Antarctic 'landfast' ice likely to reduce by end of century, important to include it in climate models, say scientists

Antarctica's 'landfast' ice, the stationary sea ice forming around and remaining attached to the coastline or among grounded icebergs, is likely to reduce by the end of this century, in its season length, thickness and extent, according to a new review.

A critical breeding habitat for emperor penguins and essential for their survival, landfast ice provides a key substrate for early-season primary production fuelling coastal marine food cycles.

Along with documenting a recent dramatic crash in its extent, the first-ever broad review of Antarctic landfast ice highlighted its far-reaching importance in the Earth system and identified priorities for future research, scientists involved in the review said.

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"Landfast ice needs to be distinguished from other types of sea ice for the different roles it plays in the global climate system," said Alex Fraser, an Australian Antarctic Program Partnership scientist who co-led the team of 23 international authors. He along with the other co-lead Pat Wongpan have published their review in the journal Reviews of Geophysics.

"Our comprehensive review synthesises the current state of knowledge of Antarctic landfast ice, from its physical and mechanical properties through to its major roles in key glaciological, oceanographic, atmospheric, biogeochemical and biological processes," said Fraser.

However, because landfast ice is not currently represented in global climate models, projections were highly uncertain, they said.

The review noted that the "incorporation of prognostic fast ice into regional and circum-Antarctic coupled sea ice-ocean models is a high priority."

"The formation of Antarctic fast ice results from complicated interactions between sea ice, ocean, atmosphere, coastal configuration, bathymetry and grounded icebergs (of which no large-scale dataset currently exists), and its accurate model representation is perhaps a more challenging problem than its Arctic counterpart," the authors wrote.

The researchers said that their analysis demonstrated the speed with which landfast ice can respond to environmental change.

"From satellite records, we created a new yearly time-series of landfast ice from 2000-2022 which shows that the annual minimum circum-Antarctic fast-ice extent reached a dramatic record low in March 2022," said Fraser.

Landfast ice extent dropped to just 123,200 sqkm (square kilometres) in March 2022 (its normal March range is between 168,600 and 295,200 sqkm).

"Regions where landfast ice was lost previously had fast-ice cover in early-mid March every year from 2000 to 2021," he said.

There was a complete loss of multi-year (present throughout the year) landfast ice in the Ross Sea, a widespread loss of persistent landfast ice along the eastern side of the Antarctic Peninsula, and across much of East Antarctica.

This unprecedented low landfast-ice extent occurred in tandem with the record low sea-ice extent minimum in 2022, indicating a similar environmental response between pack and landfast ice with possible linkage between the two.

The review recommended that "observations of fast ice, including both ground- and satellite-based, should be coordinated and expanded to allow deeper understanding of this important part of the global cryosphere and Antarctic coastal environment."

"If the recent crash in landfast ice represents a long-term trend, there are potentially catastrophic consequences for Antarctic coastal geographies and ecosystems, with knock-on effects throughout the world," Fraser said.

Antarctic fast ice can cover extensive regions of the Southern Ocean, and ranges in thickness up to several tens of metres. Seasonally, its change in extent roughly triples, from about 21,000 sqkm (mid-March) to 601,000 sqkm (late September/early October).

In most regions, it forms in autumn, persists through the winter and melts or breaks out in spring/summer. In some regions landfast ice can survive the melt season to become multi-year ice.

Despite the critical importance of Antarctic landfast ice for a wide variety of coastal processes, our knowledge of it "is limited either spatially (e.g. covering a small study region), temporally (e.g. a snapshot, or covering only some part of the annual cycle), or both", the review said.

Until quite recently Antarctic landfast ice has been overlooked in studies, likely due to insufficient knowledge of its distribution, leading to its reputation as a "missing piece of the Antarctic puzzle".