New study finds a way to better tally Antarctica's ice sheets

"So it's really important to be as accurate as we can." Especially when considering the threat melting rising sea levels pose on coastal communities.

Focusing on 20 of the 300 separate ice shelf systems encircling approximately 75 percent of the Antarctic ice sheet, researchers made a startling discovery: on average, these ice shelves are nearly 6 percent thinner than previously estimated, with a difference of roughly 17 meters.

While this percentage may seem minor, it's imperative to grasp that typical ice shelves span a thickness spectrum ranging from 50 to 600 meters.

Notably, the study highlighted the intricate nature of assumptions about ice shelf thickness. While these assumptions hold true on a grand scale, they exhibit considerable variability on a smaller scale, particularly when measuring narrow structures like valleys or crevasses.

Chartrand further underlined the domino effect of minor alterations in ice shelves. A mere displacement of inches in ice shelf position can trigger the release of thicker ice into the ocean, potentially leading to a retreat of coastlines by several feet.

What are basal channels?

This study's origins lie in investigating basal channels—pathways where warmer ocean water carves grooves into the underside of ice shelves, hastening the loss of ice mass. 

In scrutinizing these channels, the researchers discovered that prior assumptions about ice shelf thickness in various regions were sometimes exaggerated or understated.

Ultimately, the study aims to enhance our understanding of the processes that fuel rising sea levels. It reinforces the necessity for precision in estimating ice shelf thickness and recognizing the implications of uncertainties in these estimations.

"What this research really shows is that we need to be a lot more careful about the assumptions we make to estimate the ice shelf thickness and about how we account for uncertainties and what they mean for the final result," she said. 

Additionally, the study champions the exploration of older datasets and advocates for developing advanced technologies that can aid in assessing Antarctica's dynamic environment. 

Chartrand expressed optimism about the potential for new discoveries in datasets collected over the past two to 15 years, highlighting the vast uncharted territory that awaits exploration.

The full study was published in the Journal of Glaciology and can be found here. 

Study abstract:

Estimates of ice shelf mass loss are typically based on surface height measurements, assuming hydrostatic equilibrium and estimated firn thickness. Recent investigations, however, challenge the assumption that ice shelves are freely floating, particularly in proximity to narrow structures such as basal channels and shear margins. We compare contemporaneous measurements of Antarctic ice shelf thickness, from ice-penetrating radar, to freeboard height, from laser altimetry, acquired during multiple airborne surveys. On average, the hydrostatic thickness differs from observed thickness by at least ~17 ± 98 m, but this difference varies well beyond the propagated error within and among ice shelves, and depends on the corrections applied. We find that uncertainty in firn thickness can account for most, but not all, of the imbalance. Overall, errors in hydrostatic thickness do not significantly impact estimated basal melt rates. Our results indicate that localized approaches to estimating ice shelf thickness and rates of change are not applicable at large scales, and vice versa, and point to the need for more abundant and accurate firn and ice thickness measurements to improve estimates and predictions of ice shelf mass loss.