The Impact of Variable Ocean Temperatures on Totten Glacier Stability and Discharge.

A major uncertainty in Antarctica's contribution to future sea‐level rise is the ice sheet response timescales to ocean warming. Totten Glacier drains a region containing 3.9 m global sea level equivalent and has been losing mass over recent decades. We use an ice sheet model coupled to an ice‐shelf cavity combined ocean box and plume model to investigate Totten's response to variable ocean forcing. Totten's grounding line is stable for a limited range of ocean temperatures near current observations (i.e., −0.95°C to −0.75°C), with topography influencing the discharge periodicity. For increases of ≥0.2°C in temperatures beyond this range, grounding line retreat occurs. Variable ocean forcing can reduce retreat relative to constant forcing, and different variability amplitudes can cause centennial‐scale delays in retreat through interactions with topography. Our results highlight the need for long‐term ocean state observations and to include forcing variability in ice sheet model simulations of future change. Plain Language Summary: Antarctica's contribution to future sea‐level rise is dominated by uncertainties in how the ice sheet will respond to ocean warming. Totten Glacier, East Antarctica, currently contributes to sea‐level rise and is the major outlet glacier in a region with potential to significantly raise sea levels. We use an ice sheet model coupled to a combined box and plume ocean model to investigate how variability in ocean temperatures can impact ice mass loss in this region. For scenarios of ocean temperatures that are near observed, the grounding line position is close to its present‐day location. In these scenarios, interactions between the ice shelf and topography are important in controlling the timing between peak ice shelf melting and peak mass changes. For small increases in background ocean temperature, we see grounding line retreat. In these scenarios, variability in ocean temperatures can reduce ice flux across the grounding line compared with when the ocean temperature is constant. Certain amplitudes of variability can delay grounding line retreat by centuries through interactions with the topography. This highlights the need for long‐term ocean observations in this region and to include ocean variability in ice sheet model simulations of future change. Key Points: Totten's grounding line is steady and close to present‐day only for current ocean temperatures and retreats for small temperature increasesOcean variability of various amplitudes can reduce discharge and cause centennial scale delays in grounding line migrationForcing variability needs to be taken into account in ice sheet model simulations of future climate change [ABSTRACT FROM AUTHOR]