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This paper aims to reconstruct paleoenvironmental conditions and sea-level changes over the last 5500 years. Multi-proxy investigations of sediment types, foraminiferal records, geochemistry parameters and paleotidal elevation changes were conducted on a short sediment core KHAR1 (225 cm long) retrieved from the intertidal area of the Al-Kharrar Lagoon. The sediment age was determined using 14C dating of marine mollusk shells. Results showed that two prominent warming events during AD 750–1500 and 1750–present and a cooling event during AD 1500–1750 were inferred from the variation of benthic foraminiferal composition in core KHAR1. Before 3000 BC interval, the core sediment was deposited under intertidal–subtidal conditions as indicated by the presence of terrestrial sediments (siliciclastic materials), a decrease in subtidal-deep species and a slight drop in the paleotidal elevation about 0.50 cm below the present lowest astronomical tide (LAT). From 3000 to 750 BC, deep-lagoonal species such as S. costigera, T. trigonula, T. serrulata and S. communis dominated this interval and co-occurred with a decrease in coarse sand and an increase in muddy substrates, indicating a prevalence of subtidal environmental conditions during the deposition of this interval. With the beginning of the 1st millennium, symbiotic (epiphytic) species started to increase, reaching the highest abundances between AD 800 and 1500. This increase in symbiotic species during the AD 800–1500 interval coincided with a stepwise increase in sea level and may indicate the prevalence of seagrasses associated with the occurrence of warm water due to climate warming prevailed in/around the lagoon during the deposition of this interval that corresponds to the 'Medieval Warm Period' (MWP). The MWP was followed by cooler (arid) conditions of the Little Ice Age (AD 1500–1750), causing a decrease in the abundance of the epiphytic species S. orbiculus and P. planatus (up to 14%) and a drop in paleotidal elevations. After this, the modern warming conditions prevailed until the present day. [ABSTRACT FROM AUTHOR]

The climate variability and related sea-level changes during the Holocene are still under discussion, especially in a regional context. Very little information comes from the southern and south-eastern Baltic coast. The aim of the paper is to gain insight on the history of regional environmental changes, particularly sea-level and storminess, and their driving forces. The investigations were located on a peatland on the coast of Puck Lagoon (Gulf of Gdańsk, southern Baltic Sea). The analysis of peat core comprised: radiocarbon dating, analysis of stable isotopes 18O and 13C and chemical components, as well as palynological and diatomic studies. Results showed the 1.0 m peat section accumulated over 1500 years, with a time resolution of 100 years per sample. The average water level in the Puck Lagoon rose by ca. 0.85 m during the last 1500 years in a cyclic mode, with a period cycle of ca. 600–550 years and an amplitude not exceeding 0.5 m. The accelerated sea level rise and frequent storminess occurred during the first half of the Dark Ages (1500−1300 years b2k) and LIA (750−450 years b2k) and since the beginning of the 20th century. Recognized environmental changes are well correlated with both temperature changes in the North Atlantic and changes in total solar irradiance, suggesting synchronous Northern Hemisphere-wide fluctuations. The solar forcing was an important constituent of natural climate variability in the past and of forcing climate warming during modern times - after the Little Ice Age. [ABSTRACT FROM AUTHOR]