Trace element differentiation in ferruginous accumulation soil patterns under tropical rainforest of southern Cameroon, the role of climatic change

2003 ◽  
Vol 303 (3) ◽  
pp. 203-214 ◽  
Author(s):  
Emile Temgoua ◽  
Hans-Rudolf Pfeifer ◽  
Dieudonné Bitom
Keyword(s):  
Trace Element ◽  
Climatic Change ◽  
Tropical Rainforest ◽  
Southern Cameroon

scholarly journals The role of sulphur on the melting of Ca-poor sediment and on trace element transfer in subduction zones: an experimental investigation

2021 ◽  
Author(s):  
Anne-Aziliz Pelleter ◽  
Gaëlle Prouteau ◽  
Bruno Scaillet
Keyword(s):  
Trace Element ◽  
Partial Melting ◽  
Subduction Zones ◽  
Sediment Flux ◽  
Arc Magmas ◽  
Trace Element Contents ◽  
The Stability ◽  
Element Transfer ◽  
High Sediment

Abstract We performed phase equilibrium experiments on a natural Ca-poor pelite at 3 GPa, 750-1000 °C, under moderately oxidizing conditions, simulating the partial melting of such lithologies in subduction zones. Experiments investigated the effect of sulphur addition on phase equilibria and compositions, with S contents of up to ∼ 2.2 wt. %. Run products were characterized for their major and trace element contents, in order to shed light on the role of sulphur on the trace element patterns of melts produced by partial melting of oceanic Ca-poor sediments. Results show that sulphur addition leads to the replacement of phengite by biotite along with the progressive consumption of garnet, which is replaced by an orthopyroxene-kyanite assemblage at the highest sulphur content investigated. All Fe-Mg silicate phases produced with sulphur, including melt, have higher MgO/(MgO+FeO) ratios (relative to S-free/poor conditions), owing to Fe being primarily locked up by sulphide in the investigated redox range. Secular infiltration of the mantle wedge by such MgO and K2O-rich melts may have contributed to the Mg and K-rich character of the modern continental crust. Addition of sulphur does not affect significantly the stability of the main accessory phases controlling the behaviour of trace elements (monazite, rutile and zircon), although our results suggest that monazite solubility is sensitive to S content at the conditions investigated. The low temperature (∼ 800 °C) S-bearing and Ca-poor sediment sourced slab melts show Th and La abundances, Th/La systematics and HFSE signatures in agreement with the characteristics of sediment-rich arc magmas. Because high S contents diminish phengite and garnet stabilities, S-rich and Ca-poor sediment sourced slab melts have higher contents of Rb, B, Li (to a lesser extent), and HREE. The highest ratios of La/Yb are observed in sulphur-poor runs (with a high proportion of garnet, which retains HREE) and beyond the monazite out curve (which retains LREE). Sulphides appear to be relatively Pb-poor and impart high Pb/Ce ratio to coexisting melts, even at high S content. Overall, our results show that Phanerozoic arc magmas from high sediment flux margins owe their geochemical signature to the subduction of terrigenous, sometimes S-rich, sediments. In contrast, subduction of such lithologies during Archean appears unlikely or unrecorded.

From rationalization to rationality: (In)sustainability of strategic narratives in  science communication, ranging from climatic change to hydro-meteorological extremes

2021 ◽  
Author(s):  
Mónica Ribau ◽  
Rui Perdigão ◽  
Julia Hall
Keyword(s):  
Climatic Change ◽  
Science Communication ◽  
Scientific Discourse ◽  
Living Condition ◽  
High Impact ◽  
Scientific Models ◽  
Public Confidence ◽  
Scientific Culture ◽  
Strategic Narratives

<p>Strategic narratives (persuasive use of story systems) in science communication have been gathering<br>increasing support, especially in the face of misunderstandings about high-impact climatic change and hydrometeorologic extremes.<br>The use of these narratives reveals, in line with linguistic research, that traditional scientific discourse<br>conception has become outdated. Should scientific discourse be centered on the description of discoveries?<br>Should the role of political discourse be to convince someone to act? Before answering these, it is necessary to<br>understand the crucial function that uncertainty plays in communication, along with its consequences in the<br>concepts of objectivity and truth. More importantly, understanding its role in scientific society and sustainability.<br>Unable to eliminate uncertainty altogether, science becomes an essential escort to recognize, manage<br>and communicate its pertinency. However, the most popular strategic narratives sideline uncertainty as a threat.<br>Denialists follow a similar approach, though they communicate uncertainty to discredit evidence. Comparatively,<br>in their latest Assessment Report, the IPCC characterized uncertainty whilst stating: “uncertainty about impacts<br>does not prevent immediate action”.<br>Scientific discourse outputs and social reality constructions influence each other. The moralization of<br>science communication reveals how XVII century revolutionary skepticism can now be perceived as a threat, and<br>facts expected from science can be deemed dogmatic truths and perceived as decrees through rationalism and as<br>an extension of Judeo-Christian philosophical influence. Equally important, uncertainty reinforces individual<br>freedom, while society grasps and recognizes certainty as security and demands it from institutions, accepting<br>degrees of authoritarianism to maintain a tolerable living condition.<br>From “Climate Emergency” to “Thousand-Year Flood”, public interest in climatic change and extremes<br>increases following high-impact events, yet trust in science plunges into a deep polarized divide among absolute<br>acceptance and outright rejection relative to the bold headlines conveyed not only in the media but also in some<br>scientific literature.<br>Political, religious and activist leaders strike one as prophets acting in the name of science. From<br>rationalism to rationality, scientific culture is pivotal to the analysis of complexity, objectivity, and uncertainty in<br>the definition of truth (absent from epistemological discussions for centuries). Humor/sarcasm, literature or<br>dialectic are examples of how to communicate entropy of scientific models, while reflecting about the role,<br>uncertainty, and mistake, retain in life.<br>“People want certainty, not knowledge”, said Bertrand Russel. However, neither science nor democracy<br>work like that, rather taking reality as having shades of grey instead of a reduced black-or-white dichotomy.<br>Science is not about giving just one single number to problems clearly not reducible to such, as that gives a false<br>sense of certainty and security in an entropic world where we cannot control everything.<br>In order to objectively analyze discourses in light of their uncertainty features, detecting whether they<br>contain polarized, absolutistic narrative patterns, we introduce a new process-consistent Artificial Intelligence<br>framework, building from Perdigão (2020, https://doi.org/10.46337/200930). The complementarity of our<br>approach relative to both social and information technologies is brought out, along with ways forward to reinforce<br>the fundamental role of uncertainty in scientific communication, and to strengthen public confidence in the<br>scientific endeavor.</p>

scholarly journals Secondary Fluorescence in WDS: The Role of Spectrometer Positioning

2018 ◽  
Vol 24 (6) ◽  
pp. 604-611 ◽  
Author(s):  
Ben Buse ◽  
Jon Wade ◽  
Xavier Llovet ◽  
Stuart Kearns ◽  
John J. Donovan
Keyword(s):  
Trace Element ◽  
Electron Probe ◽  
Systematic Errors ◽  
Fluorescence Yield ◽  
Simulation Code ◽  
Wavelength Dispersive Spectrometer ◽  
High Fluorescence ◽  
A Minor ◽  
Secondary Fluorescence

AbstractSecondary fluorescence (SF), typically a minor error in routine electron probe microanalysis (EPMA), may not be negligible when performing high precision trace element analyses in multiphase samples. Other factors, notably wavelength dispersive spectrometer defocusing, may introduce analytical artifacts. To explore these issues, we measured EPMA transects across two material couples chosen for their high fluorescence yield. We measured transects away from the fluorescent phase, and at various orientations with respect to the spectrometer focal line. Compared to calculations using both the Monte Carlo simulation code PENEPMA and the semi-analytical model FANAL, both codes estimate the magnitude of SF, but accurate correction requires knowledge of the position of the spectrometer with respect to the couple interface. Positioned over the fluorescent phase or otherwise results in a factor of 1.2–1.8 of apparent change in SF yield. SF and spectrometer defocusing may introduce systematic errors into trace element analyses, both may be adequately accounted for by modeling. Of the two, however, SF is the dominant error, resulting in 0.1 wt% Zn apparently present in Al at 100 μm away from the Zn boundary in an Al/Zn couple. Of this, around 200 ppm Zn can be attributed to spectrometer defocusing.

scholarly journals Are tropical reptiles really declining? A six-year survey of snakes in Drake Bay, Costa Rica, and the role of temperature, rain and light

2019 ◽  
Author(s):  
Jose Pablo Barquero-González ◽  
Tracie L. Stice ◽  
Gianfranco Gómez ◽  
Julián Monge-Nájera
Keyword(s):  
Costa Rica ◽  
Environmental Factors ◽  
Sea Level ◽  
Tropical Rainforest ◽  
Transect Counts ◽  
Diet Type

AbstractIntroductionstudies in the last two decades have found declining snake populations in both temperate and tropical sites, including informal reports from Drake Bay, Costa Rica.Objectiveto investigate if reports of decreasing snake populations in Drake Bay had a real basis, and if environmental factors, particularly temperature, rain and light, have played a role in that decrease.Methodswe worked at Drake Bay from 2012 through 2017 and made over 4000 h of transect counts. Using head flashlights we surveyed a transect covered by lowland tropical rainforest at an altitude of 12–38 m above sea level, near the Agujas River, mostly at 1930–2200 hours. We counted all the snakes that we could see along the transect.Resultssnake counts increase from August to September and then decline rapidly. The May snakes/rainfall peaks coincide, but the second snake peak occurs one month before the rain peak; we counted more snakes in dry nights, with the exception of Imantodes cenchoa which was equally common despite rain conditions. We saw less Leptodeira septentrionalis on bright nights, but all other species were unaffected. Along the six years, the number of species with each diet type remained relatively constant, but the number of individuals declined sharply for those that feed on amphibians and reptiles. We report Rhadinella godmani, a highland species, at 12–38 m of altitude.Conclusionnight field counts of snakes in Drake Bay, Costa Rica, show a strong decline from 2012 through 2017.

scholarly journals Barium stable isotopes as a fingerprint of biological cycling in the Amazon River basin

2020 ◽  
Vol 17 (23) ◽  
pp. 5989-6015
Author(s):  
Quentin Charbonnier ◽  
Julien Bouchez ◽  
Jérôme Gaillardet ◽  
Éric Gayer
Keyword(s):  
Organic Matter ◽  
Stable Isotope ◽  
Trace Element ◽  
Isotope Composition ◽  
Silicate Weathering ◽  
Biological Cycling ◽  
Biological Uptake ◽  
Dissolved Load ◽  
Silicate Rocks

Abstract. The biological cycle of rock-derived nutrients on the continents is a major component of element transfer between the Earth's surface compartments, but its magnitude currently remains elusive. The use of the stable isotope composition of rock-derived nutrients, which can be fractionated during biological uptake, provides a promising path forward with respect to quantifying biological cycling and its overall contribution to global element cycling. In this paper, we rely on the nutrient-like behaviour of the trace element barium (Ba) and use its elemental and stable isotope compositions in dissolved and sediment load river samples to investigate biological cycling in the Amazon Basin. From these measurements, we show that dissolved Ba mainly derives from silicate rocks, and a correlation between dissolved Ba and K abundances suggests that biological cycling plays a role in the Ba river budget. Furthermore, the isotope composition of Ba (δ138Ba) in the dissolved load was found to be significantly different from that of the parent silicate rocks, implying that dissolved Ba isotopic signatures are affected by (i) the precipitation of soil-forming secondary phases as well as (ii) biological uptake and release from dead organic matter. Results from an isotope mass balance method applied to the river dissolved load data indicate that, after its release to solution by rock weathering, Ba is partitioned between the river dissolved load, secondary weathering products (such as those found in soils and river sediments), and the biota. In most sub-catchments of the Amazon, river Ba abundances and isotope compositions are significantly affected by biological cycling. Relationships between estimates of Ba cycled through biota and independent metrics of ecosystem dynamics (such as gross primary production and terrestrial ecosystem respiration) allow us to discuss the role of environmental parameters such as climate or erosion rates on the biological cycling of Ba and, by extension, the role of major rock-derived nutrients. In addition, catchment-scale mass and isotope budgets of Ba show that the measured riverine export of Ba is lower than the estimated delivery of Ba to the Earth surface through rock alteration. This indicates the existence of a missing Ba component, which we attribute to the formation of Ba-bearing particulate organics (possibly accumulating as soil organic matter or currently growing biomass within the catchments) and to organic-bound Ba exported as “unsampled” river particulate organic matter. Given our findings on the trace element Ba, we explore whether the river fluxes of most major rock-derived nutrients (K, Mg, Ca) might also be significantly affected by biological uptake or release. A first-order correction of river-derived silicate weathering fluxes from biological cycling shows that the carbon dioxide (CO2) consumption by silicate weathering at the mouth of the Amazon could be several times higher than the previously reported value of 13 × 109 mol CO2 yr−1 (Gaillardet et al., 1997). Overall, our study clearly shows that the chemical and isotope compositions of rivers in the Amazon – and most likely in other large river basins – bear a biological imprint, thereby challenging common assumptions made in weathering studies.

Sign in / Sign up

Export Citation Format

Share Document