Mammoth Steppes

The mammoth steppe, also known as steppe-tundra, was once the Earth's most extensive biome. During glacial periods in the later Pleistocene, it stretched east-to-west, from the Iberian Peninsula in the west of Europe, then across Eurasia and through Beringia (the region including the far northeast of Siberia, Alaska and the now submerged land between them) and into the Yukon in northwest Canada; from north-to-south, the steppe reached from the Arctic southward to southern Europe, Central Asia and northern China. The mammoth steppe was cold and dry, and relatively featureless, though climate, topography, and geography varied considerably throughout. Certain areas of the biome—such as coastal areas—had wetter and milder climates than others. Some areas featured rivers which, through erosion, naturally created gorges, gulleys, or small glens. The continual glacial recession and advancement over millennia contributed more to the formation of larger valleys and different geographical features. Overall, however, the steppe is known to be flat and expansive grassland. The vegetation was dominated by palatable, high-productivity grasses, herbs and willow shrubs.

The animal biomass was dominated by species such as reindeer, muskox, saiga antelope, steppe bison, horses, woolly rhinoceros and woolly mammoth. These herbivores, in turn, were followed and preyed upon by various carnivores, such as wolves, brown bears, ''Panthera spelaea'' (the cave or steppe-lion), cave hyenas, wolverines, among others, as well as scimitar-toothed cats and giant short-faced bears in east Beringia (with scimitar-toothed cats also having rare records from the mammoth steppe in Eurasia). This ecosystem covered wide areas of the northern part of the globe, and thrived for approximately 100,000 years without major changes, but then diminished to small regions around 12,000 years ago.

Although it was primarily a Eurasian and Beringian biome, an analog of the mammoth steppe existed on the southern edge of the Laurentide sheet in North America as well, and contained many of the same animals such as woolly mammoths, muskoxen, scimitar cats, and caribou.

Modern humans began to inhabit the biome following their expansion out of Africa, reaching the Siberian Arctic by around 45,000 years ago.

Naming

At the end of the 19th century, Alfred Nehring (1890) and Jan Czerski (Iwan Dementjewitsch Chersky, 1891) proposed that during the last glacial period a major part of northern Europe had been populated by large herbivores and that a steppe climate had prevailed there. In 1982, the scientist R. Dale Guthrie coined the term "mammoth steppe" for this paleoregion.

Origin

The steppe-tundra biome first emerged during the glacial period of Marine Isotope Stage 12, around 460,000 years ago, during the Middle Pleistocene, uniting animals that previously inhabited the previously disparate northern tundra and Central Asian steppe biomes. The size of the steppe-tundra biome would repeatedly expand and contract as a result of subsequent glacial cycles.

The last glacial period, commonly referred to as the 'Ice Age', spanned from 126,000 YBP–11,700 YBP and was the most recent glacial period within the current ice age which occurred during the last years of the Pleistocene epoch. This arctic environment was very cold and dry and probably dusty, resembling mountaintop environments (alpine tundra), and was very different from today's swampy tundra. It reached its peak during the last glacial maximum, when ice sheets commenced advancing from 33,000 years BP and reached their maximum positions 26,500 years BP. Deglaciation commenced in the Northern Hemisphere approximately 19,000 years BP, and in Antarctica approximately 14,500 years BP, which is consistent with evidence that it was the primary source for an abrupt rise in the sea level at that time.

During the peak of the last glacial maximum, a vast mammoth steppe stretched from the Iberian Peninsula across Eurasia and over the Bering land bridge into Alaska and the Yukon where it was stopped by the Wisconsin glaciation. This land bridge existed because more of the planet's water was locked up in ice than now, hence sea levels were lower. When the sea levels began to rise this bridge was inundated around 11,000 years BP.

During glacial periods, there is clear evidence for intense aridity due to water being held in glaciers and their associated effects on climate. The mammoth steppe was like a huge 'inner court' that was surrounded on all sides by moisture-blocking features: massive continental glaciers, high mountains, and frozen seas. These kept rainfall low and created more days with clear skies than are seen today, which increased evaporation in the summer leading to aridity, and radiation of warmth from the ground into the night sky in winter leading to cold. This is thought to have been caused by seven factors:

#The driving force for the core Asian steppe was an enormous and stable high-pressure system north of the Tibetan Plateau.
#Deflection of the larger portion of the Gulf Stream southward, past southern Spain onto the coast of Africa, reduced temperatures (hence moisture and cloud cover) that the North Atlantic Current brings to Western Europe.
#Growth of the Scandinavian ice sheet created a barrier to North Atlantic moisture.
#Icing over of the North Atlantic sea surface with reduced flow of moisture from the east.
#The winter (January) storm track seems to have swept across Eurasia on this axis.
#Lowered sea levels exposed a large continental shelf to the north and east producing a vast northern plain which increased the size of the continent to the north.
#North American glaciers shielded interior Alaska and the Yukon Territory from moisture flow.
These physical barriers to moisture flow created a vast arid basin spanning three continents.

Environment (or biota)

Animal biomass and plant productivity of the mammoth steppe were similar to today's African savanna. There is no comparison to it today.

Plants

The paleo-environment changed across time, a proposal that is supported from mammoth dung samples found in northern Yakutia. During Pleniglacial interstadials, alder, birch, and pine trees survived in northern Siberia, however during the Last Glacial Maximum only a treeless steppe vegetation existed. At the onset of the Late Glacial Interstadial (15,000–11,000 BP), global warming resulted in shrub and dwarf birch in northeastern Siberia, which was then colonized by open woodland with birch and spruce during the Younger Dryas (12,900–11,700 YBP). By the Holocene (10,000 YBP), patches of closed larch and pine forests developed. Researchers had previously concluded that the mammoth steppe must have been very unproductive because they assumed that its soils had a very low carbon content; however, these soils (yedoma) were preserved in the permafrost of Siberia and Alaska and are the largest reservoir of organic carbon known. It was a highly productive environment. The vegetation was dominated by palatable high-productivity grasses, herbs and willow shrubs. The herbaceous flora included graminoids such as wild rye