Atoll lagoons as archives of environmental change: tsunami deposits, reef and island development, and sea level in the Maldives, Indian Ocean

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Like many other low-lying island nations in the Indo-Pacific region, the Maldives archipelago is threatened by sea-level rise, which at present is largely a consequence of global warming. Apart from sea level, the deteriorating health of coral reefs and the acidification of the ocean reduces the growth potential of coral reefs and islands. Additional threats include tsunamis, which temporarily inundate reef islands. Our study aims at investigating these important issues. We plan a two-week expedition to the Maldives in order to collect 10-15 sediment cores from two atoll lagoons using a Rossfelder vibracorer. The study has three objectives, which have both geoscientific and socio-economic significance. (1) Atoll lagoon cores may serve as archives of the history of tsunamis in the recent geologic past. Coarse-grained tsunami beds will stand out in the successions of fine-grained lagoonal muds, and cannot be mistaken for storm deposits because the archipelago is cyclone-free due to its equatorial location. This objective is in line with the German efforts of establishing a tsunami warning system in the Indian Ocean. (2) The core material will enable us to investigate the response of low-lying land areas to post-glacial sea-level rise, which has turned saucer-shaped Pleistocene limestone islands into swamps, restricted lagoons, and eventually open atoll lagoons. Together with existing data on marginal reef development, this study will provide a comprehensive picture of post-glacial reef and island evolution in the Maldives. (3) As a valuable spin-off, we will be able to constrain the enigmatic origin of faroes, smaller circular reefs that are virtually unique to the Maldives.