A comparison of factors that led to the extreme sea ice minima in the 21st century in the Arctic Ocean

The extreme Arctic sea ice minima in the 21st century have been attributed to multiple factors, such as anomalous atmospheric circulation, excess solar radiation absorbed by open ocean, and thinning sea ice in a warming world. Most likely it is the combination of these factors that drive the extreme sea ice minima, but it has not been quantified, how the factors rank in setting the conditions for these events. To address this question, the sea ice budget of an Arctic regional sea ice-ocean model forced by atmospheric reanalysis data is analyzed to assess the development of the observed sea ice minima. Results show that the ice area difference in the years 2012, 2019, and 2007 is driven to over 60% by the difference in summertime sea ice area loss due to air-ocean heat flux over open water. Other contributions are small. For the years 2012 and 2020 the situation is different and more complex. The air-ice heat flux causes more sea ice area loss in summer 2020 than in 2012 due to warmer air temperatures, but this difference in sea ice area loss is compensated by reduced advective sea ice loss out of the Arctic Ocean mainly caused by the relaxation of the Arctic Dipole. The difference in open water area in early August leads to different air-ocean heat fluxes, which distinguishes the sea ice minima in 2012 and 2020. Further, sensitivity experiments indicate that both the atmospheric circulation associated with the Arctic Dipole and extreme storms are essential conditions for a new low record of sea ice extent.

Ice dynamics of the Haupapa/Tasman Glacier measured at high spatial and temporal resolution, Aoraki/Mount Cook, New Zealand

<p>Glaciers are among the clearest of signals for anthropogenic climate change and their retreat is considered symptomatic of the observed warming since the start of the 20th century from anthropogenic sources (Mann et al., 2004). New Zealand has 3,100 mountain glaciers, with those in the Southern Alps experiencing losses of 34% since 1977 and a decline in volume of 51 km3 in 1994 to 41 km3 in 2010 (NIWA, 2011). The direct impact of increasing atmospheric temperatures on glaciers is well understood (Chinn, 2012) through its effects on the melt and accumulation rates (Kirkbride, 2010; Purdie, 2011; Chinn, 1997; Oerlemans, 2001). However lake calving glaciers such as the Tasman Glacier exhibit different behaviour and are suggested to be at least partially decoupled from climate forcing (Benn et al., 2007). Here, I present a temporally and spatially complete study of Haupapa/Tasman Glacier, Aoraki/Mt. Cook over three years to investigate the ice dynamics at the terminus. I used oblique photogrammetry at high resolution for data acquisition and adapted computer vision algorithms for correcting this oblique view to a real-world geometry. This technique has been rarely used (Murray et al., 2015; Messerli and Grinsted, 2015; Ahn and Box, 2010; Harrison et al., 1986 and Flotron, 1973) but owing to its cost-effectiveness and high data yields, it is becoming an increasingly powerful methodology favoured by glaciologists. During the 3 year study period, Tasman Glacier terminus retreat rate Ur was 116 ± 19 m a⁻¹ (2013-2014), 83 ± 18 m a⁻¹ (2014-2015) and 204 ± 20 (2015-2016). A strong seasonal pattern was evident in the calving events. Three major calving events occurred over the study, one occurring in the summer of 2013 and two in the summer of 2016. The latter two events are responsible for the elevated Ur in 2015-2016. These events were characterised as distinct large-magnitude calving (usually as a large tabular iceberg) which continued to drift and break up in the lake for weeks to months. Three large calving events accounted for 47% of the total surface area loss for the 38 month study period with the remaining surface area loss from 2nd order calving including notching at the waterline and the spalling of lamallae of ice from surface fractures, and ice-cliff melt. During the spring/summer months of 2014 and 2015 there was no large buoyancy driven calving event such as those seen in 2013 and 2016, but there were many smaller-magnitude calving events. Smaller-magnitude events were less frequent in winter months as compared to summer months. Ice flow in winter has been shown to be less than in summer (Horgan et al, 2015). While seasonal temperatures and changes to the basal water pressure are linked to these observations, it is also likely that the relatively faster ice flow in summer/autumn could be influencing the rate of 1st and 2nd order calving mechanisms. Overall, the calving rates were calculated as 171 ± 18 m a⁻¹ (2013-2014), 136 ± 17 m a⁻¹ (2014-2015) and accelerated to 256 ± 20 m a⁻¹ in the last year (2015-2016). My results show that almost half of the ice loss at the terminus comes from large, infrequent calving events and that retreat rates for 2015-2016 were high compared to the historic record but the area loss is lower than it has been because of the relatively narrow terminus.</p>

Ice dynamics of the Haupapa/Tasman Glacier measured at high spatial and temporal resolution, Aoraki/Mount Cook, New Zealand

<p>Glaciers are among the clearest of signals for anthropogenic climate change and their retreat is considered symptomatic of the observed warming since the start of the 20th century from anthropogenic sources (Mann et al., 2004). New Zealand has 3,100 mountain glaciers, with those in the Southern Alps experiencing losses of 34% since 1977 and a decline in volume of 51 km3 in 1994 to 41 km3 in 2010 (NIWA, 2011). The direct impact of increasing atmospheric temperatures on glaciers is well understood (Chinn, 2012) through its effects on the melt and accumulation rates (Kirkbride, 2010; Purdie, 2011; Chinn, 1997; Oerlemans, 2001). However lake calving glaciers such as the Tasman Glacier exhibit different behaviour and are suggested to be at least partially decoupled from climate forcing (Benn et al., 2007). Here, I present a temporally and spatially complete study of Haupapa/Tasman Glacier, Aoraki/Mt. Cook over three years to investigate the ice dynamics at the terminus. I used oblique photogrammetry at high resolution for data acquisition and adapted computer vision algorithms for correcting this oblique view to a real-world geometry. This technique has been rarely used (Murray et al., 2015; Messerli and Grinsted, 2015; Ahn and Box, 2010; Harrison et al., 1986 and Flotron, 1973) but owing to its cost-effectiveness and high data yields, it is becoming an increasingly powerful methodology favoured by glaciologists. During the 3 year study period, Tasman Glacier terminus retreat rate Ur was 116 ± 19 m a⁻¹ (2013-2014), 83 ± 18 m a⁻¹ (2014-2015) and 204 ± 20 (2015-2016). A strong seasonal pattern was evident in the calving events. Three major calving events occurred over the study, one occurring in the summer of 2013 and two in the summer of 2016. The latter two events are responsible for the elevated Ur in 2015-2016. These events were characterised as distinct large-magnitude calving (usually as a large tabular iceberg) which continued to drift and break up in the lake for weeks to months. Three large calving events accounted for 47% of the total surface area loss for the 38 month study period with the remaining surface area loss from 2nd order calving including notching at the waterline and the spalling of lamallae of ice from surface fractures, and ice-cliff melt. During the spring/summer months of 2014 and 2015 there was no large buoyancy driven calving event such as those seen in 2013 and 2016, but there were many smaller-magnitude calving events. Smaller-magnitude events were less frequent in winter months as compared to summer months. Ice flow in winter has been shown to be less than in summer (Horgan et al, 2015). While seasonal temperatures and changes to the basal water pressure are linked to these observations, it is also likely that the relatively faster ice flow in summer/autumn could be influencing the rate of 1st and 2nd order calving mechanisms. Overall, the calving rates were calculated as 171 ± 18 m a⁻¹ (2013-2014), 136 ± 17 m a⁻¹ (2014-2015) and accelerated to 256 ± 20 m a⁻¹ in the last year (2015-2016). My results show that almost half of the ice loss at the terminus comes from large, infrequent calving events and that retreat rates for 2015-2016 were high compared to the historic record but the area loss is lower than it has been because of the relatively narrow terminus.</p>

DISTRIBUTION AND EVOLUTION OF ICE APRONS IN A CHANGING CLIMATE IN THE MONT-BLANC MASSIF (WESTERN EUROPEAN ALPS)

Ice Apron (IA) is a poorly studied ice feature, commonly existing in all the world’s major mountain regions. This study aims to map the locations of the IAs in the Mont Blanc massif (MBM), making use of the very high-resolution optical satellite images from 2001, 2012 and 2019. 423 IAs were identified and accurately delineated in the MBM on the images from 2019, and their topographic characteristics were studied. We generated our own Digital Elevation Model (DEM) at 4 m resolution since the freely available products predominantly suffer from significant inconsistencies, especially in steep mountain areas. Results show that most IAs exist at elevations above the regional Equilibrium Line Altitude (ELA), on steep slopes, on concave surfaces, on northern and southern aspects and on the most rugged terrains. They are also commonly associated with steep slope glaciers as 85% of them occur on these glaciers’ headwalls. A comparison between 2001 and 2019 shows that IAs have lost around 29% of their area over a period of 18 years. This is significant and the rate of area loss is very alarming in comparison with the larger glacier bodies. We also studied the effect of topographic parameters on the area loss. We found that topographic factors like slope, aspect, curvature, elevation and Terrain Ruggedness Index (TRI) strongly influence the rate of area loss of IAs.

Glacier changes in the Chhombo Chhu Watershed of the Tista basin between 1975 and 2018, the Sikkim Himalaya, India

Glaciers of the Tista basin represent an important water source for mountain communities and a large population downstream. The article presents observable changes in the Chhombo Chhu Watershed (CCW) glacier area of the Tista basin, the Sikkim Himalaya. The CCW contains 74 glaciers (> 0.02 km2) with a mean glacier size of 0.61 km2. We determined changes in glaciers from the declassified Hexagon Keyhole-9 (KH-9) (1975), Landsat 5 Thematic Mapper (TM) (1989), Landsat 7 Enhanced Thematic Mapper Plus (ETM+) (2000), Landsat 5 TM (2010), and Sentinel-2A (2018) images. The total glacier area in 1975 was 62.6 ± 0.7 km2; and by 2018, the area had decreased to 44.8 ± 1.5 km2, an area loss of 17.9 ± 1.7 km2 (0.42 ± 0.04 km2 a−1). Clean glaciers exhibited more area loss of 11.8 ± 1.2 km2 (0.27 ± 0.03 km2 a−1) than partially debris-covered and maximally debris-covered glaciers. The area loss is 5.0 ± 0.4 km2 (0.12 ± 0.01 km2 a−1) for partially covered glaciers and 1.0 ± 0.1 km2 (−0.02 ± 0.002 km2 a−1) for maximally covered glaciers. The glacier area loss in the CCW of the Sikkim Himalaya is 0.62 ± 0.5 km2 a−1 during 2000–2010, and it is 0.77 ± 0.6 km2 a−1 during 2010–2018. Field investigations of selected glaciers and climatic records also support the glacier recession in the CCW due to a significant increase in temperature (0.25 ∘C a−1) and more or less static precipitation since 1995. The dataset is now available from the Zenodo web portal: https://doi.org/10.5281/zenodo.4457183 (Chowdhury et al., 2021).

Respiratory exacerbations are associated with muscle loss in current and former smokers

ObjectivesMuscle wasting is a recognised extra-pulmonary complication in chronic obstructive pulmonary disease and has been associated with increased risk of death. Acute respiratory exacerbations are associated with reduction of muscle function, but there is a paucity of data on their long-term effect. This study explores the relationship between acute respiratory exacerbations and long-term muscle loss using serial measurements of CT derived pectoralis muscle area (PMA).Design and settingParticipants were included from two prospective, longitudinal, observational, multicentre cohorts of ever-smokers with at least 10 pack-year history.ParticipantsThe primary analysis included 1332 (of 2501) participants from Evaluation of COPD Longitudinally to Identify Predictive Surrogate Endpoints (ECLIPSE) and 4384 (of 10 198) participants from Genetic Epidemiology of COPD (COPDGene) who had complete data from their baseline and follow-up visits.InterventionsPMA was measured on chest CT scans at two timepoints. Self-reported exacerbation data were collected from participants in both studies through the use of periodic longitudinal surveys.Main outcome measuresAge-related and excess muscle loss over time.ResultsAge, sex, race and body mass index were associated with baseline PMA. Participants experienced age-related decline at the upper end of reported normal ranges. In ECLIPSE, the exacerbation rate over time was associated with an excess muscle area loss of 1.3% (95% CI 0.6 to 1.9, p<0.001) over 3 years and in COPDGene with an excess muscle area loss of 2.1% (95% CI 1.2 to 2.8, p<0.001) over 5 years. Excess muscle area decline was absent in 273 individuals who participated in pulmonary rehabilitation.ConclusionsExacerbations are associated with accelerated skeletal muscle loss. Each annual exacerbation was associated with the equivalent of 6 months of age-expected decline in muscle mass. Ameliorating exacerbation-associated muscle loss represents an important therapeutic target.