Open-Ocean Barrier Islands: Global Influence of Climatic, Oceanographic, and Depositional Settings

A satellite-based inventory of barrier islands was used to study the influence of depositional setting, climate, and tide regime on island distribution and morphology. The survey reveals 20,783 km of shoreline occupied by 2149 barrier islands worldwide. Their distribution is strongly related to sea level history in addition to the influence of tectonic setting. Rising sea level in the late Holocene (5000 YBP present) is associated with greatest island abundance, especially on North Atlantic and Arctic coastal plains. Stable or falling sea level in the same time frame, a pattern typical of the Southern Hemisphere, is associated with a lower abundance of islands and a higher percentage of islands along deltas rather than coastal plains. Both coastal plain and deltaic island morphology are sensitive to the wave tide regime; however, island length is 40% greater along coastal plains whereas inlet width is 40% greater on deltas. Island morphology is also fundamentally affected by climate. Island lengths in the Arctic are on average (5 km) only half the global average (10 km) because of the effect of sea ice on fetch and thus wave energy. Storm frequency in the high and middle latitudes is suggested to result in shorter and narrower islands relative to those on swell-dominated low-latitude coasts. The ratio of storm wave height to annual mean wave height is a good indicator of the degree of storm influence on island evolution. The potential for significant climate and sea level change this century underscores the need to improve understanding of the fundamental roles that these two factors have played historically in island evolution in order to predict their future impacts on the islands.