Here we present measurements of Inertinite Reflectance from the mid-Cretaceous layer in drill core 9R and 10R at MARUM-MeBo70 Site PS104_20-2 (73.57°S, 107.09°W; 946 m water depth) for reconstructing past wildfire activity and vegetation near the South Pole. The site is located within the Pine Island cross-shelf trough in the Amundsen Sea Embayment (ASE), West Antarctica and was drilled during RV Polarstern Expedition PS104 in 2017. Reflectance measurements were conducted using a reflected-light microscope (Axio Imager M2m, Zeiss) equipped with a tungsten–halogen lamp (12 V, 100 W) for incident white light and an Epiplan-Neofluar 50×/1.0 oil-immersion objective. Data acquisition was performed using a BASLER CCD camera system coupled with DISKUS Fossil software version 5.0.7563 (Technisches Büro C. Hilgers). Calibration was carried out using an yttrium–aluminum–garnet (YAG) reflectance standard with a certified reflectivity of 0.889%. Inertinite reflectance values were subsequently converted into combustion temperatures using the transfer function of Gao et al. (2024).