Nitrogen‐fixing microorganisms (diazotrophs) provide biologically available nitrogen to plankton communities and thereby greatly influence the productivity in many marine regions. Various ...cyanobacterial groups have traditionally been considered the major oceanic diazotrophs, but later noncyanobacterial and presumably heterotrophic diazotrophs were also found to be widespread and potentially important in nitrogen fixation. However, the distribution and activity of different diazotroph groups is still poorly constrained for most oceanic ecosystems. Here we examined diazotroph community structure and activity along a 7500 km south‐north transect between the central equatorial Pacific and the Bering Sea. Nitrogen fixation contributed up to 84% of new production in the upper waters of the subtropical gyre, where the diazotroph community included the gammaproteobacterium γ‐24774A11 and highly active cyanobacterial phylotypes (>50% of total nifH transcript abundance). Nitrogen fixation was sometimes detectable down to 150 m depth and extended horizontally to the edge of the gyre at around 35°N. Nitrogen fixation was even detected far north on the Bering Sea shelf. In the Alaskan Coastal Waters on the Bering Sea shelf, low nitrate together with high dissolved iron concentrations seemed to foster diazotroph growth, including a prominent role of UCYN‐A2, which was abundant near the surface (1.2×105 nifH gene copies L−1). Our study provides evidence for nitrogen fixation in the Bering Sea and suggests a clear contrast in the composition of diazotrophs between the tropical/subtropical gyre and the separate waters in the cold northern regions of the North Pacific.
Key Points
N2 fixation in the North Pacific occurred not only in the tropics and subtropics but also in the subarctic Bering Sea
Cyanobacterial nifH gene expression exceeds that of noncyanobacterial diazotrophs on a diurnal basis in the tropics and subtropics
UCYN‐A2 was the dominant diazotroph in the cold, nitrate‐depleted, and iron‐rich Bering Sea
•FTNIR & HCA used for identification of infested rice stored varieties.•Heterogeneity with infestation level was identified in rice by cluster & dendrogram analysis.•FTNIR with HCA has potential for ...sorting rice varieties where quantification is not required.
The potential and practicality of FTNIR as a screening tool, with ward’s algorithms, was performed for two different varieties of rice namely, ‘badshah bhog’ and ‘swarna’, followed by cluster, dendrogram, histogram, and conformity analysis with different storage periods (0–225) and insect infestation. Dendrogram analysis resulted in a clear differentiation between infested rice varieties with non-infested ones while hierarchical cluster analysis, lead to detection of different levels of infestations. Histograms analysis of averaged FTINR spectra of rice grains samples provided 100% classification between infested and non-infested samples. Dissimilarities between rice grains were calculated using Pearson’s correlation coefficients which were further converted to D values, and heterogeneity among the different varieties of rice along with a different level of infestation was identified. The results further revealed that the percentage accuracy (%) of classification for badshah bhog varied from 93.10 to 98.84%, while that for the swarna rice was between 95.75 and 99.74%.
The modes of occurrence for elements in coal are extremely important for deciphering geological process of coal formation and for anticipating the technological behavior and environmental and health ...impacts derived from coal utilization. Hierarchical clustering algorithm has been widely adopted to investigate the modes of occurrence of elements in coal. The traditional statistics (e.g., Pearson correlation, Euclidean distance) for the elemental data of coal may lead to misinterpretation because the elemental data of coal are of compositional nature and follow the rules of Aitchison geometry. This work applied log-ratio transformations in order to overcome this problem. Different hierarchical clustering algorithms with various data transformations can infer modes of occurrence for coal elements, but which algorithm is optimum deserves to be investigated. In this paper, we discuss four commonly used hierarchical clustering algorithms utilizing pivot coordinates and weighted symmetric pivot coordinates (WSPC), two types of log-ratio transformations, to infer modes of occurrence of elements in coal, based on published coal elemental data. Results showed that the Pearson correlation produces more meaningful results than the Euclidean distance in clustering rare earth elements and Y. WSPC produces more interpretable results than those from pivot coordinates transformed data for these coal elemental data. Compared with the single, complete, and centroid, the average-linkage algorithm is indeed the optimum.
Integration of late Quaternary continental and marine proxies allows improved reconstruction of palaeoenvironment and palaeoclimates models for the south-eastern coast of Brazil. In this paper, we ...analyse pollen, fern spores, and dinoflagellate cysts in a marine sediment core (GL74) over the last ∼109 kyr. Results showed that, between 109 and 89.5 kyr, low sea levels promoted the expansion of herbaceous taxa across open areas while climatic conditions were relatively warm and humid, as indicated by the high frequency of Atlantic rainforest Ombrophilous forest pollen types and abundant of fern spores. Between ∼79–49 kyr, higher concentrations of palynomorphs were recorded, which were likely related to the low relative sea level during the last glacial period. During this interval, there was a decrease in tree pollen grains and an increase in shrub and herbaceous pollen grains, indicating cold and relatively dry weather conditions. In the Holocene period, the low deposition of palynomorphs may have been influenced by the gradual submergence of the central part of the Brazilian coast. This process was associated with warm and humid climatic conditions, as suggested by the expansion of rainforests and the presence of hygrophyte/aquatic taxa and fern spores, as well as the retraction of grassland pollen types. Dinocyst assemblages suggest that nutrient-rich waters and/or the presence of upwelling cells were dominant between ∼109–88 kyr, but gradually reduced between 88 and 65 kyr (and/or ∼ 88–20 kyr) under the influence of subtropical fronts. The study culminated in the dominance of unproductive warm water in the upper column between 65 and 0.5 kyr.
•Correlation of continental and marine proxies in south-eastern Brazil during the late Quaternary Late•Quaternary dynamics of the South Atlantic Ocean based on dinocysts•Reconstruction of palaeovegetation and palaeoclimate for the last ∼109 kyr along the southeast coast of Brazil
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•Molecular composition of DOM differs significantly with lake salinity.•Oxidation state of carbon of DOM increases with lake salinity.•Molecular weight and number of carbon atoms in ...DOM decrease with lake salinity.•Environmental and microbial factors shape DOM composition in saline lakes.•Microbes explain lake DOM composition better than environmental factors.
Increased knowledege of the molecular composition of dissolved organic matter (DOM) is of great importance for an improved understanding of carbon cycling in lakes. However, such information remains limited for saline lakes. Here, DOM molecular compositions and microbial community structures were investigated in saline lakes with a full range of salinity from freshwater to hypersaline. An integrated approach, including Fourier transform-ion cyclotron resonance mass spectrometry and Illumina sequencing was employed. The results showed that in the studied saline lakes, aliphatic compounds, highly unsaturated and oxygen poor/rich compounds were the dominant DOM molecules. With increasing salinity, the molecular weight and carbon contents of the DOM molecules decreased, while their oxygen contents and carbon oxidation states increased. DOM molecular composition was significantly correlated with multiple environmental variables (i.e., chlorophyll a, salinity, pH) and with microbial components. The synergy of environmental and microbial factors exhibited great importance in explaining the variation of DOM molecular composition. Comparatively, microbial factors alone gave a much better explanation than environmental factors alone of the variation of DOM molecular composition, emphasizing the tight connection between DOM molecular composition and microbial communities. Taken together, these findings help improve our understanding of the molecular composition of DOM and its influencing factors in saline lakes.
To investigate the distribution, source, contamination, and ecological risk status of heavy metals in the Red Sea-Gulf of Aqaba coast, Saudi Arabia, 33 surface sediment samples were collected for Fe, ...Zn, Sb, Co, Cu, Hg, Pb, Mn, Cr, Ni, Cd, As, and TOC analysis using ICP-MS. Three single and three multi-element contamination indices were used to assess the sediment quality. Evaluation of the three single pollution indices suggested some contamination or anthropogenic inputs with Cu, Cd, Hg, and, to a great extent, As. The potential ecological risk indicated low ecological risk at all sites for Pb, Zn, Ni, Cu, Co, Cr, and Sb; and considerable risk for Cd, Hg, and As. Moreover, the average values of Hg and As were higher than those recorded in the sediment quality guidelines. The multivariate statistical tools revealed that Fe, Mn, Cd, Cu, Co, Zn, and Cr were mostly of terrestrial origin, derived from weathering of the nearby Pre-Cambrian basement rocks, Tertiary, and Quaternary sedimentary rocks; while As, Sb, Hg, Ni, and Pb were mostly attributed to anthropogenic activities from traffic emissions, industrial activities, and the dredging of marine sediments. The results of this work will guide the future projects of environmentally sustainable development in northwest Saudi Arabia.
•Fe, Zn, Sb, Co, Cu, Hg, Pb, Mn, Cr, Ni, Cd, and As were analyzed in 33 sediment.•Fe > Mn > As > Cr > Cu > Zn > Ni > Pb > Co > Cd > Hg > Sb.•Pb, Zn, Ni, Cu, Co, Cr, and Sb showed low ecological risk.•The potential ecological risk indicated considerable risk for Cd, Hg, and As.
Two phytogeographic units were defined for the Middle–Upper Triassic of Gondwana, the warm humid Onslow and the cool-temperate Ipswich microfloras; nevertheless, many uncertainties remain regarding ...the geographical scope of such assemblages, as well as to the degree of similarity between phytogeographical regions and the existence of different microfloristic domains within the Laurasian territory. To tackle these questions, a hierarchical cluster analysis complemented with ordination methods and bipartite network analysis was performed over a list of 70 palynomorph species and selected localities of the Anisian–Ladinian, Carnian and Norian time-intervals, with special emphasis on southwestern Gondwana units. Obtained results showed a clear dichotomy between tropical and extratropical associations, within which different microfloristic regions also developed from gradual changes in the frequency distribution of palynotaxa. These findings are significant because they confirm for first time through quantitative methods a phytogeographic separation between ‘Onslow’ and ‘Euro-Mediterranean’ assemblages, considered for a long time to be part of the same microflora. Furthermore, and contrary to expectations, two distinct phytogeographic units were recognized for the Laurasian territory, where the first is related to the hot and dry margins of western Tethys, and the other to the temperate and humid zones of Boreal Pangea. Likewise, a separate and well defined assemblage was recognized for southwestern Gondwanan, during the late Anisian–Carnian of central-western Argentina, named here as the Cuyo microfloristic region. This unit showed a close resemblance to microfloras of northern Laurasia due to the shared presence of several species of miospores that are largely absent from the eastern part of Pangea. We hypothesize that the migration of such species occurred through a trans-equatorial temperate and humid landway, following the rift basins and topographic highs developed along the suture lines of the Variscan orogenic belt and western South America at the beginning of Pangea separation.
•‘Onslow’ and ‘Euro-Mediterranean’ assemblages are separate microfloristic regions.•Two phytogeographic units are recognized for Laurasia: the Boreal and West-Tethyan.•A new microfloristic region is proposed for southwestern Gondwana: the Cuyo region.•A Close similarity was found between the Boreal and Cuyo microfloristic regions.•A trans-equatorial landway would have connected the Arctic with the Cuyo region.
Apart from northern and central China, the fossil record of the latest Miocene and Early Pliocene of Asia is not well documented and the record of South China during this interval is especially poor. ...Shuitangba, a site in Yunnan Province, offers a rare window into the paleoenvironment of the latest Miocene in southwestern China. Over 2400 vertebrate and macrobotanical specimens have been recovered from the site. The faunal assemblage is dominated by aquatic avian taxa and many of the mammalian taxa are those that indicate densely vegetated, water-margin habitats. Pollen and carpological remains indicate a temperate to subtropical, broad-leaved/coniferous forest around standing water, with more open areas containing grasses and herbs. Analyses of clay minerals, chemical weathering, and enamel stable isotopes suggest that Shuitangba was warmer and more humid than today, possibly with more pronounced seasonality. Results of community structure analysis indicate that the Shuitangba mammalian community was different from those of other Late Miocene Chinese sites in the high proportions of aquatic-dependent mammalian taxa. While Shuitangba shared mammalian faunal elements with other Late Miocene sites in Yunnan, it was still faunally distinct. Further, Shuitangba was depauperate in its mammalian fauna, which may have been a result of the depositional setting rather than a true reflection of regional faunal diversity.
•Shuitangba is a unique window into the Late Miocene.•Shuitangba sampled a densely vegetated water-margin habitat.•Shuitangba mammal community differed from those of other Late Miocene Chinese sites.
A key method to investigate magma dynamics is the analysis of the crystal cargoes carried by erupted magmas. These cargoes may comprise crystals that crystallize in different parts of the magmatic ...system (throughout the crust) and/or at different times. While an individual eruption likely provides a partial view of the subvolcanic plumbing system, compiling data from multiple eruptions can build a picture of a whole magmatic system. In this study, we use machine learning techniques to analyze a large (>2,000) compilation of mineral compositions from a highly active arc volcano: Villarrica, Chile. Villarrica's postglacial eruptive activity (14 ka–present) displays large variation in eruptive style (mafic ignimbrites to Hawaiian style effusive eruptions), yet its eruptive products have a near constant basalt‐basaltic andesite bulk‐rock composition. What therefore, is driving explosive eruptions at Villarrica and can differences in storage dynamics be related to eruptive style? Here, we use a hierarchical cluster analysis to detect previously unseen structure in the composition of olivine, plagioclase and clinopyroxene crystals erupted at Villarrica, revealing the presence of compositionally distinct clusters within each crystal population. Using rhyolite‐MELTS thermodynamic modeling, we related these clusters to intensive magmatic variables: temperature, pressure, water content, and oxygen fugacity. Our results provide evidence for the existence of multiple discrete (spatial and temporal) magma reservoirs beneath Villarrica where melts differentiate and mix with incoming more primitive magma. The compositional diversity within an erupted crystal cargo strongly correlates with eruptive intensity, and we postulate that mixing between primitive and differentiated magma drives explosive activity at Villarrica.
Plain Language Summary
Studies of volcanoes often focus on a single eruption. However, the magmatic systems beneath volcanoes are complex: magmas crystallize throughout the crust and the minerals erupted at the surface can be formed just prior to eruption, or thousands of years earlier. Here, we use machine‐learning methods to group mineral compositions from many eruptions of an active Chilean volcano (Villarrica) to build a picture of the magmatic system. By using the appropriate mathematical treatment, we find that there are distinct groups of mineral compositions that were not identified by past studies. These different compositions are used to demonstrate that different batches of magma have mixed throughout Villarrica's postglacial history. This suggests that mixing of different magmas drives explosive eruptions at Villarrica volcano.
Key Points
Unsupervised machine learning reveals previously undetected compositional clusters in Villarrica's crystal cargoes
Thermodynamic models demonstrate magma storage occurs in a vertically extensive system containing variably evolved mushy reservoirs
Temporal trends in crystal cargo contents and mineral zoning suggest magma mixing triggers unusual large mafic ignimbrites
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