Neodymium isotopes (εNd) are widely used to trace water-mass provenance and reconstruct past ocean circulation. Antarctic Bottom Water (AABW) is a major deep-water endmember of the global ocean, making it essential to understand how its εNd signature is established. Although commonly considered to be inherited from precursor waters through quasi-conservative mixing, this signature may also be modified by non-conservative processes such as benthic Nd fluxes. Here, we present seawater εNd and Nd concentration data from Prydz Bay, the Larsen Ice Shelf, and the Filchner–Ronne Ice Shelf systems, three source regions contributing to AABW in the Weddell Sea. Seawater samples collected throughout the water column are integrated with conductivity–temperature–depth (CTD) profiles to characterize water-mass structure, while sediment geochemical measurements from multicorer (MUC) samples are used to constrain potential benthic inputs in the source regions. These observations span contrasting hydrographic, glaciological, and sedimentary environments, allowing us to assess the spatial variability of Nd isotope systematics during AABW formation and transport. We further combine water-mass mixing calculations with process-based modelling to distinguish conservative mixing from benthic modification and evaluate their relative contributions to the εNd and Nd concentration of AABW. Comparisons between observations and modelled mixing relationships constrain the processes responsible for the observed regional differences. This study provides a mechanistic framework for understanding how the AABW Nd isotope signature is generated and improves the interpretation of εNd as a tracer of modern and past ocean circulation.