The article proposes a model for assessing ecological risk taking into account the intra-annual dynamics of the main components of the ecosystem. Based on model calculations, ecological risk assessments are given for variations in the intra-annual state of low-productive ecosystems of the Arctic shelf and the effect of technogenic stressors. The proposed approach combines ecological risk models and observational data. The calculations made it possible to obtain model estimates of the intra-annual dynamics of ecological risk and permissible impacts on ecosystems from stressors in the conditions of development of Arctic shelf resources. The obtained preliminary results of calculations allowed us to identify areas of increased risk and take into account the different degree of requirements for the exclusion of type 1 and 2 errors due to the specifics of ecological safety tasks. An important practical result of the development of the risk assessment methodology is the identification of time intervals of impacts at which a dangerous situation is hidden by external well-being (type 2 error). The conducted modelling studies allow reallocating safety expenditures throughout the year so as to reduce risks during hazardous periods of offshore resource development and exclude cost overruns during relatively safe times. In other words, it is possible to resolve environmental and economic contradictions in risk management.