Late Pleistocene and Holocene Beringia vegetation dynamic reconstructions based on a yedoma exposure, Iktilik (Alaska)

Jens.Strauss [ at ]


The cold-arid climate associated to the late Pleistocene environment of unglaciated Beringia (northeastern Russia and Alaska-Yukon) was conducive to active sedimentation processes (eolian, alluvial, proluvial, colluvial, slope wash, solifluction, and permafrost creep) and accumulation of ground ice. These processes resulted in the formation of a relict form of ice-rich syngenetic permafrost, termed yedoma. Because yedoma accumulated during all Pleistocene, it contains paleoenvironmental archives that can be use as paleoecological and paleoclimatic proxies. This type of deposit offers an interesting opportunity to examine long term vegetation and climate dynamics of high latitude environments. Often fragmented, data obtained from yedoma can be linked to the framework established from continuous sequences (lake, pond, peatland) and provide interesting snapshots of a much older period. It also can potentially be linked to marine sequences and compared to northeastern Russia studies were the distribution of quality deposits are more widespread. Knowing that Beringia has acted as a refugium for plant species and the Pleistocene megafauna during the Pleistocene, many questions remain about the environmental history of northeastern Beringia, especially the extent and temporal dynamics of the now extinct tundra-steppe biome. The yedoma from Itkillik River (69°34' N, 150°52' W) is located at the boundary of the Arctic Coastal Plain and the Arctic Foothills. The site was formed over the late Pleistocene-early Holocene (48,000 to 5,000 14C yr BP). An exposure, about 400 m long, has been eroded by the meandering of the Itkillik River. The surface elevation of the bluff ranges between 30 to 35 m above the Itkillik River, and the whole stratigraphic exposures was analyzed for this study. Pollen analysis and reconstruction of paleoclimatic parameters such as temperature and precipitation (modem analogue technique) reveal a tundra-steppe environment dominated by herbaceous community. The preliminary results suggest a relative stable climate during the late Pleistocene, as species do not change much from the late Pleistocene through the Holocene transition. The warmer and more humid Holocene conditions were favorable to the establishment of a more diverse plant community and the emergence of shrub species (Picea, Alnus, Betula) which were absent in the Pleistocene Iktilik record. Overall, Cyperaceae and Gramineae are by far the dominant taxa in the sequence. The local conditions at the study site may have favored the presence and conservation of an herbaceous cover. Implications of our findings for vegetation and local climate reconstructions using pollen-climate transfer functions are discussed and linked to the sedimentology (C, C/N, OC, particle size distribution, gravimetric and volumetric water, sedimentation rate), and cryostratigraphy (cryostructure, ice content, ice wedge volume) of the site.

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Arctic change 2014, 08 Dec 2014 - 12 Dec 2014, Ottawa, Canada.
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Lapointe Elmrabti, L. , Talbot, J. , Kanevskiy, M. , Strauss, J. , Shur, Y. and Fortier, D. (2014): Late Pleistocene and Holocene Beringia vegetation dynamic reconstructions based on a yedoma exposure, Iktilik (Alaska) , Arctic change 2014, Ottawa, Canada, 8 December 2014 - 12 December 2014 .

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