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IOC Sub-Commission for the Western Pacific (WESTPAC)

Advancing knowledge and cooperation for a healthy ocean and prosperous society

Our Programme

Ocean Deoxygenation

What is the issue?

Ocean deoxygenation, or the decrease in oxygen concentrations, is one of the most pernicious, yet under-reported threats to marine ecosystems and food security. It is said that the global oceanic oxygen reserves have already been reduced by 2% over a period of just 50-years (from 1960 to 2010).

Ocean deoxygenation is caused by two anthropogenic stressors: CO2-induced ocean warming, and increased nutrient loads from land and sewage pollution, such as finfish aquaculture and land-based agriculture. Upwelling can also bring deep water with low oxygen but high nutrients to nearshore areas.

Oxygen decline will impact marine ecosystems and the dependent human population. Even the smallest fall in oxygen levels can create significant issues with far-reaching and complex biological and biogeochemical implications.

As it alters biogeochemical cycles and food webs, drives persistent changes to habitat and species distribution. Low oxygen concentrations are expected to reduce reproductive capacity and lead to biodiversity loss. Oxygen deficiency is expected to worsen in estuaries, coastal areas, the formation of low oxygen zones and harmful algal blooms become more frequent.

Why is it important?

Ocean deoxygenation is accelerating, and the number of dead zones is increasing exponentially across the globe.

The number of open ocean and coastal areas reporting low oxygen conditions (including water bodies such as estuaries, semi-enclosed seas, and coastal lagoons) has increased exponentially since the mid-twentieth century. However, areas of low oxygen in the WESTPAC region are likely under-reported because they are fewer than expected in densely populated areas.

Eutrophic and hypoxic Sites 1

Eutrophic and hypoxic Sites in the WESTPAC region based on published papers (176 sites as of 2018) and data obtained by the World Resources Institute (WRI) indicating many more affected sites than reported in 2010 [Jacinto et al.]

Aquaculture/mariculture sites in the region are particularly vulnerable due to intensive sea farming practices, proximity to point and non-point sources of nutrients, and the resulting eutrophic and hypoxic conditions, especially during the monsoon months. Deoxygenation will have a significant impact on aquaculture product availability, as the region accounts for 80% of global aquaculture production.

Furthermore, the region is known for having the world’s highest marine biodiversity, which could be jeopardized if low-oxygen areas were to expand.

Unlike the direct threats of climate change, many of the drivers of deoxygenation can be addressed locally, so there is real potential for new knowledge to drive local action and have an impact.

As a result, there is an urgent need to promote a common concern on marine deoxygenation, and expand oxygen monitoring in the marine environment, particularly in low-oxygen coastal and open-ocean areas, in the WESTPAC region, in order to understand and predict the response of global biogeochemical cycles to deoxygenation, improve future ocean simulations, develop effective management strategies, and mitigate the threat posed by deoxygenation on valuable marine goods and services.

What we do?

The IOC Sub-Commission for the Western Pacific (WESTPAC) takes the initiative to establish a Ocean Oxygen Network (WESTPAC O2NE) in the region, aiming to:

  1. facilitate interactions and communication among researchers studying various aspects of deoxygenation, as well as to help inform policymakers on the issue of declining oxygen concentrations in the open ocean and coastal waters;
  2. provide an initial review of deoxygenation studies conducted and published in the WESTPAC region; and,
  3. identify locations and causes of deoxygenation in the region, as well as their potential impacts on people and marine ecosystems.

Furthermore, WESTPAC O2NE will

  1. Integrate disparate deoxygenation research efforts around the world and provide a regional and multidisciplinary view of the problem;
  2. Facilitate communication with established networks, observation systems, IOC WESTPAC member states, stakeholders, and policymakers in order to raise awareness about the deoxygenation issue with meaningful and understandable messages;
  3. Encourage scientific development and collaboration, as well as the identification of emerging fields of research; and,
  4. Expand research capacity and knowledge transfer.

This aquaculture farm in Luoyuan Bay has an area of approximately 4 square kilometers. Image source: DigitalGlobe/Daily Overview



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How to cite articles on the website?

The following are examples of how to cite articles on this website:

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WESTPAC. Ocean deoxygenation: What is the issue?. IOC Sub-Commission for the Western Pacific website,, 27/09/22.

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WESTPAC. Ocean deoxygenation: What is the issue?. IOC Sub-Commission for the Western Pacific website, accessed on 27/09/22.

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