The variability of water isotopes in Antarctic ice cores is of major interest for reconstructing past climate through changes in temperature and the hydrological cycle. Archived during the deposition of successive layers of snow, water molecules undergo various processes that can modify the isotopic signal initially imprinted in snowfall during the process of snow densification to ice (i.e. firn). Diffusion is a well-known effect that affects water isotope composition by smoothing the initial climate-related signal. Here, we focus on new water isotopes profiles of two firn cores from Little Dome C (LDC), dated thanks to sulphate concentration measurements, with the aim to identify the physical processes affecting the isotopic signal in the firn at the drilling site for the new Beyond Epica Oldest Ice (BELDC) deep ice core on the East Antarctic Plateau. We use a simple Virtual Firn Core model (VFC) to best fit our δ¹⁸O firn profiles. We conclude that the VFC should include a 8 cm surface mixing layer and that diffusion is overestimated below a depth of 3 meters.