Mid-late Holocene sea-level changes in the central Indian Ocean

There is nowhere on earth that directly records 'eustatic' sea-level changes. However there are a few regions in the world, far from the centres of former ice masses, where the influence of confounding factors such as solid earth movements as a result of changes in water load during the Holocene and gravity effects are very small. Recording Relative Sea-Level (RSL) in such locations provides the nearest possible estimate of the integrated total melt signal of the polar ice masses since the Last Glacial Maximum. Particularly important for our understanding of future ice sheet melt is to quantify ongoing melt from the polar ice sheets during the last few thousand years, since the disappearance of the major continental ice masses. The Chagos Islands are a remote group of coral islands located in the central Indian Ocean, where models suggest RSL has closely tracked eustasy through the Holocene. The reef islands are relatively young, but the reef flat on which they are deposited have been at RSL since the mid Holocene and support both fossil (elevated) and modern coral microatoll colonies. In this paper we report the first data on the mid-late Holocene RSL history of the Chagos Islands from 14C dated coral microatolls from reef flats across the archipelago. We report a RSL highstand of c. 0.7 m in Chagos during the past few thousand years, which closely fits with recent data from the Maldives and sites in the eastern Indian Ocean. Our data support the conclusion that a small RSL highstand occurred across a large part of the Indian Ocean basin during the mid-late Holocene. This new data is critical in evaluating the different factors affecting RSL change in locations that models suggest should closely track eustasy, and in constraining the ice melt component of glacio-isostatic adjustment models during the last few thousand years.