Recent research has extended the record of sea-level rise in the central Indian Ocean by nearly a century. Using coral microatolls, scientists have found that sea levels began rising in the late 1950s. This challenges previous beliefs that notable rise started only around 1990. The findings have important implications for understanding regional climate change and guiding adaptation efforts in vulnerable island nations.
Sea-Level Rise and Coral Reefs
Rising sea levels are a key impact of global warming. Coral reefs are highly sensitive to changes in sea level because they require sunlight. When water deepens, less light reaches corals, causing bleaching. Changes in tides and coastal erosion add stress to these ecosystems. The Indian Ocean has seen sea levels rise faster than the global average, about 3.3 mm per year, with warming waters worsening reef health.
Monitoring Efforts in the Indian Ocean
Long-term sea-level monitoring began in the Indian Ocean during the Tropical Ocean Global Atmosphere programme (1985-1994). This was integrated into the Global Sea Level Observing System. Despite this, gaps remain in data, especially in the central tropical Indian Ocean. The new study addresses these gaps by using coral microatolls as natural sea-level recorders.
Coral Microatolls as Sea-Level Recorders
Coral microatolls grow sideways when upward growth is limited by low tide height. Their upper surface reflects the lowest water levels over time. These corals live for decades or centuries and record sea-level changes precisely. Researchers studied a Porites microatoll from the Maldives, analysing its structure and growth bands like tree rings. Uranium-thorium dating helped determine historical sea levels from 1930 to 2019.
Key Findings on Sea-Level Rise
The study showed a sea-level rise of about 0.3 metres over 90 years. The rate increased from 1-1.84 mm/year (1930-1959) to 3.91-4.87 mm/year (1990-2019). Sea level rise in the region began in the late 1950s, earlier than previously thought. The Maldives, Lakshadweep, and Chagos archipelago have experienced 30-40 cm rise over the last 50 years. This data revises assumptions used in climate adaptation planning.
Environmental and Climatic Signals
Growth interruptions in the microatoll corresponded with El Niño and negative Indian Ocean Dipole events, which stress coral reefs. The data also showed influence from the 18.6-year lunar nodal cycle affecting tides. The study site’s tectonic stability ensured changes were due to sea level, not land movement. Coral microatolls complement tide gauges and satellites, especially in data-poor regions.
Regional Variations and Future Role
Sea-level rise patterns vary across the Indian Ocean basin. Coastal areas show recent acceleration, while the central ocean had an earlier rise. This is linked to changes in ocean and atmospheric dynamics, such as stronger Southern Hemisphere westerlies and shifts in the Intertropical Convergence Zone. Coral microatolls will increasingly help fill gaps in sea-level data, aiding climate projections and adaptation strategies for island nations.
Questions for UPSC:
- Taking the example of coral microatolls, discuss their significance in reconstructing historical sea-level changes and the challenges in monitoring sea-level rise in the Indian Ocean.
- Examine the impact of rising sea levels on coastal ecosystems and human settlements, with special reference to island nations in the Indian Ocean.
- Analyse the role of climatic phenomena like El Niño and the Indian Ocean Dipole in influencing marine ecosystems and regional climate variability.
- Critically discuss the implications of regional variations in sea-level rise across ocean basins for global climate change adaptation policies and strategies.
