Observations reveal end of summer Arctic sea ice extent is declining at; an accelerating rate. Model projections underestimate this decline and; continue to have a broad spread in forecasted September sea ice extent.; This suggests some important summer processes, such as melt pond; formation and evolution, may not be properly represented in current; models. Melt ponds form on the sea ice surface as snow melts, and pools; in low lying areas on the sea ice surface. The evolution of the ponds; depends on snow depth, ice thickness, and surface conditions. Melt water; may spread across a level surface, or be confined to depressions between; sea ice ridges. Ponds decrease the albedo of the surface and enhance the; positive ice albedo feedback, accelerating further melt. Until recently,; Arctic-wide observations of individual melt ponds were not available.; ICESat-2, a photon counting laser altimeter launched in 2018, provides; high resolution detail of sea ice and snow topography due to its unique; combination of a small footprint (~12 m) and; high-resolution along-track sampling (0.7 m). The green laser (532 nm); is able to penetrate water, enabling melt pond depth measurements. We; have developed methods to track the melt pond surface and bathymetry in; ICESat-2 data to determine melt pond depth. We also track melt pond; evolution through application of a sea ice classification algorithm to; 10 m resolution Sentinel-2 imagery. The combination of these two; datasets allows for an evolving, three-dimensional view of the melting; sea ice surface. We focus on the evolution of summer melt on multiyear; ice in the Central Arctic north of Greenland and Canada in 2020. Our; findings are put in context of existing literature on melt pond depth,; volume, and evolution. We also discuss our results in relation to the; melt pond fraction north of the Fram Strait, where we expect different; ice conditions in the vicinity of the 2020 MOSAiC field studies.; Observational data products comprising melt pond fraction and pond depth; are being developed for public distribution. These products may be of; interest to those studying under-ice light and biology, as well as; modelers who are interested in understanding the evolution of melt pond; parameters for model initialization and validation.
