Abstract Seasonal exchange between modified Circumpolar Deep Water (mCDW) and dense shelf water shapes Antarctic Bottom Water in the Ross Sea, making year‐round hydrographic observations indispensable, yet winter observations remain scarce. Miniaturized CTD tags deployed on 64 Weddell seals in Terra Nova Bay during three years relayed 22,661 profiles across the shelf, supplemented by 43 ship‐based CTD profiles. To characterize vertically structured and spatially irregular hydrographic observations, CTD profiles were reduced with principal component analysis and clustered using Gaussian‐mixture models, performed separately for summer and winter. Summer is characterized by stratification and mid‐depth mCDW intrusions, whereas winter reveals multiple mCDW regimes, including warm, salty inflows along troughs, fresher intrusions near Hayes Bank, and mCDW–HSSW mixed layer. These results demonstrate that, contrary to previous studies suggesting mCDW influence is confined to summer, mCDW also penetrates onto the shelf during winter, where its interaction with dense shelf waters defines distinct transformation zones.