Indicator Specification

Ocean oxygen content

Indicator Specification
  Indicator codes: CLIM 054
Published 13 Dec 2016 Last modified 04 Dec 2019
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Distribution of oxygen-depleted ‘dead zones’ in European seas Development of oxygen depletion in the Baltic Sea over time
This indicator is discontinued. No more assessments will be produced.

Assessment versions

Published (reviewed and quality assured)
  • No published assessments


Justification for indicator selection

Accelerated nutrient flow into the sea (mostly from agricultural fertilisers) in combination with warming water temperatures can lead to large phytoplankton blooms and subsequent increases in primary production (a process called eutrophication). When these organisms sink to the sea floor, oxygen is utilised in their decomposition. If mixing within the water column cannot supply enough oxygen to the sea floor, this can lead to oxygen reduction (hypoxia) to levels that severely limit biological activity and ultimately to complete oxygen depletion (anoxia).

Most organisms, including marine organisms, require oxygen for their metabolism. Therefore, lower oxygen concentrations in seawater affect the physiology, composition and abundance of species. Rising water temperatures will have knock-on effects on a number of different chemical processes in the marine environment. For example, as the temperature rises, oxygen becomes less soluble in water, resulting in lower oxygen concentrations; at the same time, the oxygen demand for metabolism increases. Insufficient oxygen supply to organisms will eventually have knock-on effects on productivity, species interactions and community composition at the ecosystem level.

Oxygen depletion can occur episodically (less than once per year), periodically (several times per year for short periods) and seasonally (each summer), and eventually it can become persistent. The Baltic Sea has the largest dead zone in the world, which includes large areas of persistent oxygen depletion. Oxygen-depleted areas are an example of how one type of anthropogenic pressure, nutrient input causing eutrophication, is exacerbated by climate change (here increasing temperature) through multiple different linkages with biology, from cellular levels to community and ecosystem levels. For example, land-based nutrient enrichment can lead to a redistribution in the vertical distribution of primary production. Such increased nutrient input can increase primary production in the surface layer, where the oxygen produced can be exchanged with the atmosphere. The organic material produced will sink through the pycnocline (i.e. the ocean layer with a stable density gradient, which hinders vertical transport) using oxygen as it decomposes. At the same time, when primary production occurs below the pycnocline, the oxygen produced will stay in the bottom layer. As climate change influences stratification parameters, and consequently the depth of the pycnocline, it could influence light availability for primary production in the deeper layer, possibly decreasing oxygen production. In this case, the interaction between climate change and eutrophication can have impacts on biodiversity, plankton communities and oxygen conditions. Oxygen depletion may also interact with other anthropogenic stressors in affecting marine ecosystems and fisheries, such as overfishing or the introduction of invasive species.

Scientific references

  • IPCC, 2013. Climate Change: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Stocker, T. F., D. Qin, G.-K. Plattner, M. Tignor, S. K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex and P. M. Midgley (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, 1535 pp.
  • IPCC, 2014: Climate Change 2014: Impacts, Adaptation, and Vulnerability. Part B: Regional Aspects. Contribution of Working Group II to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Barros, V.R., C.B. Field, D.J. Dokken, M.D. Mastrandrea, K.J. Mach, T.E. Bilir, M. Chatterjee, K.L. Ebi, Y.O. Estrada, R.C. Genova, B. Girma, E.S. Kissel, A.N. Levy, S. MacCracken, P.R. Mastrandrea, and L.L. White (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, 688 pp.

Indicator definition

  • Distribution of oxygen-depleted ‘dead zones’ in European seas
  • Development of oxygen depletion in the Baltic Sea over time


  • Location (dimensionless)
  • Estimated oxygen bottom concentrations (mg/l)

Policy context and targets

Context description

In April 2013, the European Commission (EC) presented the EU Adaptation Strategy Package. This package consists of the EU Strategy on adaptation to climate change (COM/2013/216 final) and a number of supporting documents. The overall aim of the EU Adaptation Strategy is to contribute to a more climate-resilient Europe.

One of the objectives of the EU Adaptation Strategy is Better informed decision-making, which will be achieved by bridging the knowledge gap and further developing the European climate adaptation platform (Climate-ADAPT) as the ‘one-stop shop’ for adaptation information in Europe. Climate-ADAPT has been developed jointly by the EC and the EEA to share knowledge on (1) observed and projected climate change and its impacts on environmental and social systems and on human health, (2) relevant research, (3) EU, transnational, national and subnational adaptation strategies and plans, and (4) adaptation case studies.

Further objectives include Promoting adaptation in key vulnerablesectors through climate-proofing EU sector policies and Promoting action by Member States. Most EU Member States have already adopted national adaptation strategies and many have also prepared action plans on climate change adaptation. The EC also supports adaptation in cities through the Covenant of Mayors for Climate and Energy initiative.

In September 2016, the EC presented an indicative roadmap for the evaluation of the EU Adaptation Strategy by 2018.

In November 2013, the European Parliament and the European Council adopted the 7th EU Environment Action Programme (7th EAP) to 2020, ‘Living well, within the limits of our planet’. The 7th EAP is intended to help guide EU action on environment and climate change up to and beyond 2020. It highlights that ‘Action to mitigate and adapt to climate change will increase the resilience of the Union’s economy and society, while stimulating innovation and protecting the Union’s natural resources.’ Consequently, several priority objectives of the 7th EAP refer to climate change adaptation.


No targets have been specified.

Related policy documents

  • 7th Environment Action Programme
    DECISION No 1386/2013/EU OF THE EUROPEAN PARLIAMENT AND OF THE COUNCIL of 20 November 2013 on a General Union Environment Action Programme to 2020 ‘Living well, within the limits of our planet’. In November 2013, the European Parliament and the European Council adopted the 7 th EU Environment Action Programme to 2020 ‘Living well, within the limits of our planet’. This programme is intended to help guide EU action on the environment and climate change up to and beyond 2020 based on the following vision: ‘In 2050, we live well, within the planet’s ecological limits. Our prosperity and healthy environment stem from an innovative, circular economy where nothing is wasted and where natural resources are managed sustainably, and biodiversity is protected, valued and restored in ways that enhance our society’s resilience. Our low-carbon growth has long been decoupled from resource use, setting the pace for a safe and sustainable global society.’
  • Climate-ADAPT: Adaptation in EU policy sectors
    Overview of EU sector policies in which mainstreaming of adaptation to climate change is ongoing or explored
  • Climate-ADAPT: Country profiles
    Overview of activities of EEA member countries in preparing, developing and implementing adaptation strategies
  • DG CLIMA: Adaptation to climate change
    Adaptation means anticipating the adverse effects of climate change and taking appropriate action to prevent or minimise the damage they can cause, or taking advantage of opportunities that may arise. It has been shown that well planned, early adaptation action saves money and lives in the future. This web portal provides information on all adaptation activities of the European Commission.
  • EU Adaptation Strategy Package
    In April 2013, the European Commission adopted an EU strategy on adaptation to climate change, which has been welcomed by the EU Member States. The strategy aims to make Europe more climate-resilient. By taking a coherent approach and providing for improved coordination, it enhances the preparedness and capacity of all governance levels to respond to the impacts of climate change.

Key policy question

What is the trend in oxygen-depleted ‘dead zones’ in European seas?



Methodology for indicator calculation

Scientifically reported accounts of eutrophication-associated dead zones have been used to produce an overview of the distribution of oxygen-depleted ‘dead zones’ in European seas.

Simulations using observed dissolved oxygen concentrations as input have been carried out to estimate oxygen bottom concentrations and ‘dead zone’ areas.

Methodology for gap filling

Not applicable

Methodology references


Data specifications

EEA data references

  • No datasets have been specified here.

External data references

Data sources in latest figures



Methodology uncertainty

See under "Methodology".

Data sets uncertainty

In general, changes related to the physical and chemical marine environment are better documented than biological changes. Observations of dissolved oxygen concentrations began around 1900. Since the 1960s, more regularly spaced measurements are undertaken and a more consistent data base for the assessment of the spatial extent of ‘dead zones’ is available.

Rationale uncertainty

No uncertainty has been specified

Further work

Short term work

Work specified here requires to be completed within 1 year from now.

Long term work

Work specified here will require more than 1 year (from now) to be completed.

General metadata

Responsibility and ownership

EEA Contact Info

Johnny Reker


European Environment Agency (EEA)


Indicator code
CLIM 054
Version id: 1

Frequency of updates

This indicator is discontinued. No more assessments will be produced.


DPSIR: State
Typology: Descriptive indicator (Type A - What is happening to the environment and to humans?)


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