Automated mapping of supraglacial hydrology using Machine Learning

2021 ◽  
Author(s):  
Diarmuid Corr ◽  
Amber Leeson ◽  
Malcolm McMillan ◽  
Ce Zhang
Keyword(s):  
Machine Learning ◽  
Sea Level Rise ◽  
Sea Level ◽  
False Negative ◽  
Ice Sheets ◽  
Landsat 8 ◽  
Continental Scale ◽  
Global Sea Level ◽  
Sentinel 2 ◽  
Antarctic Ice Sheets

<p>Mass loss from Greenlandic and Antarctic ice sheets are predicted to be the dominant contribution to global sea level rise in coming years. Supraglacial lakes and channels are thought to play a significant role in ice sheet mass balance by causing the speed-up of grounded ice and weakening, floating ice shelves to the point of collapse. Identifying the location, distribution and life cycle of these hydrological features on both the Greenland and Antarctic ice sheets is therefore important in understanding their present and future contribution to global sea level rise. Supraglacial hydrological features can be easily identified by eye in optical satellite imagery. However, given that there are many thousands of these features, and they appear in many hundreds of satellite images, automated approaches to mapping these features in such images are urgently needed.</p><p> </p><p>Current automated approaches in mapping supraglacial hydrology tend to have high false positive and false negative rates, which are often followed by manual corrections and quality control processes. Given the scale of the data however, methods such as those that require manual post-processing are not feasible for repeat monitoring of surface hydrology at continental scale. Here, we present initial results from our work conducted as part of the 4D Greenland and 4D Antarctica projects, which increases the accuracy of supraglacial lake and channel delineation using Sentinel-2 and Landsat-7/8 imagery, while reducing the need for manual intervention. We use Machine Learning approaches including a Random Forest algorithm trained to recognise water, ice, cloud, rock, shadow, blue-ice and crevassed regions. Both labelled optical imagery and auxiliary data (e.g. digital elevation models) are used in our approach. Our methods are trained and validated using data covering a range of glaciological and climatological conditions, including images of both ice sheets and those acquired at different points during the melt-season. The workflow, developed under Google Cloud Platform, which hosts the entire archive of Sentinel-2 and Landsat-8 data, allows for large-scale application over Greenlandic and Antarctic ice sheets, and is intended for repeated use throughout future melt-seasons.</p>

A novel technique for automated mapping of Antarctic supraglacial lakes in Sentinel-1 SAR imagery using deep learning

2021 ◽  
Author(s):  
Mariel Dirscherl ◽  
Andreas Dietz ◽  
Celia Baumhoer ◽  
Christof Kneisel ◽  
Claudia Kuenzer
Keyword(s):  
Deep Learning ◽  
Sea Level Rise ◽  
Sea Level ◽  
Ice Sheets ◽  
Training Data ◽  
Supraglacial Lakes ◽  
Sar Imagery ◽  
Global Sea Level ◽  
The Antarctic ◽  
Sentinel 2

<p>Supraglacial meltwater accumulation on ice sheets and ice shelves can have considerable impact on ice discharge, mass balance and global sea-level-rise. With further increasing surface air temperatures, surface melting and resulting processes including hydrofracturing, meltwater penetration to the glacier bed as well as surface runoff will cumulate and most likely trigger unprecedented ice mass loss from the Greenland and Antarctic ice sheets. To date, the Antarctic surface hydrological network remains understudied calling for increased monitoring efforts and circum-Antarctic mapping strategies. This is particularly important given that Antarctica’s future contribution to global sea-level-rise is the largest uncertainty in current projections.</p><p>In this study, we present a novel methodology for Antarctic supraglacial lake extent mapping in Sentinel-1 Synthetic Aperture Radar imagery using state-of-the-art deep learning techniques. The method was implemented with the aim of complementing a previously developed supraglacial lake detection algorithm applying Machine Learning on optical Sentinel-2 data in order to deliver a more complete picture of Antarctic meltwater ponding compared to single-sensor mapping products. The deep learning model was trained on 21,200 Sentinel-1 image patches using a modified ResUNet for semantic segmentation of supraglacial lakes and evaluated by means of ten spatially or temporally independent Sentinel-1 test acquisitions distributed across the Antarctic continent. Besides, George VI Ice Shelf is analyzed for intra-annual lake dynamics throughout austral summer 2019/2020 and decision-level fused Sentinel-1 and Sentinel-2 maximum lake extent mapping products are presented for selected time periods. Future work involves the integration of more training data as well as the generation of circum-Antarctic mapping products using both, Sentinel-2 and Sentinel-1 derived lake extent mappings. These will be crucial for intra-annual analyses on supraglacial lake occurrence across the whole continent and associated drivers and impacts.</p>

Trends and projections in ice sheet mass balance

2020 ◽  
Author(s):  
Andrew Shepherd ◽  
Keyword(s):  
Mass Balance ◽  
Sea Level Rise ◽  
Sea Level ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Ice Dynamics ◽  
Surface Mass ◽  
Sea Levels ◽  
Global Sea Level

<p>In recent decades, the Antarctic and Greenland Ice Sheets have been major contributors to global sea-level rise and are expected to be so in the future. Although increases in glacier flow and surface melting have been driven by oceanic and atmospheric warming, the degree and trajectory of today’s imbalance remain uncertain. Here we compare and combine 26 individual satellite records of changes in polar ice sheet volume, flow and gravitational potential to produce a reconciled estimate of their mass balance. <strong>Since the early 1990’s, ice losses from Antarctica and Greenland have caused global sea-levels to rise by 18.4 millimetres, on average, and there has been a sixfold increase in the volume of ice loss over time. Of this total, 41 % (7.6 millimetres) originates from Antarctica and 59 % (10.8 millimetres) is from Greenland. In this presentation, we compare our reconciled estimates of Antarctic and Greenland ice sheet mass change to IPCC projection of sea level rise to assess the model skill in predicting changes in ice dynamics and surface mass balance.  </strong>Cumulative ice losses from both ice sheets have been close to the IPCC’s predicted rates for their high-end climate warming scenario, which forecast an additional 170 millimetres of global sea-level rise by 2100 when compared to their central estimate.</p>

scholarly journals Antarctic climate and ice sheet configuration during a peak-warmth Early Pliocene interglacial

2016 ◽  
Author(s):  
Nicholas R. Golledge ◽  
Zoë A. Thomas ◽  
Richard H. Levy ◽  
Edward G. W. Gasson ◽  
Timothy R. Naish ◽  
...  
Keyword(s):  
Sea Level ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Co2 Concentration ◽  
Geological Evidence ◽  
Early Pliocene ◽  
Air Temperatures ◽  
Climate Envelope ◽  
Global Sea Level ◽  
Antarctic Ice Sheets

Abstract. The geometry of Antarctic ice sheets during warm periods of the geological past is difficult to determine from geological evidence, but is important to know because such reconstructions enable a more complete understanding of how the ice-sheet system responds to changes in climate. Here we investigate how Antarctica evolved under orbital and greenhouse gas conditions representative of a peak warmth interglacial in the early Pliocene at 4.23 Ma. Using offline-coupled climate and ice-sheet models, together with palaeoenvironmental proxy data to define a likely climate envelope, we simulate a range of ice-sheet geometries and calculate their likely contribution to sea level. In addition, we use these simulations to investigate the processes by which the West and East Antarctic ice sheets respond to environmental forcings and the timescales over which these behaviours manifest. We conclude that the Antarctic ice sheet contributed approximately 8.5 m to global sea level at this time, under an atmospheric CO2 concentration identical to present (400 ppm). Warmer-than-present ocean temperatures led to the collapse of West Antarctica over centuries, whereas higher air temperatures initiated surface melting in parts of East Antarctica that over one to two millennia led to lowering of the ice-sheet surface, flotation of grounded margins in some areas, and retreat of the ice sheet into the Wilkes Subglacial Basin. The results show that regional variations in climate, ice-sheet geometry, and topography produce long-term sea-level contributions that are non-linear with respect to the applied forcings, and which under certain conditions exhibit threshold behaviour associated with behavioural tipping points.

Long-term future projections for the Greenland and Antarctic ice sheets with the model SICOPOLIS

2021 ◽  
Author(s):  
Ralf Greve ◽  
Christopher Chambers ◽  
Reinhard Calov ◽  
Takashi Obase ◽  
Fuyuki Saito ◽  
...  
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
Ice Sheets ◽  
Future Climate ◽  
Model Intercomparison ◽  
Mass Losses ◽  
Intercomparison Project ◽  
Sensitive Experiment ◽  
Antarctic Ice Sheets

<p>The Coupled Model Intercomparison Project Phase 6 (CMIP6) is a major international climate modelling initiative. As part of it, the Ice Sheet Model Intercomparison Project for CMIP6 (ISMIP6) was devised to assess the likely sea-level-rise contribution from the Greenland and Antarctic ice sheets until the year 2100. This was achieved by defining a set of future climate scenarios by evaluating results of CMIP5 and CMIP6 global climate models (GCMs, including MIROC) over and surrounding the Greenland and Antarctic ice sheets. These scenarios were used as forcings for a variety of ice-sheet models operated by different working groups worldwide (Goelzer et al. 2020, doi: 10.5194/tc-14-3071-2020; Seroussi et al. 2020, doi: 10.5194/tc-14-3033-2020).</p><p>Here, we use the model SICOPOLIS to carry out extended versions of the ISMIP6 future climate experiments for the Greenland and Antarctic ice sheets until the year 3000. For the atmospheric forcing (anomalies of surface mass balance and temperature) beyond 2100, we sample randomly the ten-year interval 2091-2100, while the oceanic forcing beyond 2100 is kept fixed at 2100 conditions. We conduct experiments for the pessimistic, "business as usual" pathway RCP8.5 (CMIP5) / SSP5-8.5 (CMIP6), and for the optimistic RCP2.6 (CMIP5) / SSP1-2.6 (CMIP6) pathway that represents substantial emissions reductions. For the unforced, constant-climate control runs, both ice sheets are stable until the year 3000. For RCP8.5/SSP5-8.5, they suffer massive mass losses: For Greenland, ~1.7 m SLE (sea-level equivalent) for the 12-experiment mean, and ~3.5 m SLE for the most sensitive experiment. For Antarctica, ~3.3 m SLE for the 14-experiment mean, and ~5.3 m SLE for the most sensitive experiment. For RCP2.6/SSP1-2.6, the mass losses are limited to a two-experiment mean of ~0.26 m SLE for Greenland, and a three-experiment mean of ~0.25 m SLE for Antarctica. Climate-change mitigation during the next decades will therefore be an efficient means for limiting the contribution of the ice sheets to sea-level rise in the long term.</p>

scholarly journals Acceleration of the contribution of the Greenland and Antarctic ice sheets to sea level rise

2011 ◽  
Vol 38 (5) ◽  
pp. n/a-n/a ◽  
Author(s):  
E. Rignot ◽  
I. Velicogna ◽  
M. R. van den Broeke ◽  
A. Monaghan ◽  
J. T. M. Lenaerts
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
Ice Sheets ◽  
Antarctic Ice Sheets

Recent relative sea-level trends: an attempt to quantify the forcing factors

2006 ◽  
Vol 364 (1841) ◽  
pp. 821-844 ◽  
Author(s):  
Hans-Peter Plag
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
Tide Gauge ◽  
Spatial Scales ◽  
Ice Sheets ◽  
Global Ocean ◽  
Tide Gauges ◽  
Global Average ◽  
Global Sea Level ◽  
The Antarctic

Local sea-level is affected by a number of forcing factors, which all contribute to the trends observed by tide gauges. Here we use the fingerprints of main factors contributing to secular sea-level trends to construct an initial empirical model that explains best the trends in sea-level as recorded by the large number of coastal tide gauges over the last 50 years. The forcing factors considered include steric changes derived from observations, post-glacial rebound as predicted by geophysical models and mass changes in the Greenland and Antarctic ice sheets as predicted by the static sea-level equation. The approximation of the observed spatial pattern of sea-level trends through a model based on the spatial fingerprints of the main forcing factors fully utilizes the information contents of the available observations and models and allows the interpolation of the sea-level trends between the tide gauges. As a result, we obtain the global picture of sea-level trends due to the forcing factors accounted for in the analysis. Moreover, we derive constraints on the mass changes of the large ice sheets. The empirical models explain about 15% of the variance of the sea-level trends. Nevertheless, the models are correlated with the observations on the level of 0.38±0.07, indicating that most of the unexplained variance is due to contributions with small spatial scales. Averaged over the last five decades, the results indicate that the Antarctic and Greenland ice sheets have been melting with an equivalent contribution to global sea-level rise of 0.39±0.11 and 0.10±0.05 mm yr −1 , respectively. The steric signal derived from observations is clearly identified in the sea-level trends and is found to be at a minimum of 0.2 mm yr −1 , with the most likely value being close to 0.35 mm yr −1 . The global tide gauge network, which covers only a small fraction of the ocean surface, appears to sense an average sea-level rise larger than the global average. Extrapolating the regression models to the global ocean and taking into account the uncertainties in the extrapolation results in a most likely global average of the order of 1.05±0.75 mm yr −1 .

scholarly journals Antarctic climate and ice-sheet configuration during the early Pliocene interglacial at 4.23 Ma

2017 ◽  
Vol 13 (7) ◽  
pp. 959-975 ◽  
Author(s):  
Nicholas R. Golledge ◽  
Zoë A. Thomas ◽  
Richard H. Levy ◽  
Edward G. W. Gasson ◽  
Timothy R. Naish ◽  
...  
Keyword(s):  
Sea Level ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Co2 Concentration ◽  
Geological Evidence ◽  
Early Pliocene ◽  
Air Temperatures ◽  
Climate Envelope ◽  
Global Sea Level ◽  
Antarctic Ice Sheets

Abstract. The geometry of Antarctic ice sheets during warm periods of the geological past is difficult to determine from geological evidence, but is important to know because such reconstructions enable a more complete understanding of how the ice-sheet system responds to changes in climate. Here we investigate how Antarctica evolved under orbital and greenhouse gas conditions representative of an interglacial in the early Pliocene at 4.23 Ma, when Southern Hemisphere insolation reached a maximum. Using offline-coupled climate and ice-sheet models, together with a new synthesis of high-latitude palaeoenvironmental proxy data to define a likely climate envelope, we simulate a range of ice-sheet geometries and calculate their likely contribution to sea level. In addition, we use these simulations to investigate the processes by which the West and East Antarctic ice sheets respond to environmental forcings and the timescales over which these behaviours manifest. We conclude that the Antarctic ice sheet contributed 8.6 ± 2.8 m to global sea level at this time, under an atmospheric CO2 concentration identical to present (400 ppm). Warmer-than-present ocean temperatures led to the collapse of West Antarctica over centuries, whereas higher air temperatures initiated surface melting in parts of East Antarctica that over one to two millennia led to lowering of the ice-sheet surface, flotation of grounded margins in some areas, and retreat of the ice sheet into the Wilkes Subglacial Basin. The results show that regional variations in climate, ice-sheet geometry, and topography produce long-term sea-level contributions that are non-linear with respect to the applied forcings, and which under certain conditions exhibit threshold behaviour associated with behavioural tipping points.

scholarly journals Destabilisation of an Arctic ice cap triggered by a hydro-thermodynamic feedback to summer-melt

2014 ◽  
Vol 8 (3) ◽  
pp. 2685-2719 ◽  
Author(s):  
T. Dunse ◽  
T. Schellenberger ◽  
A. Kääb ◽  
J. O. Hagen ◽  
T. V. Schuler ◽  
...  
Keyword(s):  
Mass Loss ◽  
Sea Level Rise ◽  
Sea Level ◽  
Drainage Basin ◽  
Ice Sheets ◽  
Polar Regions ◽  
Svalbard Archipelago ◽  
Flow Acceleration ◽  
Ice Cap ◽  
Global Sea Level

Abstract. Mass loss from glaciers and ice sheets currently accounts for two-thirds of the observed global sea-level rise and has accelerated since the 1990s, coincident with strong atmospheric warming in the Polar Regions. Here we present continuous GPS measurements and satellite synthetic aperture radar based velocity maps from the Austfonna ice cap, Svalbard, that demonstrate strong links between surface-melt and multiannual ice-flow acceleration. We identify a hydro-thermodynamic feedback that successively mobilizes stagnant ice regions, initially frozen to their bed, thereby facilitating fast basal motion over an expanding area. By autumn 2012, successive destabilization of the marine terminus escalated in a surge of the ice cap's largest drainage basin, Basin-3. The resulting iceberg discharge of 4.2 ± 1.6 Gt a−1 over the period April 2012 to May 2013 triples the calving loss from the entire ice cap. After accounting for the terminus advance, the related sea-level rise contribution of 7.2 ± 2.6 Gt a−1 matches the recent annual ice-mass loss from the entire Svalbard archipelago. Our study highlights the importance of dynamic glacier wastage and illuminates mechanisms that may trigger a sustained increase in dynamic glacier wastage or the disintegration of ice-sheets in response to climate warming, which is acknowledged but not quantified in global projections of sea-level rise.

Redating the Global Abrupt Sea-Level Rise during Meltwater Pulse-1A and Implications for Global Ice Mass Loss

2021 ◽  
Author(s):  
Christian Turney ◽  
Nicholas Golledge ◽  
Paula Reimer ◽  
Tim Heaton ◽  
Alan Hogg ◽  
...  
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
North Atlantic ◽  
Ice Sheets ◽  
Ice Sheet ◽  
The North ◽  
The North Atlantic ◽  
Global Sea Level ◽  
Age Range ◽  
Ice Sheet Modelling

<div><span>Model-based projections of ice-sheet thresholds and global sea-level rise are severely constrained by </span><span>instrumental observations being only decadal to century-long. As we improve our understanding of these processes, projections just a few years old are now considered conservative, raising concerns about our ability to successfully plan for abrupt future change. </span><span>Past periods of abrupt and extreme warming offer ‘process analogues’ that can provide new insights into the future rate of response of polar ice sheets to warming of the Earth system. The Last Termination </span><span>(20,000-10,000 years ago or 20-10 ka BP) </span>in the North Atlantic region was characterised by a series of abrupt climatic changes including rapid warming at 14.7 ka BP (the start of the “Bølling”, or GI-1 in the Greenland ice-core isotope stratigraphy) which was accompanied by an Antarctic Cold Reversal (ACR) in the south. Potentially important, during the onset of GI-1, warming persisted in the south for some 256±133 calendar years before the ACR, providing a period of time during which both polar regions experienced increasing temperatures. Sometime around the onset of GI-1 and the ACR, Meltwater Pulse 1A (MWP-1A) formed an abrupt sea level rise of ~15 metres, and was coincident with a period of enhanced iceberg flux in the Southern Ocean. It seems likely the majority of the sea level rise came from the Northern Hemisphere – up to 5-6 metres from the Laurentide Ice Sheet – though the timing remains uncertain. The contribution of Antarctic Ice Sheets (AIS) to global mean sea level (GMSL) rise during MWP-1A range from ‘high-end’ scenarios (>10 m contributing over half of the total GMSL rise), to ‘low-end’ (scenarios with little to no contribution). Here we report the results of a multidisciplinary study, with refined age and Antarctic ice-sheet modelling of the MWP-1A sea-level rise. With the recently released international radiocarbon calibration curve (IntCal20), our Bayesian age modelling of terrestrial ages from flooded mangrove swamps suggests global <span>sea level rose across a mean age range of 14.58 ka BP to 14.42 ka BP, with a mean rate of sea-level rise of 0.94 metres per decade (14.97 metres over 160 years). Because the calibrated age range at 95% confidence overlaps in this age model, it is possible the 15 metre rise during MWP1A could have taken place essentially instantaneously. Even the most conservative age modelling we have undertaken indicates an extraordinary rapid rate of sea-level rise; two orders of magnitude larger than the mean rate of global sea level rise since 1993 (0.03±0.003 metres per decade). Our ice-sheet modelling suggests a substantial and rapid loss of Antarctic ice mass (mostly from the Weddell Sea Embayment and the Antarctic Peninsula), synchronous with warming and ice loss in the North Atlantic. The drivers and mechanisms of the observed near-synchronous interhemispheric changes will be discussed, with implications for the future.</span></div>

Relative control of bedrock roughness versus topography on global glacier bed friction

2021 ◽  
Author(s):  
Olivier Gagliardini ◽  
Fabien Gillet-Chaulet ◽  
Florent Gimbert
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
Inverse Method ◽  
Ad Hoc ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Grid Resolution ◽  
Classical Approach ◽  
Bed Topography ◽  
Bed Friction

<p>Friction at the base of ice-sheets has been shown to be one of the largest uncertainty of model projections for the contribution of ice-sheet to future sea level rise. On hard beds, most of the apparent friction is the result of ice flowing over the bumps that have a size smaller than described by the grid resolution of ice-sheet models. To account for this friction, the classical approach is to replace this under resolved roughness by an ad-hoc friction law. In an imaginary world of unlimited computing resource and highly resolved bedrock DEM, one should solve for all bed roughnesses assuming pure sliding at the bedrock-ice interface. If such solutions are not affordable at the scale of an ice-sheet or even at the scale of a glacier, the effect of small bumps can be inferred using synthetical periodic geometry. In this presentation,<span>  </span>beds are constructed using the superposition of up to five bed geometries made of sinusoidal bumps of decreasing wavelength and amplitudes. The contribution to the total friction of all five beds is evaluated by inverse methods using the most resolved solution as observation. It is shown that small features of few meters can contribute up to almost half of the total friction, depending on the wavelengths and amplitudes distribution. This work also confirms that the basal friction inferred using inverse method<span>  </span>is very sensitive to how the bed topography is described by the model grid, and therefore depends on the size of the model grid itself.<span> </span></p>

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