Permeable sandy sediments are abundant on continental shelves, where they are increasingly recognized as major sites of intense organic matter mineralization. In offshore wind farms (OWFs), turbine-induced changes in hydrodynamics and organic matter inputs may modify these dynamic environments, yet the quantitative impact remains poorly constrained. Here, we present PermeableDia, a two-dimensional reactive transport model that explicitly resolves advective flows and apply it to data collected from sediments along a distance gradient (7<span>–</span>75 m) from the scour protection layer (SPL) of an offshore wind turbine in the Belgian Part of the North Sea across three seasons. The model adequately reproduces observed organic carbon and porewater nutrient profiles and reveals pronounced spatial gradients in carbon mineralization. Total mineralization rates were highest nearest to the turbine (up to ~176 mmol C m<sup><span>−</span>2</sup> d<sup><span>−</span>1</sup>) and declined with distance. Oxic pathways dominated mineralization (58<span>–</span>92 % of total), reflecting efficient oxygen supply via advective exchange, while anoxic mineralization increased near the turbine (up to 41 %) consistent with enhanced organic matter loading. Denitrification contributed only a minor fraction to total mineralization (1–4.5 %). By constraining the model with in situ observations, this data-driven approach enables the quantification of mineralization pathways in permeable sediments where direct rate measurements are challenging. The dynamic nature of mineralization processes in advective conditions indicates that observed biogeochemical impacts of offshore wind, such as increased carbon storage in surface sediments, are likely transient.