Crevasses, as discovered through groundbreaking research led by Cornell, are not just fissures in the ice; they serve a crucial function in the circulation of seawater beneath Antarctic ice shelves.
The Icefin underwater vehicle has sonar, chemical, and biological sensors that help researchers characterize sub-ice environments. Image Credit: Icefin/NASA PSTAR RISE UP/Schmidt/Lawrence
This unique study, carried out with the assistance of an innovative underwater robot, suggests that crevasses may have a significant impact on the stability of these ice shelves.
The Icefin robot, operated remotely, made an ascent and descent within a crevasse located at the base of the Ross Ice Shelf. This operation marked a significant milestone by providing the first 3D measurements of ocean conditions at the vital intersection where the ice shelf meets the coastline, commonly referred to as the grounding zone.
The robotic survey uncovered a novel ocean circulation pattern within this zone – a jet that channels water laterally through the crevasse. Additionally, the survey identified vertical currents of rising and sinking water, as well as a variety of ice formations influenced by the ever-changing dynamics of flows and temperatures.
These findings will enhance the ability to model the rates at which ice shelves melt and freeze at grounding zones, especially in regions where direct observations are scarce. This, in turn, will help us better understand their potential impact on global sea-level rise.
Crevasses move water along the coastline of an ice shelf to an extent previously unknown, and in a way models did not predict. The ocean takes advantage of these features, and you can ventilate the ice shelf cavity through them.
Peter Washam, Polar Oceanographer and Research Scientist, Department of Astronomy, College of Arts and Sciences, Cornell University
Washam is the lead author of the study published in the journal Science Advances on October 27, 2023.
The study co-authors include members of the Icefin team headed by Britney Schmidt, associate professor of astronomy and earth and atmospheric sciences in A&S and Cornell Engineering, and director of the Planetary Habitability and Technology Lab; and members of a New Zealand-based research team led by Christina Hulbe, Professor at the University of Otago, and collaborators.
In late 2019, the collaborating teams deployed the Icefin vehicle, which measures approximately 12 feet in length and less than 10 inches in diameter. It was lowered down a 1,900-foot borehole created using hot water near the junction of Antarctica's largest ice shelf and the Kamb Ice Stream.
These crucial areas, known as grounding zones, play a pivotal role in regulating the equilibrium of ice sheets and are where alterations in ocean conditions can exert the greatest influence.
For instance, in the region beneath the Thwaites Eastern Ice Shelf in West Antarctica, where the seawater is relatively warmer, a distinct Icefin mission revealed melting rates along the sloping crevasse walls that were ten times higher than those observed along the flat base of the shelf. This increased melting significantly contributes to the rapid retreat of the grounding line.
In contrast, the water cavity below the Ross shelf is colder, and the Kamb Ice Stream has remained largely inactive for an extended period. This makes it an ideal location for studying the enduring effects of underwater conditions that are more representative of the largest ice shelves on the continent, as noted by the researchers.
During the team's final of three expeditions, Matthew Meister, a Senior Research Engineer (A&S), steered Icefin into one of the five crevasses located near the borehole. The vehicle, equipped with thrusters, cameras, sonar, and sensors for monitoring water temperature, pressure, and salinity, ascended nearly 150 ft up one slope and then descended the other.
The survey provided detailed observations of the evolving ice formations within the crevasse. As the crevasse narrowed, it exhibited scalloped patterns that transitioned into vertical runnels, followed by green-tinted marine ice and stalactites.
Melting at the base of the crevasse, along with salt expulsion during freezing near the top, resulted in the movement of water up and down around a horizontal jet. This circulation drove uneven patterns of melting and freezing on the two sides, with a greater degree of melting occurring along the lower downstream wall.
Each feature reveals a different type of circulation or relationship of the ocean temperature to freezing. Seeing so many different features within a crevasse, so many changes in the circulation, was surprising.
Peter Washam, Polar Oceanographer and Research Scientist, Department of Astronomy, College of Arts and Sciences, Cornell University
The scientists suggested that comparable currents probably coursed through neighboring crevasses.
Additionally, with Icefin uncovering analogous patterns beneath the Thwaites Ice Shelf, these findings underscore the potential of crevasses to facilitate the transport of evolving ocean conditions, be it warmer or colder, through the most delicate sector of an ice shelf.
If water heats up or cools off, it can move around in the back of the ice shelf quite vigorously, and crevasses are one of the means by which that happens. When it comes to projecting sea-level rise, that’s important to have in the models.
Peter Washam, Polar Oceanographer and Research Scientist, Department of Astronomy, College of Arts and Sciences, Cornell University
The additional members of Cornell’s Icefin team in A&S include Justin Lawrence, visiting scholar at the Cornell Center for Astrophysics and Planetary Science; Senior Research Engineer Andrew Mullen; Research Engineer Frances Bryson ’17; and Program Manager Enrica Quartini.
Moreover, the research group includes Benjamin Hurwitz, a Doctoral Student at the Georgia Institute of Technology, where Schmidt began developing Icefin as a platform to advance the search for life on icy worlds beyond Earth.
The study was financially supported by Project RISE UP (Ross Ice Shelf and Europa Underwater Probe), part of NASA’s Planetary Science and Technology from Analog Research program, with logistical support provided by the National Science Foundation through the US Antarctic Program.
This was made possible through the support of the New Zealand Antarctic Research Institute, the Aotearoa New Zealand Antarctic Science Platform, and the Victoria University of Wellington’s Hot Water Drilling initiative.
Journal Reference
Washam, P., et al. (2023) Direct observations of melting, freezing, and ocean circulation in an ice shelf basal crevasse. Science Advances. doi.org/10.1126/sciadv.adi7638.