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.

Hypoxic conditions in Manila Bay caused by Noctiluca bloom.

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

What we do?

Given the limited capacity of member states for developing ocean forecasting system and the demands of member states for such a system, WESTPAC has been taking the steps to develop an ocean forecasting system since its 8th Intergovernmental Session (WESTPAC-VIII, 10-13 May 2010, Bali, Indonesia). The Sub-Commission launched a Demonstration OFS for the Southeast Asian waters in 2012 (WESTPAC-IX, 9-12 May 2012, Busan, Korea), and decided in 2015 (WESTPAC-X, 12-15 May 2015, Phuket Thailand ) to step up its effort and services in developing the OFS for a larger geographic domain (800E-1500E, 200S-25N), and higher-resolution models in selected sub-domains upon the request of participating countries.

“>With the long years’ development and technological advance, the latest version of Ocean Forecast System covers the global ocean, and is made freely available via the website ( The effort has been reinforced by a close collaboration with academic and research groups, meteorological agencies, ocean resources management departments.

Meanwhile, capacity development for early career ocean professionals has been part of the development effort, with regular training and research opportunities having provided since 2011 at the Regional Training and Research Center on Ocean Dynamics and Climate (RTRC-ODC, Qingdao China), hosted by the First Institute of Oceanography, Ministry of Natural Resources of China.

The OFS ( is based on the surface wave-tide-circulation coupled model developed by the First Institute of Oceanography (FIO), Ministry of Natural Resources, China. The circulation part is based on MOM5 (Modular Ocean Model, version 5), the wave part is MASNUM-WAM model, the atmosphere forcing is from NCEP GFS products.


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How to cite articles on the website?

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

Web page with known publication date

WESTPAC. What are the marginal seas in the Western Pacific Ocean?. IOC Sub-Commission for the Western Pacific website,, 13/04/20.

Web page with unknown publication date

WESTPAC. Material exchange and transport with the Kuroshio and eddies and mixing. IOC Sub-Commission for the Western Pacific website,, accessed on 13/04/20.

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