Map showing global distribution of anoxic ocean waters. During the past 50 years, the area of low-oxygen water in the open ocean has increased by 4.5 million square km. The world's oceans are losing approximately 1 gigaton of oxygen each year. Graphic: UNESCO

KIEL, 7 September 2018 (UNESCO) – This week, more than 300 scientists from 33 countries met in Kiel, Germany, at an international conference to discuss the decline of oxygen in the ocean, the causes and the consequences. At the conclusion of the conference, the scientists published a haunting appeal, the “Kiel Declaration”, in which they call urgently for more marine and climate protection.

The numbers are alarming: over the past 50 years, oxygen has decreased by 2 percent in the global ocean. The volume of oxygen-depleted waters, has grown more than fourfold. The main reasons are the increasing global warming, but also the over-fertilization of the oceans. In the long term, these changes will not only jeopardize life in large parts of the world's oceans, but also feedbacks to the atmosphere are expected, as greenhouse gases such as nitrous oxide and methane form in oxygen-free water.

Scientists from all parts of the world who convened in Kiel for a conference organized by the Collaborative Research Centre 754 (SFB 754) “Climate and Biogeochemical Interactions in the Tropical Ocean” agreed that this problem must be immediately and urgently addressed to develop solutions in order to stop the oxygen loss as soon as possible. Therefore, they unanimously adopted an appeal for more marine and climate protection, the “Kiel Declaration”.

“The ocean is in a global crisis,” says Prof. Dr. Andreas Oschlies, spokesperson of the SFB 754 from the GEOMAR Helmholtz Centre for Ocean Research Kiel. “For the very productive areas of the world's ocean off Peru and West Africa, the supply of nutrients and oxygen is of vital importance,” Oschlies continues. But particularly in these areas, the oxygen content has decreased significantly in the past 50 years. In addition, these coastal areas are particularly affected by overfertilization, which leads to algae blooms and ultimately to increased oxygen depletion through degradation of biomass.

“Comparisons between observational data and the results of complex numerical models show that even the best simulations underestimate the changes which are already observed significantly,” Prof. Oschlies explains. “Thus, nature is changing faster than we expected.” Therefore, Oschlies and the more than 300 participants of the conference and the Global Ocean Oxygen Network (GO2NE) – an expert group established in 2016 under UNESCO’s Intergovernmental Oceanographic Commission – consider it important to publicize these changes and also to advocate increased ocean observations, leading to a better understanding of ongoing rapid changes and eventually to more robust predictions.

In the document, they call for more international efforts to sharpen global awareness of oxygen depletion, taking immediate and decisive action to limit marine pollution and in particular the excessive nutrient input into the ocean and to limit global warming by decisive climate change mitigation actions.

The researchers refer to the Paris Climate Change Agreement and the United Nations Sustainable Development Goal 14 for the sustainable development of the seas and oceans. “We still have the chance to avoid strong and irreversible effects of climate change, pollution and overuse of the oceans through rethinking and immediate action,” says Prof. Oschlies. “But we are quickly running out of time! That’s why we want to set a clear and strong signal with the ‘Kiel Declaration’ in order to stop the oxygen depletion of the ocean and thus, preserve the largest ecosystems on this planet.”


Urgent appeal for more marine and climate protection: marine scientists publish “Kiel Declaration”

Kiel Declaration on Ocean Deoxygenation

The ocean is losing its breath
Oxygen in the ocean supports the largest ecosystems on the planet. It is alarming that the ocean is losing oxygen, termed ocean deoxygenation, primarily due to global warming by greenhouse gas emissions, and pollution by nutrients and organic wastes particularly in coastal waters. We call on all nations, societal actors, scientists and the United Nations to:

  • (a) Raise global awareness about ocean deoxygenation through local, regional and global efforts, including interdisciplinary research, innovative outreach, and ocean education.
  • (b) Take immediate and decisive action to limit pollution and in particular excessive nutrient input to the ocean.
  • (c) Limit global warming by decisive climate change mitigation actions.

Both the Paris Agreement addressing Climate Change and the United Nations’ 2030 Agenda for Sustainable Development demand conservation and sustainable use of the ocean, seas and marine resources in order to safeguard ocean ecosystems and their current and future societal benefi ts. These are severely threatened by ocean deoxygenation.

Scientists assembled at the conference and from around the world agree that:

  1. During the past 50 years oxygen-depleted waters have expanded fourfold. Some areas of the ocean have lost up to 40% of their oxygen.
  2. The ongoing loss of oxygen from the ocean is a rapidly increasing threat to marine life, the ocean’s ecosystems and coastal communities.
  3. Global warming impacts ocean oxygen in two ways: the capacity to hold oxygen decreases in warming waters, whilst warming reduces ocean mixing and circulation limiting the supply of oxygen from the atmosphere. Pollution by nutrients and organic waste enhances oxygen demand by increasing biological production and oxygen consumption during decomposition.
  4. Deoxygenation disrupts marine ecosystems, affects fish stocks and aquaculture and leads to loss of habitat and biodiversity. It can, in extreme cases, lead to the production of toxic gases when all oxygen in the water has been lost.
  5. Deoxygenation can accelerate global warming via enhanced marine production of greenhouse gases under low oxygen conditions.
  6. The problem of deoxygenation is predicted to worsen in the coming years under continued global warming and increasing nutrient input to coastal regions as human populations and economies grow.
  7. Expanded observation is immediately required for accurate documentation and prediction of ocean oxygen changes, and for improved understanding of its causes and consequences.
  8. Strategies to slow and eventually reverse deoxygenation and its ecological impacts need to be co-developed between science and societal actors. This will contribute to the UN Decade of Ocean Science for Sustainable Development.

Conference Chair, Executive Board and Conveners

Prof. Andreas Oschlies, GEOMAR & Kiel University, Kiel, Germany
Prof. Eric Achterberg, GEOMAR & Kiel University, Kiel, Germany
Dr. Patricia Ayon, Marine Institute of Peru, Lima, Peru
Prof. Hermann Bange, GEOMAR, Kiel, Germany
Dr. Denise Breitburg, Smithsonian Environmental Research Centre, Edgewater, MD USA
Dr. Laura Bristow, University of Southern Denmark, Odense, Denmark
Dr. Xavier Capet, CNRS, Paris France
Prof. Minhan Dai, Xiamen University, Xiamen, China
Prof. Anja Engel, GEOMAR & Kiel University, Kiel, Germany
Prof. Katja Fennel, Dalhousie University, Halifax, Canada
Prof. Martin Frank, GEOMAR & Kiel University, Kiel, Germany
Dr. Veronique Garcon, LEGOS, CNRS, Toulouse, France
Prof. Marilaure Grégoire, University of Liège, Liège, Belgium
Dr. Helena Hauss, GEOMAR, Kiel, Germany
Dr. Babette Hoogakker, Heriot-Watt University, Edinburgh, UK
Dr. Kirsten Isensee, IOC-UNESCO, Paris, France
Prof. Samuel Jaccard, University of Bern, Bern, Switzerland
Prof. Klaus Jürgens, Leibniz Institute for Baltic Sea Research Warnemünde, Rostock, Germany
Dr. Rainer Kiko, GEOMAR, Kiel, Germany
Prof. Arne Körtzinger, GEOMAR & Kiel University, Kiel, Germany
Prof. Mojib Latif, GEOMAR & Kiel University, Kiel, Germany
Prof. Lisa Levin, Scripps Institution of Oceanography, University of California, San Diego, CA USA
Prof. Karin Limburg, SUNY, College of Environmental Science & Forestry, Syracuse, NY USA
Dr. S. Wajih A. Naqvi, Kuwait Institute for Scientific Research, Salmiya, Kuwait
Dr. Oscar Pizarro, University of Concepción, Chile
Prof. Martin Quaas, Kiel University, Kiel, Germany
Dr. Renato Quinones, University of Concepción, Concepción, Chile
Prof. Birgit Schneider, Kiel University, Kiel, Germany
Prof. Caroline Slomp, Utrecht University, Utrecht, The Netherlands
Dr. Lothar Stramma, GEOMAR, Kiel, Germany
Dr. Sören Thomsen, LOCEAN-IPSL, Sorbonne University, Paris, France
Prof. Tina Treude, University of California, Los Angeles, CA USA
Prof. Osvaldo Ulloa, University of Concepción, Concepción, Chile
Prof. Martin Visbeck, GEOMAR & Kiel University, Kiel, Germany

Kiel Declaration on Ocean Deoxygenation


  1. Unknown said...

    And back in day we were told a shipload of pesticide or fertilizer would kill the ocean. Guess there is more than a shipload now.


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