Search

Helheim Glacier, one of the largest marine‐terminating outlet glaciers draining the Greenland Ice Sheet, underwent significant retreat and acceleration in the early 2000s, accounting for an appreciable proportion of the ice sheet's mass loss during that period. Using a range of remotely sensed datasets, we show that despite a subsequent readvance, the glacier has continued to lose mass and thin, and has retreated inland of the retracted position occupied in 2005. Critically, the near‐terminus is up to 100 m thinner than during 2005, and the front 5 km is within 25–50 m of flotation, with retrograde bed slopes extending several kilometers inland of the terminus. The neighboring Fenris and Midgard Glaciers have both undergone recent large‐scale and rapid retreat once their near‐terminus regions began to float, suggesting that under projected climate warming and associated glacier thinning, Helheim Glacier is poised to pass a threshold whereby the near‐terminus region will retreat rapidly. Plain Language Summary: A significant proportion of the Greenland Ice Sheet's contribution to global sea‐level rise is as a result of mass loss from its marine‐terminating glaciers. Helheim Glacier, located in southeast Greenland, is one of the largest and fastest‐flowing glaciers draining the Greenland Ice Sheet. During the early 2000s, Helheim Glacier underwent dramatic retreat and acceleration, but subsequently readvanced during relatively cooler conditions in 2006. However, persistently high ocean and atmospheric temperatures have meant that Helheim Glacier has in fact been continuously losing mass since 2003, despite this readvance. Here, we use a range of remotely sensed data to show that since 2014, Helheim Glacier has accelerated and retreated to a greater extent than occurred in 2003–2005. More importantly, as the glacier has been losing mass over the past two decades, it is currently much thinner than during its peak retreat in 2005. As the glacier continues to lose mass, it will pass a threshold whereby the ice will float and rapidly disintegrate. We observe that this process has already occurred at the glaciers neighboring Helheim Glacier, which are subject to the same climate forcing and thus provide an analogue for the future response of Helheim Glacier to continued warming. Key Points: Helheim Glacier is more retreated and the near‐terminus region is up to 100 m thinner than during its much‐reported dramatic retreat in 2005Helheim, one of Greenland's largest ice dischargers, is now more vulnerable than at any point since the Little Ice AgeHelheim's new configuration offers potential for sustained dynamic instability and a major contribution to global sea‐level rise [ABSTRACT FROM AUTHOR]

The increasingly negative mass balance of the Greenland ice sheet (GrIS) over the last ~25 years has been associated with enhanced surface melt and increased ice loss from marine-terminating outlet glaciers. Accelerated retreat during 2000–2010 was concentrated in the southeast and northwest sectors of the ice sheet; however, there was considerable spatial and temporal variability in the timing and magnitude of retreat both within and between these regions. This behaviour has yet to be quantified and compared for all glaciers in both regions. Furthermore, it is unclear whether retreat has continued after 2010 in the northwest, and whether the documented slowdown in the southeast post-2005 has been sustained. Here, we compare spatial and temporal patterns of frontal change in the northwest and southeast GrIS, for the period 2000–2015. Our results show near-ubiquitous retreat of outlet glaciers across both regions for the study period; however, the timing and magnitude of inter-annual frontal position change is largely asynchronous. We also find that since 2010, there is continued terminus retreat in the northwest, which contrasts with considerable inter-annual variability in the southeast. Analysis of the role of glacier-specific factors demonstrates that fjord and bed geometry are important controls on the timing and magnitude of glacier retreat. [ABSTRACT FROM AUTHOR]