Anatomy of Arctic and Antarctic sea ice lows in an ocean–sea ice model

Abstract. Sea ice has exhibited a number of record lows in both hemispheres over the past two decades. While the causes of individual sea ice lows have already been investigated extensively, no systematic comparison across events and hemispheres has been conducted in a consistent framework yet. Here, the global standalone ocean--sea ice model NEMO4.2-SI³ at 1/4° resolution is used to decompose the sea ice mass budget. We separate the relative contributions of sea ice melt versus growth and thermodynamic versus dynamic processes, both from a climatological perspective and for selected individual years. The seasonal cycles of Arctic and Antarctic ice mass fluxes show similarities, such as the prevalence of basal growth and melt in the mass budget. The long-term evolution of the mass budget terms reveals an increased importance of basal melt in both hemispheres, at the expense of surface and lateral melt. Regarding sea ice lows, the model indicates that the Arctic 2007 anomaly was chiefly caused by dynamic factors, while the Arctic 2012 event was rather explained by thermodynamic factors. The Antarctic 2022 event was partly driven by a strong interplay between dynamic and thermodynamic processes. Regarding the Antarctic winter 2023 event, it was characterized by a notable lack of basal growth. This study emphasizes the dominance of processes at the ice-ocean interface in driving the ice mass evolution at all time scales considered here, and highlights the potential of the ice mass budget decomposition to further our understanding of the evolution of polar regions in a changing climate.