03.09.2025

Coral Reefs

Context

A recent study in the Maldives, using coral microatolls, has traced sea-level changes over the past 90 years. The research shows that sea levels in the Indian Ocean began rising in the late 1950s, much earlier than previously documented.

Key Aspects of the Issue

Sea-Level Rise in the Indian Ocean

• Current Trend: Average rise of approximately 3.3 mm per year, above the global mean.
   
• Half-Century Increase: Sea levels have risen by 30–40 cm over the last 50 years.
   
• Rate Acceleration:
   
  • 1930–1959: 1–1.84 mm/year
     
  • 1960–1992: 2.76–4.12 mm/year
     
  • 1990–2019: 3.91–4.87 mm/year
     

Coral Reefs and Their Vulnerability

• Light Dependence: Rising seas reduce light availability, causing stress to corals and triggering bleaching events.
   
• Environmental Pressures: Ocean warming, acidification, coastal erosion, and changing tidal patterns.
   
• Climatic Links: Coral bleaching often coincides with El Niño events and negative phases of the Indian Ocean Dipole.
   

Coral Microatolls in Research

• Definition: Flat, disk-shaped corals that grow sideways when vertical expansion is limited by tides.
   
• Function: Act as natural recorders of historical sea-level changes.
   
• Methodology: Uranium-thorium dating combined with growth band analysis (similar to tree rings) provides precise, long-term records.
   
• Benefit: Deliver high-resolution sea-level data in geologically stable regions.
   

Findings from the Study

• Sea-level rise started decades before tide-gauge records indicated.
   
• Regional Variation:
   
  • Central Indian Ocean: Rise began earlier with stronger acceleration.
     
  • Coastal Indian Ocean: Acceleration observed more recently.
     
• Drivers: Changes in oceanic and atmospheric circulation, including intensified westerlies in the Southern Hemisphere, increased ocean heat absorption, and shifts in the Intertropical Convergence Zone (ITCZ).
   

Implications for Island Nations

• High-Risk Areas: Maldives, Lakshadweep, and the Chagos Archipelago.
   
• Threats: Land submergence, biodiversity loss, infrastructure damage, and potential displacement of populations.
   
• Value of Historical Data: Helps governments plan effective climate adaptation measures.
   

Way Forward

• Expand coral microatoll monitoring across the Indian Ocean to improve long-term sea-level understanding.
   
• Strengthen adaptation strategies for island nations, including coastal protection and strategic relocation planning.
   
• Enhance international collaboration on climate finance, technology transfer, and resilience-building initiatives.
   
• Incorporate regional sea-level histories into global climate models, such as IPCC projections, to improve accuracy.

Conclusion:

Rising sea levels threaten coral reefs and island nations. Understanding historical trends through coral microatolls is vital for effective adaptation, resilience planning, and safeguarding ecosystems and vulnerable coastal communities.