Image catalog of thin sea ice samples collected during the 2019/ 2020 MOSAiC expedition to the Arctic Ocean

When sea ice forms, salty water pockets, called brine, are trapped between the ice crystals. The wave dynamics of the ocean during freezing can influence how these ice crystals align, especially in the early stages before a solid ice cover forms. Over time, as the ice grows, the salinity changes depending on how quickly the ice forms and how the brine moves or drains out. First-year ice, which has not yet survived a summer melt, retains more brine. However, if it lasts through the summer and becomes second-year ice, much of the brine drains away, leaving behind air bubbles and empty spaces. Older multiyear ice has a more complex structure, with features such as hummocks, refrozen melt ponds, and layers of snow-ice. These different structures affect how the ice interacts with microwave signals, which are used in satellite measurements. The size, shape, and arrangement of brine pockets and air bubbles within the ice influence these microwave signals, affecting how accurately we can measure the properties of sea ice from space. To better understand these processes, high-resolution image samples of Arctic sea ice were collected during the winter of 2020 as part of the MOSAiC expedition. We focused on the top 40 centimeters of the ice, which is particularly important for microwave signals in the 5 to 100 GHz range. Our analysis looked at different types of ice, including new ice, first-year ice, second-year ice, hummocks, and refrozen melt ponds. This detailed data helps us improve models that simulate how microwave signals interact with sea ice, ultimately leading to better satellite measurements and a deeper understanding of sea ice dynamics.