Comment on “Antiphasing between Rainfall in Africa's Rift Valley and North America's Great Basin”

Milly, P. C. D.

doi:10.1006/qres.1998.2011

Cited by 15 publications

(13 citation statements)

References 7 publications

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“…Both desiccation events have been linked to climatic changes that resulted in a reduction in moisture availability, with the ~17-16 ka surface tied to Heinrich Event 1 (Stager et al, 2011). Bonnefille and Chalie (2000) estimate a ~42-45% reduction in mean annual precipitation for the LGM and lateglacial based on pollen data from cores in the Rwanda, Burundi, and Democratic Republic of the Congo highlands at the headwaters of streams that feed into Lake Victoria, broadly consistent with water balance models for Lake Victoria that suggest that a 50-75% reduction in precipitation could reduce the surface of area of Lake Victoria to <10% of its present size (Broecker et al, 1998;Milly, 1999).…”

Section: The Lateglacial History Of Lake Victoriasupporting

confidence: 62%

“…A number of the buried channels of these streams can still be traced across the lake floor (Figure 1). With a surface area of 68,800 km 2 , Lake Victoria is the largest tropical lake in the world and the largest lake in Africa to changes in rainfall availability (Broecker et al, 1998;Yin and Nicholson, 1998;Milly, 1999;Bootsma and Hecky, 2003). Historical fluctuations of ~4 m have been documented during the 19 th century (Nicholson, 1998) and can be linked to changes in precipitation (Kite, 1981(Kite, , 1982Sene and Plinston, 1994).…”

Section: Introductionmentioning

confidence: 99%

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The Pleistocene prehistory of the Lake Victoria basin

Tryon

Faith

Peppe

et al. 2016

Quaternary International

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of increased aridity repeatedly facilitated the dispersal of C 4 grassland ecosystems across the basin. Archaeological evidence from Middle Stone Age and Later Stone Age sites suggest that human groups diffused into the basin during intervals of declining lake levels, likely tracking the movement of the dense and predictable resources of shoreline environments as well as the dense but less predictable C 4 grass grazing herbivores. Repeated cycles of lake expansion and contraction provide a push-pull mechanism for the isolation and combination of populations in Equatorial Africa that may contribute to observed Late Pleistocene human biological variability suggested by the fossil and genetic records. Latitudinal differences in the timing of environmental change between the Lake Victoria basin and surrounding regions may have promoted movements across, within, and possibly out of Africa.

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Section: The Lateglacial History Of Lake Victoriasupporting

confidence: 62%

Section: Introductionmentioning

confidence: 99%

The Pleistocene prehistory of the Lake Victoria basin

Tryon

Faith

Peppe

et al. 2016

Quaternary International

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“…Previous water budget models (Broecker et al, 1998;Milly, 1999) indicate that Lake Victoria would be reduced to <20% of current surface area with a MAP between 557 and 1,283 mm year −1 . A Late Pleistocene dessication surface of unknown duration is also identified in Lake Victoria at ∼80 ka using sedimentation rates and seismic stratigraphy (Stager and Johnson, 2008), which supports our interpretation.…”

Section: Discussion Paleoclimate Reconstructionmentioning

confidence: 99%

“…MAP across the catchment varies from 1,400 to 1,800 mm year −1 (Yin and Nicholson, 1998;Sutcliffe and Parks, 1999). Because MAP is almost equal to average evaporation (1,460 mm year −1 ), with local precipitation derived primarily from the lake itself, lake level responds directly to changes in rainfall (Broecker et al, 1998;Yin and Nicholson, 1998;Milly, 1999;Bootsma and Hecky, 2003). The historic vegetation from the Lake Victoria region is evergreen bushland, thicket, and forest habitats (Andrews, 1973;White, 1983).…”

Section: Geologic Setting Modern Lake Victoria Basinmentioning

confidence: 99%

Reconstruction of Late Pleistocene Paleoenvironments Using Bulk Geochemistry of Paleosols from the Lake Victoria Region

et al. 2017

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The impact of changing environments on the evolution and dispersal of Homo sapiens is highly debated, but few data are available from equatorial Africa. Lake Victoria is the largest freshwater lake in the tropics and is currently a biogeographic barrier between the eastern and western branches of the East African Rift. The lake has previously desiccated at ∼17 ka and again at ∼15 ka, but little is known from this region prior to the Last Glacial Maximum. The Pleistocene terrestrial deposits on the northeast coast of Lake Victoria (94-36 ka) are ideal for paleoenvironmental reconstructions where volcaniclastic deposits (tuffs), fluvial deposits, tufa, and paleosols are exposed, which can be used to reconstruct Critical Zones (CZ) of the past (paleo-CZs). The paleo-CZ is a holistic concept that reconstructs the entire landscape using geologic records of the atmosphere, hydrosphere, lithosphere, biosphere, and pedosphere (the focus of this study). New paleosol-based mean annual precipitation (MAP) proxies from Karungu, Rusinga Island, and Mfangano Island indicate an average MAP of 750 ± 108 mm year −1 (CALMAG), 800 ± 182 mm year −1 (CIA-K), and 1,010 ± 228 mm year −1 (PPM 1.0 ) with no statistical difference throughout the 11 m thick sequence. This corresponds to between 54 and 72% of modern precipitation. Tephras bracketing these paleosols have been correlated across seven sites, and sample a regional paleo-CZ across a ∼55 km transect along the eastern shoreline of the modern lake. Given the sensitivity of Lake Victoria to precipitation, it is likely that the lake was significantly smaller than modern between 94 and 36 ka. This would have removed a major barrier for the movement of fauna (including early modern humans) and provided a dispersal corridor across the equator and between the rifts. It is also consistent with the associated fossil faunal assemblage indicative of semi-arid grasslands. During the Late Pleistocene, the combined geologic and paleontological evidence suggests a seasonally dry, open grassland environment for the Lake Victoria region that is significantly drier than today, which may have facilitated human and faunal dispersals across equatorial East Africa.

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“…The shallow depth and dependence on direct precipitation to maintain lake levels means that the Lake Victoria region is very sensitive to changes in precipitation (e.g. Broecker et al ., ; Milly, ), making the region an ideal archive for equatorial East African palaeoclimatic and palaeoenvironmental research. Geological evidence suggests that during the Pleistocene the lake markedly increased in size (compared to modern) and desiccated multiple times, most recently at 16 ka (Heinrich Stadial 1; Johnson et al ., ; Talbot & Laerdal, ; Stager et al ., , ).…”

Section: Settingmentioning

confidence: 99%

Recurrent spring‐fed rivers in a Middle to Late Pleistocene semi‐arid grassland: Implications for environments of early humans in the Lake Victoria Basin, Kenya

et al. 2015

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The effect of changing palaeoclimate and palaeoenvironment on human evolution during the Pleistocene is debated, but hampered by few East African records directly associated with archaeological sites prior to the Last Glacial Maximum. Middle to Late Pleistocene deposits on the shoreline of eastern Lake Victoria preserve abundant vertebrate fossils and Middle Stone Age artefacts associated with riverine tufas at the base of the deposits, which are ideal for palaeoenvironmental reconstructions. New data from tufas identified on Rusinga Island and on the mainland near Karungu, Kenya are provided from outcrop, thin sections, mineralogical, stable isotopic and U-series dating analyses. Tufa is identified in four sites: Nyamita (94Á0 AE 3Á3 and 111Á4 AE 4Á2 ka); Kisaaka, Aringo (455 AE 45 ka); and Obware. The age ranges of these tufa deposits demonstrate that spring-fed rivers were a recurrent, variably preserved feature on the Pleistocene landscape for ca 360 kyr. Poor sorting of clastic facies from all sites indicates flashy, ephemeral discharge, but these facies are commonly associated with barrage tufas, paludal environments with d 13 C values of ca 10& indicative of C 3 plants and fossil Hippopotamus, all of which indicate a perennial water source. Other tufa deposits from Nyamita, Obware and Aringo have a mixed C 3 /C 4 signature consistent with a semi-arid C 4 grassland surrounding these spring-fed rivers. The d 18 O values of tufa from Nyamita are on average ca 1& more negative than calcite precipitated from modern rainfall in the region, suggesting greater contribution of depleted monsoonal input, similar to the Last Glacial Maximum. Microdebitage and surface-collected artefacts indicate that early modern humans were utilizing these spring-fed rivers. The presence of springÀfed rivers would have afforded animals a reliable water source, sustaining a diverse plant and animal community in an otherwise arid environment. 1611

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Comment on “Antiphasing between Rainfall in Africa's Rift Valley and North America's Great Basin”

Cited by 15 publications

References 7 publications

The Pleistocene prehistory of the Lake Victoria basin

The Pleistocene prehistory of the Lake Victoria basin

Reconstruction of Late Pleistocene Paleoenvironments Using Bulk Geochemistry of Paleosols from the Lake Victoria Region

Recurrent spring‐fed rivers in a Middle to Late Pleistocene semi‐arid grassland: Implications for environments of early humans in the Lake Victoria Basin, Kenya

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