Ocean Tide Influences on the Antarctic and Greenland Ice Sheets

Abstract

Ocean tides are the main source of high‐frequency variability in the vertical and horizontal motion of ice sheets near their marine margins. Floating ice shelves, which occupy about three quarters of the perimeter of Antarctica and the termini of four outlet glaciers in northern Greenland, rise and fall in synchrony with the ocean tide. Lateral motion of floating and grounded portions of ice sheets near their marine margins can also include a tidal component. These tide‐induced signals provide insight into the processes by which the oceans can affect ice sheet mass balance and dynamics. In this review, we summarize in situ and satellite‐based measurements of the tidal response of ice shelves and grounded ice, and spatial variability of ocean tide heights and currents around the ice sheets. We review sensitivity of tide heights and currents as ocean geometry responds to variations in sea level, ice shelf thickness, and ice sheet mass and extent. We then describe coupled ice‐ocean models and analytical glacier models that quantify the effect of ocean tides on lower‐frequency ice sheet mass loss and motion. We suggest new observations and model developments to improve the representation of tides in coupled models that are used to predict future ice sheet mass loss and the associated contribution to sea level change. The most critical need is for new data to improve maps of bathymetry, ice shelf draft, spatial variability of the drag coefficient at the ice‐ocean interface, and higher‐resolution models with improved representation of tidal energy sinks.

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

“…3c, d). However, largerscale reorganization of the barotropic tidal energy fluxes under FRIS also occurs (see, e.g., Rosier et al, 2014 andPadman et al, 2018), so simple scaling of modern tidal currents by the change in wct is not possible.…”

“…Studies of Larsen C Ice Shelf (Mueller et al, 2012) and Pine Island Glacier ice shelf (Schodlok et al, 2012) showed that changes to the ice shelf cavity shape can significantly alter the spatial pattern of basal melt rate, particularly in regions where tidal currents contribute substantially to the total turbulent kinetic energy near the ice base. Tides were not explicitly included in the forcing for the Hellmer et al (2012) study; however, tidal currents often play a critical role in setting the pattern and magnitude of basal melt rates under cold water ice shelves (MacAyeal, 1984;Padman et al, 2018) including FRIS (Makinson et al, 2011), which leads us to hypothesize that tides would influence changes in meltwater production from a warming ocean.…”

Projections of Future Sea Level Contributions from the Greenland and Antarctic Ice Sheets: Challenges Beyond Dynamical Ice Sheet Modeling

“…This revised view of ice sheets resulted from observations of unexpected outlet glacier accelerations in the late twentieth century (Rignot, 1998). We now know that ice sheets can respond to changes on timescales that range from hours (response to tides, see review from Padman et al, 2018) to millennia (response to past climate, Dutton et al, 2015;DeConto and Pollard, 2016).…”

Simultaneous Estimation of Ocean Tides and Underwater Topography in the Weddell Sea

“…The floating ice shelves of Antarctica play a significant role in the stability of grounded continental ice, ocean circulation and thermodynamics, and other processes related to global climate and sea level (Alley et al, ; Mengel et al, ; Orsi et al, ). Considerable uncertainty exists concerning the ice shelf processes affected by ocean tides, such as nonlinear processes near the grounding line, thermodynamics of freezing and melting on the underside of the shelf, and stress across the ice‐water interface (Padman et al, ). Therefore, the mapping and dynamical modeling of tidal heights, currents, and energetics are relevant to understanding ice shelf dynamics.…”

“…In barotropic models the drag is usually represented by doubling the friction coefficient under the floating ice, compared to its open‐ocean value, in order to account for the boundary layers at both the upper and lower water surfaces (MacAyeal, ); however, it is commonly found that best agreement between the modeled and observed tides is obtained with unrealistically large values of the friction coefficient (Padman & Kottmeier, ; Robertson et al, ; Rosier et al, ; Smithson et al, ). It has been hypothesized that the large friction coefficients are needed in order to make up for a range of dissipative processes which are neglected, such as inelastic flexure of the ice sheet near the grounding line, the generation of nonlinear overtides, the generation of baroclinic tides, and subgrid‐scale roughness of the ice‐ocean interface (Padman et al, , ).…”