Aquatic Deoxygenation (AD) and Planetary Boundaries: An Emerging Global Concern

• Aquatic Deoxygenation (AD) is gaining global attention as scientists and environmental experts call for its recognition as a new planetary boundary. 
• The term refers to the declining levels of dissolved oxygen in the world's oceans and coastal water bodies, driven by both natural processes and human-induced activities. 
• The concern is not only ecological but also deeply linked to the planet’s ability to sustain life and maintain balance.

What is Aquatic Deoxygenation?

• Aquatic Deoxygenation is defined as the overall reduction in oxygen concentration in marine and freshwater ecosystems.
• This phenomenon arises when the rate of oxygen consumption surpasses the rate of oxygen replenishment. 
• The imbalance in oxygen availability affects aquatic organisms, ecosystems, and biogeochemical cycles.

Key Characteristics

• Occurs in both coastal waters and open oceans.
• Leads to hypoxia (low oxygen levels) and anoxia (absence of oxygen).
• Triggers widespread marine biodiversity loss and ecological stress.

Causes of Aquatic Deoxygenation

Global Warming

• Rising sea surface temperatures due to greenhouse gas emissions reduce the solubility of oxygen in seawater.
• Warmer waters hold less dissolved oxygen, which intensifies oxygen stress in marine life.
• Increased stratification (layering) of ocean water prevents oxygen-rich surface water from mixing with deeper layers.

Eutrophication from Nutrient Runoff

• Excessive use of fertilizers in agriculture leads to runoff of nitrogen and phosphorus into water bodies.
• These nutrients stimulate algal blooms, which deplete oxygen as they decompose.
• This creates “dead zones” where oxygen levels are too low to support most marine life.

Pollution and Wastewater Discharge

• Untreated sewage and industrial waste increase organic matter, which requires oxygen to decompose.
• This contributes to oxygen demand and further intensifies deoxygenation.

Impacts of Aquatic Deoxygenation

Marine Dead Zones

• Areas with very low oxygen levels where most marine organisms cannot survive.
• The Bay of Bengal, Gulf of Mexico, and parts of the Arabian Sea are prominent examples.

Habitat Compression

• Fish and other marine species are forced to move to shallower, oxygen-rich zones.
• This leads to crowding, increased competition, and changes in predator-prey relationships.

Disruption of Marine Food Webs

• Deoxygenation affects phytoplankton and zooplankton, the base of the food chain.
• This impacts commercial fisheries, food security, and global protein supplies.

Altered Climate Feedbacks

• Low-oxygen zones influence carbon and nitrogen cycles, affecting the ocean’s capacity to absorb carbon dioxide.
• This could amplify climate change effects.

Aquatic Deoxygenation and Planetary Boundaries

• The Planetary Boundaries framework, developed by scientists at the Stockholm Resilience Centre, identifies nine key Earth system processes that have limits or “boundaries” within which humanity can safely operate.

Purpose of the Framework

• To avoid crossing environmental tipping points that could lead to irreversible planetary damage.
• It provides a quantitative measure of Earth’s safe operating space.

Existing Boundaries

• The nine recognized planetary boundaries are:
  • Climate Change
  • Novel Entities (e.g., plastics, synthetic chemicals)
  • Stratospheric Ozone Depletion
  • Atmospheric Aerosol Loading
  • Ocean Acidification
  • Biogeochemical Flows (Nitrogen and Phosphorus cycles)
  • Freshwater Use
  • Land System Change
  • Biosphere Integrity

Current Status

• As per the latest scientific assessments, six of the nine boundaries have been crossed, indicating severe risk to Earth’s stability:
  • The crossed boundaries include: Climate change, Biosphere integrity, biogeochemical flows, Land system change, Novel entities, and Freshwater use.

Proposal to Add Aquatic Deoxygenation

• Scientists argue that Aquatic Deoxygenation should be added as a tenth planetary boundary.
• Justification: It is a distinct process, affects multiple ecosystems, and influences Earth system feedback loops like climate regulation and ocean chemistry.

Indian Context

• The Bay of Bengal and parts of the Arabian Sea are already witnessing deoxygenation and dead zones, affecting marine biodiversity and coastal livelihoods.
• Coastal regions like Kerala, Andhra Pradesh, and Odisha are particularly vulnerable to hypoxic events due to nutrient runoff and changing ocean dynamics.

Way Forward

• Reduction in Nutrient Pollution through better agricultural practices and wastewater management.
• Mitigation of Climate Change to reduce ocean warming.
• Marine Monitoring Programs to track deoxygenation trends.
• Inclusion of AD in Global Climate and Biodiversity Agreements, like UNFCCC and CBD.
• Global Cooperation on marine pollution and research funding.