Secular Changes Research Articles

Forced signal and predictability in a prototype climate model: Implications for fingerprinting based detection in the presence of multidecadal natural variability.

Advanced numerical models used for climate prediction are known to exhibit biases in their simulated climate response to variable concentrations of the atmospheric greenhouse gases and aerosols that force a non-uniform, in space and time, secular global warming. We argue here that these biases can be particularly pronounced due to misrepresentation, in these models, of the multidecadal internal climate variability characterized by large-scale, hemispheric-to-global patterns. This point is illustrated through the development and analysis of a prototype climate model comprised of two damped linear oscillators, which mimic interannual and multidecadal internal climate dynamics and are set into motion via a combination of stochastic driving, representing weather noise, and deterministic external forcing inducing a secular climate change. The model time series are paired with pre-specified patterns in the physical space and form, conceptually, a spatially extended time series of the zonal-mean near-surface temperature, which is further contaminated by a spatiotemporal noise simulating the rest of climate variability. The choices of patterns and model parameters were informed by observations and climate-model simulations of the 20th century near-surface air temperature. Our main finding is that the intensity and spatial patterns of the internal multidecadal variability associated with the slow-oscillator model component greatly affect (i) the ability of modern pattern-recognition/fingerprinting methods to isolate the forced response of the climate system in the 20th century ensemble simulations and (ii) climate-system predictability, especially decadal predictability, as well as the estimates of this predictability using climate models in which the internal multidecadal variability is underestimated or otherwise misrepresented.

Stamps.com: secular changes in a business model

Stamps.com: secular changes in a business model

Distinct effects of Tibetan Plateau growth and global cooling on the eastern and central Asian climates during the Cenozoic

The evolution of the climate in eastern and central Asia during the Cenozoic was affected by regional paleogeographic developments and global climate change. Previous studies have mainly investigated the effects of Tibetan Plateau (TP) growth and global cooling for specific time periods. However, the respective contributions of these two factors over time are still poorly understood. In this study, we comprehensively compared the effects of TP growth and secular climate change by integrating existing paleobotanical records and model results across a total of 67 experiments. Our results demonstrate that the effects of TP growth and global cooling on the eastern and central Asian climates differed. During the early Eocene, high atmospheric CO2 concentrations contributed greatly to the relatively wet conditions in eastern and central Asia. Subsequent global cooling tended to cause long-term aridification in eastern Asia. By comparison, TP growth was the key factor for the increasing precipitation in eastern Asia and the decreasing precipitation in central Asia between the late Oligocene and the early Miocene. High atmospheric CO2 concentrations contributed to the increased wetness in eastern Asia in the geological past, and this fact has far-reaching implications for future wetter conditions in this region under anthropogenic forcing.

Trends in sports participation in adolescents: Data from a large-scale sample in the US adolescents.

Although changes in overall physical activity (PA) have been identified in adolescents, the trend in sports participation is still understudied. It is widely believed that monitoring the changes in sports participation is conducive to promote the development of sports activities. The purpose of this research was to identify the changes in sports participation in adolescents over the past years. This research selected secondary data from 2011, 2013, 2015, 2017, and 2019 Youth Risk Behavior Surveillance (YRBS). Logistic regression models were applied to discuss and analyze the secular changes across the years of data. The change differences in sports participation by sex, grade, and race/ethnicity were also explored via separate logistic regression. A declined overall trend could be observed in sports participation in adolescents, the prevalence of sport participation was 58.4% in 2011 and 57.4% in 2019. The declining trend was also observed in grades 10 (62.3% in 2011 and 57.9% in 2019) and 12 (52.5% in 2011 and 49.8% in 2019) adolescents, and an increase could be observed in grade 11 (56.2% in 2011 and 59.1% in 2019) adolescents, but few changes were found in grade 9 (61.4% in 2011 and 61.9% in 2019) adolescents. Only white adolescents reported an increasing prevalence of sports participation, slight declines in sports participation were observed in black or African American, Hispanic/Latino, and other adolescents. The declining trend in sports participation could be seen in adolescents between 2011 and 2019, but it should also note that large variations of trends in sport participation by subgroups were also found.

Fifteen-year secular changes in the care and outcomes of patients with out-of-hospital cardiac arrest in Japan: a nationwide, population-based study.

Countries have implemented initiatives to improve the outcomes of patients with out-of-hospital cardiac arrest (OHCA). However, secular changes in care and outcomes at the national level have not been extensively investigated. This study aimed to determine 15-year secular changes in the outcomes of such patients in Japan. Using population-based data of patients with OHCA, covering all populations in Japan (2005-19), patients for whom resuscitation was attempted were identified. The primary outcome was a favourable neurological outcome (Cerebral Performance Category 1 or 2: sufficient cerebral function for independent activities of daily life and work in a sheltered environment). Secular changes in outcomes were determined using a mixed-level multivariate logistic regression analysis. Overall, 1764440 patients (42.4% women; median age, 78 years) were examined. The incidence, median age, and proportion of patients who received bystander cardiopulmonary resuscitation (CPR) and dispatcher instructions for resuscitation increased significantly during the study period (P <0.001). A significant trend was noted toward improved outcomes over time (P for trend<0.001); favourable neurological outcome proportions 1 month after arrest increased from 1.7-3.0% (odds ratio, 1.03 per 1-incremental year). A remarkable increase was noted in favourable neurological outcomes in younger patients and patients with initial shockable cardiac rhythm, while improvement varied among prefectures. In Japan, collaborative efforts have yielded commendable achievements in the care and outcomes of patients with OHCA over 15 years through to 2019, while the improvement depended on patient characteristics. Further initiatives are needed to improve OHCA outcomes.

Secular change of true polar wander over the past billion years.

The rate of movement of Earth’s solid shell relative to its spin axis, or true polar wander, depends on variations in mantle convection and viscosity. We report paleomagnetic and geochronologic data from South China that constrain the rate of rapid true polar wander (>5° per million years) between 832 million years and 821 million years ago. Analysis of the paleomagnetic database demonstrates secular change of true polar wander related to mantle cooling and thermal structure across supercontinent cycles. True polar wander rates are relatively muted with a partially insulated mantle during supercontinent assembly and accelerate as mantle thermal mixing reestablishes with supercontinent breakup. Decreasing true polar wander rate through the Neoproterozoic was succeeded by overall smaller variations in the Phanerozoic. We propose that Neoproterozoic extensive plate tectonic activities enhanced mantle cooling, giving rise to a reduction in mantle convective forcing, an increase in mantle viscosity, and a decrease in true polar wander rates into the Phanerozoic.

Dark matter and motion of bodies in space

This paper investigates the degree of influence of the gravitational field of dark matter on the laws of motion of bodies in a medium in a restricted two-body problem, when a test body (planet, asteroid, artificial satellite of a star, in particular, the Sun, etc.) has its own rotation, i. e. own angular momentum impulse. The study was carried out within the framework of the post-Newtonian approximation of the general theory of relativity. In accordance with the latest experimental data, hypotheses about the average densities of dark matter ρD.M. and visible matter ρvis. in planetary systems are accepted. In particular, in the Solar system the following is accepted: ρD.M ≈ 2,8 · 10–19 g · cm–3, ρvis ≈ 3 · 10–20 g · cm–3 and ρΣ = ρvis + ρD.M ≈ 3,1 · 10–19 g · cm–3. In the post-Newtonian approximation of the general theory of relativity, the equation for the trajectory of a rotating test body with respect to ρΣ is derived, and working formulas are obtained that give the laws of secular changes in the direction of the vector of the proper angular momentum impulse of the test body and the modulus of this vector. It is shown that accounting ρD.M changes the magnitude of the periastron shift. For example, in the Solar System when taking into account ρvis, all the planets except Pluto have a directly shifted perihelion in the post-Newtonian approximation of the general theory of relativity. When taking into account ρΣ the planets from Mercury to Saturn included, they have a direct shift of perihelion, and Uranus, Neptune, Pluto have the reverse (against the planets in orbit). There is also a secular change in the eccentricity of the orbit. The formula is derived that can be used to calculate the secular deviation of the translational motion of a rotating body from motion in a plane. Accounting ρΣ enhances deviation. It is emphasized that all the noted effects for planetary systems in the vicinity of neutron stars, radio pulsars and other dense objects can be many orders of magnitude greater than in the solar system.

Early Paleozoic Plankton Evolution in the Paleo-Asian Ocean: Insights from New and Reviewed Fossil Records from the Gorny Altai, West Siberia

The mountainous Gorny Altai in southern Siberia constitutes the western part of the Altai–Sayan Folded Belt in the northwestern part of the Central Asian orogenic belt, which contains precious records of the lost major Proterozoic–Paleozoic ocean called the Paleo-Asian Ocean (PAO). This paper briefly introduces the latest microfossil (radiolarian and conodont) information recovered from the Lower Paleozoic siliceous and carbonate sequences of the Gorny Altai. The fossils of planktonic biota inhabited in PAO range back to the early Cambrian, in which the world's oldest radiolarians are included. In addition, numerous well-preserved conodonts as well as graptolites were recovered from Cambrian, Ordovician, and Silurian strata in the Gorny Altai. These recorded the Early Paleozoic biodiversity and their secular change both in pelagic and continental margin settings within PAO.

Intraplate continental basalts over the past billion years track cooling of the mantle and the onset of modern plate tectonics

The temperature of the convecting mantle exerts a first-order control on the rheology, composition, and consequently, tectonic behavior of Earth's lithosphere. Although the mantle has likely been cooling since the Archaean eon, how mantle temperature has evolved thereafter is poorly understood. Here, we apply a statistical analysis to secular changes in the alkali index [AI = whole-rock (Na2O + K2O)2/(SiO2 − 35) as weight%] of global sodic intracontinental basalts, a proxy for the degree of mantle melting, to constrain the evolution of mantle potential temperature (TP) over the past billion years. Our results show that, during the early Neoproterozoic, TP remained relatively constant until the beginning of the Cryogenian (720 Ma), when mantle temperature dropped rapidly over the following ∼180 Ma. This remarkable episode of cooling records the onset of modern-style plate tectonics characterized by continuous deep subduction of the oceanic lithosphere, consistent with the widespread appearance of blueschists in the metamorphic rock record.

The significance of cherts as markers of Ocean Plate Stratigraphy and paleoenvironmental conditions: New insights from the Neoproterozoic–Cambrian Blovice accretionary wedge, Bohemian Massif

The Ediacaran to early Cambrian Blovice accretionary complex, Bohemian Massif, hosts abundant chert bodies that formed on an oceanic plate and were involved in subduction beneath the northern margin of Gondwana. Field relationships of cherts to their host, their microstructure and elemental as well as isotopic compositions revealed diverse processes of chert petrogenesis reflecting depositional environment and position on the oceanic plate. The deep-water cherts formed through a hydrothermal precipitation of silica-rich gels on outer trench swell of the subducted slab with none or only minor addition of terrigenous material. On the contrary, the shallow-water cherts formed in lagoons on seamount slopes, and at least some of them represent a product of hydrothermal replacement of former carbonate and/or evaporite precursors. For both chert types, the hydrothermal fluids were of low temperature and continuous pervasive hydrothermal alteration of oceanic crust, together with an elevated Si content in Neoproterozoic seawater, served as the major source of silica. On the other hand, minor carbon enrichment in chert is mostly linked to variable incorporation of organic matter that was deposited on the seafloor. Rare earth element (REE) systematics of the cherts indicate predominantly oxygenated environment for the shallow-water cherts whereas the deep-water cherts were deposited in diverse redox conditions, depending on their distance from hydrothermal vent. Using these data, we demonstrate that the cherts once formed a part of Ocean Plate Stratigraphy (OPS) now dismembered and mixed with terrigenous siliciclastic material to form OPS mélanges. Combining our data with those from the existing literature, we show that cherts can serve as significant markers of OPS since the Archean, recording a complex interplay between seafloor-related volcanic (production of MORB- and OIB-like magmas) and sedimentary processes, hydrothermal activity at mid-ocean ridges and seamount chains as well as at outer slopes of subducting slabs. However, the cherts also exhibit a secular change in composition and petrogenesis most profoundly affected by an overturn in seawater silica cycle across the Precambrian–Phanerozoic boundary.

Texas Private Equity Conference 2022: Session I: The State of and Prospects for U.S. Private Equity

Kewsong Lee, CEO of the Carlyle Group was interviewed by Rich Hall, Chief Investment Officer of UTIMCO. From his vantage point at Carlyle overseeing 300 portfolio companies, Lee sees US economic growth as positive but decelerating while inflation continues to be high. So far, Carlyle‐owned firms have been able to pass through higher costs to their consumers although the expected Fed tightening would reduce asset values and general confidence.Lee identified the international focus on climate change and achieving a “net‐zero” CO2 emissions level as a secular change. He warned that decarbonizing will be expensive and difficult to achieve and that divesting of carbon producing assets offered no solution. Private equity firms make their money by improving the operations of the companies they buy and not through financial engineering, according to Lee.Lee cautioned listeners that a forty year long trend of declining interest rates is now reversing. This will have consequences for the real economy. Nevertheless, Lee emphasized, one should not underestimate the power of companies and technology to improve productivity. Relatively modest rate increases will not damage Carlyle's ability to buy companies as money is available and the leveraged finance markets are “wide open.”Despite his industry's success, lee said that PE industry has “done a very bad job in helping the outside world appreciate who we are and what we do.” Accordingly, the PE industry must become becoming more stakeholder focused, and more socially comprehensive and aware, while also generating high returns.

Desilicification Rims of Zircon Xenocrysts Record the Timing of Kimberlite Emplacement

AbstractKimberlites are deep and relatively rare mantle‐derived igneous rocks, which provide key insights into the lithospheric mantle composition beneath continents (i.e., from the entrained mantle materials) at the time of magma emplacement. In addition, the temporal distribution of kimberlites throughout Earth's history may reveal secular changes in global geodynamics. However, alteration and abundant exotic material (i.e., xenoliths and xenocrysts) of different ages, both typical of kimberlites, often hinder reliable dating of these rocks. In this study, we investigated zircon xenocrysts and their replacement by desilicification reaction rims (DSRs), which consist mainly of baddeleyite, in the metamorphosed Kimozero kimberlites from the Karelian Craton, Russia. Similar DSRs have been identified previously on mantle‐derived zircons in numerous kimberlites, but the precise timing and location of formation of these rims remain unclear. U–Pb isotope dating of mantle zircon xenocrysts in the Kimozero kimberlites indicates that these rocks were emplaced at ca. 1.97 Ga. DSRs with similar textures and baddeleyite chemistry occur on both the 1.97 Ga mantle and 2.70–2.38 Ga crustal zircon xenocrysts in these kimberlites. Pb–Pb isotope dating of the DSRs yields the same age (i.e., ca. 1.97 Ga) as the mantle zircons. The data constrain the formation of DSRs to crustal levels and, more importantly, indicate that these rims record the timing of kimberlite emplacement. Therefore, we suggest that such baddeleyite reaction rims are a new and promising material for kimberlite geochronology.

A sociology of regret

This article aims to present regret, an emotion to which sociologists so far have paid little attention, as having great sociological significance. First, it reviews recent research in social psychology and economics which cast anticipated regret as playing a major role in human decision-making. Second, it suggests a regret-based interpretation of the sunk-cost fallacy. Such an interpretation points to the need of a specifically sociological perspective on regret, calling attention to the cultural and institutional framings of regret-arousing events. The article further argues that secular changes in the types of regret imposed on individuals are paralleled by the spread of various forms of coping with it and that anticipated regret is responsible for both commitment to a chosen life-course and for sudden changes in it. The article ends with discussing the relationship between instrumental and moral regret, as well as the general implications of regret as a phenomenon for sociological understanding of rationality and human action.

Extratropical Transition of Tropical Cyclones in a Multiresolution Ensemble of Atmosphere-Only and Fully Coupled Global Climate Models

Abstract Tropical cyclones undergo extratropical transition (ET) in every ocean basin. Projected changes in ET frequency under climate change are uncertain and differ between basins, so multimodel studies are required to establish confidence. We used a feature-tracking algorithm to identify tropical cyclones and performed cyclone phase-space analysis to identify ET in an ensemble of atmosphere-only and fully coupled global model simulations, run at various resolutions under historical (1950–2014) and future (2015–50) forcing. Historical simulations were evaluated against five reanalyses for 1979–2018. Considering ET globally, ensemble-mean biases in track and genesis densities are reduced in the North Atlantic and western North Pacific when horizontal resolution is increased from ∼100 to ∼25 km. At high resolution, multi-reanalysis-mean climatological ET frequencies across most ocean basins as well as basins’ seasonal cycles are reproduced better than in low-resolution models. Skill in simulating historical ET interannual variability in the North Atlantic and western North Pacific is ∼0.3, which is lower than for all tropical cyclones. Models project an increase in ET frequency in the North Atlantic and a decrease in the western North Pacific. We explain these opposing responses by secular change in ET seasonality and an increase in lower-tropospheric, pre-ET warm-core strength, both of which are largely unique to the North Atlantic. Multimodel consensus about climate change responses is clearer for frequency metrics than for intensity metrics. These results help clarify the role of model resolution in simulating ET and help quantify uncertainty surrounding ET in a warming climate.

Sexual Dimorphism of Cranial Morphological Traits in an Italian Sample: A Population-Specific Logistic Regression Model for Predicting Sex.

Simple SummaryDespite the fact that sex estimation methods from crania are very popular in forensic anthropology, few validation studies have verified their accuracy and reliability in different populations. Different from craniometrics, for which validation studies have remarkably increased lately, the methods based on cranial morphology still need to be thoroughly investigated, even if a large consensus exists on the effects of population variability on sexual cranial dimorphism. When dealing with forensic contexts, appropriately-validated methods should be applied for building accurate biological profiles. Since the possible sexual dimorphism variation of cranial morphological traits needs to be evaluated properly in various populations, in this study, we analyzed the accuracy of existing regression models for predicting sex from cranial morphological traits in an Italian contemporary/modern population. In addition, we propose new logistic regression models that are more accurate and specific for our sample. The results also update the reference standards for populations of this geographical area and provide an additional important warning on sexual dimorphism to anthropologists working in forensic contexts.Although not without subjectivity, the cranial trait scoring method is an easy visual method routinely used by forensic anthropologists in sex estimation. The revision presented by Walker in 2008 has introduced predictive models with good accuracies in the original populations. However, such models may lead to unsatisfactory performances when applied to populations that are different from the original. Therefore, this study aimed to test the sex predictive equations reported by Walker on a contemporary Italian population (177 individuals) in order to evaluate the reliability of the method and to identify potential sexual dimorphic differences between American and Italian individuals. In order to provide new reference data to be used by forensic experts dealing with human remains of modern/contemporary individuals from this geographical area, we designed logistic regression models specific to our population, whose accuracy was evaluated on a validation sample from the same population. In particular, we fitted logistic regression models for all possible combinations of the five cranial morphological traits (i.e., nuchal crest, mastoid process, orbital margin, glabella, and mental eminence). This approach provided a comprehensive set of population-specific equations that can be used in forensic contexts where crania might be retrieved with severe taphonomic damages, thus limiting the application of the method only to a few morphological features. The results proved once again that the effects of secular changes and biogeographic ancestry on sexual dimorphism of cranial morphological traits are remarkable, as highlighted by the low accuracy (from 56% to 78%) of the six Walker’s equations when applied to our female sample. Among our fitted models, the one including the glabella and mastoid process was the most accurate since these features are more sexually dimorphic in our population. Finally, our models proved to have high predictive performances in both training and validation samples, with accuracy percentages up to 91.7% for Italian females, which represents a significant success in minimizing the potential misclassifications in real forensic scenarios.

Seismic Contributions to Secular Changes in Global Geodynamic Parameters

AbstractSecular changes in global geodynamic parameters (polar motion excitation, length of day, and J2, etc.) are significant to understand internal mass transport in the solid Earth system and surface geophysical fluids related to global climate. However, the glacial isostatic adjustment (GIA) and climate‐driven surface mass redistribution are insufficient to explain the origin. We are motivated to report the significance of seismic effect in the pursuit of understanding the budget of secular changes in geodynamic parameters. The seismic effect is comparable to the GIA effect and amounts to 20% or larger (up to 30%) of the observed secular changes in global geodynamic parameters. Therefore, the seismic effect must be treated as one key mechanism of driving secular changes in geodynamic parameters, which is critical to invert rheological structure, clarify internal dynamic processes, and reveal the physical evolution of the Earth.

Secular changes in metamorphism and metamorphic cooling rates track the evolving plate-tectonic regime on Earth

When disturbed, dynamic emergent systems, such as tectonics on Earth, may transition from one stable state to another if the perturbation is sufficiently large. Here, we identify such state shifts through examination of statistically significant change points in the time series of metamorphic pressure–temperature and cooling rate data. Change points occur in the mid-Paleoproterozoic, the Mesoproterozoic, the early and late Paleozoic and the Cenozoic. To compare the timing of change points with mantle geodynamics, we interrogate the time series of calculated mantle potential temperature, which yields a statistically significant drop of &gt;130°C in the mid-Paleoproterozoic, indicating a change in the mechanism of mantle cooling. We interpret changes in the mid-Paleoproterozoic to relate to the global emergence of stable subduction, orogenesis associated with the formation of the Nuna megacontinent, and slab breakoff, consistent with the operation of a distinctive style of Proterozoic plate tectonics. By contrast, changes from the dawn of the Cambrian onward may relate to the large volume of sediments supplied to trenches following multiple Cryogenian and Paleozoic glaciations. Sediments acted as a lubricant, allowing deeper subduction, transport of lower continental plates to mantle depths and faster metamorphic cooling rates, features characteristic of modern plate tectonics. Supplementary material: A dataset of metamorphic cooling rates is available at https://doi.org/10.6084/m9.figshare.c.5943418

Secular Changes in the Age of Menarche of Rural and Urban Girls from an Industrial Region of Poland in Relation to Family Structure.

Purpose: The consequence of better living conditions for every subsequent generation is the phenomenon of change in the rate of maturation and body dimensions. The aim of this study was to evaluate the intergenerational changes in the age of menarche of girls living in rural and urban communities in the industrial region of Poland using samples from two different centuries and to determine the relationship between family structure (two-parent and single-parent) and sexual maturation of the girls in both environments. Methods: The study included 3643 rural and urban girls aged 7–16 from southwestern Poland (Copper Basin). The research was cross-sectional in each environment around 2000 and 2010, and it was carried out twice. Two types of family structure were taken into account: two-parent and single-parent families. The median age of menarche and odds ratio (OR) of menarche depending on the place of residence and family structure were calculated. The status quo method was used when assessing the age of menarche. Results: In both groups, the age of menarche significantly decreased during the decade. The median age of menarche in the urban girls was lower compared with their rural peers, but a significant difference was found only during the second examination (a decade after the first examination). There were no significant changes in menarche during the decade regarding family structure (neither in girls from two-parent families nor those from single-parent families), except in rural girls from two-parent families. Comparing the median age of menarche of girls from two-parent families with girls from single-parent families (urban and rural) showed lower median values in the girls from two-parent families, but no differences were significant. Conclusions: The acceleration of the maturation rate over the last decade has been observed among both rural and urban girls. Environmental differences in maturation rates between rural and urban girls increased over the course of the decade, and the difference between the rural and urban girls’ age of menarche was statistically significant in the second examination (around 2010).The living conditions related to family structure did not significantly affect the timing of menarche.

Secular compositional changes in hydrated mantle: The record of arc-type basalts

We use a filtered database that tracks the composition of hydrated mantle with time using arc-type basalts, including an unknown amount of plume-type mantle in the Archean. A factor of 2–10 geochemical variability, both between and within sample sites, characterizes arc-type basalts and especially so >3.5 Ga and < 2.0 Ga. Based on which geographic sites are available for sampling, this variability is probably due to an anomalously high proportion of enriched components in some arc-type mantle sources. The proportion of an enriched component in magma sources is related to the ratio of continental to oceanic arc sites in the database, and thus is at least in part controlled by tectonic setting sample biases. We suggest that online geochemical databases of mafic igneous rocks should not be used to track secular changes in mantle composition or temperature unless they have been carefully filtered for tectonic setting, alteration/metamorphism, reliable ages, rock type, and major element composition.If the relatively few geographic sites are representative, large variations in incompatible element distributions in arc-type basalts suggest poorly mixed mantle before 3.5 Ga. However, the uniformity of incompatible element distributions from 3.5 to 2.6 Ga supports the existence of well-mixed mantle sources during this time. Long-term changes in major and compatible element contents of arc-type basalt mantle sources from 3.5 to 1.0 Ga are consistent with decreasing mantle temperature and degree of melting during this time. Although enriched mantle sources for arc-type basalts appear in the Neoarchean, they do not become widespread until after 2.0 Ga. From 2.0 to 1.0 Ga, enriched mantle contributions are relatively high but variable, probably in response to some combination of increased enriched mantle in the magma sources, sampling biases from relatively few sites with an anomalously high proportion of enriched mantle, and recycling of oceanic and continental lithosphere into the mantle in response to global propagation of subduction.Superimposed on long-term geochemical trends are five geographically widespread geochemical anomalies (deviations of greater than ±2σ from a smoothed Gaussian curve) in incompatible element distributions (2.55, 2.15, 1.75, 0.65 and 0.25 Ga) and an additional anomaly at 3.6–3.3 Ga in some compatible elements. All five incompatible element anomalies occur near age peaks in the U/Pb zircon age record (at 2.5, 2.15, 1.85, 0.60, and 0.25 Ga in both detrital and igneous zircons) and the 2.55, 2.15 and 1.75 Ga anomalies are very close to peaks in Re/Os model ages for mantle ultramafic rocks. The simplest explanation for the incompatible element anomalies is episodic enrichment of mantle sources of arc-type basalts, perhaps related to widespread mantle events (overturn or/and mantle plume) that brought enriched components into subduction-related sources of arc-type basalts.

Sulfur isotope fractionation derived from reaction-transport modelling in the Eastern Equatorial Pacific

Microbial sulfate reduction in subseafloor sediments regulates a significant portion of the marine organic matter burial flux. Over secular timescales, sulfate reduction is the fundamental process connecting the biogeochemical cycles of sulfur, carbon, oxygen and phosphorus. Similar to carbon reduction, sulfate reduction is associated with a strong isotope fractionation process that allows us to track this process through time. It depends on a variety of factors and it has been argued previously that systematic differences between shallow and deep-sea environments might explain secular changes in the marine S-isotope ratio. However, observational data of in situ fractionation from deep-sea areas are scarce. Here we use a reaction-transport model to analyse the S-isotope fractionation during microbial sulfate reduction in the interstitial water of Ocean Drilling Program (ODP) Site 1226 (Leg 201). We find that the upper 100 m below seafloor are best explained with fractionation around −76‰, whereas below this depth the degree of fractionation drops to around −42‰. We propose that this shift is caused by changes in the ratio of the rate of microbial sulfate reduction relative to the rate of abiotic sulfide oxidation. Because large parts of deep oceans are characterized by exceedingly low sulfate reduction rates, this process may be widespread and possibly explain why pyrite S-isotope data suggest that the average S-isotope fractionation is around −50‰, rather than the theoretically predicted value below −70‰. Supplementary material: Supplementary figures and model results are available at https://doi.org/10.6084/m9.figshare.c.5976772 Thematic collection: This article is part of the Sulfur in the Earth system collection available at: https://www.lyellcollection.org/cc/sulfur-in-the-earth-system