Stepwise drying of Lake Turkana at the end of the African Humid Period: an example of forced regression modulated by solar activity?

Mapping Intimacies ◽

10.5194/se-2016-95 ◽

2016 ◽

Cited By ~ 1

Author(s):

Alexis Nutz ◽

Mathieu Schuster

Keyword(s):

Solar Activity ◽

Lake Level ◽

Controlling Factors ◽

Lake Turkana ◽

Turkana Basin ◽

Orbital Precession ◽

Forced Regression ◽

Humid Period

Abstract. Although timing of the termination of the African Humid Period (AHP) is relatively well-established now, modes and controlling factors are still being determined. Here, through a geomorphological approach, we characterize the evolution of the final regression of Lake Turkana at the end of the African Humid Period. We show that lake level fall during this period was not constant, yet rather stepwise consisted of five periods marked by rapid rates of lake level fall separated by periods of lower rates of lake level fall. Even the overall regressive trend is associated with regional decreased precipitations due to reduced insolation controlled by orbital precession, we discuss the origin of the five periods of accelerated rates of lake level fall. Finally, we propose that accelerations are associated with periods marked by solar activity minima that locally resulted in the repeated westward displacement of the Congo Air Boundary (CAB), thereby reducing rainfall across the Lake Turkana basin.

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Stepwise drying of Lake Turkana at the end of the African Humid Period: a forced regression modulated by solar activity variations?

Solid Earth ◽

10.5194/se-7-1609-2016 ◽

2016 ◽

Vol 7 (6) ◽

pp. 1609-1618 ◽

Cited By ~ 3

Author(s):

Alexis Nutz ◽

Mathieu Schuster

Keyword(s):

Solar Activity ◽

Northern Hemisphere ◽

Lake Level ◽

Controlling Factors ◽

Lake Turkana ◽

Gradual Reduction ◽

Summer Insolation ◽

Orbital Precession ◽

Forced Regression ◽

Humid Period

Abstract. Although the timing of the termination of the African Humid Period (AHP) is now relatively well established, the modes and controlling factors of this drying are still debated. Here, through a geomorphological approach, we characterize the regression of Lake Turkana at the end of the AHP. We show that lake level fall during this period was not continuous but rather stepwise and consisted of five episodes of rapid lake level fall separated by episodes marked by slower rates of lake level fall. Whereas the overall regressive trend reflects a decrease in regional precipitations linked to the gradual reduction in Northern Hemisphere summer insolation, itself controlled by orbital precession, we focus discussion on the origin of the five periods of accelerated lake level fall. We propose that these periods are due to temporary reductions in rainfall across the Lake Turkana area associated with repeated westward displacement of the Congo Air Boundary (CAB) during solar activity minima.

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

The Holocene ◽

10.1177/09596836211011655 ◽

2021 ◽

pp. 095968362110116

Author(s):

Tanzhuo Liu ◽

Christopher J Lepre ◽

Sidney R Hemming ◽

Wallace S Broecker

Keyword(s):

East Africa ◽

Lake Level ◽

Drainage System ◽

Early Holocene ◽

Lake Turkana ◽

Moisture Condition ◽

Turkana Basin ◽

Rock Varnish ◽

Geomorphic Features ◽

Humid Period

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.

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Onset of the African Humid Period by 13.9 kyr BP at Kabua Gorge, Turkana Basin, Kenya

The Holocene ◽

10.1177/0959683619831415 ◽

2019 ◽

Vol 29 (6) ◽

pp. 1011-1019 ◽

Cited By ~ 4

Author(s):

Catherine C Beck ◽

Craig S Feibel ◽

James D Wright ◽

Richard A Mortlock

Keyword(s):

Cultural Change ◽

Drainage System ◽

Climatic Conditions ◽

Human Adaptation ◽

Lake Turkana ◽

Climatic Forcing ◽

Level Curves ◽

Turkana Basin ◽

Time Period ◽

Humid Period

The shift toward wetter climatic conditions during the African Humid Period (AHP) transformed previously marginal habitats into environments conducive to human exploitation. The Turkana Basin provides critical evidence for a dynamic climate throughout the AHP (~15–5 kyr BP), as Lake Turkana rose ~100 m multiple times to overflow through an outlet to the Nile drainage system. New data from West Turkana outcrops of the late-Pleistocene to early-Holocene Galana Boi Formation complement and extend previously established lake-level curves. Three lacustrine highstand sequences, characterized by laminated silty clays with ostracods and molluscs, were identified and dated using AMS radiocarbon on molluscs and charcoal. This study records the earliest evidence from the Turkana Basin for the onset of AHP by at least 13.9 kyr BP. In addition, a depositional hiatus corresponds to the Younger Dryas (YD), reflecting the Turkana Basin’s response to global climatic forcing. The record from Kabua Gorge holds additional significance as it characterized the time period leading up to Holocene climatic stability. This study contributes to the paleoclimatic context of the AHP and YD during which significant human adaptation and cultural change occurred.

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Pliocene archaeological occurrences in the Lake Turkana basin

Journal of Human Evolution ◽

10.1006/jhev.1994.1040 ◽

1994 ◽

Vol 27 (1-3) ◽

pp. 159-171 ◽

Cited By ~ 80

Author(s):

Mzalendo Kibunjia

Keyword(s):

Lake Turkana ◽

Turkana Basin

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A New and Open CoiledValvata(Gastropoda) from the Pliocene Koobi Fora Formation of the Turkana Basin, Northern Kenya

Journal of Paleontology ◽

10.1666/10-014.1 ◽

2010 ◽

Vol 84 (5) ◽

pp. 996-1002 ◽

Cited By ~ 6

Author(s):

Henning Scholz ◽

Matthias Glaubrecht

Keyword(s):

New Species ◽

Environmental Stress ◽

Environmental Conditions ◽

Lake Level ◽

Shell Morphology ◽

Koobi Fora ◽

Northern Kenya ◽

Turkana Basin ◽

High Level ◽

Stratigraphic Interval

New field collections allow the study and description ofValvata juliaenew species from the Pliocene upper Burgi Member of the Koobi Fora Formation of Kenya. The shell morphology of this species varies from trochospiral to planispiral to open coiled. The species is restricted to a short stratigraphic interval.Valvata juliaeis considered as an invader of the Turkana Basin during a lacustrine transgression event. The open coiling of the species is interpreted as an ecophenotypic response to a high level of environmental stress caused by lake level fluctuations and emergence of delta systems. These environmental conditions broughtValvata juliaeto extinction soon after it invaded the Turkana Basin.

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