The 6,000 cal. yr BP event: Ecosystem modelling, palaeoclimate and archaeology. Increasing SST after 6,000 cal. yr BP likely improved conditions for farming in the region and thus prompted the migration of the Funnel Beaker culture north. (A) Using 3D Ecosystem modelling based on paleobathymetry, the extent of hypoxia in the Baltic Sea is shown for the cold phase (right panel) before 6,000 cal. yr BP and for the warm phase (left panel) after 6,000 cal. yr BP. Note the remarkable spreading of hypoxic areas to the whole basin after 6,000 cal. yr BP, suggesting i) the regional wide scale of the climatic changes and ii) a close relationship between SST rise and spread of anoxia (see SI), which may have had consequences for marine life, therefore affecting the hunter-gatherer-fisher society. (B) Regional environmental changes in the Baltic Region at this time. The sequence from non-laminated to laminated sediments along with the significant increase in organic carbon content reveals that the development of anoxic bottom water conditions which is related to the substantial increase in SST. (C) Population density based on SPD. Note the population growth rate increases at the boundary between the Meso- and Neolithic. The maps were created using the software package GrADS 2.1.1.b0 (http://cola.gmu.edu/grads/), using published bathymetry data42,43.