Tidal Pressurization of the Ocean Cavity Near an Antarctic Ice Shelf Grounding Line

Abstract

Mass loss from the Antarctic ice sheet is sensitive to conditions in ice shelf grounding zones, the transition between grounded and floating ice. To observe tidal dynamics in the grounding zone, we moored an ocean pressure sensor to Ross Ice Shelf, recording data for 54 days. In this region the ice shelf is brought out of hydrostatic equilibrium by the flexural rigidity of ice, yet we found that tidal pressure variations at a constant geopotential surface were similar within and outside of the grounding zone. This implies that the grounding zone ocean cavity was overpressurized at high tide and underpressurized at low tide by up to 10 kPa with respect to glaciostatic pressure at the ice shelf base. Phase lags between ocean pressure and vertical ice shelf motion were tens of minutes for diurnal and semidiurnal tides, an effect that has not been incorporated into ocean models of tidal currents below ice shelves. These tidal pressure variations may affect the production and export of meltwater in the subglacial environment and may increase basal crevasse heights in the grounding zone by several meters, according to linear elastic fracture mechanics. We find anomalously high tidal energy loss at the K 1 constituent in the grounding zone and hypothesize that this could be explained by seawater injection into the subglacial environment at high tide or internal tide generation through interactions with topography. These observations lay the foundation for improved representation of the grounding zone and its tidal dynamics in ocean circulation models of sub-ice shelf cavities.Plain Language Summary One of the challenges for sea level rise prediction is understanding how the Antarctic ice sheets and the Southern Ocean interact. Ocean tides are an important component of this interaction, influencing ice shelf melting and the flow rate of grounded ice toward the coast. We report new observations relevant to this interaction: tidally varying ocean pressures where the ice first goes afloat to become an ice shelf. These tidal ocean pressure variations influence tidal currents below the ice shelf, and we propose that they also push seawater beneath the ice inland of the ice shelf and extend fractures at the ice shelf base. This study identifies tidal processes that may affect melt and fracture near the inland edge of ice shelves, a highly sensitive zone for ice dynamics.

Towards modelling of corrugation ridges at ice-sheet grounding lines

“…The first of these issues is probably the hardest to counter. Water velocities of only a few cm s -1 , which are in fact in line with the few existing hydrographic observations of extremely low to undetectable tidal current velocities in grounding-zone cavities (Begeman et al, 2020;Davis et al, accepted), would only allow for transport of the very finest particles (clay and fine silts <10 μm). Velocities above ~20 cm s -1 are required to keep sand-sized grains (diameters 63 μm -2 mm) mobile in suspension (McCave & Hall, 2006).…”

Mid‐Holocene Grounding Line Retreat and Readvance at Whillans Ice Stream, West Antarctica

“…Instead, the sedimentary system accessed as part of the WISSARD Project (2014–2015) consists of recent sedimentation from basal melt (Movie S1 in the supporting information) underlain by subglacial till (Horgan, Christianson, et al, 2013). We collected a 70 cm‐long gravity core through a hot‐water‐drilled borehole (Rack, 2016; Tulaczyk et al, 2014) located ~3 km downstream from the modern grounding line of Whillans Ice Stream (Begeman et al, 2018, 2020).…”

Barotropic Tides in MPAS-Ocean: Impact of Ice Shelf Cavities

“…In this work we have primarily focused on tidal errors in the open ocean near the ice shelf cavities. However, a more detailed analysis of tides and tidal pressures near the grounding line is possible as shown by Begeman et al (2020). Also, investigations of sea ice dynamics and floating ice shelves are expected to improve tidal errors (Sun et al, 2022;Lei et al, 2017).…”