1. Introduction and fundamental reorientation of the discourse
The postglacial development of the Baltic Sea, particularly the transition from a lacustrine to a brackish-marine system, represents one of the most significant paleogeographic, paleoclimatological, and paleoecological transformations of the entire Holocene.1 The central chronostratigraphic event of this far-reaching development is the so-called Littorina Transgression. Triggered by the eustatic sea-level rise, which was primarily caused by the final melting of the large continental ice sheets of the Pleistocene (especially the Laurentide Ice Sheet), marine water masses flooded the topographic barriers of the Danish straits and penetrated deep into the hitherto largely freshwater-dominated Baltic Sea basin.1 This complex, multi-phase process profoundly changed not only the entire hydrographic system of the region but also completely reshaped the coastlines of Northern and Central Europe.1
In the classical geoscientific paradigm, the course of this transgression is understood as a gradual process dominated by climatic and eustatic factors, which culminated in the early to middle Holocene – roughly between 8,500 and 4,000 years before present (cal. BP).8 After reaching the transgression and salinity maximum, according to the established doctrine, the system transitioned into a phase of relative stability or slight regression, driven primarily by the isostatic rebound of the Scandinavian landmass interacting with a decelerating eustatic rise.9
Recent interdisciplinary research, specifically the detailed geodynamic, geochemical, and cartometric re-evaluation of the geographic data of Germania Magna transmitted by Claudius Ptolemy (c. 150 AD), now fundamentally challenges this paradigm of calm, fading coastal dynamics in the Late Holocene.\[13, 13\] The modeling of the ancient geographic coordinates based on a strictly affine transformation suggests that the coastline of the Oceanus Germanicus (the southern North and Baltic Sea) in late antiquity was located about 120 kilometers further south than it is today.\[13, 13\]
If this interdisciplinary hypothesis proves true, it forces the scientific community to massively revise the current understanding of the exact course, duration, and above all, the definitive end of the Littorina Transgression. It implies that the transgression did not transition into a static Post-Littorina stage in the middle Holocene but continued continuously over millennia into the Roman Imperial Period, and was only abruptly ended in the 6th century AD by a catastrophic, primarily tectonically driven event.\[13, 13\] This report analyzes the empirical evidence of the classical model, systematically contrasts it with the new geodynamic findings, and evaluates the far-reaching implications for Quaternary geology, geoarchaeology, and the understanding of postglacial geodynamics in Europe.
