Abstract A conceptual model is presented for the provenance and dispersal patterns of small dust that falls on Europe. Generally its sources are in North Africa, and it is distributed across all Europe. Several key sources can be distinguished: ‘Sahelian’ dust comes largely from the old Lake Chad region—this is a clay-rich unimodal material. ‘Saharan’ dust comes from the great sand sheets—it contains small monomineralic particles and may have a bimodal size range. Three simple deposition zones can be recognised; a D1a zone where sufficient dust is deposited to form a discrete soil layer (not well classified as a Rendoll), in the extreme south of Europe; a D1b zone where the airborne dust simply provided a silty admixture to soil systems—across Middle Europe; and a northern zone D1c where the dust is a fugitive cloud, but very occasionally forms noticeable deposits. Two particle formation methods can be noted. Particle control in Sahelian dust is via the sedimentation in the original lake. This gives an open structure which can be modelled using a simple Monte Carlo approach. The open structure ensures that only small particles are produced; size control is via particle packing. A chipping mechanism can produce fine quartz particles from sandy deserts. The aeolian energy is, by and large, not sufficient to cause major impact fracturing but small mineral chips can be produced in the small dust size (fine and very fine silt), which go into high-level suspension and travel to Europe and beyond. The Saharan material can have a wider, more variable size distribution than the Sahelian material. The Canary Islands ‘loess’ is largely Sahelian material; the Cape Verde Islands deposits, from the nearby sandy regions, are Saharan deposits. Large dust has fallen on Europe, and produced widespread loess deposits. Large dust is essentially an ‘in-continent’ deposit; small dust comes from outside—from Africa.

Aeolian dust in Europe: African sources and European deposits

A 3 million year index for North African humidity/aridity and the implication of potential pan-African Humid periods

The last extended time period when climate may have been warmer than today was during the Last Interglacial (LIG; ca. 129 to 120 thousand years ago). However, a global view of LIG precipitation is lacking. Here, seven new LIG climate models are compared to the first global database of proxies for LIG precipitation. In this way, models are assessed in their ability to capture important hydroclimatic processes during a different climate. The models can reproduce the proxy-based positive precipitation anomalies from the preindustrial period over much of the boreal continents. Over the Southern Hemisphere, proxy-model agreement is partial. In models, LIG boreal monsoons have 42% wider area than in the preindustrial and produce 55% more precipitation and 50% more extreme precipitation. Austral monsoons are weaker. The mechanisms behind these changes are consistent with stronger summer radiative forcing over boreal high latitudes and with the associated higher temperatures during the LIG.

Agreement between reconstructed and modeled boreal precipitation of the Last Interglacial

There is an unexplained terrestrial mass extinction at the Devonian-Carboniferous boundary (359 million years ago). The discovery in east Greenland of malformed land plant spores demonstrates that the extinction was coincident with elevated UV-B radiation demonstrating ozone layer reduction. Mercury data through the extinction level prove that, unlike other mass extinctions, there were no planetary scale volcanic eruptions. Importantly, the Devonian-Carboniferous boundary terrestrial mass extinction was coincident with a major climatic warming that ended the intense final glacial cycle of the latest Devonian ice age. A mechanism for ozone layer reduction during rapid warming is increased convective transport of ClO. Hence, ozone loss during rapid warming is an inherent Earth system process with the unavoidable conclusion that we should be alert for such an eventuality in the future warming world.

https://advances.sciencemag.org/content/advances/6/22/eaba0768.full.pdf

UV-B radiation was the Devonian-Carboniferous boundary terrestrial extinction kill mechanism

Millennial-scale fluctuations in Saharan dust supply across the decline of the African Humid Period

North Africa experienced dramatic changes in hydrology and vegetation during the late Quaternary driven by insolation-induced shifts of the tropical rain belt and further modulated by millennial-scale droughts and vegetation-climate feedbacks. While most past proxy and modelling studies concentrated on the temporal and spatial dynamics of the last African humid period, little is known about the intensities and characteristics of pre-Holocene humid periods. Here we present a high-resolution record of fine-grained eastern Saharan dust from the Eastern Mediterranean Sea spanning the last 180 kyr, which is based on the clay mineral composition of the marine sediments, especially the kaolinite/chlorite ratio. Minimum aeolian kaolinite transport occurred during the African Humid Periods because kaolinite deflation was hampered by increased humidity and vegetation cover. Instead, kaolinite weathering from kaolinite-bearing Cenozoic rocks was stored in lake basins, river beds and soils during these periods. During the subsequent dry phases, fine-grained dust was mobilised from the desiccated lakes, rivers and soils resulting in maximum aeolian uptake and transport of kaolinite. The kaolinite transport decreased again when these sediment sources exhausted. We conclude that the amount of clay-sized dust blown out of the Sahara into the Eastern Mediterranean Sea is proportional to the intensity of the kaolinite weathering and accumulation in soils and lake sediments, and thus to the strength of the preceding humid period. These humid periods provided the windows for the migration of modern humans out of Africa, as postulated previously. The strongest humid period occurred during the Eemian and was followed by two weaker phases centred at ca. 100 ka and ca. 80 ka.

/pdf/intensity-of-african-humid-periods-estimated-from-saharan-1tya94rmty.pdf

Intensity of African Humid Periods Estimated from Saharan Dust Fluxes.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/DC3E4A111557F7F07573A13992164D5C/S0033589419000711a.pdf/div-class-title-reconstructing-saharan-dust-transport-to-the-eastern-mediterranean-sea-during-the-last-180-ka-using-endmember-modelling-of-grain-size-data-div.pdf

Reconstructing Saharan dust transport to the Eastern Mediterranean Sea during the last 180 ka using endmember modelling of grain size data

The Eastern Mediterranean Sea is a sink for terrigenous sediments from North Africa, Europe and Asia Minor Its sediments therefore provide valuable information on the climate dynamics in the source areas and the associated transport processes We present a high-resolution dataset of sediment core M40/4_SL71, which was collected SW of Crete and spans the last ca 180 kyr We analysed the clay mineral composition, the grain size distribution within the silt fraction, and the abundance of major and trace elements We tested the potential of end-member modelling on these sedimentological datasets as a tool for reconstructing the climate variability in the source regions and the associated detrital input For each dataset, we modelled three end members All end members were assigned to a specific provenance and sedimentary process In total, three end members were related to the Saharan dust input, and five were related to the fluvial sediment input One end member was strongly associated with the sapropel layers The Saharan dust end members of the grain size and clay mineral datasets generally suggest enhanced dust export into the Eastern Mediterranean Sea during the dry phases with short-term increases during Heinrich events During the African Humid Periods, dust export was reduced but may not have completely ceased The loading patterns of two fluvial end members show a strong relationship with the Northern Hemisphere insolation, and all fluvial end members document enhanced input during the African Humid Periods The sapropel end member most likely reflects the fixation of redox-sensitive elements within the anoxic sapropel layers Our results exemplify that end-member modelling is a valuable tool for interpreting extensive and multidisciplinary datasets

/pdf/end-member-modelling-as-a-tool-for-climate-reconstruction-an-1d2glov5h6.pdf

End-member modelling as a tool for climate reconstruction-An Eastern Mediterranean case study.

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Intensity of African Humid Periods Estimated from Saharan Dust Fluxes.

Reconstructing Saharan dust transport to the Eastern Mediterranean Sea during the last 180 ka using endmember modelling of grain size data

End-member modelling as a tool for climate reconstruction-An Eastern Mediterranean case study.