Palaeolimnological evidence for environmental transformation in southern Greece

Seguin, Joana ORCID

The richness of archaeological sites in Greece reflects the long history of human activity in the area and thus makes it an attractive region for studying human-environmental interaction. Palaeoclimatic and palaeoenvironmental archives in the area, however, are still relatively sparse or discontinuous. The main aims of this thesis are to reconstruct palaeoenvironmental conditions and hydrological dynamics in southern Greece for the past approximately 5,000 years and to infer climatic variations on different spatial and temporal scales. For this purpose, lake sediments present meaningful geoarchives, because they can provide continuous, high-resolution proxy records of palaeoenvironmental changes. The study area around the Gulf of Corinth is located in a limestone rich environment and in a climatic transition zone between the temperate high latitudes and the dry subtropics that is highly sensitive to changes in both climatic zones. Four lake and palaeolake sites (Stymphalia, Kaisari, Pheneos, and Trichonida) have been investigated using a multi-proxy approach, mainly concentrating on the geochemical composition of the sediments. The log(Rb/Sr) ratio, obtained from X-ray fluorescence (XRF) core scanning, was identified as the most valuable proxy and allowed to reconstruct palaeohydrological, palaeoenvironmental and palaeoclimatic changes for the area. The results are discussed in six manuscripts. A interdisciplinary consilience allowed the reconstruction of palaeoenvironmental changes at Lake Stymphalia for the last 2,500 years. The construction of the Hadrianic Aqueduct (ca. 130 AD) was identified as the main trigger for unbalancing the lake ecosystem, increasing its vulnerability over the following centuries. The proxies record complex interactions of climatic variations, such as the Late Antique Little Ice Age (LALIA), coupled with anthropogenic landscape changes that induce erosion, such as medieval deforestation, and result in a more balanced and deeper understanding of landscape transformation. Furthermore, a multi-archive approach was performed by applying the same set of sedimentological, geochemical, and statistical analyses to four lacustrine archives on the Peloponnese. This allowed studying proxy variation on different spatial scales and differentiate supra-regional fluctuations in the climate system from local signals for the last 5,000 years. Site-specific differences occurred e.g. due to differences in sedimentation rates, temporary desiccation of the palaeolakes, or varying human impact in the catchment areas. On a meso-scale level, the archives indicated drier conditions during the Bronze Age / Iron Age transition (ca. 3,200 – 2,800 cal BP). The sediment sequence from Lake Trichonida suggested that the climatic variation during the last 2,600 years was considerably influenced by changes in the North Atlantic Oscillation pattern. Besides, a methodological refinement of a master core compilation from parallel sediment cores based on continuous colour parameters was developed and contributes to enhancing transparent, reproducible research in palaeoenvironmental sciences. Additionally, a spatial modelling approach was developed by an interdisciplinary collaboration and implemented for the NE Peloponnese. It investigates how much cultivable land was required to supply a society with its basic needs and what the consequences were, when environmental conditions aggravated. The results indicated that potential societal crisis were less a factor of changing climatic conditions or a shortage of arable land but primarily caused by socio-economic factors. As the author was a member of the Science Party of the International Ocean Discovery Programme (IODP) Expedition 381, the first joint results on climate-driven environmental and sedimentary changes in the Corinth Rift during the Pleistocene were also included in this thesis. Research on the Gulf of Corinth is covered by the spatial scale of the PhD project and expands the temporal scale to the last ca. 2 million years. This thesis contributes to increased knowledge on climate variability and environmental transformations in southern Greece on multiple temporal and spatial scales, notably during the Late Holocene.

Die Reichhaltigkeit archäologischer Stätten in Griechenland spiegelt dessen lange Geschichte menschlicher Aktivität wider und macht es so zu einer attraktiven Region für Studien zu Mensch-Umwelt-Beziehungen. Paläoklima- und Paläoumweltarchive in der Gegend sind jedoch vergleichsweise selten oder weisen diskontinuierliche Datensätze auf. Die Hauptziele dieser Dissertation sind die Rekonstruktion der Umweltbedingungen und hydrologischen Schwankungen in Südgriechenland während der letzten ca. 5000 Jahre und, daraus abgeleitet, klimatische Schwankungen auf unterschiedlichen räumlichen und zeitlichen Skalen. Zu diesem Zweck wurden Seesedimente als bedeutsame Geoarchive untersucht, da sie zumeist kontinuierliche, hoch aufgelöste Proxy Datensätze liefern, aus denen sich Paläoumweltveränderungen ablesen lassen. Das Untersuchungsgebiet rund um den Golf von Korinth liegt in einer kalksteinreichen Umgebung sowie in einer klimatischen Übergangszone zwischen den gemäßigten Breiten und den trockenen Subtropen und ist somit sehr sensibel gegenüber Veränderungen in beiden Klimazonen. Vier Seen und Paläoseen (Stymphalia, Kaisari, Pheneos und Trichonida) wurden mittels eines Multi-Proxy-Ansatzes analysiert, wobei die geochemische Zusammensetzung der Sedimente im Fokus stand. Das mittels Röntgenfluoreszenz (XRF) Kernscanning gemessene log(Rb/Sr) Verhältnis wurde als aussagekräftigster Proxy identifiziert und ermöglichte die Rekonstruktion paläohydrologischer, paläoumwelt- und paläoklimatischer Schwankungen an den entsprechenden Standorten. Die Ergebnisse der Arbeit sind in sechs Manuskripten festgehalten. [...] Die vorliegende Doktorarbeit trägt zu einem verbesserten Verständnis von Klimaschwankungen und Umwelttransformationen in Südgriechenland auf diversen räumlichen und zeitlichen Skalen, insbesondere im Spätholozän, bei.

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Seguin, Joana: Palaeolimnological evidence for environmental transformation in southern Greece. 2020.

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