A synthesis of ice-ocean boundary observations from the underwater vehicle Icefin

Abstract:

Mass loss from the Earth’s cryosphere currently represents the largest contribution to global sea level rise. A large portion of this mass loss is driven by physical processes occurring at the marine margin of the Antarctic and Greenland ice sheets, where the ice sheet interacts with the ocean. However, there are extremely limited direct observations of the ice-ocean interface where these two physical environments meet. Here we synthesize three years of ice and ocean observations in Antarctica from McMurdo Sound and beneath the Ross and Thwaites ice shelves, using hydrographic and sonar data, and video footage from the underwater vehicle Icefin. Near-ice ocean conditions vary between these environments from below freezing to greater than two degrees above freezing, with considerable variability in current velocities. Ice base morphology likewise varies within and between environments, with ablating ice forming scallops, runnels, and terraces with horizontal scales of meters and vertical scales of centimeters to meters. Supercooled waters in turn form marine ice platelets, which accumulate in both unconsolidated and rigid bulbous masses observed at meter scales. These variations in ice basal roughness affect the turbulent transfer of heat and salt from the ocean to the ice, and represent one of the most poorly constrained parameters in the equations that dictate ice-ocean interactions. Our results provide direct observations of the ice-ocean boundary in several environments, and therefore inform on these processes that are critical for the future behavior of the Antarctic and Greenland ice sheets.