Eroding coastal sandy barriers under changing aeolian flux in the Gulf of Tunis (Tunisia).

Abstract

Sandy barriers are coastal features formed and reworked by terrestrial and marine-induced processes along decadal to millenary scale periods. In the semi-arid areas along the extended North African coast, these coastal landscapes are undergoing accelerated morphodynamical changes induced by intensifying anthropogenic and climate drivers in the last century. To quantify the latter, we assess the changes in sediment dynamics of the Ghar El Melh sandy barrier extended over the northern part of the Gulf of Tunis in Tunisia using sedimentological analysis and quantification of the aeolian flux. A total of 37 subsurface samples and 30 surface aeolian trapped ones were collected at the coastal dunes of Ghar El Melh. Our sedimentological analysis reveals a distribution of 97% of sandy sediments and 3% of silty facies. The modal statistical analysis suggests that there are three distinguishable sediment types with 87% of samples formed by fine sands with modal value of 0.16 mm. The mixture of these indicates mixed terrigenous and marine sources redistributed by the hydrodynamic processes. The measurement of the aeolian flow suggests a maximum value of 0.0022 kg.m.-1min-1 which occurs in dust storms. This study reveals the low detrital sand supplies to the lagoon-sea barrier of Ghar El Melh, results in its gradual submersion, further exposing the coastal lagoon and engendering severe ecological degradations.