On the Response of Shallow-water Tidal Regime by Geological Characteristic of Waterway and Man-made Structures in a Macrotidal Estuary: Han River Estuary (Korea)
Résumé
Composed of biodetritic sediments and lying just a few meters above present sea-level, atoll reef islands are liable to
be highly exposed to coastal flooding and shoreline erosion. Nevertheless, the analysis of multi-decadal shoreline
change has shown that most reef islands either remain stable in area or are expanding within the context of current sea
level rise. This article addresses the key issue of future atoll-island persistence using a simple morphodynamic model
based on the computation of sediment production and fluxes, vertical coral growth and reef island accretion, with
special reference to Mururoa Atoll (French Polynesia). The model parameters are calibrated from previously gained
stratigraphic frameworks and sediment production rates. While a proper validation is a challenge with the scares data
available, the model fits well with the atoll-rim and atoll-islands evolution schemes of Mururoa Atoll since the last
glacial maximum. Multi-millennial projections of sea-level rise (Clark et al., 2016) are used to examine future reef
island response to rising sea-level. Assuming that all sediment volumes available on the atoll rim maintain in place and
that the sediment production remains unaffected by ocean warming and acidification, the reef is interpreted as able to
catch up sea level rise in the near future. Even in this very optimistic evolution scheme, the new reef edifice would be
filnally drown in a high carbon emission scenario. The present study, along with others, strongly suggests that the
persistence of reef islands in the future requires the conservation of already available sediments together with a
continued production of coral detritus, not only from the outer slopes, but also on the atoll rim as water depths increase.