Mid- to late Holocene seasonal variability in northern Germany and adjacent oceans and its potential impact on human societies
In northern Germany and southern Scandinavia, the onset of farming around 6000 cal. yrs BP occurred coincidentally with one of the cold events recorded from the North Atlantic. It is therefore discussed whether the transition towards a Neolithic subsistence in this region could have been shaped by climate change. However, at a regional scale, high resolution climate reconstructions are lacking or missing the sensitivity to record abrupt climate changes. Indeed, most of these reconstructions represent the mean annual or summer climate variability, while some evidence show that winter variability in the North Hemisphere plays an important role during major rapid climate changes of the Holocene. The strength of this thesis lies in the reconstruction of winter climate variability during the mid- and late Holocene. Here, winter and warm season thermal reconstructions are based on benthic foraminifera Mg/Ca and oxygen isotopes from two Skagerrak cores. Cold events, roughly corresponding to the Atlantic Bond events, are evidenced during winter in the Skagerrak region over the mid- and late Holocene, and only partially during the warm season. Interestingly, an abrupt cooling between 6200 and 5900 cal. yrs BP, only found during winter, coincides with the onset of neolithisation in northern Germany and southern Scandinavia. Most likely, it resulted in a shortening of the vegetation growing season and an increased Baltic sea-ice extent that probably affected the marine food resources. In turn, these environmental changes must have lead the hunter-gatherer-fisher communities to abandon their previous subsistence strategies and adopt an economy based on agriculture. Other changes in subsistence and material culture from societies in the region coincide with climate changes recorded in the Skagerrak during the mid- to late Holocene transition, and are discussed in this thesis. The origin of short term variability found in the climate records is also discussed.