Porosity of sea ice were measured by micro-CT scanning. Micro-CT samples are collected from melt pond using an ice corer (Mark II coring system, Kovacs Enterprises, Inc., Indianapolis, USA). The microstructure of the ice cores was measured onboard R/V Polarstern with a micro-CT (Scanco Medical micro-CT 9. SCANCO Medical AG, Switzerland). The core samples were immediately transported to a cold laboratory at –15°C to prevent structural changes prior to measuring. Ice sections (5 cm × 5 cm × 5 cm) were cut off from the ice cores for measurement in the band saw in the cold laboratory. The temperature inside the micro-CT was consistently –12°C during the scan. The samples were scanned, and using this sampling collection method, we could measure the microstructure to a resolution of 26–42 mm in an approximate 20 mm × 20 mm footprint, depending on the sample diameter. After scanning the samples and producing the 3-D model reconstruction, we segmented the voxels of ice and air within the 3-D structure and used the segmented images to calculate the geometrical parameters. We used IPL Version 5.42 (Scanco Medical AG) to evaluate porosity using a triangulation-based estimate from the micro-CT samples. Details for micro-CT measuring method are explained in Nicolaus et al. (2022).