Coral reefs around islands develop a wide variety of forms, including narrow platforms fringing the coast, barrier reefs encircling deep lagoons, and flights of terraces that have been raised above or drowned deep below the sea surface.
Charles Darwin, who was also something of a geologist, suggested that reefs take on a fixed sequence of forms as a volcanic island gradually sinks below sea level. Reefs on some island chains, such as the Society Islands, appear to follow this sequence, but Darwin's idea cannot explain much of the diversity of reef forms found around the world, such as the reefs of the Hawaiian Islands.
In addition to island sinking, reefs are shaped by the interaction of coral growth, wave erosion, and sea level changes. In this study, Michael Toomey and colleagues use a computer simulation of reef development to understand these interactions, and compare their results with a global compilation of rates of coral growth and island sinking or uplift.
They find that large sea-level cycles driven by ice ages have left a clear fingerprint on coral reefs around the world, and that Darwin's proposed sequence of reef forms only develops in a small subset of environments.
Michael Toomey et al., DOI:10.1130/G34109.1.