South America East Research Articles

Sedimentological and geochemical proxies reveal changes in the South Atlantic Convergence Zone in Southeast South America during the Late-Holocene

Today, the South Atlantic Convergence Zone (SACZ), a convective band that extends across central Brazil to the western South Atlantic Ocean, modulates Southern Hemisphere summer rainfall in Southeastern Brazil. During the Holocene, however, the role of the SACZ over the rainfall regime in this part of South America is still under debate. This study aims to provide new insights into the SACZ Late-Holocene variability through analysis of the geochemical (XRF-based bulk sediment Metal/Metal ratios) and sedimentological (grain size and end-member modeling) variations along four cores retrieved in a coastal area (24–49 m water depth) located in the core of modern SACZ. Our records show an increase in Ti/Ca ratios, suggesting increased rainfall and that the terrigenous input to the Brazilian southeastern inner shelf changed in the Late-Holocene (last 4200 years). These changes are also followed by a decrease in the K/Ti ratio, indicative of an increase in chemical weathering in the sediment source, and an increase in the Mn/Ti, suggesting an increase in oxidation. Additionally, decadal-scale variability with periodicities of 25 and 55 years obtained by a time-series (Redfit) analysis highlights a potential role of the Pacific Decadal Oscillation and the Atlantic Multidecadal Oscillation, respectively, as drivers of the SACZ variability over the last 4200 years.

Preseason maize and wheat yield forecasts for early warning of crop failure

Provided the considerable logistical challenges of anticipatory action and disaster response programs, there is a need for early warning of crop failures at lead times of six to twelve months. But crop yield forecasts at these lead times are virtually nonexistent. By leveraging recent advances in climate forecasting, we demonstrate that global preseason crop yield forecasts are not only possible but are skillful over considerable portions of cropland. Globally, maize and wheat forecasts are skillful at lead times of up to a year ahead of harvest for 15% and 30% of harvested areas, respectively. Forecasts are most skillful in Southeast Africa and Southeast Asia for maize and parts of South and Central Asia, Australia, and Southeast South America for wheat. Wheat forecasts, furthermore, remain skillful at lead times of over 18 months ahead of harvest in some locations. Our results demonstrate that the potential for preseason crop yield forecasts is greater than previously appreciated.

La última búsqueda de E.O. Wilson: ¿hay hormigas en las Islas Malvinas?

The Falkland Islands constitute a remote archipelago in the South Atlantic Ocean that is about 450 km east of continental South America. The invertebrate fauna of the Falkland Islands is poorly known, and thus far no ants have been reported. We conducted surveys for ants on East Falkland Island during the austral summer 2019. No ants were found during our surveys, such that East Falkland Island is one of few oceanic islands that lack native and non-native ants.

Climate change is aggravating dengue and yellow fever transmission risk

Dengue and yellow fever have complex cycles, involving urban and sylvatic mosquitoes, and non‐human primate hosts. To date, efforts to assess the effect of climate change on these diseases have neglected the combination of such crucial factors. Recent studies only considered urban vectors. This is the first study to include them together with sylvatic vectors and the distribution of primates to analyse the effect of climate change on these diseases. We used previously published models, based on machine learning algorithms and fuzzy logic, to identify areas where climatic favourability for the relevant transmission agents could change: 1) favourable areas for the circulation of the viruses due to the environment and to non‐human primate distributions; 2) the favourability for urban and sylvatic vectors. We obtained projections of future transmission risk for two future periods and for each disease, and implemented uncertainty analyses to test for predictions reliability. Areas currently favourable for both diseases could keep being climatically favourable, while global favourability could increase a 7% for yellow fever and a 10% increase for dengue. Areas likely to be more affected in the future for dengue include West Africa, South Asia, the Gulf of Mexico, Central America and the Amazon basin. A possible spread of dengue could take place into Europe, the Mediterranean basin, the UK and Portugal; and, in Asia, into northern China. For yellow fever, climate could become more favourable in Central and Southeast Africa; India; and in north and southeast South America, including Brazil, Paraguay, Bolivia, Peru, Colombia and Venezuela. In Brazil, favourability for yellow fever will probably increase in the south, the west and the east. Areas where the transmission risk spread is consistent to the dispersal of vectors are highlighted in respect of areas where the expected spread is directly attributable to environmental changes. Both scenarios could involve different prevention strategies.

Influence of Eastern, Central and Mix El Niño on the variability of rainfall in southeastern South America

El Niño/Southern Oscillation (ENSO) plays a very important role in modulating rainfall variability in South America. Although the effects of conventional ENSO are well known, there are significant variations in rainfall patterns when sea surface temperature anomalies manifest over the different regions along the equatorial Pacific, namely, Niño 3 (East), Niño 3 and Niño 4 (Mix), and Niño 4 (Central) ENSO. This work aims to analyze the variability of precipitation in southeastern South America associated with different types of El Niño (EN). For this, composite analyzes of precipitation, winds at low and high levels, vertical velocity and geopotential height were carried out. The results indicate that the rainfall pattern associated with Eastern Pacific (EP) El Niño shows the classic features expected from EN described in previous literature, i.e., a stronger and well-defined positive precipitation anomaly over southeast South America, while Central Pacific (CP) El Niño shows weaker and even an opposite sign over the region. Mix (MX) El Niño events present a spatial pattern of precipitation anomalies similar to EP El Niño events, but with lower intensity in the study area. The heterogeneity of EN-related precipitation effects results from a change in large-scale atmospheric circulation patterns: the Walker cell in the tropics, the Rossby waves in the extratropics, and the circulation of low and high-level jet streams. EP El Niño events feature a configuration similar to the South American Low-Level Jet, the strengthening of the subtropical jet, better structured Rossby waves and the Pacific-South America pattern. These characteristics are observed in MX El Niños, but in a weaker way compared to EP El Niños. CP El Niño events, on the other hand, present a weakening and spatial displacement of the aforementioned conditions, which is reflected in negative precipitation anomalies in most seasons. Thus, more significant rainfall variations are noted between the EP El Niños and CP El Niños, with a predominance of positive and negative rainfall anomalies in the study area, respectively.

Design of a solar air heater for a direct-contact packed-bed humidification–dehumidification desalination system

The performance of solar desalination systems based on a humidification–dehumidification (HDH) approach is significantly enhanced by preheating the air entering the evaporator. To estimate this potential benefit, we present an analysis of integrating a novel solar air heater (SAH) with an HDH system. The combination of both units leads to intriguing applications, such as incorporating these systems into buildings. A model of the solar thermal system is developed, and its predictions are validated with experimental data. The SAH model is combined with a previously validated model of an HDH. This allows us to estimate the performance of a combined SAH/HDH system under different environmental conditions and to evaluate the annual water treatment capacity at various sites around the world. Simulations suggest that a system with a 3.5 m2 solar collector in arid regions (Middle-East, north of Africa, south-west of the USA, East of South America), has the potential to treat 30 tons of water and reduce the CO2 emission by 150 kg annually.

Unravelling the origin of the atmospheric moisture deficit that leads to droughts

AbstractDrought is one of the most catastrophic natural hazards, and precipitation plays a major role in the development and intensification of drought events. The amount of precipitation resulting from humidity transported from a given moisture source can be key in revealing the origin of the atmospheric moisture deficit underlying drought occurrence. Here this study demonstrates, for the first time, the predominant role of moisture transport deficit in drought genesis. In most land areas, the estimated conditional probability of drought given an equivalent moisture deficit received either from the ocean or from the continents is higher than 10%. This probability is over 15% in the regions where the main atmospheric moisture transport mechanisms are active and over 20% in some hotspot regions, such as central-east North America, south-east South America and east Europe, where lower incoming moisture is almost synonymous with drought occurrence. Our results indicated that the contribution deficit of the dominant moisture source to the precipitation of a region could improve the predictability of droughts, with enormous hydrological, socioeconomic and environmental implications.

Revealing the diversity of Paleogene cingulates from Brazil: a new species of Parutaetus (Euphractinae) in the Guabirotuba Formation (middle–late Eocene)

ABSTRACT Parutaetus is an early-diverging Euphractinae cingulate that inhabited South America during the middle Eocene–early Oligocene. Four species are known: P. chicoensis, P. clusus, P. chilensis, and P. punaensis. Here, we describe a new species of this genus from Guabirotuba Formation (middle-upper Eocene of Brazil). The osteoderms differ from other species of the genus by presenting: (i) more surface glandular and piliferous foramina; (ii) the articulation surface of the area between the osteoderms is flat and full of pronounced, round, and anastomosed projections forming serrated external and medial edges with a median projection (indentations); and (iii) larger size than other species of the genus. In combination, this suite of traits is not present in other species of the genus. The increase in the number of surface glandular and piliferous foramina may be associated with the global cooling that occurred during the middle–late Eocene that affected the South American fauna. Finally, the new species expands the knowledge about the diversity of taxa that inhabited southeast South America during the Paleogene.

Tornadoes in Southeast South America: Mesoscale to Planetary-Scale Environments

Abstract A multiscale analysis of the environment supporting tornadoes in southeast South America (SESA) was conducted based on a self-constructed database of 74 reports. Composites of environmental and convective parameters from ERA5 were generated relative to tornado events. The distribution of the reported tornadoes maximizes over the Argentine plains, while events are rare close to the Andes and south of Sierras de Córdoba. Events are relatively common in all seasons except in winter. Proximity environment evolution shows enhanced instability, deep-layer vertical wind shear, storm-relative helicity, reduced convective inhibition, and a lowered lifting condensation level before or during the development of tornadic storms in SESA. No consistent signal in low-level wind shear is seen during tornado occurrence. However, a curved hodograph with counterclockwise rotation is present. The Significant Tornado Parameter (STP) is also maximized prior to tornadogenesis, most strongly associated with enhanced CAPE. Differences in the convective environment between tornadoes in SESA and the U.S. Great Plains are discussed. On the synoptic scale, tornado events are associated with a strong anomalous trough crossing the southern Andes that triggers lee cyclogenesis, subsequently enhancing the South American low-level jet (SALLJ) that increases moisture advection to support deep convection. This synoptic trough also enhances vertical shear that, along with enhanced instability, sustains organized convection capable of producing tornadic storms. At planetary scales, the tornadic environment is modulated by Rossby wave trains that appear to be forced by convection near northern Australia. Madden–Julian oscillation phase 3 preferentially occurs 1–2 weeks ahead of tornado occurrence. Significance Statement The main goal of this study is to describe what atmospheric conditions (from local to global scales) are present prior to and during tornadic storms impacting southeast South America (SESA). Increasing potential for deep convection, wind shear, and potential for rotating updrafts, as well as reducing convective inhibition and cloud-base height, are predominant a few hours before and during the events in connection to low-level northerly winds enhancing moisture transport to the region. Remote convective activity near northern Australia appears to influence large-scale atmospheric circulation that subsequently triggers convective storms supporting tornadogenesis 1–2 weeks later in SESA. Our findings highlight the importance of accounting for atmospheric processes occurring at different scales to understand and predict tornado occurrences.

Taxonomía del género Arachis (Leguminosae)

Taxonomía del género Arachis (Leguminosae)

ENSO Modulation of Global MJO and Its Impacts on South America

Abstract Changes in the Madden–Julian oscillation (MJO) and its impacts on the South American monsoon season during different El Niño–Southern Oscillation (ENSO) states [El Niño (EN), La Niña (LN), neutral (NT)] are analyzed in the global context of the MJO-propagating anomalies of convection and circulation. The background ENSO-related changes influence several aspects of MJO (relative occurrence of phases, propagation, convection, and teleconnections), and therefore modify the MJO impacts on South America (SA), such as precipitation anomalies and frequency of extreme events, as well as their distribution throughout the MJO cycle. Among the changes are the following: 1) a delay in the teleconnection between the central-east Pacific and SA, from MJO phase 8 in LN (MJOLNphase8) to MJO phase1 in EN (MJOENphase1); 2) enhanced MJO convection in the central-east subtropical South Pacific in MJOLNphases7 + 8 and a little farther east in MJOENphases8 + 1, in a region efficient in generating teleconnections that produce rainfall anomalies over central-east SA (CESA), especially the South Atlantic convergence zone (SACZ), strongest one phase earlier in LN (MJOLNphase8) than in EN (MJOENphase1), and a little shifted east in the latter than in the former; 3) enhancement of the extratropical teleconnection and its impacts over the SACZ in both EN and LN (with regard to NT), indicating nonlinear effects on MJO impacts over SA; 4) predominant increase (or reduction) in the frequency of extreme events over SA regions where both ENSO and MJO contribute in the same direction, with the greatest increase over CESA during EN in MJOENphase1 and over Southeast SA (SESA) in MJOENphase3. Significance Statement The changes produced by different El Niño–Southern Oscillation background states (neutral, El Niño, La Niña) in the Madden–Julian oscillation (MJO) and its impacts on precipitation over South America (SA) are disclosed for the austral summer monsoon season, when MJO is strongest. The reliability of the results is enhanced by using observed rainfall data. The background states affect MJO propagation, circulation, and convection, producing significant differences in precipitation and extremes over densely populated regions, besides phase shifts of the strongest impacts. The results are relevant to subseasonal prediction, since MJO is a key predictability source, to validate models and describe realistically the impacts over SA in each MJO phase. Models’ skill in simulating these results is assessed in a follow-up work.

Satellite monitoring of chlorophyll-a threshold levels during an exceptional cyanobacterial bloom (2018-2019) in the Río de la Plata

ABSTRACT The Río de la Plata estuary, located in southeast South America, is of great social and environmental relevance for the region. In the summer of 2018–2019, an exceptional cyanobacterial bloom was detected along the northern coast of the estuary, which greatly affected tourism and recreation, as reported in previous studies and the public press. This is the first work that uses satellite images to quantitatively monitor the evolution of this bloom in an intermediate zone of the estuary, including its initial and ending stages. Chlorophyll-a threshold maps of 10 and 24 µg/L were detected from Sentinel-2 imagery between November 2018-May 2019, while the presence of cyanobacteria was confirmed from phytoplankton field samples and a continuous (point) record of phycocyanin fluorescence. The combination of both satellite and in-situ information was crucial to analyze the spatiotemporal variability of the bloom, and to study its qualitative relationship to environmental drivers: local winds, discharge of the Río de la Plata main tributaries, discharge of a local tributary, water temperature and salinity. Our study shows the complexity of short-term bloom dynamics in a coastal region of the Río de la Plata, particularly highlighting the role of local winds on surface transport and mixing conditions.

Reply to the comments on Souza et al. (2022) “Recent geomorphological changes in the Paraiba do Sul delta, South America East Coast”

Scientific knowledge advances by the discussions on hypotheses, methods, and results, wherein the contradictory plays a positive role developing new theoretical-methodological approaches. In a positive debate to the progress of the science, the agreements and disagreements must only permeate the scientific scope and based on ethics to be away from the conflicts of interest. From this perspective, after knowing the submission titled Comments on Souza et al. (2022) “Recent geomorphological changes in the Paraiba do Sul delta, South America East Coast” to the journal Progress in Physical Geography: Earth and Environment (PPG), which addressed several issues concerning the results published in that article, we wrote this response to clarify the doubts related to the original paper. The comment’s authors focus mainly on da Rocha et al . (2019), a locally published article that did not fully encompass the complexity of processes and geomorphological dynamics related to the delta evolution. Furthermore, it did not present the parameters used in the geochronological analyses in accordance with the international literature. Finally, the discussions presented in the original article contribute to advances in knowledge about the responses of the Paraíba do Sul delta to the Little Ice Age.

Deep learning methods for intra-day cloudiness prediction using geostationary satellite images in a solar forecasting framework

Accurate solar resource forecasting remains a challenge. Electricity grid applications require both days-ahead and intra-day prediction. Satellite-based methods are known to be the best option for hourly intra-day solar forecasts up to some hours ahead. An adapted Deep Learning (DL) method has been recently reported to outperform the traditional Cloud Motion Vectors (CMV) strategy. This article analyzes the utilization of a well-documented computer vision DL architecture, the U-Net in various forms, for the satellite Earth albedo forecast problem (cloudiness), a straightforward proxy for solar irradiance forecast. It is shown that the U-Net performs better than advanced and optimized CMV techniques and previous art IrradianceNet, setting it at the state-of-the-art. The tests are done over the Pampa Húmeda region of southeast South America, an area in which challenging cloud conditions are frequent. The data for this study are GOES-16 visible channel images. These images present a finer spatial (≃1 km/pixel) and temporal (10 min) resolution than previously explored data sources for solar forecasting. Moreover, the image size used here is ×4 bigger (1024 × 1024 pixels) and the predictions reach further into the future (5 h) than in previous works. The analysis includes several ablation studies, involving different architectures, optimization objectives, inputs, and network sizes. The U-Net is optimized for direct and differential image prediction, being the latter a better-performing option. More notably, the U-Net models are shown to be able to predict cloud extinction, something that has been a barrier for CMV methods.

Revision of the generic classification of pike cichlids using an integrative phylogenetic approach (Cichlidae: tribe Geophagini: subtribe Crenicichlina)

AbstractPike cichlids form the largest clade of Neotropical cichlids, with over 100 species presently classified in two genera: Crenicichla (93 species widespread in rivers of South America east of the Andes) and Teleocichla (nine rheophilic Amazonian species). Here, we combined a new dataset of 216 morphological characters with molecular data compiled from published sources, comprising 74 terminal taxa of pike cichlids (68 out of 102 valid species, plus four putative new species), and performed phylogenetic analyses using maximum likelihood, Bayesian inference, and parsimony. Based on a synthesis of our results and previous phylogenies, we propose a new classification in which the clade including all pike cichlids is elevated to the rank of subtribe (Crenicichlina) and the genus Crenicichla is redefined, including three subgenera: Crenicichla (monotypic with the type species), Batrachops (resurected as subgenus), and Lacustria (new subgenus). Teleocichla is maintained as a valid genus and four new genera are proposed: Wallaciia, Saxatilia, Hemeraia, and Lugubria. Our results on character mapping support the hypothesis that resource partitioning in environments with fast-flowing water and rocky beds might have played a role in the origin or maintenance of the great diversity of pike cichlids, resulting in parallel evolution of similar ecomorphs.

Persistent La Niñas drive joint soybean harvest failures in North and South America

Abstract. Around 80 % of global soybean supply is produced in southeast South America (SESA), central Brazil (CB) and the United States (US) alone. This concentration of production in few regions makes global soybean supply sensitive to spatially compounding harvest failures. Weather variability is a key driver of soybean variability, with soybeans being especially vulnerable to hot and dry conditions during the reproductive growth stage in summer. El Niño–Southern Oscillation (ENSO) teleconnections can influence summer weather conditions across the Americas, presenting potential risks for spatially compounding harvest failures. Here, we develop causal structural models to quantify the influence of ENSO on soybean yields via mediating variables like local weather conditions and extratropical sea surface temperatures (SSTs). We show that soybean yields are predominately driven by soil moisture conditions in summer, explaining ∼50 %, 18 % and 40 % of yield variability in SESA, CB and the US respectively. Summer soil moisture is strongly driven by spring soil moisture, as well as by remote extratropical SST patterns in both hemispheres. Both of these soil moisture drivers are again influenced by ENSO. Our causal models show that persistent negative ENSO anomalies of −1.5 standard deviation (SD) lead to a −0.4 SD soybean reduction in the US and SESA. When spring soil moisture and extratropical SST precursors are pronouncedly negative (−1.5 SD), then estimated soybean losses increase to −0.9 SD for the US and SESA. Thus, by influencing extratropical SSTs and spring soil moisture, persistent La Niñas can trigger substantial soybean losses in both the US and SESA, with only minor potential gains in CB. Our findings highlight the physical pathways by which ENSO conditions can drive spatially compounding events. Such information may increase preparedness against climate-related global soybean supply shocks.

The combined influences of Amazon deforestation and Pacific Decadal Oscillation on the South America climate variability

AbstractIn this study we analyse the climatic impact over South America due to Amazon deforestation for positive (PDO+) and negative (PDO−) PDO phases. The regional climatic model RegCM4 was run from 1968 to 2003 for the domain including a great area of the Pacific Ocean and South America, using 50 km as spatial resolution. The Amazon deforestation scenario is that one extrapolated to the 2050 year. Under deforestation, the results show precipitation depletion over the extreme northern South America and precipitation increase over areas to the south, including deforested pixels and east‐southern sectors. These changes are more intense and occupy larger areas during the rainy season. Simulations also indicate that deforestation may impose a drier corridor following the Andes Mountains oriental slopes, from northwestern to south‐southeastern South America, in the rainy season. The impact from deforestation in distinct PDO phases presents the greatest signals over central‐southern South America, in a northwest–southeast direction. Over southeast Brazil, deforestation presents a slightly northeastward displacement of the PDO+ positive precipitation anomalies, intensifying the precipitation anomalies in the north sector and weakening over the south sector. The deforestation effects are more intense in the rainy season and have opposite signals between PDO+ and PDO−. Over the southeast South America, deforestation provides a weaker signal on PDO+ negative precipitation than in PDO−. The increased air temperature over the northern South America, near the northern coast, due to the joint effect of deforestation and PDO variability is more evident during PDO+ dry season than PDO− rainy season. This study illustrates the importance of considering long‐term climate simulations to better understand the role of deforestation in the lower frequency variability over South America.

A cold wave of winter 2021 in central South America: characteristics and impacts.

The online version contains supplementary material available at 10.1007/s00382-023-06701-1.

Timing of breeding as a determinant of nest success of the vulnerable Chestnut Seedeater (Sporophila cinnamomea) in grasslands of southern South America

The breeding traits of Sporophila seedeaters have been relatively well studied in recent years; nevertheless, a group of ten species in the genus, known as southern capuchinos, remain understudied. That is the case with Chestnut Seedeater (Sporophila cinnamomea), a species vulnerable to extinction, which breeds in the grasslands of southeast South America and, after reproduction, migrates towards the Cerrado region in central Brazil. Here, we investigated breeding ecology and calculated average clutch size, productivity, the sex ratio of nestlings, and estimated nest success. Then we tested (1) whether there is a relationship between the number of active nests and environmental variables, (2) whether the nestling sex ratio deviates from the 1:1 ratio, (3) whether clutch size varies between breeding seasons, and (4) whether the nest success is related to starting date, nest age, plant support, nest height from the ground, and clutch size. During two breeding seasons (October–March 2018–2020), we monitored 98 nests. We generated survival models with five interacting covariates to assess the survival of the nests. We recorded the entire breeding period for Chestnut Seedeater, which was estimated to be 4.6 months, similar to other migratory seedeaters. Clutch size did not differ between breeding seasons. The sex ratio of nestlings was not significantly different from the 1:1 ratio. Nest success was 31%, and predation was the leading cause of unsuccessful nests (83%). The daily survival rate was 0.95 ​± ​0.01. The main predictor of nest survival was the covariate starting date. These findings, added to other aspects of the species' natural history described here, may help illuminate the ecology and behavior of Chestnut Seedeater and other southern endangered capuchinos, and grassland-dependent species of South America.

Skill and sources of skill in seasonal streamflow hindcasts for South America made with ECMWF’s SEAS5 and VIC

The first aim of the present paper is the determination of the magnitude, annual variation and spatial distribution of skill in seasonal hindcasts of runoff and discharge in the entire continent of South America. We evaluated 35 years of hindcasts generated with the Variable Infiltration Capacity (VIC) hydrological model forced with SEAS5 hindcasts. Initial conditions of terrestrial water and so-called pseudo-observations were computed with a reference (i.e. historic) simulation. Skill was determined with monthly temporal resolution for the entire annual cycle and mostly using the pseudo-observations for verification. The second aim of the paper is the explanation of skill in terms of its sources, namely meteorological forcing and the initial conditions. Therefore, two sets of restricted hindcasts, which isolate the sources of skill, were analysed. The SEAS5 precipitation hindcasts exhibit significant skill even at the longest lead times (7 months). Beyond the first lead month we found significant skill in 13–43 % of the grid cells, depending on target and lead month. Levels of skill are higher in the full hindcasts (significant skill in 31–89 % of the grid cells). At the continental scale more of the skill is caused by the forcing than by the initial conditions. The runoff hindcasts are skilful in large parts of the continent. In a 1000 km wide band along the north coast of the continent and in southeast South America, most of the skill is due to the forcing. A typical feature of these regions is an increase of skill with lead time during specific parts of the year, which is against the common tendency. In Argentina and north Chile most of the skill in the runoff hindcasts can be attributed to the initial conditions of soil moisture. Verification with real observations of discharge broadly confirmed the skill pattern obtained with pseudo-observations.