Temporal variations in the surface hydrology across Antarctic ice shelves

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.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 NDWIice 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.

Download Full-text

Lateral meltwater transfer across an Antarctic ice shelf

10.5194/tc-2019-316 ◽

2020 ◽

Cited By ~ 1

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.

Download Full-text

Lateral meltwater transfer across an Antarctic ice shelf

The Cryosphere ◽

10.5194/tc-14-2313-2020 ◽

2020 ◽

Vol 14 (7) ◽

pp. 2313-2330 ◽

Cited By ~ 2

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.

Download Full-text

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

10.5194/egusphere-egu21-16349 ◽

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

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.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.&#160;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.

Download Full-text

Long-Term Changes of Open-Surface Water Bodies in the Yangtze River Basin Based on the Google Earth Engine Cloud Platform

Remote Sensing ◽

10.3390/rs11192213 ◽

2019 ◽

Vol 11 (19) ◽

pp. 2213 ◽

Cited By ~ 8

Author(s):

Yue Deng ◽

Weiguo Jiang ◽

Zhenghong Tang ◽

Ziyan Ling ◽

Zhifeng Wu

Keyword(s):

Surface Water ◽

Yangtze River Basin ◽

Google Earth ◽

Water Bodies ◽

Open Surface ◽

Cloud Platform ◽

Long Term Changes ◽

The Yangtze River Basin ◽

Surface Water Bodies

The spatiotemporal changes of open-surface water bodies in the Yangtze River Basin (YRB) have profound influences on sustainable economic development, and are also closely relevant to water scarcity in China. However, long-term changes of open-surface water bodies in the YRB have remained poorly characterized. Taking advantage of the Google Earth Engine (GEE) cloud platform, this study processed 75,593 scenes of Landsat images to investigate the long-term changes of open-surface water bodies in the YRB from 1984 to 2018. In this study, we adopted the percentile-based image composite method to collect training samples and proposed a multiple index water detection rule (MIWDR) to quickly extract the open-surface water bodies. The results indicated that (1) the MIWDR is suitable for the long-term and large-scale Landsat water bodies mapping, especially in the urban regions. (2) The areas of permanent water bodies and seasonal water bodies were 29,076.70 km2 and 21,526.24 km2, accounting for 57.46% and 42.54% of the total open-surface water bodies in the YRB, respectively. (3) The permanent water bodies in the YRB increased along with the decreases in the seasonal water bodies from 1984 to 2018. In general, the total open-surface surface water bodies in the YRB experienced an increasing trend, with an obvious spatial heterogeneity. (4) The changes of open-surface water bodies were associated with the climate changes and intense human activities in the YRB, however, the influences varied among different regions and need to be further investigated in the future.

Download Full-text