Tropical Latitudes Research Articles

Simulation of cosmic rays in the Earth’s atmosphere and interpretation of observed counts in an X-ray detector at balloon altitude near tropical region

The study of secondary particles produced by the cosmic-ray interaction in the Earth’s atmosphere is very crucial as these particles mainly constitute the background counts produced in the high-energy detectors at balloon and satellite altitudes. In the present work, we calculate the abundance of cosmic-ray generated secondary particles at various heights of the atmosphere by means of a Monte Carlo simulation and use this result to understand the background counts in our X-ray observations using balloon-borne instruments operating near the tropical latitude (geomagnetic latitude: ~14.50°N). For this purpose, we consider a 3D description of the atmospheric and geomagnetic field configurations surrounding the Earth, as well as the electromagnetic and nuclear interaction processes using Geant4 simulation toolkit. Subsequently, we use a realistic mass model description of the detector under consideration, to simulate the counts produced in the detector due to secondary cosmic-ray particles.

Environmental risk factors for acute kidney injury in agricultural workers in Spain

TPS 792: Occupational health 2, Exhibition Hall, Ground floor, August 27, 2019, 3:00 PM - 4:30 PM A high burden of kidney diseases, including acute kidney injury (AKI), has been reported among agricultural workers in tropical areas. Dehydration caused by strenuous work at high temperatures has been suggested as a risk factor for AKI. In the Mediterranean region, agricultural workers are exposed during the summer months to temperatures similar to those observed in tropical latitudes. The aim of the study is to evaluate if agricultural work during the summer months in Spain is a risk factor for AKI. Seventy-four agricultural workers were enrolled in two provinces of Spain: 57 were enrolled in Alicante during the grape harvest season (summer months) and 17 were enrolled in Tarragona during the citrus harvest (winter months). From each participant we obtained the following information before and after the work-shift: i) blood and urine samples to analyse creatinine serum levels and creatinine, albumin and neutrophil gelatinase-associated lipocalin (NGAL) urine levels; ii) anthropometric measurements; and iii) information about life-style and working conditions. Temperature and humidity were measured at the workplace to estimate the wet-bulb globe temperature (WBGT) Age and sex distribution were similar between regions (% of men: 84% in Alicante, 94% in Tarragona, p-value= 0.294; mean (SD) age: 41 (1.7) in Alicante, 43 (2.1) in Tarragona, p-value=0.386). There were no differences in mean NGAL levels between provinces before the work-shift [Alicante=2.7 (0.4), Tarragona=3.5 (0.8), t-test p-value=0.347] or after it [Alicante=7.7 (0.9), Tarragona=5.9 (1.3), t-test p-value=0.321). NGAL levels were higher after work-shift in workers from Alicante (Wilcoxon matched-pairs p –value<0.001) but no differences were observed in workers from Tarragona (Wilcoxon matched-pairs p –value=0.166). Results are in concordance with the hypotheses under study. These results have to be verified with measurements of serum and urine creatinine levels, urine albumin levels, and estimates of WBGT. These data will be available before the ISEE conference.

Vertical Dependence of Horizontal Scaling Behavior of Orographic Wind and Moisture Fields in Atmospheric Models

AbstractPrevious work showed that atmospheric model simulations exhibit different scaling behavior of vertically averaged horizontal wind (u,v) and moisture (q) in the mesoscales for convective (spectral slopes β~−5/3) and nonconvective (β~−11/5) conditions. Here, the focus is on the transient behavior of horizontal scaling in the vertical during the evolution of extreme orographic precipitation storms in middle (Appalachians, &lt;2,500m) and high mountains (Andes). The results show that β exhibits a strong diurnal cycle switching between convective and nonconvective behavior following the space‐time evolution of atmospheric stability in the lower troposphere (below 700 hPa) depending on latitude, topography, landform, and the synoptic environment. Anomalous flattening of the wind and moisture spectra (i.e., spectral saturation, ∣β ∣ &lt; 5/3) at high wavenumbers and up to 200 hPa is tied to convective activity, where and when strong vertical motions develop, corresponding to an abrupt directional switch from horizontal energy transfer to vertical energy transfer including latent heating release and parameterized microphysical processes. In the small mesoscales (&lt;50 km), β~ − 5/3 at all times up to 200 hPa with nighttime steepening (β~−11/5) below the orographic envelope where cold air pools form at low elevations and vertical motion weakens in the Appalachians. In the Andes, the scaling behavior exhibits a stronger diurnal cycle at low levels (below 700 hPa) with significant shoaling between tropical and high latitudes. Blocking and strong modification of regional circulations result in nighttime anisotropy at midlevels on the altitudinal profile along the North‐South topographic divide.

Jupiter’s Atmospheric Variability from Long-term Ground-based Observations at 5 μm

Abstract Jupiter’s banded structure undergoes strong temporal variations, changing the visible and infrared appearance of the belts and zones in a complex and turbulent way through physical processes that are not yet understood. In this study, we use ground-based 5-μm infrared data captured between 1984 and 2018 by eight different instruments mounted on the Infrared Telescope Facility in Hawai’i and on the Very Large Telescope in Chile to analyze and characterize the long-term variability of Jupiter’s cloud-forming region at the 1–4 bar pressure level. The data show a large temporal variability mainly at the equatorial and tropical latitudes, with a smaller temporal variability at mid-latitudes. We also compare the 5-μm-bright and -dark regions with the locations of the visible zones and belts, and we find that these regions are not always colocated, especially in the southern hemisphere. We also present Lomb–Scargle and Wavelet Transform analyses in order to look for possible periodicities of the brightness changes that could help us understand their origin and predict future events. We see that some of these variations occur periodically in time intervals of 4–8 yr. The reasons for these time intervals are not understood, and we explore potential connections to both convective processes in the deeper weather layer and dynamical processes in the upper troposphere and stratosphere. Finally, we perform a Principal Component analysis to reveal a clear anticorrelation on the 5 μm brightness changes between the North Equatorial Belt and the South Equatorial Belt, suggesting a possible connection between the changes in these belts.

Paleobiogeographic Analysis of the Assemblages of Late Vendian Macrofossils

The similarity analysis of the taxonomic composition of the 13 main localities of the Vendian macrofossils worldwide was performed according to the Ohai coefficient. There are two distinct subgroups among shallow-marine localities. The first subgroup consists of the following localities: Australia, the southeastern White Sea area, Podolia, India, and the Urals (degree of similarity 0.16–0.38). The second subgroup includes the localities of Siberia, Northwest Canada, Southern China, South America, Southern Namibia, and the USA (degree of similarity is up to 0.58). Such a division of the shallow-marine localities corresponds to the spread of carbonate sediments and the distribution of the tubular problematical species Cloudina . It can be assumed that this difference occurs due to the association of the localities of the second subgroup to warm-water climatic conditions (precipitation of carbonates, distribution of problematical remains with a carbonate skeleton), while the localities of the first subgroup are confined to cold-water conditions. Thus, the performed analysis indicates the location of the cratons of Australia, Baltica, and India at high latitudes (which differs from the results demonstrated in some paleotectonic reconstructions based on paleomagnetic studies) and confirms the hypothesis of the location of the Siberian platform at tropical and subtropical latitudes. Based on the conducted analysis, two paleobiogeographical areas were identified for the Late Vendian: the Subpolar area (Australia, Baltica, India) and the Equatorial area (Siberia, Laurentia, Kalahari, South China, Rio de la Plata).

Investigating the GPM Dual‐frequency Precipitation Radar signatures of low‐level precipitation enhancement

AbstractHigh‐intensity precipitation represents a threat for several regions of the world because of the related risk of natural disasters (e.g. floods and landslides). This work focuses on low‐level precipitation enhancement that occurs in the cloud warm layer and has been observed in relation to collision‐coalescence (CC) leading to flash floods and extreme rainfall events in tropical and temperate latitudes. Specifically, signatures of precipitation enhancement (referred to as CC‐dominant precipitation) are investigated in the observations from the Global Precipitation Measurement (GPM) core mission Dual‐frequency Precipitation Radar (DPR) over the central/eastern Contiguous United States (CONUS) during June 2014–May 2018. A classification scheme for CC‐dominant precipitation, developed for dual‐polarization S‐band radar measurements and applied in a previous work to X‐band radar observations in complex terrain, is used as a benchmark. The scheme is here applied to the GPM ground validation dataset that matches ground‐based radar observations across CONUS to space‐borne DPR retrievals. The occurrence of CC‐dominant precipitation is documented and the corresponding signatures of CC‐dominant precipitation at Ku‐ and Ka‐band are studied. CC‐dominant profiles show distinguishing features when compared to profiles not dominated by CC, e.g. characteristic vertical slopes of reflectivity at Ku‐ and Ka‐band in the liquid layer, lower freezing‐level height, and shallower ice layer, which are linked to environmental conditions driving the peculiar CC microphysics. This work aims at improving satellite quantitative precipitation estimation, particularly GPM retrievals, by targeting CC development in precipitation columns.

Ancestral biogeography and ecology of marine angelfishes (F: Pomacanthidae)

Marine angelfishes (F: Pomacanthidae) are amongst the most conspicuous reef fish families inhabiting reefs on tropical and subtropical latitudes. While being disproportionately represented in the marine ornamental fish trade, only a handful of taxonomically restricted studies explored their biogeographic history and the evolution body size and trophic guilds. Here, we reconstruct the phylogenetic history for 70 pomacanthid species (85% of nominal species), based on previously published data for three nuclear and four mitochondrial markers. We use the resulting phylogenetic framework to explore the ancestral biogeography and ecological diversification of the family. Divergence times and ancestral range estimation highlight the origins of the family most likely lie in the Central Pacific region. Vicariance among ocean basins reflects the impact of the Terminal Tethyan Event and the closure of the Isthmus of Panama in the historical biogeography of Pomacanthus and Holacanthus genera. The reconstruction also uncovers ancestral colonization pathways via the Pacific Ocean into the western Atlantic waters for Holacanthus. We confirm the Indian Ocean invasion scenario previously proposed for the “acanthops” complex (genus: Centropyge). Finally, interspecific variation in body size among clades appeared to be correlated to some degree with trophic guilds, whereby 15% of variance in body size was explained by trophic modes. This suggests that the higher ecological diversification observed in the Centropyge clade might be promoted by smaller body sizes acting as an ecological novelty allowing the expansion of the genus within available niches.

A reappraisal of the phylogeny of Mylodontidae (Mammalia, Xenarthra) and the divergence of mylodontine and lestodontine sloths

AbstractThe phylogeny of mylodontid sloths has recently been the subject of multiple studies. Contrasting hypotheses have been proposed, especially for the relationships among late Miocene–Pleistocene mylodontines and lestodontines. In this paper, a new and detailed phylogenetic analysis is conducted, after adding new characters and taxa previously unexplored from a phylogenetic point of view. New features derived from postcranial skeletal anatomy are added to previous studies based on craniodental evidence. In this way, the current reappraisal represents the first exhaustive phylogenetic study on the Mylodontidae that incorporates features coded for the entire skeleton. When available, multiple specimens of each bony element are observed for each operational taxonomic unit, in order to take into account intraspecific variation. The taxonomic sample of this study considers Mylodontinae at the specific level. However, many other Mylodontidae are considered, and their phylogenetic relationships tested. The taxonomic sample of this study is enriched with new taxa from central and northern South America, with the aim of compensating for the knowledge bias in favour of austral mylodontids, which have historically been more extensively studied than those from tropical latitudes. Special emphasis is given to the phylogenetic relationships of Mylodontinae, and particularly to the mylodontine and lestodontine sloths, that are recovered in the present study as monophyletic clades, and together form a larger monophyletic group. According to the present results, the Mylodontini–Lestodontini split occurred at the middle–late Miocene transition, giving rise to independent adaptive radiations across South and North America.

Tropopause altitude determination from temperature profile measurements of reduced vertical resolution

Abstract. Inference of the lapse rate tropopause or the cold point from temperature profiles of finite vertical resolution entails an uncertainty of the tropopause altitude. For tropical radiosonde profiles the tropopause altitude inferred from coarse-grid profiles was found to be lower than that inferred from the original profiles. The mean (median) displacements of the lapse rate tropopause altitude when inferred from a temperature profile of 3 km vertical resolution and a Gaussian kernel are −130, −400, −730, and −590 m (−70, −230, −390, and −280 m) for Nairobi, Hilo, Munich, and Greifswald, respectively. In the case of a Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) averaging kernel, the displacement of the lapse rate tropopause altitude is −640 m. The mean (median) displacement of the cold point tropopause inferred from a temperature profile of 3 km vertical resolution (Gaussian kernels) was found to be −510, −610, −530, and −390 m (−460, −510, −370, and −280 m) for the stations mentioned above. Unsurprisingly, the tropopause altitude displacement is larger for coarser resolutions. The effect of the tropopause displacement on the water vapor saturation mixing ratio is roughly proportional to the vertical resolution. In tropical latitudes the resulting error is about 1 to 2 ppmv per vertical resolution in kilometers. The spread of the tropopause displacements within each sample of profiles seems too large as to recommend a correction scheme for tropical temperature profiles, while for midlatitudinal temperature profiles of vertical resolutions of 1 to 5 km a lapse rate of −1.3 K km−1 reproduces tropopause altitudes determined from high-resolution temperature profiles with the nominal lapse rate criterion of −2 K km−1 fairly well.

Seasonal gas exchange and resource-use efficiency in evergreen versus deciduous species from a tropical dry forest.

Tropical dry forests (TDFs) experience a long dry season in which plant species are subject to several months of water deficit. However, TDFs maintain a diverse group of plant life forms, growth forms and leaf phenology, and it is not clear how they vary in their mechanisms for coping with seasonal drought. We studied seasonal changes in leaf water potential (Ψleaf), gas exchange, photochemical activity and functional traits in evergreen and drought-deciduous species from a TDF to determine if leaf phenology mediates plant responses to drought. We found seasonal decreases in Ψleaf, stomatal conductance (gs) and transpiration rate (E), and increases in both intrinsic and instantaneous water-use efficiency. We did not find seasonal differences in photosynthetic rate (Aarea) and carbon isotope composition (δ13C); however, these traits differed between leaf phenology groups, with drought-deciduous plants having higher Aarea and δ13C than evergreen plants. We also found that plants with high leaf nitrogen concentration (Narea) also had low mass-based photosynthetic rate (Amass), photosynthetic-nitrogen-use efficiency and specific leaf area, contrary to the expected relationships given by the leaf economics spectrum. Despite higher Narea, sclerophyllous leaves maintained lower Amass, and this increased structural toughness of leaves may be imposing a stronger limitation for CO2 diffusion and hence photosynthesis. Overall, we found more water-conservative traits in deciduous than in evergreen plants, contrary to what is known about these two leaf phenology groups in other seasonal sites both at tropical and temperate latitudes.

Influence of Arctic stratospheric ozone on surface climate in CCMI models

Abstract. The Northern Hemisphere and tropical circulation response to interannual variability in Arctic stratospheric ozone is analyzed in a set of the latest model simulations archived for the Chemistry-Climate Model Initiative (CCMI) project. All models simulate a connection between ozone variability and temperature/geopotential height in the lower stratosphere similar to that observed. A connection between Arctic ozone variability and polar cap surface air pressure is also found, but additional statistical analysis suggests that it is mediated by the dynamical variability that typically drives the anomalous ozone concentrations. While the CCMI models also show a connection between Arctic stratospheric ozone and the El Niño–Southern Oscillation (ENSO), with Arctic stratospheric ozone variability leading to ENSO variability 1 to 2 years later, this relationship in the models is much weaker than observed and is likely related to ENSO autocorrelation rather than any forced response to ozone. Overall, Arctic stratospheric ozone is related to lower stratospheric variability. Arctic stratospheric ozone may also influence the surface in both polar and tropical latitudes, though ozone is likely not the proximate cause of these impacts and these impacts can be masked by internal variability if data are only available for ∼40 years.

A global analysis of distribution and endemism within Late Llandovery (Telychian) brachiopods

Cocks, L.R.M. & Jiayu, R. 10 July 2019. A global analysis of distribution and endemism within Late Llandovery (Telychian) brachiopods. Alcheringa 43, 406–422. ISSN 0311–5518The genera of brachiopods of early Silurian (late Llandovery: Telychian) age have been critically reviewed and are listed from the major continental areas: South China, Avalonia-Baltica, Laurentia, Siberia and adjacent areas, and Gondwana (including the adjacent Kazakh terranes, Southwest Tien Shan and Iran). All those continents lay within tropical latitudes, apart from the South American sector of Gondwana, which hosted the Clarkeia Fauna, the earliest constituent of the largely high-latitude Devonian Malvinokaffric Province in the southern hemisphere. Additionally, the then northern (today’s southern) part of the Siberian continent, which included parts of Mongolia and North China, was at temperate latitudes in the northern hemisphere so that it hosted the Tuvaella Fauna, which was also dominated by endemic brachiopod genera. Of the 202 genera listed, 50 are endemic to one of the six regions, and a further eight must have lived during Telychian times since they are known from both the underlying Aeronian and the overlying Sheinwoodian.L. Robin M. Cocks [rcocks@nhmacuk], Department of Earth Sciences, The Natural History Museum, Cromwell Road, London SW7 5BD, UK; Rong Jiayu [jyrong@nigpasaccn], State Key Laboratory, Nanjing Institute of Geology and Palaeontology, 39 East Beijing Road, Nanjing 210008, PR China.

Parallels between natural selection in the cold-adapted crop-wild relative Tripsacum dactyloides and artificial selection in temperate adapted maize.

Artificial selection has produced varieties of domesticated maize that thrive in temperate climates around the world. However, the direct progenitor of maize, teosinte, is indigenous only to a relatively small range of tropical and subtropical latitudes and grows poorly or not at all outside of this region. Tripsacum, a sister genus to maize and teosinte, is naturally endemic to the majority of areas in the western hemisphere where maize is cultivated. A full-length reference transcriptome for Tripsacum dactyloides generated using long-read Iso-Seq data was used to characterize independent adaptation to temperate climates in this clade. Genes related to phospholipid biosynthesis, a critical component of cold acclimation in other cold-adapted plant lineages, were enriched among those genes experiencing more rapid rates of protein sequence evolution in T.dactyloides. In contrast with previous studies of parallel selection, we find that there is a significant overlap between the genes that were targets of artificial selection during the adaptation of maize to temperate climates and those that were targets of natural selection in temperate-adapted T.dactyloides. Genes related to growth, development, response to stimulus, signaling, and organelles were enriched in the set of genes identified as both targets of natural and artificial selection.

World distribution, diversity and endemism of aquatic macrophytes

To test the hitherto generally-accepted hypothesis that most aquatic macrophytes have broad world distributions, we investigated the global distribution, diversity and endemism patterns of 3457 macrophyte species that occur in permanent, temporary or ephemeral inland freshwater and brackish waterbodies worldwide. At a resolution of 10 × 10° latitude x longitude, most macrophyte species were found to have narrow global distributions: 78% have ranges (measured using an approach broadly following the IUCN-defined concept “extent of occurrence”) that individually occupy <10% of the world area present within the six global ecozones which primarily provide habitat for macrophytes. We found evidence of non-linear relationships between latitude and macrophyte α- and γ-diversity, with diversity highest in sub-tropical to low tropical latitudes, declining slightly towards the Equator, and also declining strongly towards higher latitudes. Landscape aridity and, to a lesser extent, altitude and land area present per gridcell also influence macrophyte diversity and species assemblage worldwide. The Neotropics and Orient have the richest ecozone species-pools for macrophytes, depending on γ-diversity metric used. The region around Brasilia/Goiás (Brazil: gridcell 10–20 °S; 40–50 °W) is the richest global hotspot for macrophyte α-diversity (total species α-diversity, ST: 625 species/gridcell, 350 of them Neotropical endemics). In contrast, the Sahara/Arabian Deserts, and some Arctic areas, have the lowest macrophyte α-diversity (ST <20 species/gridcell). At ecozone scale, macrophyte species endemism is pronounced, though with a>5-fold difference between the most species-rich (Neotropics) and species-poor (Palaearctic) ecozones. Our findings strongly support the assertion that small-ranged species constitute most of Earth’s species diversity.

Weather satellites to launch

On June 24, the US and Taiwan are scheduled to launch a coterie of six small satellites that will orbit tropical latitudes. The satellites, a joint project of the US National Oceanic and Atmospheric Administration (NOAA) and the Taiwan National Space Agency, will provide more frequent high-resolution data about temperature, pressure, and water vapor, improving tropical-storm forecasts. The project, called COSMIC-2 in the US and FORMOSAT-7 in Taiwan, will also provide an unprecedented level of detail about the planet’s ionosphere. This upper level of the atmosphere is a swirl of electrons and ions, blasted by the sun and adjacent to the Earth’s magnetosphere. So far, atmospheric scientists have had limited tools for monitoring this region. Previous satellite and ground-based systems provided infrequent, low-resolution data about the ionosphere. COSMIC-2 will continuously monitor the electron density of the ionosphere from 40° north of the equator to 40° south, tracking how charges move

Climatic shifts drove major contractions in avian latitudinal distributions throughout the Cenozoic

Many higher level avian clades are restricted to Earth's lower latitudes, leading to historical biogeographic reconstructions favoring a Gondwanan origin of crown birds and numerous deep subclades. However, several such "tropical-restricted" clades (TRCs) are represented by stem-lineage fossils well outside the ranges of their closest living relatives, often on northern continents. To assess the drivers of these geographic disjunctions, we combined ecological niche modeling, paleoclimate models, and the early Cenozoic fossil record to examine the influence of climatic change on avian geographic distributions over the last ∼56 million years. By modeling the distribution of suitable habitable area through time, we illustrate that most Paleogene fossil-bearing localities would have been suitable for occupancy by extant TRC representatives when their stem-lineage fossils were deposited. Potentially suitable habitat for these TRCs is inferred to have become progressively restricted toward the tropics throughout the Cenozoic, culminating in relatively narrow circumtropical distributions in the present day. Our results are consistent with coarse-scale niche conservatism at the clade level and support a scenario whereby climate change over geological timescales has largely dictated the geographic distributions of many major avian clades. The distinctive modern bias toward high avian diversity at tropical latitudes for most hierarchical taxonomic levels may therefore represent a relatively recent phenomenon, overprinting a complex biogeographic history of dramatic geographic range shifts driven by Earth's changing climate, variable persistence, and intercontinental dispersal. Earth's current climatic trajectory portends a return to a megathermal state, which may dramatically influence the geographic distributions of many range-restricted extant clades.

Cyanobacteria Proliferation in the Cenomanian‐Turonian Boundary Interval of the Apennine Carbonate Platform: Immediate Response to the Environmental Perturbations Associated With OAE‐2?

AbstractOceanic Anoxic Event‐2 (OAE‐2; Cenomanian‐Turonian) is characterized by extensive deposition of organic carbon‐rich deposits (black shales) in ocean basins worldwide as result of a major perturbation of the global carbon cycle. While the sedimentological, geochemical, and paleontological aspects of deep water expressions of OAE‐2 have been intensively studied in the last few decades, much less attention has been given to the coeval shallow water deposits. In this study, we present the results of a detailed facies and petrographic (optical microscope and scanning electron microscopy) and geochemical studies (δ13Ccarb, δ 13C org, δ 15Nbulk, TOC, and Rock‐Eval pyrolysis) on two key shallow marine sections from the Apennine Carbonate Platform (ACP; Italy). Here a continuous record of shallow water carbonates through the OAE‐2 interval is preserved, offering the unique opportunity to document the archive of paleoenvironmental changes in a neritic setting, at a tropical latitude and far from the influence of a large continental block. Two conspicuous intervals are characterized by abundant and closely spaced “dark” microbial laminites found at correlative stratigraphic horizons in the two stratigraphic sections. These laminites contain elevated concentrations of TOC (up to 1%) relative to microbial capping cycles laminites stratigraphically above and below. The organic matter preserved in these fine‐grained laminites is dominated by cyanobacteria remains, which accounted for most of the organic matter produced on the ACP in these intervals. Our study suggests that Tethyan carbonate platforms experienced significant biological changes during OAE‐2, alternating, in few kiloyears, between eutrophic phases dominated by microbial communities and mesotrophic/oligotrophic conditions favoring “normal” carbonate production/sedimentation. The synchronous occurrence of microbialite facies at different locations across the ACP and on other platforms worldwide (e.g., Mexico and Croatia) suggests a causal link between Large Igneous Province volcanism and the environmental conditions necessary to trigger cyanobacterial proliferation on shallow carbonate platforms.

Retrieval of Martian ozone and dust from SPICAM spectrometer for MY27–MY28

Ozone \((\hbox {O}_{3})\) is important in the stabilisation of \(\hbox {CO}_{{2}}\) in the Martian atmosphere and thus it is important to study the spatio-temporal variability of \(\hbox {O}_{{3}}\). We retrieve two years of total columnar \(\hbox {O}_{{3}}\) from raw spectral data provided by the SPectroscopy for the Investigation of the Characteristics of the Atmosphere of Mars (SPICAM) instrument aboard the Mars Express. The seasonal variability is studied in tropical, mid- and high latitudes and is compared with simulations by a photochemical coupled general circulation model (GCM). The high latitudes exhibit the largest seasonal variations in \(\hbox {O}_{{3}}\), with a winter high and a summer low and a comparison with GCM results is good in general. We have studied the correlation of \(\hbox {O}_{{3}}\) with dust, retrieved simultaneously from SPICAM observations. In southern tropical latitudes, the columnar \(\hbox {O}_{{3}}\) is seen to increase during a global dust storm year (Martian year (MY) 28) compared to the \(\hbox {O}_{{3}}\) column values during a year without global dust storm (MY27), although the water vapour column between these years remains unchanged. This indicates the radiative impact of dust on \(\hbox {O}_{{3}}\) and its retrieval. We also study the ozone–carbon monoxide correlation as a tracer of dynamics. The dynamical contribution to the \(\hbox {O}_{{3}}\) column is found to be the highest during winter over the southern polar region.

Differences in the Cyanobacterial Community Composition of Biocrusts From the Drylands of Central Mexico. Are There Endemic Species?

In drylands worldwide, biocrusts, topsoil microbial communities, are prevalent, contributing to the biostabilization of soils and allowing the subsequent establishment and growth of vascular plants. In early successional biocrusts, cyanobacteria are the first dominant colonizers of bare ground, largely determining their functioning. However, there are large gaps in our knowledge of the cyanobacterial diversity in biocrusts, particularly in understudied geographic regions, such as the tropical latitudes. We analyzed the diversity of the cyanobacteria inhabiting the biocrusts of semideserts from Central Mexico in two localities belonging to the same desert system (Chihuahuan Desert) that are separated by a cordillera that crosses the center of Mexico. Morphological identification of the cyanobacteria was carried out after cultivation in parallel with the direct observation of the environmental samples and was supported by genetic characterization through analysis of the 16S rRNA gene of the isolated strains and by next-generation sequencing of the soil samples. Taxonomic assignment revealed a clear dominance of heterocystous cyanobacteria at one of the studied locations (Actopan, Hidalgo state). Although heterocystous forms were abundant at the other location (Atexcac, Puebla state), almost a third of the cyanobacterial phylotypes were represented by unicellular/colonial cyanobacteria, mostly Chroococcidiopsis spp. Only 28.4% of the phylotypes were found to be common to both soils. Most of the other taxa, however, were biocrust-type specific, and approximately 35% of the phylotypes were found to be unique to the soil they were collected in. In addition, differences in the abundances of the shared cyanobacteria between the locations were also found. These differences in the cyanobacterial distribution were supported by the distinct responses of the isolated strains representative of the sites to extreme heat and desiccation in bioassays. Some cyanobacteria with high abundance or only present at the hottest Actopan site, such as Scytonema hyalinum, Scytonema crispum, Nostoc commune, Nostoc sp., and Calothrix parietina, survived extreme heat and desiccation. However, Tolypothrix distorta and Chroococcidiopsis spp. were clearly sensitive to these extreme conditions in relation to their lower abundances at Actopan as opposed to Atexcac. Since novel biocrust-associated phylotypes were also found, the emergence of endemic cyanobacterial taxa is discussed.

A corridor of exposed ice-rich bedrock across Titan’s tropical region

Global maps of Titan show great diversity in terrain types, but their associations with specific compositions on a large scale are obscured by Titan’s thick atmosphere, which shrouds the weak spectral features. Here we develop a principal component analysis (PCA) that enables the identification of subtle spectral features. The PCA was applied to over 13,000 Cassini/VIMS spectra that cover half of Titan’s globe, focused on tropical latitudes. Our analysis detected an ice-rich linear feature of bedrock, which extends a length equivalent to 40 per cent of Titan’s circumference. This corridor is puzzling because it does not correlate with topography or measurements of the subsurface. Ice-rich terrains in other areas of Titan occur only in local regions excavated by craters or exposed by erosion, suggesting that cryovolcanism, if active, is currently not widespread. We also find evidence for a diversity of organic sediments, formed by the photolysis of Titan’s past atmospheres, which remain to be investigated, perhaps using a similar approach. A principal component analysis of Cassini’s infrared spectral maps of Titan reveals the main features of Titan’s equatorial surface, effectively removing the obscuring atmospheric effects. A 6,300-kilometre-long strip of exposed icy bedrock—uncorrelated with topography or measurements of the subsurface—is visible, surrounded by organic deposits.