E. Lambert, A. Jüling, R. V. D. van de Wal, P. Holland
Abstract. A major source of uncertainty in future sea level projections is the ocean-driven basal melt of Antarctic ice shelves. While ice sheet models require a kilometre-scale resolution to realistically resolve ice shelf stability and grounding line migration, global or regional 3D ocean models are computationally too expensive to produce basal melt forcing fields at this resolution on long timescales. To bridge this resolution gap, we introduce the 2D numerical model LADDIE (one-layer Antarctic model for dynamical downscaling of ice–ocean exchanges), which allows for the computationally efficient modelling of detailed basal melt fields. The model is open source and can be applied easily to different geometries or different ocean forcings. The aim of this study is threefold: to introduce the model to the community, to demonstrate its application and performance in two use cases, and to describe and interpret new basal melt patterns simulated by this model. The two use cases are the small Crosson–Dotson Ice Shelf in the warm Amundsen Sea region and the large Filchner–Ronne Ice Shelf in the cold Weddell Sea. At ice-shelf-wide scales, LADDIE reproduces observed patterns of basal melting and freezing in warm and cold environments without the need to re-tune parameters for individual ice shelves. At scales of 0.5–5 km, which are typically unresolved by 3D ocean models and poorly constrained by observations, LADDIE produces plausible basal melt patterns. Most significantly, the simulated basal melt patterns are physically consistent with the applied ice shelf topography. These patterns are governed by the topographic steering and Coriolis deflection of meltwater flows, two processes that are poorly represented in basal melt parameterisations. The kilometre-scale melt patterns simulated by LADDIE include enhanced melt rates in grounding zones and basal channels and enhanced melt or freezing in shear margins. As these regions are critical for ice shelf stability, we conclude that LADDIE can provide detailed basal melt patterns at the essential resolution that ice sheet models require. The physical consistency between the applied geometry and the simulated basal melt fields indicates that LADDIE can play a valuable role in the development of coupled ice–ocean modelling.
{"title":"Modelling Antarctic ice shelf basal melt patterns using the one-layer Antarctic model for dynamical downscaling of ice–ocean exchanges (LADDIE v1.0)","authors":"E. Lambert, A. Jüling, R. V. D. van de Wal, P. Holland","doi":"10.5194/tc-17-3203-2023","DOIUrl":"https://doi.org/10.5194/tc-17-3203-2023","url":null,"abstract":"Abstract. A major source of uncertainty in future sea level projections is the ocean-driven basal melt of Antarctic ice shelves. While ice sheet models require a kilometre-scale resolution to realistically resolve ice shelf stability and grounding line migration, global or regional 3D ocean models are computationally too expensive to produce basal melt forcing fields at this resolution on long timescales. To bridge this resolution gap, we introduce the 2D numerical model LADDIE (one-layer Antarctic model for dynamical downscaling of ice–ocean exchanges), which allows for the computationally efficient modelling of detailed basal melt fields. The model is open source and can be applied easily to different geometries or different ocean forcings. The aim of this study is threefold: to introduce the model to the community, to demonstrate its application and performance in two use cases, and to describe and interpret new basal melt patterns simulated by this model. The two use cases are the small Crosson–Dotson Ice Shelf in the warm Amundsen Sea region and the large Filchner–Ronne Ice Shelf in the cold Weddell Sea. At ice-shelf-wide scales, LADDIE reproduces observed patterns of basal melting and freezing in warm and cold environments without the need to re-tune parameters for individual ice shelves. At scales of 0.5–5 km, which are typically unresolved by 3D ocean models and poorly constrained by observations, LADDIE produces plausible basal melt patterns. Most significantly, the simulated basal melt patterns are physically consistent with the applied ice shelf topography. These patterns are governed by the topographic steering and Coriolis deflection of meltwater flows, two processes that are poorly represented in basal melt parameterisations. The kilometre-scale melt patterns simulated by LADDIE include enhanced melt rates in grounding zones and basal channels and enhanced melt or freezing in shear margins. As these regions are critical for ice shelf stability, we conclude that LADDIE can provide detailed basal melt patterns at the essential resolution that ice sheet models require. The physical consistency between the applied geometry and the simulated basal melt fields indicates that LADDIE can play a valuable role in the development of coupled ice–ocean modelling.\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":"41643699","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}
Oona Leppiniemi, O. Karjalainen, J. Aalto, M. Luoto, J. Hjort
Abstract. Anthropogenic climate change threatens northern permafrost environments. This compromises the existence of permafrost landforms, such as palsas and peat plateaus, which have been assessed to be critically endangered habitats. In this study, we integrated geospatial datasets and statistical methods to model the suitable environments for palsas and peat plateaus across the Northern Hemisphere permafrost region. The models were calibrated using data from years 1950–2000. The effects of climate change on the suitable environments for the landforms were assessed by using low-, moderate-, and high-emissions scenarios (Representative Concentration Pathway climate scenarios: RCP2.6, RCP4.5, and RCP8.5, respectively) for two periods (2041–2060 and 2061–2080). Hotspots for palsa and peat plateau environments occurred in northern Europe, western Siberia, and subarctic Canada. Climate change was predicted to cause an almost complete loss (decrease of 98.2 %) of suitable environmental spaces under the high-emissions scenario by 2061–2080, while under low- and moderate-emissions scenarios the predicted loss was 76.3 % and 89.3 % respectively. Our modeling results are in line with previously published thermokarst data pointing out areas of recent degradation of palsa and peat plateau environments. Our results provide new insights into the distribution of the permafrost landforms in less studied areas such as central and eastern Siberia. In addition, the predictions provide new understanding of the changing geoecological conditions of the circumpolar region with important implications for greenhouse gas emissions.
{"title":"Environmental spaces for palsas and peat plateaus are disappearing at a circumpolar scale","authors":"Oona Leppiniemi, O. Karjalainen, J. Aalto, M. Luoto, J. Hjort","doi":"10.5194/tc-17-3157-2023","DOIUrl":"https://doi.org/10.5194/tc-17-3157-2023","url":null,"abstract":"Abstract. Anthropogenic climate change threatens northern\u0000permafrost environments. This compromises the existence of permafrost\u0000landforms, such as palsas and peat plateaus, which have been assessed to be\u0000critically endangered habitats. In this study, we integrated geospatial\u0000datasets and statistical methods to model the suitable environments for\u0000palsas and peat plateaus across the Northern Hemisphere permafrost region.\u0000The models were calibrated using data from years 1950–2000. The effects of\u0000climate change on the suitable environments for the landforms were assessed\u0000by using low-, moderate-, and high-emissions scenarios (Representative\u0000Concentration Pathway climate scenarios: RCP2.6, RCP4.5, and RCP8.5,\u0000respectively) for two periods (2041–2060 and 2061–2080). Hotspots for\u0000palsa and peat plateau environments occurred in northern Europe, western\u0000Siberia, and subarctic Canada. Climate change was predicted to cause an\u0000almost complete loss (decrease of 98.2 %) of suitable environmental\u0000spaces under the high-emissions scenario by 2061–2080, while under low- and\u0000moderate-emissions scenarios the predicted loss was 76.3 % and 89.3 %\u0000respectively. Our modeling results are in line with previously published\u0000thermokarst data pointing out areas of recent degradation of palsa and peat\u0000plateau environments. Our results provide new insights into the distribution\u0000of the permafrost landforms in less studied areas such as central and\u0000eastern Siberia. In addition, the predictions provide new understanding of\u0000the changing geoecological conditions of the circumpolar region with\u0000important implications for greenhouse gas emissions.\u0000","PeriodicalId":56315,"journal":{"name":"Cryosphere","volume":" ","pages":""},"PeriodicalIF":5.2,"publicationDate":"2023-08-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47395672","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. Vidaller, E. Izagirre, L. M. Del río, E. Alonso‐González, F. Rojas-Heredia, E. Serrano, A. Moreno, J. López‐Moreno, J. Revuelto
Abstract. The Aneto glacier, although it may be considered a very small glacier (<0.5 km2), is the largest glacier in the Pyrenees. Its surface and thickness loss have been continuous in recent decades, and there have been signs of accelerated melting in recent years. In this study, thickness and surface losses of the Aneto glacier from 1981 to 2022 are investigated using historical aerial imagery, airborne lidar point clouds and unoccupied aerial vehicle (UAV) imagery. A ground-penetrating radar (GPR) survey conducted in 2020, combined with data from photogrammetric analyses, allowed us to reconstruct the current ice thickness and also the existing ice distribution in 1981 and 2011. Over the last 41 years, the total glacierised area has decreased by 64.7 %, and the ice thickness has decreased, on average, by 30.5 m. The mean remaining ice thickness in autumn 2022 was 11.9 m, as against the mean thickness of 32.9, 19.2 and 15.0 m reconstructed for 1981 and 2011 and observed in 2020, respectively. The results demonstrate the critical situation of the glacier, with an imminent segmentation into two smaller ice bodies and no evidence of an accumulation zone. We also found that the occurrence of an extremely hot and dry year, as observed in the 2021–2022 season, leads to a drastic degradation of the glacier, posing a high risk to the persistence of the Aneto glacier, a situation that could extend to the rest of the Pyrenean glaciers in a relatively short time.
{"title":"The Aneto glacier's (Central Pyrenees) evolution from 1981 to 2022: ice loss observed from historic aerial image photogrammetry and remote sensing techniques","authors":"I. Vidaller, E. Izagirre, L. M. Del río, E. Alonso‐González, F. Rojas-Heredia, E. Serrano, A. Moreno, J. López‐Moreno, J. Revuelto","doi":"10.5194/tc-17-3177-2023","DOIUrl":"https://doi.org/10.5194/tc-17-3177-2023","url":null,"abstract":"Abstract. The Aneto glacier, although it may be considered a very small\u0000glacier (<0.5 km2), is the largest glacier in the Pyrenees.\u0000Its surface and thickness loss have been continuous in recent decades, and\u0000there have been signs of accelerated melting in recent years. In this study,\u0000thickness and surface losses of the Aneto glacier from 1981 to 2022 are\u0000investigated using historical aerial imagery, airborne lidar point clouds\u0000and unoccupied aerial vehicle (UAV) imagery. A ground-penetrating radar (GPR) survey conducted in 2020, combined with data from\u0000photogrammetric analyses, allowed us to reconstruct the current ice\u0000thickness and also the existing ice distribution in 1981 and 2011. Over the\u0000last 41 years, the total glacierised area has decreased by 64.7 %, and the\u0000ice thickness has decreased, on average, by 30.5 m. The mean remaining ice\u0000thickness in autumn 2022 was 11.9 m, as against the mean thickness of 32.9, 19.2 and 15.0 m reconstructed for 1981 and 2011 and observed in 2020,\u0000respectively. The results demonstrate the critical situation of the glacier,\u0000with an imminent segmentation into two smaller ice bodies and no evidence of\u0000an accumulation zone. We also found that the occurrence of an extremely hot\u0000and dry year, as observed in the 2021–2022 season, leads to a drastic\u0000degradation of the glacier, posing a high risk to the persistence of the\u0000Aneto glacier, a situation that could extend to the rest of the Pyrenean\u0000glaciers in a relatively short time.\u0000","PeriodicalId":56315,"journal":{"name":"Cryosphere","volume":" ","pages":""},"PeriodicalIF":5.2,"publicationDate":"2023-08-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44641572","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}
Max Thomas, Briana Cate, J. Garnett, I. Smith, M. Vancoppenolle, C. Halsall
Abstract. We investigate the effect of partial dissolution on the transport of chemicals in sea ice. Physically plausible mechanisms are added to a brine convection model that decouples chemicals from convecting brine. The model is evaluated against a recent observational dataset where a suite of qualitatively similar chemicals (poly- and perfluoroalkylated substances, PFASs) with quantitatively different physico-chemical properties were frozen into growing sea ice. With no decoupling the model performs poorly – underestimating the measured concentrations of high-chain-length PFASs. A decoupling scheme where PFASs are decoupled from salinity as a constant fraction of their brine concentration and a scheme where decoupling is proportional to the brine salinity give better performance and bring the model into reasonable agreement with observations. A scheme where the decoupling is proportional to the internal sea-ice surface area performs poorly. All decoupling schemes capture a general enrichment of longer-chained PFASs and can produce concentrations in the uppermost sea-ice layers above that of the underlying water concentration, as observed. Our results show that decoupling from convecting brine can enrich chemical concentrations in growing sea ice and can lead to bulk chemical concentrations greater than that of the liquid from which the sea ice is growing. Brine convection modelling is useful for predicting the dynamics of chemicals with more complex behaviour than sea salt, highlighting the potential of these modelling tools for a range of biogeochemical research areas.
{"title":"The effect of partial dissolution on sea-ice chemical transport: a combined model–observational study using poly- and perfluoroalkylated substances (PFASs)","authors":"Max Thomas, Briana Cate, J. Garnett, I. Smith, M. Vancoppenolle, C. Halsall","doi":"10.5194/tc-17-3193-2023","DOIUrl":"https://doi.org/10.5194/tc-17-3193-2023","url":null,"abstract":"Abstract. We investigate the effect of partial dissolution on the transport of chemicals in sea ice. Physically plausible mechanisms are added to a brine convection model that decouples chemicals from convecting brine. The model is evaluated against a recent observational dataset where a suite of qualitatively similar chemicals (poly- and perfluoroalkylated substances, PFASs) with quantitatively different physico-chemical properties were frozen into growing sea ice. With no decoupling the model performs poorly – underestimating the measured concentrations of high-chain-length PFASs. A decoupling scheme where PFASs are decoupled from salinity as a constant fraction of their brine concentration and a scheme where decoupling is proportional to the brine salinity give better performance and bring the model into reasonable agreement with observations. A scheme where the decoupling is proportional to the internal sea-ice surface area performs poorly. All decoupling schemes capture a general enrichment of longer-chained PFASs and can produce concentrations in the uppermost sea-ice layers above that of the underlying water concentration, as observed. Our results show that decoupling from convecting brine can enrich chemical concentrations in growing sea ice and can lead to bulk chemical concentrations greater than that of the liquid from which the sea ice is growing. Brine convection modelling is useful for predicting the dynamics of chemicals with more complex behaviour than sea salt, highlighting the potential of these modelling tools for a range of biogeochemical research areas.","PeriodicalId":56315,"journal":{"name":"Cryosphere","volume":" ","pages":""},"PeriodicalIF":5.2,"publicationDate":"2023-08-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47803998","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}
Mathieu Le Breton, É. Larose, L. Baillet, Y. Lejeune, A. van Herwijnen
Abstract. The amount of water contained in a snowpack, known as snow water equivalent (SWE), is used to anticipate the amount of snowmelt that could supply hydroelectric power plants, fill water reservoirs, or sometimes cause flooding. This work introduces a wireless, non-destructive method for monitoring the SWE of a dry snowpack. The system is based on an array of low-cost passive radiofrequency identification (RFID) tags, placed under the snow and read at 865–868 MHz by a reader located above the snow. The SWE was deduced from the phase delay of the tag's backscattered response, which increases with the amount of snow traversed by the radiofrequency wave. Measurements taken in the laboratory, during snowfall events and over 4.5 months at the Col de Porte test field, were consistent with reference measurements of cosmic rays, precipitation and snow pits. SWE accuracy was ±18 kg m−2 throughout the season (averaged over three tags) and ±3 kg m−2 during dry snowfall events (averaged over data from two antennas and four or five tags). The overall uncertainty compared to snow weighing was ±10 % for snow density in the range 61–390 kg m−3. The main limitations observed were measurement bias caused by wet snow (biased data were discarded) and the need for phase unwrapping. The method has a number of advantages: it allows for continuous measurement (1 min sampling rate in dry snow), it can provide complementary measurement of tag temperature, it does not require the reception of external data, and it opens the way towards spatialized measurements. The results presented also demonstrate that RFID propagation-based sensing can remotely monitor the permittivity of a low-loss dielectric material with scientific-level accuracy.
{"title":"Monitoring snow water equivalent using the phase of RFID signals","authors":"Mathieu Le Breton, É. Larose, L. Baillet, Y. Lejeune, A. van Herwijnen","doi":"10.5194/tc-17-3137-2023","DOIUrl":"https://doi.org/10.5194/tc-17-3137-2023","url":null,"abstract":"Abstract. The amount of water contained in a snowpack, known as\u0000snow water equivalent (SWE), is used to anticipate the amount of snowmelt that could supply hydroelectric power plants, fill water reservoirs, or\u0000sometimes cause flooding. This work introduces a wireless, non-destructive\u0000method for monitoring the SWE of a dry snowpack. The system is based on an\u0000array of low-cost passive radiofrequency identification (RFID) tags, placed\u0000under the snow and read at 865–868 MHz by a reader located above the snow.\u0000The SWE was deduced from the phase delay of the tag's backscattered\u0000response, which increases with the amount of snow traversed by the\u0000radiofrequency wave. Measurements taken in the laboratory, during snowfall events and over\u00004.5 months at the Col de Porte test field, were consistent with reference\u0000measurements of cosmic rays, precipitation and snow pits. SWE accuracy was\u0000±18 kg m−2 throughout the season (averaged over three tags) and\u0000±3 kg m−2 during dry snowfall events (averaged over data from two\u0000antennas and four or five tags). The overall uncertainty compared to snow\u0000weighing was ±10 % for snow density in the\u0000range 61–390 kg m−3. The main limitations observed were measurement\u0000bias caused by wet snow (biased data were discarded) and the need for phase\u0000unwrapping. The method has a number of advantages: it allows for continuous\u0000measurement (1 min sampling rate in dry snow), it can provide complementary\u0000measurement of tag temperature, it does not require the reception of\u0000external data, and it opens the way towards spatialized measurements. The\u0000results presented also demonstrate that RFID propagation-based sensing can remotely monitor the permittivity of a low-loss dielectric material with\u0000scientific-level accuracy.\u0000","PeriodicalId":56315,"journal":{"name":"Cryosphere","volume":" ","pages":""},"PeriodicalIF":5.2,"publicationDate":"2023-08-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42042110","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. Arctic sea ice has declined in all seasons accompanied by rapid atmospheric warming. Here, the focus lies on the wider Fram Strait region where the connection between trends in observed near-surface variables (temperature, humidity, wind speed) and local sea ice conditions are analyzed. Reanalysis data from ERA5 and MERRA-2 and Special Sensor Microwave/Imager ARTIST Sea Ice (SSM/I-ASI) sea ice concentrations for the winters of 1992 to 2022 are used for the analyses. Two focus regions are identified for which trends are largest. In the western Nansen Basin (WNB), sea ice cover decreased by −10 % per decade with especially large open water areas in 2022, and temperature and humidity increased by up to 3.7 K and 0.29 g kg−1 per decade, respectively. In the Greenland sea region (GRL), trends were slightly smaller, with −4.7 % per decade for sea ice and up to 1.3 K and 0.15 g kg−1 per decade for temperature and humidity. Trends for wind speed were mostly not significant. As a next step, two typical flow directions for this region were studied: cold-air outbreaks with northerly winds originating from ice covered areas (off-ice flow) and warm-air intrusions with southerly winds from open ocean regions (on-ice flow). To identify possible relationships between sea ice changes and atmospheric trends, correlation maps were calculated, and the results for off- and on-ice flow were compared. Up to two thirds of the observed temperature and humidity variability in both regions are related to upstream sea ice variability and an influence of sea ice cover is still present up to 500 km downstream of the ice edge. In the marginal sea ice zone the impact of a decreasing sea ice cover in this region is largest for off-ice flow conditions during cold-air outbreaks.
摘要随着大气快速变暖，北极海冰在所有季节都在减少。在这里，重点放在弗拉姆海峡沿岸地区，在那里分析了观测到的近地表变量（温度、湿度、风速）的趋势与当地海冰条件之间的联系。分析使用了1992年至2022年冬季ERA5和MERRA-2以及特殊传感器微波/成像仪ARTIST海冰（SSM/I-ASI）海冰浓度的再分析数据。确定了两个趋势最大的重点区域。在南森盆地西部（WNB），海冰覆盖减少了−10 % 2022年，开放水域面积特别大，温度和湿度每十年增加3.7 K和0.29 g 千克−每十年一次。在格陵兰海域（GRL），趋势略小，为−4.7 % 海冰为每十年，最高可达1.3 K和0.15 g kg−温度和湿度为每十年1次。风速的趋势大多不显著。作为下一步，研究了该地区的两个典型流动方向：来自冰层覆盖地区的带有北风的冷空气爆发（冰外流动）和来自公海地区的带有南风的暖空气入侵（冰上流动）。为了确定海冰变化和大气趋势之间的可能关系，计算了相关图，并对冰下和冰上流动的结果进行了比较。在这两个地区观测到的温度和湿度变化中，多达三分之二与上游海冰变化有关，海冰覆盖的影响仍然存在，高达500 冰缘下游km处。在边缘海冰区，该地区海冰覆盖减少对冷空气爆发期间冰外流动条件的影响最大。
{"title":"Attributing near-surface atmospheric trends in the Fram Strait region to regional sea ice conditions","authors":"A. Schmitt, C. Lüpkes","doi":"10.5194/tc-17-3115-2023","DOIUrl":"https://doi.org/10.5194/tc-17-3115-2023","url":null,"abstract":"Abstract. Arctic sea ice has declined in all seasons accompanied by rapid atmospheric warming. Here, the focus lies on the\u0000wider Fram Strait region where the connection between trends in observed near-surface variables (temperature, humidity, wind speed) and local sea ice conditions are analyzed. Reanalysis data from ERA5 and MERRA-2 and Special Sensor Microwave/Imager ARTIST Sea Ice (SSM/I-ASI) sea ice concentrations for the winters of 1992 to 2022 are used for the analyses. Two focus regions are identified for which trends are largest. In the western Nansen Basin (WNB), sea ice cover decreased by −10 % per decade with especially large open water areas in 2022, and temperature and humidity increased by up to 3.7 K and 0.29 g kg−1 per decade, respectively. In the Greenland sea region (GRL), trends were slightly smaller, with −4.7 % per decade for sea ice and up to 1.3 K and 0.15 g kg−1 per decade for temperature and humidity. Trends for wind speed were mostly not significant. As a next step, two typical flow directions for this region were studied: cold-air outbreaks with northerly winds originating from ice covered areas (off-ice flow) and warm-air intrusions with southerly winds from open ocean regions (on-ice flow). To identify possible relationships between sea ice changes and atmospheric trends, correlation maps were calculated, and the results for off- and on-ice flow were compared. Up to two thirds of the observed temperature and humidity variability in both regions are related to upstream sea ice variability and an influence of sea ice cover is still present up to 500 km downstream of the ice edge. In the marginal sea ice zone the impact of a decreasing sea ice cover in this region is largest for off-ice flow conditions during cold-air outbreaks.\u0000","PeriodicalId":56315,"journal":{"name":"Cryosphere","volume":" ","pages":""},"PeriodicalIF":5.2,"publicationDate":"2023-08-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45095136","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. Arctic warming accelerates snowmelt, exposing soil surfaces with shallow or no snow cover to freeze–thaw cycles (FTCs) more frequently in early spring and late autumn. FTCs influence Arctic soil C dynamics by increasing or decreasing the amount of dissolved organic carbon (DOC); however, mechanism-based explanations of DOC changes that consider other soil biogeochemical properties are limited. To understand the effects of FTCs on Arctic soil responses, we designed microcosms with surface organic soils from Alaska and investigated several soil biogeochemical changes for seven successive temperature fluctuations of freezing at −9.0 ± 0.3 ∘C and thawing at 6.2 ± 0.3 ∘C for 12 h each. FTCs significantly changed the following soil variables: soil CO2 production (CO2), DOC and total dissolved nitrogen (TDN) contents, two DOC quality indices (SUVA254 and A365 / A254), microaggregate (53–250 µm) distribution, and small-sized mesopore (0.2–10 µm) proportion. Multivariate statistical analyses indicated that the FTCs improved soil structure at the scale of microaggregates and small-sized mesopores, facilitating DOC decomposition by soil microbes and changes in DOC quantity and quality by FTCs. This study showed that FTCs increased soil CO2 production, indicating that FTCs affected DOC characteristics without negatively impacting microbial activity. Soil microaggregation enhanced by FTCs and the subsequent increase in microbial activity and small-sized pore proportion could promote DOC decomposition, decreasing the DOC quantity. This study provides a mechanism-based interpretation of how FTCs alter DOC characteristics of the organic soil in the active layer by incorporating structural changes and microbial responses, improving our understanding of Arctic soil C dynamics.
{"title":"Responses of dissolved organic carbon to freeze–thaw cycles associated with the changes in microbial activity and soil structure","authors":"You Jin Kim, Jinhyun Kim, J. Jung","doi":"10.5194/tc-17-3101-2023","DOIUrl":"https://doi.org/10.5194/tc-17-3101-2023","url":null,"abstract":"Abstract. Arctic warming accelerates snowmelt, exposing soil surfaces with shallow or no snow cover to freeze–thaw cycles (FTCs) more frequently in early spring and late autumn. FTCs influence Arctic soil C dynamics by increasing or decreasing the amount of dissolved organic carbon (DOC); however, mechanism-based explanations of DOC changes that consider other soil biogeochemical properties are limited. To understand the effects of FTCs on Arctic soil responses, we designed microcosms with surface organic soils from Alaska and investigated several soil biogeochemical\u0000changes for seven successive temperature fluctuations of freezing at\u0000−9.0 ± 0.3 ∘C and thawing at 6.2 ± 0.3 ∘C for 12 h each. FTCs significantly changed the following soil variables: soil CO2 production (CO2), DOC and total dissolved nitrogen (TDN) contents, two DOC quality indices (SUVA254 and A365 / A254), microaggregate (53–250 µm) distribution, and small-sized mesopore (0.2–10 µm) proportion. Multivariate statistical analyses indicated that the FTCs improved soil structure at the scale of microaggregates and small-sized mesopores, facilitating DOC decomposition by soil microbes and changes in DOC quantity and quality by FTCs. This study showed that FTCs increased soil CO2 production, indicating that FTCs affected DOC characteristics without negatively impacting microbial activity. Soil microaggregation enhanced by FTCs and the subsequent increase in microbial activity and small-sized pore proportion could promote DOC decomposition, decreasing the DOC quantity. This study provides a mechanism-based interpretation of how FTCs alter DOC characteristics of the organic soil in the active layer by incorporating structural changes and microbial responses, improving our understanding of Arctic soil C dynamics.\u0000","PeriodicalId":56315,"journal":{"name":"Cryosphere","volume":" ","pages":""},"PeriodicalIF":5.2,"publicationDate":"2023-07-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43425133","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. Over the past decade, Greenland has experienced several extreme melt events, the most pronounced ones in the years 2010, 2012 and 2019. With progressing climate change, such extreme melt events can be expected to occur more frequently and potentially become more severe and persistent. So far, however, projections of ice loss and sea level change from Greenland typically rely on scenarios which only take gradual changes in the climate into account. Using the Parallel Ice Sheet Model (PISM), we investigate the effect of extreme melt events on the overall mass balance of the Greenland Ice Sheet and the changes in ice flow, invoked by the altered surface topography. As a first constraint, this study estimates the overall effect of extreme melt events on the cumulative mass loss of the Greenland Ice Sheet. We find that the sea level contribution from Greenland might increase by 2 to 45 cm (0.2 % to 14 %) by the year 2300 if extreme events occur more frequently in the future under a Representative Concentration Pathway 8.5 (RCP8.5) scenario, and the ice sheet area might be reduced by an additional 6000 to 26 000 km2 by 2300 in comparison to future warming scenarios without extremes. In conclusion, projecting the future sea level contribution from the Greenland Ice Sheet requires consideration of the changes in both the frequency and intensity of extreme events. It is crucial to individually address these extremes at a monthly resolution as temperature forcing with the same excess temperature but evenly distributed over longer timescales (e.g., seasonal) leads to less sea level rise than for the simulations of the resolved extremes. Extremes lead to additional mass loss and thinning. This, in turn, reduces the driving stress and surface velocities, ultimately dampening the ice loss attributed to ice flow and discharge. Overall, we find that the surface elevation feedback largely amplifies melting for scenarios with and without extremes, with additional mass loss attributed to this feedback having the greatest impact on projected sea level.
{"title":"Effects of extreme melt events on ice flow and sea level rise of the Greenland Ice Sheet","authors":"J. Beckmann, R. Winkelmann","doi":"10.5194/tc-17-3083-2023","DOIUrl":"https://doi.org/10.5194/tc-17-3083-2023","url":null,"abstract":"Abstract. Over the past decade, Greenland has experienced several extreme melt events, the most pronounced ones in the years 2010, 2012 and 2019.\u0000With progressing climate change, such extreme melt events can be expected to occur more frequently and potentially become more severe and persistent.\u0000So far, however, projections of ice loss and sea level change from Greenland typically rely on scenarios which only take gradual changes in the climate into account.\u0000Using the Parallel Ice Sheet Model (PISM), we investigate the effect of extreme melt events on the overall mass balance of the Greenland Ice Sheet and the changes in ice flow, invoked by the altered surface topography.\u0000As a first constraint, this study estimates the overall effect of extreme melt events on the cumulative mass loss of the Greenland Ice Sheet.\u0000We find that the sea level contribution from Greenland might increase by 2 to 45 cm (0.2 % to 14 %) by the year 2300 if extreme events occur more frequently in the future under a Representative Concentration Pathway 8.5 (RCP8.5) scenario, and the ice sheet area might be reduced by an additional 6000 to 26 000 km2 by 2300 in comparison to future warming scenarios without extremes.\u0000In conclusion, projecting the future sea level contribution from the Greenland Ice Sheet requires consideration of the changes in both the frequency and intensity of extreme events. It is crucial to individually address these extremes at a monthly resolution as temperature forcing with the same excess temperature but evenly distributed over longer timescales (e.g., seasonal) leads to less sea level rise than for the simulations of the resolved extremes.\u0000Extremes lead to additional mass loss and thinning. This, in turn, reduces the driving stress and surface velocities, ultimately dampening the ice loss attributed to ice flow and discharge.\u0000Overall, we find that the surface elevation feedback largely amplifies melting for scenarios with and without extremes, with additional mass loss attributed to this feedback having the greatest impact on projected sea level.\u0000","PeriodicalId":56315,"journal":{"name":"Cryosphere","volume":" ","pages":""},"PeriodicalIF":5.2,"publicationDate":"2023-07-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47147748","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. Diffusive smoothing of signals on the water stable isotopes (18O and D) in ice sheets fundamentally limits the climatic information retrievable from these ice-core proxies. Past theories explained how, in polycrystalline ice below the firn, fast diffusion in the network of intergranular water veins “short-circuits” the slow diffusion within crystal grains to cause “excess diffusion”, enhancing the rate of signal smoothing above that implied by self-diffusion in ice monocrystals. But the controls of excess diffusion are far from fully understood. Here, modelling shows that water flow in the veins amplifies excess diffusion by altering the three-dimensional field of isotope concentration and isotope transfer between veins and crystals. The rate of signal smoothing depends not only on temperature, the vein and grain sizes, and signal wavelength, but also on vein-water flow velocity, which can increase the rate by 1 to 2 orders of magnitude. This modulation can significantly impact signal smoothing at ice-core sites in Greenland and Antarctica, as shown by simulations for the GRIP (Greenland Ice Core Project) and EPICA (European Project for Ice Coring in Antarctica) Dome C sites, which reveal sensitive modulation of their diffusion-length profiles when vein-flow velocities reach ∼ 101–102 m yr−1. Velocities of this magnitude also produce the levels of excess diffusion inferred by previous studies for Holocene ice at GRIP and ice of Marine Isotope Stage 19 at EPICA Dome C. Thus, vein-flow-mediated excess diffusion may help explain the mismatch between modelled and spectrally derived diffusion lengths in other ice cores. We also show that excess diffusion biases the spectral estimation of diffusion lengths from isotopic signals (by making them dependent on signal wavelength) and the reconstruction of surface temperature from diffusion-length profiles (by increasing the ice contribution to diffusion length below the firn). Our findings caution against using the monocrystal isotopic diffusivity to represent the bulk-ice diffusivity. The need to predict the pattern of excess diffusion in ice cores calls for systematic study of isotope records for its occurrence and improved understanding of vein-scale hydrology in ice sheets.
摘要冰盖中水稳定同位素（18O和D）信号的扩散平滑从根本上限制了从这些冰芯代理中获取的气候信息。过去的理论解释说，在冰下的多晶冰中，内部水脉网络中的快速扩散“短路”了内部晶粒中的缓慢扩散，导致“过度扩散”，使信号平滑率高于冰单晶中的自扩散率。但对过度扩散的控制还远远没有完全理解。在这里，建模表明，矿脉中的水流通过改变同位素浓度的三维场以及矿脉和晶体之间的同位素转移来放大过度扩散。信号平滑的速率不仅取决于温度、纹理和晶粒尺寸以及信号波长，还取决于水流速度的变化，这可以使速率增加1到2个数量级。这种调制可以显著影响格陵兰岛和南极洲的冰芯点的信号平滑，如GRIP（格陵兰冰芯项目）和EPICA（欧洲南极冰芯项目 101–102 m yr−1。这种量级的速度也产生了先前对GRIP全新世冰和EPICA圆顶C海洋同位素第19阶段冰的研究所推断的过量扩散水平。因此，脉流介导的过量扩散可能有助于解释其他冰芯中模拟和光谱推导的扩散长度之间的不匹配。我们还表明，过量扩散使同位素信号对扩散长度的光谱估计产生偏差（使其取决于信号波长），并使表面温度从扩散长度剖面的构建产生偏差（通过增加冰对低于firn的扩散长度的贡献）。我们的研究结果警告不要使用单晶同位素扩散率来表示大块冰的扩散率。预测冰芯中溢出扩散模式的必要性要求对其发生的同位素记录进行系统研究，并提高对冰原中矿脉尺度水文的理解。
{"title":"Isotopic diffusion in ice enhanced by vein-water flow","authors":"F. Ng","doi":"10.5194/tc-17-3063-2023","DOIUrl":"https://doi.org/10.5194/tc-17-3063-2023","url":null,"abstract":"Abstract. Diffusive smoothing of signals on the water stable\u0000isotopes (18O and D) in ice sheets fundamentally limits the climatic\u0000information retrievable from these ice-core proxies. Past theories explained\u0000how, in polycrystalline ice below the firn, fast diffusion in the network of\u0000intergranular water veins “short-circuits” the slow diffusion within\u0000crystal grains to cause “excess diffusion”, enhancing the rate of signal\u0000smoothing above that implied by self-diffusion in ice monocrystals. But the\u0000controls of excess diffusion are far from fully understood. Here, modelling\u0000shows that water flow in the veins amplifies excess diffusion by altering\u0000the three-dimensional field of isotope concentration and isotope transfer\u0000between veins and crystals. The rate of signal smoothing depends not only on\u0000temperature, the vein and grain sizes, and signal wavelength, but also on\u0000vein-water flow velocity, which can increase the rate by 1 to 2 orders of\u0000magnitude. This modulation can significantly impact signal smoothing at\u0000ice-core sites in Greenland and Antarctica, as shown by simulations for the\u0000GRIP (Greenland Ice Core Project) and EPICA (European Project for Ice Coring in Antarctica) Dome C sites, which reveal sensitive modulation of their\u0000diffusion-length profiles when vein-flow velocities reach ∼ 101–102 m yr−1. Velocities of this magnitude also produce\u0000the levels of excess diffusion inferred by previous studies for Holocene ice\u0000at GRIP and ice of Marine Isotope Stage 19 at EPICA Dome C. Thus, vein-flow-mediated excess diffusion may help explain the mismatch between modelled and\u0000spectrally derived diffusion lengths in other ice cores. We also show that\u0000excess diffusion biases the spectral estimation of diffusion lengths from\u0000isotopic signals (by making them dependent on signal wavelength) and the\u0000reconstruction of surface temperature from diffusion-length profiles (by\u0000increasing the ice contribution to diffusion length below the firn). Our\u0000findings caution against using the monocrystal isotopic diffusivity to\u0000represent the bulk-ice diffusivity. The need to predict the pattern of\u0000excess diffusion in ice cores calls for systematic study of isotope records\u0000for its occurrence and improved understanding of vein-scale hydrology in ice\u0000sheets.\u0000","PeriodicalId":56315,"journal":{"name":"Cryosphere","volume":" ","pages":""},"PeriodicalIF":5.2,"publicationDate":"2023-07-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42890452","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. Bocquet, S. Fleury, F. Piras, E. Rinne, Heidi Sallila, F. Garnier, F. Rémy
Abstract. Sea ice volume's significant interannual variability requires long-term series of observations to identify trends in its evolution. Despite improvements in sea ice thickness estimations from altimetry during the past few years thanks to CryoSat-2 and ICESat-2, former ESA radar altimetry missions such as the Environmental Satellite (Envisat) and especially the European Remote-Sensing Satellite (ERS-1 and ERS-2) have remained under-exploited so far. Although solutions have already been proposed to ensure continuity of measurements between CryoSat-2 and Envisat, there is no time series integrating ERS. The purpose of this study is to extend the Arctic radar freeboard time series back to 1995. The difficulty in handling ERS measurements comes from a technical issue known as the pulse blurring effect, altering the radar echoes over sea ice and the resulting surface height estimates. Here we present and apply a correction for this pulse blurring effect. To ensure consistency of the CryoSat-2, Envisat and ERS-2 time series, a multiparameter neural-network-based method to calibrate Envisat against CryoSat-2 and ERS-2 against Envisat is presented. The calibration is trained on the discrepancies observed between the altimeter measurements during the mission-overlap periods and a set of parameters characterizing the sea ice state. Monthly radar freeboards are provided with uncertainty estimations based on a Monte Carlo approach to propagate the uncertainties all along the processing chain, including the neural network. Comparisons of corrected radar freeboards during overlap periods reveal good agreement between the missions, with a mean bias of 0.30 cm and a standard deviation of 9.7 cm for Envisat and CryoSat-2 and a 0.20 cm bias and a standard deviation of 3.8 cm for ERS-2 and Envisat. The monthly corrected radar freeboards obtained from Envisat and ERS-2 are then validated by comparison with several independent datasets such as airborne, mooring, direct-measurement and other altimeter products. Except for two datasets, comparisons lead to correlations ranging from 0.41 to 0.94 for Envisat and from 0.60 to 0.74 for ERS-2. The study finally provides radar freeboard estimation for winters from 1995 to 2021 (from the ERS-2 mission to CryoSat-2).
摘要海冰量的显著年际变化需要长期的一系列观测来确定其演变趋势。尽管在过去几年中，由于CryoSat-2和ICESat-2，通过测高技术估算海冰厚度有所改善，但欧洲航天局以前的雷达测高任务，如环境卫星(Envisat)，特别是欧洲遥感卫星(ERS-1和ERS-2)，到目前为止仍未得到充分利用。虽然已经提出了解决方案，以确保CryoSat-2和Envisat之间测量的连续性，但没有时间序列集成ERS。本研究的目的是将北极雷达干舷时间序列延后至1995年。处理ERS测量的困难来自于一个被称为脉冲模糊效应的技术问题，它会改变海冰上的雷达回波和由此产生的地表高度估计值。在这里，我们提出并应用这种脉冲模糊效果的校正。为了确保CryoSat-2、Envisat和ERS-2时间序列的一致性，提出了一种基于多参数神经网络的方法来校准Envisat与CryoSat-2和ERS-2与Envisat的对比。校准是根据在任务重叠期间高度计测量值与表征海冰状态的一组参数之间观察到的差异进行训练的。每月雷达干舷提供基于蒙特卡罗方法的不确定性估计，将不确定性沿处理链传播，包括神经网络。在重叠期间对校正后的雷达干深进行比较，结果显示两项任务之间存在良好的一致性，Envisat和CryoSat-2的平均偏差为0.30 cm，标准差为9.7 cm, ERS-2和Envisat的偏差为0.20 cm，标准差为3.8 cm。从Envisat和ERS-2获得的每月校正雷达干舷，然后通过与几个独立数据集(如机载、系泊、直接测量和其他高度计产品)进行比较来验证。除了两个数据集外，比较结果显示Envisat的相关性为0.41至0.94,ERS-2的相关性为0.60至0.74。该研究最后提供了1995年至2021年冬季(从ERS-2任务到CryoSat-2)的雷达干舷估计。
{"title":"Arctic sea ice radar freeboard retrieval from the European Remote-Sensing Satellite (ERS-2) using altimetry: toward sea ice thickness observation from 1995 to 2021","authors":"M. Bocquet, S. Fleury, F. Piras, E. Rinne, Heidi Sallila, F. Garnier, F. Rémy","doi":"10.5194/tc-17-3013-2023","DOIUrl":"https://doi.org/10.5194/tc-17-3013-2023","url":null,"abstract":"Abstract. Sea ice volume's significant interannual variability requires long-term series of observations to identify trends in its evolution. Despite improvements in sea ice thickness estimations from altimetry during the past few years thanks to CryoSat-2 and ICESat-2, former ESA radar altimetry missions such as the Environmental Satellite (Envisat) and especially the European Remote-Sensing Satellite (ERS-1 and ERS-2) have remained under-exploited so far. Although solutions have already been proposed to ensure continuity of measurements between CryoSat-2 and Envisat, there is no time series integrating ERS. The purpose of this study is to extend the Arctic radar freeboard time series back to 1995. The difficulty in handling ERS measurements comes from a technical issue known as the pulse blurring effect, altering the radar echoes over sea ice and the resulting surface height estimates. Here we present and apply a correction for this pulse blurring effect. To ensure consistency of the CryoSat-2, Envisat and ERS-2 time series, a multiparameter neural-network-based method to calibrate Envisat against CryoSat-2 and ERS-2 against Envisat is presented. The calibration is trained on the discrepancies observed between the altimeter measurements during the mission-overlap periods and a set of parameters characterizing the sea ice state. Monthly radar freeboards are provided with uncertainty estimations based on a Monte Carlo approach to propagate the uncertainties all along the processing chain, including the neural network. Comparisons of corrected radar freeboards during overlap periods reveal good agreement between the missions, with a mean bias of 0.30 cm and a standard deviation of 9.7 cm for Envisat and CryoSat-2 and a 0.20 cm bias and a standard deviation of 3.8 cm for ERS-2 and Envisat. The monthly corrected radar freeboards obtained from Envisat and ERS-2 are then validated by comparison with several independent datasets such as airborne, mooring, direct-measurement and other altimeter products. Except for two datasets, comparisons lead to correlations ranging from 0.41 to 0.94 for Envisat and from 0.60 to 0.74 for ERS-2. The study finally provides radar freeboard estimation for winters from 1995 to 2021 (from the ERS-2 mission to CryoSat-2).\u0000","PeriodicalId":56315,"journal":{"name":"Cryosphere","volume":" ","pages":""},"PeriodicalIF":5.2,"publicationDate":"2023-07-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41560907","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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