A model for interaction between conduits and surrounding hydraulically connected distributed drainage based on geomorphological evidence from Keewatin, Canada

© 2020 Author(s). We identify and map visible traces of subglacial meltwater drainage around the former Keewatin Ice Divide, Canada, from high-resolution Arctic Digital Elevation Model (ArcticDEM) data. We find similarities in the characteristics and spatial locations of landforms traditionally treated separately (i.e. meltwater channels, meltwater tracks and eskers) and propose that creating an integrated map of meltwater routes captures a more holistic picture of the large-scale drainage in this area. We propose the grouping of meltwater channels and meltwater tracks under the term meltwater corridor and suggest that these features in the order of 10s-100sm wide, commonly surrounding eskers and transitioning along flow between different types, represent the interaction between a central conduit (the esker) and surrounding hydraulically connected distributed drainage system (the meltwater corridor). Our proposed model is based on contemporary observations and modelling which suggest that connections between conduits and the surrounding distributed drainage system within the ablation zone occur as a result of overpressurisation of the conduit. The widespread aerial coverage of meltwater corridors (5%-36% of the bed) provides constraints on the extent of basal uncoupling induced by basal water pressure fluctuations. Geomorphic work resulting from repeated connection to the surrounding hydraulically connected distributed drainage system suggests that basal sediment can be widely accessed and evacuated by meltwater

Brief communication : subglacial lake drainage beneath Isunguata Sermia, west Greenland : geomorphic and ice dynamic effects

We report three active subglacial lakes within 2 km of the lateral margin of Isunguata Sermia, West Greenland, identified by differencing time-stamped ArcticDEM strips. Each lake underwent one drainage–refill event between 2009 and 2017, with two lakes draining in < 1 month in August 2014 and August 2015. The 2015 drainage caused a ∼ 1-month down-glacier slowdown in ice flow and flooded the foreland, aggrading the proglacial channel by 8 m. The proglacial flooding confirms the ice-surface elevation anomalies as subglacial water bodies and demonstrates how their drainage can significantly modify proglacial environments. These subglacial lakes offer accessible targets for geophysical investigations and exploration

Changes in the firn structure of the western Greenland Ice Sheet caused by recent warming

Atmospheric warming over the Greenland Ice Sheet during the last 2 decades has increased the amount of surface meltwater production, resulting in the migration of melt and percolation regimes to higher altitudes and an increase in the amount of ice content from refrozen meltwater found in the firn above the superimposed ice zone. Here we present field and airborne radar observations of buried ice layers within the near-surface (0–20 m) firn in western Greenland, obtained from campaigns between 1998 and 2014. We find a sharp increase in firn-ice content in the form of thick widespread layers in the percolation zone, which decreases the capacity of the firn to store meltwater. The estimated total annual ice content retained in the near-surface firn in areas with positive surface mass balance west of the ice divide in Greenland reached a maximum of 74 ± 25 Gt in 2012, compared to the 1958–1999 average of 13 ± 2 Gt, while the percolation zone area more than doubled between 2003 and 2012. Increased melt and column densification resulted in surface lowering averaging −0.80 ± 0.39 m yr−1 between 1800 and 2800 m in the accumulation zone of western Greenland. Since 2007, modeled annual melt and refreezing rates in the percolation zone at elevations below 2100 m surpass the annual snowfall from the previous year, implying that mass gain in the region is retained after melt in the form of refrozen meltwater. If current melt trends over high elevation regions continue, subsequent changes in firn structure will have implications for the hydrology of the ice sheet and related abrupt seasonal densification could become increasingly significant for altimetry-derived ice sheet mass balance estimates

Brief Communication: Outburst floods triggered by periodic drainage of subglacial lakes, Isunguata Sermia, West Greenland

We report three active subglacial lakes within 2 km of the lateral margin of Isunguata Sermia, West Greenland, identified by differencing time-stamped ArcticDEM strips. Each lake underwent one drainage-refill event between 2009 and 2017, with two lakes draining in < 1 month during August 2014 and August 2015, and all three characterised by 2–3-year refill periods. The 2015 drainage flooded the foreland aggrading 8 m of the proglacial channel, confirming the ice-surface elevation anomalies as subglacial water bodies and demonstrating how subglacial lake drainages can significantly modify proglacial environments. These subglacial lakes offer accessible targets for future geophysical investigations and exploration

Automated mapping of the seasonal evolution of surface meltwater and its links to climate on the Amery Ice Shelf, Antarctica

Surface meltwater is widespread around the Antarctic Ice Sheet margin and has the potential to influence ice shelf stability, ice flow and ice–albedo feedbacks. Our understanding of the seasonal and multi-year evolution of Antarctic surface meltwater is limited. Attempts to generate robust meltwater cover time series have largely been constrained by computational expense or limited ice surface visibility associated with mapping from optical satellite imagery. Here, we add a novel method for calculating visibility metrics to an existing meltwater detection method within Google Earth Engine. This enables us to quantify uncertainty induced by cloud cover and variable image data coverage, allowing time series of surface meltwater area to be automatically generated over large spatial and temporal scales. We demonstrate our method on the Amery Ice Shelf region of East Antarctica, analysing 4164 Landsat 7 and 8 optical images between 2005 and 2020. Results show high interannual variability in surface meltwater cover, with mapped cumulative lake area totals ranging from 384 to 3898 km2 per melt season. By incorporating image visibility assessments, however, we estimate that cumulative total lake areas are on average 42 % higher than minimum mapped values. We show that modelled melt predictions from a regional climate model provide a good indication of lake cover in the Amery region and that annual lake coverage is typically highest in years with a negative austral summer SAM index. Our results demonstrate that our method could be scaled up to generate a multi-year time series record of surface water extent from optical imagery at a continent-wide scale

Diverse supraglacial drainage patterns on the Devon ice Cap, Arctic Canada

The Devon Ice Cap (DIC) is one of the largest ice masses in the Canadian Arctic. Each summer, extensive supraglacial river networks develop on the DIC surface and route large volumes of meltwater from ice caps to the ocean. Mapping their extent and understanding their temporal evolution are important for validating runoff routing and melt volumes predicted by regional climate models (RCMs). We use 10 m Sentinel-2 images captured on 28 July and 10/11 August 2016 to map supraglacial rivers across the entire DIC (12,100 km2). Both dendritic and parallel supraglacial drainage patterns are found, with a total length of 44,941 km and a mean drainage density (Dd ) of 3.71 km−1. As the melt season progresses, Dd increases and supraglacial rivers form at progressively higher elevations. There is a positive correlation between RCM-derived surface runoff and satellite-mapped Dd , suggesting that supraglacial drainage density is primarily controlled by surface runoff