Rapid coastal subsidence in the central Ganges-Brahmaputra Delta (Bangladesh) since the 17th century has been deduced from submerged salt-producing kilns.
The densely populated low-lying Ganges-Brahmaputra Delta is highly vulnerable to the global sea-level rise. In order to estimate the subsidence of the delta over historical time scales, as a complement to existing entire-Holocene or modern data, we examined submerged salt-producing kiln sites in the coastal Sundarbans.
These kilns were built just above the previous winterly spring high-tide level, but are currently located ~155 (plus or minus 15) cm below the corresponding modern level. The kilns were ultimately fired ~300 years ago (1705 plus or minus 35 AD), as shown by optically stimulated luminescence (OSL) dating.
Salt production was terminated abruptly by a catastrophic event (major cyclone). Radiocarbon ages additionally measured on the charcoal layers at the kiln's bases and on associated mangrove stump horizons support the OSL ages.
Consequently, the outer delta sank at 5.2 plus or minus 1.2 mm/a, including a 0.8 mm/a global sea-level rise over this period. Expecting an accelerating eustatic sea-level rise of up to 7 mm/a, a coastal sinking of up to 8.9 plus or minus 3.3 mm/a is calculated for the next few decades, which will dramatically aggravate the already present problematic situation.
Only a prudently-managed control of sediment accretion will keep southern Bangladesh above the sea level.
Paper: Till J.J. Hanebuth et al., MARUM–Center for Marine Environmental Sciences, University of Bremen, Leobener Strasse, 28359 Bremen, Germany. DOI: 10.1130/G34646.1.