Anu Kaakinen

The chemical and physical properties of atmospheric mineral dust play a key role in determining its climatic and environmental effects. These properties also vary globally, highlighting the importance of observational studies and regional investigations in enhancing global models. One of the major global dusty regions is Central-East Asia, where severe dust events occur frequently. It also hosts the largest terrestrial mineral dust record on Earth, the Chinese Loess Plateau (CLP), where dust has been deposited over the past 2.6 million years and beyond. The CLP region thus offers a globally unique archive to investigate the role of dust in both past and present climate states.In this ongoing project, dust was collected in 2019–2021 by passive and active dust samplers from a total of six locations across the CLP region. Active collectors were placed at the Lanzhou University Semi-Arid Climate and Environment Observatory (SACOL; Gansu) and in the Shapotou District of Zhongwei (Ningxia) in the southeastern margin of the Tengger Desert. Passive samplers were placed at SACOL, Lingtai (Gansu), Yinchuan (Ningxia), Luochuan (Shaanxi), and Fugu (Shaanxi).Grain size distributions and grain shape parameters (e.g., circularity, convexity, elongation) were measured simultaneously by Dynamic Image Analysis (DIA), while magnetic susceptibility measurements were also applied to the samples. The mineralogy of different size fractions was analysed using a single grain approach by Raman spectroscopy in the 2–10, 10–20, 20–63, and >63 µm grain size windows. Future investigations will include X-ray diffraction mineralogical analysis of the

Hydroclimate variability in northern Africa, driven by the interactions between the mid-latitude westerlies and the West African Monsoon (WAM) and by variations in their intensity, represents a key control on hominin dispersal. However, the response of these atmospheric circulation systems to changing boundary conditions and their influence on precipitation during past climate states remain poorly constrained, largely because most well-dated terrestrial hydroclimate records are limited to the Holocene interglacial period. Here, we present a 300,000-year hydroclimate record from northernmost Africa based on speleothem growth in Tunisia. This record captures alternating humid and arid phases across multiple glacial–interglacial cycles, as well as superimposed millennial-scale variability. Speleothem growth occurred predominantly during interglacials, indicating humid conditions, whereas growth hiatuses correspond to arid glacial periods. The cave record suggests that humid phases in northernmost Africa were primarily driven by a southward displacement and intensification of the mid-latitude westerlies and the Mediterranean storm track during interglacials. Comparison with Saharan palaeolake records further indicates that both enhanced winter westerlies and a strengthened summer WAM were required to generate widespread wet conditions across northern Africa during interglacial periods. These results highlight the combined influence of winter and summer moisture sources in shaping long-term hydroclimate variability and defining habitable corridors across northern Africa over the past 300,000 years.

The transport medium, mode, energy, and distance are recorded in the grain‐size and grain‐shape distributions in a sedimentary deposit. While grain‐size analysis has long been used in sedimentology, grain‐shape analysis is increasingly recognized as a valuable tool for reconstructing sedimentary processes and palaeoenvironments. Using Dynamic Image Analysis, this study focuses on endmember modeling of combined grain‐size‐shape distributions as an additional and robust sedimentological tool. To refine the technique, the topmost 10 m of a sedimentary section from the Mangshan Loess Plateau, China, was analyzed. Endmember modeling of the size‐shape distributions revealed three sediment populations indicating different transport modes: sandy silt via short‐term modified saltation (decreasing convexity with increasing grain‐size), coarse silt via short‐term suspension (decreasing aspect ratio and Cox circularity with grain‐size), and coarse silt via long‐term suspension (relatively low decreasing aspect ratio with grain‐size, relatively high Cox circularity and convexity). A strong negative correlation was found between the finest endmember and a loess microcodium oxygen isotope record (precipitation proxy) from a nearby site, indicating that analyzing shape of the particles may help distinguish between dry and wet deposition. The nature of shape sorting seems to change with grain‐size, transport mode and transport distance. For silt‐sized sediments, shape sorting mainly occurs during deposition and is dominated by overall shape of the particles, whereas for the sand‐sized sediments predominant shape sorting occurs already during entrainment based on grain regularity. These findings highlight the significance of integrating grain‐shape with grain‐size analyses to better resolve sediment transport processes.

Aeolian parabolic dunes in Arctic Fennoscandia are widely scattered across diverse biomes from tundra to mountain birch and pine forest, with many systems in more sparsely vegetated locations still showing signs of current degradation or partial activity. Dune stratigraphy reveals that these dunes have also undergone multiple phases of Holocene activity and reactivation, following initial dune formation immediately post deglaciation. Multiple buried soil, charcoal and homogenous dune sand layers demonstrate that dune stability is repeatedly interrupted by multiple fire events and dune reworking episodes during the Holocene. As such, these systems have great potential as archives of Arctic landscape, climate and fire history in a highly sensitive environment, and over a range of biomes.However, few of these dunes, especially in Sweden, have been independently dated using modern luminescence and radiocarbon techniques in order to constrain the timing of phases of dune stability, fire activity and reworking. As such, there is limited understanding of whether fire frequency or landscape degradation episodes have changed over the Holocene, whether there are wider patterns in these events over Arctic Fennoscandia, and if so what the climatic or anthropogenic drivers of such changes may be. Luminescence dating of aeolian sands constrains the timing of dune sand movement (or rather the cessation of movement), allowing direct dating of reworking events, while radiocarbon dating of charcoal constrains the timing of fires that may have marked the end of periods of stability, and the initiation of dune degradation and reworking.Here we address this by applying detailed quartz optical stimulated luminescence (OSL) and feldspar post infrared - infrared stimulated luminescence (pIR-IRSL) dating to cross bedded (initial dune form) and homogenous sand (reactivation layers) units in multiple dunes in Arctic Sweden and Finland over a diverse range of biomes. We also apply detailed AMS 14C dating to multiple charcoal fragments from charcoal bands exposed in the stratigraphy of these dunes, which often separate dune reactivation sand units. In this way, not only can we cross check multiple independent chronological techniques, but we can also construct detailed local dune development and reworking histories across a wide area of Arctic Europe. Combining these histories allows testing of potential wider climatic and human drivers for fire and landscape changes in Arctic Fennoscandia over the Holocene. Our results show that the choice of best luminescence dosimeter mineral varies substantially by location, and that scattered charcoal fragments exposed in dune sands are often reworked from previous fires. However, our detailed, multi-technique approach allows development of detailed fire and reactivation histories for these dunes, and reveals substantial differences in these histories across biome type and location. Despite these differences, some wider trends are also apparent, notably a substantial increase in fire and dune activity after the Holocene Optimum and in recent centuries. We discuss possible causes for these changes.

Atmospheric dust is an important component of the global climate system. It has large-scale effects on the planetary radiation budget, the albedo of snow/ice, and biogeochemical cycles. Despite this, particularly the magnetic minerals in atmospheric dust have been poorly described in aerosol models. The absorption effects of magnetic particles can be comparable to black carbon, they promote ice nucleation and therefore play a role in cloud formation, and they increase the input of iron into ocean ecosystems. We aim to contribute to characterizing these dust particles and their source areas, long-range transport, and scattering effects. The research material consists of Saharan dust deposited on snow in Finland, collected as an extensive citizen science campaign by the Finnish Meteorological Institute during 2021. The first results regarding the dust samples were published by Meinander et al. (2023). The multidisciplinary study showed that the dust originated from the Sahara and the Sahel regions (south of Sahara), based on the magnetic properties of the particles, and the System for Integrated modeLling of Atmospheric coMposition (SILAM) model. The results form the basis for the present project. A detailed magnetic characterization of the dust samples is one of the main objectives. Identifying properties such as the types and grain sizes of the magnetic particles is crucial in indicating the source area of the dust and improving the light scattering and absorption models of dust. Magnetic measurements, including initial susceptibility with two frequencies, anhysteretic remanence, and isothermal remanence, have been carried out for a set of 47 dust samples. The preliminary results are in good agreement with the previously published magnetic analyses (Meinander et al. 2023), showing signs of the presence of both Saharan and anthropogenic dust. In the future, the scattering and absorption of light by the dust particles will be studied both experimentally and theoretically. The existing numerical methods will be extended for the treatment of magnetic particles, particularly. Meinander, O., Kouznetsov, R., Uppstu, A. et al. African dust transport and deposition modelling verified through a citizen science campaign in Finland. Sci Rep 13, 21379 (2023). https://doi.org/10.1038/s41598-023-46321-7

On 21–23 February 2021, dust from a sand and dust storm (SDS) in northern Africa was transported to Finland, north of 60°N. The episode was predicted 5 days in advance by the Finnish Meteorological Institute (FMI) global operational SILAM forecast (silam.fmi.fi), and its key features (e.g., spatial distribution of wet and dry deposition amounts and particle sizes) were confirmed and detailed by a retrospective analysis. SILAM is among the dust forecast models included in the Word Meteorological Organization Sand and Dust Storm Warning Advisory and Assessment System WMO SDS-WAS. Dust deposition was observed on 23 February over a large area in the Southern and Central Finland from 60°N to >63.8°N. The ground was covered with snow making dust more easily detectable. The coloured snow caused people to contact FMI asking what is happening. FMI launched a citizen science campaign on Saharan dust with the help of social media, and people were asked to report their observations and to collect dust-containing snow and to extract the dust according to the guidelines. The campaign gained wide national interest in television, radio, newspapers and social media, and resulted in success in receiving citizen samples from 525 locations, with one to over ten samples in each. The amounts of deposition calculated from the citizen samples were found to be up to 1.1 g/m2 and such maximum amounts per unit area agree with the SILAM calculations. The SILAM model and particle magnetic properties confirmed that dust came from a wide Sahara and Sahel area, from 5000 km away. The median diameters of the dust particles were in the modes of 20 µm. The mineral composition was dominated by quartz, feldspars, and soft phyllosilicates such as micas and clay minerals.To extract dust from snow, Meinander et al. (2023) protocol recommends: 1. Collect snow samples within one week of the deposition event to minimize post-deposition changes. 2. Evaporate snow under 75oC to preserve the magnectic properties (particles should not be subjected to temperatures higher than 90oC). 3. Keep the remaining particles in the container in which the evaporation took place (e.g., a sheet of aluminium folio on a large oven tray and evaporating the snow in the oven) to best preserve all the particle sizes. Reference: Meinander, O., Kouznetsov, R., Uppstu, A. et al. African dust transport and deposition modelling verified through a citizen science campaign in Finland. Sci Rep 13, 21379 (2023). https://doi.org/10.1038/s41598-023-46321-7.

The Chinese Loess Plateau (CLP) in northern China is home to one of the most prominent loess records in the world, reflecting past eolian dust activity in East Asia. However, their interpretation is hampered by ambiguity in the origin of loess‐forming dust and an incomplete understanding of the circulation forcing dust accumulation. In this study, we used a novel modeling approach combining a dust emission model FLEXDUST with simulated back trajectories from FLEXPART to trace the dust back to where it was emitted. Over 21 years (1999–2019), we modeled back trajectories for fine (∼2 μm) and super‐coarse (∼20 μm) dust particles at six CLP sites during the peak dust storm season from March to May. FLEXPART source‐receptor relationships are combined with the dust emission inventory from FLEXDUST to create site‐dependent high‐resolution maps of the source contribution of deposited dust. The nearby dust emission areas were found to be the main source of dust to the CLP. Dust deposition across the CLP was found to predominantly occur via wet removal, with also some super‐coarse dust from distant emission regions being wet deposited following high‐level tropospheric transport. The high topography located on the downwind side of the emission area plays an essential role in forcing the emitted super‐coarse dust upward. On an interannual scale, the phase of the Arctic Oscillation in the preceding winter was found to have a strong association with the spring deposition rate on the CLP, while the strength of the East Asian Winter Monsoon was less influential.

Atmospheric mineral dust is a poorly constrained yet extremely important component of the climate system. Provenance studies from geologic dust archives are crucial to understand the drivers of the dust cycle over long time scales. Our multi‐technique provenance analysis of a rare Paleogene (35–27 Ma) eolian dust sequence from Ulantatal, ∼400 km northwest of the Chinese Loess Plateau (CLP), shows that Paleogene dust transporting winds generally varied between northwesterly and westerly, the same as those in the late Neogene‐Quaternary bipolar icehouse. We propose that, as today, westerly wind circulation patterns would have been modulated by an Arctic Oscillation (AO)‐like situation, and that the warm Eocene favored a long‐term negative phase of AO, leading to meridional westerly circulation and the dominance of a northwesterly dust transport pathway. After the Eocene‐Oligocene transition (EOT), long‐term positive phase of AO‐like conditions initiated, leading to stronger and more zonal westerlies. The Siberian High (SH) also formed or strengthened at the EOT and started to control dust storm activity along the northwesterly transport pathway. We argue that increased Paleogene Northern Hemisphere (NH) ice volume was the ultimate driver of this modern‐type dust transport regime in the Ulantatal region, possibly also controlling initial Ulantatal dust sequence formation via the development of the SH and modern‐type eolian regime. The similarity between the Ulantatal and late Neogene northern CLP dust provenance signals suggests that the increased NH ice volume, via its control on the northwesterly dust transport, could have promoted increased loess formation also in the late Miocene.