The Lake of Olympia: Sedimentary evidence of a mid- to late Holocene lake environment in the vicinity of ancient Olympia (western Peloponnese, Greece)

Olympia (western Peloponnese, Greece) is known as venue for the Panhellenic Games in ancient times. The wider region is located within a complex tectonic setting and was affected by crustal uplift up to 30 m since the mid-Holocene. Our study consists of a comprehensive investigation of the Basin of Makrisia and the adjacent Basin of Ladiko in the vicinity of ancient Olympia aiming to reconstruct the Holocene landscape development. In addition to Direct Push measurements, we present stratigraphic data of 15 sediment cores. Multi-proxy analyses of selected sediment cores, including sedimentological, geochemical and ostracod studies, allow to detect and interpret alterations in the depositional processes. We found widespread fine-grained, low-energy sediments, implying distinct phases of limnic conditions. Radiocarbon dating indicate that this lake, the so-called Lake of Olympia, persisted from the 8th millennium BC at least until the 6th century AD, covering the main period of the cult site. Ancient Olympia was then located at the direct lake shore. The lake finally disappeared during the 13th/14th century, when the water level of the Alpheios River abruptly dropped by several meters to its present position, forming the Olympia Terrace. We identified different ecological lake phases ranging from freshwater to eutrophic conditions. During ancient times, the water quality in front of Olympia was characterized by strong, possibly man-made eutrophication. We reconstructed lake level changes since the 1st millennium BC, noting a continuous rise until around 600 AD followed by abrupt drops in the 13th/14th century AD. In ancient times, the water depth around Olympia was deepest south of the Southern Hall. The presence of a lake has significant consequences for the discharge regime and sediment transport of the Alpheios River and its tributaries. Also, the Lake of Olympia has relevant historical, archaeological, and geomorphological implications and raises several unsolved questions.