Abstract

The densely populated, low-lying Ganges-Brahmaputra Delta is highly vulnerable to global sea-level rise. In order to estimate the rate of subsidence of the delta, we examined submerged salt-producing kiln sites in the coastal Sundarbans (a huge UNESCO-protected mangrove forest). These kilns were built just above the winterly spring high-tide level of the time, but their bases are currently located ∼155 cm below the corresponding modern level. According to optically stimulated luminescence (OSL) dating, the kilns were last fired ∼300 yr ago, and salt production was terminated by a catastrophic event that affected the kiln sites at different levels and locations. 14C ages of charcoal at the kilns’ bases and associated mangrove stump horizons support the OSL dates. Based on the elevations and ages, the 300 yr average rate of sinking of the outer delta is 5.2 ± 1.2 mm/yr, which includes 0.8 mm/yr of eustatic sea-level rise. With the expectation of further acceleration of sea-level rise, the already-present problematic situation will be aggravated, and only prudent control of sediment accretion will keep southern Bangladesh above sea level.

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