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Timing and causes of mid-Holocene mammoth extinction on St. Paul Island, Alaska

  1. Matthew J. Woollerc,m
  1. aDepartment of Geosciences, College of Earth and Mineral Sciences, The Pennsylvania State University, University Park, PA 16802;
  2. bLaboratory of Tree Ring Research, University of Arizona, Tucson, AZ 85721;
  3. cAlaska Stable Isotope Facility, Water and Environmental Research Center, Institute of Northern Engineering, University of Alaska Fairbanks, Fairbanks, AK 99775;
  4. dHuman Paleoecology and Isotope Geochemistry Laboratory, Department of Anthropology, The Pennsylvania State University, University Park, PA 16802;
  5. eDepartment of Earth and Atmospheric Sciences, University of Alberta, Edmonton, AB, Canada T6G 2E3;
  6. fDepartment of Ecology and Evolutionary Biology, University of California, Santa Cruz, CA 95064;
  7. gAAAS Science and Technology Policy Fellow, National Science Foundation, Arlington, VA 22230;
  8. hDepartment of Anthropology, The Pennsylvania State University, University Park, PA 16802;
  9. iPenn State Institutes of Energy and the Environment, The Pennsylvania State University, University Park, PA 16802;
  10. jUC Santa Cruz Genomics Institute, University of California, Santa Cruz, CA 95064;
  11. kDepartment of Geography, University of Wisconsin–Madison, Madison, WI 53706;
  12. lCenter for Climatic Research, University of Wisconsin–Madison, Madison, WI 53706;
  13. mSchool of Fisheries and Ocean Sciences, University of Alaska Fairbanks, Fairbanks, AK 99775
  1. Edited by Adrian M. Lister, The Natural History Museum, London, United Kingdom, and accepted by Editorial Board Member David Jablonski June 10, 2016 (received for review March 25, 2016)

Significance

St. Paul Island, Alaska, is famous for its late-surviving population of woolly mammoth. The puzzle of mid-Holocene extinction is solved via multiple independent paleoenvironmental proxies that tightly constrain the timing of extinction to 5,600 ± 100 y ago and strongly point to the effects of sea-level rise and drier climates on freshwater scarcity as the primary extinction driver. Likely ecosystem effects of the mega-herbivore extinction include reduced rates of watershed erosion by elimination of crowding around water holes and a vegetation shift toward increased abundances of herbaceous taxa. Freshwater availability may be an underappreciated driver of island extinction. This study reinforces 21st-century concerns about the vulnerability of island populations, including humans, to future warming, freshwater availability, and sea level rise.

Abstract

Relict woolly mammoth (Mammuthus primigenius) populations survived on several small Beringian islands for thousands of years after mainland populations went extinct. Here we present multiproxy paleoenvironmental records to investigate the timing, causes, and consequences of mammoth disappearance from St. Paul Island, Alaska. Five independent indicators of extinction show that mammoths survived on St. Paul until 5,600 ± 100 y ago. Vegetation composition remained stable during the extinction window, and there is no evidence of human presence on the island before 1787 CE, suggesting that these factors were not extinction drivers. Instead, the extinction coincided with declining freshwater resources and drier climates between 7,850 and 5,600 y ago, as inferred from sedimentary magnetic susceptibility, oxygen isotopes, and diatom and cladoceran assemblages in a sediment core from a freshwater lake on the island, and stable nitrogen isotopes from mammoth remains. Contrary to other extinction models for the St. Paul mammoth population, this evidence indicates that this mammoth population died out because of the synergistic effects of shrinking island area and freshwater scarcity caused by rising sea levels and regional climate change. Degradation of water quality by intensified mammoth activity around the lake likely exacerbated the situation. The St. Paul mammoth demise is now one of the best-dated prehistoric extinctions, highlighting freshwater limitation as an overlooked extinction driver and underscoring the vulnerability of small island populations to environmental change, even in the absence of human influence.

Footnotes

  • ?1To whom correspondence should be addressed. Email: rgraham{at}ems.psu.edu.
  • Author contributions: Proxy analyses were conducted by R.W.G. (mammoth paleobiology), S.B. (14C dates and age model), K.C. (stable isotopes and geochemistry), B.J.C. (14C dates and age model), L.J.D., D.F. (tephra), P.D.H., J.D.K. (sedaDNA), L.A.N. (plant macrofossils), R.R. (cladocerans), é.S.T. (diatoms), B.S. (sedaDNA), Y.W., J.W.W. (pollen and spores), and M.J.W. (stable isotopes and geochemistry); K.C., L.J.D., D.F., P.D.H., L.A.N., B.S., Y.W., J.W.W., and M.J.W. conducted fieldwork, led by R.W.G. and S.B.; K.C. and M.J.W. led paleoenvironmental interpretations; Y.W. conducted statistical analyses; S.B. created core stratigraphy, led sampling strategy, and coordinated data acquisition; R.W.G. coordinated project; C.H. built GIS model of St. Paul Island area; and all authors contributed to manuscript writing, led by R.W.G., P.D.H., and J.W.W.

  • The authors declare no conflict of interest.

  • This article is a PNAS Direct Submission. A.M.L. is a guest editor invited by the Editorial Board.

  • Data deposition: Data have been deposited at the Neotoma Paleoecological Database (www.neotomadb.org/).

  • This article contains supporting information online at www.danielhellerman.com/lookup/suppl/doi:10.1073/pnas.1604903113/-/DCSupplemental.

Freely available online through the PNAS open access option.

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