Pattern of extinction of the woolly mammoth in Beringia.

Extinction of the woolly mammoth in Beringia has long been subject to research and speculation. Here we use a new geo-referenced database of radiocarbon-dated evidence to show that mammoths were abundant in the open-habitat of Marine Isotope Stage 3 (∼45-30 ka). During the Last Glacial Maximum (∼25-20 ka), northern populations declined while those in interior Siberia increased. Northern mammoths increased after the glacial maximum, but declined at and after the Younger Dryas (∼12.9-11.5 ka). Remaining continental mammoths, now concentrated in the north, disappeared in the early Holocene with development of extensive peatlands, wet tundra, birch shrubland and coniferous forest. Long sympatry in Siberia suggests that humans may be best seen as a synergistic cofactor in that extirpation. The extinction of island populations occurred at ∼4 ka. Mammoth extinction was not due to a single cause, but followed a long trajectory in concert with changes in climate, habitat and human presence.

Climate change and the northern Russian treeline zone.

The Russian treeline is a dynamic ecotone typified by steep gradients in summer temperature and regionally variable gradients in albedo and heat flux. The location of the treeline is largely controlled by summer temperatures and growing season length. Temperatures have responded strongly to twentieth-century global warming and will display a magnified response to future warming. Dendroecological studies indicate enhanced conifer recruitment during the twentieth century. However, conifers have not yet recolonized many areas where trees were present during the Medieval Warm period (ca AD 800-1,300) or the Holocene Thermal Maximum (HTM; ca 10,000-3,000 years ago). Reconstruction of tree distributions during the HTM suggests that the future position of the treeline due to global warming may approximate its former Holocene maximum position. An increased dominance of evergreen tree species in the northern Siberian forests may be an important difference between past and future conditions. Based on the slow rates of treeline expansion observed during the twentieth century, the presence of steep climatic gradients associated with the current Arctic coastline and the prevalence of organic soils, it is possible that rates of treeline expansion will be regionally variable and transient forest communities with species abundances different from today's may develop.

Siberian peatlands a net carbon sink and global methane source since the early Holocene.

Interpolar methane gradient (IPG) data from ice cores suggest the "switching on" of a major Northern Hemisphere methane source in the early Holocene. Extensive data from Russia's West Siberian Lowland show (i) explosive, widespread peatland establishment between 11.5 and 9 thousand years ago, predating comparable development in North America and synchronous with increased atmospheric methane concentrations and IPGs, (ii) larger carbon stocks than previously thought (70.2 Petagrams, up to approximately 26% of all terrestrial carbon accumulated since the Last Glacial Maximum), and (iii) little evidence for catastrophic oxidation, suggesting the region represents a long-term carbon dioxide sink and global methane source since the early Holocene.