An ice arch forms when sea ice is pushed together by ocean currents and wind, causing the edges to buckle and rise, creating an arch-shaped formation. An ice arch is a key patch of block ice that prevents other pieces of ice from entering a strait or other body of water.
Ice arches are natural seasonal structures that form during the winter months and typically last until late spring or summer.
These arches are most commonly observed where there are narrow passageways between landmasses, such as between islands or at the entrances to bays. The pressure exerted by the moving sea ice against the landmasses or against other ice floes causes the ice to deform and rise into an arch.
Where do ice arches form?
Ice arches typically occur in polar regions, where conditions are favorable for their formation. One such structure found every year is the ice arch that typically forms between Ellesmere Island and Greenland every January. While the ice arch is in place, typically for roughly six months out of every year, flowing ice is prevented from flowing through the Nares Strait.
This narrow waterway which separates Greenland and Ellesmere Island, experiences a significant among of ice passing through it due to a southward flowing current, fueled by the Beaufort Gyre.
The Nares Strait ice arch typically crumbles in June or July each year although the breakdown has occurred usually early in some years such as the disintegration of the ice arch starting in March/April of 2019 and in May of 2017.
Researchers believe the 2017 early ice arch collapse was due to “presence of a polynya in northern Nares Strait, thin ice in the Lincoln Sea, and an unusual wind regime characterized by strong northerly flow.”
Ice arches that temporarily formed at the Nares Strait (between Greenland and Ellesmere Island) can prevent older, thicker ice from drifting southward into warmer waters where it would melt more quickly. Shorter lived and thinner ice arches increased the amount of free flowing ice that exits the Nares Strait. A 2021 study on ice arches by researcher Kent Moore found a nearly twofold increase in ice volume passing through Nares Strait compared to the early 2000s due to less stable or absent arches,
How long do ice arches last?
The lifespan of an ice arch can vary significantly. Some may last only a few days or weeks, while others may persist throughout the winter season, depending largely on temperature fluctuations, the strength of the currents, and the overall dynamics of the ice.
As global temperatures rise, the formation and stability of these ice arches can be affected, which is a concern for researchers studying the impacts of climate change on polar regions. Research published in 2021 by University of Toronto Mississauga in Nature Communications found that in general, ice arches in the Nares Strait are trending towards an earlier breakup or failure to form at all. The study highlighted an ice arch at the northern end of Nares Strait that collapsed in early May in 2017, lasting about 120 days.
On the other extreme, there are ice arches that can be much longer lived. An ice arch at the southern end of Nares Strait that formed in mid December of 2020 lasted until well into July 2021 for a total lifespan of about 200 days.
This article was originally written on June 8, 2020 and has since been updated.
References
Hansen, K. (2019, June 25). Ice arch crumbles early. NASA Earth Observatory. https://earthobservatory.nasa.gov/images/145232/ice-arch-crumbles-early
Moore, G. W. K., & McNeil, K. (2018). The early collapse of the 2017 Lincoln Sea ice arch in response to anomalous sea ice and wind forcing. Geophysical Research Letters, 45(16), 8343-8351. DOI: 10.1029/2018GL078428
Moore, G. K., Howell, S. E. L., Brady, M., Xu, X., & McNeil, K. (2021). Anomalous collapses of Nares Strait ice arches leads to enhanced export of Arctic sea ice. Nature communications, 12(1), 1. DOI: 10.1038/s41467-020-20314-w
Voiland, A. (2017, May 20). Breakdown of an ice arch. NASA Earth Observatory. https://earthobservatory.nasa.gov/images/90245/breakdown-of-an-ice-arch
Fonte : National Geographic
