Continued retreat of Thwaites Glacier, West Antarctica, controlled by bed topography and ocean circulation

Abstract

The Amundsen Sea sector is experiencing the largest mass loss, glacier acceleration, and grounding line retreat in Antarctica. Enhanced intrusion of Circumpolar Deep Water onto the continental shelf has been proposed as the primary forcing mechanism for the retreat. Here we investigate the dynamics and evolution of Thwaites Glacier with a novel, fully coupled, ice‐ocean numerical model. We obtain a significantly improved agreement with the observed pattern of glacial retreat using the coupled model. Coupled simulations over the coming decades indicate a continued mass loss at a sustained rate. Uncoupled simulations using a depth‐dependent parameterization of sub‐ice‐shelf melt significantly overestimate the rate of grounding line retreat compared to the coupled model, as the parameterization does not capture the complexity of the ocean circulation associated with the formation of confined cavities during the retreat. Bed topography controls the pattern of grounding line retreat, while oceanic thermal forcing impacts the rate of grounding line retreat. The importance of oceanic forcing increases with time as Thwaites grounding line retreats farther inland.

Retreat of Thwaites Glacier, West Antarctica, over the next 100 years using various ice flow models, ice shelf melt scenarios and basal friction laws

“…The major difference between the models is on the time it takes for each model to overcome ridges in bed topography along the pathway of the retreat. In all simulations, TG experiences grounding line retreat and mass loss over the entire period, which is consistent with previous studies (Joughin et al, 2014;Feldmann 15 and Levermann, 2015;Seroussi et al, 2017). The retreat rate is highly dependent on bed topography.…”

“…The rapid mass loss and grounding line retreat of TG have been attributed to an increase in ice shelf melt rate induced by warmer ocean conditions (Rignot, 2001; Joughin et al, 2014;Seroussi et al, 2017). The strengthening of westerlies around the Antarctic continent over the past decades has caused more warm, salty Circumpolar Deep Water (CDW) to intrude onto 5 the continental shelf, flow along troughs in the sea floor, reach the sub-ice-shelf cavities and glacier grounding lines and melt them from below (Schneider and Steig, 2008;Spence et al, 2014; Dutrieux et al, 2014; Li et al, 2015;Scambos et al, 2017).…”

“…Based on prior studies, TG will experience continuous and rapid retreat, however, the timing and extent of the projected retreat varies significantly between models (Parizek et al, 2013; Joughin et al, 2014; Feldmann and Levermann, 2015;Seroussi et al, 2017;Rignot et al, 2014; Cornford et al, 2015). One important factor explaining the differences between models is that they employ different model configurations and ocean forcings, so it is 20 not clear which model best captures the behavior of TG.…”

Representing grounding line migration in synchronous coupling between a marine ice sheet model and a z-coordinate ocean model

“…7(d)-(f)). A number of studies have suggested that, in the absence of tidal mixing or significant subglacial runoff, melt rates are small within a short distance (3-5 km) of the grounding line, as water flowing up the underside of the shelf must gain sufficient buoyancy before substantial mixing of heat to the ice-ocean interface can occur Seroussi et al, 2017). Thus we are confident that this relative unimportance of melt rates where the ocean column is < 10 m will carry to other settings.…”

Stopping the Flood: Could We Use Targeted Geoengineering to Mitigate Sea Level Rise?

“…Neither of these two points is controversial (e.g. Joughin et al, 2014;Seroussi et al, 2017), but taken together they suggest that consensus ice physics provide an opening for a large-scale 5 civil engineering project to make a meaningful difference in the probability an ice sheet collapse.…”