Submarine canyons key to Antarctic ice sheet instability

Antarctic canyons play a crucial role in the instability of the East Antarctic Ice Sheet, as they facilitate the transfer of relatively warm water (Circumpolar Deep Water) from the abyssal areas to the continental shelf and from there to the base of the ice sheet, thereby contributing to its melting.

THE new studyconducted by an international team of researchers led by the National Institute of Oceanography and Applied Geophysics (OGS) and including the University of Southampton, highlights the discovery of sedimentary bodies within major canyon systems that represent the geological footprint of persistent bottom currents flowing along the canyons and transporting heat from the ocean to the Antarctic continent.

“The intrusion of relatively warm water onto the continental shelf is widely recognized as a threat to the Antarctic ice sheet,” comments Federica Donda, a marine geologist in the OGS Department of Geophysics and lead author of the paper. “Constraining the magnitude and long-term persistence of this phenomenon is fundamental to analyzing potential responses of the ice sheet to global warming.”

The work focused on the Totten and Ninnis glaciers, which lie at the mouths of the two most prominent subglacial features in East Antarctica: the Aurora-Sabrina and Wilkes subglacial basins.

“The analysis of geophysical and oceanographic data collected during a multidisciplinary Italian-Australian cruise led to the discovery of dome-shaped sedimentary bodies (sedimentary drifts) several thousand metres wide and 40 to 80 metres thick, whose internal and external characteristics indicate that they were formed by bottom currents directed towards the continental shelf,” Donda continues.

“This is confirmed by oceanographic data obtained in one of the Totten Glacier canyons, which recorded currents of about 10 cm/s near the seabed, at a depth of about 3,500 meters. These currents are associated with an ocean circulation characterized by the presence of large cyclonic eddies that transport different water masses, including warm water from the circumpolar deep waters. The southern component of these eddies is carried by the canyons, which locally have a relief of more than 700 meters and are therefore the preferred routes for the transfer of these water masses to the continent. The thickness of the sedimentary bodies identified in the canyons indicates that oceanic heat transfer has been ongoing for at least the last million years.”

“Until a few years ago, we thought the East Antarctic ice sheet was stable,” adds Dr Alessandro Silvano, from the University of Southampton. “Today, not only do we know that some East Antarctic glaciers are melting, but through this work we have also discovered that there are preferential pathways for warm waters to persistently reach two of the largest glaciers on the planet and melt them from below.”

The East Antarctic Ice Sheet is attracting increasing scientific attention because its melting, even partial, could contribute significantly to sea level rise. Indeed, the Aurora-Sabrina and Wilkes subglacial basins contain the equivalent of more than 8 meters of global mean sea level rise.

The results of this study highlight the key role of submarine canyons, which therefore constitute key areas for understanding the mechanisms associated with the melting of the ice sheet in the past and present, thus contributing to the formulation of predictions of future sea level rise.

The research activity involved the National Institute of Oceanography and Applied Geophysics – OGS, University of Southampton, Rutgers, State University of New Jersey, Colgate University, Geoscience Australia, All-Russian Scientific Research Institute of Geology and Mineral Resources of the Ocean, St. Petersburg State University, University of Tasmania and Macquarie University.