Brief communication: Sankey diagrams of the simulated mass balance of sea ice and its overlying snow cover across both hemispheres

Abstract. The mass budget of sea ice and its overlying snow cover integrates the thermodynamic and dynamic processes that govern their variability. Here we investigate how Sankey flow diagrams, a widely used and intuitive data visualisation technique for integrated budgets, can provide insight into sea ice and snow-on-ice mass budgets. We draw on multiple model sources, including fully coupled climate models and an ERA5-forced ocean--sea ice reanalysis. The sea ice and snow-on-sea-ice budget terms are defined following established Coupled Model Intercomparison Project protocols, area-integrated over the Northern and Southern Hemispheres for a prescribed modern-era climatological period (2015 to 2034), and displayed as flows whose width is proportional to the annual mass flux. The sources and sinks are labelled by their percentage contribution to the total budget, including the ensemble spread of each relative term. Both the climate model ensemble and the reanalysis show a similar relative budget partitioning, an encouraging sign of reliability in our budget estimates. Overall, we find the diagrams provide an accessible, process-level reference for understanding and visualizing the sea ice and snow mass budgets. The framework we provide is intended as a living resource that can be extended with additional climate simulation output (e.g. the upcoming CMIP7 release) and ocean-sea ice reanalyses, as well as suggested changes in Sankey configuration (or alternative visualization approaches) to emphasize different aspects of the mass budgets. This work has been undertaken in support of the IPCC Seventh Assessment Report (AR7).