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

## TL;DR

This study uses sedimentary ancient DNA to show that temperate trees and extinct species were present in Doggerland earlier than previously known, suggesting a favorable environment for early human settlement.

## Contribution

The study introduces a taphonomic model to distinguish secure from insecure sedaDNA signals, revealing early colonization from northern glacial refugia.

## Key findings

- Temperate tree genera like Quercus and Ulmus were present in Doggerland over 16,000 years ago.
- The extinct genus Pterocarya was detected, indicating possible northern glacial refugia proximity.
- Fine sediments provide more reliable ecological data compared to sandy deposits due to reworking.

## Abstract

The Doggerland landmass connected North-Western Europe during the Late Pleistocene (approximately 129 to 11.7 ka) and Early Holocene (approximately 11.7 to 8.2 ka) and was likely a key area for Mesolithic peoples. In this study, we show the early presence of temperate species including a species thought extinct, indicating a likely close proximity of refugia with important resource implications for Mesolithic peoples. We also show that ecological turnover combined with sediment turnover can be used to understand the taphonomic processes leading to sedimentary ancient DNA (sedaDNA) deposition and reworking. Using this approach, we show that in alluvial systems fine sediments are associated with secure deposits, but more sandy deposits are at greater risk of giving mixed ecological profiles through reworked sedaDNA.

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 Quercus, Ulmus, and Corylus over 16,000 y ago in the Late Pleniglacial, and thermal indicator genus Tilia several thousand years earlier than has been recorded for surrounding European areas. In this area, we also detect an anomalous signal of the genus Pterocarya, considered extinct in the region since the Hoxnian Stage (~400 ka). These observations are consistent with colonization from nearby northern glacial refugia, suggesting a favorable environment in which the cultural Mesolithic could develop.