Aquatic Deoxygenation

Experts are advocating for the recognition of Aquatic Deoxygenation (AD) as a new planetary boundary, highlighting the critical decline in oxygen content in oceanic and coastal waters.

Understanding Aquatic Deoxygenation (AD)

• Definition: AD refers to the overall decline in the oxygen content of water bodies, occurring when oxygen consumption exceeds oxygen replenishment.

Current Status of Aquatic Deoxygenation

• Oceans: Since the 1960s, approximately 2% of oxygen in the oceans has been lost. More than 500 low-oxygen sites have been identified in coastal waters.
• Lakes and Reservoirs: Oxygen levels in lakes have decreased by 5.5%, while reservoirs have experienced a more significant decline of 18.6% since 1980.

Causes of Aquatic Deoxygenation

• Global Warming:
• Rising temperatures lead to decreased solubility of oxygen in water.
• Warm surface layers in the ocean inhibit the mixing of oxygen into deeper waters, contributing to low oxygen levels in the deep sea.
• Eutrophication:
• Nutrient over-enrichment from anthropogenic sources (e.g., fertilizers from agriculture) results in algal blooms, which subsequently increase oxygen consumption when the algae decompose.

Impacts on Ecosystems

• Dead Zones: Areas of hypoxia (low oxygen) can create "dead zones," where aquatic life struggles to survive.
• Habitat Compression: Reduced habitat quality and quantity for fisheries leads to diminished biomass and species loss.
• Climate Regulation: AD affects the regulation of Earth's climate, as microbiotic processes in low-oxygen areas produce greenhouse gases.
• Marine Food Web Changes: Increased predation risk and factors like ocean acidification disrupt marine food webs.

Planetary Boundaries Framework

• Definition: Planetary boundaries are limits on the impacts of human activities on the Earth system. Exceeding these boundaries risks the environment's ability to self-regulate.
• Recognized Boundaries: There are nine planetary boundaries, including climate change, ocean acidification, land use change, and biodiversity loss.

Conclusion

Recognizing Aquatic Deoxygenation as a new planetary boundary is vital for addressing the ecological crisis stemming from human activities. Acknowledging and mitigating the factors contributing to AD can help preserve marine ecosystems, maintain biodiversity, and support climate regulation, ultimately safeguarding the health of our planet.