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Postglacial viability and colonization in North America’s ice-free corridor

Abstract

During the Last Glacial Maximum, continental ice sheets isolated Beringia (northeast Siberia and northwest North America) from unglaciated North America. By around 15 to 14 thousand calibrated radiocarbon years before present (cal. kyr bp), glacial retreat opened an approximately 1,500-km-long corridor between the ice sheets. It remains unclear when plants and animals colonized this corridor and it became biologically viable for human migration. We obtained radiocarbon dates, pollen, macrofossils and metagenomic DNA from lake sediment cores in a bottleneck portion of the corridor. We find evidence of steppe vegetation, bison and mammoth by approximately 12.6 cal. kyr bp, followed by open forest, with evidence of moose and elk at about 11.5 cal. kyr bp, and boreal forest approximately 10 cal. kyr bp. Our findings reveal that the first Americans, whether Clovis or earlier groups in unglaciated North America before 12.6 cal. kyr bp , are unlikely to have travelled by this route into the Americas. However, later groups may have used this north–south passageway.

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Figure 1: Setting and study area.
Figure 2: Selected pollen, DNA and biometrical results.
Figure 3: Ecological interpretation and implications of this study.
Figure 4: Colonization models.

Accession codes

Data deposits

DNA sequence data are available through the European Nucleotide Archive under accession number PRJEB14494 and bioinformatics scripts are available at (https://github.com/ancient-eDNA/Holi).

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Acknowledgements

We thank M. L. Tobiaz, T. Murchie, G. Carroll, S. Overballe-Petersen, M. Reasoner, K. Walde, D. Wilson, F. Malekani, A. Freeman, J. Holm, St John’s College in Cambridge, and the Danish National Sequencing Centre for help and support. The Fig. 1b map contains a digital elevation model licensed under the Open Government Licence – Canada (http://open.canada.ca/en/open-government-licence-canada). This study was supported by the Danish National Research Foundation (DNRF94), the Lundbeck Foundation and KU2016.

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Authors and Affiliations

Authors

Contributions

E.W. initiated and led the study. M.W.P., K.H.K., and E.W. designed and conducted the study. A.R., C.S., C.Z. and H.F. processed and counted pollen and macrofossils. R.A.S. performed the 14C dating and Bayesian age modelling. N.K.L. and R.A.R. scanned cores for X-ray fluorescence and magnetic susceptibility. K.K.K., M.W.P. and K.H.K. performed the cartographic analysis and representation. M.L.Z.M. and M.W.P. processed and analysed the metabarcode data set. M.W.P. performed the molecular work under supervision by L.O. and E.W. M.W.P., C.S., A.B.B., B.A.P., D.J.M., K.H.K. and E.W. did the main interpretations of the results, with additional statistical analysis from R.N. M.W.P., D.J.M. and E.W. wrote the paper with input from all authors.

Corresponding author

Correspondence to Eske Willerslev.

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The authors declare no competing financial interests.

Additional information

Reviewer Information Nature thanks P. Gibbard, S. McGowan, A. P. Roberts and the other anonymous reviewer(s) for their contribution to the peer review of this work.

Extended data figures and tables

Extended Data Figure 1 Topographic transects.

The red and white lines on Fig. 1b mark topographic transects of Charlie Lake and Spring Lake in relation to the four phases of Glacial Lake Peace13. CIC, Cordilleran ice complex; m.a.s.l., metres above sea level.

Extended Data Figure 2 Visual and physical descriptions and age-depth model for the studied lake sediments.

a, b, Charlie Lake (a) and Spring Lake (b) span the Pleistocene to Holocene transition (dotted grey line); magnetic susceptibility (continuous black line); and compressed high-resolution images from the ITRAX core scanner and the sedimentary log are shown. Age-depth models for Charlie Lake (a) and Spring Lake (b) were generated with P_Sequence deposition models in OxCal v. 4.2 using the IntCal13 radiocarbon calibration curve57,59,61. The probability envelopes represent the 68.2% and 95.4% confidence ranges, respectively (see Methods and Supplementary Information).

Extended Data Figure 3 Charlie Lake pollen and macrofossil diagrams.

a, Pollen are presented as influx and bullet points indicate taxa with less than 2 grains cm−2 year−1. The diagram was zoned using CONIIC31 with a stratigraphically constrained cluster analysis on the information statistic. b, Relative proportions of ecologically important taxa. c, Macrofossils were identified but not enumerated. Bullet points represent presence.

Source data

Extended Data Figure 4 Spring Lake pollen and macrofossil diagrams.

a, Pollen are presented as influx and bullet points represent taxa with less than 50 grains cm−2 year−1. The diagram was zoned using CONIIC31 with a stratigraphically constrained cluster analysis on the information statistic. b, Relative proportions of ecologically important taxa. c, Macrofossils were identified but not enumerated. Bullet points represent presence.

Source data

Extended Data Figure 5 Charlie Lake DNA diagram.

DNA results are presented as normalized counts to allow comparison on the temporal scale for each taxon. All are unique sequences with 100% sequence identity to taxa. Histogram width equals the accumulation period. a, Viridiplantae, bullet points represent counts less than 50. b, Algae, bullet points represent counts less than 50. c, Metazoans, bullet points represent counts equal to 1.

Source data

Extended Data Figure 6 Spring Lake DNA diagram.

DNA results are presented as normalized counts to allow comparison on the temporal scale for each taxon. All are unique sequences with 100% sequence identity to taxa. Histogram width equals the accumulation period. a, Viridiplantae, bullet points represent counts less than 50. b, Algae, bullet points represent counts less than 50. c, Metazoans, bullet points represent counts equal to 1.

Source data

Extended Data Figure 7 DNA damage accumulation model.

Maximum-likelihood DNA damage rates were estimated from nucleotide misincorporation patterns using MapDamage2.0 (ref. 40). a, Each full circle is the mean of cytosine to thymine mutation frequencies at the first position (n ≥ 2 species) with above 500 reads aligned to reference bars that represent ± 1 s.d. b, Table of species used for determining the DNA damage rates.

Source data

Extended Data Table 1 AMS 14C determinations of terrestrial plant macrofossil samples from Charlie and Spring Lakes

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Pedersen, M., Ruter, A., Schweger, C. et al. Postglacial viability and colonization in North America’s ice-free corridor. Nature 537, 45–49 (2016). https://doi.org/10.1038/nature19085

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