Footprint of sustained poleward warm water flow within East Antarctic submarine canyons

The intrusion of relatively warm Circumpolar Deep Water (CDW) onto the Antarctic continental shelf is widely recognized as a threat to ice shelves and glaciers grounded below sea level, as enhanced ocean heat increases their basal melt. CDW incursion onto the continental shelf is currently causing ice mass loss, thinning and extensive grounding line retreat of the Totten Glacier (Sabrina Coast), which drains one of the vastest East Antarctic subglacial basin complexes, the Aurora-Sabrina subglacial basin, and holds more than 3.5 m of Sea Level Equivalent (SLE). Another ice stream, the Ninnis Glacier, buttressing a large sector of the East Antarctic Ice Sheet (EAIS), is currently losing mass, although its melting from CDW incursion near the grounding zone is prevented by the formation of Antarctic Bottom Water that currently maintains a cold subglacial cavity. However the geological record indicates that the Ninnis glacier retreated inland during past warmer and prolonged interglacials, e.g., the Marine Isotope Stage 11 about 425 Ky ago. While the intrusion of warm water has been documented on the East Antarctic continental shelf, the locations where such warm water transport is sustained through time are still uncertain. The recognition of preferential conduits for enhanced CDW incursions toward the ice grounding zone is key to predict rates and modes of future responses of major Antarctic marine-based ice streams, such as the Totten and the Ninnis glaciers. We provide new evidence of the role of East Antarctic submarine canyons in conveying southward flowing currents that transport CDW toward the shelf break, thus facilitating relatively warm water intrusion on the continental shelf. The discovery of dozen-meter-thick sediment drifts on the eastern flank of the canyons testifies to the occurrence of sustained southward-directed bottom flows potentially prone to enhanced ocean heat transport toward the continental shelf. The investigated canyons and sediment drifts indicate that long-lasting flow of CDW onto the continental slope and rise have occurred offshore of both the Aurora and Wilkes sub-glacial basins, thus likely helping trigger and/or accelerate the destabilization of these key marine based sectors of the EAIS, with implications to global sea level both in the past and future. New, deep sediment archives from the sediment drifts flanking these canyons are, however, required to document the response and sensitivity of the EAIS, particularly the marine-based Aurora Basin system, to climate changes throughout the Neogene especially during warmer than pre-industrial climate states. To partially fill this knowledge gap, the new, multidisciplinary DIONE project, funded by the Italian Antarctic Research Program (PNRA), will collect geological, geophysical and oceanographic data, which will provide a comprehensive reconstruction of the climatic and environmental evolution of the Sabrina Coast since the Pliocene. However, a complete history of the ice sheet-climate interactions will only be achieved with a new deep sea drilling campaign.

Donda F., et al 2024. Footprint of sustained poleward warm water flow within East Antarctic submarine canyons. Nature Communications, 15, 6028 (2024) https://doi.org/10.1038/s41467-024-50160-z