Earth's precession cycle and Quaternary climatic change in tropical Africa

Pokras, Edward M.; Mix, Alan C

doi:10.1038/326486a0

Cited by 154 publications

(74 citation statements)

References 12 publications

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“…During the most arid intervals, Lake Malawi became a shallow alkaline, saline lake, with lake levels at least as low as Ϫ580 m, and its surrounding watershed was converted into a semidesert. In conjunction with previous studies (16,(44)(45)(46), these results document a wide-ranging, tropical African event of broad ecological significance. Furthermore, our continuous and regionally significant record of aridity during this period shows it to have been much more severe than during the LGM, a period assigned great importance in hypotheses regarding the impacts of aridity on African ecosystems and evolution (3,47).…”

Section: Discussionsupporting

confidence: 72%

Ecological consequences of early Late Pleistocene megadroughts in tropical Africa

Cohen¹,

Stone

Beuning

et al. 2007

Proc. Natl. Acad. Sci. U.S.A.

258

187

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This resulted in extraordinarily low lake levels, even in Africa's deepest lakes. On the basis of well dated paleoecological records from Lake Malawi, which reflect both local and regional conditions, we show that this aridity had severe consequences for terrestrial and aquatic ecosystems. During the most arid phase, there was extremely low pollen production and limited charred-particle deposition, indicating insufficient vegetation to maintain substantial fires, and the Lake Malawi watershed experienced cool, semidesert conditions (<400 mm/yr precipitation). Fossil and sedimentological data show that Lake Malawi itself, currently 706 m deep, was reduced to an Ϸ125 m deep saline, alkaline, well mixed lake. This episode of aridity was far more extreme than any experienced in the Afrotropics during the Last Glacial Maximum (Ϸ35-15 ka). Aridity diminished after 95 ka, lake levels rose erratically, and salinity/alkalinity declined, reaching near-modern conditions after 60 ka. This record of lake levels and changing limnological conditions provides a framework for interpreting the evolution of the Lake Malawi fish and invertebrate species flocks. Moreover, this record, coupled with other regional records of early Late Pleistocene aridity, places new constraints on models of Afrotropical biogeographic refugia and early modern human population expansion into and out of tropical Africa. cichlid evolution ͉ Lake Malawi ͉ Out-of-Africa Hypothesis ͉ paleoclimate ͉ paleolimnology

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Section: Discussionsupporting

confidence: 72%

Ecological consequences of early Late Pleistocene megadroughts in tropical Africa

Cohen¹,

Stone

Beuning

et al. 2007

Proc. Natl. Acad. Sci. U.S.A.

258

187

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“…Indeed, the markedly deepened megadrought behavior over the last 450,000 y in particular, resembles the tempo of enhanced northern hemisphere glacial-interglacial variability during that time interval, and suggests a strong linkage to highlatitude forcing and Indo-Arabian monsoon dynamics, as indicated in some shorter tropical records (21,23). The lack of steady precessional rhythms in this terrestrial hydroclimate record is consistent with recent modeling efforts (24) that suggest that moisture transport in southeastern Africa is a more complex and nuanced process than previously postulated, and orbital forcing alone (2,5,(25)(26)(27)(28)) is insufficient to explain 10 4-5 -y moisture variability over million-year time frames. Calibrated lake level [the first principal component, PC (1)] demonstrates cyclic behavior from ∼200 to ∼600 ka ( Fig.…”

Section: Causative Mechanisms For Climate Variabilitysupporting

confidence: 76%

Continuous 1.3-million-year record of East African hydroclimate, and implications for patterns of evolution and biodiversity

Lyons

Scholz

Cohen

et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

118

164

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The transport of moisture in the tropics is a critical process for the global energy budget and on geologic timescales, has markedly influenced continental landscapes, migratory pathways, and biological evolution. Here we present a continuous, first-of-its-kind 1.3-My record of continental hydroclimate and lake-level variability derived from drill core data from Lake Malawi, East Africa (9-15°S). Over the Quaternary, we observe dramatic shifts in effective moisture, resulting in large-scale changes in one of the world's largest lakes and most diverse freshwater ecosystems. Results show evidence for 24 lake level drops of more than 200 m during the Late Quaternary, including 15 lowstands when water levels were more than 400 m lower than modern. A dramatic shift is observed at the Mid-Pleistocene Transition (MPT), consistent with far-field climate forcing, which separates vastly different hydroclimate regimes before and after ∼800,000 years ago. Before 800 ka, lake levels were lower, indicating a climate drier than today, and water levels changed frequently. Following the MPT high-amplitude lake level variations dominate the record. From 800 to 100 ka, a deep, often overfilled lake occupied the basin, indicating a wetter climate, but these highstands were interrupted by prolonged intervals of extreme drought. Periods of high lake level are observed during times of high eccentricity. The extreme hydroclimate variability exerted a profound influence on the Lake Malawi endemic cichlid fish species flock; the geographically extensive habitat reconfiguration provided novel ecological opportunities, enabling new populations to differentiate rapidly to distinct species. Lake Malawi | tropical paleoclimatology | East African rift | cichlid fish | quaternary I nsolation forcing of tropical convection and shifts in the Intertropical Convergence Zone (ITCZ) are considered principal mechanisms driving tropical climate variability on geologic time scales (1-5). However, instrumental records show that the ITCZ over land is poorly characterized compared with the oceans (Fig. 1), and the transport of oceanic moisture to the hinterlands is complex, because topographic barriers redirect winds and block advection to the continental interiors (6). To document moisture transport onto the continents over geological time scales, terrestrial records of tropical paleoclimate with the length and continuity of ocean drilling records are required. Continental drilling in long-lived tropical lakes provides continuous, high-resolution paleoclimate records that extend well past the last glacial maximum (7,8), and augment shorter, well-dated records from outcrops. Lakes of great antiquity also contain numerous endemic species-notably, cichlid fishes-whose modern assemblages evolved in concert with changing climates, and which figure prominently into models of speciation and diversification (9, 10).Lake Malawi and Its Catchment Lake Malawi (Nyasa) is one of the world's largest and oldest lakes, and is situated at the southern end of the East Afri...

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“…There is a growing body of literature suggesting wet/dry cycles occur in the East African Rift in concert with astronomically driven (Milankovitch) glacial-interglacial obliquity cycles (~ 41,000 yrs) in addition to precession cycles (19,000-23,000 yrs; Pokras and Mix, 1987;Gasse et al, 1989;Ruddiman et al, 1989;Imbrie et al, 1993;deMenocal and Bloemendal, 1995;Trauth et al, 2005;Deino et al, 2006). Alhough the continental record is discontinuous and cannot be expected to mirror the marine sedimentary sequence (see Sikes, 1999), stable isotopic studies of paleosols have been correlated with other continental or global proxy records of paleoclimate (Smith et al, 1993;deMenocal, 1995;Quade et al, 1995).…”

Section: Paleoclimatementioning

confidence: 99%

Stable isotopes of pedogenic carbonates as indicators of paleoecology in the Plio-Pleistocene (upper Bed I), western margin of the Olduvai Basin, Tanzania

Sikes

Ashley

2007

Journal of Human Evolution

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Earth's precession cycle and Quaternary climatic change in tropical Africa

Cited by 154 publications

References 12 publications

Ecological consequences of early Late Pleistocene megadroughts in tropical Africa

Ecological consequences of early Late Pleistocene megadroughts in tropical Africa

Continuous 1.3-million-year record of East African hydroclimate, and implications for patterns of evolution and biodiversity

Stable isotopes of pedogenic carbonates as indicators of paleoecology in the Plio-Pleistocene (upper Bed I), western margin of the Olduvai Basin, Tanzania

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