Synchronous Changes Research Articles

Deciphering Controls of Pore‐Pressure Evolution on Sediment Bed Erosion by Debris Flows

AbstractPore‐fluid pressure (PP) plays an important role in bed erosion, but the mechanisms that control PP evolution and the resulting feedbacks on flow dynamics are unclear. Here, we develop a general formulation, allowing quantification of the propensity for PP evolution of saturated and unsaturated bed sediments. We conduct erosion experiments by systematically varying grain composition and water content of beds, for investigating effects of PP evolution on flow erosion. With increasing water content, PP shows a slight rise in deforming beds with drained behavior but significant larger rise in undrained beds. Regardless of bed composition, the erosion rate of beds presents a synchronous change tendency with PP evolution due to the loss in basal friction. PP instigates positive feedback that induces a remarkable gain of flow velocity and momentum on wet beds with undrained behavior. Our results help explain observations of volume growth and long run out of debris flows.

Learning and Neural Activity: Beyond Localization

Learning is classified into two types: "classical conditioning," which modifies simple reflexes, and "operant conditioning," which modifies complex voluntary behaviors. The neural circuits underlying these two types differ significantly. During the learning process of operant conditioning tasks, various changes in firing rate and firing synchrony of neurons can be observed across multiple brain regions. Additionally, neuronal firing rate and synchrony in several brain regions can be voluntarily controlled through operant conditioning. Consequently, it is evident that neurons in widespread brain regions have the potential for plastic changes to facilitate learning. It may be suggested that the learning of complex voluntary behaviors is underlined by widespread dynamic changes in neural activity and is not restricted to only a few brain regions.

Quantitative Holocene climate reconstruction and anthropogenic impact analysis based on the pollen records in peat sediment in Southern China

The quantitative reconstruction of Holocene paleoclimate is pivotal for unraveling the evolution of East Asian Monsoon (EAM). Some recent studies have highlighted the escalating human activities in the late Holocene, which could potentially pose significant challenges to the precise quantitative reconstruction of paleoclimate. In this study, we undertake a quantitative reconstruction of Holocene climate and human influence index (HII) based on pollen data from the Shiwangutian (SWGT) in Southern China. This is achieved by developing and applying a pollen-based calibration model utilizing Locally Weighted Average-Partial Least Squares Regression (LWWA-PLS) and the Modern Analogue Technique (MAT). Our findings reveal that evergreen forests experienced expansion between 11.6 and 9.0 cal ka BP, coinciding with elevated Mean Annual Precipitation (Map) and Mean Annual Temperature (Mat) levels. These patterns signify a progressively warm and wet climate during this period. Subsequently, evergreen forests achieved their maximum abundance between 9.0 and 4.0 cal ka BP, aligning with a notable increase in vegetation richness, indicating a warmer and wetter climate during the mid-Holocene. Notably, during the interval of 6.0–4.0 cal ka BP, the Map, Mat, and Precipitation of Warmest Month (Mpwa) reached the Holocene optimum, approximately 14% higher than modern. Consequently, we deduce that in the early and middle Holocene, when the monsoon was particularly strong, synchronous changes in precipitation fostered the regional expansion of evergreen broad-leaved forests. Furthermore, the record demonstrates a substantial reduction in forest cover and a noteworthy increase in the HII value since 4.0 cal ka BP, likely attributable to anthropogenic impacts. Our analysis suggests that the influence of anthropogenic activities surpassed that of natural climate factors in shaping regional vegetation cover. These findings offer insights into potential drivers of climate change. As a preliminary conclusion, we propose that the summer insolation, ice sheets, and meltwater fluxes were the primary controlling factors for climate variations during the early to mid-Holocene in Southern China.

Indian summer monsoon drives synchronous interdecadal hydroclimate changes in the Tibetan Plateau and surroundings

The interdecadal relationship (10–100 years) between the Indian Summer Monsoon (ISM) and arid climate is pivotal in comprehending Asian hydroclimate dynamics. Despite extensive tree-ring based climate reconstructions conducted across both monsoonal and arid regions in the Tibetan Plateau (TP) and surroundings, the correlation between the ISM and arid climate on interdecadal scales remains contentious. In this study, we assembled a tree-ring network from 242 moisture-sensitive sites around the TP. We established composite chronologies over three regions each in southern and northern TP, revealing more pronounced interdecadal fluctuations than those identified using traditional methods. These moisture-sensitive composite chronologies demonstrated synchronous variations on interdecadal timescales throughout their common period from 1517 to 2003, encompassing the most severe drought. The concurrent hydroclimate changes around the TP exhibited the strongest correlations with the ISM-dominated Himalayan region on interdecadal scales, signifying ISM-driven synchronous changes. Furthermore, the synchronous interdecadal hydroclimate changes displayed positive associations with solar irradiance. Notably, the driest periods coincided with the most intense solar Maunder Minimum (∼1645–1715) and Dalton Minimum (∼1790–1830), further underscoring the influence of solar activity on regional hydroclimate conditions.

Assessing the hydroclimate changes in Western Himalayas during the Little Ice Age

The Little Ice Age (LIA) was a period of most recent glacial advancement and had pronounced cooling effect in the North Atlantic region. Synchronous hydroclimate changes are also reported from the Himalayas, however owing to the heterogeneity within the proxy reconstructions, their relationship with LIA cooling is unclear. Varied topography, huge glacial mass, and multiple moisture sources (both from the Indian Summer Monsoon (ISM) and the Westerlies) makes understanding of the impact of LIA cooling on this region ambiguous. In this study, we review and assess the existing paleoclimatic proxy records for a comprehensive analysis of the regional response of the Western Himalayas to LIA cooling. Using the existing meteorological reanalysis data for back trajectory analysis for the last 20 years, the Western Himalayan region was classified into three different zones based on the relative percentage of moisture-bearing-wind-source contribution. The upper Western Himalayas receive most of the moisture from the Westerlies, both Middle and Lower Western Himalayas receive majority of rainfall from the ISM, with a relatively higher contribution of Westerlies in the Lower Western Himalayas. Comparison of reconstructions using Principal Component Analysis reveal consistent high moisture conditions during the LIA, with increased winter precipitation and decreased summer precipitation coherently in all the records. Spectral analysis of the available proxy records and various climate forcing for LIA cooling show similar dominant frequency, attesting that the LIA cooling drove the hydroclimate changes in the Western Himalayan region. External forcings such as decreased solar activity and increased volcanic activity caused cooling, influenced the Inter Tropical Convergence Zone, and resulted in weaker summer rainfall during the LIA. Synchronous changes in the North Atlantic Oscillations and El Niño–Southern Oscillation records with precipitation records suggest a link between “monsoon breaks” and enhanced Westerly intensity and an intensified winter precipitation in this region.

Modeling the Role in pH on Contaminant Sequestration by Zerovalent Metals: Chromate Reduction by Zerovalent Magnesium.

The role of pH in sequestration of Cr(VI) by zerovalent magnesium (ZVMg) was characterized by global fitting of a kinetic model to time-series data from unbuffered batch experiments with varying initial pH values. At initial pH values ranging from 2.0 to 6.8, ZVMg (0.5 g/L) completely reduced Cr(VI) (18.1 μM) within 24 h, during which time pH rapidly increased to a plateau value of ∼10. Time-series correlation analysis of the pH and aqueous Cr(VI), Cr(III), and Mg(II) concentration data suggested that these conditions are controlled by combinations of reactions (involving Mg0 oxidative dissolution and Cr(VI) sequestration) that evolve over the time course of each experiment. Since this is also likely to occur during any engineering applications of ZVMg for remediation, we developed a kinetic model for dynamic pH changes coupled with ZVMg corrosion processes. Using this model, the synchronous changes in Cr(VI) and Mg(II) concentrations were fully predicted based on the Langmuir-Hinshelwood kinetics and transition-state theory, respectively. The reactivity of ZVMg was different in two pH regimes that were pH-dependent at pH < 4 and pH-independent at the higher pH. This contrasting pH effect could be ascribed to the shift of the primary oxidant of ZVMg from H+ to H2O at the lower and higher pH regimes, respectively.

The color/shape/flavor of yam gel with double emulsified microcapsules changed synchronously in 4D printing induced by microwave

The feasibility of 3D printing the color, aroma and shape changes of yam gel with microwave heating as stimulus and soybean protein isolate-chitosan-maltodextrin complex coacervated microcapsules rich in water-soluble betacyanin and rose essence as stimulus-response materials was discussed. The morphology of microcapsules presented irregular spherical structure, and the surface was relatively smooth and slightly concave. Microwave heating led to the gradual destruction of microcapsules in yam gel, releasing internal pigments and essence, and enhancing the redness and flavor of printed samples. The release of the water phase and oil phase of the microcapsules and the hot-spot expansion effect of the models made the 3D printed bird models bend and deform, realizing the deformation effect of “spreading of wings”, which realized a three-response synchronous change in color, shape, and flavor of the printed samples within 45 s. In this study, a variety of 4D printed foods with synchronous changes in sensory characteristics were created, which increased sensory enjoyment on the basis of ensuring the nutritional needs of food.

Перспективы работы с лингвистическим корпусом в аспекте исследования фразеологического фонда национального языка

The research is aimed at obtaining evidence of the effectiveness of using the resources of a national linguistic corpus to clarify the semantic development of phraseological units. The work attempts to consider the prospects for involving a national linguistic corpus while studying phraseological units as exemplified by the Russian nominative phraseological unit ‘зеленая улица’ (green light). The authors describe the methodology of dealing with a linguistic corpus to obtain the necessary information on the basis of which diachronic and synchronic changes in the phraseological meaning are examined. The scientific novelty lies in the fact that the semantics of the phraseological unit ‘зеленая улица’ is reviewed using the resources of the Russian National Corpus. As a result of the empirical research, the efficiency of its use has been proved: using the corpus of a national language as a source of linguistic, cultural information and extralinguistic factors makes it possible to trace the semantic development of a phraseological unit by expanding its sphere of application, highlighting additional shades of its phraseological meaning and, in some cases, independent meanings.

Experimental and numerical study on characteristics of super-linear mass flow rate and asymmetric cavitation in novel rotary-baffle curved-channel electronic expansion valve for refrigerator

Capillary tubes, as the expansion devices in refrigerators, are unable to actively match cooling capacity and load, which will increase the energy consumption. Moreover, due to the limitations of miniature valve needle machining accuracy and structural strength, orifice-type EEVs are not suitable for low mass flow rate in refrigerators. A novel rotary-baffle curved-channel electronic expansion valve (RBCC-EEV) is proposed to replace capillary tube to achieve flow regulation in household refrigerators. Based on the special structure and regulation principle of RBCC-EEV, characteristics of mass flow rate and cavitation are studied experimentally and numerically, respectively. Experimental results show that, as opening ratio (OR) increases, the synchronous changes in the inlet area and length of the curved channel lead to a super-linear variation in mass flow rate, with increase rate growth from 0.018 kg h−1 OR−1 to 0.061 kg h−1 OR−1. Numerical results show that, under centrifugal forces, the pressure difference along the normal direction of the streamline leads to the differences in degree of cavitation, which is called asymmetric cavitation phenomenon. In addition, under the influence of this phenomenon, the prematurely cavitation of refrigerant near the inside surface will block the inlet of curved channel early, resulting in a 3.4 % decrease in mass flow rate.

Magnetic resonance imaging in the diagnosis of functional changes of the brain in menstrual disorders: a review

INTRODUCTION: Currently, the most common variant of the reproductive system disorders, in particular menstrual cycle disorders, in adolescent girls is oligomenorrhea. In situations after a complete diagnostic screening no organic and endocrine pathology of the reproductive system is detected in this group of patients, it is possible to conduct functional MRI as a method of identifying cause-and-effect relationships and clarifying the pathogenesis of menstrual disorders.OBJECTIVE: To analyze the available foreign and domestic literature to determine the role of magnetic resonance imaging in the diagnosis of functional brain changes in menstrual disorders in adolescent girls.MATERIALS AND METHODS: A search was conducted for scientific publications in the information and analytical systems PubMed and Google Scholar for 2013–2023 by keywords: «resting-state functional MRI» («functional resting MRI»), «oligomenorrhhea» («oligomenorrhea»), «adolescent girls» («teenage girls»), «reproductive system functional disorders» («functional disorders of the reproductive system»), «magnetic resonance imaging» («magnetic resonance imaging»), «diagnostic radiology» («radiation diagnostics»). 46 publications related to the diagnosis of functional brain changes in menstrual disorders in the form of resting state fMRI were analyzed.RESULTS: Resting state fMRI allows us to assess the basic brain activity in the absence of certain sensory or cognitive stimuli and visualize working networks that include various parts of the brain demonstrating synchronous changes in the BOLD-signal at rest. There are a number of patterns of changes in the BOLD-signal that can be observed in various phases of the menstrual cycle, as well as under the influence of stress factors, which makes it possible to visualize the morphological substrate of oligomenorrhea that occurs against the background of the absence of organic and endocrine pathology of the reproductive system in adolescent girls. Currently, there is little data in the scientific literature on the use of functional resting MRI in this cohort of patients, however, this method can have a significant impact on the formation of an individual plan for the correction of reproductive disorders in adolescence, and therefore requires further study.CONCLUSION: The use of fMRI can open up new possibilities in the diagnosis of functional brain disorders in girls with «unexplained» oligomenorrhea.

A multiproxy reconstruction of Asian winter monsoon variability since the last glacial from southeast offshore Hainan Island, South China Sea

The evolution of East Asian winter monsoon (EAWM) in tropical oceans has been a key issue in the climatic coupling between high- and low-latitudes. This study aims to investigate the EAWM variability using multiproxy of sediment core XB19S40 in the southeast offshore of Hainan Island, South China Sea. Alkenone derived sea surface temperature (SST), sediment grain size, and elemental ratios show consistent changes over the last 20.7 ka. There were synchronous abrupt changes in the SST, Zr/Rb, K/Ti, and End-members (EMs) during the Bølling-Allerød warming period, Younger Dryas and 8.2 ka cooling events. The Zr/Rb and EM2 (18.7–84.6 μm, 40.1 μm) changes reflect the EAWM and are highly coincident with records in high latitudes. These changes suggest that the EAWM gradually weakened from the last glacial maximum to early Holocene, experienced minor strengthening in the late Holocene but has diminished since 1 ka. In contrast, the indicators K/Ti and EM1 (0.2–18.7 μm, 9.9 μm) suggest that the East Asian summer monsoon is in the opposite phase. Spectral analysis demonstrates that the intensity of East Asian monsoons in the SCS were mainly affected by solar activity on a centennial-scale. The results of this study provide new insight into the complexity of the EAWM system and emphasize the importance of understanding multiple components of the climate system.

Tensile damage self-monitoring of carbon fiber/epoxy 3D braided composites with electrical resistance method

Electrical resistance method (ERM) has great potential in self-monitoring structural health for carbon fiber composites due to carbon fiber conductivity. Here we report the correlation between tensile damages and electrical resistance changes of 3D braided composites subjected to monotonic and cyclic tensile loading. Experimental and finite element methods were utilized to reveal the electrical resistance variation and damage evolution under monotonic tensile loading. We found that the electrical resistance changes under monotonic tensile loading could be segmented into three regions, namely, linear growth region, transition region and exponential growth region, corresponding to different damage modes. Synchronous and reversible electrical resistance changes at a low strain level (12% of fracture strain) cyclic loading proved the stability and repeatability of self-monitoring capability. While, the abrupt electrical resistance changes at a high strain level (75% of fracture strain), indicated catastrophic failure of the composites. Such kind of correspondence between tensile damages and electrical resistance change under tensile loading enables ERM to achieve the in-situ structural health monitoring of 3D braided composites without relying on external sensors.

Resting-state EEG measures cognitive impairment in Parkinson’s disease

Cognitive dysfunction is common in Parkinson’s disease (PD). We developed and evaluated an EEG-based biomarker to index cognitive functions in PD from a few minutes of resting-state EEG. We hypothesized that synchronous changes in EEG across the power spectrum can measure cognition. We optimized a data-driven algorithm to efficiently capture these changes and index cognitive function in 100 PD and 49 control participants. We compared our EEG-based cognitive index with the Montreal cognitive assessment (MoCA) and cognitive tests across different domains from National Institutes of Health (NIH) Toolbox using cross-validations, regression models, and randomization tests. Finally, we externally validated our approach on 32 PD participants. We observed cognition-related changes in EEG over multiple spectral rhythms. Utilizing only 8 best-performing electrodes, our proposed index strongly correlated with cognition (MoCA: rho = 0.68, p value < 0.001; NIH-Toolbox cognitive tests: rho ≥ 0.56, p value < 0.001) outperforming traditional spectral markers (rho = −0.30–0.37). The index showed a strong fit in regression models (R2 = 0.46) with MoCA, yielded 80% accuracy in detecting cognitive impairment, and was effective in both PD and control participants. Notably, our approach was equally effective (rho = 0.68, p value < 0.001; MoCA) in out-of-sample testing. In summary, we introduced a computationally efficient data-driven approach for cross-domain cognition indexing using fewer than 10 EEG electrodes, potentially compatible with dynamic therapies like closed-loop neurostimulation. These results will inform next-generation neurophysiological biomarkers for monitoring cognition in PD and other neurological diseases.

Mobile fNIRS for exploring inter-brain synchrony across generations and time.

While still relatively rare, longitudinal hyperscanning studies are exceptionally valuable for documenting changes in inter-brain synchrony, which may in turn underpin how behaviors develop and evolve in social settings. The generalizability and ecological validity of this experimental approach hinges on the selected imaging technique being mobile-a requirement met by functional near-infrared spectroscopy (fNIRS). fNIRS has most frequently been used to examine the development of inter-brain synchrony and behavior in child-parent dyads. In this position paper, we contend that dedicating attention to longitudinal and intergenerational hyperscanning stands to benefit the fields of social and cognitive neuroscience more broadly. We argue that this approach is particularly relevant for understanding the neural mechanisms underpinning intergenerational social dynamics, and potentially for benchmarking progress in psychological and social interventions, many of which are situated in intergenerational contexts. In line with our position, we highlight areas of intergenerational research that stand to be enhanced by longitudinal hyperscanning with mobile devices, describe challenges that may arise from measuring across generations in the real world, and offer potential solutions.

Precessional hydroclimatic synchronicity changes in the Indo-Pacific Warm Pool driven by the intertropical convergence zone over the past 450 kyr

Abstract The Indo-Pacific Warm Pool (IPWP) significantly influences the global hydrological cycle through its impact on atmospheric-oceanic circulation. However, gaining a comprehensive understanding of the hydrologic climate dynamics within the IPWP and its broader effects on the global climate have been hindered by spatial and temporal limitations in paleoclimate records on orbital timescales. In this study, we reconstructed precipitation records (approximated from δ18Osw-ivc) over the past 450 kyr, based on planktonic foraminiferal Mg/Ca and δ18O data obtained from International Ocean Discovery Program Site U1486 in the western tropical Pacific. The δ18Osw-ivc record revealed a generally consistent pattern with precession variations over the past 450 kyr, closely corresponding to changes in boreal summer insolation at the equator. The δ18Osw-ivc record displayed an anti-phased relationship with Chinese speleothem δ18O records on the precession band, with lower precipitation in the western tropical Pacific and higher precipitation in the East Asia summer monsoon region during periods of high Northern Hemisphere summer insolation. This anti-phased correlation primarily resulted from the north-south migration of the Intertropical Convergence Zone (ITCZ), influenced by the interhemispheric insolation contrast. By considering additional δ18Osw-ivc records from various locations within the IPWP region, we identified synchronous precipitation changes within the IPWP on the precession band. The synchronization of precipitation on both margins of the ITCZ’s seasonal range and differences between central and marginal regions of the ITCZ within the IPWP revealed the expansion and contraction of the ITCZ on precession band.

Simulating Non-Adiabatic Dynamics of Photoexcited Phenyl Azide: Investigating Electronic and Structural Relaxation en Route to the Formation of Phenyl Nitrene.

Excited state molecular dynamics simulations of the photoexcited phenyl azide have been performed. The semi-classical surface hopping approximation has enabled an unconstrained analysis of the electronic and nuclear degrees of freedom which contribute to the molecular dissociation of phenyl azide into phenyl nitrene and molecular nitrogen. The significance of the second singlet excited state in leading the photodissociation has been established through electronic structure calculations, based on multi-configurational schemes, and state population dynamics. The investigations on the structural dynamics have revealed the N-N bond separation to be accompanied by synchronous changes in the azide N-N-N bond angle. The 100 fs simulation results in a nitrene fragment that is electronically excited in the singlet manifold.

Southward shifts and enhancements of the westerlies over the Tibetan Plateau during North Atlantic cooling events

Variations in mid-latitude westerlies have an important influence on climate change, but their impact on the Tibetan Plateau (TP) since the Last Glacial Maximum is still debated, due to shortage of direct proxies reflecting the variations in the westerlies. Here we present an exotic (Cedrus) pollen record from the interior of the TP since 26.5 cal ka BP to reconstruct the changes in westerlies. Combined with its modern distribution, the Cedrus pollen in our record is considered to reflect the change in the intensity and position of the westerlies. Increased Cedrus pollen inputs are consistent with cooling phases during the Heinrich Stadial (HS) 2, HS 1a, HS 1c and Younger Dryas, suggesting that the westerlies were abruptly enhanced and southward-shifted, which can be attributed to the increased equator-to-pole temperature gradients and sea ice advance. Our record over the TP is in agreement with other reconstructions from the lower altitudes suggests a synchronous change in the westerlies at different levels.

Mechanism of width effects on cavity-induced transitions at hypersonic speed using direct numerical simulation

Cavities on the surfaces of hypersonic vehicles cannot be avoided easily. Moreover, they can trigger boundary layer transition under certain conditions. However, little progress has been reported on boundary layer transitions induced by a three-dimensional (3-D) shallow cavity. In this study, transitions induced by six 3-D shallow cavities with the same length–depth ratios of 20 and different widths of 0.25, 0.5, 0.75, 1.0, and 1.5 times the baseline width (W), as well as infinite width, were investigated. A direct numerical simulation was conducted using the Roe scheme with 4th-order minimum dispersion and controllable dissipation, and weighted essentially non-oscillatory reconstruction, based on our in-house code: Unsteady NavIer–STokes equations solver. Cavity width was observed to have non-monotonic influences on transition. Both the 0.25 and 1.0 W cavities could induce transition constantly. Moreover, flow was maintained as laminar past the 1.5 W and InfW cavities. For the 0.5 and 0.75 W cavities, intermittent transition was observed with different intermittency factors. The intermittent transition phenomenon was determined to be caused by the periodic increase and decrease in the adverse pressure gradient (APG) in the front part of cavity. Notably, the recirculation with a synchronic size change was the origin of the APG oscillation.

Comparing the dynamics of financial and business cycles in the BRICS countries

Subject. The BRICS countries are among the fastest developing and growing economies. However, research on relationship between their financial and business cycles is insufficient. The article intends to address this gap and provide such information. Objectives. The aim is to determine the main characteristics of cycle phases (amplitude and duration) for the BRICS countries and to assess the degree of their synchronization. Methods. The study employs an algorithm for periodization of various phases of financial and business cycles, proposed by D. Harding and A. Pagan in 2003, the analysis of concordance coefficients to determine the degree of synchronization of different cycles, and the logistic regression to quantify the probability of recession in the real sector, if there is a crisis in the financial sector. Results. The findings revealed a high degree of synchronization of financial and business cycles in the BRICS countries, comparable to the EU member States. At the same time, the degree of synchronization changes during crisis events and after political decisions. The degree of synchronization of business cycles turns out to be much higher than financial cycles. Conclusions. The findings should be considered when coordinating the economic policies of the BRICS countries. Using certain fiscal, monetary, or macroprudential tools, countries should take into account that their decisions will also affect other member countries of this organization.

Permafrost microbial communities follow shifts in vegetation, soils, and megafauna extinctions in Late Pleistocene NW North America

AbstractWe analyzed the microbial constituent of sedimentary ancient DNA sequence data recovered from subarctic loessal permafrost sediments dating between 30,000 and 4000 years ago. These data were originally studied for paleo‐ecological shifts in plants and animals associated with the Pleistocene–Holocene transition. Here, we explore whether there were changes in microbial communities paralleling the transition from distinctive cold‐adapted Ice Age megafauna and vegetation communities—the mammoth steppe ecosystem—toward the expansion of woody shrubs, extirpation of grazing megaherbivores, and development of the boreal forest. We observe a clear shift in the relative proportions of prokaryotic taxa after ca. 13,300 years ago associated with the collapse of the mammoth steppe. These data are consistent among study sites and between replicates processed with different methodologies (shotgun sequencing and targeted capture), which highlights that the “off‐target” fraction of metagenomic data used to study macro‐ecosystems can also be used to investigate synchronous changes in microbial communities. Functional analyses were performed with SEED and KEGG databases where we observed a shift in methane metabolism pathways after ~13,100 years ago, which suggests that there was a shift in methanogenesis away from animal gut microflora at the end of the Pleistocene. There does not appear to be a significant shift in the overall diversity of microbial communities despite the observed taxonomic and functional changes.