Limited Impact of Thwaites Ice Shelf on Future Ice Loss From Antarctica.

Thwaites Ice Shelf (TWIS), the floating extension of Thwaites Glacier, West Antarctica, is changing rapidly and may completely disintegrate in the near future. Any buttressing that the ice shelf provides to the upstream grounded Thwaites glacier will then be lost. Previously, it has been argued that this could lead to onset of dynamical instability and the rapid demise of the entire glacier. Here we provide the first systematic quantitative assessment of how strongly the upstream ice is buttressed by TWIS and how its collapse affects future projections. By modeling the stresses acting along the current grounding line, we show that they deviate insignificantly from the stresses after ice shelf collapse. Using three ice‐flow models, we furthermore model the transient evolution of Thwaites Glacier and find that a complete disintegration of the ice shelf will not substantially impact future mass loss over the next 50 years. Plain Language Summary: As ice is lost, global sea levels rise. Currently glaciers and ice sheets contribute about half of observed sea level rise (SLR). Some ice is lost through surface melting, but sea levels can also be impacted by ice that flows directly into the ocean. This loss of ice, from the grounded interior into the surrounding ocean, is particularly important for the Antarctic Ice Sheet. There the grounded sections of the ice sheet are sometimes surrounded by floating seaward extensions referred to as ice shelves. These ice shelves can restrict, that is, buttress, upstream flow. Here we estimate the buttressing provided to one of the largest and most dynamical glaciers of the Antarctic Ice Sheet, the Thwaites Glacier. The glacier is currently abutted by an ice shelf, which has become progressively smaller and weaker over the last few decades. It has been suggested that a disintegration of the ice shelf might lead to greatly enhanced ice flow. However, we find that the ice shelf does not significantly buttress upstream flow, and removing the ice shelf has little effect on SLR over the next 50 years. Key Points: Thwaites Ice Shelf provides limited buttressing to the grounded upstream Thwaites GlacierRemoval of the ice shelf changes the contribution of the West Antarctic Ice Sheet to sea level rise by at most a few millimeters over 50 yearsObservations and modeling suggest that Thwaites Glacier is currently unsteady and stable [ABSTRACT FROM AUTHOR]