Early colonization before inundation consistent with northern glacial refugia in Southern Doggerland revealed by sedimentary ancient DNA.

Prior to the formation of the present-day North Sea during the mid-Holocene, North-Western Europe was connected through the Doggerland landmass. While it has been known for the past century that Doggerland was forested, it has not been clear when the onset of forestation occurred or whether the environment was more habitable for humans than surrounding European areas. In this study, we reconstruct the paleoecology of a river system, the Southern River, from the late Late Pleistocene to the late Holocene using sedimentary ancient DNA (sedaDNA) from 252 sediment samples from 41 cores spanning the length of the river system and headwater area. We identify secure and insecure sedaDNA signals by integrating sedimentological and sedaDNA data into a taphonomic model. Secure sedaDNA signals are found in silty and fine sand deposits where 95 to 98% originates from local deposition, but coarse sands and gravels are insecure with 60 to 70% of the sedaDNA associated with mixed ecosystem signals from reworked and influxed sediments. Secure sediments reveal the presence of several temperate tree genera such as