Multi-decadal atoll-island dynamics in the Indian Ocean Chagos Archipelago

International audienceThis study calls upon recently discovered aerial photographs for two atolls in the Indian Ocean Chagos Archi- pelago. Pairing these vintage data with modern satellite imagery allows the coastline dynamics of a suite of islands to be quantified over a 36-to-50-yr. period. Peros Banhos represents one of the few atolls globally where natural island dynamics can be appraised; withstanding just one of its 35 islands, this atoll has never been settled by humans. By contrast, Diego Garcia has undergone pronounced anthropogenic change in the last fifty years. Statistics bring new insights to the persistence of these atoll islands under the contemporary conditions of sea level rise. Key findings include: (i) Coastlines facing the prevailing trade winds retreat through time, while those in leeward positions expand; (ii) coastline expansion and retreat are in balance such that total land area of all the considered islands is virtually static over the last 50 years; and, (iii) small islands (