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Final Report Summary - PRETM (Prehistoric Transitions in the Mediterranean: Cultural and economic responses to climate change during the Mesolithic-Bronze Age)

Prehistoric Transitions in the Mediterranean: Cultural and economic responses to climate change during the Mesolithic-Bronze age (PRETM)
Samantha Elsie Jones:
Project website:

PRETM was a two year funded IEF-Marie Curie fellowship, aimed at exploring the effects of abrupt climatic events on prehistoric economies and culture in the Mediterranean ranging from the Mesolithic to the Bronze age. To achieve these goals, multi-proxy palaeo-environmental data was undertaken from two pond/lake deposits, at Casa Corona and the Villena lagoon, in the Upper Vinalopó Valley (Eastern Spain).

Site Description: The Villena basin is located in the south-eastern Iberian Peninsula about 80 km from the coast, on the upper course of the Vinalopó River. It occupies a wide corridor with an average altitude of 500 m. The region is bounded by calcareous mountain ranges no higher than 1000 m. The Villena Lagoon, an endorheic lake and Casa Corona, an inter-dune depression pond were selected for this investigation because of their close proximity to archaeological sites ranging from the Mesolithic-Bronze age.

Methodologies: Three cores (ranging from 3-9.30 m) were extracted from the Villena lagoon and one core was extracted from Casa Corona, former pond during the 14th-15th April 2014. A mechanical corer was hired to extract the samples. The most intact core was selected for further analysis from the Villena lagoon (VL3-9.3 m). Multi-proxy analysis undertaken on the VL3 core has included twenty 14C dates, Loi & TOC, pollen and other palynomorph analysis; Magnetic susceptibility; XRF analysis and training; lithological descriptions; grain-size analysis and phytolith training and slide preparations. Further analysis is currently being undertaken using x-ray diffraction to identify the mineral composition (by Prof. Santiago Giralt at ICTJA-CSIC, Barcelona) and micro-charcoal analysis (being undertaken by Itxaso Euba, IPHES). The further analyses are hoped to solve some uncertainties regarding a distinct sedimentary shift and 1 m age reversal in the VL3 record during the Younger Dryas-Pre-boreal transition. Pollen and phytolith analysis were also undertaken on the Casa Corona core but due to poor preservation did not produce results.

Results: The VL3 results identified a 20,000 year record of complex catchment processes linked to oscillating climate and much later to human activity. During the cooler-dry late Pleistocene, prior to 20,000 cal BP, the pollen record suggests a patchwork of open steppe vegetation and Pine woodland dominated the Vinalopó Valley, although the presence of mesophilic woodland, particularly oak infers refugia was provided by the lake catchment. The Palynomorph record (low Botryococcus, high Type 112 and the presence of Foraminifera) and the geochemical record (high sulphur-S and salts-Cl) suggest a hypersaline lake/wetland with low lake levels and a low nutrient input, probably fed by ground water supply and low energy streams. An abrupt sedimentation shift, after 18,000 cal BP is thought to represent a hiatus between the Younger Dryas and Holocene transition.

The Holocene transition is characterised by a strong increase in wetness and terrigenous input, shown by the appearance of laminated bands, an increase in grain size, a sharp rise in Zr/Rb (often used to indicate coarse grain input), decline in Pine and a pronounced increase in mesophilic woodland (Hazel, Birch, Oaks, etc.). Increased wetness would have increased nutrient input into the lake causing algal blooms, particularly Botryococcus, which shows a positive agreement with the Zr/Rb ratio. A major age reversal is recorded during the Pre-boreal (1 m of Pre-boreal ages below 1 m of Younger Dryas ages). A number of potential hypothesis were proposed for this age reversal but based on the combined multi-proxy results, evidence seems to point towards erosion. This is perhaps due to shoreline erosion during periods of fluctuating aridity. Oscillating peaks in Botryococcus suggests oscillating freshwater input whilst a more frequent appearance of brown soils and algal mats suggests at times lake levels disappeared during this period. After 10 ka cal BP lake levels rose again, although this may have been associated with a rise in ground-water since terrigenous input declined. This period is further punctuated by aridity oscillations, the most prominent being the 8.2 ka event (rise in Pine, decline in mesophilic taxa, fluctuations in S & Sr etc). After 7000 cal BP the lake seems to have become completely cut-off from terrigenous input (shown by the disappearance of Botryococcus & sharp decline in Zr/Rb). This may be related to a general trend towards increasing dryness, as reported from many Mediterranean sites during this time. Mesophilic woodland was eventually replaced by drier sclerophll vegetation, & Pine became once more a dominant vegetation component. A further but slight increase in wetness occurred between 6000-3000 cal BP. The Mediterranean region was becoming drier during the mid-late Holocene therefore this may be attributed to increased ground-water caused by anthropogenic clearance. Three punctuated aridity events were also recorded between 4000-3000 cal BP.

Socio-economic impact and the wider societal implications of the project:
The outcome of this project highlights the sensitivity of salt lakes to small changes in the hydrological budget. Even though woodland ecosystems at Villena have been reliant on the lake/wetlands existence for thousands of years (including during the late Glacial) vegetation composition and lake biota have not remained constant but have fluctuated in response to climatically induced changes in groundwater supply and in stream/river input. Human impact, particularly after the complete drainage of the lake, has had a pronounced impact: A positive outcome at the time may have been the reduction of disease caused by breeding mosquitos on the stagnant water; however, as suggested by the pollen & palynomorph record, the drainage of the lake also caused the complete disappearance of woodlands and the aquatic ecosystem. Low water levels are needed for the precipitation of minerals but with the drainage of the lake, mining of minerals would no longer have been an economic option. Furthermore a complete loss of habitat means the landscape is more susceptible to erosion, aridification and fire, as shown by a dramatic increase in Chenopodiaceae scrub in the top sediments. Drainage would affect ground water supply and perhaps increased the precipitation of salts, affecting land suitable for agriculture. Increased global warming may exasperate these effects. Understanding how environments respond to climate change and human induced environmental stress in the past therefore has wider societal implications for the future since it highlights potential scenarios, which may occur and which can lead to better management strategies in the future. The results of this research have been presented at the International MEDINES conference held in Tarragona 3rd-5th Feb 2016. See: Two publications are also in the final stages of completion: 1) exploring the environmental significance and 2) the social-economic significance.

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