Dr Vasile Ersek, a senior lecturer in the Department of Geography and Environmental Sciences,
writes for The Conversation about the discovery of new evidence of a drought
that finished off the Akkadian Empire 4,000 years ago.
Gol-e-Zard Cave lies in the shadow of Mount Damavand, which at more than
5,000 metres dominates the landscape of northern Iran. In this cave,
stalagmites and stalactites are growing slowly over millennia and preserve in
them clues about past climate events. Changes in stalagmite chemistry from this
cave have now linked the collapse of the Akkadian Empire to climate changes more than 4,000 years ago.
Akkadia was the world’s first empire. It was established in Mesopotamia
around 4,300 years ago after its ruler, Sargon of Akkad, united a series of
independent city states. Akkadian influence spanned along the Tigris and
Euphrates rivers from what is now southern Iraq, through to Syria and Turkey.
The north-south extent of the empire meant that it covered regions with
different climates, ranging from fertile lands in the north which were highly
dependent on rainfall (one of Asia’s “bread baskets”), to the irrigation-fed
alluvial plains to the south.
It appears that the empire became increasingly dependent on the
productivity of the northern lands and used the grains sourced from this region
to feed the army and redistribute the food supplies to key supporters. Then,
about a century after its formation, the Akkadian Empire suddenly collapsed,
followed by mass migration and conflicts. The anguish of the era is perfectly
captured in the ancient Curse of Akkad text, which describes a period of turmoil with water
and food shortages:
… the large arable tracts yielded no grain, the inundated fields yielded
no fish, the irrigated orchards yielded no syrup or wine, the thick clouds did
not rain.
Drought and dust
The reason for this collapse is still debated by historians,
archaeologists and scientists. One of the most prominent views, championed by
Yale archaeologist Harvey Weiss (who built on earlier ideas by Ellsworth Huntington), is that it was caused
by an abrupt onset of drought conditions which severely affected the productive
northern regions of the empire.
Weiss and his colleagues discovered evidence in northern Syria that this
once prosperous region was suddenly abandoned around 4,200 years ago, as
indicated by a lack of pottery and other archaeological remains. Instead, the
rich soils of earlier periods were replaced by large amounts of wind-blown dust
and sand, suggesting the onset of drought conditions. Subsequently, marine
cores from the Gulf of Oman and the Red
Sea which linked the input of dust into the sea to distant
sources in Mesopotamia, provided further evidence of a regional drought at the
time.
Many other researchers viewed Weiss’s interpretation with scepticism,
however. Some argued, for example, that the archaeological and marine evidence
was not accurate enough to demonstrate a
robust correlation between drought and societal change in Mesopotamia.
A new detailed climate record
Now, stalagmite data from Iran sheds new light on the controversy. In a
study published in the journal PNAS, led by Oxford palaeoclimatologist Stacy
Carolin, colleagues and I provide a very well dated and high resolution record
of dust activity between 5,200 and 3,700 years ago. And cave dust from Iran can
tell us a surprising amount about climate history elsewhere.
Gol-e-Zard Cave might be several hundred miles to the east of the former
Akkadian Empire, but it is directly downwind. As a result, around 90% of the
region’s dust originates in the deserts of Syria and Iraq.
That desert dust has a higher concentration of magnesium than the local
limestone which forms most of Gol-e-Zard’s stalagmites (the ones which grow
upwards from the cave floor). Therefore, the amount of magnesium in the
Gol-e-Zard stalagmites can be used as an indicator of dustiness at the surface,
with higher magnesium concentrations indicating dustier periods, and by
extension drier conditions.
The stalagmites have the additional advantage that they can be dated
very precisely using uranium-thorium chronology. Combining these
methods, our new study provides a detailed history of dustiness in the area,
and identifies two major drought periods which started 4,510 and 4,260 years
ago, and lasted 110 and 290 years respectively. The latter event occurs
precisely at the time of the Akkadian Empire’s collapse and provides a strong
argument that climate change was at least in part responsible.
The collapse was followed by mass migration from north to south which
was met with resistance by the local populations. A 180km wall – the “Repeller of the Amorites" – was even built
between the Tigris and Euphrates in an effort to control immigration, not
unlike some strategies proposed today. The stories of abrupt climate change in
the Middle East therefore echo over millennia to the present day.
This article was originally published in The Conversation.
