Humid Phase Research Articles

Tracking orbital and suborbital climate variability in the westernmost Mediterranean over the past 13,000 years: New insights from paleoperspectives on marine productivity responses

This study presents a comprehensive analysis of a sediment record from the Western Alboran Basin (core GP04PC), utilizing palynological and geochemical tools to investigate marine productivity responses to orbital and suborbital climate variability over the past 13,000 years. High productivity during the Younger Dryas humid phase (∼12.4–11.7 ka) and the Holocene humidity optimum (∼10.5–8.5 ka) was driven by increased local river discharges resulting from rapid mountain glaciers melting and enhanced regional precipitation. During the late Holocene, frequent flood events linked to negative North Atlantic Oscillation (NAO) incursions potentially led to multicentennial-scale productivity increases. The findings indicate that periods characterized by wet regional conditions and increased river run-off, influenced by orbital (e.g., insolation cycles) and suborbital factors (e.g., NAO and Atlantic Meridional Overturning Circulation changes), consistently enhanced marine productivity in the Western Alboran Basin. The study also reveals that the current high productivity and carbon export in the Western Alboran Basin are maintained by active upwelling and downwelling systems driven by a persistent positive NAO phase following the southward migration of the Intertropical Convergence Zone (ITCZ) that occurred around 6.5 ka. Furthermore, geochemical proxies support a strong detrital influence on trace metal concentrations, including barium (Ba), in deep Western Alboran sediments during the Holocene. This limits the use of Ba/Al ratios for accurately reconstructing productivity changes and highlights the importance of dinocyst analysis as a complementary tool for robust marine productivity reconstructions in this region. These observations provide valuable paleoperspectives on marine ecosystem responses to climate variability, contributing to the development of robust long-term productivity models essential for adapting to ongoing environmental changes in the region, and demonstrating the strong influence of North Atlantic climate and ocean dynamics on centennial-scale productivity oscillations in this region.

Climate-driven peatlands development and vegetation dynamics in Northeastern China since the mid-Holocene: New evidence from Huanan peatlands

Studying peatland evolution and vegetation patterns in response to climate change provides valuable insights into future ecosystem trends. This study focuses on the Huanan peatland located in Changbai Mountain regions in Northeast China, utilizing phytolith analysis and stable carbon isotope composition (δ13C) to reconstruct late Holocene vegetation dynamics. Additionally, grain size, total organic carbon (TOC), and total nitrogen (TN) analyses were conducted to understand peatland development and paleoclimate since the late Holocene. The research identifies three distinct climate periods since 5500 cal yr BP: an initial warm, humid phase (5500–4000 cal yr BP) characterized by high river levels that formed lacustrine sediments; a subsequent transition to cold, dry conditions (4000–1500 cal yr BP) that initiated peat formation; and continued dry, cold conditions (1500 cal yr BP to the present) with sustained peat growth. Phytolith data reveal a dominant forest vegetation type since 2000 cal yr BP, further divided into three periods: 2000–1300 cal yr BP, marked by diverse and dense vegetation; 1300–750 cal yr BP, with declining plant cover; and 750 cal yr BP to the present, characterized by an increase in woody plants but a reduction in local grass cover.

Desert-oasis evolutionary process in the Tarim Basin since ∼ 2.2 ka B.P. during the late Holocene and their environmental implications

Oases, serving as ideal locations for human settlements in arid regions, exhibit extreme sensitivity to regional climatic fluctuations. Consequently, the oasis deposition sediments play a pivotal role in the study of regional paleoenvironmental changes and the exploration of prehistoric human-environment interactions. The YSD and STM sections, both typical aeolian-lacustrine sections located at the edge of the Tarim Basin, were investigated in this study. By analyzing optically stimulated luminescence (OSL) dating results and grain-size proxy indicators, the environmental evolution patterns in the Tarim Basin since approximately 2.2 ka BP were reconstructed. Additionally, the parametric end-member analysis on the grain-size data was conducted to explore the environmental significance revealed by each end-member. The research findings indicate that: (1) ∼ 2.2–1.8 ka B.P., sediment morphology and grain-size parameters indicate that the climate in the Tarim Basin recorded by the STM section was relatively dry, with rivers gradually receding and frequent sand-drift activities. During the development of the YSD section (∼1.67–1.5 ka B.P.), the environmental conditions in the Tarim Basin transitioned to a relatively humid phase, with the Yarkand River experienced multiple episodes of natural diluvial deposition. The grain-size data of two sections both comprise five sedimentary dynamic components, serving as sensitive indicators of regional humidity conditions and winter monsoon intensity. (2) The oasis development in the Tarim Basin during the late Holocene (particularly refers to between ∼ 2.2 ka B.P. and ∼ 1.4 ka B.P.) exhibits a significant positive correlation with temperature records. (3) Environmental changes and human activities jointly regulate the spatial and temporal distribution and number of archeological sites during the development of both sections. However, the dominance of the two factors varied across different historical periods.

Fine-Tuning of Sub-Annual Resolution Spectral Index Time Series from Eifel Maar Sediments, Western Germany, to the NGRIP δ18O Chronology, 26–60 ka

Recent technological advancements in spectral imaging core-scanning techniques have proved to be a promising tool to study lake sediments at extremely high resolution. We used this novel analytical approach to scan core AU3 of the Pleistocene Auel maar, Western Germany. The resulting ultra-high-resolution RABD670 spectral index, a proxy for the lake’s primary production, shows an almost complete succession of Greenland Interstadials of the NGRIP ice core chronology back to around 60,000 years. Using the ELSA-20 chronology and its anchor points to the NGRIP record as a stratigraphic basis, we were able to compare and fine-tune prominent climate signals occurring in both regions. This in-depth correlation yields strong evidence that the climates of Greenland and Central Europe were not only strongly coupled on timescales of stadials and interstadials but even on multidecadal scales, showing prominent climate cycles between 20 and 125 years. As climate changes in these regions were ultimately driven by variations in the North Atlantic meridional heat transport, their strong coupling becomes most apparent during cold and arid intervals. In contrast, longer-lasting warmer and more humid phases caused the activation of various regional feedback mechanisms (e.g., soil formation, forest growth), resulting in more complex patterns in the proxy records.

Environmental and climatic significance of the Pliocene-Pleistocene calcretes in North Africa

The North African calcretes formed during the Plio-Pleistocene are a prominent and stratigraphically significant palaeoclimatic marker. We studied the calcrete along a north–south transect in Tunisia that crosses the climatic boundaries between the latitudes 33° and 37° N to elucidate the palaeoenvironmental and climatic significance of the calcrete for the Plio-Pleistocene. Macroscopic, petrographic, Scanning Electron Microscopy (SEM), and Cathodoluminescence (CL) observations obtained in the field and from thin sections of the non-powdery horizons of all sites allowed to identify 4 facies: Pisolithic (limestones with clast(s) coated by laminae), laminar (limestones with a succession of laminae), massive brecciated (brecciated limestones), and groundwater facies (limestones with no biogenic features). Notably, soil-forming processes were evident at all sites except for those situated further south, which exhibited characteristics indicative of a groundwater environment. The comparison with modern analogues suggests for our study area the climate was similar to modern central Spain (Hot-summer Mediterranean climate Csa) in central Tunisia which is, in turn, similar to the modern climate in North Tunisia. The climate was characterized by strong seasonal contrast: higher winter rainfall than today followed by long dry hot summers modified by a North-South gradient. This gradient was the result of the interplay between westerly winter winds and the orographic effect of the Atlas Mountains confirming the North Atlantic origin of precipitations. We conclude that during the late Pliocene to early Pleistocene, the climate in Northern Africa was more humid than today, with enhanced winter rainfall at all study sites probably at the same time of the establishment of Saharan humid periods. These humid phases may have been long enough, spanning more than 10.000 years, to reduce recharged groundwater salinity and, subsequently, form thick calcareous soil.

Holocene vegetation and climatic changes in the coastal tropical rainforests of Nigeria

A Mid-Late Holocene palynological and charcoal record of vegetation and climatic changes in the tropical rainforest of West Africa is presented based on sediment cores from four localities in southwest Nigeria. The localities namely Ahanve, Ogudu, Otolu-Lekki and Ikorigho are situated along gradients in riverine and coastal systems that drain into the Atlantic Ocean. The aim was to reconstruct the vegetation history of the tropical rainforest, infer past climate variabilities and ascertain the presence of humans and their impact on the landscape. The record shows that the Mid Holocene, c.6600-5600 BP, was characterised by predominantly diverse and extensive tropical rain forests that comprised lowland rainforest, mangrove swamp forest and freshwater swamp forest that are consistent with the African Humid Phase (AHP); climatic conditions were warm and wet with high sea levels. In the early stages of the Late Holocene, there is evidence of decline in the tropical rainforests with brief spells of climatic variability signalling the gradual end of the AHP. Subsequently, the pollen record revealed evidence of forest disturbance: specifically the replacement of the mangroves and lowland rainforests by coastal savannas and an Elaeis guineensis-dominated secondary forest, respectively, in Ahanve at cal. 3100 yr BP; and the decline and eventual recovery of the vegetation types in Ogudu after cal. 2760-2730 yr BP. These environmental disturbances are attributed to prolonged period of increased desiccation within a warm climate as well as the differentia in marine and riverine influence of both localities. Further decline in the tropical rainforest after cal. 1240-1200 yr BP were accompanied by substantial increase in oil palm (Elaeis guineensis), the emergence of exotic plants of South American and Asian origin, substantial increases in charcoal particles that were complemented by archaeological data. The pollen and charcoal data have shown that the decline of the tropical rain forests in the area beginning from the late Holocene was initially climate driven while subsequent and recent decline has been exacerbated by anthropogenic factors.

Archaeology and ecology of acavus snails in Sri Lanka’s semi-arid to intermediate zones: uncovering holocene microclimatic changes

This study presents a discovery of Acavus haemastoma, wet-humid favouring arboreal land snails from Semi-Arid coastal lagoon habitat during the late Holocene period in Southern Sri Lanka, occurring around the mid-4th millennium BP. These findings challenge established notions regarding palaeoecological conditions within the Semi-Arid and Transitional Zones (SATZ), prompting a re-evaluation of prevailing archaeological assumptions. We propose that the presence of Acavus sp. in the SATZ is primarily attributed to their natural behaviours rather than anthropogenic influences. In conjunction with an examination of early archaeological literature, we explore the implications of humid phases within the SATZ, aligning these phases with Acavus snails’ distribution patterns and climatic fluctuations and proposing the value of land snails in Sri Lanka as a potential proxy for small scale micro-climatic conditions.

CONCEPTUAL FOUNDATIONS OF AN ALTERNATIVE PHYSICAL MODEL OF MODERN CLIMATE

CONCEPTUAL FOUNDATIONS OF AN ALTERNATIVE PHYSICAL MODEL OF MODERN CLIMATE

Summer heatwaves in China during 1961–2021: The impact of humidity

In additon to temperature, heatwaves are also closely related to humidity. In this study, daily wet-bulb temperature was used to define heatwaves (WBHWs) with a unified threshold for more than 2000 meteorological stations throughout China. The climatic averages of summer heatwaves and changes from 1961 to 2021 were investigated. WBHWs primarily occur in three key subregions, namely North China, South China, and Yangtze River valley (YRV). Humidity makes heatwaves in South China more severe, with an average of 25 days per summer. Over the past decades, the frequency and intensity of WBHWs in China considerably increased accompanied by decreasing relative humidity (RH) and increasing temperature. South China experiences the strongest increase in WBHWs, with change rate fivefold higher than the national average. The occurrence of WBHWs in YRV is dominated by temperature, whereas in North and South China it is controlled by RH. The long-term increases in WBHWs for China and its three key subregions are primarily caused by temperature changes, but RH affects WBHWs at interdecadal time scales and generally exerts a negative contribution. The average contribution rates of temperature and RH to the increase in WBHWs in China for the period 1991–2021 are 2.3 days and − 0.6 days. Changes in WBHWs in North China are almost completely controlled by temperature, since the opposite phases of specific humidity and temperature result in a negligible effect of RH. Temperature and RH in other two subregions have substantial positive and negative effects, respectively. The negative effect of RH in South China is mainly attributed to the indirect effect of temperature, while that in YRV, particularly in the lower reaches, is a combination of specific humidity and temperature.

High‐frequency palaeoenvironmental changes in the mixed siliciclastic–carbonate sedimentary system from a lower Permian restricted basin (West Gondwana, southern Brazil)

ABSTRACTGlobal climatic and palaeogeographical changes generated a siliciclastic–carbonate system with high organic matter accumulations in a shallow sea during the lower Permian in Western Gondwana. The 60 m thick mixed siliciclastic–carbonate succession (Irati Formation and the base of the Serra Alta Formation) from the Paraná Basin represents a singular record of the interplay between carbonate production and siliciclastic input, providing a window of opportunity to integrate large‐scale depositional architecture with facies and geochemical analyses. The detailed study of cores supported by outcrop columnar sections revealed a siliciclastic‐dominated, retrogradational to aggradational facies, and a carbonate‐dominated, mixed aggradational to progradational facies composing three depositional sequences that record an outer‐ramp and mid to upper‐ramp. An integrated approach based on the description of facies and microfacies, organic geochemistry and mineralogical composition, indicated high‐frequency palaeoenvironmental changes during the evolution of this restricted basin. Climate changes, resulting in humid and dry phases, produced ideal conditions for high organic matter production and dolomite formation. The high organic matter production (humid phases) in addition to the restricted condition was responsible for the anoxic bottom waters that were widespread due to the low angle and homoclinal platform. Nutrient‐rich freshwater inflows in the anoxic and hypersaline restricted basin created a density‐stratified water column causing low‐salinity surface and anoxic bottom water, which allowed planktonic life, typical of lakes, such Botryococcus braunii, to flourish in the photic zone and sulphur bacteria to populate below the chemocline. Microbial activity induced primary dolomite precipitation (dry phases) and widespread formation of synsedimentary dolostone. Freshwater inflow and marine incursions are reflected in the organic matter accumulation (kerogen types I and II, respectively), generating bituminous shale with high total organic carbon (5 to 27 wt.%).

Monsoon-driven changes in aeolian and fluvial sediment input to the central Red Sea recorded throughout the last 200 000 years

Abstract. Climatic and associated hydrological changes controlled the transport processes and composition of the sediments in the central Red Sea during the last ca. 200 kyr. Three different source areas for mineral dust are identified. The dominant source is located in the eastern Sahara (Sudan and southernmost Egypt). We identify its imprint on Red Sea sediments by high smectite and Ti contents, low 87Sr / 86Sr, and high εNd. The availability of deflatable sediments was controlled by the intensity of tropical rainfall and vegetation cover over North Africa linked to the African monsoon. Intense dust input to the Red Sea occurred during arid phases, and low input occurred during humid phases. A second, less significant source indicated by palygorskite input is probably located on the eastern Arabian Peninsula and/or Mesopotamia, while the presence of kaolinite suggests an additional minor dust source in northern Egypt. Our grain size data reflect episodes of fluvial sediment discharge to the central Red Sea and document the variable strength in response to all of the precession-paced insolation maxima during our study interval including both those that were strong enough to trigger sapropel formation in the eastern Mediterranean Sea and those that were not. The African humid period most strongly expressed in our Red Sea record was the one during the Eemian last interglacial at ca. 125 ka (when the Baraka River was far more active than today), followed by those at 198, 108, 84, and 6 ka.

Late Quaternary palaeoclimatic records from the Indian Himalaya and Ganga foreland basin: Assessment on current understanding and future prospective

In this comprehensive review, an extensive analysis has been conducted on paleoclimate datasets from climatically sensitive regions in the Indian Himalaya and Indo-Gangetic plain. Our main objective was to gain valuable insights into the broad palaeoclimatic variability during the Late Quaternary-Holocene period. To achieve this, careful categorization was focused for various archives from multi-proxy studies into three groups: glacial moraine, glacio-fluvial and lake records, and speleothems. The compilation of climate records from different geographical settings has revealed an overall coherence during warm and humid phases, with minor variations influenced by variable moisture sources and topographic changes. The analysis reveals that Indian Summer Monsoon (ISM) reached its peak during approximately 9-5 ka BP and subsequently weakened around the Mid-Holocene (ca. 4–5 ka BP). Notably, the Last Glacial Maximum (LGM) and early Holocene were characterized by significant glacial advances in the Himalayan region. Furthermore, the sedimentation rates derived from lacustrine records in different regions exhibit considerable variability. In conclusion, the compilation and comparisons of diverse palaeoclimate records have significantly improved our understanding of the regions palaeoclimate. These findings hold substantial value for planning future focused studies in the crucial climatic zone. By refining our understanding of past climate dynamics in the Indian Himalaya and Indo-Gangetic alluvium, a better comprehension of the regions susceptibility to climate change can be achieved. This, in turn, facilitates informed decisions for sustainable development and environmental management.

Soils of Lakeside Depressions of Pulsing Chloride Lakes of Internal Runoff in Central Asia: Morphology, Physical-Chemical and Geochemical Features

Data on saline soils of drainless lakeside depressions, which are formed in areas of extra continental climate with a cyclic 25–30-year change in the level of lakes within the arid and humid climatic phases, were obtained first. Different types of soils are shown to be formed on the landscapes adjacent to highly mineralized chloride lakes of southeastern Trans-Baikal Region: on superaqueous–subaqueous positions– gleyic solonchaks (Gleyic Solonchak (Loamic, Chloridic)); on superaqueous – humus–gley saline soils (Calcaric Mollic Gleysol (Arenic, Endosalic, Sodic)); on eluvial-superaqueous – light-humus saline soils (Fluvic Kastanozem (Epiarenic, Amphiloamic, Sodic)). Salinity degree of the soils under the study is different. Salinity chemistry is sodium taking into account cations. Anion content in solonchaks and upper horizon of humus-gley soil is mostly chloride. Soda-chloride and chloride-soda anion composition prevail in other soils. Gleyic solonchaks have strongly alkaline pH values, high content of carbonates, and a sharp dominance of Na+ among exchangeable cations. Many chemical elements are concentrated in the solonchakous horizon (Sr, S, Li, Mg, Ca); a high content of As is a regional feature. The humus-gley saline soil has the same properties as the light-humus saline soil in terms of physico-chemical parameters, and in terms of elemental composition and texture as solonchaks. This is due to it functions periodically in a semihydromorphic or hydromorphic regimes when changing the arid and humid phases. The high level of groundwater contributes to the enrichment of soils with the elements typomorphic for lake waters. The paleohydromorphic stage of development has been established to be recorded in lower layers of light-humus saline soil in the form of a high content of easily soluble salts and carbonates. The geochemical specialization of soil-forming rocks is associated with the significant accumulation of As, as well as concentration of Li, Ba, and Pb. It was also revealed that low Ca/Sr ratio is their geochemical feature. The use of cluster analysis of indicators of soils under the study revealed that both dynamic and stable soil parameters are reflected in humus-gley soil and it is recommended for monitoring of the dynamics of endorheic lakeside ecosystems in Central Asia with cyclic climatic phases.

New insights into sedimentological and geochemical conditions of marine Pleistocene sediments in the Tangier region (Morocco): First implications for paleoenvironmental and paleoclimatic reconstructions

The Pleistocene period is characterized by important periodic climatic variations, marked by alternating arid and humid phases. This work aims to reconstruct the prevailing Pleistocene paleoenvironment and paleoclimate in the Tangier area based on a multidisciplinary study of a marine formation dating from 125 ka. Field investigations and sedimentological, micropaleontological, mineralogical, and geochemical analyses were carried out on samples from the Pleistocene Achakkar formation. The granulometric study, combined with a morphoscopic, exoscopic analysis of quartz grains and evidence for diverse benthic foraminifera, suggests a low-energy marine depositional environment, most likely foreshore to shoreface. Moreover, analysis of clay minerals and major elements suggests mineralogical evolution, indicating an arid climate. The sedimentary successions of the Pleistocene Achakkar littoral are progressively more and more coarse; emplacement was subject to several interactive factors, such as climatic and eustatic responsible for reconstituting the geological history of the Tangier Peninsula.

An Upper Pleistocene and Holocene Black Carbon‐Related Fire Record From the SW Balkans

AbstractLake sediments are unique archives of human environment interactions. Lake Prespa is one of the oldest lakes in Europe, lying in the southwestern Balkans and thus on a possible dispersal route of anatomically modern humans from Africa. In this study, we investigated the effects of climate, vegetation and human activity on fire over the last 92,000 years in this region. Sediment samples were taken from Lake Prespa, and nearby Lake Ohrid for comparison of the regional relevance, and analyzed for benzene polycarboxylic acids as markers for burned organic carbon residues (black carbon, BC). Peaking contents of BC (up to 1 g BC kg−1 sediment) coincided with warm and humid phases, when forests expanded at marine isotope stages (MIS) 5 and 1. During the colder and more arid climates of MIS 4 and 2, BC contents were lowered by a factor of 10, with a distinct minimum during the Last Glacial Maximum (0.07 g BC kg−1). The ratio of pentacarboxylic acid to mellitic acid (B5CA/B6CA) declined from 1.2 at MIS 5 to values of 0.3 at MIS 2, confirming a change in fire regime. Overall, BC contents peaked at cycles of solar radiation, vegetation composition and fuel availability, and thus correspond to the BC signal of other environmental archives. However, in the Late Holocene and as a result of human sedentary settlement, BC production increased, independent of decreasing insolation forcing.

Palynological Evidence From the Altai Mountains for the Links Between the Asian Westerly Jet Streams and Monsoon System During the Holocene

AbstractThe Asian westerly jet streams in the upper troposphere play a pivotal role in shaping precipitation patterns, sustaining the diverse but fragile ecosystems in arid Central Asia. Despite their significance, the evolution history of these jet streams and their synergistic effects with the monsoon systems on regional climate change in Asia during the Holocene remain poorly understood. To address this gap, we present a continuous pollen record since 8.6 cal ka BP from Lake Shuang in the Altai Mountains. The first two principal components of the pollen data are employed to track regional changes in vegetation, summer moisture, and winter temperature. Meanwhile, the pollen data and the TraCE‐21ka simulation results were compared to reveal the dynamic mechanism of regional climate change. Results indicate a humid phase spanning the interval ∼8 to 5 cal ka BP in this region, which broadly coincides with the intensification of the Indian Summer Monsoon. This temporal correlation is potentially linked to the poleward shift of the Asian jet, as suggested by simulation results. Furthermore, our data show a consistent winter warming trend throughout the Holocene, indicated by changes in the dominant tree pollen taxa and a reduction of cold‐resistant‐taxa. This trend is associated with the weakening of the East Asian Winter Monsoon, influenced by increasing winter solar insolation and atmospheric CO2 concentration. Overall, our research provides strong paleoclimatological evidence highlighting the interconnected meteorological roles of the Asian jet and monsoon systems in shaping regional climates.

Humid phases on the southwestern Arabian Peninsula are consistent with the last two interglacials

Past environmental and climatic conditions within the Arabian Peninsula are key to understanding the setting for hominin dispersal across the Saharo-Arabian dryland belt. The tufa deposits within the volcanic harrats on the southwest coast of Saudi Arabia fill a significant spatial gap in the distribution of palaeoenvironmental records on the west coast of the Arabian Peninsula adjacent to the Red Sea. In the catchment of Wadi Dabsa in the Harrat Al Birk, there are widespread fossil palustrine to shallow-lacustrine tufa deposits with fluvial elements. Several phases of tufa accumulation, separated by fluvial downcutting, are observable within these powerful palaeoenvironmental proxies. U–Th dating of targeted dense, banded tufa facies, yield ages that are stratigraphically consistent at the landscape scale, and indicate that tufa accumulation occurred during distinct humid phases broadly coeval with the last two warm interglacial Marine Isotope Stages (MIS 7 and MIS 5). For the first time this shows humid intervals in southwest Arabia coincident with the southern coast. There is a simlar pattern emerging further north in the Arabian Peninsula, The Sinai and Levant and further on into continental Europe. Furthermore, tufa δ18O ranges from −14.6 to −1.9‰, covering a range similar to those reported for tufa from north African oasis sites and speleothems elsewhere on the Arabian Peninsula and The Levant. The lowest δ18O values are derived from MIS 5e samples, a pattern in agreement with speleothems in Yemen and Oman, and consistent with an isotopic-enabled climate model simulation for this time slice. The δ13C and Sr isotopic compositions of dated tufa samples indicate deposition from shallow-circulating meteoric water, with no geothermal influence. This, along with the δ18O values, suggest a freshwater supply that was a potable water source in this landscape. The δ13C signatures at Wadi Dabsa are more negative than for parts of north Africa, suggesting Wadi Dabsa may have experienced comparatively higher biomass, thicker soils and wetter conditions with lower evaporative losses. This new record of tufa deposition during the middle and late Pleistocene, suggests for the first time that the west coast of Arabia experienced a similar history of humid phases over the past 250 ka as southern Arabia and the Nefud in the northern interior. These regional changes in hydroclimatic regime occur at timescales coincident with hominin dispersals.

Flax-Glass Fiber Reinforced Hybrid Composites Exposed to a Salt-Fog/Dry Cycle: A Simplified Approach to Predict Their Performance Recovery.

Despite natural fibers gaining significant attention in recent decades, their limited performance and poor durability under humid environments cannot allow them to fully replace their synthetic counterparts as reinforcement for structural composites. In such a context, this paper aims to investigate how exposure to a humid/dry cycle affects the mechanical response of epoxy laminates reinforced with flax and glass fibers. In particular, the main goal is to assess the performance evolution of a glass-flax hybridized stacking sequence in comparison with the full glass and flax fiber reinforced composites. To this end, the investigated composites were first exposed to salt-fog for 15 or 30 days and then to dry conditions (i.e., 50% R.H. and 23 °C) for up to 21 days. The presence of glass fibers in the stacking sequence significantly stabilizes the mechanical performance of composites during the humid/dry cycle. Indeed, hybridization of inner flax laminae with outer glass ones, acting as a protective shield, hinders the composite degradation due to the humid phase also promoting performance recovery during the dry phase. Hence, this work showed that a tailored hybridization of natural fibers with glass fibers represents a suitable approach to extend the service-life of natural fiber reinforced composites exposed to discontinuous humid conditions, thus allowing their employment in practical indoor and outdoor applications. Finally, a simplified theoretical pseudo-second-order model that aimed to forecast the performance recovery shown by composites was proposed and experimentally validated, highlighting good agreement with the experimental data.

Spodosol formation on sandy ruins in a semi-arid climate in the Catimbau National Park, Northeast Brazil

The Catimbau National Park (CNP) is found in the Caatinga biome under a semi-arid climate. The soils of certain humid areas have horizons with morphology typical of Spodosols, and their occurrence in the CNP seems to be in discord with their formation model. This study aimed to investigate the genesis of Spodosols in the semi-arid climate of the CNP, testing the hypothesis that these soils are the result of local tectonic conditions associated with a past climate. As such, a sandy soils toposequence over sandstone of the Tacaratu Formation, under Caatinga vegetation and a semi-arid climate in northeast Brazil was studied. Sampling was based on the structural model of the pedological coverage, whereby physical and chemical analyses, Fourier transform infrared spectroscopy, X-ray diffraction, and soil micromorphological analysis were carried out. The results indicate that paludization of the soils occurred in two more humid phases, being compounded by the occurrence of distended faults/fractures related to the geology of the CNP. Microbiological decomposition under hydromorphic conditions led to humification of the organic constituents, which acidified the environment and increased Al solubility, forming organometallic complexes with fulvic and humic acids. The FTIR spectra and the presence of charcoal confirm the condensed aromatic nature and the abundance of carboxylic groups in the soils, these being related to the pyrolysis of biotransformed plant residues. Podzolization occurred in pulses promoted by intense rains under a dry climate and Fe-poor parent material, which favored the translocation of organometallic compounds of Al. The dense packing of fine organomineral material in the Bh horizons and the open matrix in the adjacent horizons indicate that the narrowing of the porous environment may be an important factor for the immobilization of translocated material. With the return of the current drier conditions in Brazil’s semi-arid, the podzolization process remains incipient.

Floral response to the Late Triassic Carnian Pluvial Episode

The Late Triassic Carnian Pluvial Episode (CPE; ca. 234–232 Ma) was characterized by dramatic global temperature and humidity increases, which in many terrestrial settings was accompanied by changes from arid to humid vegetation types. This study reviews current evidence of terrestrial floral composition and distribution during the CPE and analyzes spatial and temporal variation with relation to potential environmental driving mechanisms. Available evidence suggests the CPE was a globally significant event that triggered significant increases in the abundance of ferns and hygrophytes in terrestrial floras and freshwater algae in fluvial and lacustrine settings. These changes ended a long interval of relatively arid terrestrial climatic conditions since the Early Triassic and are linked temporally with eruptions of the oceanic plateau Wrangellia Large Igneous Province (LIP). The massive release of greenhouse gasses including isotopically light CO2 during 3–4 distinct pulses of Wrangellia volcanism appears to have been the main driver of CPE climate change. Each pulse enhanced global atmospheric circulation and the hydrological cycle and resulted in changes from arid to humid conditions that affected floral abundance and composition. Higher terrestrial primary productivity in humid phases facilitated increased burial of terrestrial organic carbon and led to the recommencement of peat accumulation, ending the coal gap that had persisted since the Earliest Triassic times. Enhanced movement of carbon from the atmosphere through the biosphere into the geosphere may have counteracted the warming effects of Wrangellia volcanic greenhouse gas emissions and ultimately led to the return of a steady climate state that terminated the warm and humid conditions of the CPE.