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A multi-proxy record of Holocene and late-Pleistocene aeolian mineral dust is reconstructed using a combination of geochemical (trace elements), mineralogical and grain-size analyses on cores from the Hani peatland in north-eastern (NE) China. The dust record displays a sharp increase in dust deposition during the late Holocene in comparison to the rest of the Holocene. This trend is in line with climatic records from the Chinese dust source regions and their downwind areas, which generally show an increase in aridity and aeolian activity during the late Holocene. The larger part of the Chinese dust source regions experienced a gradual increase in effective moisture and vegetation cover reaching maxima during the middle Holocene (6.0–8.0 kyr cal. BP) co-occurring with the minima in dust deposition in Hani. These changes in the dust source regions are likely to have been modulated by the variations in the East Asian summer monsoon (EASM), which is the principal mechanism controlling climate in the region. The intensified EASM during the middle Holocene is also likely to have resulted in a sediment recharge at the margin of the Chinese drylands providing additional material and enhancing the atmospheric dust load after the late-Holocene aridification of the region. Combined together, these changes promoted a remobilization of dust sources increasing the amount of material available for transport by the East Asian winter monsoon (EAWM) and the Westerlies. Human activities might also have played a role in the increased dust emissions during the late Holocene, but further research is needed to assess the extent of those impacts at a regional level. [ABSTRACT FROM AUTHOR]

High-resolution studies of palaeorecords located closer to the dust source areas of South America are relevant for increasing the knowledge on past climatic conditions in the Southern Hemisphere. In this sense, the Pampean loess archives can offer explicit records of dust source, transport, and deposition in the region, providing new insights which may be used to better understand the role of dust in future climate change scenarios. In this work, we studied a loess sequence located at the westernmost Pampean Plain. The studied sequence covers a span of time from the late Marine Isotope Stage (MIS 2) period up to the early Holocene. Loess samples from this record have two grain-size populations, indicating more than one dust source area. The dominance of a coarse-silt subpopulation during the transition from the late MIS 2 to the early Holocene suggests that proximal dust sources were dominant at that time. Two of the most proximal dust sources were analyzed as probable contributors to the Lozada site: sediments derived from the Eastern Pampean Ranges and sediments derived from the shorelines of the Mar Chiquita Lake. The geochemical data suggest that neither area was a significant dust source to the eastern Pampean Plain during the studied interval. Instead, our geochemical data suggest a dominant supply from a southern and relatively closer area, linked to the foothills of the Andes, and the increased activation during the early Holocene of a more distant source to the north in the Puna region, which contributed finer loess. [ABSTRACT FROM AUTHOR]

Mineral aerosols profoundly impact global climate. Modeling of the dust cycle is the main tool used to gauge this effect. However, the scarcity of in situ modern dust flux measurements is the main reason why validation of existing models is hampered. We present the first long-term (14-year) record of dust flux in the Pampas, southern South America, home to the largest loess deposit in the Southern Hemisphere. Measured 14-year mean deposition (40 g m−2 year−1) and horizontal (362 g m−2 year−1) fluxes imply that current models underestimate the power of the central Pampas as a dust sink. Based on cross-spectral analysis, both wet and, to a lesser extent, dry deposition are found to play significant roles in atmospheric dust extraction. Dust is sourced regionally from the South American Arid Diagonal and from the shores of Mar Chiquita lake (~260 km), which we find to be the main contributor of dust particles >30 µm. Cross-spectral and satellite image analyses show that surface wind speed and precipitation at the Puna-Altiplano Plateau are controlling factors for horizontal dust flux in the Pampas. El Niño Southern Oscillation probably plays a role in controlling interannual horizontal dust flux periodicities. Finally, preliminary comparisons between modern vertical dust fluxes and loess accumulation rates point to the Pampas as a more powerful dust sink during the last deglaciation and Antarctic Cold Reversal (18–12.5 ka). [ABSTRACT FROM AUTHOR]

The Puna-Altiplano plateau represents a regionally significant dust source, which is critically located at the nexus between the tropical and sub-polar synoptic systems that dominate the South American climate. Dust emissions in this region would therefore be expected to be sensitive to changes in these systems, in particular the strength and position of the South American Summer Monsoon (SASM). Here, we present a late-Holocene multi-proxy study where changes in dust flux, reconstructed from a high-altitude peat mire, are examined in light of climate variability and human impacts. Results show that for most the 4300 cal. yr BP record, dust flux sensitively tracked changes in SASM activity. Prior to 2600 cal. yr BP relatively high dust flux implies dry conditions prevailed across the Puna-Altiplao in association with reduced SASM activity. The chemistry of dust deposited at this time matched the large endorheic basins on the Puna, which host ephemeral lakes and terminal fans, indicating these were actively supplying dust to the airstream. After 2600 cal. yr BP, SASM activity increased while dust flux decreased and the dust chemistry changed, collectively implying the shutting down of the Puna-Altiplano as a significant dust source. Dust flux increased after 1000 cal. yr BP during the 'Medieval Warm Period', associated with a return to drier conditions and reactivation of dust sources across the endorheic basins of the Puna. Natural variability in dust flux was dwarfed, however, by the very significant increase in flux after 400 cal. yr BP following Spanish Colonisation and associated changing landuse practices. This finding attests to the globally significant role of humans on dust emissions. [ABSTRACT FROM AUTHOR]

Atmospheric dust plays an important role in terrestrial and marine ecosystems, particularly those that are nutrient limited. Despite that most dust originates from arid and semi-arid regions, recent research has shown that past dust events may have been involved in boosting productivity in nutrient-poor peatlands. We investigated dust deposition in a mid-latitude, raised bog, which is surrounded by a complex geology (paragneiss/schist, granite, quartzite and granodiorite). As proxies for dust fluxes, we used accumulation rates of trace (Ti, Zr, Rb, Sr and Y) as well as major (K and Ca) lithogenic elements. The oldest, largest dust deposition event occurred between ~8.6 and ~7.4 ka BP, peaking at ~8.1 ka BP (most probably the 8.2 ka BP event). The event had a large impact on the evolution of the mire, which subsequently transitioned from a fen into a raised bog in ~1500 years. From ~6.7 to ~4.0 ka BP, fluxes were very low, coeval with mid-Holocene forest stability and maximum extent. In the late Holocene, after ~4.0 ka BP, dust events became more prevalent with relatively major deposition at ~3.2–2.5, ~1.4 ka BP and ~0.35–0.05 ka BP, and minor peaks at ~4.0–3.7, ~1.7, ~1.10–0.95 ka BP and ~0.74–0.58 ka BP. Strontium fluxes display a similar pattern between ~11 and ~6.7 ka BP but then became decoupled from the other elements from the mid Holocene onwards. This seems to be a specific signal of the granodiorite batholith, which has an Sr anomaly. The reconstructed variations in dust fluxes bear a strong climatic imprint, probably related to storminess controlled by North Atlantic Oscillation conditions. Complex interactions also arise because of increased pressure from human activities. [ABSTRACT FROM AUTHOR]

In this paper, we provide a comprehensive overview of the state-of-knowledge of dust flux and variability in time and space in different sectors of East Antarctica during the Holocene. By integrating the literature data with new evidences, we discuss the dust flux and grain-size variability during the current interglacial and its provenance in the innermost part of the East Antarctic plateau as well as in peripheral regions located close to the Transantarctic Mountains. The local importance of aeolian mineral dust aerosol deflated from low-elevation areas of peripheral East Antarctica is also discussed in the light of new data from several coastal, low-elevation sites. [ABSTRACT FROM AUTHOR]

Millions of people in the arid Southwest United States rely on snow-fed Colorado River water. Dust deposition on snow accelerates snowmelt, posing a challenge for water managers who also need to grapple with increased likelihood of drought due to climate change. Dust production is thought to increase during drought, but the impact of drought on dust deposition is unclear. To answer this question, total dust mass accumulation rate (DMAR) reconstructions were developed from sediment cores from three lakes in the San Juan Mountains, Colorado, spanning the last ~15,000 years. Monte-Carlo end-member analysis of particle size and elemental composition, which incorporates measurement and model uncertainties, was combined with age uncertainty to estimate DMAR for each lake. We also synthesize the records providing the first Holocene DMAR reconstruction for the region. The records show little relation between periods of frequent and severe drought (e.g. during medieval megadroughts) and periods of higher DMAR, although there is considerable uncertainty at short timescales. We find instead that sediment availability, modulated by natural or human-mediated geomorphic processes that generate sediment, and transport mechanisms are the key drivers. DMAR was highest during the Late Glacial-Interglacial Transition (LGIT, 15–11 kyr BP) and in the last 250 years, periods when sediment availability was enhanced. DMAR increased by 60% (16–85% 75% highest density region range) compared with the late-Holocene baseline starting in the 1770s and peaking in the 1840s, associated with the intensification of human activities. Human-induced dustiness also represents the highest interval of dust deposition in the last 11,000 years. Our results demonstrate that although the Colorado Plateau is naturally prone to dustiness, drought is a secondary driver of dust accumulation in the mountains. This suggests that land-use management decisions aimed at reducing land disturbance can mitigate future dust accumulation, despite projected increases in regional aridity. [ABSTRACT FROM AUTHOR]

In barren alpine catchments of the Colorado Rocky Mountains, microorganisms are typically carbon (C)-limited, and C-limitation can influence critical heterotrophic processes, such as denitrification. In these remote locations, organic matter deposited during dust intrusion events and other forms of aerosol deposition may be an important C source for heterotrophs; however, little is known regarding the biodegradability of atmospherically deposited organic matter. This study evaluated the extent to which organic matter in Holocene dust and other types of atmospheric deposition in the Colorado Rocky Mountains could support metabolic activity and be biodegraded by alpine bacteria. Microplate bioassays revealed that all atmospheric deposition samples were able to activate microbial metabolism. Decreases in dissolved organic carbon (DOC) concentrations over time in biodegradability incubations reflect the presence of two pools of dissolved organic matter (DOM), a rapidly decaying pool with rate constants in the range of 0.0130–0.039 d–1 and a slowly decaying pool with rate constants in the range of 0.0008–0.009 d–1. Changes in the fluorescence excitation-emission matrix of solutions evaluated over time indicated a transformation of organic matter by bacteria resulting in a more humic-like fluorescence signature. Fluorescence spectroscopic analyses, therefore, suggest that the degradation of non-fluorescent DOM in glutamate and dust-derived C sources by bacteria results in the production of fluorescent DOM. [ABSTRACT FROM AUTHOR]

This article is a brief introduction to the Special Issue on Holocene Dust Dynamics, which brings together recent research on a key aspect of the Earth's changing climate through its effects on radiative balance, cloud cover and biogeochemical cycles. The aim of the Special Issue is to contribute to a better understanding of the role of dust aerosols by analysing the evolution and climatic impact of atmospheric dust over long and short timescales within the Holocene. Here, we introduce the rationale behind the Special Issue and the eight research papers, which include long-term records of dust deposition from different types of natural archive (e.g. peatlands, ice, loess and lake sediments) as well as present-day multi-annual dust trap records and process studies from various climatic regimes that have global implications. [ABSTRACT FROM AUTHOR]

Southwest Africa is an important region for paleo-climatic studies, being influenced by both tropical and temperate climate systems and thus reflecting the interplay of variable controls. The aim of this study was to unravel the interaction of sea-surface temperature (SST) changes in the southernmost Benguela upwelling system with precipitation changes in South Africa's winter rainfall zone (WRZ) during the late Holocene. Therefore, a marine sediment core from the southernmost Benguela upwelling system was investigated to reconstruct climate changes in this region for the past ~2000 years. Grain size and geochemical analyses were conducted to reconstruct changes in fluvial sediment discharge and weathering intensity, while SST changes were estimated using alkenone paleo-thermometry. Results show that the southernmost Benguela behaves distinctly in comparison with the rest of the Benguela system reflecting amplified SST changes. Decreasing SSTs accompanied increasing river discharge during times of increased precipitation in the WRZ, reflecting northerly shifted westerly winds during austral winter. We infer a control of past SST changes by processes not analogous to modern processes driving seasonal SST changes by changes through upwelling intensity. The findings suggest that late-Holocene SST changes in the southernmost Benguela upwelling system and the precipitation in the WRZ were both driven by latitudinal shifts of the austral westerly wind belt and associated changes in advection of cold sub-Antarctic waters and/or changes in Agulhas leakage of warm Indian Ocean waters. [ABSTRACT FROM AUTHOR]