SRA

Palaeo-archives from periods with rapid climatic change often provide the only opportunity to observe species and community turnover following previous dramatic climatic and environmental transitions. These archives are essential to help improve predictions of species' resilience and the response of ecosystems and biodiversity today, especially in those areas with the fastest rates of change such as the Arctic. Here, we combine morphological analyses and bulk-bone metabarcoding to investigate a unique chronology of bone deposits sealed in the high-latitude Storsteinhola cave system (68°50' N 16°22' E) at Kjøpsvik, Norway. This deposit is dated to a period of climate warming from the end of the Late Glacial (~13 cal ka BP) to the Holocene Thermal Maximum (~ 5.6 cal ka BP). Complementing osteology with palaeogenetic approaches has allowed us to exploit the 1000s of morphologically unidentifiable bone fragments, resulting in a high-resolution sequence showing the borealization in both the marine and terrestrial environments above the Arctic Circle following the Last Glacial retreat. Identifying 36 taxa, including species not previously expected to have occupied this region during this period (e.g. wildcat, amberjack, gudgeon), we obtain convincing evidence for major shifts in marine and terrestrial fauna in the high Arctic during the Holocene. Several of these responses, especially those within the marine environment, have clear parallels to current shifts in species distribution. Our observation of borealization as a naturally recurring phenomenon in periods of warming therefore provides fundamental insights in the ecosystem-wide responses that are ongoing today.