What are Microatolls?

A new study from Mahutigalaa reef in the Maldives used Porites microatolls to reconstruct sea-level changes from 1930 to 2019. It found that sea-level rise began in the late 1950s and has been accelerating, earlier than what conventional tide gauges and satellite data suggested.

About Microatolls

Microatolls are disk-shaped coral colonies with living outer margins but with flat, dead upper surfaces.
They are commonly found growing in the lower intertidal zone on reef flats and in shallow-water lagoonal environments.
Upward vertical growth is limited because the colony lives at or near the lowest low tide; exposure to air at the top stops upward extension, so the coral spreads laterally and forms a flattened “doughnut” or pancake shape often several metres across.
Their upper surfaces accurately record minimum local water levels across decades.

Outer surface: Microatolls record the highest level at which coral can grow, corresponding to the lowest tide level, thereby serving as precise natural markers for reconstructing past sea-level changes and studying Holocene sea-level and climate variations.
Growth bands: Growth layers (annual bands) can reveal past sea-surface temperatures and environmental conditions.
Climate signals: Growth interruptions correspond with El Niño & negative Indian Ocean Dipole events.
Tectonic and Earthquake Studies: Changes in coral growth patterns due to uplift or subsidence from earthquakes are preserved in microatolls, enabling scientists to trace past seismic and tectonic events, as seen in studies from Sumatra and the 2004 Indian Ocean Earthquake.