Holocene dust records from the West African Sahel and their implications for changes in climate and land surface conditions

Cockerton, Helen E.; Holmes, Jonathan A.; Street-Perrott, F. Alayne; Ficken, Katherine J.

doi:10.1002/2013jd021283

Cited by 21 publications

(22 citation statements)

References 60 publications

(83 reference statements)

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“…Therefore, the present-day mode and scale of dust production from the Bodélé Basin could not have occurred between ∼15 and 1 ka. Many studies exclude biogenic contributions from their dust flux calculations (52,53), thereby removing the main diatomaceous component of present-day Bodélé dust. However, both studies cited above (52,53) still record an increase in dust flux over the last 2 millennia, which is consistent with the release of mineral (not diatomaceous) dust from the Bodélé Basin in response to drying after 2.4 ± 0.1 ka.…”

Section: Water and Dust: Bodélé Basin As A Tipping Elementmentioning

confidence: 99%

“…Many studies exclude biogenic contributions from their dust flux calculations (52,53), thereby removing the main diatomaceous component of present-day Bodélé dust. However, both studies cited above (52,53) still record an increase in dust flux over the last 2 millennia, which is consistent with the release of mineral (not diatomaceous) dust from the Bodélé Basin in response to drying after 2.4 ± 0.1 ka. Nonetheless, the existence of a small standing-water body in the lowest-elevation parts of the Bodélé Basin would have limited the emission of present-day quantities of diatomaceous dust until after 1 ka.…”

Section: Water and Dust: Bodélé Basin As A Tipping Elementmentioning

confidence: 99%

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West African monsoon dynamics inferred from abrupt fluctuations of Lake Mega-Chad

Armitage

Bristow

Drake

2015

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

124

116

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From the deglacial period to the mid-Holocene, North Africa was characterized by much wetter conditions than today. The broad timing of this period, termed the African Humid Period, is well known. However, the rapidity of the onset and termination of the African Humid Period are contested, with strong evidence for both abrupt and gradual change. We use optically stimulated luminescence dating of dunes, shorelines, and fluviolacustrine deposits to reconstruct the fluctuations of Lake Mega-Chad, which was the largest pluvial lake in Africa. Humid conditions first occur at ∼15 ka, and by 11.5 ka, Lake Mega-Chad had reached a highstand, which persisted until 5.0 ka. Lake levels fell rapidly at ∼5 ka, indicating abrupt aridification across the entire Lake Mega-Chad Basin. This record provides strong terrestrial evidence that the African Humid Period ended abruptly, supporting the hypothesis that the African monsoon responds to insolation forcing in a markedly nonlinear manner. In addition, Lake Mega-Chad exerts strong control on global biogeochemical cycles because the northern (Bodélé) basin is currently the world’s greatest single dust source and possibly an important source of limiting nutrients for both the Amazon Basin and equatorial Atlantic. However, we demonstrate that the final desiccation of the Bodélé Basin occurred around 1 ka. Consequently, the present-day mode and scale of dust production from the Bodélé Basin cannot have occurred before 1 ka, suggesting that its role in fertilizing marine and terrestrial ecosystems is either overstated or geologically recent.

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Section: Water and Dust: Bodélé Basin As A Tipping Elementmentioning

confidence: 99%

Section: Water and Dust: Bodélé Basin As A Tipping Elementmentioning

confidence: 99%

West African monsoon dynamics inferred from abrupt fluctuations of Lake Mega-Chad

Armitage

Bristow

Drake

2015

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

124

116

View full text Add to dashboard Cite

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“…The change in dust flux has been attributed to varying Saharan vegetation cover predicted by Brovkin et al (1998) and Claussen et al (1999) or was related to a change in lake surface area (Cockerton et al, 2014;Armitage et al, 2015). Alternatively, the enhanced dust accumulation is linked to enhanced surface winds and a consequent intensification of coastal upwelling (Adkins et al, 2006;Bradtmiller et al, 2016).…”

Section: Introductionmentioning

confidence: 99%

The link between marine sediment records and changes in Holocene Saharan landscape: simulating the dust cycle

et al. 2016

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Abstract. Marine sediment records reveal an abrupt and strong increase in dust deposition in the North Atlantic at the end of the African Humid Period about 4.9 to 5.5 ka ago. The change in dust flux has been attributed to varying Saharan land surface cover. Alternatively, the enhanced dust accumulation is linked to enhanced surface winds and a consequent intensification of coastal upwelling. Here we demonstrate for the first time the direct link between dust accumulation in marine cores and changes in Saharan land surface. We simulate the mid-Holocene (6 ka BP) and preindustrial (1850 AD) dust cycle as a function of Saharan land surface cover and atmosphere-ocean conditions using the coupled atmosphere-aerosol model ECHAM6.1-HAM2.1. Mid-Holocene surface characteristics, including vegetation cover and lake surface area, are derived from proxy data and simulations. In agreement with data from marine sediment cores, our simulations show that mid-Holocene dust deposition fluxes in the North Atlantic were two to three times lower compared with pre-industrial fluxes. We identify Saharan land surface characteristics to be the main control on dust transport from North Africa to the North Atlantic. We conclude that the increase in dust accumulation in marine cores is directly linked to a transition of the Saharan landscape during the Holocene and not due to changes in atmospheric or ocean conditions alone.

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“…Clay minerals were identified by Xray diffraction (XRD) every 2 cm for core BAS13P4 using a PANalytical diffractometer at the Laboratoire GEOPS (Université de Paris XI) on oriented mounts of non-calcareous clay-sized particles (< 2 µm). The oriented mounts were obtained following the methods described in detail by Colin et al (1999). Three XRD trials were performed, each proceeded by air-drying, ethylene glycol solvation for 24 h, and heating at 490 • C for 2 h. Semiquantitative estimates of clay miner-als were mainly made according to the position of the (001) series of basal reflections on the three XRD diagrams using MacDiff software.…”

Section: Methodsmentioning

confidence: 99%

Past African dust inputs in the western Mediterranean area controlled by the complex interaction between the Intertropical Convergence Zone, the North Atlantic Oscillation, and total solar irradiance

et al. 2020

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North Africa is the largest source of mineral dust on Earth, which has multiple impacts on the climate system; however, our understanding of decadal to centennial changes in African dust emissions over the last few millenniums is limited. Here, we present a high-resolution multiproxy analysis of sediment core from high-elevation Lake Bastani, on the island of Corsica, to reconstruct past African dust inputs to the western Mediterranean area over the last 3150 cal BP. Clay mineralogy with palygorskite and a clay ratio associated with geochemical data allow us to determine that terrigenous fluxes are almost exclusively related to atmospheric dust deposition from the western Sahara and Sahel areas over this period. High-resolution geochemical contents provide a reliable proxy for Saharan dust inputs with long-term (millennial) to short-term (centennial) variations. Millennial variations have been correlated with the long-term southward migration of the Intertropical Convergence Zone (ITCZ), with an increase in dust input since 1070 cal BP. This correlation suggests a strong link with the ITCZ and could reflect the increased availability of dust sources to be mobilized with an increase in wind and a decrease in precipitation over western and North Africa. For centennial to decadal variations, wavelet analyses show that since 1070 cal BP, the North Atlantic Oscillation (NAO) has been the main climatic forcing, with an increase in Saharan dust input during the positive phase, as suggested by previous studies over the last decades. However, when the ITCZ is in a northern position, before 1070 cal BP, wavelet analyses indicate that total solar irradiance (TSI) is the main forcing factor, with an increase in African dust input during low TSI. With climate reanalysis over the instrumental era, during low TSI we observe a significant negative anomaly in pressure over Africa, which is known to increase the dust transport. These two climatic forcing factors (NAO, TSI) modulate Saharan dust inputs to the Mediterranean area at a centennial timescale through changes in wind and transport pathways.Published by Copernicus Publications on behalf of the European Geosciences Union.

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Holocene dust records from the West African Sahel and their implications for changes in climate and land surface conditions

Cited by 21 publications

References 60 publications

West African monsoon dynamics inferred from abrupt fluctuations of Lake Mega-Chad

West African monsoon dynamics inferred from abrupt fluctuations of Lake Mega-Chad

The link between marine sediment records and changes in Holocene Saharan landscape: simulating the dust cycle

Past African dust inputs in the western Mediterranean area controlled by the complex interaction between the Intertropical Convergence Zone, the North Atlantic Oscillation, and total solar irradiance

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