Offshore hydrogen production leaves a local hydrographic footprint on stratification in the North Sea

Abstract Offshore production of hydrogen powered by offshore wind energy offers a promising alternative to fossil fuels. However, current technologies return waste heat and brine into the sea, raising questions of potential effects on local and regional hydrography. This study evaluates the hydrographic footprint of offshore hydrogen in the context of anthropogenic pressures from offshore energy production, focusing on a scenario for the German Bight. Cross-scale modeling shows that waste heat emerges as the primary influence, causing temperature changes of up to 2 °C within 10’s of meters around a 500 MW hydrogen plant. While tides prove to be decisive for the dilution of density plumes, we demonstrate that production capacity and discharge method determine the hydrographic footprint. Large-scale effects are minor and negligible compared to the impact of offshore wind farm wakes, however, waste heat can raise annual mean sea surface temperature by up to 0.2 °C near production sites.