Decades of observations uncover secrets of Antarctic fast ice

Sea ice that has persisted for at least 15 days and is held fast to the shoreline is called “fast ice.” Around Antarctica, fast ice protects continental ice from ocean waves, creates unique ecological habitats for everything from zooplankton to penguins, and provides an important staging ground for research.

The conditions that form thick, strong, fast ice have historically been difficult to measure. Satellite observations allow for powerful analysis of other aspects of Antarctic sea ice cover, such as extent, but they’re not well suited to assessing the thickness of fast ice.

In the Journal of Geophysical Research: Oceans, researchers provide a historical record of fast ice thickness in McMurdo Sound, off the coast of Antarctica, from 1986 to 2022 and describe environmental variables that correlate with fast ice thickness.

The results could inform scientists as to when they can traverse fast ice safely, and they shed light on how climate change may affect ecosystems that fast ice supports.

The researchers based their work on a variety of information. Manual measurements through drill holes along with coincident records of internal ice temperatures and ocean temperatures let the researchers measure the thickness of the fast ice and infer the ocean heat flux acting on the ice from below.

The thickness of McMurdo Sound’s fast ice was remarkably stable on a decadal basis, the researchers found, with no obvious trend toward thicker or thinner ice over the 37 years they studied.

On an interannual basis, however, ice thickness varied by up to 0.7 of a meter. The researchers also confirmed earlier findings that different climate drivers work on different timescales: Global climate influences fast ice formation on a decadal timescale, whereas monthly and seasonal weather fluctuations influence year-to-year variations.

Three factors in particular led to thicker fast ice, the team observed: lower air temperatures, winds blowing from the south, and decreased “storminess” (a measurement of temperature and pressure) during the winter months. Long stretches of cold days without storms but with winds from the south made for the thickest fast ice.

This story is republished courtesy of Eos, hosted by the American Geophysical Union. Read the original story here.