Geological, Paleoclimatological, and Archaeological History of the Baltic Sea Region Since the Last Glaciation

The correlation of climate variability; the change environment, in particular the change of coastlines; and the development of human societies during the last millennia can be studied exemplarily in the Baltic area. The retreat of the Scandinavian ice-sheet vertical crustal movement (glacio-isostatic adjustment), together with climatically controlled sea-level rise and a continuously warming atmosphere, determine a dramatic competition between different forcings of the environment that advancing humans are occupying step by step after the glaciation. These spatially and temporally changing life conditions require a stepwise adjustment of survival strategies. Changes in the natural environment can be reconstructed from sedimentary, biological proxy data and archaeological information. According to these reconstructions, the main shift in the Baltic area’s environment happened about 8,500 years before present (BP) when the Baltic Sea became permanently connected to the Atlantic Ocean via the Danish straits and the Sound, and changed the environment from lacustrine to brackish-marine conditions. Human reaction to environmental changes in prehistoric times is mainly reconstructed from remains of ancient settlements—onshore in the uplifting North and underwater in the South dominated by sea-level rise. According to the available data, the human response to environmental change was mainly passive before the successful establishment of agriculture. But it became increasingly active after people settled down and the socioeconomic system changed from hunter-gatherer to farming communities. This change, mainly triggered by the climatic change from the Holocene cool phase to the warming period, is clearly visible in Baltic basin sediment cores as a regime shift 6,000 years (BP). But the archaeological findings prove that the relatively abrupt environmental shift is reflected in the socioeconomic system by a period of transition when hunter-gatherer and farming societies lived in parallel for several centuries. After the Holocene warming, the permanent regression in the Northern Baltic Sea and the transgression in the South did affect the socioeconomic response of the Baltic coastal societies, who migrated downslope at the regressive coast and upslope at the transgressive coast. The following cooling phases, in particular the Late Antique Little Ice Age (LALIA) and the Little Ice Age (LIA), are directly connected with migration and severe changes of the socioeconomic system. After millennia of passive reaction to climate and environmental changes, the Industrial Revolution finally enabled humans to influence and protect actively the environment, and in particular the Baltic Sea shore, by coastal constructions. On the other hand, this ability also affected climate and environment negatively because of the disturbance of the natural balance between climate, geosystem, and ecosystem.