Using non-combustible residual particles as a proxy for mineral dust deposition to estimate its contribution to light absorption in the 300-year Holtedahlfonna ice core

<p>Mineral dust accumulation is often causally associated with aridity, with higher dust deposition rates are assumed to reflect increasing magnitude of aridity. However, the relation between dust deposition and aridity is not straightforward; grain sizes play a crucial role in processes associated with mineral dust generation, transportation and deposition in sedimentary settings.</p><p>In this study, we apply grain-size analyses in six well-studied cores (spanning the late Holocene) previously collected from alpine lake sites distributed across the arid and semi-arid regions of west, southwest, and the Great Plains of North America. Previous work with these cores has demonstrated that the lake sediments are predominantly detrital, windblown particles and little to no impact of fluvial proceeses . We find that the most commonly occurring grain sizes are a fine fraction (typically <4 microns, which is easily lofted and transported long distances) and a coarse fraction (typically >25 microns and in some cases with a distinct peak at 100 microns, both of which are are too large to be carried long distances and suggest short distance transportation). We used grain size separation techniques to separate the two size fractions and geochemically fingerprinted those from three sites.</p><p>We find that more rapid accumulation of the coarser coarser-grain size fractions occurred during wetter intervals in the Holocene. Furthermore, the geochemistry of the coarse fractions indicates regional rather than local sourcing of the material from bedrock weathering. We do not find any clear relationships between the fine fraction and aridity patterns, nor a clear source region for this material.</p><p>We hypothesize that the increase in coarser dust deposition during wetter intervals is related to either intensification of land-use patterns associated with agriculture and/or to episodically strong winds. Warmer and wetter intervals in the areas under consideration have been associated with intensified cyclogenesis. Our study demonstrates the critical need to incorporate grain-size analysis as well as geochemical fingerprinting of the different size fractions in interpreting mineral dust record.</p><p> </p><p>Acknowledgement: James Sickman, Jason Neff (for sharing samples), Jacob Ashford, Tyler Vollmer, Audriana Pollen, Alejandra Pedrazza, (for assistance with analyses and archival visits), John Morton, Wendy Freeman (for assisting students in the laboratory), Aradhna Tripati and Juan Lora (for assisting with data interpretation).</p><p> </p>

Mineral dust aerosols represent an active component of the Earth’s climate system, by interacting with radiation directly, and by modifying clouds and biogeochemistry. Mineral dust from polar ice cores over the last million years can be used as paleoclimate proxy, and provide unique information about climate variability, as changes in dust deposition at the core sites can be due to changes in sources, transport and/or deposition locally. Here we present results from a study based on climate model simulations using the Community Climate System Model. The focus of this work is to analyze simulated differences in the dust concentration, size distribution and sources in current climate conditions and during the Last Glacial Maximum at specific ice core locations in Antarctica, and compare with available paleodata. Model results suggest that South America is the most important source for dust deposited in Antarctica in current climate, but Australia is also a major contributor and there is spatial variability in the relative importance of the major dust sources. During the Last Glacial Maximum the dominant source in the model was South America, because of the increased activity of glaciogenic dust sources in Southern Patagonia-Tierra del Fuego and the Southernmost Pampas regions, as well as an increase in transport efficiency southward. Dust emitted from the Southern Hemisphere dust source areas usually follow zonal patterns, but southward flow towards Antarctica is located in specific areas characterized by southward displacement of air masses. Observations and model results consistently suggest a spatially variable shift in dust particle sizes. This is due to a combination of relatively reduced en route wet removal favouring a generalized shift towards smaller particles, and on the other hand to an enhanced relative contribution of dry coarse particle deposition in the Last Glacial Maximum.

A model‐based investigation of the transport, distribution and deposition of mineral dust in the Southern Hemisphere (SH) is performed by using the GFDL Atmospheric Model (AM2). The study represents an attempt to quantify the contribution of the major sources by tagging dust based on its origin. We evaluate the contribution of each source to the emission, distribution, mass burden and deposition of dust in the Southern Ocean and Antarctica, and show that each source produces distinctive meridional transport, vertical distribution, and deposition patterns. The dust in SH originates primarily from Australia (120 Tg a−1), Patagonia (38 Tg a−1) and the inter‐hemispheric transport from Northern Hemisphere (31 Tg a−1). A small fraction of it (7 Tg a−1) is transported and deposited in the Southern Ocean and Antarctica, where dust from South America, Australia, and Northern Hemisphere are essentially located in the boundary layer, mid‐troposphere, and upper‐troposphere, respectively. These three sources contribute to nearly all the dust burden in the Southern Ocean and Antarctica. South America and Australia are the main sources of the dust deposition, but they differ zonally, with each one dominating half of a hemisphere along 120°E–60°W: the half comprising the Atlantic and Indian oceans in the case of the South American dust and the Pacific half in the case of the Australian dust. Our study also indicates a potentially important role of Northern Hemisphere dust, as it appears to be a significant part of the dust burden but contributing little to the dust deposition in Antarctica.

Dispersion and deposition of mineral dust from natural or anthropogenic sources such as proglacial rivers, mines and haul roads can have both positive and negative effects on the environment, depending on the geochemical and mineralogical composition of the dust. Some elements in dust may act as nutrients for, for example, plants, lichens and soil communities, while other elements may act as pollutants with negative impacts on growth or reproduction or cause diseases in animals and plants.To support the sustainable development of environmentally safe mining in sensitive Arctic land areas and reduce airborne environmental pollution, an improved understanding of processes leading to the dispersion of mineral dust in a changing Arctic is needed. This involves improved methods for monitoring dust emissions and dust deposition in a cold environment as well as analytical tools and methods to source trace and differentiate between natural and mining related dust. Accurate identification of individual dust sources subsequently makes it possible to mitigate emissions and target the regulation of mining activities towards these sources.In this study, we present preliminary results from two new arctic dust monitoring stations in West Greenland and Svalbard. In Kangerlussuaq, West Greenland, mineral dust has been collected using a wide array of passive and active dust samplers, including a continuously operated high volume dust sampler at a weekly sampling frequency over 2022/2023. In Svalbard, mineral dust has been collected in Adventdalen using passive dust collectors in a transect along the haul road to the active coal mines. Samples have been collected on a weekly sampling frequency in the period September to November 2023 to investigate the temporal and spatial variations in dust deposition rates, as well as the impact of haul road traffic relative to the natural dust emissions and depositions.

Black carbon (BC) is the most effective insoluble light-absorbing particulate (ILAP), which can strongly absorb solar radiation at visible wavelengths. Once BC is deposited in snow via dry or wet process, even a small amount of BC could significantly decrease snow albedo, enhance absorption of solar radiation, accelerate snow melting, and cause climate feedback. BC is considered the second most important component next to CO2 in terms of global warming. Similarly, mineral dust (MD) is another type of ILAP. So far, little attention has been paid to quantitative measurements of BC and MD deposition on snow surface in the midlatitudes of East Asia, especially over northern China. In this paper, we focus on reviewing several experiments performed for collecting and measuring scavenging BC and MD in the high Asian glaciers over the mount’ range (such as the Himalayas) and in seasonal snow over northern China. Results from the surveyed literature indicate that the absorption of ILAP in seasonal snow is dominated by MD in the Qilian Mount’s and by local soil dust in the Inner Mongolian region close to dust sources. The detection of BC in snow and ice cores using modern techniques has a large bias and uncert’ty when the snow sample is mixed with MD. Evidence also indicates that the reduction of snow albedo by BC and MD perturbations can significantly increase the net surface solar radiation, cause surface air temperature to rise, reduce snow accumulation, and accelerate snow melting.

<div><span>Mineral dust and black carbon are potent drivers of the snow cover evolution. After their deposition on the snow surface, they can impact snow albedo and thus the snowpack evolution including the timing of snow-melt. While BC deposition is rather constant along the winter season, mineral dust deposition is more sporadic in the French Alps, subject to large dust outbreak events coming from Sahara. The dust deposition drastically changes the snow color, its absorption of solar energy and, as a consequence, modifies the internal temperature of the snow layers and their metamorphism. While mountain practitioners often report higher avalanche activities after dust deposition events, there is, up to now, no clear evidence neither from observations nor modelling that dust deposition enhances avalanche activity. Here, we investigate, using ensemble detailed snowpack simulations, the impact of dust outbreak on snow metamorphism, snow stratigraphy and mechanical stability by comparing simulations with and without dust deposition under several meteorological conditions. The results show that the dust deposition can impact the spatial and temporal distribution of the unstable slopes. The effect of the deposition largely depends on the timing of dust deposition with respect to subsequent snowfalls. It also depends on the elevation, the aspect and the time since deposition event. By using multiphysics simulations, we were able to assess the robustness of our conclusions with respect to snowpack modelling errors.</span></div>

Geochemical characterization of critical dust source regions in the American West

Dispersion and deposition of mineral dust from natural or anthropogenic sources can have both positive and negative effects on the environment depending on the geochemical and mineralogical composition of the dust. In Greenland, proglacial river systems draining the Greenland Ice Sheet occupy extensive areas of dust prone deposits, which are commonly mobilized and transported by winds of both katabatic and cyclonic origin and subsequently deposited as high latitude dust. The geochemical fingerprint of natural dust emitted along the latitudinal transect reflects the mineralogical and elemental composition of the bedrock underlying the Ice Sheet in the different geological provinces of Greenland. As dust emissions respond to changes in climate-sensitive drivers such as soil moisture, winds speed and precipitation, marked variations in natural dust emissions are present along the climatic gradient in Greenland, ranging from high latitude arctic deserts in North Greenland to low latitude shrub tundra in the South.With a changing climate, interest has increased to access and exploit the rich mineral resources located in the Arctic. In Greenland, development of large-scale mines range from rare earth element mines in the sub-arctic South to zinc-lead mines in the high-arctic North. While the mining sector provides society with essential raw materials for a wide range of industrial processes as well as forming the basis for the transition into a global green economy, it also has significant environmental pitfalls, which should be avoided or mitigated. Mobilization, transport, and deposition of mineral dust from mine sites is often significant in regions susceptible to wind erosion because of the dry climate and lack of vegetation. Once dispersed into the environment, this mineral dust may impair important ecosystem functions due to its potential content of heavy metals and other trace elements, as well as cause concerns for public health.To support the sustainable development of environmentally safe mining in sensitive Arctic land areas and reduce airborne environmental pollution, an improved understanding of processes leading to the dispersion of mineral dust in a changing Arctic is needed. This involves improved methods for monitoring dust emissions and dust deposition in a cold environment as well as analytical tools and methods to source trace and differentiate between natural and mining related dust. Accurate identification of individual dust sources subsequently makes it possible to mitigate emissions and target the regulation of mining activities towards these sources.In the following, we present a new high latitude dust sampling location in Kangerlussuaq, West Greenland, where dust is collected using a wide array of passive and active dust samplers, including a continuously operated high volume dust sampler, which will offer filter samples of large air volumes (13.000 m3) at a weekly sampling frequency over multiple years. In addition, we would like to present data from a study (1) in which we developed a fast and cost-effective surface screening methodology that is easily applicable for dust source characterization in remote Arctic areas such as Greenland, where dry conditions and high winds create a high natural dust generation potential.(1) Søndergaard, J. & Jørgensen, C.J. (2021) DOI: 10.1007/s11270-021-05095-2

<p>Light absorbing particles such as black carbon(BC) or mineral dust are known to darken the snow surface when deposited on the snow cover and amplify several snow-albedo feedbacks, drastically modifying the snowpack evolution and the snow cover duration. Mineral dust deposition on snow is generally more variablein time than black carbon deposition and can exhibit both a high inter and intra annual variability. In France, the Alps and the Pyrenees mountain ranges are affected by large dust deposition events originating from the Sahara . The aim of this study is to quantify the impact of these impurities on the snow cover variability over the last 39 years (1979-2018).</p><p>For that purpose, the detailed snowpack model Crocus with an explicit representation of impurities is forced by SAFRAN meteorological reanalysis and a downscaling of the simulated deposition fluxes from a regional climate model (ALADIN-Climate). Different simulations are performed: (i) considering dust and/or BC (i.e. explicit representation), (ii) without impurities and (iii) considering an implicit representation (i.e. empirical parameterization based on a decreasing law of the albebo with snow age).</p><p>Simulations are compared at point scale to the snow depth measured at more than 200 Meteo-France’s stations in each massif, and spatially evaluated over the 2000-2018 period in comparing thesnow cover area, snow cover duration and the Jacard index to MODIS snow products. Scores are generally better when considering the explicit representation of the impurities than when using the snow age as a proxy for light absorbing particles content.</p><p>Results indicate that dust and BC have a significant impact on the snow cover duration with strong variations in the magnitude of the impact from one year to another and from one location to another.We also investigate the contribution of light absorbing particles depositionto snow cover inter-annual variability based on statistical approaches.</p>

Abstract. The mineral dust cycle responds to climate variations and plays an important role in the climate system by affecting the radiative balance of the atmosphere and modifying biogeochemistry. Polar ice cores provide unique information about deposition of aeolian dust particles transported over long distances. These cores are a palaeoclimate proxy archive of climate variability thousands of years ago. The current study is a first attempt to simulate past interglacial dust cycles with a global aerosol–climate model ECHAM5-HAM. The results are used to explain the dust deposition changes in Antarctica in terms of quantitative contribution of different processes, such as emission, atmospheric transport and precipitation, which will help to interpret palaeodata from Antarctic ice cores. The investigated periods include four interglacial time slices: the pre-industrial control (CTRL), mid-Holocene (6000 yr BP; hereafter referred to as "6 kyr"), last glacial inception (115 000 yr BP; hereafter "115 kyr") and Eemian (126 000 yr BP; hereafter "126 kyr"). One glacial time interval, the Last Glacial Maximum (LGM) (21 000 yr BP; hereafter "21 kyr"), was simulated as well to be a reference test for the model. Results suggest an increase in mineral dust deposition globally, and in Antarctica, in the past interglacial periods relative to the pre-industrial CTRL simulation. Approximately two-thirds of the increase in the mid-Holocene and Eemian is attributed to enhanced Southern Hemisphere dust emissions. Slightly strengthened transport efficiency causes the remaining one-third of the increase in dust deposition. The moderate change in dust deposition in Antarctica in the last glacial inception period is caused by the slightly stronger poleward atmospheric transport efficiency compared to the pre-industrial. Maximum dust deposition in Antarctica was simulated for the glacial period. LGM dust deposition in Antarctica is substantially increased due to 2.6 times higher Southern Hemisphere dust emissions, 2 times stronger atmospheric transport towards Antarctica, and 30% weaker precipitation over the Southern Ocean. The model is able to reproduce the order of magnitude of dust deposition globally and in Antarctica for the pre-industrial and LGM climates.

Mineral dust is one of the main natural sources of atmospheric particulate matter, with the Sahara being one of the most important source regions for the occurrence and deposition of mineral dust in Europe. The occurrence of dust events in the European Alps is documented via measurements of airborne dust and its deposits onto the glaciers. Dust events occur mainly in spring, summer, and early autumn. Dust layers are investigated in ice cores spanning the last millennium as well as in annual snow packs. They strongly affect the overall flux of dust-related compounds (e.g., calcium and magnesium), provide an alkaline input to wet deposition chemistry, and change the microbial abundance and diversity of the snow pack. Still airborne mineral dust particles can act as ice nuclei and cloud condensation nuclei, influencing the formation of cloud droplets and hence cloud formation and precipitation. Dust deposits on the snow lead to a darkening of the surface, referred to as “surface albedo reduction,” which influences the timing of the snowmelt and reduces the annual mass balance of glaciers, showing a direct link to glacier retreat as observed presently in a warming climate.

<p>By darkening the snow surface, mineral dust and black carbon (BC) deposition accelerate snowmelt and triggers numerous feedbacks. Assessments of their long-term impact at the regional scale are still largely missing despite the environmental and socio-economic implications of snow cover changes. Using detailed snowpack simulations, we show that dust and BC deposition advance snowmelt by 17 days on average in the French Alps and the Pyrenees over the 1979-2018 period, with major implications for water availability and ground temperature. The effect of BC compared to dust is generally prevailing except in the Southern Pyrenees more exposed to Saharan dust events. We also quantify a contribution of BC and dust deposition up to 30% to the variance of the snow melt-out date. Lastly, we demonstrate that the decrease in BC deposition since the 80's alleviated the impact of current warming on snow cover decline. Therefore, this study highlights the importance of accounting for the inter-annual fluctuations in light absorbing particles deposition to improve the accuracy of snow cover reanalyses and climate projections.</p>

Aerosols such as mineral dust particles reduce the surface albedo when deposited on snow. This leads to increased absorption of solar radiation. Especially in spring, this phenomenon can lead to increased snowmelt, which triggers further feedbacks at the land surface and in the atmosphere. Quantifying the magnitude of dust-induced variations is difficult because of the high variability in the spatial distribution of mineral dust and snow. We present an extension of a fully coupled atmospheric and land surface model system to investigate the effects of mineral dust on snow albedo across Eurasia. In a comprehensive ensemble simulation study, we investigated the short-term effects of an extreme Saharan dust deposition event in 2018. We found region-dependent feedbacks. Mountainous regions and areas near the snowline showed a strong impact from mineral dust deposition. The former showed a particularly strong decrease in snow depth. For instance, in the Caucasus Mountains we found a mean significant decrease in snow depth of -1.4 cm after one week. The latter showed a stronger feedback effect on surface temperature. In the flat region around the snow line, we found a mean significant surface warming of 0.9 K after one week. This study shows that the effects of mineral dust deposition depend on several factors. Primarily, these are elevation, slope, snow depth, and fraction of snow cover. Therefore, especially in complex terrain, it is necessary to use fully coupled models to study the effects of mineral dust on the snowpack and the atmosphere.

Assessing the potential for black carbon (BC) and dust deposition to reduce albedo and accelerate glacier melt is of interest in Washington because snow and glacier melt are an important source of water resources, and glaciers are retreating. In August 2012 on Snow Dome, Mount Olympus, Washington, we measured snow surface spectral albedo and collected surface snow samples and a 7 m ice core. The snow and ice samples were analyzed for iron (Fe, used as a dust proxy) via inductively coupled plasma sector field mass spectrometry, total impurity content gravimetrically, BC using a single‐particle soot photometer (SP2), and charcoal through microscopy. In the 2012 summer surface snow, BC (54 ± 50 µg/L), Fe (367±236 µg/L) and gravimetric impurity (35 ± 18 mg/L) concentrations were spatially variable, and measured broadband albedo varied between 0.67–0.74. BC and dust concentrations in the ice core 2011 summer horizon were a magnitude higher (BC = 3120 µg/L, Fe = 22000 µg/L, and gravimetric impurity = 1870 mg/L), corresponding to a modeled broadband albedo of 0.45 based on the measured BC and gravimetric impurity concentrations. The Big Hump forest fire is the likely source for the higher concentrations. Modeling constrained by measurements indicates that the all‐sky 12 h daily mean radiative forcings in summer 2012 and 2011 range between 37–53 W m−2 and 112–149 W m−2, respectively, with the greater forcings in 2011 corresponding to a 29–38 mm/d enhancement in snowmelt. The timing of the forest fire impurity deposition is coincident with an increase in observed discharge in the Hoh River, highlighting the potential for BC and dust deposition on glaciers from forest fires to accelerate melt.

<p>Deposition of dust on the Antarctic continent is controlled by many factors, such as the primary supply of dust particles from the continents [1], the long range transport, the hydrological cycle and the snow accumulation rate [2, 3]. Thus, the study of mineral dust in ice cores gives the possibility to reconstruct past climatic and environmental conditions.</p><p>Generally, when an ice core sample is melted, soluble elements dissolve in water, while insoluble elements remain in the solid phase. Other elements, such as iron, calcium, potassium and sulfur, typically partition between the soluble and the insoluble fractions. However recent studies have shown how the dust record may be chemically and physically altered in deep ice cores [4, 5], posing a challenge in the interpretation of the climatic signal that may lie within such samples. In particular, relative abundance of specific elements was shown to be different when comparing shallow and deep dust samples, suggesting that post depositional processes are taking place.</p><p>In this study we present a comparison between samples belonging to the Talos Dome ice core analyzed through two different techniques: instrumental neutron activation analysis (INAA) and inductively coupled plasma mass spectrometry (ICP-MS). While the former is used to investigate only the insoluble fraction of dust, as it can only be applied to solid samples, the latter is used to assess the elemental composition of both the total and the soluble fraction of dust. We determined 45 elements through ICP-MS and 39 through INAA, with a good overlapping of the elements between the two techniques. Besides the determination of major elements, the high sensibility of both techniques also permitted the determination of trace elements. Among these, rare earth elements (REE) are of particular importance as they have been widely used as a geochemical tracer of aeolian dust sources [6]. We here present depth profiles for each analysed element, covering discrete portions of the entire ice core.</p><p> </p><p>Bibliography</p><p>[1] Petit, Jean-Robert, et al. "Climate and atmospheric history of the past 420,000 years from the Vostok ice core, Antarctica." Nature 399.6735 (1999): 429-436.</p><p>[2] Lambert, Fabrice, et al. "Dust-climate couplings over the past 800,000 years from the EPICA Dome C ice core." Nature 452.7187 (2008): 616.</p><p>[3] Wegner, Anna, et al. "The role of seasonality of mineral dust concentration and size on glacial/interglacial dust changes in the EPICA Dronning Maud Land ice core." Journal of Geophysical Research: Atmospheres 120.19 (2015): 9916-9931.</p><p>[4] Baccolo, Giovanni, et al. “The contribution of synchrotron light for the characterization of atmospheric mineral dust in deep ice cores: Preliminary results from the Talos Dome ice core (East Antarctica).” Condensed Matter 3, no. 3 (2018): 25.</p><p>[5] De Angelis, Martine, et al. “Micro-investigation of EPICA Dome C bottom ice: Evidence of long term in situ processes involving acid-salt interactions, mineral dust, and organic matter.” Quaternary Science Reviews 78 (2013): 248-265.</p><p>[6] Gabrielli, Paolo, et al. “A major glacial-interglacial change in aeolian dust composition inferred from Rare Earth Elements in Antarctic ice.” Quaternary Science Reviews 29, no. 1-2 (2010): 265-273.</p><p><strong> </strong></p>