cheaper, it is limited due to its dependency on favourable acquisition\u0000conditions (weather, light conditions). In this study, we present\u0000photogrammetrically processed high-spatial-resolution (0.5 m) annual snow\u0000depth maps, recorded during the peak of winter over a 5-year period under\u0000different acquisition conditions over a study area around Davos,\u0000Switzerland. Compared to previously carried out studies, using the Vexcel\u0000UltraCam Eagle Mark 3 (M3) sensor improves the average ground sampling distance to\u00000.1 m at similar flight altitudes above ground. This allows for very\u0000detailed snow depth maps in open areas, calculated by subtracting a snow-off\u0000digital terrain model (DTM, acquired with ALS) from the snow-on digital\u0000surface models (DSMs) processed from the airborne imagery. Despite\u0000challenging acquisition conditions during the recording of the UltraCam\u0000images (clouds, shaded areas and fresh snow), 99 % of unforested areas\u0000were successfully photogrammetrically reconstructed. We applied masks (high\u0000vegetation, settlements, water, glaciers) to increase the reliability of the\u0000snow depth calculations. An extensive accuracy assessment was carried out\u0000using check points, the comparison to DSMs derived from unpiloted aerial\u0000systems and the comparison of snow-free DSM pixels to the ALS DTM. The\u0000results show a root mean square error of approximately 0.25 m for the\u0000UltraCam X and 0.15 m for the successor, the UltraCam Eagle M3. We developed\u0000a consistent and reliable photogrammetric workflow for accurate snow depth\u0000distribution mapping over large regions, capable of analysing snow\u0000distribution in complex terrain. This enables more detailed investigations\u0000on seasonal snow dynamics and can be used for numerous applications related\u0000to snow depth distribution, as well as serving as a ground reference for new\u0000modelling approaches and satellite-based snow depth mapping.\u0000","PeriodicalId":56315,"journal":{"name":"Cryosphere","volume":" ","pages":""},"PeriodicalIF":5.2,"publicationDate":"2023-08-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47568364","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. Leads in sea ice cover have been studied extensively because of the climatic relevance of the intense ocean–atmosphere heat exchange that occurs during winter. Leads are also preferential locations of heat exchange and melting in early summer, but their oceanography and climate relevance, if any, remains largely unexplored during summertime. In particular, the development of a near-surface temperature maximum (NSTM) layer typically 10–30 m deep under different Arctic basins has been observationally related to the penetration of solar radiation through the leads. These observations reveal that the concatenation of calm and wind events in the leads could facilitate the development of the NSTM layer. Using numerical modeling and an idealized framework, this study investigates the formation of the NSTM layer under a summer lead exposed to a combination of calm and moderate wind periods. During the calm period, solar heat accumulates in the upper layers under the lead. Near-surface convection cells are generated daily, extending from the lead sides to its center. Convection cells affect the heat storage in the mixed layer under the lead and the adjacent ice cap. A subsequent wind event (and corresponding ice drift) mixes and spreads fresh and cold meltwater into the warm layers near the surface. Surface mixing results in temperatures in the near-surface layers that are lower than in the deeper layers, where the impact of the surface stresses is weaker. Additionally, the warm waters initially located under the lead surface stretch and spread horizontally. Thus, an NSTM layer is formed. The study analyzes the sensitivity of the depth and temperature of the NSTM layer to buoyancy forcing, wind intensity, ice drift, stratification, and lead geometry. Numerical results suggest that the NSTM layer appears with moderate wind and ice drift and disappears when the wind intensity is higher than 9 m s−1. Depending on the background stratification, the calm period reinforces or becomes critical in NSTM layer formation. According to the results, ice drift is key to the development of the NSTM layer.
摘要由于冬季发生的强烈海洋-大气热交换的气候相关性，海冰覆盖中的铅已被广泛研究。铅也是初夏热交换和融化的首选地点，但它们的海洋学和气候相关性，如果有的话，在夏季仍未得到很大程度的探索。特别是，在不同的北极盆地下，一个典型的10 - 30 m深的近地表最高温度(NSTM)层的发展，在观测上与太阳辐射穿过引线的穿透有关。这些观测结果表明，导联中的平静事件和风事件的串联可以促进NSTM层的发展。利用数值模拟和一个理想化的框架，本研究调查了夏季铅暴露在平静和温和风期的组合下NSTM层的形成。在平静期，太阳热量在铅下的上层积聚。近地表对流单元每天都在产生，从前边一直延伸到中心。对流细胞影响铅和邻近冰盖下的混合层中的热量储存。随后的风事件(以及相应的冰漂移)将新鲜和冷的融水混合并传播到靠近地表的温暖层中。表面混合导致近表层温度低于深层温度，而深层温度受表面应力的影响较弱。此外，最初位于铅表面下的温暖水域伸展并水平扩散。因此，形成了一个NSTM层。该研究分析了NSTM层的深度和温度对浮力强迫、风强度、冰漂移、分层和铅几何形状的敏感性。数值结果表明，NSTM层以中等风和冰漂移出现，当风强度大于9 m s−1时消失。根据背景分层的不同，平静期在NSTM层的形成中会加强或变得至关重要。结果表明，冰的漂移是NSTM层发育的关键。
{"title":"A model for the Arctic mixed layer circulation under a summertime lead: implications for the near-surface temperature maximum formation","authors":"A. Alvarez","doi":"10.5194/tc-17-3343-2023","DOIUrl":"https://doi.org/10.5194/tc-17-3343-2023","url":null,"abstract":"Abstract. Leads in sea ice cover have been studied extensively because of the climatic relevance of the intense ocean–atmosphere heat exchange that occurs\u0000during winter. Leads are also preferential locations of heat exchange and melting in early summer, but their oceanography and climate relevance, if\u0000any, remains largely unexplored during summertime. In particular, the development of a near-surface temperature maximum (NSTM) layer typically\u000010–30 m deep under different Arctic basins has been observationally related to the penetration of solar radiation through the leads. These\u0000observations reveal that the concatenation of calm and wind events in the leads could facilitate the development of the NSTM layer. Using numerical\u0000modeling and an idealized framework, this study investigates the formation of the NSTM layer under a summer lead exposed to a combination of calm\u0000and moderate wind periods. During the calm period, solar heat accumulates in the upper layers under the lead. Near-surface convection cells are\u0000generated daily, extending from the lead sides to its center. Convection cells affect the heat storage in the mixed layer under the lead and the\u0000adjacent ice cap. A subsequent wind event (and corresponding ice drift) mixes and spreads fresh and cold meltwater into the warm layers near the\u0000surface. Surface mixing results in temperatures in the near-surface layers that are lower than in the deeper layers, where the impact of the surface\u0000stresses is weaker. Additionally, the warm waters initially located under the lead surface stretch and spread horizontally. Thus, an NSTM layer is\u0000formed. The study analyzes the sensitivity of the depth and temperature of the NSTM layer to buoyancy forcing, wind intensity, ice drift, stratification,\u0000and lead geometry. Numerical results suggest that the NSTM layer appears with moderate wind and ice drift and disappears when the wind intensity is\u0000higher than 9 m s−1. Depending on the background stratification, the calm period reinforces or becomes critical in NSTM layer\u0000formation. According to the results, ice drift is key to the development of the NSTM layer.\u0000","PeriodicalId":56315,"journal":{"name":"Cryosphere","volume":" ","pages":""},"PeriodicalIF":5.2,"publicationDate":"2023-08-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48957268","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}
Dotan Rotem, V. Lyakhovsky, H. Christiansen, Y. Harlavan, Y. Weinstein
Abstract. Deglaciation in Svalbard was followed by seawater ingression and deposition of marine (deltaic) sediments in fjord valleys, while elastic rebound resulted in fast land uplift and the exposure of these sediments to the atmosphere, whereby the formation of epigenetic permafrost was initiated. This was then followed by the accumulation of aeolian sediments, with syngenetic permafrost formation. Permafrost was studied in the eastern Adventdalen valley, Svalbard, 3–4 km from the maximum up-valley reach of post-deglaciation seawater ingression, and its ground ice was analysed for its chemistry. While ground ice in the syngenetic part is basically fresh, the epigenetic part has a frozen freshwater–saline water interface (FSI), with chloride concentrations increasing from the top of the epigenetic part (at 5.5 m depth) to about 15 % that of seawater at 11 m depth. We applied a one-dimensional freezing model to examine the rate of top-down permafrost formation, which could be accommodated by the observed frozen FSI. The model examined permafrost development under different scenarios of mean average air temperature, water freezing temperature and degree of pore-water freezing. We found that even at the relatively high air temperatures of the Early to mid-Holocene, permafrost could aggrade quite fast down to 20 to 37 m (the whole sediment fill of 25 m at this location) within 200 years. This, in turn, allowed freezing and preservation of the freshwater–saline water interface despite the relatively fast rebound rate, which apparently resulted in an increase in topographic gradients toward the sea. The permafrost aggradation rate could also be enhanced due to non-complete pore-water freezing. We conclude that freezing must have started immediately after the exposure of the marine sediment to atmospheric conditions.
{"title":"Permafrost saline water and Early to mid-Holocene permafrost aggradation in Svalbard","authors":"Dotan Rotem, V. Lyakhovsky, H. Christiansen, Y. Harlavan, Y. Weinstein","doi":"10.5194/tc-17-3363-2023","DOIUrl":"https://doi.org/10.5194/tc-17-3363-2023","url":null,"abstract":"Abstract. Deglaciation in Svalbard was followed by seawater\u0000ingression and deposition of marine (deltaic) sediments in fjord valleys,\u0000while elastic rebound resulted in fast land uplift and the exposure of these sediments to the atmosphere, whereby the formation of epigenetic permafrost was initiated. This was then followed by the accumulation of aeolian sediments, with syngenetic permafrost formation. Permafrost was studied in the eastern Adventdalen valley, Svalbard, 3–4 km from the maximum up-valley reach of\u0000post-deglaciation seawater ingression, and its ground ice was analysed for\u0000its chemistry. While ground ice in the syngenetic part is basically fresh,\u0000the epigenetic part has a frozen freshwater–saline water interface (FSI), with\u0000chloride concentrations increasing from the top of the epigenetic part (at\u00005.5 m depth) to about 15 % that of seawater at 11 m depth. We applied a one-dimensional freezing model to examine the rate of top-down permafrost\u0000formation, which could be accommodated by the observed frozen FSI. The model\u0000examined permafrost development under different scenarios of mean average\u0000air temperature, water freezing temperature and degree of pore-water\u0000freezing. We found that even at the relatively high air temperatures of the\u0000Early to mid-Holocene, permafrost could aggrade quite fast down to 20 to 37 m (the whole sediment fill of 25 m at this location) within 200 years. This, in turn, allowed freezing and preservation of the freshwater–saline water\u0000interface despite the relatively fast rebound rate, which apparently\u0000resulted in an increase in topographic gradients toward the sea. The\u0000permafrost aggradation rate could also be enhanced due to non-complete pore-water freezing. We conclude that freezing must have started immediately\u0000after the exposure of the marine sediment to atmospheric conditions.\u0000","PeriodicalId":56315,"journal":{"name":"Cryosphere","volume":" ","pages":""},"PeriodicalIF":5.2,"publicationDate":"2023-08-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43979485","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. We use a novel sea-ice lead climatology for the winters of 2002/03 to 2020/21 based on satellite observations with 1 km2 spatial resolution to identify predominant patterns in Arctic wintertime sea-ice leads. The causes for the observed spatial and temporal variabilities are investigated using ocean surface current velocities and eddy kinetic energies from an ocean model (Finite Element Sea Ice–Ice-Shelf–Ocean Model, FESOM) and winds from a regional climate model (CCLM) and ERA5 reanalysis, respectively. The presented investigation provides evidence for an influence of ocean bathymetry and associated currents on the mechanic weakening of sea ice and the accompanying occurrence of sea-ice leads with their characteristic spatial patterns. While the driving mechanisms for this observation are not yet understood in detail, the presented results can contribute to opening new hypotheses on ocean–sea-ice interactions. The individual contribution of ocean and atmosphere to regional lead dynamics is complex, and a deeper insight requires detailed mechanistic investigations in combination with considerations of coastal geometries. While the ocean influence on lead dynamics seems to act on a rather long-term scale (seasonal to interannual), the influence of wind appears to trigger sea-ice lead dynamics on shorter timescales of weeks to months and is largely controlled by individual events causing increased divergence. No significant pan-Arctic trends in wintertime leads can be observed.
{"title":"Patterns of wintertime Arctic sea-ice leads and their relation to winds and ocean currents","authors":"S. Willmes, G. Heinemann, F. Schnaase","doi":"10.5194/tc-17-3291-2023","DOIUrl":"https://doi.org/10.5194/tc-17-3291-2023","url":null,"abstract":"Abstract. We use a novel sea-ice lead climatology for the winters of 2002/03 to 2020/21 based on satellite observations with 1 km2 spatial resolution to identify predominant patterns in Arctic wintertime sea-ice leads. The causes for the observed spatial and temporal variabilities are investigated using ocean surface current velocities and eddy kinetic energies from an ocean model (Finite Element Sea Ice–Ice-Shelf–Ocean Model, FESOM) and winds from a regional climate model (CCLM) and ERA5 reanalysis, respectively. The presented investigation provides evidence for an influence of ocean bathymetry and associated currents on the mechanic weakening of sea ice and the accompanying occurrence of sea-ice leads with their characteristic spatial patterns. While the driving mechanisms for this observation are not yet understood in detail, the presented results can contribute to opening new hypotheses on ocean–sea-ice interactions. The individual contribution of ocean and atmosphere to regional lead dynamics is complex, and a deeper insight requires detailed mechanistic investigations in combination with considerations of coastal geometries. While the ocean influence on lead dynamics seems to act on a rather long-term scale (seasonal to interannual), the influence of wind appears to trigger sea-ice lead dynamics on shorter timescales of weeks to months and is largely controlled by individual events causing increased divergence. No significant pan-Arctic trends in wintertime leads can be observed.\u0000","PeriodicalId":56315,"journal":{"name":"Cryosphere","volume":" ","pages":""},"PeriodicalIF":5.2,"publicationDate":"2023-08-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45672204","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}
Y. Onuma, Koji Fujita, N. Takeuchi, M. Niwano, T. Aoki
Abstract. Cryoconite holes (CHs) are water-filled cylindrical holes with cryoconite (dark-coloured sediment) deposited at their bottoms, forming on ablating ice surfaces of glaciers and ice sheets worldwide. Because the collapse of CHs may disperse cryoconite on the ice surface, thereby decreasing the ice surface albedo, accurate simulation of the temporal changes in CH depth is essential for understanding ice surface melt. We established a novel model that simulates the temporal changes in CH depth using heat budgets calculated independently at the ice surface and CH bottom based on hole-shaped geometry. We evaluated the model with in situ observations of the CH depths on the Qaanaaq ice cap in northwestern Greenland during the 2012, 2014, and 2017 melt seasons. The model reproduced the observed depth changes and timing of CH collapse well. Although earlier models have shown that CH depth tends to be deeper when downward shortwave radiation is intense, our sensitivity tests suggest that deeper CH tends to form when the diffuse component of downward shortwave radiation is dominant, whereas CHs tend to be shallower when the direct component is dominant. In addition, the total heat flux to the CH bottom is dominated by shortwave radiation transmitted through ice rather than that directly from the CH mouths when the CH is deeper than 0.01 m. Because the shortwave radiation transmitted through ice can reach the CH bottom regardless of CH diameter, CH depth is unlikely to be correlated with CH diameter. The relationship is consistent with previous observational studies. Furthermore, the simulations highlighted that the difference in albedo between ice surface and CH bottom was a key factor for reproducing the timing of CH collapse. It implies that lower ice surface albedo could induce CH collapse and thus cause further lowering of the albedo. Heat component analysis suggests that CH depth is governed by the balance between the intensity of the diffuse component of downward shortwave radiation and the turbulent heat transfer. Therefore, these meteorological conditions may be important factors contributing to the recent surface darkening of the Greenland ice sheet and other glaciers via the redistribution of CHs.
{"title":"Modelling the development and decay of cryoconite holes in northwestern Greenland","authors":"Y. Onuma, Koji Fujita, N. Takeuchi, M. Niwano, T. Aoki","doi":"10.5194/tc-17-3309-2023","DOIUrl":"https://doi.org/10.5194/tc-17-3309-2023","url":null,"abstract":"Abstract. Cryoconite holes (CHs) are water-filled cylindrical holes with cryoconite (dark-coloured sediment) deposited at their bottoms, forming on ablating\u0000ice surfaces of glaciers and ice sheets worldwide. Because the collapse of CHs may disperse cryoconite on the ice surface, thereby decreasing the\u0000ice surface albedo, accurate simulation of the temporal changes in CH depth is essential for understanding ice surface melt. We established a novel\u0000model that simulates the temporal changes in CH depth using heat budgets calculated independently at the ice surface and CH bottom based on\u0000hole-shaped geometry. We evaluated the model with in situ observations of the CH depths on the Qaanaaq ice cap in northwestern Greenland during the\u00002012, 2014, and 2017 melt seasons. The model reproduced the observed depth changes and timing of CH collapse well. Although earlier models have\u0000shown that CH depth tends to be deeper when downward shortwave radiation is intense, our sensitivity tests suggest that deeper CH tends to form when\u0000the diffuse component of downward shortwave radiation is dominant, whereas CHs tend to be shallower when the direct component is dominant. In\u0000addition, the total heat flux to the CH bottom is dominated by shortwave radiation transmitted through ice rather than that directly from the\u0000CH mouths when the CH is deeper than 0.01 m. Because the shortwave radiation transmitted through ice can reach the CH bottom regardless of\u0000CH diameter, CH depth is unlikely to be correlated with CH diameter. The relationship is consistent with previous observational\u0000studies. Furthermore, the simulations highlighted that the difference in albedo between ice surface and CH bottom was a key factor for reproducing\u0000the timing of CH collapse. It implies that lower ice surface albedo could induce CH collapse and thus cause further lowering of the albedo. Heat\u0000component analysis suggests that CH depth is governed by the balance between the intensity of the diffuse component of downward shortwave radiation\u0000and the turbulent heat transfer. Therefore, these meteorological conditions may be important factors contributing to the recent surface darkening of\u0000the Greenland ice sheet and other glaciers via the redistribution of CHs.\u0000","PeriodicalId":56315,"journal":{"name":"Cryosphere","volume":" ","pages":""},"PeriodicalIF":5.2,"publicationDate":"2023-08-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42470333","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}
E. Alonso‐González, S. Gascoin, Sara Arioli, G. Picard
Abstract. The assimilation of data from Earth observation satellites into numerical models is considered to be the path forward to estimate snow cover distribution in mountain catchments, providing accurate information on the mountainous snow water equivalent (SWE). The land surface temperature (LST) can be observed from space, but its potential to improve SWE simulations remains underexplored. This is likely due to the insufficient temporal or spatial resolution offered by the current thermal infrared (TIR) missions. However, three planned missions will provide global-scale TIR data at much higher spatiotemporal resolution in the coming years. To investigate the value of TIR data to improve SWE estimation, we developed a synthetic data assimilation (DA) experiment at five snow-dominated sites covering a latitudinal gradient in the Northern Hemisphere. We generated synthetic true LST and SWE series by forcing an energy balance snowpack model with the ERA5-Land reanalysis. We used this synthetic true LST to recover the synthetic true SWE from a degraded version of ERA5-Land. We defined different observation scenarios to emulate the revisiting times of Landsat 8 (16 d) and the Thermal infraRed Imaging Satellite for High-resolution Natural resource Assessment (TRISHNA) (3 d) while accounting for cloud cover. We replicated the experiments 100 times at each experimental site to assess the robustness of the assimilation process with respect to cloud cover under both revisiting scenarios. We performed the assimilation using two different approaches: a sequential scheme (particle filter) and a smoother (particle batch smoother). The results show that LST DA using the smoother reduced the normalized root mean square error (nRMSE) of the SWE simulations from 61 % (open loop) to 17 % and 13 % for 16 d revisit and 3 d revisit respectively in the absence of clouds. We found similar but higher nRMSE values by removing observations due to cloud cover but with a substantial increase in the standard deviation of the nRMSE of the replicates, highlighting the importance of revisiting times in the stability of the assimilation performance. The smoother largely outperformed the particle filter algorithm, suggesting that the capability of a smoother to propagate the information along the season is key to exploit LST information for snow modelling. Finally, we have compared the benefit of assimilating LST with synthetic observations of fractional snow cover area (FSCA). LST DA performed better than FSCA DA in all the study sites, suggesting that the information provided by LST is not limited to the duration of the snow season. These results suggest that the LST data assimilation has an underappreciated potential to improve snowpack simulations and highlight the value of upcoming TIR missions to advance snow hydrology.
{"title":"Exploring the potential of thermal infrared remote sensing to improve a snowpack model through an observing system simulation experiment","authors":"E. Alonso‐González, S. Gascoin, Sara Arioli, G. Picard","doi":"10.5194/tc-17-3329-2023","DOIUrl":"https://doi.org/10.5194/tc-17-3329-2023","url":null,"abstract":"Abstract. The assimilation of data from Earth observation satellites into\u0000numerical models is considered to be the path forward to estimate snow cover\u0000distribution in mountain catchments, providing accurate information on the\u0000mountainous snow water equivalent (SWE). The land surface temperature (LST)\u0000can be observed from space, but its potential to improve SWE simulations\u0000remains underexplored. This is likely due to the insufficient temporal or\u0000spatial resolution offered by the current thermal infrared (TIR) missions.\u0000However, three planned missions will provide global-scale TIR data at much\u0000higher spatiotemporal resolution in the coming years. To investigate the value of TIR data to improve SWE estimation, we developed\u0000a synthetic data assimilation (DA) experiment at five snow-dominated sites\u0000covering a latitudinal gradient in the Northern Hemisphere. We generated\u0000synthetic true LST and SWE series by forcing an energy balance snowpack\u0000model with the ERA5-Land reanalysis. We used this synthetic true LST to\u0000recover the synthetic true SWE from a degraded version of ERA5-Land. We\u0000defined different observation scenarios to emulate the revisiting times of\u0000Landsat 8 (16 d) and the Thermal infraRed Imaging Satellite for\u0000High-resolution Natural resource Assessment (TRISHNA) (3 d) while\u0000accounting for cloud cover. We replicated the experiments 100 times at each\u0000experimental site to assess the robustness of the assimilation process with\u0000respect to cloud cover under both revisiting scenarios. We performed the\u0000assimilation using two different approaches: a sequential scheme (particle\u0000filter) and a smoother (particle batch smoother). The results show that LST DA using the smoother reduced the normalized root\u0000mean square error (nRMSE) of the SWE simulations from 61 % (open loop) to\u000017 % and 13 % for 16 d revisit and 3 d revisit respectively in the\u0000absence of clouds. We found similar but higher nRMSE values by removing\u0000observations due to cloud cover but with a substantial increase in the\u0000standard deviation of the nRMSE of the replicates, highlighting the\u0000importance of revisiting times in the stability of the assimilation\u0000performance. The smoother largely outperformed the particle filter\u0000algorithm, suggesting that the capability of a smoother to propagate the\u0000information along the season is key to exploit LST information for snow\u0000modelling. Finally, we have compared the benefit of assimilating LST with\u0000synthetic observations of fractional snow cover area (FSCA). LST DA\u0000performed better than FSCA DA in all the study sites, suggesting that the\u0000information provided by LST is not limited to the duration of the snow\u0000season. These results suggest that the LST data assimilation has an\u0000underappreciated potential to improve snowpack simulations and highlight the\u0000value of upcoming TIR missions to advance snow hydrology.\u0000","PeriodicalId":56315,"journal":{"name":"Cryosphere","volume":" ","pages":""},"PeriodicalIF":5.2,"publicationDate":"2023-08-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48549670","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}
I. Glissenaar, J. Landy, D. Babb, G. Dawson, S. Howell
Abstract. This study presents a long-term winter sea ice thickness proxy product for the Canadian Arctic based on a random forest regression model – applied to ice charts and scatterometer data, trained on CryoSat-2 observations, and applying an ice type–sea ice thickness correction using the Pan-Arctic Ice Ocean Modeling and Assimilation System (PIOMAS) – that provides 25 years of sea ice thickness in the Beaufort Sea, Baffin Bay, and, for the first time, the Canadian Arctic Archipelago. An evaluation of the product with in situ sea ice thickness measurements shows that the presented sea ice thickness proxy product correctly estimates the magnitudes of the ice thickness and accurately captures spatial and temporal variability. The product estimates sea ice thickness within 30 to 50 cm uncertainty from the model. The sea ice thickness proxy product shows that sea ice is thinning over most of the Canadian Arctic, with a mean trend of −0.82 cm yr−1 in April over the whole study area (corresponding to 21 cm thinning over the 25-year record), but that trends vary locally. The Beaufort Sea and Baffin Bay show significant negative trends during all months, though with peaks in November (−2.8 cm yr−1) and April (−1.5 cm yr−1), respectively. The Parry Channel, which is part of the Northwest Passage and relevant for shipping, shows significant thinning in autumn. The sea ice thickness proxy product provides, for the first time, the opportunity to study long-term trends and variability in sea ice thickness in the Canadian Arctic, including the narrow channels in the Canadian Arctic Archipelago.
{"title":"A long-term proxy for sea ice thickness in the Canadian Arctic: 1996–2020","authors":"I. Glissenaar, J. Landy, D. Babb, G. Dawson, S. Howell","doi":"10.5194/tc-17-3269-2023","DOIUrl":"https://doi.org/10.5194/tc-17-3269-2023","url":null,"abstract":"Abstract. This study presents a long-term winter sea ice thickness proxy product for the Canadian Arctic based on a random forest regression model – applied to ice charts and scatterometer data, trained on CryoSat-2 observations, and applying an ice type–sea ice thickness correction using the Pan-Arctic Ice Ocean Modeling and Assimilation System (PIOMAS) – that provides 25 years of sea ice thickness in the Beaufort Sea, Baffin Bay, and, for the first time, the Canadian Arctic Archipelago. An evaluation of the product with in situ sea ice thickness measurements shows that the presented sea ice thickness proxy product correctly estimates the magnitudes of the ice thickness and accurately captures spatial and temporal variability. The product estimates sea ice thickness within 30 to 50 cm uncertainty from the model. The sea ice thickness proxy product shows that sea ice is thinning over most of the Canadian Arctic, with a mean trend of −0.82 cm yr−1 in April over the whole study area (corresponding to 21 cm thinning over the 25-year record), but that trends vary locally. The Beaufort Sea and Baffin Bay show significant negative trends during all months, though with peaks in November (−2.8 cm yr−1) and April (−1.5 cm yr−1), respectively. The Parry Channel, which is part of the Northwest Passage and relevant for shipping, shows significant thinning in autumn. The sea ice thickness proxy product provides, for the first time, the opportunity to study long-term trends and variability in sea ice thickness in the Canadian Arctic, including the narrow channels in the Canadian Arctic Archipelago.\u0000","PeriodicalId":56315,"journal":{"name":"Cryosphere","volume":" ","pages":""},"PeriodicalIF":5.2,"publicationDate":"2023-08-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43963712","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}
F. Brun, O. King, M. Réveillet, C. Amory, Anton Planchot, E. Berthier, A. Dehecq, T. Bolch, Kévin Fourteau, J. Brondex, M. Dumont, C. Mayer, S. Leinss, R. Hugonnet, P. Wagnon
Abstract. The South Col Glacier is a small body of ice and snow (approx. 0.2 km2) located at the very high elevation of 8000 m a.s.l. (above sea level) on the southern ridge of Mt. Everest. A recent study by Potocki et al. (2022) proposed that South Col Glacier is rapidly losing mass. This is in contradiction to our comparison of two digital elevation models derived from aerial photographs taken in December 1984 and a stereo Pléiades satellite acquisition from March 2017, from which we estimate a mean elevation change of 0.01 ± 0.05 m a−1. To reconcile these results, we investigate some aspects of the surface energy and mass balance of South Col Glacier. From satellite images and a simple model of snow compaction and erosion, we show that wind erosion has a major impact on the surface mass balance due to the strong seasonality in precipitation and wind and that it cannot be neglected. Additionally, we show that the melt amount predicted by a surface energy and mass balance model is very sensitive to the model structure and implementation. Contrary to previous findings, melt is likely not a dominant ablation process on this glacier, which remains mostly snow-covered during the monsoon.
摘要南科尔冰川(South Col Glacier)是一个小的冰雪体。0.2平方公里)，位于海拔8000米的高海拔地区。(海拔以上)在珠穆朗玛峰的南山脊上。Potocki等人(2022)最近的一项研究提出，南冷冰川正在迅速失去质量。这与我们对1984年12月拍摄的航空照片和2017年3月获得的立体声placimiades卫星拍摄的两个数字高程模型的比较相矛盾，我们从中估计平均高程变化为0.01±0.05 ma - 1。为了调和这些结果，我们研究了南冷冰川表面能量和物质平衡的一些方面。从卫星图像和一个简单的雪压实和侵蚀模型中，我们表明，由于降水和风的强烈季节性，风蚀对地表物质平衡有重大影响，并且不可忽视。此外，我们还表明，表面能和质量平衡模型预测的熔体量对模型结构和实现非常敏感。与先前的发现相反，融化可能不是这个冰川的主要消融过程，在季风期间，它仍然大部分被雪覆盖。
{"title":"Everest South Col Glacier did not thin during the period 1984–2017","authors":"F. Brun, O. King, M. Réveillet, C. Amory, Anton Planchot, E. Berthier, A. Dehecq, T. Bolch, Kévin Fourteau, J. Brondex, M. Dumont, C. Mayer, S. Leinss, R. Hugonnet, P. Wagnon","doi":"10.5194/tc-17-3251-2023","DOIUrl":"https://doi.org/10.5194/tc-17-3251-2023","url":null,"abstract":"Abstract. The South Col Glacier is a small body of ice and snow (approx. 0.2 km2) located at the very high elevation of 8000 m a.s.l. (above sea level) on the southern ridge of Mt. Everest. A recent study by Potocki et al. (2022) proposed that South Col Glacier is rapidly losing mass. This is in contradiction to our comparison of two digital elevation models derived from aerial photographs taken in December 1984 and a stereo Pléiades satellite acquisition from March 2017, from which we estimate a mean elevation change of 0.01 ± 0.05 m a−1. To reconcile these results, we investigate some aspects of the surface energy and mass balance of South Col Glacier. From satellite images and a simple model of snow compaction and erosion, we show that wind erosion has a major impact on the surface mass balance due to the strong seasonality in precipitation and wind and that it cannot be neglected. Additionally, we show that the melt amount predicted by a surface energy and mass balance model is very sensitive to the model structure and implementation. Contrary to previous findings, melt is likely not a dominant ablation process on this glacier, which remains mostly snow-covered during the monsoon.\u0000","PeriodicalId":56315,"journal":{"name":"Cryosphere","volume":" ","pages":""},"PeriodicalIF":5.2,"publicationDate":"2023-08-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43216723","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. Throughout winter, the winds of migrating weather systems drive the recurrent opening of sea ice leads from Alaska's northernmost headland, Point Barrow. As leads extend offshore into the Beaufort and Chukchi seas, they produce sea ice velocity discontinuities that are challenging to represent in models. We investigate how synoptic wind patterns form leads originating from Point Barrow and influence patterns of sea ice drift across the Pacific Arctic. We identify 135 leads from satellite thermal infrared imagery between January–April 2000–2020 and generate an ensemble of lead-opening sequences by averaging atmospheric conditions and ice velocity across events. On average, leads open as migrating atmospheric highs drive differing ice–coast interactions across Point Barrow. Northerly winds compress the Beaufort ice pack against the coast over several days, slowing ice drift. As winds west of Point Barrow shift offshore, the ice cover fractures and a lead extends from the headland into the pack interior. Ice west of the lead accelerates as it separates from the coast, drifting twice as fast (relative to winds) as ice east of the lead, which remains coastally bound. Consequently, sea ice drift and its contribution to climatological ice circulation becomes zonally asymmetric across Point Barrow. These findings highlight how coastal boundaries modify the response of the consolidated ice pack to wind forcing in winter, producing spatially varying regimes of ice stress and kinematics. Observed connections between winds, ice drift, and lead opening provide test cases for sea ice models aiming to capture realistic ice transport during these recurrent deformation events.
{"title":"Atmospheric highs drive asymmetric sea ice drift during lead opening from Point Barrow","authors":"MacKenzie E. Jewell, J. Hutchings, C. Geiger","doi":"10.5194/tc-17-3229-2023","DOIUrl":"https://doi.org/10.5194/tc-17-3229-2023","url":null,"abstract":"Abstract. Throughout winter, the winds of migrating weather systems drive the recurrent opening of sea ice leads from Alaska's northernmost headland, Point Barrow. As leads extend offshore into the Beaufort and Chukchi seas, they produce sea ice velocity discontinuities that are challenging to represent in models. We investigate how synoptic wind patterns form leads originating from Point Barrow and influence patterns of sea ice drift across the Pacific Arctic. We identify 135 leads from satellite thermal infrared imagery between January–April 2000–2020 and generate an ensemble of lead-opening sequences by averaging atmospheric conditions and ice velocity across events. On average, leads open as migrating atmospheric highs drive differing ice–coast interactions across Point Barrow. Northerly winds compress the Beaufort ice pack against the coast over several days, slowing ice drift. As winds west of Point Barrow shift offshore, the ice cover fractures and a lead extends from the headland into the pack interior. Ice west of the lead accelerates as it separates from the coast, drifting twice as fast (relative to winds) as ice east of the lead, which remains coastally bound. Consequently, sea ice drift and its contribution to climatological ice circulation becomes zonally asymmetric across Point Barrow. These findings highlight how coastal boundaries modify the response of the consolidated ice pack to wind forcing in winter, producing spatially varying regimes of ice stress and kinematics. Observed connections between winds, ice drift, and lead opening provide test cases for sea ice models aiming to capture realistic ice transport during these recurrent deformation events.\u0000","PeriodicalId":56315,"journal":{"name":"Cryosphere","volume":" ","pages":""},"PeriodicalIF":5.2,"publicationDate":"2023-08-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45921171","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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