Search

Dry lakebeds exposed by shrinking water bodies in arid regions constitute sodium (Na)‐rich mineral dust emission hotspots that may potentially affect agriculture through soil sodification. However, no soluble Na mass balance has so far been attempted. We modeled 13 years (2005–2017) of dust emission from Mar Chiquita (MC), the most extensive shrinking saline lake in South America. Based on a chemical characterization of dust, we found that a mean ∼15–150 mg m−2 of soluble Na was deposited 300 km from the source during the season of strongest dust emissions. We estimated the impact of this atmospheric input on 13 agricultural soils, with different rainfall regimes and water holding capacities. At most sites, dust‐equilibrated infiltrated rainfall water had a Na concentration 8–7,000 times lower than the lowest concentration threshold proposed to trigger sodification. Additionally, this rainfall water is diluted ∼2–20 times as it infiltrates in saturated soils, and its sodium adsorption ratio is probably reduced due to the abundance of soluble calcium and magnesium in the soil solution. Thus, there is no risk of short‐term, seasonal sodification, except possibly at two sites and in close proximity to the dust source (<50 km), where dust deposition is maximum. At these sites, we estimated potential dust‐related rises in the proportion of soil exchangeable Na. Under scenarios of enhanced salt‐rich dust emissions from shrinking lakes in the twenty‐first century, agricultural soils close to salt‐rich dust sources worldwide should be monitored for potential Na enrichment related to Na‐rich dust. Plain Language Summary: When lakes rich in dissolved salts shrink, the lakes' bed becomes exposed, and upon drying, these areas may emit salt‐rich dust to the atmosphere. This dust may be deposited on soils used for agriculture in the surrounding areas, and depending on the dust chemistry it may affect soil productivity, with sodium‐rich dust posing the highest potential threat. In this study, we analyzed dust emission from Mar Chiquita lake, the most extensive shrinking saline lake in South America, and its potential effect on agricultural soils in the region. To do this, we sampled dust, characterized its chemistry, modeled dust emission, transport in the atmosphere and final deposition to the soils, sampled soils at sites located at different distances from the lake, and finally compared the inputs of dust‐derived sodium, magnesium, and calcium with preexisting concentrations of these elements in the soils. We found that the short‐term input of sodium to the soils derived from dust is comparatively low, except close to the lake. However, the long‐term effect remains uncertain. Given that more intense dust emissions from shrinking lakes are projected globally in the twenty‐first century, agricultural soils exposed to salt‐rich dust deposition should be monitored to gauge threats to food production. Key Points: Mar Chiquita, the largest South American shrinking saline lake, has emitted ∼0.5 Tg of dust in August plus September of each year since 2004Despite a marked dust enrichment in soluble sodium, dust inputs are low compared to agricultural soil sodium stocks at most studied sitesWhile short‐term soil sodification risk is low, potential long‐term effects and projected stronger dust emissions merit soil monitoring [ABSTRACT FROM AUTHOR]

The magnitude of the climatic forcing associated with mineral dust aerosols remains uncertain due in part to a lack of observations on dust sources. While modeling and satellite studies provide spatially extensive constraints, they must be supported by surface‐validating dust monitoring. Southern South America is the main dust source to the southern oceans (>45°S), a region of low biological productivity potentially susceptible to increased micronutrient fertilization through dust deposition, as well as one of the main dust sources to Antarctica, implying long‐range transport of dust from Patagonia and potentially affecting snow cover albedo. We present multiyear time series of dust‐related visibility reduction (DRVR) and dust mass flux in Patagonia. We find that local DRVR is partly controlled by long‐term (i.e., months) water deficit, while same‐day conditions play a smaller role, reflective of water retention properties of fine‐grained dust‐emitting soils in low‐moisture conditions. This is supported independently by reanalysis data showing that large‐scale dust outbreaks are usually associated with anomalously high long‐term water deficit. By combining visibility data, surface dust sampling, and particle dispersion modeling, we derive regional dust emission rates. Our results suggest that the inclusion of long‐term soil hydrologic balance parameterizations under low‐moisture conditions may improve the performance of dust emission schemes in Earth system models. Key Points: Large‐scale Patagonian dust outbreaks are linked to anomalously high surface winds during cyclonic cold fronts and long‐term water deficitLong‐term water deficit also controls local dust emissions and reflects water retention properties of fine‐grained, low‐moisture sourcesDust emission rates of 1.4 ± 0.7 Tg yr−1 (2009–2019, ∼54°S) and 6.2 ± 2.5 Tg yr−1 (2004–2005, ∼49°S) were derived in southern Patagonia [ABSTRACT FROM AUTHOR]

Mineral aerosols may affect global climate indirectly by enhancing net primary productivity (NPP) upon deposition to the oceans and associated atmosphere‐to‐ocean CO2 flux. This mechanism is hypothesized to have contributed significantly to the last interglacial‐to‐glacial climatic transition. However, the dust‐NPP connection remains contentious for the present‐day climate system. We analyze the impact of southernmost Patagonian dust emissions on southwestern Atlantic Ocean continental shelf and proximal open ocean satellite chlorophyll‐a concentration. We use the first decadal time series of surface dust mass flux in southern Patagonia, along with in situ visibility data, to model dust emission, transport, and deposition to the ocean. We then perform a dust event‐based analysis of chlorophyll‐a time series, using a novel approach by which time series are corrected for post‐depositional particle advection due to ocean currents. Finally, we performed chemical analysis of iron in dust samples, a key micronutrient limiting phytoplankton biomass in high‐nutrient, low‐chlorophyll oceans such as offshore of the 200‐m isobath off Patagonia. We find no compelling evidence for an influence of dust as an enhancer of phytoplankton biomass either on shelf or proximal open ocean waters of the southwestern Atlantic Ocean. For open ocean waters this is consistent with a lack of source‐inherited bioavailable iron in dust samples. Future case studies addressing similar questions should concentrate on dust sources with identified high contents of bioavailable iron, particularly in the Southern Hemisphere where atmospheric processing of iron is weak. Key Points: We present the first decadal time series of surface dust mass flux in PatagoniaThe first event‐based study in the southwestern Atlantic Ocean shows no evidence for an influence of dust on chlorophyll‐a concentrationsSource‐inherited low concentrations of bioavailable iron preclude enhancement of primary producers' biomass in proximal open ocean waters [ABSTRACT FROM AUTHOR]

Patagonia, due to its geographic position and the dominance of westerly winds, is a key area that contributes to the supply of nutrients to the Southern Ocean, both through mineral dust and through the periodic deposits of volcanic ash. Here we evaluate the characteristics of Fe dissolved (into soluble and colloidal species) from volcanic ash for three recent southern Andes volcanic eruptions having contrasting features and chemical compositions. Contact between cloud waters (wet deposition) and end-members of andesitic (Hudson volcano) and rhyolitic (Chaitén volcano) materials was simulated. Results indicate higher Fe release and faster liberation rates in the andesitic material. Fe release during particle-seawater interaction (dry deposition) has higher rates in rhyolitic-type ashes. Rhyolitic ashes under acidic conditions release Fe in higher amounts and at a slower rate, while in those samples containing mostly glass shards, Fe release was lower and faster. The 2011 Puyehue eruption was observed by a dust monitoring station. Puyehue-type eruptions can contribute soluble Fe to the ocean via dry or wet deposition, nearly reaching the limit required for phytoplankton growth. In contrast, the input of Fe after processing by an acidic eruption plume could raise the amount of dissolved Fe in surface ocean waters several times, above the threshold required to initiate phytoplankton blooms. A single eruption like the Puyehue one represents more than half of the yearly Fe flux contributed by dust. [ABSTRACT FROM AUTHOR]

Iron (Fe) is a limiting nutrient for phytoplankton productivity in many different oceanic regions. A critical aspect underlying iron limitation is its low solubility in seawater as this controls the distribution and transport of iron through the ocean. Processes which enhance the solubility of iron in seawater, either through redox reactions or organic complexation, are central to understanding the biogeochemical cycling of iron. In this work we combined iron solubility measurements with parallel factor (PARAFAC) data analysis of Coloured Dissolved Organic Matter (CDOM) fluorescence along a meridional transect through the Atlantic (PS ANT XXVI-4) to examine the hypothesis that marine humic fluorescence is a potential proxy for iron solubility in the surface ocean. PARAFAC analysis revealed 4 components (C1-4), two humic like substances (C2&4) and two protein-like (Cl&3). Overall none of the 4 components were significantly correlated with iron solubility, though humic-like components were weakly correlated with iron solubility in iron replete waters. Our analysis suggests that the ligands responsible for maintaining iron in solution in the euphotic zone are sourced from both remineralisation processes and specific ligands produced in response to iron stress and are not easily related to bulk CDOM properties. The humic fluorescence signal was sharply attenuated in surface waters presumably most likely due to photo bleaching, though there was only a weak correlation with the transient photo product H2O2, suggesting longer lifetimes in the photic zone for the fluorescent components identified here. [ABSTRACT FROM AUTHOR]

Between June 1995 and November 1998, eight Patagonian rivers were sampled for the suspended and dissolved loads delivered to the SW Atlantic, The most important rivers (Negro and Santa Cruz; jointly deliver ∼90% of the total Patagonian freshwater budget (∼ 60 km³ y-1). Of the total sediment load (∼1.7 1012 g y-1), 2.8% was accounted for by particulate organic carbon (POC), 0.9% by inorganic particulate carbon (PC), 0.7% by particulate nitrogen (PN), and 0.7% by particulate phosphorus (PP). The mean dissolved organic carbon (DOC) yield was ∼0.50 g m-2 y-1, and POC ∼0.3 g m-2y-1. Nitrogen is the limiting nutrient in all rivers; the mean molecular C:N:P ratio is 37:1:1. POC:PN ratios (4.4-10) indicate an autochthonous origin for the organic matter in suspended particulate matter (TSS). Many factors, such as proglacial oligotrophic lakes, coal-hearing strata, wetlands, aridity, as well as various human impacts, suggest a complex typology. The analysis (Euclidean distance cluster analysis) of biogeochemical variables [SiO2, NO3-, PO43-, DOC, POC, PC, PP, PN, C:N, DOC:POC, PC:POC, POC (%) indicates that runoff, superimposed on biogeochemical variables, plays an important role in Patagonian riverine typology: a) Low runoff rivers (<100 mm y-1): the Chubut, Chico, Deseado are characterized by low yields and POC:PN ratios; the Coyle River, by high DOC:POC; b) Medium discharge rivers (100-300 mm y-1: the Negro River bas high dissolved yields and high POC(%TSS); the Colorado is distinguished by high PP and PC specific yields, and POC:PN ratio; c) High runoff rivers (>1000 mm y-1): Santa Cruz and Gallegos rivers, are both characterized by above-average specific yields; the Gallegos has high POC(%TSS), POC:PN and DOC:POC. [ABSTRACT FROM AUTHOR]

The bulk of particulate transition metals transported by Patagonian rivers shows an upper crustal composition. Riverine particulate 0.5 N HCl leachable trace metal concentrations are mainly controlled by Fe-oxides. Complexation of Fe by dissolved organic carbon (DOC) appears to be an important determinant of the phases transporting trace metals in Patagonian rivers. In contrast, aeolian trace elements have a combined crustal and anthropogenic origin. Aeolian materials have Fe, Mn, and Al contents similar to that found in regional topsoils. However, seasonal concentrations of some metals (e.g., Co, Pb, Cu, and Zn) are much higher than expected from normal crustal weathering and are likely pollutant derived.We estimate that Patagonian sediments are supplied to the South Atlantic shelf in approximately equivalent amounts from the atmosphere (∼30 × 106 T yr−1) and coastal erosion (∼40 × 106 T yr−1) with much less coming from the rivers (∼2.0 × 106 T yr−1). Low trace metal riverine fluxes are linked to the low suspended particulate load of Patagonian rivers, inasmuch most of it is retained in pro-glacial lakes as well as in downstream reservoirs. Based on our estimation of aeolian dust fluxes at the Patagonian coastline, the high nutrient-low chlorophyll sub Antarctic South Atlantic could receive 1.0 to 4.0 mg m−2 yr−1 of leachable (0.5 N HCl) Fe. Past and present volcanic activity in the southern Andes—through the ejection of tephra—must be highlighted as another important source of Fe to the South Atlantic Ocean. Based on the 1991 Hudson volcano eruption, it appears that volcanic events can contribute several thousand-fold the mass of “leachable” Fe to the ocean as is introduced by annual Patagonian dust fallout. [Copyright &y& Elsevier]

The occurrence and geochemical behaviour of Fe, Mn, Pb, Cu, Ni, Cr, Zn and Co are studied in riverine detrital materials transported by Patagonian rivers. Their riverine inputs have been estimated and the nature of these inputs to the Atlantic Ocean is discussed. Most of the metals are transported to the ocean via the suspended load; there is evidence that Fe oxides and organic matter are important phases controlling their distribution in the detrital non-residual fraction. Most heavy metal concentrations found in bed sediments, in suspended matter, and in the dissolved load of Patagonian rivers were comparable to those reported for non-polluted rivers. There is indication that human activity is altering riverine metal inputs to the ocean. In the northern basins – and indicating anthropogenic effects – heavy metals distribution in the suspended load is very different from that found in bed sediments. The use of pesticides in the Negro River valley seems correlated with increased riverine input of Cu, mostly bound to the suspended load. The Deseado and Chico Rivers exhibit increased specific yield of metals as a consequence of extended erosion within their respective basins. The Santa Cruz is the drainage basin least affected by human activity and its metal-exporting capacity should be taken as an example of a relatively unaffected large hydrological system. In contrast, coal mining modifies the transport pattern of heavy metals in the Gallegos River, inasmuch as they are exported to the coastal zone mainly as dissolved load. [ABSTRACT FROM AUTHOR]

The Suquia is a semiarid (rainfall, 700--900 mm y{sup}-1{end}), medium-size (7700 km{sup}2{end}) river system located in central Argentina. Its mountainous upper catchment includes pristine areas as well asa variety of human settlements and a reservoir lake. A large city (Cordoba, ca. 1.3 million inhabitants) and a terminal hypersaline lake are included in the middle and lower basin. Total non-residual (TNR) heavy metals (Pb, Cu, Ni, Zn, Mn, and Fe) have been determined in river bed sediments in two seasons (spring and autumn), seeking to establish the factors which control the temporal and spatial variability. The major findings were: a) concentrations of TNR metals were, in general, higher during springtime than during autumn, particularly downstream from the city of Cordoba; b) organic matter played a significant role as a controlling factor wherever it defined reducing conditions, lowering the concentrations of Mn and Fe hydrous oxides; c) a higher organic load (e.g., downstream the city) and more pronounced reducing conditions could be the causes for the increased Fe concentration, probably precipitated as sulfides; d) organic matter exhibited a closer correlation with some TNR metals in autumn, probably caused by alarger capacity for complexation in the biologically-processed organic debris; and, e) the existence of pristine areas in the drainage basin allowed for the calculation of enrichment factors (EF) which showthe significance of several environmental impacts in the Suquia system. [ABSTRACT FROM AUTHOR]