Photo: Peter Bondo Christensen


Oxygen concentrations in both the global ocean and coastal waters have been declining since at least the middle of the 20th century. This oxygen loss is one of the most important changes occurring in an ocean increasingly modified by human activities that have raised temperatures, CO2 levels, and increased nutrient inputs that have altered the abundances and distributions of marine species.

Oxygen is naturally low or absent where biological oxygen consumption through respiration exceeds the rate of oxygen supplied by physical transport, air-sea fluxes, and photosynthesis. The enhanced production in surface waters of the coastal zone from nutrient inputs from sewage and agricultural activities increases the delivery rate of degradable organic matter to bottom waters where microbial decomposition by aerobic respiration consumes oxygen. In addition, ocean warming reduces the solubility of oxygen and raises metabolic rates also accelerating the rate of oxygen consumption. Under current trajectories, anthropogenic activities could drive the ocean toward widespread oxygen deficiency within the next thousand years.


Lectures by:

Denise Breitburg, Smithsonian Environmental Research Center, USA

Jacob Carstensen, Aarhus University, Denmark

Christoph Humborg, Stockholm University Baltic Sea Center, Sweden

Alf Norkko, University of Helsinki, Finland

Andreas Oschlies, GEOMAR Helmholtz Centre for Ocean Research Kiel, Germany

Caroline Slomp, Utrecht University, The Netherlands

Bess B. Ward, Princeton University, USA


The symposium was held 21 February at the Beijer Hall, Royal Swedish Academy of Sciences. All the lectures were recorded and can now be watched at


This symposium is funded by Baltic Sea Centre at Stockholm University, BalticSea2020, the Swedish Agency for Marine and Water Management and the Royal Swedish Academy of Sciences.