Tidal influences on a future evolution of the Filchner–Ronne Ice Shelf cavity in the Weddell Sea, Antarctica

Abstract

Abstract. Recent modeling studies of ocean circulation in the southern Weddell Sea, Antarctica, project an increase over this century of ocean heat into the cavity beneath Filchner-Ronne Ice Shelf (FRIS). This increase in ocean heat would lead to more basal melting and a modification of the FRIS ice draft. The corresponding change in cavity shape will affect advective pathways and the spatial distribution of tidal currents, which play important roles in basal melting under FRIS. These feedbacks between heat flux, basal melting, and tides will affect the evolution of FRIS under the influence of a changing climate. We explore these feedbacks with a three-dimensional ocean model of the southern Weddell Sea that is forced by thermodynamic exchange beneath the ice shelf and tides along the open boundaries. Our results show regionally dependent feedbacks that, in some areas, substantially modify the melt rates near the grounding lines of buttressed ice streams that flow into FRIS. These feedbacks are introduced by variations in meltwater production as well as the circulation of this meltwater within the FRIS cavity; they are influenced locally by sensitivity of tidal currents to water column thickness (wct) and non-locally by changes in circulation pathways that transport an integrated history of mixing and meltwater entrainment along flow paths. Our results highlight the importance of including explicit tidal forcing in models of future mass loss from FRIS and from the adjacent grounded ice sheet as individual ice-stream grounding zones experience different responses to warming of the ocean inflow.

Ocean Tide Influences on the Antarctic and Greenland Ice Sheets

“…The tidal range under the eastern Ross Ice Shelf (Siple Coast) exceeds 2 m in some locations. Strong tidal currents (Figure 9b) occur in the Weddell Sea, including under Ronne Ice Shelf along a broad band near the ice front and the channel south of Henry Ice Rise (Figure 10a; Makinson & Nicholls, 1999;Makinson et al, 2006;Mueller et al, 2018;Robertson et al, 1998). Other regions of strong tidal currents around Antarctica include the outer continental slope of the Weddell Sea south of Larsen C Ice Shelf, the northeastern Larsen C Ice Shelf (Mueller et al, 2012), the South Scotia Ridge that forms the northern boundary of the Weddell Sea (Flexas et al, 2015), and along the outer continental shelf and upper slope of the Ross Sea (Gordon et al, 2004;Padman et al, 2009;Whitworth & Orsi, 2006).…”

“…The properties of DTVWs are sensitive to small-scale variations in bathymetry and to stratification and along-slope flows (Semper & Darelius, 2017;Skarðhamar et al, 2015). Sensitivity of DTVW energy to gradients of water depth suggests potential for feedbacks between changes in ice shelf thickness and the contribution of ocean turbulence at the ice base to the basal melt rate; see Mueller et al (2012) and Mueller et al (2018). In general, tidal current speeds increase with increasing ice thickness and decrease with decreasing ice thickness, particularly along the Ronne Ice Shelf front and between Henry Ice Rise (marked in Figure 10a) and the southern grounding line.…”

Spatial and temporal variations in basal melting at Nivlisen ice shelf, East Antarctica, derived from phase-sensitive radars

“…At Nivlisen, we have no observations of ocean currents near the ice rumple, but the bathymetry must be shallow since the ice shelf grounds in this region. Ice shelf thinning could potentially increase the water column thickness, leading to a negative (stabilizing) feedback on the melting by reducing the ocean currents (Mueller et al, 2012(Mueller et al, , 2018. In terms of ice thickness change, the observed thinning from the basal melt is compensated by a positive vertical strain that implies compressional thickening towards the ice rumple (up to 4 m yr −1 ).…”

Response of sub-ice platelet layer thickening rate to variations in Ice Shelf Water supercooling in McMurdo Sound, Antarctica

“…To this end, observations in MMS, particularly focused in the western sound, near the ISW outflow region, where the supercooled ISW plume and SIPL are prominent, would be particularly useful, as would observations that help to constrain 10 the frazil size spectrum within the sea ice-ocean boundary layer. A simple relationship between supercooling and marine ice formation would be the key to parameterize the process in more three-dimensional, primitive equation ocean models which frequently neglect the ice-ocean boundary layer processes and the details of an evolving FIC distribution Mueller et al, 2018;Stern et al, 2013). Further process studies, including the influence of vertical structure of current within the ice shelf (or sea ice) -ocean boundary layer (Jenkins 2016) could also contribute.…”