Formation conditions of coastal palaeolakes and associated abiotic aragonite deposition in the eastern Mediterranean during the upper Pleistocene

During the Last Glacial Period (LGP), when sea level was up to ∼130 m lower than today, many of the currently semi-enclosed gulfs in the Eastern Mediterranean were isolated from the open sea, functioning as palaeolakes. This was the case for the western Saronikos Gulf in Greece, which was isolated from the Aegean Sea. The palaeogeographic evolution of this area was investigated by analyzing a 350 cm sediment core for grain size, inorganic geochemistry, mineralogy, and bulk δ 13 C and δ 18 O compositions. An age model was developed by combining radiocarbon ( 14 C) and uranium-thorium (U/Th) dating methods. Integrating all available data and accounting for eustatic sea-level fluctuations, the sedimentary units of core SARC-18 cover the last glacial-interglacial cycle, spanning from 44.5 kyr BP to the present. Two marine sedimentation intervals were identified, characterized by clay minerals, biogenic calcite, and light δ 13 C and δ 18 O isotopic signatures. These intervals are separated by a lacustrine sedimentation phase, marked by the exclusive deposition of authigenic aragonite and a significant enrichment in δ 13 C and δ 18 O. The latter elevated δ 13 C and δ 18 O values suggest carbonate mineral formation in an evaporative and saline environment under low temperatures (5–10 °C). Sedimentation rates during the marine intervals range from 5.8 to 6.0 cm kyr⁻ 1 , and are more than double during the lacustrine interval (11.9–14.0 cm kyr⁻ 1 ) due to the extensive deposition of authigenic aragonite. • The western Saronikos Gulf during the last ∼44.5 kyr BP was twice connected to the Aegean Sea; in between it was a palaeolake. • During the lacustrine period, the deposition of abiotic aragonite through evaporative processes was predominant. • The deposition of aragonite was facilitated by the low lake water temperatures, ranging from 5 to 10 °C. • During the lacustrine period, sedimentation rates were 2-fold or higher than at typical marine conditions.