Mammoth Steppes

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.

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.[18] 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

1. The driving force for the core Asian steppe was an enormous and stable high-pressure system north of the Tibetan Plateau.

2. 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.

3. Growth of the Scandinavian ice sheet created a barrier to North Atlantic moisture.

4. Icing over of the North Atlantic sea surface with reduced flow of moisture from the east.

5. The winter (January) storm track seems to have swept across Eurasia on this axis.

6. 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.

7. 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.

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, bluegrass, junegrass, fescue, and sedge, and also diverse forbs such as fringed sagebrush, campion, rock-jasmine, cinquefoil, goosefoot, buttercup, and plantain. Herbs were far more widespread than they are today, and were the main food source of the large plant eating mammals.

Many giant mammals such as woolly mammoths, woolly rhinoceroses, and cave lions inhabited the mammoth steppe during the Pleistocene.

Varying slightly by geographical location, the mammoth steppe was dominated (in biomass) primarily by giant deer, caribou, steppe bison, horses, woolly mammoth and yak, among other mammals, and was the center for the evolution of the Pleistocene “woolly” fauna. Woolly rhinoceros, moose, saiga antelope and musk ox also lived in different regions of the steppe. In what-is-today Siberia were the relatives of extant animals like the argali, snow sheep, Siberian roe deer, and the Mongolian gazelle. Not long before the last glacial maximum (roughly 40,000 years ago), an extinct paleospecies of argali (Ovis argaloides) also lived in Europe.[30] Notable carnivores found across the whole range of the mammoth steppe included the cave lion (Panthera spelaea), the wolverine (Gulo gulo), wolves (Canis lupus) and the brown bear (Ursus arctos). While the cave hyena was a part of the mammoth steppe fauna in Europe, it did not range into the core high-latitude, northern Eurasian-Siberian reaches of the biome. The short faced bear (Arctodus simus) was found across the tundra of North America, but never crossed over into Asia. Bird remains are rare because of their fragile structure, but there is some evidence for the snowy owl, willow ptarmigan, gyrfalcon, common raven and great bustard. Other bird species included the white-tailed and golden eagles. Vultures, like the griffon and cinereous vulture, are not known but they were likely common scavengers on the mammoth steppe, following the large herds and scavenging on predated or deceased animals. On Wrangel Island, the remains of woolly mammoth, woolly rhinoceros, horse, bison and musk ox have been found. Reindeer (caribou) and smaller animal remains do not preserve well, but reindeer excrement has been found in sediment. However, small animals on the mammoth steppe included, for example, steppe pika, ground squirrels and alpine marmot. In the most arid regions of the mammoth steppe (that were to the south of Central Siberia and Mongolia), woolly rhinoceroses were common, while woolly mammoths were rare. Reindeer still live in the far north of Mongolia today and, historically, their southern boundary passed through Germany and along the steppes of eastern Europe, indicating they once covered much of the mammoth steppe.

Mammoths survived on the Taimyr Peninsula until the Holocene. A small population of mammoths survived on St. Paul Island, Alaska, up until 3750 BC, and the small mammoths of Wrangel Island survived until 1650 BC. Bison in Alaska and the Yukon, and horses and muskox in northern Siberia, have survived the loss of the mammoth steppe. One study has proposed that a change of suitable climate caused a significant drop in the mammoth population size, which made them vulnerable to hunting from expanding human populations. The coincidence of both of these impacts in the Holocene most likely set the place and time for the extinction of the woolly mammoth.