Search

This research delves into the intricate nexus of particle size, mineralogical composition, surface attributes, elemental mapping, and rare earth element (REE) adsorption mechanisms within an ion-adsorption clay sample from South America. The investigation entails the fractionation of the ion-adsorption clay into three size categories: S1 (< 0.25 mm), S2 (0.25–0.5 mm), and S3 (0.5–2 mm). Each fraction undergoes meticulous characterization to unveil its elemental composition, mineralogical composition, surface area, morphological characteristics, elemental mapping, and the mechanisms governing REE incorporation. The results indicate that S1 has 31% physiosorbed, 8% chemisorbed, and 61% mineralized REEs, while S2 has 40% physiosorbed, 5% chemisorbed, and 55% mineralized REEs, and S3 has 24% physiosorbed, 5% chemisorbed, and 71% mineralized REEs. The physisorbed REEs are attributed to the presence of kaolinite, conducive to mostly physisorption. In terms of grain size and REE content/type relationship, the results show that REE content decreases with increasing grain size; however, there is not a clear trend in terms of REE occurrence modes with grain size. Heavy rare earth elements (HREEs) are discernibly favored in adsorption over light rare earth elements (LREEs). This preference is underpinned by the weathering processes that led to the formation of ion-adsorption clay, which facilitated the transport and accumulation of HREEs. Notably, the ion-adsorption clay encompasses a substantial content of mineralized REEs, necessitating more demanding extraction methodologies, such as acid baking followed by water leaching if complete extraction of all REEs is desired. Among the desorbable REEs, physisorption dominates, encompassing over 80% of the total. Chemisorbed REEs exhibit versatility in association with various minerals, encompassing kaolinite, quartz, and goethite. In essence, this study unveils the intricate interplay between particle dimensions, mineralogical constitution, surface attributes, and REE adsorption modes within this ion-adsorption clay sample. The ion-adsorption clay in this study contains a significant portion of mineralized REEs that cannot be extracted using the mild conditions typically employed for the desorption process. Additionally, the REE concentration in this ion-adsorption clay is notably higher than the average found in clay deposits worldwide, reaching levels comparable to those of regolith deposits in China, which are a major global source of REEs. This remarkable concentration of REEs, along with the unique modes of their occurrence in this deposit, presents a significant interest to the scientific community. [ABSTRACT FROM AUTHOR]

Mineral dust accumulated on the ocean floor is an important archive for reconstructing past atmospheric circulation changes and climatological conditions in the source areas. Dust emitted from Southern Hemisphere dust sources is widely deposited over the oceans. However, there are few records of dust deposition over the open ocean, and a large need for extended geographical coverage exists. We present a large data set (134 surface sediment samples) of Late Holocene dust deposition from seafloor surface sediments covering the entire South Atlantic Ocean. Polymodal grain‐size distributions of the lithogenic fraction indicate that the sediments are composed of multiple sediment components. By using end‐member modeling, we attempt to disentangle the dust signal from non‐aeolian sediments. Combined with 230Th‐normalized lithogenic fluxes, we quantified the specific deposition fluxes for mineral dust, crrent‐sorted sediments and ice‐rafted debris (IRD). Although the method could not completely separate the different components in every region, it shows that dust deposition off the most prominent dust source for the South Atlantic Ocean—southern South America—amounts up to approximately 0.7 g cm−2 Kyr−1 and decreases downwind. Bottom‐current‐sorted sediments and IRD are mostly concentrated around the continental margins. The ratio of the coarse to fine dust end members reveals input from north African dust sources to the South Atlantic. The majority of the observations are in good agreement with new model simulations. This extensive and relevant data set of dust grain size and deposition fluxes to the South Atlantic could be used to calibrate and validate further model simulations. Plain Language Summary: Ocean records of mineral dust can be used to reconstruct past climatic changes such as wind strength and aridity in the source regions, and also marine biological productivity. However, in the remote open ocean, dust samples are difficult to obtain and therefore records are sparse. We present a large data set of dust deposition, determined from the top centimeter of ocean floor sediments, covering the entire South Atlantic Ocean. These appeared to be complex mixtures of different sediment types, which we attempted to unmix mathematically. This resulted in four individual components, which are fine and coarse mineral dust, current‐sorted sediments and ice‐rafted debris (IRD). Although the unmixing has its limitations, it shows that the dust deposition off the most prominent dust source for the South Atlantic Ocean—southern South America—is significant and decreases downwind as dust settles during transport across the ocean. Current‐sorted sediments and IRD are mostly concentrated around the continental margins. The results also reveal dust transport across the equator from north African dust sources and show similarities with new model simulations. This extensive and relevant data set of dust grain size and deposition fluxes to the South Atlantic can be used to calibrate and validate further model simulations. Key Points: End‐member (EM) modeling is used to disentangle different sediment components from polymodal grain‐size distributionsCombined with 230Th‐normalized lithogenic fluxes, specific fluxes for dust, current‐sorted sediments and ice‐rafted debris are obtainedThis independent quantification provides more specific dust fluxes compared to global compilations of lithogenic fluxes [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]

Gerdau Ouro Branco ́s plate mill started operation in 2016 with high-level technology and production capacity of 1.2 million tons per year. The plant has the capacity to produce different thicknesses in a single plate, therefore is able to supply special requirements of sectors such as building structures, bridges, shipbuilding and mechanical applications. This paper presents the first results obtained in this innovative product in South America market. Some slabs of EN10025-2 S355JR+AR steel were rolled and were evaluated for dimensional tolerances, mechanical properties uniformity, grain size, surface and internal qualities. In addition, a correlation was observed between slab and plate thickness reduction and internal plate quality. The results show that this technology can be used with adequate performance for steel grades in the current market. [ABSTRACT FROM AUTHOR]

The 'quimbalete' is a kind of grindstone used notably in Potosi (Bolivia) during the Spanish conquest of South America. It was used to grind pieces of ore gravel from centimetric sizes to the size of sand. Its physical functioning, as well as the reason why this strictly Andean tool occupied a central place in a mainly European production chain, have never been addressed. This study is aimed at answering these questions as a result of physics-based modelling. After introducing the historical context, we address geometrical and physical parameters relevant for understanding how this oscillating grindstone was used and what one can expect in terms of grinding. Then, a suitable approach for estimating the yield makes use of the modern industrial empirical estimator: the 'power index'. We offer our conclusions about the position of this tool, which appears as an ideal intermediate tool between the roughening process of the ore at the centimetre scale, and the suitable size for the material to be sorted by the subsequent methods in the chain (such as washing), which involve sandy-sized grains. The study also shows how classical physics can help in addressing questions concerning minerallurgy. [ABSTRACT FROM AUTHOR]

• Canyon landscapes present higher resistance to flow than floodplain landscapes. • Differences between canyon and floodplain are remarkable. • Canyon and transition present similar flow resistance during high-flow conditions. • Dimensionless unit discharge is an important flow velocity predictor. • Hydraulic geometry can be useful to describe mountain rivers. We conducted several field surveys to measure velocity and channel geometry in 15 cross-sections distributed along three reaches in the Boi River (Southern Brazil), a canyon river that belongs to the most extensive canyon chain in South America. The three reaches present, respectively, canyon, transition, and floodplain landscapes. The resulting data were used to compute the flow resistance. A downstream hydraulic geometry analysis indicates that the exponent describing the velocity increases with the discharge and that these values were between 0.3043 and 0.3507. A downstream hydraulic geometry analysis indicates that changes in velocity with discharge are greater than the rate of change of width or depth. It is typically found in steep mountain streams laterally confined, and it was verified in the canyon reach. However, despite the transition presents a considerable lateral constriction and the floodplain reach presents mountain river characteristics, both reaches did not present such behavior. The findings are coherent with other mountain river datasets, although the Boi River presents distinct geomorphic units such as glide-runs. In contrast, other available datasets are usually characterized by step-pool channels. Flow resistance in the canyon and transition reaches differ in many ways from floodplain reach, indicating larger resistance inside the canyon than outside, probably related to the landform and grain size in the canyon. Regression analysis of the combined field dataset indicated that dimensionless unit discharge is an important independent variable to explain variations in velocity and flow resistance. We also verified that the use of Rickenmann's Equation can be helpful to estimate velocity in canyon rivers. Our findings include: i) canyon landscape presents higher friction factors than floodplain landscape; and ii) canyon and transition landscapes are similar in terms of flow resistance during high-flow conditions, while floodplain present remarkably differences. [ABSTRACT FROM AUTHOR]

Grindstones from Eva 2 and St. John, two of the earliest sites in northeastern South America and the southern Caribbean respectively, were subjected to starch grain analysis. Results of this study revealed that these stone artifacts were utilized to process a variety of cultivars such as maize ( Zea mays ), sweet potato ( Ipomoea batatas ), chili pepper ( Capsicum spp.), achira ( Canna spp.), legumes (Fabaceae), and yams (Dioscoreaceae), coupled with wild resources, most notably marunguey ( Zamia spp.). Radiocarbon dates indicate that the use of plants identified at these two sites were much older than previously considered, going back to at least 7790 cal. BP at St. John and 5990 cal. BP at Eva 2. This new evidence showcases the importance of the Caribbean basin as an arena for early phytocultural dispersals. It also focuses attention on the role of navigation as a mechanism for crop diffusion in the Neotropics. [ABSTRACT FROM AUTHOR]

The roles ofSarcocornia perennisand tidal flooding on sediment biogeochemistry were evaluated within a wetland in the Bahía Blanca estuary.pH and Eh were measured in sediments while particulate organic carbon (POC) and dissolved inorganic nutrient concentrations were determined in porewater, at three sites with different conditions according to vegetation and flooding. Grain size was also analysed. pH varied in a narrow range (7–8.2) and was lower in the vegetated site.Eh values (50–250 mV) imply that sediment conditions were moderately reduced, in agreement with the relatively high percentage of sand; it was influenced by both factors. POC concentration was high (26.24±1.62 mg/l), especially at the vegetated site. The concentrations of ammonium and nitrate were similar (21.30±1.83 and 18.77±3.06 µmol/l, respectively) and not affected by flooding; only nitrate was affected by vegetation. Phosphate was rather constant (13.43±1.19 µmol/l) and affected mainly by flooding. Silicate was high (566.45±76.06 µmol/l) and not affected by either factor. These results suggest that the sediment biogeochemistry of this environment is significantly influenced by flooding and, especially, byS. perennis, as vegetation affected a higher number of parameters. [ABSTRACT FROM PUBLISHER]

During the Quaternary, in particular during glacial times, different grassland ecosystems played a much larger role and had a significantly larger distribution. Little is known yet about past development, biodiversity and dynamics of grassland ecosystems. In this innovative study, we attempt to distinguish between different South American grassland types in space and time based on morphological pollen grain characteristics of Poaceae. For this purpose >60-80 Poaceae pollen grains of 20 grassland samples were measured using their length, width and pore diameter as well as annulus width. Samples were taken from five sites in wet Páramo vegetation from the Late Pleistocene to the Late Holocene in South Ecuador and from two sites in the south-eastern Brazilian highlands (Campos do Altitude) of the same period. Additionally, we investigated two samples from a Pampa site as well as six samples from one Campos grassland site in southern Brazil from the Late Pleistocene to the Late Holocene. Subsets of samples of the Campos grasslands and of the Páramo were investigated in order to retrieve more detailed information on patterns within these vegetation types. Multivariate data analysis of the complete data set shows changes in taxonomic composition along an elevational gradient in the Páramo grasslands. Our results reveal a highly dynamic development of the individual grassland types; they also provide interesting information on Poaceae taxa composition patterns, development and possibly changes in biodiversity within these ecosystems. Moreover, our data provide an indication about the origin and dynamics of the Campos ecosystems in the southern Brazilian highlands during the Late Pleistocene and the Holocene before and after the onset of human activities. [ABSTRACT FROM AUTHOR]

High-resolution paleomagnetic investigations were performed on Río Valdez outcrop at the Fagnano Lake, central Isla Grande de Tierra del Fuego, southernmost South America. Our aims were to develop a full-vector paleomagnetic secular variation (PSV) record and establish paleomagnetic chronostratigraphy for the outcrop based on radiocarbon dating and the correlation of the PSV record with other dated PSV records in the region. We detected two distinct anomalous directional intervals at 35,400 and 33,800 cal. years BP and at 41,500 and 39,000 cal. years BP, which could be associated with Mono Lake and Laschamp excursions. Rock magnetic investigations revealed slight changes in concentration, mineralogy, and magnetic grain size along the sedimentary sequence, but the reconstruction of past direction and relative paleointensity variations in the geomagnetic field remained feasible. The record provides new insights into the behavior of the geomagnetic field at high latitudes in the Southern Hemisphere, about which very little is currently known. [Display omitted] • We report new paleomagnetic results for the Fagnano Lake, central Isla Grande de Tierra del Fuego, southernmost South America. • The results confirm the existence of two intervals of anomalous paleomagnetic directions. • This is the first record with these characteristics reported at this latitude. [ABSTRACT FROM AUTHOR]

Several billion tonnes of mineral dust is emitted, and transported through winds every year from arid-semiarid areas. North African dust hot spots located in the Sahara are responsible for 50-70% of the global mineral dust budget. Dust-loaded air-masses originated from these sources can be transported over long distances and can also affect remote areas, such as North and South Americas, Europe, and the Middle East. In this study, we analysed 218 identified Saharan dust events (SDEs) in the Carpathian Basin (Central Europe) during 1979 to 2018. Systematic identification of SDEs and analyses of dust emission, dust source area activity, dust transporting wind systems, and transport routes revealed that different synoptic meteorological patterns are responsible for SDEs, and these are occurring mostly in spring and summer. The characteristic synoptic meteorological background of episodes was also identified, and three major types of atmospheric pressure-system patterns were distinguished. In recent years, several intense wintertime dust deposition events have been recorded in Central Europe. All of the identified unusual episodes were characterised by severe washout of mineral dust material and were related to very similar synoptic meteorological situations. Enhanced southward propagation of a high-latitude upper-level atmospheric trough to north-western Africa and orographic blocking of Atlas Mountains played an essential role in the formation of severe dust storms, whereas the long-range transport was associated with the northward branch of the meandering jet. The occurrence and southerly penetration of high-latitude upper-level atmospheric trough to low-latitudes and the increased meridionality of the dominant flow patterns may be associated with enhanced warming of the Arctic, leading to more meandering jet streams. Particles size of sampled dust material of some intense deposition episodes were very coarse with a considerable volumetric proportion of > 20 µm particles., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 The Author. Published by Elsevier Ltd.. All rights reserved.)