Environmental changes contributed to Mediterranean cultural crisis

Researchers uncovered evidence of past droughts at Hala Sultan Tekke in Cyprus.

Credit: 

D. Kaniewski/Geological Survey of Belgium

Research at Tell Tweini in Syria shows a similar environmental change and cultural collapse during the Late Bronze Age.

Credit: 

Tell Tweini Project, KU Leuven

About 3,200 years ago, urban cultures thrived in the Eastern Mediterranean until invasions in coastal and inland areas, compounded by agricultural decline, created a regional crisis. “When the dust settled,” says Harvey Weiss, an archaeologist at Yale University, “entirely new ethnic groups and polities and ideologies [were] emergent in west Asia and the eastern Mediterranean.” Scientists have long puzzled over the cause of this period of social and agricultural instability, known as the Late Bronze Age Crisis. Now, new research suggests that environmental changes — especially a prolonged drought — contributed to the unrest.

David Kaniewski, associate professor in the Biology and Geosciences Department at the Université Paul Sabatier-Toulouse III in France, Joel Guiot, research director at the Centre National de la Recherche Scientifique in France, and their colleagues set out to place the archaeological record from this time period in an environmental context. This study is an attempt to understand “the environmental conditions when everything started to decline [and] to finally collapse,” Kaniewski says. 

The team explored the correlation between environmental and archaeological data, as they reported in PLOS ONE. They started by collecting pollen samples from a sediment core from Larnaca Salt Lake (Hala Sultan Tekke) in Cyprus. Using a hierarchical grouping method, the large dataset was simplified as these samples were sorted into vegetation categories, with each group suggesting a different type of environment. Next, the team performed a multivariate analysis, which assigned each sample a score, based on the types of pollen it contained, along an axis. Using their vegetation groupings, the authors interpreted this axis as a moisture gradient. This reflects the fact that “precipitation is the main driver of the vegetation changes in Cyprus,” notes Guiot, with trees more common in wet conditions and grasses occurring more in dry conditions. The authors also used the core pollen assemblage to identify shifting proportions of cultivated species (indicating agricultural activity) during this period; radiocarbon-dated samples established temporal parameters for the changes. This indicated a prolonged drought, they wrote.

“But we cannot only rely on one country for suggesting a clear link between climate shift and socioeconomic decline, especially for a wide area such as the Eastern Mediterranean,” Kaniewski says. Therefore, in addition to studying the environment at Hala Sultan Tekke, the authors also looked at a corresponding shift in agriculture and precipitation in Syria. By comparing the climate-proxy axes for the current study and a previously studied corresponding pollen study from Gibala-Tell Tweini in Syria, the team confirmed that climate shifts were strongly temporally correlated with one another; in other words, climate changed at the same time, in the same way, in both Syria and Cyprus.

The team also examined published environmental and climate proxies from multiple other localities, including Israel, the Dead Sea, and the Nile Delta, and found that other regional records reflect substantial precipitation decreases at this time as well.

In Cyprus, the samples varied from higher-precipitation (usually tree-dominated) assemblages to drier conditions indicated by grass-dominated assemblages, the team reported. This showed that the climate shifted gradually from wet to dry. Particularly dry-dominated pollen assembles during the Late Bronze Age indicate a drought occurring during this time. In Syria and in other regional locations, too, pollen data reflect the dramatic climatic shift during the Late Bronze Age Crisis.

With the confirmation of a strong temporal correlation between pollen-derived climatic shifts in Syria and Cyprus, the current study extends the record spatially and suggests that a larger-scale climatic change may explain this regional crisis, says Weiss, who was not involved in the new study. “Defining abrupt and century-scale drought with complementary high-resolution pollen cores at coastal Syria and Cyprus, this study marks a serious, and long-awaited, methodological advance in Mediterranean studies,” he says. The study provides “an empirical platform for re-testing, falsification, confirmation, and refinement,” he adds. “Science replaces story-telling, at last.”

Pollen- and isotope-based reconstructions from other regional samples published elsewhere confirm precipitation shifts across the Bronze-Iron Age boundary. Furthermore, percentage-based analyses of cultivated plants revealed an agricultural falloff during Late Bronze Age drought. Data from Cyprus suggest that plants such as plantains and cereals would have been less productive at this time, Guiot notes. “We know that climate is not the only cause behind the Late Bronze Age collapse, but it becomes clear that the drought hastened or precipitated the decline and amplified the crisis,” Kaniewski adds.

With their focus on environmental data, the authors brought a unique perspective to the question of what caused the Late Bronze Age Crisis, Weiss says. This study helps to elucidate the cause of this event by providing a testable explanation of “why these events transpired, and their causal succession through time and space,” he says. Although this study has taken a substantial step forward, further work remains at the intersection of the social and environmental sciences, Kaniewski adds.

“If you have a firm chronological link between climate change and societal response, you have a first clue, but not the whole [story]. This is why we need more interdisciplinary studies where hard sciences and humanities mix their data and their thoughts,” Kaniewski says. 

“This is the kind and quality of programmatic research which suggests substantial follow-up funding for additional testing and refinement throughout the Mediterranean lands,” Weiss adds.

Lauren Milideo
Friday, September 13, 2013 - 09:30

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