Nutrients such as phosphate and inorganic nitrogen compounds (nitrate, nitrite, ammonium) as well as silicate are of fundamental importance for marine life. They are vital substances for the formation of phytoplankton (the microscopic unicellular algae drifting in the sea), on whose biomass production the entire marine food chain is based. Since these substances promote growth, they are referred to as nutrients. Nutrients enter marine waters particularly via rivers and the atmosphere. Excessive inputs caused by industry, transport and agriculture in the 1970s and 1980s led to a high accumulation of nutrients in seawater and thus to overfertilisation (eutrophication), which still continues today in coastal regions. One consequence of this may be the increased occurrence of algal blooms (phytoplankton and green algae). If these die off and sink to the bottom, increased oxygen depletion occurs due to the degradation of organic matter, which can lead to oxygen deficiency situations near the bottom.
In the marine chemical laboratory in Hamburg-Sülldorf, nutrient and chlorophyll-a concentrations are determined in the water samples taken at sea. Directly during the sampling at sea the oxygen concentrations near the bottom are measured as well as the pH-values and the alkalinity (buffer capacity of the sea). The totality of these parameters, which directly determine primary production and thus life in the ocean, can be used to make statements on the productivity and functionality of the ocean and thus on the status of the marine environment. In addition, interactions between ocean and atmosphere are recorded, which are influencing variables and indicators for climate change.