Forty Years of Morphological Change at a Great Barrier Reef Island

Authors Dawson and Smithers (2010) note that low-lying reef islands are widely perceived to be particularly sensitive to ongoing and projected sea level increases; but they add that "a number of geomorphologists have argued that rising sea levels do not always cause reef islands to erode." For example, they state that "a rise in sea level may promote reef island growth by: i) increasing accommodation space for new sediment; ii) reinvigorating carbonate production on reef flats where further reef growth has been inhibited by a stable sea level; and iii) increasing the efficiency of waves to transport new and stored sediment to an island depocentre (Hopley, 1993; Hopley et al., 2007; Smithers et al., 2007; Woodroffe, 2007)."

Working on Raine Island (11°35'28"S, 144°02'17"E) at the northwest end of a planar reef on the outer edge of Australia's Great Barrier Reef -- which is one of the world's most important nesting sites for marine turtles -- Dawson and Smithers employed three historic survey maps and five topographic survey datasets of earlier researchers, supplementing them with digital elevation data collected in 1998, 2006 and 2007, to reconstruct a 40-year (1967-2007) shoreline history of the island.

The two Australian researchers report that their "detailed quantitative surveys and analyses demonstrate that Raine Island increased in area (~6%) and volume (~4%) between 1967 and 2007," and that "in the 40 years between 1967 and 2007 Raine Island underwent a net accretion of 68,400 ± 6,700 m³."

In summing up their findings, Dawson and Smithers write that "contrary to perceptions, Raine Island did not erode but instead modestly accreted during the 40-year study period," and they therefore conclude that "future management strategies of Raine Island and other islands of the Great Barrier Reef should recognize that perceptions of reef island erosion can arise from large short-term seasonal and storm-derived sediment redistribution from one part of the island to another or to a temporary storage on the adjacent reef flat," but that these phenomena do not necessarily lead to "a net permanent loss from the island sediment budget." And considering the similar positive findings of Webb and Kench (2010), it can be concluded that the most likely effect of a rising sea level is to actually add to the area and volume of low-lying reef islands.

Additional References
Hopley, D. 1993. Coral reefs in a period of global sea level rise. In: Saxena, N. (Ed.), PACON International: Recent advances in marine science and technology. PACON, Honolulu, Hawaii, USA, pp. 453-462.

Hopley, D., Smithers, S.G. and Parnell, K.E. 2007. The Geomorphology of the Great Barrier Reef: Development, Diversity and Change. Cambridge University Press, Cambridge, UK, 532 p.

Smithers, S.G., Harvey, N., Hopley, D. and Woodroffe, C.D. 2007. Vulnerability of geomorphological features in the Great Barrier Reef to climate change. In: Johnson, J.E. and Marshall, P.A. (Eds.), Climate Change and the Great Barrier Reef. Great Barrier Reef Marine Park Authority and Australian Greenhouse Office, Australia, pp. 667-716.

Webb, A.P. and Kench, P.S. 2010. The dynamic response of reef islands to sea-level rise: Evidence from multi-decadal analysis of island change in the Central Pacific. Global and Planetary Change 72: 234-246.

Woodroffe, C.D. 2007. Reef-island topography and the vulnerability of atolls to sea-level rise. Global and Planetary Change 62: 77-96.