Global Tidal Impacts of Large‐Scale Ice Sheet Collapses

Abstract

Recent studies show that the glaciers draining both the West Antarctic and the Greenland Ice Sheets are experiencing an accelerated ice loss, highlighting the possibility of large‐scale ice sheet retreat and sea level rise in the coming centuries and millennia. These sea level changes would vary spatially and could significantly alter global tides as the latter are highly dependent on bathymetry (or water column thickness under ice shelves) and basin shape. This paper investigates how the principal semidiurnal (M2) tidal amplitudes and energy dissipation respond to the nonuniform sea level changes induced by complete ice sheet collapses. The sea level changes are calculated using gravitationally self‐consistent sea level theory, and the tides are simulated using an established tidal model. Results from the simulations show global and spatially heterogeneous changes in tidal amplitudes. In addition, pronounced changes in tidal energy dissipation occur in both the open ocean and in shelf‐seas, also altering the location of tidal mixing fronts. These changes have the potential to impact ocean mixing, and hence large‐scale currents and climate patterns, and the contribution of shelf‐sea to the global carbon cycle. The new results highlight the importance of considering changes in the tides in predictions of future climate and reconstructions of past climate phases such as the Last Interglacial.

Glacial Ice Sheet Extent Effects on Modeled Tidal Mixing and the Global Overturning Circulation

“…The Oregon State Tidal Inversion Software (OTIS) has been widely used for modeling of tides in both regional and global applications for the past, present, and future (Egbert et al, ; Green, ; Green et al, ; Pelling & Green, ; Wilmes & Green, ; Wilmes et al, ). OTIS solves the linearized shallow water equations (Egbert et al, ) which are given by where U = u H is the depth integrated volume transport, which is calculated as tidal current velocity u times water depth H .…”

The Tides They Are A‐Changin': A Comprehensive Review of Past and Future Nonastronomical Changes in Tides, Their Driving Mechanisms, and Future Implications

“…This makes sense dynamically: There is no reason to have large tides during a supercontinental gathering, because basins are too large to be resonant. Also, sensitivity simulations in Green et al () indicated that with higher MSL, the tides became even less energetic, something Wilmes et al () also note.…”

“…Remarkably, the rates of tidal level changes observed are of similar magnitudes to the rate of mean sea level (MSL) rise at some sites; for example, Mawdsley et al () found increases in tidal range at Astoria (USA), Wilmington (USA), Delfzijl (the Netherlands), Cuxhaven (Germany), and Calais (France) of >25 cm over the last century. Furthermore, a number of modeling studies at local (e.g., Chernetsky et al, ; Familkhalili & Talke, ; Holleman & Stacey, ; Lee et al, ; Orton et al, ), regional (e.g., Arns et al, , ; Devlin et al, ; Greenberg et al, ; Idier et al, ; Luz Clara et al, ; Pickering et al, ; Pelling, Green, et al, ; Pelling, Uehara, et al, ; Ross et al, ; Ward et al, ), and global scales (e.g., Müller et al, ; Pickering, ; Pickering et al, ; Schindelegger et al, ; Wilmes et al, ) confirm that altered conditions (e.g., MSL, bathymetry, or stratification) affect tide levels and currents. Moving forward, these studies suggest that further changes to tidal levels and currents due to nonastronomical causes are possible over the 21st century and beyond.…”

Ocean Tide Influences on the Antarctic and Greenland Ice Sheets

“…Pickering et al () investigated the impact of uniform global sea level rise of 0.5–10 m on global tidal fields and found substantial changes (both increases and decreases) in tidal amplitudes throughout the world's coastal oceans. Wilmes et al () estimated the changes in global tidal amplitude and dissipation rates of tidal energy resulting from complete collapse of the West Antarctic and Greenland ice sheets. Following Pickering et al (), Wilmes et al () also studied uniform sea level rise, but they also simulated the spatially varying sea level change due to changes in load and self‐attraction; for example, in their model, complete loss of the West Antarctic Ice Sheet (WAIS) contributed +5 m to mean global sea level, but water depth close to WAIS actually decreased by up to 87 m. These authors concluded that using spatially varying sea level rise was critical to accurate modeling of global tidal changes as the ice sheets thin or collapse.…”