Present climate and biological change - Climate Change: Biological and Human Aspects - page 207

and high-resolution palaeolake sediment cores. It was driven by variation in orbital
insolation and magnified by feedback between monsoonal rainfall and vegetation.
Human adaptation during this climate fluctuation is best known in the Eastern Sahara
to the west of the Nile valley. This region saw continuous occupation from 10 500
years ago, when hunter - gatherers expanded across open grass savannah habitats, to
about 5500 years ago, when drought drove pastoralists from most areas of the Sahara.
Regions of occupation elsewhere in the Sahara most closely resemble those of the
Eastern Sahara during the early Holocene ( 10 000-9000 years ago), when pottery-

producing hunter - fisher - gatherers resided beside palaeolakes. In other words this
area can be considered as fairly representative of the broader region. By the mid-
Holocene, occupational patterns diverged in the Central and Western Sahara due to
wet - arid cycles. During periods of little rain small communities moved to transient
bodies of water, rivers and upland refugia. Despite increasing knowledge regarding
occupational succession in the Sahara from early to late Holocene, this record is
based on individual sites that typically preserve short intervals of occupation, include
few if any intact burials and rely largely on indirect dating of human remains and
artefacts.
In 2008 it was reported that a new site complex called Gobero, located at the western
tip of the hyperarid Tenere Desert in the southern Sahara in Niger, on the north-
western rim of the Chad Basin, provided a clearly variable habitation record (Sereno
et al., 2008). It showed evidence of periods of human occupation and in-between times
when the land was devoid of any settlement. Approximately 200 burials were found,
ranging in age over five millennia. As such, Gobero preserves the earliest and largest
Holocene prehistorical cemetery in the Sahara, so its archaeological exploration
opened a new window on the funerary practices, distinctive skeletal anatomy, health
and diet of early Holocene hunter - fisher - gatherers, who expanded into the Sahara
when climatic conditions were favourable. Associated middens (rubbish dumps) and
an exceptional faunal and pollen record help illuminate the area's history of episodic
human occupation under conditions of severe climatic change. The time 16 000-9700
years ago, at the end of the last glacial (the Devensian or Weichsel as it is sometimes
known in Europe, or Wisconsin in North America) and beginning of the current
Holocene interglacial, was mainly arid, and dune sands accumulated. At the time
9700-8200 years ago there were wet climatic conditions that sustained a population
of hunter - fisher - gatherers who were largely sedentary with lakeside burial sites that
include the earliest recorded cemetery in the Sahara, dating to approximately 8500
years ago. Then, around approximately 8500-8300 years ago, the level of palaeo-
Lake Gobero rose, submerging the dunes and forcing humans out. Well-aerated
permanent water at depths of 5 m or more is suggested by the remains of Nile perch
( Lates niloticus ). This was followed 8200-7200 years ago by a millennial drought;
a time that correlates well with the arid interruption in the central Sahara, which
was a somewhat shorter interval (

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8400-8000 years ago, with a duration of around
400 years) of severe climatic deterioration across the Chad Basin that was linked
to cooling events in the North Atlantic. (It was the time that a pulse of fresh water
from Lakes Agassiz and Ojibway entered the North Atlantic disrupting the Broecker
thermohaline circulation. This period of climate change is sometimes known as the
8.2 kiloyear event; see section 4.6.3.) This was immediately followed by the return

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