Zachariæ Isstrøm, a large glacier in the northeast coast of Greenland, is in a state of accelerated retreat after it detached from an important sill. This shift has caused great instability for the glacier, according to a new study from Science Magazine.
Recognizing 0.5 meters of possible sea level rise held within Zachariæ, and its acceleration expected to continue, the authors point to an increased likelihood of sea level rise coming from this area in the next 20 or 30 years. This study is noteworthy since Zachariæ is found far north, close to 79 degrees N. The Greenland glaciers which have been highlighted for their fast retreats to date are found further south.
Jeremie Mouginot from the University of California, Irvine and his coauthors looked specifically at the effects of warming ocean and air temperatures on the melting and discharge dynamics of the glacier. (More Greenland work from the UCI team can be found here.)
The precise measurements of the ice discharge data were made possible by NASA, who provided funds and much of the data and equipment.
The researchers observed a 50% increase in the retreating speed since 2000. There was also a doubling of ice thinning. On the ice shelf, this process was extensive enough to be measured by satellites. Data showed Zachariæ in a stable state up until 2003 when a large piece broke off. Since that breaking point Zachariæ retreated at a steady state until 2013-14 when the retreat accelerated. It is now retreating at a rate of 125 meters per year and losing 5 gigatons of mass yearly.
The increased mass loss is attributed by the authors to a combination of warming air and ocean temperatures. These changes lead to increased ice loss by way of calving, as opposed to changes in the accumulation of mass through precipitation.
Ocean temperatures play an important role in glacier retreat; the authors argue that the nearly 1 degree C increase in ocean temperatures near the glacier is largely responsible for triggering the enhanced retreat.
Warming air temperatures lead to an increase in ice thinning which affects the placement of the grounding line below the surface – an important transition area where the glacier begins floating. As the grounding line retreats there is increased surface area of the glacier exposed to the melting from below. Zachariæ began to calve so rapidly at the grounding line in 2014 that the remaining ice shelf was “95% smaller than in 2002” according to the researcher’s Landsat optical imagery data.
The authors did speak of another glacier in the Northeast of Greenland that is also experiencing accelerations-Nioghalvfjerdsfjorden Glacier (NG). Though the overall changes on NG were not as rapid as Zachariæ, the authors suggest that NG will become more vulnerable in the future.
“Not long ago, we wondered about the effect on sea levels if Earth’s major glaciers were to start retreating,” said one of the authors, Eric Rignot. “We no longer need to wonder; for a couple of decades now, we’ve been able to directly observe the results of climate warming on polar glaciers. The changes are staggering and are now affecting the four corners of Greenland.”
Isstrøm, a Danish phrase that translates as ice stream, seems to take on a poetic meaning when one thinks of the drastic amount of ice now “streaming” from the glacier.
As Zachariæ transitions into a tidewater glacier, it can be expected to calve more icebergs and become more vulnerable to increases in ocean temperatures. With other glaciers in this area retreating quickly Greenland will be an important region to watch in the coming decades, the authors concluded.
Here is a quick video illustrating how the position of the grounding line can accelerate retreat of a glacier by increasing the area exposed to currents.