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![(a) Map of southern California and adjacent areas, showing patterns of wind direction during ''Santa Ana'' events. Map simplified from model simulations courtesy of Robert Fovell, Department of Atmospheric and Oceanic Sciences, University of California, Los Angeles (http://www.atmos.ucla.edu/$fovell/ASother/ mm5/SantaAna/winds.html). (b) Map of southern California and adjacent areas, showing location of San Clemente Island and dust trap localities [Reheis, 2003, 2006; Reheis et al., 1995, 2002] in the Mojave Desert.](profile/Daniel-Muhs/publication/228491678/figure/fig2/AS:339580948631564@1457973815677/a-Map-of-southern-California-and-adjacent-areas-showing-patterns-of-wind-direction.png)
(a) Map of southern California and adjacent areas, showing patterns of wind direction during ''Santa Ana'' events. Map simplified from model simulations courtesy of Robert Fovell, Department of Atmospheric and Oceanic Sciences, University of California, Los Angeles (http://www.atmos.ucla.edu/$fovell/ASother/ mm5/SantaAna/winds.html). (b) Map of southern California and adjacent areas, showing location of San Clemente Island and dust trap localities [Reheis, 2003, 2006; Reheis et al., 1995, 2002] in the Mojave Desert.
Source publication
1] Islands are natural dust traps, and San Clemente Island, California, is a good example. Soils on marine terraces cut into Miocene andesite on this island are clay-rich Vertisols or Alfisols with vertic properties. These soils are overlain by silt-rich mantles, 5–20 cm thick, that contrast sharply with the underlying clay-rich subsoils. The silt...
Contexts in source publication
Context 1
... Despite the evidence of long-range transport of dust from Asia to the north Pacific Ocean, North America can also be a source of dust during ''Santa Ana'' wind con- ditions, at least to the eastern Pacific Ocean (Figure 4). In contrast to the usual westerly flow of air from the Pacific Ocean to southern California, Santa Ana conditions bring about winds that blow offshore (Figure 5a). These winds develop when there is relatively low pressure over the eastern Pacific Ocean off southern California and a high- pressure cell settles in the Great Basin region of Nevada, Utah, eastern Oregon, and southern Idaho (Figure 4) after the passage of a cold front [Raphael, 2003;Lu et al., 2003]. ...
Context 2
... In order to compare the San Clemente Island samples with the geochemistry of average upper continental crustal material, we used selected samples of Mojave Desert dust, at localities shown in Figure 5b and described by Reheis and Kihl [1995], Reheis et al. [2002], and Reheis [2003,2006]. Mojave Desert dust trap samples were selected to cover a broad range of landscape settings, local bedrock types, and spatial distribution in order to capture the potential range in compositional variation. ...
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Citations
... Rogers et al. (1977), Clinkenbeard and Walawender (1989), and Joo et al. (2016Joo et al. ( , 2018. e Muhs (1983), Muhs, Budahn, Reheis, et al. (2007), Muhs, Budahn, Prospero, and Carey (2007), and Reheis et al. ( , 2002. ...
... Elements considered to be relatively immobile in low-temperature and near-surface environments are commonly utilized in dust and sedimentary rock provenance studies (Bhatia & Crook, 1986;Cullers et al., 1979;McLennan, 1989;Muhs, Budahn, Prospero, & Carey 2007;Muhs, Budahn, Reheis, et al., 2007;Nakai et al., 1993;Olivarez et al., 1991;Reheis et al., 2009;Sun, 2002). We applied a Tau calculation (Equation 1, Anderson et al., 2002;Brantley & Lebedeva, 2011;Brimhall & Dietrich, 1987;Chadwick et al., 1990) normalized to Ti and plotted results on element-depth plots to determine whether immobile elements are enriched or depleted in soil samples compared to weathered bedrock and fresh bedrock. ...
... For example, a τ of −1 indicates 100% loss of the element. We plotted the elements Nb and Zr (immobile and common elements used to indicate allochthonous material), Ta and Th (commonly used in soil provenance, e.g., Muhs, Budahn, Prospero, & Carey, 2007;Muhs, Budahn, Reheis, et al., 2007) and Fe and Al (typically highlight redistribution or illuviation; e.g., Chadwick et al., 1990) normalized to Ti in both AB and PR localities ( Figure 6). Similar to the AB profile, the PR element-depth plot shows enriched values for Th, Ta, Nb, and Al, while Fe has an immobile pattern and Zr is almost completely depleted from the soil samples compared to the bedrock ( Figure 6). ...
The origin and production of silt are key factors in the formation of loess deposits. Although many processes can potentially lead to silt generation, few are known to produce silt in the volumes and particle‐size modes required to form geologically significant loess deposits. Here, we investigate the hypothesis that soil‐associated weathering in tropical and Mediterranean climates can generate abundant in situ silt, and therefore contribute significantly to loess formation throughout geologic time. We utilize granulometric and geochemical data from two granitoid‐hosted soils formed in Puerto Rico (hot‐humid climate) and Southern California (hot‐arid climate) to discern whether the silt + clay fraction (<62.5 μm) is generated from bedrock weathering (autochthonous) or sourced from eolian contributions (allochthonous). Our study demonstrates that the PR soil contains abundant (up to 72%) silt‐ and clay‐sized particles compared to the Southern California soil (<6%). However, the silt fraction of the PR soil is at least partially derived from eolian inputs, and the silt fraction of the Southern California soil is geochemically indistinguishable from allochthonous dust sources. Furthermore, while intense chemical weathering in PR can produce abundant fines, the majority are significantly finer (average mode ∼15 μm) than the modes of most “typical” loess deposits (modes more than 20–30 μm). In contrast, weathering in the Southern California soil produces volumetrically sparse silt. Hence, weathering processes within these two profiles, representing hot‐humid and hot‐dry climates, appear to be ineffectual for producing the volume and size distributions of silt needed to generate significant loess deposits.
... The latter have been identified as the probable source of fine dust originating on the mainland that mantles the surface of San Clemente Island (ca. 93 km from the California mainland) and other California Channel Islands (Muhs 1983;Muhs et al. 2007;Muhs 2013;Jardine et al. 2021). Seeds germinate readily, and seedlings are tiny and grow slowly. ...
Dudleya brittonii Johans. sensu lato (Crassulaceae) es una planta en roseta de gran tamaño endémica de la costa noroeste de Baja California, México que históricamente ha incluido las formas glauca y verde. En este estudio determinamos que las formas verdes son distintas a D. brittonii y exhiben una variabilidad morfológica que justifican su reconocimiento taxonómico a nivel específico y subespecífico. Reconocemos y describimos tres nuevos taxa, D. josedelgadilloi Mulroy, Guilliams, & Hasenstab sp. nov., D. reidmoranii Mulroy, Guilliams, & Hasenstab sp. nov. subsp. reidmoranii, y D. reidmoranii subsp. cascada Mulroy, Guilliams, & Hasenstab subsp. nov., basados en numerosas mediciones de especímenes frescos en campo que fueron analizadas con morfometría cuantitativa y estadística multivariada. Estas entidades han sido consideradas por mucho tiempo como parte de D. brittonii, sin embargo no fueron incluidas en la descripción original (Johansen 1933). Demostramos también un evento de desplazamiento de caracteres (divergencia en simpatría) relacionado con un desfase en los tiempos de floración entre D. brittonii (glauca) y D. reidmoranii subsp. reidmoranii (verde). Poblaciones de D. reidmoranii subsp. reidmoranii que co-ocurren con D. brittonii muestran un retraso de 6 semanas a tres meses en el promedio de inicio y término de floración con respecto a poblaciones de D. reidmoranii subsp. reidmoranii cercanas que no co-ocurren con D. brittonii. Este desfase en los tiempos de floración podría representar un mecanismo de aislamiento precigótico importante entre estas plantas que de otra manera son altamente interfértiles. Un estudio preliminar de cultivo de D. reidmoranii subsp. reidmoranii (verde) creciendo en presencia y ausencia de D. brittonii (glauca) mostró el mismo patrón en los tiempos de floración observado en el campo, lo que sugiere que este patrón tiene una base genética. El desfase temporal en D. reidmoranii subsp. reidmoranii y subsp. cascada resulta en una floración durante el verano en estos taxa, mientras que D. josedelgadilloi y D. brittonii tienen su floración en primavera, lo cual podría atraer a un diferentes tipos de de polinizadores principales (e.g., colibríes vs. insectos). Describimos adaptaciones a polinización por colibríes, como infloresecencias y flores pendientes, asociadas a la floración durante el verano en las dos subespecies de D. reidmoranii, en contraste con adaptaciones que favorecen polinización por insectos durante la primavera en D. brittonii y D. josedelgadilloi. El reconocimiento de estas novedades taxonómicas en una región relativamente bien documentada confirma la extraordinaria diversidad y alto endemismo de la flora asociada al clima Mediterráneo del noroeste de Baja California. La velocidad de la expansión de las actividades humanas en la región resalta la urgencia de aumentar la exploración botánica y continuar la implementación de medidas de conservación antes de que la pérdida de biodiversidad sea mayor.
... This REE pattern is typical of sediments derived from UCC and loess. Furthermore, rare earth element ratios (LaN/YbN and GdN/YbN) along with δEu parameters can reflect the evolution trend and source of sediments [24,50] ...
... This REE pattern is typical of sediments derived from UCC and loess. Furthermore, rare earth element ratios (La N /Yb N and Gd N /Yb N ) along with δEu parameters can reflect the evolution trend and source of sediments [24,50]. Post-Archean sedimentary rocks usually have REE composition values of La N /Yb N <15 [43] while Chinese and Alaskan loesses have values ranging from 7-10 [26]. ...
Clay-rich red soil profiles developed in different lithologies in Indonesia were assessed using geochemical evidence, the migration coefficient and elemental ratios. Our study aimed to ascertain the source of red soil materials and to investigate the elemental behavior in tropical soils. The results indicate carbonate profiles were derived from in situ weathering, while basalt profiles, even though having close affinity to their bedrock, also showed the contribution of external materials. Elemental behavior was dynamic with carbonate profiles indicating relatively constant depletion and even distribution. Basalt profiles indicated uneven distribution with enrichment and depletion. The variation in elemental behavior was linked to difference in lithologies, age and physiochemical conditions. Our findings support evidence of both residual and multiple source parent materials in red soil formation and provide insights into elemental behavior during weathering, while highlighting the influence of external materials’ contribution in deeply weathered tropical soils.
... African dust from the Saharan and Sahel 133 deserts contains mostly fine-silt sized quartz (4 -20 μm) and clay-sized (<4 μm) mica; 30 -50% 134 of the dust is <2.5 μm (e.g., Prospero et al.,1970;Glaccum and Prospero, 1980). Volcanoes Rogers et al. (1977); Clinkenbeard and Walawender (1989); Joo et al. (2016Joo et al. ( , 2018 5 Muhs (1983); Muhs et al. (2007aMuhs et al. ( , 2007b; Reheis et al. ( , 2002 manuscript submitted to replace this text with name of AGU journal depicting typical crystal size, weathering, and mineralogy of the La-Posta tonalite from Anza 166 Borrego (XPL); F) photomicrograph from E in PPL. (Fig. 4). The mud fraction is predominantly coarse silt (32.8 -38.2%) with lesser 230 amounts of medium (25.3 -30.1%) and fine silt (14.9 -18.4%), and minor very-fine silt (6.9 -231 8.6%) and clay (6.2 -8.3% ; Table 2). ...
The origin and production of silt are key factors in the formation of loess deposits. Although many processes can potentially lead to silt generation, few are known to produce silt in the volumes and particle-size modes required to form geologically significant loess deposits. Here we investigate the hypothesis that pedogenic weathering in tropical and Mediterranean climates can generate abundant in situ silt, and therefore contribute significantly to loess formation throughout geologic time. We utilize granulometric and geochemical data from soils formed in Puerto Rico (hot-humid) and Southern California (hot-arid) to discern whether the mud fraction (<62.5 μm) is generated from bedrock (autochthonous) or sourced from eolian contributions (allochthonous). Our study demonstrates that the Puerto Rico soil contains abundant (up to 72%) silt- and clay-sized grains compared to the Anza Borrego soil (<6%). However, the silt fraction of the Puerto Rico soil is at least partially derived from eolian inputs, and the silt fraction of the Anza Borrego soil is geochemically indistinguishable from allochthonous dust sources. Furthermore, while intense chemical weathering in a tropical climate can produce abundant fines, the majority are significantly finer (average mode ~15 µm) than the modes of most “typical” loess deposits (modes more than 20 – 30 µm). In contrast, weathering in Mediterranean climates produces volumetrically sparse silt. Hence, pedogenic weathering in hot climates appears to be ineffectual for producing the volume and size distributions of silt-sized material needed to generate significant loess deposits.
... The measurement of trace elements and REEs is prepared for tracing the provenance of the Xiashu loess and Xuancheng loess. Based on their high stability within the surface environment, the high-field strength elements Ti, Sc, Ta, Th, and Nb; transition trace element Cr; and REEs are often used as tracers of sediment provenance (Muhs et al., 2007a(Muhs et al., , 2007b(Muhs et al., , 2016Hu and Yang, 2016;Han et al., 2019;Wu et al., 2021a). ...
... Therefore, the geochemical compositions of the loess in southern China have been altered by chemical weathering. Generally, the influence of chemical weathering on source rock compositions can be reduced by using the ratios of immobile elements (Yang et al., 2004;Muhs et al., 2007aMuhs et al., , 2007bWu et al., 2021a). Because the chemical stability of Sr is less than that of Rb, Rb/Sr ratio has been viewed as an indicator of chemical weathering intensity and it has been widely applied in studies of the paleoclimatic evolution of loess (Chen et al., 1999;Zhang et al., 2007). ...
The loess-paleosol sequences of southern China are valuable paleoclimatic archives since the Middle Pleistocene, on the regional and global scales. Knowledge of loess provenance can shed light on dust transport and the development of paleoclimatic proxies for loess deposits. However, there is a research gap regarding the provenance of the Oldest (~0.9 Ma) Xiashu loess near the Yangtze River valley. The precise source area of the
Xuancheng loess in southern China remains to be unidentified. In this study, we used elemental geochemistry and detrital zircon U–Pb ages to identify the sources of the Oldest Xiashu loess and Xuancheng loess in southern China. The Oldest Xiashu loess is dominantly derived from Yangtze River sediments, and part of its fine-grained dust component originates from the arid regions of Central Asia or northern China. The elemental compositions
of the size-fractionated silicates and detrital zircon U–Pb ages of the Xuancheng loess are like those of the Shuiyang River sediments in the Xuancheng region. These results demonstrate that the Xuancheng loess is mainly the product of local dust activity in the Xuancheng regions, and thus that the Xiashu and Xuancheng loess are the products of independent dust transport processes. This spatial differentiation of loess provenance may be a widespread phenomenon in southern China, and consequently, the grain size compositions of the various loess sections in southern China cannot be used to recover paleo-wind directions on a regional scale. Overall, our study shows that when the grain size compositions from the southern China loess are used to reconstruct East Asian winter monsoon intensity, the signals from local wind fields should first be removed.
... Characterization of dust emission, transport, and deposition across the Sierra Nevada has been investigated using various data. Isotopic analyses (i.e., concentrations of Pb and Nd) are widely used to distinguish and quantify the respective contribution of dust emission from local (dried Owens Lake), regional (Central Valley and the Mojave Desert), and global sources (Asia and Africa) on the dust deposition on the mountain (Muhs et al., 2007;Jardine et al., 2021;Aciego et al., 2017;Aarons et al., 2019). Their source attribution has been generally confirmed by the analyses of dust particle size and composition (Creamean et al., 2014(Creamean et al., , 2013Reheis and Kihl, 1995). ...
Mineral dust contributes up to one-half of surface aerosol loading in spring over the southwestern United States, posing an environmental challenge that threatens human health and the ecosystem. Using self-organizing map (SOM) analysis with dust deposition and flux data from WRF-Chem and Modern-Era Retrospective analysis for Research and Applications, Version 2 (MERRA-2), we identify four typical dust transport patterns across the Sierra Nevada, associated with the mesoscale winds, Sierra barrier jet (SBJ), North Pacific High (NPH), and long-range cross-Pacific westerlies, respectively. We find that dust emitted from the Central Valley is persistently transported eastward, while dust from the Mojave Desert and Great Basin influences the Sierra Nevada during mesoscale transport occurring mostly in winter and early spring. Asian dust reaching the mountain range comes either from the west through straight isobars (cross-Pacific transport) or from the north in the presence of the NPH. Extensive dust depositions are found on the west slope of the mountain, contributed by Central Valley emissions and cross-Pacific remote transport. In particular, the SBJ-related transport produces deposition through landfalling atmospheric rivers, whose frequency might increase in a warming climate.
... A third possibility is that the large barite microcrystals might reach our site via dust transport from the Southwestern deserts; Santa Ana winds transport large amounts of dust and soot offshore into the Eastern Pacific (e.g., Jardine et al. 2021). This possible origin is made more plausible by observations that the large barite microcrystals are on the small end of the grain-size spectrum for loess deposited on the Channel Islands, where the mean grain size is about 35 μm (Muhls et al. 2007). In addition, authigenic barite is observed in paleosols in Southern Nevada Robins et al. 2012). ...
The accumulation rate of authigenic barite (BaSO4) in marine sediments is a promising proxy for reconstructing marine export production, but many aspects of barite precipitation and dissolution in the water column remain unknown. Here, we collected, imaged, and quantitatively analyzed 5481 barite microcrystals in bottle casts from the Eastern Pacific water column to gain a better understanding of in situ barite dynamics. Barite crystal abundance increases rapidly between the surface and 500 m in depth and then declines to predominantly low abundances below ~ 1000 m. The falloff in barite abundance between the oxygen minimum zone (OMZ) and the ocean interior suggests 60% ± 20% loss of barite by dissolution, nearly all of which is complete by water depths of 1000 m. However, there are occasional samples, as deep as 1250 m, with unusually high barite abundance that may represent marine snow deposition events. We found that microcrystals associated with organic matter substrates were smaller and less solid than free crystals, which suggests ongoing barite precipitation toward larger, more regularly shaped microcrystals within organic matter aggregates. Trends in barite microcrystal size with depth suggest that organic matter aggregates also play a role in shielding barite microcrystals from dissolution. In addition, our extensive data set raises new questions regarding marine barite nucleation and spatial heterogeneity. By helping bridge the gap between hypothesized barite dynamics and in situ observations of barite microcrystals, this study advances our understanding of water column Ba processes and the utility of sediment barite as an export production proxy.
... To decipher better the climate record imprinted on sediment cores we need to 74 distinguish between different terrigenous sources and different modes of delivery to the ocean. 75 The Channel Island silt mantles are described by Muhs et al. (2007Muhs et al. ( , 2008 as massive, silt-114 rich horizons that resemble loess, or aeolian silt, ranging from 2-30cm thick, which contrast 115 sharply with the lower subsoil. Precise dating of the silt mantles on San Clemente is difficult but 116 they drape the youngest marine terrace which gives a maximum age of ~80 ka, although they 117 could possibly be younger than 3 ka, based upon a single radiocarbon data point (Muhs et al., 118 2007). ...
... Precise dating of the silt mantles on San Clemente is difficult but 116 they drape the youngest marine terrace which gives a maximum age of ~80 ka, although they 117 could possibly be younger than 3 ka, based upon a single radiocarbon data point (Muhs et al., 118 2007). Mineralogical, geochemical and grain size profile measurements (Muhs et al., 2007;119 Muhs et al., 2008) suggest that the dominant source of the island silt mantles is from the North 120 ...
... American continent (not from the island bedrock), implying a windblown origin, but the influence 121 of an Asian dust source (Muhs et al., 2007) and perhaps the Sahara cannot be ruled out. Muhs 122 et al. (2007) and Muhs et al. (2008) also report that the geochemical fingerprint of the fine 123 fraction (< 2 µm; clay) in these silt mantles differs slightly from that of the coarser (2-53 µm; silt 124 sized) fraction of the samples, hinting that the silts and clays within the silt mantles may have 125 different provenances. ...
Climate projections for the North American Southwest (NASW) predict an increasing frequency and duration of droughts over the 21st century in response to human-induced warming, with potentially severe economic and social consequences. The geological record provides a way to contextualise this prediction because of the past occurrence of abrupt hemispheric warming events and sustained intervals of atmospheric carbon dioxide loading equivalent to those projected for AD 2100 (between ∼500 and 900 ppmv). Yet, terrestrial climate archives are typically too short and incomplete to provide a full record of these events. In principle, drill cores from deep sea sediments in the eastern Pacific Ocean can be used to overcome this problem because they contain long records of continental dust and distal riverine-supplied sediments from North America. Yet our limited understanding of the provenance and transport pathways of these sediments impedes use of these marine archives for this purpose. Here we present radiogenic isotope data (Sr, Nd and Pb) from known NASW dust-producing hot spots – playa lakes in the Mojave Desert, Quaternary silts mantling the California Channel Islands and the terrigenous fraction from marine sediments of the eastern Pacific Ocean, supported by new maps of bedrock isotopic composition in the NASW. We use these and published data sets to infer the origin of playa lake silts in the Mojave Desert and the source of windblown sediments to the California Channel Islands and nearby ocean basins. Our Results rule out a significant contribution from the distal tails of either the Pacific Asian dust plume or the North African dust plume to the Quaternary Channel Island silt mantles, corroborating the suggestion that they are aeolian in origin and sourced from the NASW on the Santa Ana winds. We identify the Outer California Borderland basins as an attractive proposition for studying past dust flux and palaeoaridity in the North American Southwest.
... Data on the frequency and rates of dust deposition suggest that the rates of aeolian accumulation may be of a similar order of magnitude as rates of fluvial erosion (Goudie 1978;Wells et al. 2007). Although dust is a result of soil erosion from some areas, it is also a major contributor to soil in other areas, as noted in the dust deposition in Oman (Badawy et al. 1992); Riyadh (Al-Tayeb and Jarrar 1993); Australia, New Zeeland (Marx et al. 2005); Canary Islands (Moreno et al. 2006); Florida, Bahamas, Barbados (Muhs et al. 2007); and Spain (Querol et al. 2007). "Desert areas are important sources of mineral dust to the atmosphere, which upon deposition, can influence oceanic and terrestrial biochemical cycles and affect forest productivity" (Avila and Penuelas 1999). ...
Brunauer, Emmett, and Teller (BET) test were applied to dust samples in which samples (BET) surface area is highly related to the roundness of dust particles. The higher angularity and low roundness of the dust particles show a higher (BET) surface area. The roundness is also related to the particlesize distribution and mineralogical composition.
The electrical conductivity test relates very well with the chemical and physical properties of dust samples in the transmission of an electrical current.
The organic matter content was measured using the ignition method and the pH of the samples was recorded.
Maps of the distribution of high and low BET concentrations, electrical conductivity EC, organic matter content, pH.
... Data on the frequency and rates of dust deposition suggest that the rates of aeolian accumulation may be of a similar order of magnitude as rates of fluvial erosion (Goudie 1978;Wells et al. 2007). Although dust is a result of soil erosion from some areas, it is also a major contributor to soil in other areas, as noted in the dust deposition in Oman (Badawy et al. 1992); Riyadh (Al-Tayeb and Jarrar 1993); Australia, New Zeeland (Marx et al. 2005); Canary Islands (Moreno et al. 2006); Florida, Bahamas, Barbados (Muhs et al. 2007); and Spain (Querol et al. 2007). "Desert areas are important sources of mineral dust to the atmosphere, which upon deposition, can influence oceanic and terrestrial biochemical cycles and affect forest productivity" (Avila and Penuelas 1999). ...
A dust storm is meteorologically defined whenever visibility is less than 1,000 meters (Al-Kulaib 1990). Al-Dousari (2009) lists Kuwait as having one of the highest dust precipitation rates in the world. Safar (1980) states that the annual average number of dusty days due to dust storms or rising dust or suspended dust in Kuwait is 255.4. Forty-seven sampling sites representing all the geomorphological and sedimentological provinces in Kuwait were selected for the installation of dust traps to measure the average annual amount of deposited dust during 2009–2010 and 2010–2011 in tons.km ⁻² .
