Archaeology of Early Pastoralism in East Africa

The first East African pastoralists arrived at the shores of Lake Turkana soon after the end of the African Humid Period, about 5,000 years ago. In the preceding millennia of the Holocene, fishing economies characterized East Africa. The domestic animals of the early pastoralists were not indigenous to East Africa, nor did they spread through the region simultaneously. Early pastoralist archaeological sites around Lake Turkana comprise settlements and remarkable monumental cemeteries. The expansion of pastoralists further south through East Africa was a two-stage process, probably because of the challenges posed by the presence of diseases fatal to livestock. First, caprines spread south and appear to have been integrated into existing forager subsistence systems. Then, starting toward the end of the 2nd millennium bce, specialized pastoralism began to be established across central and southern Kenya and into northern Tanzania. While analysis of lipid residues on potsherds has demonstrated that these Pastoral Neolithic (PN) peoples milked their animals, the question of whether agriculture was also practiced remains unresolved. Analyses of ancient DNA have shown there were at least two episodes of demic diffusion associated with the spread and establishment of the PN in East Africa. Considerable diversity is present in the PN, with three distinct cultures generally recognized across East Africa south of Lake Turkana. Moreover, there is even greater diversity observed in the decoration and shapes of ceramics. However, this cultural diversity is not matched by human genetic diversity, at least among the analyzed skeletons from two of the three cultures—the Elmenteitan and the Savanna Pastoral Neolithic.

Rock varnish record of the African Humid Period in the Lake Turkana basin of East Africa

Rock varnish is a manganiferous dark coating accreted on subaerially exposed rocks in drylands. It often contains a layered microstratigraphy that records past wetness variations. Varnish samples from latest Pleistocene and Holocene geomorphic features in the Lake Turkana basin, East Africa display a regionally replicable microstratigraphy record of Holocene millennial-scale wetness variability and a broad interval of wetter conditions during the African Humid Period (AHP). Three major wet pulses in the varnish record occurred during the generally wet interval of the early Holocene (11.5–8.5 ka) when the lake attained its maximum high stand (MHS) at 455–460 m. A >23 m drop from the MHS occurred between 8.5 and 8 ka. Subsequently two additional wet pulses occurred during the early to middle Holocene (8–5 ka) when the lake occupied its secondary high stand at 445 m. Collectively, these five wet phases represent an extended wet interval coincident with the AHP in the region. One moderate wet phase occurred during the subsequent climatic transition from the humid to arid regime (5–4.3 ka) after the lake level dropped rapidly from 445 m to <405 m. Five minor wet phases took place during the overall arid period of the late Holocene (4.3–0 ka) when the lake level oscillated below 405 m. These findings indicate that the AHP terminated rapidly around 5 ka in the Turkana basin in terms of lake level drop, but the regional shift in relative humidity from the AHP mode to its present-day condition lagged for about 700 years until 4.3 ka, hinting at a gradual phasing out in terms of moisture condition. These findings further suggest that Lake Turkana overflowed intermittently into the Nile drainage system through its topographic sill at 455–460 m during the early Holocene and has become a closed-basin lake thereafter for the past 8 ky.

How dry was the LGM? A Biosphere-Hydrosphere modelling approach for the paleo-lake Chew Bahir and Omo-River catchment in southern Ethiopia

&lt;p&gt;The formation of the East African Rift System led to the emergence of large topographical contrasts in southern Ethiopia. This extreme topography is in turn responsible for an extreme gradient in the distribution of precipitation between the dry lowlands (~500 mm a&lt;sup&gt;-1&lt;/sup&gt;) in the surrounding of Lake Turkana and the moist western Ethiopian Highlands (~2,000 mm a&lt;sup&gt;-1&lt;/sup&gt;). As a consequence, the prevailing vegetation is fractionated into a complex mosaic that includes desert scrubland along the Lake Turkana shore, woodlands and wooded grasslands in the Omo-River lowlands and the paleo-lake Chew Bahir catchment, afro-montane forests of the Ethiopian Highlands, and afro-alpine heath in most elevated parts. During the past 25 ka, southern Ethiopia has been exposed to significant climate changes, from a dry and cold Last Glacial Maximum (LGM, 25-18 ka BP) to the African Humid Period (AHP, 15-5 ka BP), and back to present-day dry conditions. These shifts in temperature and precipitation may have affected the vegetation pattern and landscape in the area, but environmental data especially from LGM times are rare. This is because in times of a dry climate the paleo-lake Chew Bahir was dried up and hence the climate record in lake sediments was interrupted.&lt;/p&gt;&lt;p&gt;In this study, we investigate the hydrological conditions during the LGM using a previously-developed lake balance model (LBM) for southern Ethiopia, which is now coupled with a new predictive vegetation model (PVM) to better understand the biosphere-hydrosphere interactions and thus possible precipitation thresholds. The PVM is based on the method of boosted regression trees using elevation and monthly precipitation as input to predict land-cover, tree-cover and vegetation greenness for a ~1 km grid covering the Omo-River, paleo-lake Chew Bahir, Lake Chamo and Lake Abaya catchments. We linked the PVM and the resulting land surface parameters with the LBM to model the impact of a changing land-cover to the actual evaporation. Furthermore, we used the glycerol dialkyl glycerol tetraethers (GDGT) based paleo-temperature and tropical lapse rate reconstructions from Mount Kenya to consider the orographic temperature distribution in southern Ethiopia during the LGM. Using both, we simulated different precipitation amounts from 100% to 50% compared to the modern-day multi-annual averages and their effect on vegetation and lake levels of paleo-lake Chew Bahir. Our biosphere-hydrosphere modelling approach suggests 25 to 30% lower moisture availability during the LGM compared to the modern conditions and provides a high-resolution spatial reconstruction of the potential prevailing vegetation in the southern Ethiopian region.&lt;/p&gt;

Little Ice Age to modern lake-level fluctuations from Ferguson's Gulf, Lake Turkana, Kenya, based on sedimentology and ostracod assemblages

Lacustrine sedimentary records and the proxies contained within them are valuable archives of past climate. However, the resolution of these records is frequently coarse or contains a high degree of uncertainty, making it difficult to resolve how climatic variability impacts the ecosystems on which humans depend. The goal of this study is to couple recent sediment cores sampled at centimeter-scale resolution with paleo- and historical information about lake levels to document how changes in the paleoenvironment impact the paleoecology of a rift basin lake. We present multiproxy data from three short cores collected from Ferguson's Gulf (FG), a shallow embayment connected to the western shore of Lake Turkana, Kenya. Five distinct biozones were interpreted on the basis of ostracods and geochemistry (δ18O, δ13C, and major elements), spanning the Little Ice Age (LIA) to the modern. Overall, ostracod total abundance and assemblage diversity decreased up-core, with the largest total abundance and genera diversity occurring during the LIA. This fits with regional datasets that indicate the Eastern Branch of the East African Rift System was wetter during the LIA than it is today. This also suggests that human impact in and around Lake Turkana has weakened the resiliency of the ecosystems in FG.