A record of slush and water extent on Antarctic ice shelves from 2013 to present day

2021 ◽  
Author(s):  
Rebecca Dell ◽  
Alison Banwell ◽  
Neil Arnold ◽  
Ian Willis ◽  
Anna Ruth W. Halberstadt ◽  
...  
Keyword(s):  
Clustering Algorithm ◽  
Google Earth ◽  
Expert Elicitation ◽  
Water Bodies ◽  
Landsat 8 ◽  
Ice Shelf ◽  
Ice Shelves ◽  
Air Temperatures ◽  
Run Off ◽  
Shelf Dynamics

<p>Supraglacial melt is observed across the majority of Antarctic ice shelves and is expected to increase in line with rising air temperatures. Surface meltwater may run off the ice shelf edge and into the ocean, or be stored within firn pore spaces (slush) and supraglacial water bodies (ponds, lakes or streams). When stored either as slush or supraglacial water bodies, the water can indirectly impact ice shelf dynamics, and potentially facilitate ice shelf collapse. Numerous studies have quantified ice shelf meltwater in supraglacial water bodies, however, despite its importance, no studies exist that quantify the extent of slush on a pan-Antarctic scale.</p><p>Here, we develop a supervised classifier in Google Earth Engine capable of identifying both slush and ponded water on a pan-Antarctic scale using Landsat 8 imagery. We train and test our classifier on six ice shelves: (1) Nivlisen, (2) Roi Baudouin, (3) Amery, (4) Shackleton, (5) Nansen, (6) George VI. A k-means clustering algorithm is applied to selected Landsat 8 training scenes, and the output clusters are manually interpreted to form training classes (i.e. slush, water, and other surface types (e.g. blue ice, dirty ice)). These training classes are then used to train a Random Forest Classifier, and the accuracy of the outputs are assessed using expert elicitation. Overall, the classifier accuracy for water and slush is 78 % and 70 % respectively. The validated classifier is then applied to numerous ice shelves across Antarctica, in order to produce estimates of slush and water extent from 2013 to the present day.</p>

scholarly journals Supervised classification of slush and ponded water on Antarctic ice shelves using Landsat 8 imagery

2021 ◽  
pp. 1-14
Author(s):  
Rebecca L. Dell ◽  
Alison F. Banwell ◽  
Ian C. Willis ◽  
Neil S. Arnold ◽  
Anna Ruth W. Halberstadt ◽  
...  
Keyword(s):  
Supervised Classification ◽  
Clustering Algorithm ◽  
Google Earth ◽  
Expert Elicitation ◽  
Future Research ◽  
Landsat 8 ◽  
Ice Shelf ◽  
Ice Shelves ◽  
Air Content

Abstract Surface meltwater is becoming increasingly widespread on Antarctic ice shelves. It is stored within surface ponds and streams, or within firn pore spaces, which may saturate to form slush. Slush can reduce firn air content, increasing an ice-shelf's vulnerability to break-up. To date, no study has mapped the changing extent of slush across ice shelves. Here, we use Google Earth Engine and Landsat 8 images from six ice shelves to generate training classes using a k-means clustering algorithm, which are used to train a random forest classifier to identify both slush and ponded water. Validation using expert elicitation gives accuracies of 84% and 82% for the ponded water and slush classes, respectively. Errors result from subjectivity in identifying the ponded water/slush boundary, and from inclusion of cloud and shadows. We apply our classifier to the Roi Baudouin Ice Shelf for the entire 2013–20 Landsat 8 record. On average, 64% of all surface meltwater is classified as slush and 36% as ponded water. Total meltwater areal extent is greatest between late January and mid-February. This highlights the importance of mapping slush when studying surface meltwater on ice shelves. Future research will apply the classifier across all Antarctic ice shelves.

scholarly journals Lateral meltwater transfer across an Antarctic ice shelf

2020 ◽  
Author(s):  
Rebecca Dell ◽  
Neil Arnold ◽  
Ian Willis ◽  
Alison Banwell ◽  
Andrew Williamson ◽  
...  
Keyword(s):  
Surface Water ◽  
Large Scale ◽  
Water Bodies ◽  
Seasonal Development ◽  
Water Volume ◽  
Landsat 8 ◽  
Ice Shelf ◽  
Ice Shelves ◽  
Melt Ponds ◽  
Track Surface

Abstract. Surface meltwater on ice shelves can be stored as slush, in melt ponds, in surface streams and rivers, and may also fill crevasses. The collapse of the Larsen B Ice Shelf in 2002 has been attributed to the sudden drainage of ~ 3000 surface lakes, and has highlighted the potential for surface water to cause ice shelf instability. Surface meltwater systems have been identified across numerous Antarctic ice shelves, however, the extent to which these systems impact ice shelf instability is poorly constrained. To better understand the role of surface meltwater systems on ice shelves, it is important to track their seasonal development, monitoring the fluctuations in surface water volume and the transfer of water across the ice shelf. Here, we use Landsat 8 and Sentinel-2 imagery to track surface meltwater across the Nivlisen Ice Shelf in the 2016–2017 melt season. Using the Fully Automated Supraglacial-Water Tracking algorithm for Ice Shelves (FASTISh), we identify and track the development of 1598 water bodies. The total volume of surface meltwater peaks on 26th January 2017 at 5.5 × 107 m3. 63 % of this total volume is held within two large linear surface meltwater systems, which are orientated along the ice shelves north-south axis and appear to migrate away from the grounding line during the melt season, facilitating large scale lateral water transfer towards the ice shelf front. This transfer is facilitated by two large surface streams, which encompass smaller water bodies and follow the surface slope of the ice shelf.

scholarly journals Lateral meltwater transfer across an Antarctic ice shelf

2020 ◽  
Vol 14 (7) ◽  
pp. 2313-2330 ◽  
Author(s):  
Rebecca Dell ◽  
Neil Arnold ◽  
Ian Willis ◽  
Alison Banwell ◽  
Andrew Williamson ◽  
...  
Keyword(s):  
Surface Water ◽  
Large Scale ◽  
Water Bodies ◽  
Seasonal Development ◽  
Water Volume ◽  
Landsat 8 ◽  
Ice Shelf ◽  
Ice Shelves ◽  
Track Surface ◽  
South Axis

Abstract. Surface meltwater on ice shelves can exist as slush, it can pond in lakes or crevasses, or it can flow in surface streams and rivers. The collapse of the Larsen B Ice Shelf in 2002 has been attributed to the sudden drainage of ∼3000 surface lakes and has highlighted the potential for surface water to cause ice-shelf instability. Surface meltwater systems have been identified across numerous Antarctic ice shelves, although the extent to which these systems impact ice-shelf instability is poorly constrained. To better understand the role of surface meltwater systems on ice shelves, it is important to track their seasonal development, monitoring the fluctuations in surface water volume and the transfer of water across ice-shelf surfaces. Here, we use Landsat 8 and Sentinel-2 imagery to track surface meltwater across the Nivlisen Ice Shelf in the 2016–2017 melt season. We develop the Fully Automated Supraglacial-Water Tracking algorithm for Ice Shelves (FASTISh) and use it to identify and track the development of 1598 water bodies, which we classify as either circular or linear. The total volume of surface meltwater peaks on 26 January 2017 at 5.5×107 m3. At this time, 63 % of the total volume is held within two linear surface meltwater systems, which are up to 27 km long, are orientated along the ice shelf's north–south axis, and follow the surface slope. Over the course of the melt season, they appear to migrate away from the grounding line, while growing in size and enveloping smaller water bodies. This suggests there is large-scale lateral water transfer through the surface meltwater system and the firn pack towards the ice-shelf front during the summer.

scholarly journals The 32-year record-high surface melt in 2019/2020 on the northern George VI Ice Shelf, Antarctic Peninsula

2021 ◽  
Vol 15 (2) ◽  
pp. 909-925
Author(s):  
Alison F. Banwell ◽  
Rajashree Tri Datta ◽  
Rebecca L. Dell ◽  
Mahsa Moussavi ◽  
Ludovic Brucker ◽  
...  
Keyword(s):  
High Surface ◽  
Microwave Radiometer ◽  
Austral Summer ◽  
Landsat 8 ◽  
Ice Shelf ◽  
Near Surface ◽  
Ice Shelves ◽  
Air Content ◽  
Air Temperatures ◽  
Surface Melt

Abstract. In the 2019/2020 austral summer, the surface melt duration and extent on the northern George VI Ice Shelf (GVIIS) was exceptional compared to the 31 previous summers of distinctly lower melt. This finding is based on analysis of near-continuous 41-year satellite microwave radiometer and scatterometer data, which are sensitive to meltwater on the ice shelf surface and in the near-surface snow. Using optical satellite imagery from Landsat 8 (2013 to 2020) and Sentinel-2 (2017 to 2020), record volumes of surface meltwater ponding were also observed on the northern GVIIS in 2019/2020, with 23 % of the surface area covered by 0.62 km3 of ponded meltwater on 19 January. These exceptional melt and surface ponding conditions in 2019/2020 were driven by sustained air temperatures ≥0 ∘C for anomalously long periods (55 to 90 h) from late November onwards, which limited meltwater refreezing. The sustained warm periods were likely driven by warm, low-speed (≤7.5 m s−1) northwesterly and northeasterly winds and not by foehn wind conditions, which were only present for 9 h total in the 2019/2020 melt season. Increased surface ponding on ice shelves may threaten their stability through increased potential for hydrofracture initiation; a risk that may increase due to firn air content depletion in response to near-surface melting.

scholarly journals 32-year record-high surface melt in 2019/2020 on north George VI Ice Shelf, Antarctic Peninsula

2020 ◽  
Author(s):  
Alison F. Banwell ◽  
Rajashree Tri Datta ◽  
Rebecca L. Dell ◽  
Mahsa Moussavi ◽  
Ludovic Brucker ◽  
...  
Keyword(s):  
High Surface ◽  
Microwave Radiometer ◽  
Austral Summer ◽  
Landsat 8 ◽  
Ice Shelf ◽  
Near Surface ◽  
Ice Shelves ◽  
Air Content ◽  
Air Temperatures ◽  
Surface Melt

Abstract. In the 2019/2020 austral summer, the surface melt duration and extent on the northern George VI Ice Shelf (GVIIS) was exceptional compared to the 31 previous summers of dramatically lower melt. This finding is based on analysis of near-continuous 41-year satellite microwave radiometer (and scatterometer) data, which are sensitive to meltwater on the ice-shelf surface and in the near-surface snow. Using optical satellite imagery from Landsat 8 (since 2013) and Sentinel-2 (since 2017), record volumes of surface meltwater ponding are also observed on north GVIIS in 2019/2020, with 23 % of the surface area covered by 0.62 km3 of meltwater on January 19. These exceptional melt and surface ponding conditions in 2019/2020 were driven by sustained air temperatures ≥ 0 °C for anomalously long periods (55–90 hours) from late November onwards, likely driven by warmer northwesterly and northeasterly low-speed winds. Increased surface ponding on ice shelves may threaten their stability through increased potential for hydrofracture initiation; a risk that may increase due to firn air content depletion in response to near-surface melting.

Surface lake depths on an Antarctic ice shelf: comparing in-situ measurements with ground and satellite multispectral methods

2020 ◽  
Author(s):  
Ian Willis ◽  
Alison Banwell ◽  
Grant Macdonald ◽  
Michael Willis ◽  
Doug MacAyeal
Keyword(s):  
Light Attenuation ◽  
Ice Sheet ◽  
Austral Summer ◽  
Greenland Ice Sheet ◽  
Water Bodies ◽  
Subsurface Water ◽  
Landsat 8 ◽  
Ice Shelf ◽  
Ice Shelves ◽  
Water Volumes

<p>There is growing interest in surface and shallow subsurface water bodies across Antarctic ice shelves as they impact the ice shelf mass balance. Additionally, the filling and draining of lakes has the potential to flex and fracture ice shelves, which may even lead to their catastrophic break up. The study of lakes on ice shelf surfaces typically uses optical satellite imagery to delineate their area and a parameterised physically-based light attenuation theory to calculate their depths. The approach has been developed and validated using various data sets collected on the Greenland Ice Sheet, but so far the approach has not been validated for Antarctic ice shelves. Here we use simultaneous field measurements of lake water depth and surface spectral properties (red, blue, green, panchromatic), to parameterise the light attenuation theory for use during the filling and draining of shallow lakes on the McMurdo Ice Shelf during the 2016/2017 austral summer. We then apply the approach to calculate lake areas, depths and volumes across several water bodies observed in high resolution Worldview imagery, which helps validate the approach to calculating water volumes across a larger part of the ice shelf using Landsat 8 imagery. Results suggest that using parameter values relevant to the Greenland Ice Sheet may bias the calculation of water volumes when applied to Antarctic ice shelves, and we suggest more appropriate values.</p>

Temporal variations in the surface hydrology across Antarctic ice shelves

2020 ◽  
Author(s):  
Rebecca Dell ◽  
Ian Willis ◽  
Neil Arnold ◽  
Alison Banwell ◽  
Hamish Pritchard ◽  
...  
Keyword(s):  
Surface Water ◽  
Deep Water ◽  
Temporal Variations ◽  
Google Earth ◽  
Water Bodies ◽  
Ice Shelf ◽  
Surface Hydrology ◽  
Ice Shelves ◽  
Landsat 7 ◽  
Surface Water Bodies

<p>Widespread surface meltwater systems have been identified across numerous Antarctic ice shelves and have been implicated in their possible instability and eventual breakup. It is crucial to better understand the seasonal and year-to-year development of these surface meltwater systems, which comprise saturated firn (slush) as well as distinct water bodies (lakes and streams). It has been suggested that repeated melting and re-freezing of the surface firn pack over successive years reduces the firn air content, and therefore its porosity, encouraging the formation of surface water bodies over time. Firn air depletion and the formation of surface water bodies may contribute to ice shelf instability, as the ice becomes increasingly susceptible to hydrofracture.</p><p>Here, we use Google Earth Engine to investigate the distributions of slush and deeper water bodies across all Antarctic ice shelves known to have surface melt, to quantify how surface meltwater systems evolve both seasonally and over successive summers. To do this, we use supervised classification of Sentinel-2 and Landsat 7/8 imagery to guide the selection of suitable NDWI<sub>ice</sub> thresholds for both the detection of slush and deep surface meltwater. Preliminary results for the George VI Ice Shelf between 2000 and 2017 reveal seasonal patterns in the overall extent of surface meltwater, and the overall meltwater extent typically peaks between January and March each year. The 2009-2010 melt season was characterised by significant melt, and over the course of the melt season the proportion of the overall surface meltwater extent that was held within deep water bodies varied between 0 % (November) and 60 % (January). An increase in the proportion of deep water vs. slush typically aligns with warmer air surface temperatures and, therefore periods of more intense melt.</p>

scholarly journals Formation of sea ice ponds from ice-shelf runoff, adjacent to the McMurdo Ice Shelf, Antarctica

2020 ◽  
Vol 61 (82) ◽  
pp. 73-77 ◽  
Author(s):  
Grant J. Macdonald ◽  
Predrag Popović ◽  
David P. Mayer
Keyword(s):  
Sea Ice ◽  
Added Mass ◽  
Surface Melting ◽  
Landsat 8 ◽  
Ice Shelf ◽  
Surface Hydrology ◽  
Ice Shelves ◽  
Arctic Ponds ◽  
Sentinel 2

AbstractPonds that form on sea ice can cause it to thin or break-up, which can promote calving from an adjacent ice shelf. Studies of sea ice ponds have predominantly focused on Arctic ponds formed by in situ melting/ponding. Our study documents another mechanism for the formation of sea ice ponds. Using Landsat 8 and Sentinel-2 images from the 2015–16 to 2018–19 austral summers, we analyze the evolution of sea ice ponds that form adjacent to the McMurdo Ice Shelf, Antarctica. We find that each summer, meltwater flows from the ice shelf onto the sea ice and forms large (up to 9 km2) ponds. These ponds decrease the sea ice's albedo, thinning it. We suggest the added mass of runoff causes the ice to flex, potentially promoting sea-ice instability by the ice-shelf front. As surface melting on ice shelves increases, we suggest that ice-shelf surface hydrology will have a greater effect on sea-ice stability.

scholarly journals Summer surface melt thins Petermann Gletscher Ice Shelf by enhancing channelized basal melt

2019 ◽  
Vol 65 (252) ◽  
pp. 662-674 ◽  
Author(s):  
PETER WASHAM ◽  
KEITH W. NICHOLLS ◽  
ANDREAS MÜNCHOW ◽  
LAURIE PADMAN
Keyword(s):  
Time Series Data ◽  
Series Data ◽  
Ice Shelf ◽  
Ice Shelves ◽  
Air Temperatures ◽  
External Forcings ◽  
Grounding Line ◽  
A Site ◽  
Strong Seasonality ◽  
Specific Contribution

ABSTRACTIncreasing ocean and air temperatures have contributed to the removal of floating ice shelves from several Greenland outlet glaciers; however, the specific contribution of these external forcings remains poorly understood. Here we use atmospheric, oceanographic and glaciological time series data from the ice shelf of Petermann Gletscher, NW Greenland to quantify the forcing of the ocean and atmosphere on the ice shelf at a site ~16 km from the grounding line within a large sub-ice-shelf channel. Basal melt rates here indicate a strong seasonality, rising from a winter mean of 2 m a−1 to a maximum of 80 m a−1 during the summer melt season. This increase in basal melt rates confirms the direct link between summer atmospheric warming around Greenland and enhanced ocean-forced melting of its remaining ice shelves. We attribute this enhanced melting to increased discharge of subglacial runoff into the ocean at the grounding line, which strengthens under-ice currents and drives a greater ocean heat flux toward the ice base.

scholarly journals Antarctic Supraglacial Lake Identification Using Landsat-8 Image Classification

2020 ◽  
Vol 12 (8) ◽  
pp. 1327 ◽  
Author(s):  
Anna Ruth W. Halberstadt ◽  
Colin J. Gleason ◽  
Mahsa S. Moussavi ◽  
Allen Pope ◽  
Luke D. Trusel ◽  
...  
Keyword(s):  
Large Scale ◽  
Seasonal Pattern ◽  
Ice Sheet ◽  
Training Data ◽  
Landsat 8 ◽  
Ice Shelf ◽  
Ice Shelves ◽  
Continental Scale ◽  
Lake Evolution ◽  
Supervised Classifiers

Surface meltwater generated on ice shelves fringing the Antarctic Ice Sheet can drive ice-shelf collapse, leading to ice sheet mass loss and contributing to global sea level rise. A quantitative assessment of supraglacial lake evolution is required to understand the influence of Antarctic surface meltwater on ice-sheet and ice-shelf stability. Cloud computing platforms have made the required remote sensing analysis computationally trivial, yet a careful evaluation of image processing techniques for pan-Antarctic lake mapping has yet to be performed. This work paves the way for automating lake identification at a continental scale throughout the satellite observational record via a thorough methodological analysis. We deploy a suite of different trained supervised classifiers to map and quantify supraglacial lake areas from multispectral Landsat-8 scenes, using training data generated via manual interpretation of the results from k-means clustering. Best results are obtained using training datasets that comprise spectrally diverse unsupervised clusters from multiple regions and that include rock and cloud shadow classes. We successfully apply our trained supervised classifiers across two ice shelves with different supraglacial lake characteristics above a threshold sun elevation of 20°, achieving classification accuracies of over 90% when compared to manually generated validation datasets. The application of our trained classifiers produces a seasonal pattern of lake evolution. Cloud shadowed areas hinder large-scale application of our classifiers, as in previous work. Our results show that caution is required before deploying ‘off the shelf’ algorithms for lake mapping in Antarctica, and suggest that careful scrutiny of training data and desired output classes is essential for accurate results. Our supervised classification technique provides an alternative and independent method of lake identification to inform the development of a continent-wide supraglacial lake mapping product.

Sign in / Sign up

Export Citation Format

Share Document