Here’s something you don’t see every day — hundreds of new islands have been discovered around the world.
The Earth has 657 more barrier islands than previously thought, according to a new global survey by researchers from Duke University and Meredith College in Raleigh, N.C.
The researchers identified a total of 2,149 barrier islands worldwide using satellite images, topographical maps and navigational charts. The new total is significantly higher than the 1,492 islands identified in a 2001 survey conducted without the aid of publicly available satellite imagery.
Barrier islands often form as chains of long, low, narrow offshore deposits of sand and sediment, running parallel to a coast but separated from it by bays, estuaries or lagoons. Unlike stationary landforms, barrier islands build up, erode, migrate and rebuild over time in response to waves, tides, currents and other physical processes in the open ocean environment.
All told, the world’s barrier islands measure about 13,000 miles (21,000 kilometers) in length. They are found along all continents except Antarctica and in all oceans, and they make up roughly 10 percent of the Earth’s continental shorelines. The northern hemisphere is home to 74 percent of these islands.
Barrier islands help protect low-lying mainland coasts against erosion and storm damage, and can be important wildlife habitats. The nation with the most barrier islands is the United States, with 405, including those along the Alaskan Arctic shoreline.
“This provides proof that barrier islands exist in every climate and in every tide-wave combination,” said study team member Orrin H. Pilkey of Duke University. “We found that everywhere there is a flat piece of land next to the coast, a reasonable supply of sand, enough waves to move sand or sediment about, and a recent sea-level rise that caused a crooked shoreline, barrier islands exist.”
There, but overlooked
The newly identified barrier islands didn’t miraculously appear in the last decade, said study team member Matthew L. Stutz of Meredith. They’ve long existed but were overlooked or misclassified in past surveys.
Full story here
Here’s the full paper:
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.
A New Classification of Barrier Islands?A useful and efficient global classification of barrier islands does not yet exist. However, global distribution and morphologic patterns do emerge from a broad-based investigation. In particular, the influence of sea level rise and storm impacts on barrier island distribution and morphology can perhaps be more appreciated than before.It is clear that no simple hierarchical relationship exists among the factors that influence barrier island distribution and morphology. It is more apparent that any single factor may be most influential in a given setting and more useful as a basis for describing variability between islands. For example, locations such as south Texas have extreme climatic gradients but little change in the oceanographic regime. In other settings, such as the Georgia Bight and German Bight, there are substantial gradients in the wave–tide regime but little climatic variability (Hayes, 1979).
Our examination of barrier island distribution shows that whether barrier islands can exist or not exist in a particular place is mostly determined by the history of tectonics and sea level changes. As is true for most geologic processes, inheritance plays a crucial role. Within these constraints, barrier islands will form most preferentially along low-gradient coastal plains under rising sea level, with deltaic island abundance greatest along higher-gradient coasts experiencing falling sea level. The varying roles of marine vs. fluvial processes on coastal plains and deltas result in fundamentally different island morphologies at the global scale. Islands will form virtually anywhere if the sediment supply is favorable, even given low energy levels. The greatest influence on sediment supply—both quantity and quality—is the climate (Milliman and Meade, 1983). The relative roles of storms vs. swells can determine the typical morphologic features present on islands, and the dominant vegetation can significantly influence island evolution. Within a given tectonic and climate setting, the balance of wave and tidal energy can account for much of the variability in island morphology and evolution, although more clearly in coastal plain island systems.
There does not appear to be a clear prototype island for each division and subdivision. However, the influence of the lowest-level factors on barrier island evolution can be most accurately analyzed when the higher-level factors are understood and accounted for. The high-order factors of sea level and climate are likely to experience dramatic change in this century, signaling a potential large-scale response of barrier islands worldwide. The most climatically sensitive barrier islands, in the Arctic, will likely experience the most dramatic climate change and the most severe impacts. The combined roles of climate and sea level rise in barrier island evolution need to be better understood in all regions to improve predictions about the impacts of future sea level and climate change.
Just a reminder…
From the same journal, this interesting study: