Intense bird activity on coastal ice-free areas of Admiralty Bay, Maritime Antarctica, leads to the formation of the so-called ornithogenic soils. The interaction of P-rich guano with the mineral substrate results in diverse secondary P phases. In the present work XRD, SEM/EDS, TEM/EDS and selective chemical dissolution were used to characterize P-rich phases in ornithogenic cryosols from Admiralty Bay, King George Island. Crystalline Al and Fe phosphates (leucophosophite, minyulite and variscite) occur only at sites directly affected by penguin activity where they constitute up to 30 % of the clay fraction. Highly reactive non-crystalline Al, Si, Fe and P phases are dominant in the clay fraction sometimes accounting for over 50 % of the clay fraction. On abandoned rookery sites on basaltic substrates the interaction between penguin guano and inherited clay-sized minerals has lead to the formation of crystalline Al and Fe phosphates which constitute the large P reserves of these soils. Leaching of P-rich solutions from upslope rookeries affects soils in downslope areas where the phosphate reacts with soil organic matter complexes and allophane-like phases. The extremely high proportions of non-crystalline phases in soils at this locality results in the chemical characteristics of ornithogenic sites and in particular the speciation of phosphate being determined by these highly reactive phases. Knowledge of the chemistry of such phases may be useful in assessing anthropogenic impacts and environmental health in this fragile environment.