Equatorial South America Research Articles

Increased extreme humid heat hazard faced by agricultural workers

Increases in population exposure to humid heat extremes in agriculturally-dependent areas of the world highlights the importance of understanding how the location and timing of humid heat extremes intersects with labor-intensive agricultural activities. Agricultural workers are acutely vulnerable to heat-related health and productivity impacts as a result of the outdoor and physical nature of their work and by compounding socio-economic factors. Here, we identify the regions, crops, and seasons when agricultural workers experience the highest hazard from extreme humid heat. Using daily maximum wet-bulb temperature data, and region-specific agricultural calendars and cropland area for 12 crops, we quantify the number of extreme humid heat days during the planting and harvesting seasons for each crop between 1979–2019. We find that rice, an extremely labor-intensive crop, and maize croplands experienced the greatest exposure to dangerous humid heat (integrating cropland area exposed to >27 °C wet-bulb temperatures), with 2001–2019 mean rice and maize cropland exposure increasing 1.8 and 1.9 times the 1979–2000 mean exposure, respectively. Crops in socio-economically vulnerable regions, including Southeast Asia, equatorial South America, the Indo-Gangetic Basin, coastal Mexico, and the northern coast of the Gulf of Guinea, experience the most frequent exposure to these extremes, in certain areas exceeding 60 extreme humid heat days per year when crops are being cultivated. They also experience higher trends relative to other world regions, with certain areas exceeding a 15 day per decade increase in extreme humid heat days. Our crop and location-specific analysis of extreme humid heat hazards during labor-intensive agricultural seasons can inform the design of policies and efforts to reduce the adverse health and productivity impacts on this vulnerable population that is crucial to the global food system.

The Collection of Feather Ornaments from Enrique Stanko Vráz’s Journey across Equatorial America

Enrique Stanko Vráz (1860–1932) was a multifaceted individual known for his roles as a traveller, photographer, hunter, and collector of natural history specimens and artifacts from non-European cultures. While travelling through equatorial South America up the Amazon River from 1892 to 1893, he amassed a remarkable collection of four hundred ethnographic artifacts from two dozen groups of Indigenous peoples. More than one hundred and thirty years after the acquisition of this collection by the Náprstek Museum, the first part of the collection is published – a collection of feather ornaments. Particular attention is paid to the circumstances of the acquisition of the objects from the Indigenous peoples, their use by the ethnic groups visited, their transport to Europe and their further handling. The inspirational sources of E. S. Vráz’s ideas, which were also reflected in his contact with the Indigenous people and his collecting activities, are briefly presented.

Late middle Miocene Metatheria (Mammalia: Didelphimorphia and Paucituberculata) from Juan Guerra, San Martín Department, Peruvian Amazonia

Currently, marsupials (modern members of the Metatheria clade) are widely distributed in tropical and subtropical areas of South America, but poorly represented in the fossil record of these regions. Except for the species-rich fossiliferous localities of La Venta in Colombia, additional Miocene metatherians from tropical, equatorial South America are sparsely reported in Bolivia, Brazil, Peru, and Venezuela. Here, we introduce new metatherian remains recovered from the late middle Miocene locality of TAR-31, San Martín Department, Peru, which has been assigned to the Laventan South American Land Mammal Age (∼13 Ma) by mammalian biostratigraphy. Three metatherian taxa are recognized at TAR-31: the didelphid didelphimorph ‘Thylamys’ cf. ‘T.’ colombianus, and the paucituberculatans aff. Palaeothentes and Pitheculites ipururensis sp. nov. This assemblage and the presence of a cebid primate at TAR-31 suggests predominantly humid and warm tropical conditions, with the occurrence of both forests and drier habitats in the surroundings. Comparisons with other Miocene metatherian assemblages at low and mid latitudes of South America clearly confirm close relationships between TAR-31 and La Venta (agreeing with observations based on monkeys and rodents), as well as, to a lesser extent, with Acre River local faunas and Madre de Dios (MD-67) in Brazil and Peru, respectively. The current results support the hypothesis that Western Amazonia was a single and consistent biogeographical region for land mammals over middle Miocene times, at the western edge of the Pebas Mega-Wetland System, and highlight the role of the Amazonian region concerning marsupial Neogene radiation. U–Pb analysis made on detrital zircon grains from TAR-31 gave a maximum depositional age of 17.4 ± 0.12 Ma (i.e., 4 Ma older than the biostratigraphical age), with a mixed detrital source likely comprising Precambrian (Western Amazon Craton), Neoproterozoic (Neoproterozoic mobile belts), and Phanerozoic rocks (Andes).

Episodic deposition of stalagmites in the northeastern Democratic Republic of the Congo suggests Equatorial Humid Periods during insolation maxima

Matupi Cave, near the equator at 1.2°N in the northeastern Democratic Republic of the Congo, is in an inland region of equinoctial (March–May and August–November) rainfall distinct from summer rainfall to the north (e.g., in the Sahara) and to the south. Investigation of one entire stalagmite, parts of two others, and a core through a fourth from Matupi reveals stalagmite growth, and faster deposition, during two periods at ∼18.1 to ∼13.4 and ∼9.2 to 3.1 ka, with stalagmite deposition ending at 3.1 ka during a transition to drier conditions. The two periods of inferred wetter conditions at Matupi coincide with the two maxima in equatorial insolation over the most recent 25 kyr. The inferred periods of wetness extend earlier and later than the North African Humid Period, which resulted from a maximum in solstitial (June) insolation at 11–12 ka rather than equinoctial (March or September) insolation at 6 and 17 ka. Matupi's pattern of two wet periods that are coincident with maxima in equatorial insolation over the most recent 25,000 years is also seen in a paleoclimate record from inland equatorial South America (and earlier periods of wetness in that record coincide with earlier maxima in equatorial insolation). The two records combine to suggest the concept of insolation-driven Equatorial Humid Periods at ∼11-kyr intervals, analogous to – but distinct in long-term timing and in seasonality of rainfall from – the more familiar North African Humid Periods recognized across the Northern Hemisphere from roughly 10°N to 25°N.

Ethnobotanical Diversity of Cassava (Manihot esculenta Crantz) in the Peruvian Amazon

Cassava is a key tropical crop that serves as a major source of nutrition throughout equatorial South America, Africa, and Asia. Genetic and paleoethnobotanical findings indicate that it was first domesticated on the southern margin of Amazonia ~10,000 years ago. However, anthropogenic processes underlying its subsequent diversification remain unclear. To shed light on them, we investigated agricultural practices and phenotypic variation in cassava on the upper Amazon River, in Loreto, Perú. We interviewed subsistence growers on five Amazon tributaries and collected data on the husbandry, morphology, and nutritional composition of their crops. We found 45 distinct cultivars. Many of their morphological features, such as stature and leaf dimensions, exhibited expected phenotype–phenotype associations. However, starch content showed no association with any other phenotype (mean p = 0.57), suggesting it has been under selective pressure exerted by growers. In addition, all cultivars’ tubers had cyanide content under 25 ppm, a low level of toxicity by global standards. Evidence of sexual reproduction and cultivar hybridization was common and a probable source of new variation. However, cultivars from different rivers showed little evidence of differentiation, possibly as the result of human transport. Thus, human influences in the region simultaneously enhance and constrain variability in the crop.

Maastrichtian–Danian palynomorphs from the Pedro Luro Formation, Ombucta 1 Borehole, Colorado Basin, Argentina

In this contribution, the palynomorphs of the Pedro Luro Formation, Ombucta 1 Borehole, Colorado Basin, Argentina, were recorded to perform palinostratigraphic analysis, evaluate dinoflagellate cyst provincialism, recognise trends in sea surface temperature (SST) and estimate palaeobiogeographic affinities. Sixty eight species of palynomorphs were identified and three informal biostratigraphic intervals were recognised. The first, determined by Hafniasphaera australis associated with Alterbidinium acutulum, implies that deposits below 984 mbrf would not be younger than late Maastrichtian (calcareous nannofossil biozone CC26). The second interval between 982 and 954 mbrf is assigned to the upper Maastrichtian–Danian. It is difficult to give more accuracy to the age of this interval due to the absence of species with LADs (last appearance datum) in the latest Maastrichtian and the lack of early Danian taxa. This together with the recognition of CC26 (Maastrichtian) followed by NP2-NP3 (Danian) could suggest that the K/Pg boundary is not represented. The third interval includes Senoniasphaera inornata (LAD: 62.6 Ma), suggesting an age no younger than Danian for deposits between 952 and 946 mbrf (NP2-NP3). The typical taxa of the Tropical-subtropical Province predominate (Phelodinium magnificum, Lejeunecysta spp. and Senegalinium leavigatum) followed by genera from the Warm-temperate Province (Alterbidinium acutulum, Spinidinium macmurdoense, Spinidinium styloniferum and Diconodinium lurense), suggesting changes in SST trends, from tropical-subtropical to warm-temperate conditions. The coincidences of dinoflagellate cyst species recorded between the Colorado Basin and basins of equatorial South America, the African counterpart, Brazil and Uruguay, would suggest the exchange of dinoflagellates, reflecting palaeobiogeographic affinities.

Improving seasonal predictions of meteorological drought by conditioning on ENSO states

Useful hindcast skill of meteorological drought, assessed with the 3-month standardized precipitation index (SPI), has been so far limited to one lead month (time horizon of the prediction). Here, we quadruple that lead time by demonstrating useful skill up to lead month 4. To obtain useful hindcast skill of meteorological drought at these long lead times, we exploit well-known El Niño-Southern Oscillation (ENSO)–precipitation teleconnections through ENSO-state conditioning. We condition initialized seasonal SPI hindcasts, derived from the Max-Planck-Institute Earth System Model (MPI-ESM) over the period 1982–2013, on ENSO states by exploring significant agreements between two complementary analyses: hindcast skill ENSO–composites, and observed ENSO–precipitation correlations. Such conditioned hindcast skill of meteorological drought is in MPI-ESM significant and reliable for lead months 2 to 4 in equatorial South America and southern North America during these regions’ dry ENSO phases. When a region’s dry ENSO phase is present at the initialization in autumn (ASO), predictions of meteorological drought show useful hindcast skill for the upcoming winter (DJF) in the respective region. The area of this useful hindcast skill is further enlarged in both regions when the respective region’s dry ENSO phase is already present in the antecedent summer (conditioning on ENSO states in JJA). Active ENSO events constitute windows of opportunity for drought predictions that are insufficiently covered by typical predictability analyses. For these windows, we demonstrate predictive skill at unprecedented lead times with a single model whose output is not bias corrected. This contribution exemplifies the value of ENSO-state conditioning in identifying these windows of opportunity for regions that are arguably most affected by ENSO–precipitation teleconnections. During these regions’ dry ENSO phases, reliable predictive skill of meteorological drought is at long lead times particularly valuable and moves the frontier of meteorological drought predictions.

Influence of the Indian Ocean Dipole on the Large-Scale Circulation in South America

AbstractThe influence of each phase of the Indian Ocean dipole (IOD) on the large-scale circulation in South America is investigated using rainfall observations, fully coupled, large-ensemble, historical simulations (LENS), and forced experiments using the coupled model’s atmospheric component. IOD events often occur when El Niño–Southern Oscillation (ENSO), the largest source of interannual variability of precipitation in South America, is active. To distinguish from effects of ENSO, only cases during neutral ENSO conditions are analyzed in LENS and observations. During the positive IOD polarity, a perturbation in the local Walker circulation leads to increased convection over equatorial South America, resulting in wet anomalies in the Amazon basin. This signal is the opposite of what is expected during El Niño events. Tropical convection anomalies in the Indian Ocean also force an extratropical Rossby wave train that reaches subtropical South America. During positive IOD, the moisture flux from the Amazon to central and southeastern Brazil weakens, resulting in a drying of the area associated with the South Atlantic convergence zone. Meanwhile, the South Atlantic subtropical high strengthens, contributing to a drying in southeastern Brazil. During negative IOD, the induced wave train from the Indian Ocean leads to increased moisture transport to the La Plata basin, leading to wet anomalies in the region.

A South American snake lineage from the Eocene Greenhouse of North America and a reappraisal of the fossil record of “anilioid” snakes

“Anilioidea” is a likely paraphyletic assemblage of pipe snakes that includes extant Aniliidae from equatorial South America, Uropeltoidea from South and Southeast Asia, and a fossil record that consists primarily of isolated precloacal vertebrae ranging from the earliest Late Cretaceous and includes geographic distributions in North America, South America, Europe, and Africa. Articulated precloacal vertebrae from the middle Eocene Bridger Formation of Wyoming, attributed to Borealilysia nov. gen., represent an unambiguous North American aniliid record and prompts a reconsideration of described pipe snakes and their resultant biogeographic histories. On the basis of vertebral apomorphies, the vast majority of reported fossils cannot be assigned to “Anilioidea”. Instead, most records represent stem taxa and macrostomatans erroneously assigned to anilioids on the basis of generalized features associated with fossoriality. A revised fossil record demonstrates that the only extralimital distributions of fossil “anilioids” consist of the North American aniliid record, and there is no unambiguous fossil record of Old World taxa. The occurrence of aniliids in the mid-high latitudes of the late early Eocene of North America is consistent with histories of northward shifts in equatorial ecosystems during the early Paleogene Greenhouse.

Piacenzian Environmental Change and the Onset of Cool and Dry Conditions in Tropical South America

AbstractThe Piacenzian (3.60–2.58 Ma) covers the last stage of the Neogene just before the Earth's climate turned from relatively stable warm conditions to the cooler climate with high amplitude glacial‐interglacial oscillations of the Pleistocene. Even during this period early fluctuations towards cooler conditions occurred, and sea surface temperature (SST) reconstructions show stepwise increasing gradients. The zonal Pacific SST gradient which indicates the strength of the Walker circulation appears to have increased in two steps starting in the Piacenzian. We investigated vegetation and climate change in western equatorial South America under the influence of the Walker circulation and to detect signs for the onset of cooling in the tropics. We studied vegetation changes in western Ecuador using palynological analysis of 88 sediment samples from marine Ocean Drilling Program Site 1239 dated between 3.9 and 2.7 Ma. A general trend towards more open vegetation is observed. The climate changes towards cooler conditions, which is manifested by a lowering of the forest line from 3.3 Ma on. The increase of Amaranthaceae pollen after 3.1 Ma suggests drier conditions along the coast. A comparison with mid‐Piacenzian warm period (mPWP) modeling shows that data and models agree regarding a drier coastal climate during the mPWP. The isochronous occurrence of environmental changes in the presented record, that is, cooling and coastal drying, with the first major pulse of ice‐rafted debris and cooling temperatures in the Northern Hemisphere (between 3.28 and 3.31 Ma) suggests that these changes might have been a precursor of the intensification of the Northern Hemisphere glaciation.

Skillful seasonal prediction of key carbon cycle components: NPP and fire risk

We investigate the skill of the GloSea5 seasonal forecasting system for two carbon cycle processes, which are strong contributors to global CO2 variability: the impact of meteorological conditions on CO2 uptake by vegetation (characterised by net primary productivity, NPP), and on fire occurrences (characterised by fire risk indices). Current seasonal forecasts of global CO2 concentrations rely on the relationship with the El Niño–Southern Oscillation (ENSO), combined with estimated anthropogenic emissions. NPP and fire are key processes underlying that global CO2–ENSO relationship: In the tropics, during El Niño events, CO2 uptake by vegetation is reduced and fires occur more frequently, leading to higher global CO2 levels. Our study assesses the skill of these processes in the forecast model for the first time. We use the McArthur forest fire index, calculated from daily data from several meteorological variables. We also assess a simpler fire index, based solely on seasonal mean temperature and relative humidity, to test the need for additional complexity. For NPP, the skill is high in regions that respond strongly to ENSO, such as equatorial South America in boreal winter, and northeast Brazil in boreal summer. There is also skill in some regions without a strong ENSO response. The fire risk indices show significant skill across much of the tropics, including Indonesia, southern and eastern Africa, and parts of the Amazon. We relate this skill to the underlying meteorological variables, finding that fire risk in particular follows similar patterns to relative humidity. On the seasonal-mean timescale, the McArthur index offers no benefits over the simpler fire index: they show the same relationship to burnt area and response to ENSO, and the same levels of skill, in almost all cases. Our results highlight potentially useful prediction skill, as well as important limitations, for seasonal forecasts of land-surface impacts of climate variability.

Projected late 21st century changes to the regional impacts of the El Niño-Southern Oscillation

As the dominant driver of interannual climate variability globally, any changes in the remote impacts of the El Nino-Southern Oscillation (ENSO) due to climate change are of considerable importance. Here we assess whether climate models from Phase 5 of the Coupled Model Intercomparison Project (CMIP5) project robust changes in ENSO’s regional temperature and precipitation teleconnections in the late 21st century, comparing the historical simulations (between 1950 and 1999) and high-emission future simulations (between 2040 and 2089). In order to quantify the importance of internal variability in these projected changes, we examine an ensemble of coupled model simulations from the Max-Planck-Institute Grand Ensemble (MPI-GE). Except for a few regions, the changes in ENSO’s temperature and precipitation teleconnections for most regions are not significant across the majority of models. Exceptions include consistent projected changes to temperature teleconnections over equatorial South America and East Africa, which are robust during La Nina events. Despite this, by assessing all regions together, a significant amplification of the temperature teleconnections is identified for La Nina events. Additionally, we find an overall projected weakening relative to the historical precipitation teleconnection when analysis is limited to regions that correctly reproduce the observed precipitation teleconnections. It remains unclear to what extent a change in regional ENSO teleconnections will be apparent, as it is clear that the changes in ENSO’s teleconnections are relatively small compared to the regional variability during the historical period.

Asteraceae: Host to the Greatest Diversity of Leafmining Nepticulidae (Lepidoptera) in South America?

Pygmy moths (Nepticulidae) associated with Asteraceae are poorly known and very rare worldwide. Recently, we discoveredmany leaf-mining nepticulids in South America feeding on Asteraceae. We review all known records of Asteraceae-feeding Nepticulidae, which in the Neotropics (including the Andes and Patagonia) previously included only Stigmella Schrank. We describe six new species of Stigmella from equatorial South America: S. jungiae Diskus and Stonis, n. sp. (feeding on Jungia L.f.), S. aeneola Diskus and Stonis, n. sp., S. violea Diskus and Stonis, n. sp., S. bracteata Diskus and Stonis, n. sp. (feeding on Liabum Adans.), S. spatiosa Diskus and Stonis, n. sp. (feeding on Ageratina Spach), and S. auripennata Diskus and Stonis, n. sp. (feeding on Baccharis L.). All new taxa are illustrated with photographs of the adults, their genitalia, and leaf mines. Additionally, leaf mines of three unknown nepticulid taxa on Jungia (aff. J. polita Griseb.), Piptocoma discolor (Kunth) Pruski, Gynoxys laurifolia (Kunth) Cass., and G. acostae Cuatrec. are documented for the first time. We diagnose and designate two new species groups and one new species complex in Stigmella.We discuss the origin and diversity of Asteraceae in the Neotropics and illustrate the distribution of Stigmella species feeding on representatives of Asteraceae at the tribal level.

Early Pliocene vegetation and hydrology changes in western equatorial South America

Abstract. During the early Pliocene, two major tectonic events triggered a profound reorganization of ocean and atmospheric circulation in the eastern equatorial Pacific (EEP), in the Caribbean Sea, and on adjacent land masses: the progressive closure of the Central American Seaway (CAS) and the uplift of the Northern Andes. These affected, among other things, the mean latitudinal position of the Intertropical Convergence Zone (ITCZ). The direction of an ITCZ shift, however, is still debated, as numeric modeling results and paleoceanographic data indicate shifts in opposite directions. To provide new insights into this debate, an independent hydrological record of western equatorial South America was generated. Vegetation and climate of this area were reconstructed by pollen analysis of 46 samples from marine sediments of Ocean Drilling Program (ODP) Hole 1239A from the EEP comprising the interval between 4.7 and 4.2 Ma. The study site is sensitive to latitudinal ITCZ shifts insofar as a southward (northward) shift would result in increased (decreased) precipitation over Ecuador. The presented pollen record comprises representatives from five ecological groups: lowland rainforest, lower montane forest, upper montane forest, páramo, and broad range taxa. A broad tropical rainforest coverage persisted in the study area throughout the early Pliocene, without significant open vegetation beyond the páramo. Between 4.7 and 4.42 Ma, humidity increases, reaching its peak around 4.42 Ma and slightly decreasing again afterwards. The stable, permanently humid conditions are rather in agreement with paleoceanographic data, indicating a southward shift of the ITCZ, possibly in response to CAS closure. The presence of páramo vegetation indicates that the Ecuadorian Andes had already reached considerable elevation by the early Pliocene. Future studies could extend the hydrological record of the region further back into the late Miocene to see if a more profound atmospheric response to tectonic changes occurred earlier.

Weakening of the biennial relationship between Central American and equatorial South American rainfall in recent decades

There is a rainfall variability biennial relationship between Central America (CA) and equatorial South America (ESA) over the tropical western hemisphere, which is known to have arisen due to the ...

Directional change during a Miocene R‐N geomagnetic polarity reversal recorded by mafic lava flows, Sheep Creek Range, north central Nevada, USA

AbstractRecurring transitional field directions during three Miocene geomagnetic reversals provide evidence that lateral inhomogeneity of the lower mantle affects flow in the outer core. We compare new paleomagnetic results from a composite sequence of 15.2 Ma lava flows in north central Nevada (Sheep Creek Range; 40.7°N, 243.2°E), erupted during a polarity reversal, to published data from Steens Mountain (250 km to the northwest in Oregon) and the Newberry Mountains (650 km to the south in California) that document reversals occurring millions of years and many polarity switches earlier. Alternating field demagnetization, followed by thermal demagnetization in half the samples, clearly isolated the primary thermoremanent magnetization of Sheep Creek Range flows. We correlated results from our three sampled sections to produce a composite record that begins with a single virtual geomagnetic pole (VGP) at low latitude in the Atlantic, followed by two VGPs situated near latitude 30°N in NE Africa. After jumping to 83°N (one VGP), the pole moves to equatorial South America (one VGP), back to NE Africa (three VGPs), to high southern latitudes (two VGPs), back to equatorial South America (three VGPs), and finally to high northern latitudes (nine VGPs). The repeated visits of the transitional VGP to positions in South America and near NE Africa, as well as the similar behavior recorded at Steens Mountain and the Newberry Mountains, suggest that lower mantle or core‐mantle boundary features localize core flow structures, thereby imparting a discernible regional structure on the transitional geomagnetic field that persists for millions of years.

Ozone structure over the equatorial Andes from balloon-borne observations and zonal connection with two tropical sea level sites

In this paper we present first-time measurements of ozone profiles from a high altitude station in Quito, Ecuador (0.19°S, 78.4°W, and 2391 masl) taken from June 2014 to September 2015. We interpret ozone observations in the troposphere, tropopause, and stratosphere through a zonal comparison with data from stations in the Atlantic and Pacific (Natal and San Cristobal from the SHADOZ network). Tropospheric ozone concentrations above the Andes are lower than ozone over San Cristobal and Natal for similar time periods. Ozone variability and pollution layers are also reduced in the troposphere above the Andes. We explain these differences in terms of reduced contributions from the boundary layer and from horizontal transport. In the tropical tropopause layer, ozone is well-mixed up to near the cold point tropopause level. In this regard, our profiles do not show constraints to deep mixing above 14 km, as has been consistently observed at other tropical stations. Total column ozone and stratospheric column ozone are comparable among the three sites. However, the contribution of tropospheric column ozone to total column ozone is significantly lower above the Andes. Our comparisons provide a connection between observations from tropical stations in equatorial South America separated by the wide continental mass. Identified differences in ozone throughout the atmospheric column demonstrate the global benefit of having an ozone sounding station at the equatorial Andes in support of global monitoring networks.

Carbonate sediment production in the equatorial continental shelf of South America: Quantifying Halimeda incrassata (Chlorophyta) contributions

The middle and outer continental shelves of eastern equatorial South America (ESA) are characterized by intense production of carbonate sediments. Qualitative analyses of sediment deposits suggest that the calcareous green alga Halimeda incrassata is among the top CaCO3 producers. Nevertheless, no study so far has quantified its real contributions. To better understand the sediment dynamic in this area, we measured biomass, growth rates and calcium carbonate production by this alga. The species exhibited high growth rates (3.38 segments.individual−1.day−1), coverage (174 individuals.m−2) and biomass (214.02 g.m−2). Substitution of segments may allow a sedimentation rate of 1.53 mm.yr−1 and a complete turnover of the population every 60.2 days. The rapid growth indicates that this alga can produce as much CaCO3 (1.19 kg CaCO3.m−2.year−1) as other tropical organisms, such as corals and rhodoliths. In a conservative estimate, 773.500 tonnes of CaCO3 are produced per year in a 5000 km2 area off the northern coast of Brazil. Sedimentation rate seems to be higher than that promoted by continental inputs in middle and outer continental shelf. On the other hand, population turnover is twice as slow as in other H. incrassata assemblages, suggesting that South American populations are sensible to physical disturbances. New studies are necessary to accurately estimate H. incrassata coverage along the Brazilian coast and to integrate data on other CaCO3 producers, such as foraminifera and coralline algae. This would allow a better understanding of the role of South American continental shelf on the global carbon budget. Furthermore, analysis on the health of these organisms is urgent, since a decline in their populations could negatively affect ecosystems functioning and services.

The influence of different El Niño types on the South American rainfall

ABSTRACTThe impacts of El Niño (EN) on the rainfall over South America are investigated considering three EN types differing in the locations of the maximum sea surface temperature (SST) anomalies in the equatorial Pacific: the Central‐Pacific (CP), Eastern‐Pacific (EP) and the Mixed (MIX) types. The largest positive (SST) anomalies for the EP and CP types occur, respectively, in the eastern and central sectors of the tropical Pacific during all seasons. The SST anomaly pattern for the MIX‐EN resembles that of the EP–EN during its onset stage, and of the CP–EN during its mature and demise stages. The different SST anomaly patterns affect the large‐scale (Walker circulation and the tropospheric Rossby‐wave trains) and local (South American low‐level jet – SALLJ) atmospheric circulation patterns in different ways and lead to distinct precipitation anomaly patterns over South America. Variations in the position and longitudinal extension of the downward motions of the EN‐related eastward‐displaced Walker circulation explain the differences in the dryness over equatorial South America. For the CP–EN, a double Walker cell defines a more zonal configuration of the equatorial dryness over South America during the first three analysed seasons. This feature is not noted for the other two EN types. The Rossby‐wave train pattern path depends on the EN types and seasons. In consequence, the associated local atmospheric circulation patterns depend also on the season and EN types. In all seasons, an intense SALLJ for the EP EN contrasts with weak or inexistence SALLJ for the other two EN types. Thus, a wetter condition over southeastern South America, southern and eastern Brazil occurs for the EP EN in relation to the other EN types. The results shown here, in particular considering the MIX EN type, have not been discussed before and might be useful mainly for climate monitoring purposes.

Vertical Profiles of Radar Reflectivity Factor in Intense Convective Clouds in the Tropics

AbstractThis study is based on the analysis of 10 years of data for radar reflectivity factor Ze as derived from the TRMM Precipitation Radar (PR) measurements. The vertical structure of active convective clouds at the PR pixel scale has been extracted by defining two types of convective cells. The first one is cumulonimbus tower (CbT), which contains Ze ≥ 20 dBZ at 12-km altitude and is at least 9 km deep. The other is intense convective cloud (ICC), which belongs to the top 5% of the population of the Ze distribution at a prescribed reference height. Here two reference heights (3 and 8 km) have been chosen. Regional differences in the vertical structure of convective cells have been explored by considering 16 locations distributed across the tropics and two locations in the subtropics. The choice of oceanic locations is based on the sea surface temperature; that of the land locations is based on propensity for intense convection. One of the main findings of the study is the close similarity in the average vertical profiles of CbTs and ICCs in the mid- and lower troposphere across the ocean basins whereas differences over land areas are larger and depend on the selected reference height. The foothills of the western Himalaya, southeastern South America, and the Indo-Gangetic Plain contain the most intense CbTs; equatorial Africa, the foothills of the western Himalaya, and equatorial South America contain the most intense ICCs. Close similarity among the oceanic profiles suggests that the development of vigorous convective cells over warm oceans is similar and that understanding gained in one region is extendable to other areas.