Dust cycle, loess and climate
Today we know that the dust cycle is a fundamental part of the Earth system, with tremendous effects on the environment and human health. However, this was not the case decades ago. During the 1960s, ’70s, and ’80s, Israeli scientists (Dan Yaalon, Ran Gerson) had a vital role in advancing the ideas that loess can be formed in hot deserts and that dust is important component in soils located at the desert fringe, at the time when these ideas were not in general agreement as today. We study all aspects of the dust cycle in Israel and worldwide, focusing mainly on loess formation, geomorphology of dust sources, and dust addition to soils.
Current dust storms originating from afar are common in Israel and the Eastern Mediterranean; most dust sources for these storms are considered to be distal, originating from Sahara and Arabian deserts. However, recent studies suggest that the Quaternary loess accreted in the Northern Negev can serve as a proximal source of dust. This proximal source was mostly neglected in past discussions as contributor of dust.
We study the activity of current proximal dust sources and demonstrate that such proximal dust sources, mostly the Negev loess, currently contribute relatively large amounts of recycled dust to the regional dust cycle.
A haboob dust storm over the northern Negev, May 2nd, 2007 (Crouvi et al., 2017)
Publications:
Shalom, O., Crouvi, O., Enzel, Y., and Rosenfeld, D. (2020). Locally recycled late Pleistocene loess feeds modern dust storms at the desert margins of the eastern Mediterranean, Israel. Aeolian Research, 46, 100612. https://doi.org/10.1016/j.aeolia.2020.100612.
Crouvi, O., Dayan, U., Amit, R., and Enzel, Y. (2017). An Israeli haboob: Sea breeze activating local anthropogenic dust sources in the Negev loess. Aeolian Research, 24, 39-52. https://doi.org/10.1016/j.aeolia.2016.12.002.
Bacon, S. N., McDonald, E. V., Amit, R., Enzel, Y., and Crouvi, O. (2011). Total suspended particulate (TSP) emissions at high friction velocities from landforms in the Negev Desert. Journal of Geophysical Research – Earth Surface, 116, F03019. https://doi.org/10.1029/2011JF001965.
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A topographic cross section from North Africa to Israel showing the main proximal and distal dust sources for the Negev (Crouvi et al., 2017)
Loess is a widespread eolian deposit dominated by coarse silt and very fine sand quartz grains (20 - 80 µm) that serve as an important archive of information on Quaternary climate change. Despite the intensive research during the past century on desert loess formation, its origin remains poorly understood and is still a fundamental problem in sedimentology. The ongoing debate is focused on the first stage of loess formation - the production of coarse silt quartz grains.
Quaternary loess covers vast areas of the Negev desert and the Jordanian Plateau. The Negev loess is one of the best-studied true desert loess in the world; the carbonate lithology of the Negev and its physiography provides a unique opportunity to reveal the sources of the silicate-rich loess and to shed new light on the formation process of silt grains in deserts. Our group focus on new perspectives on the origin, ages, and paleoclimatic significance of the Negev loess, how it affects regional soils, and how it relates to other worldwide desert loess regions.
Publications:
Amit, R., Enzel, Y., and Crouvi, O. (2021). Quaternary influx of proximal coarse-grained dust altered circum-Mediterranean soil productivity and impacted early human culture. Geology, 49 (1), 61-65. https://doi.org/10.1130/G47708.1
Crouvi, O., Amit, R., Ben Israel, M., and Enzel, Y. (2017). Chapter 53. Loess in the Negev Desert: Sources, Loessial Soils, Palaeosols, and Palaeoclimatic Implications. In: Y. Enzel, O. Bar-Yosef (Eds.), Quaternary Environments, Climate Change and Humans in the Levant, Cambridge University Press, 471-482. https://doi.org/10.1017/9781316106754.053.
Amit, R., Enzel, Y., Mushkin, A., Gillespie, A. R., Batbaatar, J., Crouvi, O., Vandenberghe, J., and Zhisheng, A. (2014). Linking coarse silt production in Asian sand deserts and Quaternary accretion of the Chinese Loess Plateau. Geology, 42 (1), 23-26. https://doi.org/10.1130/G34857.1
Crouvi, O., Amit, R., Enzel, Y., and Gillespie, A. R. (2010). The role of active sand seas in the formation of desert loess. Quaternary Science Reviews, 29, 2087-2098. https://doi.org/10.1016/j.quascirev.2010.04.026.
Enzel, Y., Amit, R., Crouvi, O., and Porat, N. (2010). Abrasion-derived sediments under intensified winds at the latest Pleistocene leading edge of the advancing Sinai–Negev erg. Quaternary Research, 74, 121-131. doi:10.1016/j.yqres.2010.04.002.
Crouvi, O., Amit, R., Porat, N., Gillespie, A. R., McDonald, E. V., and Enzel, Y. (2009). Significance of primary hilltop loess in reconstructing dust chronology, accretion rates, and sources: An example from the Negev Desert, Israel. Journal of Geophysical Research – Earth Surface, 114, F02017. doi:10.1029/2008JF001083.
Crouvi, O., Amit, R., Enzel, Y., Porat, N., and Sandler, A. (2008). Sand dunes as a major proximal dust source for late Pleistocene loess in the Negev desert, Israel. Quaternary Research, 70, 275-282. doi:10.1016/j.yqres.2008.04.011.
Mineral dust is a key element in controlling physical and biogeochemical exchanges among the atmosphere, land, and ocean. In order to estimate past, current and future impacts of dust on climate and on the environment, quantitative data on the chemical, physical and optical properties of dust are necessary. As these characteristics differ between regions of dust sources, and affect dust emission, the knowledge of the geomorphology of sources of dust is crucial to accurately model the dust cycle.
Frequency of >2600 individual dust emitting events between January 2005 and December 2006 over North Africa (Lavi Bekin et al., 2020)
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The Sahara desert is considered the world’s largest dust source. Field studies and remote sensing techniques were used in the past to identify specific dust sources within this region. However, despite these recent advances, our understanding of dust availability from different geomorphic units and the accurate identification of dust sources over North Africa remains poorly constrained. Our studies contribute data and understandings to this research field.
Publications:
Lavi Bekin, O., Crouvi, O., and Blumberg D. G. (2020). Areal extent of dust emission events and source geomorphology in Northern Africa from MSG SEVIRI data. Remote Sensing, 12, 2775. https://doi.org/10.3390/rs12172775.
Crouvi, O., Schepanski, K., Amit, R., Gillespie, A. R., and Enzel, Y. (2012). Multiple dust sources in the Sahara Desert: The importance of sand dunes. Geophysical Research Letters, 39, L13401. https://doi.org/10.1029/2012GL052145.
Dust storms in the Sonoran Desert are frequent, leading to severe health problems and fatal car accidents. Whereas the synoptic climatology of these dust storms is well known, the geomorphic nature of dust sources in this region, and their response to changing climate, are unknown, for both present and Holocene time. During the Younger Dryas (12.9-11.7 ka) and the early Holocene (11.7-8.2 ka), the climate was characterized by high rainfall amounts; during the Middle Holocene Drought (8.2-4.2 ka), a warmer and drier climate prevailed, followed by wetter climate towards the late Holocene (<4.2 ka). Therefore, this era can serve as an ideal test of the climate - dust emission relationships.
Field photo of a current dust source in the Sonoran Desert (Tau et al., 2021)
Our group works on two main aspects: long-term feedbacks between climate change and dust emission, and dust emission from current dust sources.
Publications:
Tau, G., Crouvi, O., Enzel, Y., Teutsch, N., Ginoux, P., and Rasmussen, C. (2021). Shutting down dust emission during the middle Holocene drought in the Sonoran Desert, Arizona, Geology. https://doi.org/10.1130/G48550.1