When the Mangroves Disappeared

Deep beneath the dunes
fossilised roots whisper
golden memories
of emerald lagoons.
When sapphire seas
lapped tenderly
at knotted feet,
bathing sunken stems
with the tidal surge
of their brackish embrace.

Dredged up alongside
buried treasures,
dark reflections stir.
Open wounds that sing
of their betrayal –
silted, shifting waters
suffocating with
dry and barren soils.

Until their waves
broke in silence
upon the dead
and burning sands.

6,000 years ago, mangroves were widespread in Oman. Today, only one particularly robust mangrove species remains there, and this is found in just a few locations (Image Credit: Valeska Decker / University of Bonn).

This poem is inspired by recent research, which has shown that the mangrove forests on the coasts of Oman disappeared about 6,000 years because of climate change.

A mangrove is a shrub or small tree that grows in coastal saline or brackish water. They also like a warm climate and are more tolerant to salt than many other types of vegetation, but only up to a finite limit. Mangrove forests, or lagoons, occur worldwide, in the tropics and subtropics and mainly between latitudes 25° N and 25° S. Fossil records show that there used to be many mangroves on the coast of Oman, but that these disappeared almost entirely approximately 6,000 years ago. Nowadays, the only mangroves in Oman are those of a particularly robust species and they can only be found in a very few places. The reasons for their disappearance have previously been disputed, with some researchers claiming that a drop in sea level led to their collapse, whilst others have blamed an anthropogenic (or human-caused) ecological catastrophe.

In this new study, researchers have compiled numerous geochemical, sedimentological, and archaeological findings to present a more accurate picture of what led to the large-scale collapse of the Oman mangroves. These results indicate that the collapse of these ecosystems was because of a relatively sudden change in both the local and the global climate. The Intertropical Convergence Zone, or ITCZ, is a band of low pressure around the Earth which generally lies near to the equator. The trade winds of the northern and southern hemispheres come together here, which leads to the development of frequent thunderstorms and heavy rain, including the Indian summer monsoon. Around 10,000 years ago this zone was much further north than it is today, which meant that these rains affected large parts of the Arabian Peninsula. Just over 6,000 years ago the ITCZ then shifted to the south, for reasons that are still not entirely clear. This sudden change in climate over the Arabian Peninsula had two effects. Firstly, it caused the salt levels in the soils to rise dramatically, which put the mangroves under extreme stress. Secondly, the vegetation cover in this region decreased due to the greater drought, thereby increasing soil erosion and meaning that the winds carried large amounts of this barren soil into the mangrove lagoons. These two factors meant that the lagoons became silted and dried up, with the whole process occurring extremely rapidly – the mangrove ecosystems likely disappeared within a few decades. The researchers also found no evidence of a drop in sea level 6,000 years ago that could have triggered the mangrove extinction. Similarly, whilst it is true that there were humans living in the coastal regions who used the mangroves as firewood, the researchers determined that these people were nomads who did not build permanent settlements, meaning that their need for wood was relatively low, and certainly not enough to cause the destruction of the mangrove ecosystems. As such, the disappearance of the mangrove lagoons in coastal Oman was not caused by sea-level variation or anthropogenic interferences; rather, it was the consequence of the climatic change brought about by the southward shift of the ITCZ approximately 6,000 years ago.

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