New proposed title: Behaviour and effects of natural and anthropogenic radionuclides in the marine environment and their use as tracers for oceanography studies (possible acronym NAROC) The marine environment is a major recipient of anthropogenic radionuclides released by both atmospheric and aquatic pathways. In addition, it is subject, in certain areas, to enhanced levels of natural radionuclides as a result of human activities. Due to changing inputs and practices, and to transport and transfer processes within the marine environment, levels of anthropogenic and natural radionuclides can vary significantly, both spatially and with time. These changes are important for MSs which rely on marine resources, as they can have economic, social, and human and environmental health impacts. The existing knowledge of marine radioactivity varies significantly between different marine areas: obtaining a comprehensive and reliable baseline, to which future changes can be compared, requires careful validation of data and a rigorous advanced mathematical approach to data processing. Further modelling of radionuclide specific measurements of concentrations in seawater, suspended and bottom sediment and marine biota provides unique insight into physical, chemical and biological oceanographic processes. This CRP aims to provide MSs with a methodology to assess levels, trends and effects of radionuclides in the marine environment and with new information on oceanographic processes in coastal and open-sea areas obtained from radiotracer applications. An additional valuable outcome will be on-line access of Member States to validated up-to-date marine radioactivity data and information through IAEA’s MARiS database. The coordination of the research undertaken by the participating institutes will ensure that the results are based on a broad scientific participation under the common umbrella of critically reviewed, up-to-date and harmonised methodologies.