Kohlenstoffspeicher Meer: Taucher unter Wasser kontrolliert den entfalteteten Wassersack, eine 55 Kubikmeter große Wassersäule samt allen darin lebenden Plankton-Organismen

Marine Carbon Sinks


The problem is well known: More and more carbon is entering the atmosphere as a result of human activities. The atmosphere is heating up. The climate is changing and with it the living conditions on our planet. In the first research mission of the German Marine Research Alliance (DAM), some 200 scientists working on six collaborative projects are investigating how the climate-regulating effect of the ocean can be reinforced in the future.

The element carbon is found in an almost limitless number of compounds and forms the basis for life on earth. Its distribution also determines the climate on our planet. When a lot of carbon is bound in the Earth’s interior or in the oceans and only small amounts remain in the atmosphere as gaseous carbon dioxide, the Earth tends to be cool. The more carbon that enters the atmosphere, the warmer it becomes. Over the past 250 years, human beings have released enormous amounts of carbon dioxide into the atmosphere. The noticeable and measurable consequence is global warming.

The Paris Climate Agreement sets clear targets. The signatory states have committed themselves to limiting global warming to well below 2 °C. Plausible scenarios as to how this can be achieved by avoiding emissions alone are lacking. This means that additional CO2 must be removed from the atmosphere. Apart from terrestrial methods, marine methods of removing CO2 are increasingly being investigated, because the ocean, which functions as a heat and carbon reservoir, is one of the most important regulators of the climate.

The DAM research mission “Marine Carbon Sinks in Decarbonisation Pathways” investigates whether and to what extent the ocean can play a key, sustainable role in absorbing and storing carbon dioxide from the atmosphere. In addition, it is studying how this is connected with and affects the marine environment, the Earth system and society at large.

Ocean and clouds
Can the ocean help to actively remove carbon dioxide from the atmosphere and store it in order to limit climate change? This is one of the core questions being addressed by the DAM's first research mission. | ©Ralf Prien | IOW
Prof. Dr. Matthes, Member of the DAM Executive Board
Prof. Dr. Katja Matthes, Member of the DAM Executive Board | ©Sinje Hasheider

“How can we protect the oceans and use their invaluable services sustainably to protect the climate? The German Marine Research Alliance’s mission on the absorption of carbon dioxide by the oceans is making important contributions to mitigating climate change and achieving the Paris climate goals. In six collaborative projects, some 200 scientists are investigating potential courses of action to increase the uptake of this greenhouse gas by the oceans and analysing risks and benefits from an inter- and transdisciplinary perspective. The DAM is thereby supporting political and societal decisions for a climate-friendly future with the oceans.”

Marine carbon sinks in decarbonisation pathways

Analysing and evaluating measures to increase carbon dioxide uptake and storage by the oceans takes into account both risks and benefits, and assesses their potential as well as the economic, political, social and legal context and impacts. To achieve this, a transdisciplinary and interdisciplinary approach is required, as well as a close dialogue with stakeholders. By proposing concrete courses of action and consistently implementing knowledge transfer and data provision measures, the findings can subsequently be used by policy-makers and society. The DAM is thus fulfilling its mandate to develop science-based decision-making options for the sustainable management of coasts, seas and oceans.

“Marine carbon sinks in decarbonisation pathways”
Short title: CDRmare

Prof. Dr. Andreas Oschlies
GEOMAR Helmholtz Centre for Ocean Research Kiel
Prof. Dr. Gregor Rehder
Leibniz Institute for Baltic Sea Research Warnemünde (IOW)

Dr. Christiane Schelten (Project Manager CDRmare)
Ulrike Bernitt (Knowledge Transfer Manager CDRmare)

project partners


  • Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research
  • Federal Institute for Geosciences and Natural Resources
  • Carl von Ossietzky University of Oldenburg
  • Kiel University
  • German Oceanographic Museum
  • Kiel University of Applied Sciences
  • Fichtner GmbH & Co. KG
  • Fraunhofer Institute for Physical Measurement Techniques
  • GEOMAR Helmholtz Centre for Ocean Research Kiel
  • Helmholtz Zentrum Hereon
  • Institute for the World Economy (IfW Kiel)
  • U.M. Environmental and Marine Technology Kiel GmbH,
  • Gottfried Wilhelm Leibniz University Hanover
  • Leibniz Institute for Baltic Sea Research Warnemünde
  • Leibniz University of Hannover
  • Leibniz Centre for Tropical Marine Research
  • Max Planck Institute for Marine Microbiology
  • Potsdam Institute for Climate Impact Research
  • Sea & Sun Technology GmbH
  • German Institute for International and Security Affairs
  • TrueOcean GmbH
  • University of Bremen
  • Universität Hamburg


Six different consortia are studying various methods of marine carbon dioxide removal and storage with regard to their potential, risks and possible side effects, as well as their impact on the marine environment, the Earth system and society, bringing these together in the form of a transdisciplinary assessment framework.

is gathering information about marine options for actively reducing carbon dioxide levels in the atmosphere and will develop a uniform assessment framework for the different approaches. In addition to the basic scientific facts and the question of technical feasibility, it will also take into account legal, social and ethical aspects as well as the political framework. Coordination: Prof. Dr. Gregor Rehder, IOW, more

is investigating whether and in what form ocean alkalinity enhancement can be a viable method of permanently removing significant amounts of carbon dioxide from the atmosphere in an environmentally sound and socially responsible manner. Coordination: Prof. Dr. Andreas Oschlies, GEOMAR, more

focuses on carbon storage in vegetation-rich coastal ecosystems. Innovative approaches are being developed to enhance this natural potential for carbon storage, taking into account its further utilisation by society, as well as potential risks. Coordination: Prof. Dr. Martin Zimmer, Leibniz Centre for Tropical Marine Research – ZMT, more

is looking at the potential for storing carbon dioxide underground in sandstone formations beneath the North Sea. The aim is to quantify the storage capacities in the German North Sea and to analyse the associated risks and opportunities. Coordination: Prof. Dr. Klaus Wallmann, GEOMAR, more

is investigating whether and in what form the upwelling of nutrient-rich deep water can promote near-surface plankton growth and thus bind more atmospheric carbon. Coordination: Prof. Dr. Ulf Riebesell, GEOMAR, more

is investigating the extent to which carbon dioxide can be permanently stored in the basaltic upper ocean crust in the form of carbonates. Laboratory experiments are planned which will flank studies of the natural systems along the Mid-Atlantic Ridge. Innovative monitoring systems will keep track of the environmental impact. Coordination: Prof. Dr. Achim Kopf, MARUM – Centre for Marine Environmental Sciences, University of Bremen, more

Ocean-based methods of removing carbon dioxide from the atmosphere | Creative Commons license: BY-NC-ND // Artwork: Rita Erven, GEOMAR
The RETAKE and TestArtUp consortia are carrying out various mesocosm experiments, looking at the feasibility and potential, but also the environmental risks of the tested methods for promoting carbon uptake by the ocean. | ©Ulf Riebesell | GEOMAR


The oceans contain more than 50 times as much carbon as the atmosphere. By absorbing a high proportion of carbon dioxide, they have so far counteracted anthropogenic climate change. Since the beginning of industrialisation in the 1800s, the oceans have stored around a quarter of the additional carbon dioxide that humans have released into the atmosphere, mainly by burning coal, oil and natural gas and destroying forests.

But because the concentration of climate-damaging gases in the air has risen steadily in recent decades, this storage effect is becoming weaker. The oceans absorb carbon dioxide from the atmosphere and dissolve it in the form of carbonic acid. As a result, the seawater becomes more acidic and warmer due to climate change, and its oxygen content decreases. These effects reduce the capacity of the oceans to absorb carbon dioxide. If the water in the oceans becomes too warm and too acidic, this also has consequences for marine life and ecosystems, which also play a significant role in carbon storage in the ocean.

In addition to physical and chemical processes, marine organisms control carbon dioxide uptake in the ocean via the so-called biological pump. Tiny algae, called phytoplankton, are suspended in the uppermost layer of water. They absorb carbon dioxide and use the energy of sunlight to build up biomass through photosynthesis. When they die, part of the biomass formed sinks to the bottom – including the carbon that is bound in it. However, only the part that does not enter biological cycles to be released again as carbon dioxide is stored for extended periods.

Uncertainty remains as to how the biological pump will change in the future. A multitude of mechanisms are involved, and how these interact with each other is still being studied. What is certain is that marine organisms play a significant role in the function of the oceans as carbon sinks. Protecting marine and coastal ecosystems is therefore immediately relevant to our climate and also ensures the preservation of biodiversity and ecosystem services, such as the supply of food from the sea and the mental and physical recreation of human beings.

Seagrass meadows are carbon reservoirs and at the same time valuable habitats
Seagrass meadows are carbon reservoirs and at the same time valuable habitats | Photo: Dirk Schories

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