A LiDAR-based glacial landform map of the Kebnekaise massif, northern Sweden

2020 ◽  
Author(s):  
Calum Edward ◽  
Robin Blomdin ◽  
Gunhild Rosqvist
Keyword(s):  
Global Climate ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Aerial Photographs ◽  
Terrain Model ◽  
Scandinavian Ice Sheet ◽  
The Face ◽  
Ice Retreat ◽  
Ground Truthing ◽  
Glacial Landforms

<p>In the face of global climate change, and the associated melting of the modern-day ice sheets, the understanding and reconstruction of the dynamics and retreats of former ice sheets has become an increasingly valuable tool and indicator of the future behaviour of present-day ice masses. The deglacial period that followed the Last Glacial Maximum (~22-9 thousand years ago) represents the most recent major warming event, and final ice sheet decay, in Earth history, and is an important analogue for the threat of present-day ice sheet collapse. The recent availability of the 2m-resolution Swedish LiDAR based terrain model provides the opportunity to map glacial landforms and landscapes over large areas with greater accuracy than was previously possible through satellite images or aerial photographs. In combination with field observation-based ground-truthing, this LiDAR resource is employed to map the geomorphology of the Kebnekaise region of the northern Swedish mountains with the principal aim of producing a landform-driven reconstruction of the deglaciation of the remnant Scandinavian Ice Sheet during its final stage of retreat. The complex ‘palimpsest’ landscape is delineated and interpreted through the classification of landforms according to their relative age and respective origin. In particular, attention will be given to the segregation of glacial (e.g., terminal moraines, lineations), deglacial (e.g., eskers, lateral meltwater channels, glacial lake shorelines) and ‘relict’ (i.e., pre-glacial palaeosurfaces) landform assemblages, in order to demarcate those formed during the final deglaciation.   The resulting landform selections are used to delineate high-resolution ice retreat patterns, giving indication to the nature of the basal thermal regime, topographic response and final remnant location of the ice sheet. Additionally, this assay serves as an evaluation of the use of the Swedish LiDAR database as a means of efficiently and accurately mapping previously-glaciated landscapes. Our deglaciation reconstruction will finally be tested against formerly produced regional reconstructions.</p>

scholarly journals Attention Multi-Scale Network for Automatic Layer Extraction of Ice Radar Topological Sequences

2021 ◽  
Vol 13 (12) ◽  
pp. 2425
Author(s):  
Yiheng Cai ◽  
Dan Liu ◽  
Jin Xie ◽  
Jingxian Yang ◽  
Xiangbin Cui ◽  
...  
Keyword(s):  
Deep Learning ◽  
Global Climate ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Sheet Thickness ◽  
Learning Methods ◽  
Convolutional Network ◽  
Multi Scale ◽  
Ice Surface ◽  
Layer Extraction

Analyzing the surface and bedrock locations in radar imagery enables the computation of ice sheet thickness, which is important for the study of ice sheets, their volume and how they may contribute to global climate change. However, the traditional handcrafted methods cannot quickly provide quantitative, objective and reliable extraction of information from radargrams. Most traditional handcrafted methods, designed to detect ice-surface and ice-bed layers from ice sheet radargrams, require complex human involvement and are difficult to apply to large datasets, while deep learning methods can obtain better results in a generalized way. In this study, an end-to-end multi-scale attention network (MsANet) is proposed to realize the estimation and reconstruction of layers in sequences of ice sheet radar tomographic images. First, we use an improved 3D convolutional network, C3D-M, whose first full connection layer is replaced by a convolution unit to better maintain the spatial relativity of ice layer features, as the backbone. Then, an adjustable multi-scale module uses different scale filters to learn scale information to enhance the feature extraction capabilities of the network. Finally, an attention module extended to 3D space removes a redundant bottleneck unit to better fuse and refine ice layer features. Radar sequential images collected by the Center of Remote Sensing of Ice Sheets in 2014 are used as training and testing data. Compared with state-of-the-art deep learning methods, the MsANet shows a 10% reduction (2.14 pixels) on the measurement of average mean absolute column-wise error for detecting the ice-surface and ice-bottom layers, runs faster and uses approximately 12 million fewer parameters.

scholarly journals Impact of mid-glacial ice sheets on deep ocean circulation and global climate: Role of surface cooling on the AMOC

2020 ◽  
Author(s):  
Sam Sherriff-Tadano ◽  
Ayako Abe-Ouchi ◽  
Akira Oka
Keyword(s):  
North Atlantic ◽  
General Circulation ◽  
Global Climate ◽  
Surface Wind ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Meridional Overturning Circulation ◽  
Strengthening Effect ◽  
Surface Cooling ◽  
Glacial Ice

Abstract. This study explores the effect of southward expansion of mid-glacial ice sheets on the global climate and the Atlantic meridional overturning circulation (AMOC), as well as the processes by which the ice sheets modify the AMOC. For this purpose, simulations of Marine Isotope Stage (MIS) 3 and 5a are performed with an atmosphere-ocean general circulation model. In the MIS3 and MIS5a simulations, the global average temperature decreases by 5.0 °C and 2.2 °C, respectively, compared with the preindustrial climate simulation. The AMOC weakens by 3 % in MIS3, whereas it is enhanced by 16 % in MIS5a, both of which are consistent with a reconstruction. Sensitivity experiments extracting the effect of the expansion of glacial ice sheets from MIS5a to MIS3 show a global cooling of 1.1 °C, contributing to about 40 % of the total surface cooling from MIS5a to MIS3. These experiments also demonstrate that the ice sheet expansion leads to a surface cooling of 2 °C over the Southern Ocean as a result of colder North Atlantic deep water. We find that the southward expansion of the mid-glacial ice sheet exerts a small impact on the AMOC. Partially coupled experiments reveal that the global surface cooling by the glacial ice sheet tends to reduce the AMOC by increasing the sea ice at both poles, and hence compensates for the strengthening effect of the enhanced surface wind over the North Atlantic. Our results show that the total effect of glacial ice sheets on the AMOC is determined by the two competing effects, surface wind and surface cooling. The relative strength of surface wind and surface cooling depends on the ice sheet configuration, and the strength of the surface cooling can be comparable to that of surface wind when changes in the extent of ice sheet are prominent.

8. Glaciers of the past

2018 ◽  
pp. 146-152
Author(s):  
David J. A. Evans
Keyword(s):  
Numerical Models ◽  
Ice Core ◽  
Three Dimensional ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Aerial Imagery ◽  
The Past ◽  
Glacial Landforms

To reconstruct the former extent and dynamics of ice sheets and glaciers requires a knowledge of process-form relationships that goes beyond individual landform types. Instead, glacial geomorphologists need to analyse large areas of glaciated terrain in a more holistic way, combining the whole range of glacial landforms and sediments to reconstruct glacier systems of the past, a subject now known as palaeoglaciology. ‘Glaciers of the past’ explains how the combination of aerial imagery and landform analysis is used in palaeoglaciological reconstruction. Increasingly powerful computers are making it possible to compile sophisticated numerical models that use our knowledge of glaciological processes and ice-core-derived palaeoclimate data to create three-dimensional glacier and ice sheet reconstructions.

New results on the dynamics of the NW part of the Svalbard Ice Sheet during the deglaciation of the Woodfjorden Trough

2020 ◽  
Author(s):  
Tom Arne Rydningen ◽  
Amando Lasabuda ◽  
Jan Sverre Laberg ◽  
Christine Tømmervik Kollsgård ◽  
Stine Bjordal Olsen ◽  
...  
Keyword(s):  
Continental Shelf ◽  
Ice Sheet ◽  
Outer Part ◽  
Middle Part ◽  
The Arctic ◽  
Quality Data ◽  
Glacier Front ◽  
Ice Retreat ◽  
Late Weichselian ◽  
Glacial Landforms

<p>Present-day warming is most pronounced at high latitudes, raising concern for the stability of modern ice caps such as the ones overlying the Svalbard archipelago. Palaeo-records give us opportunity to understand past behavior of these systems, including the ice retreat from the continental shelf at the end of the last glaciation. In order to evaluate and reconstruct this in a robust way, it is essential that we acquire high-quality data sets covering key areas in the Arctic.</p><p>New multi-beam bathymetric data was acquired in July 2019 from the Woodfjorden Trough; an up to 60 km long and 40 km wide transverse trough on the northwestern part of the Svalbard continental shelf. Previous investigations have shown that this trough was occupied by a major ice stream draining the Svalbard Ice Sheet during the last glacial, but the deglacial dynamics of this sector of the Svalbard Ice Sheet are presently not well constrained.</p><p>The new data reveal a complex seabed morphology including larger (2 km wide, 50 m high) and smaller (100 m wide, 3 m high) ridges, as well as sediment wedges (1 to 2 km wide, 30 m high), partly showing crosscutting relationships. These ridges and wedges are discontinuous in the outer part of the trough, where they are partly superposed by glacial lineations and small- to larger sized iceberg ploughmarks (up to 1500 m wide and 30 m deep). In the middle part of the trough, more continuous ridges dominate.</p><p>The ridges and wedges are interpreted to be glacial landforms formed by grounded ice within the Woodfjorden Trough. Their crosscutting relationships testify to a complex deglaciation, including several advances and still stands of the ice front during overall ice retreat, and their size could indicate that the glacier front was stable for some time. Smaller ridges may be retreat moraines formed during shorter (annual?) still stands of the glacier front. Based on their discontinuous characteristics, the ridges and wedges in the outer part of the trough may pre-date the final Late Weichselian deglaciation, i.e. they may have been overridden by a grounded glacier. The more continuous character of the ridges in the middle part of the trough indicate that these likely date from the Late Weichselian deglaciation.</p><p>The glacial landforms identified here are rather atypical for glacial troughs, commonly dominated by mega-scale glacial lineations superposed by one or a few grounding zone wedges and/or smaller retreat moraines. The abundant morainal systems and glacial lineations of the Woodfjorden Trough, instead, testify to highly dynamic grounded ice occupying the trough, and a retreat which was characterized by several periods of ice margin stability, interrupted by readvances. This fits with recent studies from onshore areas, showing that the deglaciation of northern Svalbard was at least partly characterized by glacial readvances during the overall ice retreat.</p>

Did a Beringian ice sheet once exist?

2020 ◽  
Author(s):  
Zhongshi Zhang ◽  
Qing Yan ◽  
Ran Zhang ◽  
Florence Colleoni ◽  
Gilles Ramstein ◽  
...  
Keyword(s):  
North Pacific ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Climate Modelling ◽  
Mountain Glaciers ◽  
The Past ◽  
The North ◽  
Paleoclimate Records ◽  
Glacial Landforms ◽  
The North Pacific

<p>Did a Beringian ice sheet once exist? This question was hotly debated decades ago until compelling evidence for an ice-free Wrangel Island excluded the possibility of an ice sheet forming over NE Siberia-Beringia during the Last Glacial Maximum (LGM). Today, it is widely believed that during most Northern Hemisphere glaciations only the Laurentide-Eurasian ice sheets across North America and Northwest Eurasia became expansive, while Northeast Siberia-Beringia remained ice-sheet-free. However, recent recognition of glacial landforms and deposits on Northeast Siberia-Beringia and off the Siberian continental shelf has triggered a new round of debate.These local glacial features, though often interpreted as local activities of ice domes on continental shelves and mountain glaciers on continents,   could be explained as an ice sheet over NE Siberia-Beringia. Only based on the direct glacial evidence, the debate can not be resolved. Here, we combine climate and ice sheet modelling with well-dated paleoclimate records from the mid-to-high latitude North Pacific to readdress the debate. Our simulations show that the paleoclimate records are not reconcilable with the established concept of Laurentide-Eurasia-only ice sheets. On the contrary, a Beringian ice sheet over Northeast Siberia-Beringia causes feedbacks between atmosphere and ocean, the result of which well explains the climate records from around the North Pacific during the past four glacial-interglacial cycles. Our ice-climate modelling and synthesis of paleoclimate records from around the North Pacific argue that the Beringian ice sheet waxed and waned rapidly in the past four glacial-interglacial cycles and accounted for ~10-25 m ice-equivalent sea-level change during its peak glacials. The simulated Beringian ice sheet agrees reasonably with the direct glacial and climate evidence from Northeast Siberia-Beringia, and reconciles the paleoclimate records from around the North Pacific. With the Beringian ice sheet involved, the pattern of past NH ice sheet evolution is more complex than previously thought, in particular prior to the LGM.</p>

scholarly journals Ice sheet velocity tracking by Sentinel-1 satellite images at Graham Coast Kyiv Peninsula

2021 ◽  
pp. 24-31
Author(s):  
S. Kadurin ◽  
◽  
K. Andrieieva ◽  
Keyword(s):  
Remote Sensing ◽  
Global Climate ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Remote Sensing Data ◽  
Ice Cover ◽  
Satellite System ◽  
Time Interval ◽  
Radar Images ◽  
Ocean Level

The study of Antarctic glaciers and ice sheets velocity is one of the most discussed topics. Such high interest in this topic is primarily because the ice from the Antarctic glaciers, which gets to the ocean, significantly affects the ocean level and the global climate. Development of modern satellite technologies for Earth remote sensing made it possible to elaborate a number of methods for ice sheets’ displacements estimation and calculation of such displacements velocities. This work uses remote sensing data from the satellite system Copernicus Sentinel-1 to estimate the ice cover velocities in the Kyiv Peninsula in the time interval from December 2020 to March 2021. To this end, 10 radar images of the study area from early December to the end of March were used with an interval of 12–14 days. All selected images were analyzed in pairs to establish changes on the surface for the selected time interval. GRD-format images from Copernicus Sentinel-1 satellite, corrected for Earth's ellipsoid shape, were used. Based on the offset tracking operation, we calculated the speeds of ice cover movements within the Kyiv Peninsula for each pair of images with approximately two weeks' time difference. As a result, the speed of ice movements varies considerably and at the glacier mouth can reach 3.5–4 meters per day. Also, the rate of ice displacement in the glacier body changed over time. Thus, the highest ice velocities were in the glacier's mouth. However, short-term time intervals of intensification were recorded for the rear and even the marginal parts of the glaciers in contact with the ice sheet. Thus, the lowest part of the glacier activating sequence leads to the upper part shifting. Notably, this increase in the displacement of ice cover was recorded in February, one of the warmest months in this part of Antarctica.

scholarly journals Influence of albedo parameterization on surface mass balance in the perspective of Greenland ice sheet modelling in EC-Earth

2016 ◽  
Author(s):  
Michiel Helsen ◽  
Roderik Van de Wal ◽  
Thomas Reerink ◽  
Richard Bintanja ◽  
Marianne Sloth Madsen ◽  
...  
Keyword(s):  
Mass Balance ◽  
Climate Model ◽  
Global Climate ◽  
Global Climate Model ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Surface Mass Balance ◽  
Surface Mass

Abstract. The albedo of the surface of ice sheets changes as a function of time, due to the effects of deposition of new snow, ageing of dry snow, melting and runoff. Currently, the calculation of the albedo of ice sheets is highly parameterized within the Earth System Model EC-Earth, by taking a constant value for areas with thick perennial snow cover. This is one of the reasons that the surface mass balance (SMB) of the Greenland ice sheet (GrIS) is poorly resolved in the model. To improve this, eight snow albedo schemes are evaluated here. The resulting SMB is downscaled from the lower resolution global climate model topography to the higher resolution ice sheet topography of the GrIS, such that the influence of these different SMB climatologies on the long-term evolution of the GrIS is tested by ice sheet model simulations. This results in an optimised albedo parameterization that can be used in future EC-Earth simulations with an interactive ice sheet component.

scholarly journals Asynchronous Antarctic and Greenland ice-volume contributions to the last interglacial sea-level highstand

2020 ◽  
Author(s):  
Eelco Rohling ◽  
Fiona Hibbert
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
Global Climate ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Climate Forcing ◽  
Potential Contribution ◽  
Last Interglacial ◽  
Ice Shelf

<p>Sea-level rise is among the greatest risks that arise from anthropogenic global climate change. It is receiving a lot of attention, among others in the IPCC reports, but major questions remain as to the potential contribution from the great continental ice sheets. In recent years, some modelling work has suggested that the ice-component of sea-level rise may be much faster than previously thought, but the rapidity of rise seen in these results depends on inclusion of scientifically debated mechanisms of ice-shelf decay and associated ice-sheet instability. The processes have not been active during historical times, so data are needed from previous warm periods to evaluate whether the suggested rates of sea-level rise are supported by observations or not. Also, we then need to assess which of the ice sheets was most sensitive, and why. The last interglacial (LIG; ~130,000 to ~118,000 years ago, ka) was the last time global sea level rose well above its present level, reaching a highstand of +6 to +9 m or more. Because Greenland Ice Sheet (GrIS) contributions were smaller than that, this implies substantial Antarctic Ice Sheet (AIS) contributions. However, this still leaves the timings, magnitudes, and drivers of GrIS and AIS reductions open to debate. I will discuss recently published sea-level reconstructions for the LIG highstand, which reveal that AIS and GrIS contributions were distinctly asynchronous, and that rates of rise to values above 0 m (present-day sea level) reached up to 3.5 m per century. Such high pre-anthropogenic rates of sea-level rise lend credibility to high rates inferred by ice modelling under certain ice-shelf instability parameterisations, for both the past and future. Climate forcing was distinctly asynchronous between the southern and northern hemispheres as well during the LIG, explaining the asynchronous sea-level contributions from AIS and GrIS. Today, climate forcing is synchronous between the two hemispheres, and also faster and greater than during the LIG. Therefore, LIG rates of sea-level rise should likely be considered minimum estimates for the future.</p>

Ice sheet unzipping in the mountain-piedmont region of west-central Sweden: complex late-deglaciation of the Scandinavian ice sheet

2021 ◽  
Author(s):  
Robin Blomdin ◽  
Gustaf Peterson Becher ◽  
Colby Smith ◽  
Carl Regnéll ◽  
Christian Öhrling ◽  
...  
Keyword(s):  
Regional Scale ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Spatial Density ◽  
Ice Flow ◽  
Westward Expansion ◽  
West Central ◽  
Scandinavian Ice Sheet ◽  
Elevation Model ◽  
Piedmont Region

<p>Regional-scale glacial geomorphological maps provide important empirical data for reconstructions of former ice sheets, which may serve as analogues for the behaviour of modern ice sheets under climate warming. In particular, the extensive LiDAR-derived record of former ice sheet beds, provides an outstanding archive from which to infer former ice sheet behaviour. The stacking together and analysis of, tens of thousands of individual landforms, based on their spatial coherency, provides a powerful tool to reconstruct ice flow dynamics, temporally evolving ice divide positions and the “unzipping” of ice sheets into separate masses during deglaciation. In this study, we develop a glacial geomorphological dataset focussing on the mountain-piedmont region of Jämtland in west-central Sweden. We focus on this region because it is where the last (Weichselian) ice sheet is believed to have unzipped into separate domes and was inundated by vast ice dammed lakes. Jämtland also records a complex temporal evolution of subglacial processes and was formerly mapped without the benefit of a LiDAR-based elevation model. The dataset was created by mapping in GIS and covers an area of 50 000 km<sup>2</sup> and almost 88 000 landforms, including glacial lineations, crag-and-tails, ice marginal moraines, lateral meltwater channels, eskers, and glacial lake shorelines. We use this unique dataset–in terms of spatial density and resolution–and quantitatively analyse cross-cutting relationships to establish a relative ice flow chronology. Our key findings include 1) a previously unmapped landform system, formed by the Early-to-Middle Weichselian westward expansion of a mountain centred ice sheet, and 2) a complex early Holocene deglaciation sequence with ice sheet unzipping occurring in southern and east-central Jämtland. The ice sheet split into a larger sheet retreating northward and a smaller ice sheet remaining southeast of the mountain piedmont. Our results provide new insights into the late deglaciation of the Scandinavian Ice Sheet.</p>

Impact of mid-glacial ice sheets on deep ocean circulation and global climate

2021 ◽  
Author(s):  
Sam Sherriff-Tadano ◽  
Ayako Abe-Ouchi ◽  
Akira Oka
Keyword(s):  
North Atlantic ◽  
Global Climate ◽  
Surface Wind ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Meridional Overturning Circulation ◽  
Strengthening Effect ◽  
Surface Cooling ◽  
Glacial Ice ◽  
Cooling Effects

<p>This study explores the effect of southward expansion of Northern Hemisphere (American) mid-glacial ice sheets on the global climate and the Atlantic Meridional Overturning Circulation (AMOC), as well as the processes by which the ice sheets modify the AMOC. For this purpose, simulations of Marine Isotope Stage (MIS) 3 (36ka) and 5a (80ka) are performed with an atmosphere-ocean general circulation model. In the MIS3 and MIS5a simulations, the global average temperature decreases by 5.0 °C and 2.2 °C, respectively, compared with the preindustrial climate simulation. The AMOC weakens by 3% in MIS3, whereas it strengthens by 16% in MIS5a, both of which are consistent with an estimate based on <sup>231</sup>Pa/<sup>230</sup>Th. Sensitivity experiments extracting the effect of the southward expansion of glacial ice sheets from MIS5a to MIS3 show a global cooling of 1.1 °C, contributing to about 40% of the total surface cooling from MIS5a to MIS3. These experiments also demonstrate that the ice sheet expansion leads to a surface cooling of 2 °C over the Southern Ocean as a result of colder North Atlantic deep water. We find that the southward expansion of the mid-glacial ice sheet exerts a small impact on the AMOC. Partially coupled experiments reveal that the global surface cooling by the glacial ice sheet tends to reduce the AMOC by increasing the sea ice at both poles, and hence compensates for the strengthening effect of the enhanced surface wind over the North Atlantic. Our results show that the total effect of glacial ice sheets on the AMOC is determined by the two competing effects, surface wind and surface cooling. The relative strength of surface wind and surface cooling effects depends on the ice sheet configuration, and the strength of the surface cooling can be comparable to that of surface wind when changes in the extent of ice sheet are prominent.</p>

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