The Cryosphere: Present and Future

Ice-cliff failure that leads to marine ice-cliff instability could accelerate Antarctic Ice Sheet retreat. Here, the authors use 3D glacier models to investigate ice-cliff failure, derive a retreat rate relationship, and quantify mélange back force necessary to suppress ice-cliff failure.

Systematic satellite, ocean and atmosphere records show the pace and extent of melting in West Antarctica vary by location, with glaciers flowing to the Amundsen Sea most sensitive to atmosphere‒ocean variability atop a marine ice-sheet instability.

The Getz region of West Antarctica is losing ice at an increasing rate; however, the forcing mechanisms remain unclear. Here we show for the first time that since 1994, widespread speedup has occurred on the majority of glaciers in the Getz drainage basin, with some glaciers speeding up by over 44 %.

Historical velocity maps reveal over five decade-long acceleration and high-level discharge in Totten Glacier, East Antarctica, from 1963-2018, induced by warm modified Circumpolar Deep Water.

The authors combine measurements of ice loss from West Antarctica with climate modelling to show that periods of drought or extremely heavy precipitation can significantly increase or decrease rates of mass loss for periods lasting several years.

This study uses ice sheet modeling experiments to show that thawing portions of the Antarctic ice sheet bed can increase century-scale mass loss, particularly in the Wilkes and Enderby Land regions of East Antarctica.

A new metric measuring the exposure of the Antarctic coastline to full open-ocean conditions reveals strong regional and seasonal change and variability occurred over the past four decades due to the loss and/or gain of an offshore sea-ice buffer.

Glacial melt can modify heat transport, and therefore ocean processes, associated with ice front retreat, as revealed by direct observations from the Pine Island Bay region of Antarctica.

New simulations find that one of Antarctica’s largest ice shelves, the Filchner–Ronne, may be less vulnerable to climate change than previously thought. Melting of the ice shelf initially decreases for many decades, and only increases when global warming exceeds approximately 7 °C.

The East Antarctic Ice Sheet is currently surrounded by relatively cool water but changes in ocean dynamics may lead to warmer ocean water on the shelf in the future. This has the potential to dramatically increase its future sea level contribution.

As glaciers terminate into the ocean, mass is lost through frontal ablation where the ice meets the ocean. Here the authors estimate decadal frontal ablation from 2000 to 2020 of 1496 glaciers in the Northern Hemisphere, and find that frontal ablation makes up 79% of ice discharge to the ocean.

Accurate assessments of ice-sheet runoff are essential for sea-level projections. A new method using satellite altimeter observations can provide near real-time surface mass balance measurements across an entire ice sheet and reveal runoff variability not captured by global climate models.

Melting at the base of the Greenland Ice Sheet is often disregarded as a source of quantifiable mass loss. In this study, the authors find the basal mass loss is equivalent to 8% of the ice sheet’s present imbalance, and that the loss of mass from basal melt is likely to increase in the future.

This study uses radio-echo sounding measurements, ice-core data and models to map the spatial variation in ice-crystal orientation in the northeast Greenland Ice Stream and shows how it potentially affects the ice-flow dynamics in this region.

From 2018 to 2021, KIV Steenstrups Nordre Bræ, a marine-terminating outlet glacier of the Greenland Ice Sheet, retreated ~7 km, thinned ~20%, doubled in discharge, and accelerated ~300%. This rate of change is unprecedented in the observational record.

Extreme ice sheet melt events in northeast Greenland occur after intense water vapor transport into northwest Greenland by atmospheric rivers. Through the foehn effect, the air becomes warmer and drier as it descends the ice sheet slope.

The effect of increasing surface melt on annual discharge is unknown for the Greenland Ice Sheet. Here, the authors find that Greenland’s largest single-glacier contributor to sea-level rise accommodates basal floods following supraglacial lake-drainage events with limited impact on ice flow.

Factors driving ice flow variability in Greenland vary by timescale. At seasonal scale, Helheim Glacier ice velocity responds most strongly to meltwater runoff. Glacier terminus position drives velocity variability at longer time scales.

A new study finds that the North East Greenland ice stream is not as stable as previously thought and that this will affect its future evolution.

Anomalously slow seismic velocities in the upper Greenlandic crust reveal soft sedimentary substrates beneath major outlet glaciers. This, together with elevated geothermal heat flux observed at the onset of fast ice flow, has major implications for ice-sheet dynamics.

New experiments suggest that the Petermann Ice Shelf in northwest Greenland is unlikely to recover once a breakup occurs in the future. If this is not unique to this ice shelf, continued ocean warming may lead to high discharge from polar ice sheets.

The North Atlantic biological pump has the most intense absorption of C globally, but how this will fare in light of climate changes (especially sea-ice melting) is poorly understood. Here the authors present a 24-month continuous time series of physical, chemical, and biological observations in the Fram Strait.

Water mass transformation in the Nordic and Barents Seas is important for the Atlantic Meridional Overturning Circulation (AMOC). Here, the authors show increases in air-sea heat fluxes linked to sea ice retreat along the boundary currents of the Nordic and Barents Seas that could influence how the AMOC reacts to climate change.

Delayed Antarctic sea-ice decline is linked to Southern Ocean eddies - and their explicit treatment in models is crucial. New multi-resolution climate change projections give a possible reason for low confidence in IPCC’s current 21st-century Antarctic sea-ice projections.

Processes controlling the onset of the Antarctic sea ice season remain unclear. Here, analyses of observations show that ocean solar energy storage and sea ice drift are key drivers, providing insights to understand variations in sea ice season duration.

Winter sea ice production appears to have been increasing, despite Arctic warming being most intense during winter. Here the authors examine the competing factors controlling sea ice production in the Kara and Laptev seas, and develop a simple model that explains the rise and subsequent fall of ice production under climate change.

Fram Strait is the major gateway connecting the Arctic Ocean and North Atlantic Ocean, where nearly 90% of the sea ice export from the Arctic Ocean takes place. Here, the authors show that in 2018, ice export showed an unprecedented decline since at least the 1990s, attributed to ongoing Arctic-wide ice thinning and regional-scale atmospheric anomalies.

The fastest sea-ice decline has been observed in the western Arctic, but the underlying mechanisms are still unclear. Here, the authors show that the Pacific North American pattern plays an important role in western Arctic sea-ice variability.

Climate model simulations show that for 1970-2017 externally-forced sea surface temperature increases in the Gulf Stream explain up to 56% of the sea-ice decline in the Barents-Kara Sea during winter via poleward oceanic heat transport.

Arctic sea ice extent continues to decline at an unprecedented rate that climate projection models commonly underestimate. In this study, authors reveal a positive feedback between ocean-ice heat fluxes, sea ice cover, and upper-ocean vortices that is missing in coarse-resolution climate models.