Plant macrofossils from perennially frozen deposits of the last interglacial on Bol'shoy Lyakhovsky Island, the New Siberian Archipelago, reveal former existence of a shrubland dominated by Alnus fruticosa, Betula папа, and Ledum palustre and interspersed with lakes and grasslands. The reconstructed palaeovegetation differs fundamentally from the high arctic tundra that exists in this region today, but resembles the subarctic shrub tundra near the tree line about 350 km southwest of the study site, however being more open. Similar vegetation was reconstructed also from pollen data. Such vegetation implies that, during the last interglacial, the mean summer temperature was considerably higher, the growing season was longer, and soils outside the range of thermokarst depressions were drier than today, possibly due to increased evaporation,. Pollen-based climatic reconstructions for the warmest interval yielded a mean July temperature of at least by 7-8° С higher than the present 2.5°C. Reconstructions from plant macrofossils, representing more local environments, gained even more than 12°C in contrast to today's 2.5°C.

We explain the higher summer temperatures and more arid environment of the last interglacial as compared to the present day by a combination of higher insolation due to changes in the Earth's orbital parameters and higher continentality in arctic Yakutia as result of a considerably less inundated Laptev Shelf. The great Holocene marine transgression, possibly due to tectonic extension and intense subsidence of the Laptev Sea shelf, had a dramatic impact on the arctic biota.

Reference:

Kienast F., Schirrmeister L., Andreev A., Tarasov P., Grosse G. Climate and vegetation in the East Siberian Arctic during the Eemian: implications from paleobotanical records. Correlation of Pleistocene Events in the Russian North. International Workshop Abstracts. 4-6 December 2006. Saint-Petersburg, 2006, p. 46.