Southern Ocean ecosystems are undergoing rapid change under climate warming, with strong impacts from shifting sea ice, stratification and light availability. Primary production forms the base of these ecosystems, yet projections from Earth system models (ESMs) remain uncertain and often show increasing trends that are not fully supported by observations. Here, we use temperature-normalised net primary production (TNNPP) to isolate resource-driven changes in Southern Ocean productivity, separating the effects of temperature from those of other environmental drivers. Using multiple CMIP6 models under future climate scenarios, we compare projected changes in NPP and TNNPP across the Southern Ocean. While total NPP increases across the Southern Ocean, TNNPP reveals strong regional differences in environmental control. In lower-latitude regions, productivity shows weak sensitivity to environmental changes. In contrast, in the Antarctic Zone, productivity is strongly driven by changes in light availability, with increased shortwave radiation associated with sea-ice retreat explaining most of the variability. These results highlight that future changes in Southern Ocean productivity, and therefore marine ecosystems, are likely to be strongly shaped by light-driven processes linked to sea-ice decline, rather than uniformly enhanced by warming. This work has important implications for understanding ecological responses across high-latitude marine communities under climate change.