“MarGate” is a 270 x 60 m large underwater experimental area off Helgoland installed in February 2010 with support of the company HC-Hagemann. The field is designed as experimental facility to study processes in costal hard-bottom ecosystems and to develop and test state-of-the art scientific equipment in high-energy (stormy) coastal environments. The area comprises 3 tetrapod-fields (four-footed concrete breakwaters) in the 5 and the 10 m depth stratum each serving as study object for the effects of complex structures in strong tidal environments. Furthermore the structures serve as carrier system for in situ experimental installations. Since summer 2012, the MarGate “lab” contains the first German COSYNA (Costal Observation System for Northern and Arctic Seas) underwater node system. This system provides online measurements of the main abiotic and biotic variables (temperature, salinity, depth (tide), turbidity, oxygen, chl-a fluorescence, 3D-current) in real time (1 Hz). Recent projects at the node system focus on online zooplankton and fish recording devices. The technical systems of the COSYNA node are operated by the Helmholtz-Zentrum Geesthacht (HZG) in close cooperation with the Alfred Wegener Institute for Polar and Marine Research. The AWI Center for Scientific Diving, located on Helgoland, provide access to the experimental field all the year round. The experimental field MarGate and its technological components are specifically designed for national and international cooperation in the field of climate change related sciences and offer joint projects to external researchers.