Pollen and isotopic records in Late Holocene sediments from Lake Turkana, Kenya

Mohammed, Mebruk; Bonnefille, Raymonde; Johnson, Thomas C.

doi:10.1016/0031-0182(95)00020-8

Cited by 45 publications

(16 citation statements)

References 13 publications

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“…Seismic unconformities dated to approximately 2,300 years BP indicate that the lake may have been 40 m below its current level (Morrissey and Scholz 2014). The terrigenous pollen record from the lake core infers a local arid interval centered between 2,500 and 1,600 years BP (Mohammed et al 1995). Inversely, more pluvial adapted taxa are abundant during the subsequent period spanning from 1,600 to 600 years BP (Mohammed et al 1995), which dates to the inferred transgression of the lake based on TOC and Total Inorganic Carbon (TIC) assayed from the core (Morrissey and Scholz 2014).…”

Section: Late Holocene 2500-200 Years Bpmentioning

confidence: 96%

“…The terrigenous pollen record from the lake core infers a local arid interval centered between 2,500 and 1,600 years BP (Mohammed et al 1995). Inversely, more pluvial adapted taxa are abundant during the subsequent period spanning from 1,600 to 600 years BP (Mohammed et al 1995), which dates to the inferred transgression of the lake based on TOC and Total Inorganic Carbon (TIC) assayed from the core (Morrissey and Scholz 2014). Charcoal from the archaeological site of Apaget 1 located at 9 m above the present lake level dates to 1,800±300 14 C years BP (1,070-2,430 cal.…”

Section: Late Holocene 2500-200 Years Bpmentioning

confidence: 99%

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Lakeside View: Sociocultural Responses to Changing Water Levels of Lake Turkana, Kenya

et al. 2015

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Throughout the Holocene, Lake Turkana has been subject to drastic changes in lake levels and the subsistence strategies people employ to survive in this hot and arid region. In this paper, we reconstruct the position of the lake during the Holocene within a paleoclimatic context. Atmospheric forcing mechanisms are discussed in order to contextualize the broader landscape changes occurring in eastern Africa over the last 12,000 years. The Holocene is divided into five primary phases according to changes in the strand-plain evolution, paleoclimate, and human subsistence strategies practiced within the basin. Early Holocene fishing settlements occurred adjacent to high and relatively stable lake levels. A period of high-magnitude oscillations in lake levels Afr Archaeol Rev (2015) ensued after 9,000 years BP and human settlements appear to have been located close to the margins of the lake. Aridification and a final regression in lake levels ensued after 5,000 years BP and human communities were generalized pastoralists-fishers-foragers. During the Late Holocene, lake levels may have dropped below their present position and subsistence strategies appear to have been flexible and occasionally specialized on animal pastoralism. Modern missionary and government outposts have encouraged the construction of permanent settlements in the region, which are heavily dependent on outside resources for their survival. Changes in the physical and cultural environments of the Lake Turkana region have been closely correlated, and understanding the relationship between the two variables remains a vital component of archaeological research.Résumé Tout l'Holocène, le lac Turkana a été soumis à des changements drastiques dans l'altitude des lacs et les stratégies de subsistance des gens utilisent pour survivre dans cette région chaude et aride. Dans cet article, nous reconstruisons la position du lac au cours de l'Holocène dans un contexte paléoclimatique. Mécanismes de forçage atmosphériques sont discutées afin de contextualiser les changements de paysage plus larges qui se produisent en Afrique orientale au cours des 12.000 dernières années. L'Holocène est divisé en cinq phases principales en fonction des changements dans l'évolution altitude du lac, paléoclimats et les stratégies de subsistance humains pratiqués dans le bassin. Premiers établissements de pêche de l'Holocène ont eu lieu à proximité d'altitude d'eau élevés et relativement stables. Une période d'oscillations de grande amplitude dans l'altitude du lac s'ensuit après 9000 années BP et les établissements humains semblent avoir été situé à proximité des marges sur le lac. Aridification et une régression finale du altitude des lacs s'ensuit après 5000 années BP et les communautés humaines sont généralisées éleveurs-pêcheurs-cueilleurs. Au cours de l'Holocène tardif, les altitudes des lacs pourraient avoir chuté en dessous de leur position actuelle et les stratégies de subsistance semblent avoir fait preuve de souplesse et de temps en temps spécialisé sur le pas...

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Section: Late Holocene 2500-200 Years Bpmentioning

confidence: 96%

Section: Late Holocene 2500-200 Years Bpmentioning

confidence: 99%

Lakeside View: Sociocultural Responses to Changing Water Levels of Lake Turkana, Kenya

et al. 2015

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“…The pollen record shows a shift to wetter conditions at ≈ 700 BP consistent with other high‐resolution palaeoclimate studies in the area (Mohammed et al ., 1995; Verschuren et al ., 2000). The diatom record begins at ≈ 700 BP consistent with a fairly abrupt shift to wetter conditions.…”

Section: Palaeoclimate Recordmentioning

confidence: 99%

Sedimentation and recent history of a freshwater wetland in a semi‐arid environment: Loboi Swamp, Kenya, East Africa

Ashley¹,

Mworia

Muasya

et al. 2004

Sedimentology

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Loboi Swamp is a 1·5 km2 freshwater wetland situated near the equator in the Kenya Rift Valley. The climate is semi‐arid: precipitation is ≈ 700 mm year−1, and evapotranspiration is ≈ 2500 mm year−1. Some of the wetland water is currently used for irrigation. An interdisciplinary study was conducted on the geology, hydrology, pedology and biology of the wetland to determine its origin and history and to assess its longevity under present hydrological conditions. Sedimentary records from two piston cores (1·8 and 4 m long) indicate that the present wetland developed during the late Holocene on a low‐relief alluvial plain. Floodplain deposits (sandy silts) are capped with wetland sediments (organic‐rich clay and peat), which began to form at ≈ 700 BP. The swamp is dominated by Typha domingensis Pers. (≈ 80%) and floating Cyperus papyrus L. (20%). It is fed by warm springs (T ≈ 35 °C; pH ≈ 6·4–6·9) emanating from grid faults of the rift floor. Water compositions suggest that sources are dominated by shallow meteoric water, with little contribution from deeper geothermal fluids. Siderite concretions in the floodplain silts reflect the Fe‐reducing conditions that developed as the surface became submerged beneath the water table. The pollen record captured both local and more regional vegetation, showing the prevailing dry rift valley climate despite development of the wetter conditions on the valley floor. The diatom record also suggests a dramatic change in local hydrology. The combined biological records of this semi‐arid wetland indicate an abrupt change to wetter conditions, most probably as a result of a regional change in climate. Rift tectonics provided accommodation space, maintained the wetland at or below the water table and enabled spring recharge. The size of the modern wetland has been reduced by about 60% since 1969, which suggests that the system may now be under hydrological stress due to anthropogenic impacts from land‐use change.

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“…Lakes Naivasha, Victoria, Turkana, Edward, Tanganyika, and Malawi all experienced pronounced and prolonged drought during the A.D. 1050-1400 period (Halfman and Johnson 1988;Owen et al 1990;Mohammed et al 1996;Verschuren et al 2000;Vershcuren 2000;Johnson et al 2001;Alin and Cohen 2003;Lamb et al 2001;Russell et al 2003;Stager et al 2005). Close by, Mt.…”

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confidence: 99%

North American Droughts of the Last Millennium from a Gridded Network of Tree-Ring Data

et al. 2007

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Drought is the most economically expensive recurring natural disaster to strike North America in modern times. Recently available gridded drought reconstructions have been developed for most of North America from a network of drought-sensitive tree-ring chronologies, many of which span the last 1000 yr. These reconstructions enable the authors to put the famous droughts of the instrumental record (i.e., the 1930s Dust Bowl and the 1950s Southwest droughts) into the context of 1000 yr of natural drought variability on the continent. We can now, with this remarkable new record, examine the severity, persistence, spatial signatures, and frequencies of drought variability over the past milllennium, and how these have changed with time.The gridded drought reconstructions reveal the existence of successive "megadroughts," unprecedented in persistence (20-40 yr), yet similar in year-to-year severity and spatial distribution to the major droughts experienced in today's North America. These megadroughts occurred during a 400-yr-long period in the early to middle second millennium A.D., with a climate varying as today's, but around a drier mean. The implication is that the mechanism forcing persistent drought in the West and the Plains in the instrumental era is analagous to that underlying the megadroughts of the medieval period. The leading spatial mode of drought variability in the recontructions resembles the North American ENSO pattern: widespread drought across the United States, centered on the Southwest, with a hint of the opposite phase in the Pacific Northwest.Recently, climate models forced by the observed history of tropical Pacific SSTs have been able to successfully simulate all of the major North American droughts of the last 150 yr. In each case, cool "La Niña-like" conditions in the tropical Pacific are consistent with North American drought. With ENSO showing a pronounced signal in the gridded drought recontructions of the last millennium, both in terms of its link to the leading spatial mode, and the leading time scales of drought variability (revealed by multitaper spectral analysis and wavelet analysis), it is postulated that, as for the modern day, the medieval megadroughts were forced by protracted La Niña-like tropical Pacific SSTs. Further evidence for this comes from the global hydroclimatic "footprint" of the medieval era revealed by existing paleoclimatic archives from the tropical Pacific and ENSO-sensitive tropical and extratropical land regions. In general, this global pattern matches that observed for modern-day persistent North American drought, whereby a La Niña-like tropical Pacific is accompanied by hemispheric, and in the midlatitudes, zonal, symmetry of hydroclimatic anomalies.

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Pollen and isotopic records in Late Holocene sediments from Lake Turkana, Kenya

Cited by 45 publications

References 13 publications

Lakeside View: Sociocultural Responses to Changing Water Levels of Lake Turkana, Kenya

Lakeside View: Sociocultural Responses to Changing Water Levels of Lake Turkana, Kenya

Sedimentation and recent history of a freshwater wetland in a semi‐arid environment: Loboi Swamp, Kenya, East Africa

North American Droughts of the Last Millennium from a Gridded Network of Tree-Ring Data

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