The release of terrigenous organic carbon to the Arctic Ocean, due to the reduction of the permafrost and the consequent increase of freshwater inflow to the sea, is one of the major consequences of global climate change. This process is also called brownification. The objective of the Ny-Ålesund-Plankton project is to study experimentally in natural conditions the response of the Arctic marine plankton community to brownification. The Ny-Ålesund-Plankton project will be realized in Svalbard in June 8-28 2020 as the French contribution to the AQUACOSM European project. Mobile in situ mesocosms will be brought and established by the Norwegian and German partners of AQUACOSM with financial and logistic supports of the European project. Mesocosms will be immerged in the Ny-Ålesund coast and brownification will be simulated by the addition of organic matter. In these in situ mesocosms we will deploy six set of autonomous sensors, measuring physical and biogeochemical parameters, which we developed in the frame of AQUACOSM project for real time data acquisition and transmission. Each set of sensors includes 5 sensors that will monitor continuously at high frequency fluorescence of chlorophyll, dissolved oxygen, conductivity, water temperature and underwater light during two weeks of non-stop mesocosm experiment. In addition, using conventional approaches we will study the dynamics of different phytoplankton groups and its photosynthetic activity, dissolved oxygen, growth rates of bacterioplankton, pico- and nanophytoplankton and that of the whole phytoplankton community and of major groups, and their predator grazing rates, as well as net community production, respiration and gross primary production. The results highlighting the response of Ny-Ålesund plankton community to brownification based on high frequency measurements and other obtained data will be presented in an international symposium and published in open-access journal.