Oxygen deficiency is coupled to the amount of organic material produced in the euphotic zone by primary producers. Model simulations have shown that oxygen depletion will increase with increasing temperatures in Inner Danish waters, whereas simulations with less organic material results in considerably higher oxygen concentrations. One unanswered question is; how will the amount of organic material be influenced by climate change in the future. Climate change will affect the structure of the watercolumn such as the strength and duration of pycnoclines. Deep primary production maxima (DPPM) develop in the summertime around the pycnoclines because of limiting nutrients in the upper waters. When pycnoclines are situated deeper than the euphotic zone, DPPM is limited by light and the overall primary production (PP) decreases. In situations where the duration of a pycnocline is prolonged, a higher percentage of the overall production will occur in the deeper waters. In this study, we analyse existing data on PP in the past and present. Preliminary results show that DPPM are responsible for more than 20% of the total annual PP in one location in the Inner Danish waters. During the rest of the project more stations will be analysed to draw a picture of distribution and importance of DPPM. Furthermore seasonal field expeditions will be conducted to study the distribution of PP, export production and oxygen concentrations in further detail. Statistical analyses and process studies will be combined in ecosystem models estimating future oxygen concentrations.