ALKOR AL458

The Baltic Sea is a marine ecosystem, which is influenced by multiple stressors. Eutrophication leads to a high productivity and thus an increasing oxygen demand in the deep water layers. In consequence of the increased biological oxygen demand and the increased production of CO2, the spread of hypoxic zones is predicted. The microbial respiration of dissolved organic material is an important process that contributes to the attrition of oxygen. The production of organic material and its subsequent re-mineralization by microorganisms are thus biological processes that have a high potential to help determine the direction and magnitude of future changes in oxygen content and pH. Yet little is known about how much nutrient inputs and the CO2 concentration in seawater affect the phytoplankton productivity. The importance of the composition of the organic material, the pH of the seawater and the oxygen availability for the remineralization of carbon are largely unexplored. The aim of the expedition is to study the production, the composition and the depletion of particulate and dissolved organic material along natural nutrient, oxygen and CO2 gradients in the Baltic Sea.