Localized fractionation of sea salts, i.e. a change in their relative concentration from the standard sea-water ratios, may occur in sea ice due to precipitation of solid salts and due to differential diffusion of ions in temperature gradients. Fluid flow in complex pore networks and thin boundary layers then determines to what degree some ions are more rapidly released to the sea water underneath, leading to ion fractionation in the bulk ice. Previous studies have mainly studied bulk sea-ice samples to conclude that ion fractionation strongly depends on the thermal history of the ice (and presumably the details of pore networks). Here we document both brine and bulk ice fractionation signatures of the major sea-water ions in young sea ice from Kongsfjorden, Svalbard. Temperature-controlled sampling and centrifugation at in situ temperatures let us identify the centrifugable (interconnected) and entrapped (likely disconnected) contributions to the bulk ice salinity. We analyse how brine and bulk ion fractionation vary with the entrapped pore fraction and with bulk properties like ice salinity, temperature and porosity. The variability is further discussed with respect to detailed pore-space observations obtained by synchrotron-based X-ray microtomography.