GS3 – Environment
Context
- A recent study (TH) used coral microatolls in the Maldives to reconstruct 90 years of Indian Ocean sea-level history, showing that sea-level rise began earlier and progressed faster than previously recorded.
About Microatolls
- Flat, disk-shaped coral colonies that grow just below the lowest tide level.
- Growth Pattern:
- Upward growth stops once they reach the lowest tide level.
- They expand laterally instead.
- Significance: Their upper surfaces serve as precise markers of minimum local sea levels across decades.
How Microatolls Record Sea-Level Changes
- Outer Surface Surveying: Maps long-term sea-level positions.
- Growth Bands: Annual bands, like tree rings, record year-wise sea-level fluctuations.
- Climatic Signals: Interruptions in growth coincide with El Niño and negative Indian Ocean Dipole events.
- Lunar Influence: Preserve signals of 18.6-year tidal cycles linked to the lunar nodal cycle.
Key Findings of the Study
- Early Onset: Sea-level rise in the Indian Ocean began in the late 1950s, much earlier than instrumental records suggested.
- Magnitude: Central Indian Ocean levels rose by ~0.3 metres between 1930–2019, higher than at many coastal sites.
- Acceleration:
- 1930–59: ~1.5 mm/year
- 1990–2019: ~4.5 mm/year
- Regional Impact: Maldives and Lakshadweep recorded a rise of 30–40 cm in the last 50 years.