Coral Microatolls Trace Early Indian Ocean Sea-Level Rise

Studies based on new coral microatolls have shown that the sea-level rise in the central Indian Ocean started decades before it was first registered. Using sea-level records dating back to the 1930s scientists have demonstrated that changes caused by warming are attacking the delicate reef ecosystems at a faster rate than anticipated.

Rising Seas and Reef Stress

• The rise in sea level decreases sunlight on coral reefs leading to bleaching, erosion and habitat loss.
• The Indian Ocean is warming more rapidly as compared to the rest of the world, exacerbating environmental effects.

Monitoring and Data Gaps

• Monitoring of the sea level in the area started with the TOGA programme (1985-94) and is now under the Global Sea Level Observing System.
• India is recording an increase in 3.3 mm/year that is higher than that of the world, but there has been little long-term data in central Indian Oceans.

Microatolls as records of Nature.

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• Sea-level history is written when vertical growth is constrained by tides, so the coral microatolls grow outward.
• Growth bands, slab analysis and uranium-thorium dating were used to study a Porites microatoll on the Maldives (1930-2019).

Key Findings

• Total rise: 0.3 m over 90 years.
• Acceleration over time:
• 1-1.84 mm/year (1930-59)
• 2.76-4.12 mm/year (1960-92)
• 3.91-4.87 mm/year (1990-2019)
• In the past 50 years, there was 30-40 cm increase in the Maldives, Lakshadweep and Chagos.

Climatic Signals Captured

• Interruptions in growth were equivalent to El Nino and negative Indian Ocean Dipole.
• Another 18.6-year lunar nodal cycle affecting tides was also recorded by corals.
• The location was very stable, allowing precision in the sea-level records.

Significance to Climate Science.

• Gaps in tide gauges and satellites are filled by microatolls which provides a long term regional picture.
• Results verify that the process of sea-level rise started in the late 1950s, which is earlier than thought.
• Winds, ocean circulation and changes in ITCZ influence regional patterns.

Future Role

Coral microatolls are becoming essential instruments to learn more about sea-level change and implement adaptation measures to islands and coastal areas at risk.