<p>Climate may have played a critical role in early hominin evolution and d... more <p>Climate may have played a critical role in early hominin evolution and dispersion, with rapid changes from humid to hyper-arid observed in East African palaeoclimate records. Many studies show linkages between these climate changes and hominin speciation and dispersion; however, few of them have focused on annual to decadal climate variability. This new study presents paleoenvironmental records (diatom assemblages and oxygen isotopes in diatom biogenic silica, d<sup>18</sup>O<sub>diatom</sub>) from the Ol Njorowa Gorge in Kenya. The study site is located west of the African Rift Valley, from where important hominin dispersals are believed to have taken place. The study site preserves a stratigraphic record of interbedded diatomite beds spanning a key period of theorised hominin dispersals; 150,000 to 80,000 years ago. In this study, diatom assemblages and d<sup>18</sup>O<sub>diatom</sub>records are used to understand past changes in moisture and precipitation patterns over East Africa as well as changes in lake water chemistry. d<sup>18</sup>O<sub>diatom</sub> has been used in both lacustrine and oceanic settings since the early 2000s. It is however an under-utilised proxy that holds great potential, especially for diatomites from exposed lake beds where carbonate material is scarce or inexistant. The study also uses high resolution scanning XRF data from diatomite blocks to develop an age model for the diatomite beds at an annual timescale.</p>
Diatoms from a 30-cm thick sedimentary unit have been sampled each 0.5 cm to reconstruct the late... more Diatoms from a 30-cm thick sedimentary unit have been sampled each 0.5 cm to reconstruct the late Pleistocene lake phase of Lake Palaeo-Makgadikgadi in the Middle Kalahari (Botswana).
(1) University of Plymouth, Geography, Earth and Environmental Sciences, Plymouth, United Kingdom... more (1) University of Plymouth, Geography, Earth and Environmental Sciences, Plymouth, United Kingdom , (2) CNRS EDYTEM Laboratory, University of Savoie, Chambéry, France, (3) NERC Isotope Geosciences Facilities, British Geological Survey, Keyworth, NG12 5GG, UK, (4) School of Geography, Earth and Environmental Sciences, University of Birmingham, B15 2TT, UK, (5) School of Geography, University of Nottingham, NG7 2RD, UK, (6) Department of Geography, Ankara University, Turkey
Rapid development and climate change in southeast Asia is placing unprecedented pressures on fres... more Rapid development and climate change in southeast Asia is placing unprecedented pressures on freshwater ecosystems, but long term records of the ecological consequences are rare. Here we examine one basin of Tasik Chini (Malaysia), a UNESCO‐designated flood pulse wetland, where human disturbances (dam installation, iron ore mining, oil palm and rubber cultivation) have escalated since the 1980s. Diatom analysis and organic matter geochemistry (δ13Corg and C/N ratios) were applied to a sediment sequence to infer ecological changes in the basin since c. 1900 CE. As the Tasik Chini wetland is a rare ecosystem with an unknown diatom ecology, contemporary diatom habitats (plant surfaces, mud surfaces, rocks, plankton) were sampled from across the lake to help interpret the sedimentary record. Habitat specificity of diatoms was not strongly defined and, although planktonic and benthic groupings were distinctive, there was no difference in assemblages among the benthic habitat surfaces. An...
ABSTRACTIndividual palaeoenvironmental records represent a combination of regional‐scale (e.g. cl... more ABSTRACTIndividual palaeoenvironmental records represent a combination of regional‐scale (e.g. climatic) and site‐specific local factors. Here we compare multiple climate proxies from two nearby maar lake records, assuming that common signals are due to regional‐scale forcing. A new core sequence from Nar Lake in Turkey is dated by varves and U–Th to the last 13.8 ka. Markedly dry periods during the Lateglacial stadial, at 4.3–3.7 and at 3.2–2.6 ka BP, are associated with peaks in Mg/dolomite, positive δ18O, elevated diatom‐inferred electrical conductivity, an absence of laminated sediments and low Quercus/chenopod ratios. Wet phases occurred during the early–mid Holocene and 1.5–0.6 ka BP, characterized by negative δ18O, calcite precipitation, high Ca/Sr ratios, a high percentage of planktonic diatoms, laminated sediments and high Quercus/chenopod ratios. Comparison with the record from nearby Eski Acıgöl shows good overall correspondence for many proxies, especially for δ18O. Diff...
<p>Climate may have played a critical role in early hominin evolution and d... more <p>Climate may have played a critical role in early hominin evolution and dispersion, with rapid changes from humid to hyper-arid observed in East African palaeoclimate records. Many studies show linkages between these climate changes and hominin speciation and dispersion; however, few of them have focused on annual to decadal climate variability. This new study presents paleoenvironmental records (diatom assemblages and oxygen isotopes in diatom biogenic silica, d<sup>18</sup>O<sub>diatom</sub>) from the Ol Njorowa Gorge in Kenya. The study site is located west of the African Rift Valley, from where important hominin dispersals are believed to have taken place. The study site preserves a stratigraphic record of interbedded diatomite beds spanning a key period of theorised hominin dispersals; 150,000 to 80,000 years ago. In this study, diatom assemblages and d<sup>18</sup>O<sub>diatom</sub>records are used to understand past changes in moisture and precipitation patterns over East Africa as well as changes in lake water chemistry. d<sup>18</sup>O<sub>diatom</sub> has been used in both lacustrine and oceanic settings since the early 2000s. It is however an under-utilised proxy that holds great potential, especially for diatomites from exposed lake beds where carbonate material is scarce or inexistant. The study also uses high resolution scanning XRF data from diatomite blocks to develop an age model for the diatomite beds at an annual timescale.</p>
Diatoms from a 30-cm thick sedimentary unit have been sampled each 0.5 cm to reconstruct the late... more Diatoms from a 30-cm thick sedimentary unit have been sampled each 0.5 cm to reconstruct the late Pleistocene lake phase of Lake Palaeo-Makgadikgadi in the Middle Kalahari (Botswana).
(1) University of Plymouth, Geography, Earth and Environmental Sciences, Plymouth, United Kingdom... more (1) University of Plymouth, Geography, Earth and Environmental Sciences, Plymouth, United Kingdom , (2) CNRS EDYTEM Laboratory, University of Savoie, Chambéry, France, (3) NERC Isotope Geosciences Facilities, British Geological Survey, Keyworth, NG12 5GG, UK, (4) School of Geography, Earth and Environmental Sciences, University of Birmingham, B15 2TT, UK, (5) School of Geography, University of Nottingham, NG7 2RD, UK, (6) Department of Geography, Ankara University, Turkey
Rapid development and climate change in southeast Asia is placing unprecedented pressures on fres... more Rapid development and climate change in southeast Asia is placing unprecedented pressures on freshwater ecosystems, but long term records of the ecological consequences are rare. Here we examine one basin of Tasik Chini (Malaysia), a UNESCO‐designated flood pulse wetland, where human disturbances (dam installation, iron ore mining, oil palm and rubber cultivation) have escalated since the 1980s. Diatom analysis and organic matter geochemistry (δ13Corg and C/N ratios) were applied to a sediment sequence to infer ecological changes in the basin since c. 1900 CE. As the Tasik Chini wetland is a rare ecosystem with an unknown diatom ecology, contemporary diatom habitats (plant surfaces, mud surfaces, rocks, plankton) were sampled from across the lake to help interpret the sedimentary record. Habitat specificity of diatoms was not strongly defined and, although planktonic and benthic groupings were distinctive, there was no difference in assemblages among the benthic habitat surfaces. An...
ABSTRACTIndividual palaeoenvironmental records represent a combination of regional‐scale (e.g. cl... more ABSTRACTIndividual palaeoenvironmental records represent a combination of regional‐scale (e.g. climatic) and site‐specific local factors. Here we compare multiple climate proxies from two nearby maar lake records, assuming that common signals are due to regional‐scale forcing. A new core sequence from Nar Lake in Turkey is dated by varves and U–Th to the last 13.8 ka. Markedly dry periods during the Lateglacial stadial, at 4.3–3.7 and at 3.2–2.6 ka BP, are associated with peaks in Mg/dolomite, positive δ18O, elevated diatom‐inferred electrical conductivity, an absence of laminated sediments and low Quercus/chenopod ratios. Wet phases occurred during the early–mid Holocene and 1.5–0.6 ka BP, characterized by negative δ18O, calcite precipitation, high Ca/Sr ratios, a high percentage of planktonic diatoms, laminated sediments and high Quercus/chenopod ratios. Comparison with the record from nearby Eski Acıgöl shows good overall correspondence for many proxies, especially for δ18O. Diff...
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