Southern Ocean response and sensitivity to idealized freshwater perturbation experiments

Recent observations show that mass loss from Antarctic ice sheets and ice shelves is accelerating and is projected to increase further in the coming decades. The resulting freshwater input from melting of the grounded ice sheet and ice shelves is expected to have significant impacts on Southern Ocean dynamics that could also feedback onto the global climate system and its future changes. However, most state-of-the-art coupled models do not include interactive ice sheets and shelves, resulting in large uncertainty in future climate projections. Additionally, the physical response within the Southern Ocean and beyond remains elusive and largely dependent on the model used and the experimental design.

Here, we present results from a model participating in the Southern Ocean Freshwater Input from Antarctica (SOFIA) initiative, an international model intercomparison project in which freshwater is added to the ocean surrounding Antarctica to simulate the otherwise missing ice-sheet mass loss. Contrary to most models participating in SOFIA, we have performed our experiments with an ocean-sea ice model in which sea surface salinity restoring is deactivated and previously computed restoring-induced surface fluxes are provided at the ocean surface in order to keep a stable climate. Besides the missing atmospheric feedback, an ocean-only SOFIA experiment allows the investigation of the ocean's response to Antarctic freshwater discharge and, through the comparison with SOFIA coupled models, the quantification of the role of atmospheric feedbacks.

Preliminary results, based on a suite of experiments using varying strengths of the freshwater perturbation, are presented for both Southern Ocean physics and dynamics, with implications for the global circulation.