Ocean deoxygenation

Global areas of hypoxia

Drivers of hypoxia and acidification in upwelling shelf systems

CC-BY icon

Ocean deoxygenation refers to the reduction in the concentration of oxygen in the ocean. This phenomenon is a significant global issue, impacting marine ecosystems, biodiversity, and the services oceans provide to humanity. Ocean deoxygenation is primarily caused by climate change and nutrient runoff from land.

Causes

The primary cause of ocean deoxygenation is the increase in global temperatures due to climate change. Warmer water holds less oxygen, and as the ocean's surface temperature rises, oxygen solubility decreases, leading to lower oxygen levels. Additionally, global warming affects ocean circulation patterns, which can further reduce the transport of oxygen from the surface to deeper waters.

Another significant cause is nutrient runoff, primarily from agriculture. Excessive nutrients, such as nitrogen and phosphorus, enter the ocean through rivers, leading to eutrophication. This process results in algal blooms, which, upon decomposition, consume a large amount of oxygen, creating hypoxic conditions or "dead zones" where marine life cannot survive.

Effects

Ocean deoxygenation has widespread effects on marine ecosystems. Reduced oxygen levels can lead to habitat loss for many marine species, altering food webs and decreasing biodiversity. Species that are less tolerant of low oxygen levels may decline or disappear, while others may migrate to areas with higher oxygen levels, potentially leading to overcrowding and increased competition for resources.

Furthermore, deoxygenation can exacerbate the effects of ocean acidification and warming, creating additional stress for marine life. For example, lower oxygen levels can impair the ability of fish to perform essential functions, such as growth, reproduction, and movement.

Mitigation and Adaptation

Addressing ocean deoxygenation requires global efforts to reduce greenhouse gas emissions and mitigate climate change. This includes transitioning to renewable energy sources, improving energy efficiency, and adopting sustainable land use practices to reduce nutrient runoff.

Adaptation strategies for marine ecosystems may include establishing marine protected areas to conserve vulnerable species and habitats, restoring ecosystems that can naturally sequester carbon and nutrients, and improving fisheries management to ensure sustainable practices.

Conclusion

Ocean deoxygenation is a pressing environmental issue with far-reaching consequences for marine ecosystems and human societies. Addressing the root causes of deoxygenation, particularly climate change and nutrient runoff, is essential for the health of the ocean and the preservation of its biodiversity.