Climatic Episodes Research Articles

Intra-Turonian stratigraphic reorganization on the Arabian Plate

Shallow-marine carbonate deposition was widespread across the Arabian Plate during much of the Late Permian–Mesozoic but was significantly interrupted by a major tectonically driven stratigraphic reorganization that took place within the Turonian. Published literature terms this the ‘Wasia–Aruma Break’, the ‘mid-Turonian Unconformity’, or the ‘K150 Sequence Boundary (SB)’. It is widely understood that this event relates to subduction in a closing Neotethys Ocean and obduction onto the continental margin, especially in the southeastern part of the plate. As well as a change in facies, a hiatus of variable duration is present, associated with erosion of the underlying stratigraphy. Despite the event being known for several decades, precision on its timing has been lacking due to the limitations of biostratigraphic data and because few other chronostratigraphic proxies have been employed. In order to rectify this, all relevant biostratigraphic data from across the Arabian Plate have been synthesized and evaluated in the context of a review of chronostratigraphic calibration of standard biozones from multiple fossil groups. This shows that the youngest preserved rocks beneath the K150 SB can be assigned to the middle Turonian Helvetoglobotruncana helvetica planktonic foraminifera zone or Collignoniceras woollgari ammonite zone. The oldest rocks above the K150 SB can be assigned to the same biozones, supporting the assertions that it is a very short duration event. Whilst obduction may have initiated earlier (as supported by the recognition of precursor events), crustal loading was sufficient by 91.5 Ma to develop a forebulge in the eastern part of the plate with associated uplift and erosion. A review of relative sea-level change during the Turonian has been carried out to investigate eustatic signals during this time. In multiple sections around the world, a sea-level fall in the upper part of the woollgari Zone of European usage can be detected. This appears to coincide with an episode of climate cooling. However, despite there being correspondence between the K150 SB and a significant eustatic event, this seems mostly coincidental as the tectonic drivers at this time across Arabia were much more dramatic. This is especially true in southeastern Arabia. In northwestern Arabia, tectonic quiescence may have allowed eustasy to dominate. In any case, a eustatic fall would have amplified the effects of tectonics across the entire region.

A dwarf conifer tree from the Triassic of Antarctica: the first fossil evidence of suppressed growth in a favorable climate?

The complexity of fossil forest ecosystems is difficult to reconstruct due to the fragmentary nature of the fossil record. However, detailed morpho-anatomical studies of well-preserved individual fossils can provide key information on tree growth and ecology, including in biomes with no modern analog such as the lush forests that developed in the polar regions during past greenhouse climatic episodes. We describe an unusual-looking stem from Middle Triassic (ca 240 Ma) deposits of Antarctica with over 100 very narrow growth-rings and conspicuous persistent vascular traces through the wood. Sections of the specimen were prepared using the cellulose acetate peel technique to determine its systematic affinities and analyse its growth. The new fossil shows similarities with the form genus Woodworthia and with conifer stems from the Triassic of Antarctica, and is assigned to the conifers. Vascular traces are interpreted as those of small branches retained on the trunk. Growth-ring analyses reveal one of the slowest growth rates reported in the fossil record, with an average of 0.2mm/season. While the tree was growing within the Triassic polar circle, sedimentological data and growth-ring information from other fossil trees, including from the same locality, support the presence of favorable conditions in the region. The specimen is interpreted as a dwarf conifer tree that grew under a generally favorable regional climate but whose growth was suppressed due to stressful local site conditions. This is the first time that a tree with suppressed growth is identified as such in the fossil record, providing new insights on the structure of polar forests under greenhouse climates and, more generally, on the complexity of tree communities in deep time.

Hardwoods: Anatomy and Functionality of Their Elements—A Short Review

Hardwoods are complex heterogeneous and orthotropic structures that have evolved to the present day, adapting to successive climate episodes to prosper on Earth. Attributing a specific functionality to individual hardwood elements is difficult because of their interconnection in this heterogeneous three-dimensional network. However, tree physiology research is helping to enhance knowledge in this field. This work is a short review of the possible functionalities of hardwood elements, in some cases supported by experimentation and in others by comparative anatomy. It is intended for students or researchers starting out in the world of hardwood anatomy to aid their understanding of the functionality of hardwood elements.

Heat-altered scent marks of males of a fossorial reptile still allow recognition by females but lose information on male quality

The efficacy of sexual signals in communication is often maximized under specific environmental conditions. Anthropic alterations of these conditions might, thus, negatively affect communication during reproductive behavior. In fossorial animals, inhabiting visually restricted environments, chemical senses are very important. We examined whether climatic episodes of heat-waves with unusual high temperatures may affect the information provided to females by the sexual chemical signals of males of a fossorial reptile, the amphisbaenian Blanus cinereus. The results showed that experimentally heat-altered substrate scent marks of males can still provide information to females about the presence of a male. Females spent more time on males’ scent marks, irrespective of the temperature treatment, than on control clean ones. However, heat-altered scent marks did not seem to convey information about the health state (immune response) of the producer. Females spent more time on unaltered scent marks of healthier males (probably indicating mating preferences for these males), while female preferences for some heat-altered scent marks were not related to size or immune response of the same individual males. Chemical analyses indicated that the overall chemical profile of precloacal secretions (used for scent marking) did not change with increased temperatures. However, the relationship between proportions of some compounds in secretions and males’ immune response found in unaltered secretions was lost in heat-altered ones. We conclude that unusual increased environmental temperatures may decrease the efficacy of underground sexual chemical signals in this amphisbaenian (i.e., a loss of information on male quality), and consequently, may negatively affect sexual selection and reproduction.

Sedimentary Organic Nitrogen Isotopic Constraints on the Mid‐Holocene Transition in the Nitrogen Dynamics of the Northern South China Sea

AbstractMillennial‐scale nitrogen (N) cycling processes in marginal seas and their response to climate change have not been well understood. Here, we present high‐resolution (ca. 110 years) organic nitrogen isotope (δ15Norg) data since the last deglaciation (16.1 ka) derived from a highly resolved sediment core in the northern South China Sea, aiming to explore millennial‐scale N cycling processes in this area. Unlike most bulk nitrogen isotope (δ15Nbulk) records from the South China Sea, the δ15Norg records show a clear response to well‐defined climatic episodes during the last deglaciation and early Holocene (EH, ∼11.7 to 9 ka), but exhibit a gradually decreasing trend in mid‐to‐late Holocene (since ca. 9 ka). During the last deglaciation and EH, the upper water column N dynamics are controlled by the lateral transport of surface nitrate from eastern tropical Pacific (ETP) presumably via the North Pacific Intermediate Water (NPIW) and to some extent, influenced by the altered input of terrigenous matter driven by sea level change. The significant decrease in δ15Norg since the mid‐Holocene (at ca. 9 ka) can be best explained by the increase in local N2 fixation forced by enhanced El Niño. This mechanism is consistent with modern observations. Overall, our results may reflect the main controlling factors of surface ocean N dynamics have shifted from zonal transport of nitrate from the ETP to El Niño since the mid‐Holocene.

Incidence of the El Niño-Southern Oscillation Cycle on the Existing Fundamental Niche and Establishment Risk of Some Anastrepha Species (Diptera-Tephritidae) of Horticultural Importance in the Neotropics and Panama.

To compare the environmental space of four Anastrepha species in different ENSO episodes (El Niño, El Neutro and La Niña), we built ecological niche models with NicheA software. We analysed the fundamental niche and the combined establishment risk maps of these species developed with the ArcGisPro combine geoprocess. A comparison of the ellipsoids that represent the fundamental niche existing for the species showed changes in the El Niño, El Neutro and La Niña episodes. For A. grandis in the El Niño vs. El Neutro episodes, there was a Jaccard index of 0.3841, while the comparison between the La Niña vs. El Neutro episodes presented a Jaccard index of 0.6192. A. serpentina in the El Niño vs. El Neutro and La Niña vs. El Neutro episodes presented Jaccard indices of 0.3281 and 0.6328, respectively. For A. obliqua, the comparison between the El Niño vs. El Neutro and La Niña vs. El Neutro episodes presented Jaccard indices of 0.3518 and 0.7472, respectively. For A. striata, comparisons between the episodes of El Niño vs. El Neutro and La Niña vs. El Neutro presented Jaccard indices of 0.3325 and 0.6022, respectively. When studying the comparison between Anastrepha species and the different ENSO climatic episodes, we found that in the El Niño episode, the comparisons with the best environmental similarity were A. obliqua vs. A. striata and A. obliqua vs. A. serpentina, with higher Jaccard indices (0.6064 and 0.6316, respectively). In the El Neutro episode, the comparisons with the best environmental similarity were A. serpentina vs. A. striata and A. obliqua vs. A. striata, which presented higher Jaccard indices (0.4616 and 0.6411, respectively). In the La Niña episode, the comparisons that presented the best environmental similarity were A. obliqua vs. A. serpentina and A. obliqua vs. A. striata, with higher Jaccard indices (0.5982 and 0.6228, respectively). Likewise, our results present the risk maps for the establishment of these species throughout the Neotropics, allowing us to predict the level of risk in order to develop integrated pest management plans.

Sex-dependent resilience to extreme drought events: implications for climate change adaptation of a South American endangered tree species

BackgroundRecent changes in climatic trends are resulting in an increased frequency and intensity of extreme events, with unknown effect on ecosystem dynamics in the near future. Extreme drought episodes are recognized as disturbance factors capable of modifying forest dynamics and tree growth. Within this context, dioecious tree species may be impacted by climatic extremes, affecting male/female proportions and, consequently, reproductive processes and species persistence. Therefore, there is an urgent need for species-specific assessments of growth tolerance to extreme dry spells in dioecious tree species, to establish effective conservation strategies for these particular natural resources. Araucaria araucana (araucaria), an endangered dioecious Patagonian tree species, has recently undergone decay and mortality episodes in response to increasing dry climatic conditions. While sex-dependent tolerance to extreme drought episodes has been assessed in the species’ humid distribution range, there is still a lack of information on the gender-based resilience of trees growing in the drier environments of the species’ distribution.MethodsWe reconstructed, through dendrochronological methods, the sex-dependent response of 105 araucaria individuals (55 female and 50 male trees) to five regional extreme dry spells employing a set of different indices. Resistance, recovery period, and average growth reduction of standardized tree-ring growth were examined, analysing the effect of biotic (sex, pre-drought stem tree growth) and abiotic (local climatic conditions before, during, and after extreme climatic episodes) factors on tree resilience.ResultsSex influences only the species resistance to climatic disturbance, with male individuals showing lower tolerance to extreme drought events. Pre-drought radial growth rates and local meteorological conditions preceding, during, and following extreme dry spells strongly modulated araucaria radial growth resilience regardless of tree sex, influencing the species resistance, recovery period, and average growth reduction.ConclusionsWe provide novel and crucial information for the species conservation and management in the current climate change scenario, and contribute to the debate regarding the role of tree sex as a factor influencing woody species growth under particularly adverse climatic conditions. In the face of climate change, an increase in extreme drought events is expected in the easternmost araucaria xeric end distribution area, which will likely decrease the species resilience.

A global compilation of diatom silica oxygen isotope records from lake sediment – trends and implications for climate reconstruction

Abstract. Oxygen isotopes in biogenic silica (δ18OBSi) from lake sediments allow for quantitative reconstruction of past hydroclimate and proxy-model comparison in terrestrial environments. The signals of individual records have been attributed to different factors, such as air temperature (Tair), atmospheric circulation patterns, hydrological changes, and lake evaporation. While every lake has its own local set of drivers of δ18O variability, here we explore the extent to which regional or even global signals emerge from a series of paleoenvironmental records. This study provides a comprehensive compilation and combined statistical evaluation of the existing lake sediment δ18OBSi records, largely missing in other summary publications (i.e. PAGES network). For this purpose, we have identified and compiled 71 down-core records published to date and complemented these datasets with additional lake basin parameters (e.g. lake water residence time and catchment size) to best characterize the signal properties. Records feature widely different temporal coverage and resolution, ranging from decadal-scale records covering the past 150 years to records with multi-millennial-scale resolution spanning glacial–interglacial cycles. The best coverage in number of records (N = 37) and data points (N = 2112) is available for Northern Hemispheric (NH) extratropical regions throughout the Holocene (roughly corresponding to Marine Isotope Stage 1; MIS 1). To address the different variabilities and temporal offsets, records were brought to a common temporal resolution by binning and subsequently filtered for hydrologically open lakes with lake water residence times < 100 years. For mid- to high-latitude (> 45° N) lakes, we find common δ18OBSi patterns among the lake records during both the Holocene and Common Era (CE). These include maxima and minima corresponding to known climate episodes, such as the Holocene Thermal Maximum (HTM), Neoglacial Cooling, Medieval Climate Anomaly (MCA) and the Little Ice Age (LIA). These patterns are in line with long-term air temperature changes supported by previously published climate reconstructions from other archives, as well as Holocene summer insolation changes. In conclusion, oxygen isotope records from NH extratropical lake sediments feature a common climate signal at centennial (for CE) and millennial (for Holocene) timescales despite stemming from different lakes in different geographic locations and hence constitute a valuable proxy for past climate reconstructions.

Extreme drought triggers parallel shifts in wood anatomical and physiological traits in upper treeline of the Mediterranean Andes

BackgroundTreeline ecotones of Mediterranean ecoregions have been affected by the increasing intensity and severity of droughts. Even though the effect of droughts on forest dynamics has been widely documented, knowledge is relatively scarce of how extreme climate episodes affect the hydraulic structure and, therefore, the physiology of woody plants. The Mediterranean Andes have experienced an uninterrupted period of drought since 2010, including an extremely dry year in 2019 with approximately 80% rainfall deficit. Here, we investigated shifts in wood anatomical and physiological traits of Kageneckia angustifolia, an endemic treeline species, in response to this drought period.MethodsWe evaluated the xylem plasticity of three K. angustifolia populations across their natural distribution (31–35° SL) based on anatomical (vessel structure and distribution) and physiological (intrinsic water-use efficiency) variables in the tree rings. We focused on the period 2000–2020 that corresponds to before the megadrought (2000–2007), (ii) megadrought (2008–2018) and (iii) hyperdrought (2019–2020). The variables were annualized and analyzed by linear mixed-effects models.ResultsOur results provide insights to the anatomical and physiological mechanisms underlying the resilience of treeline forests to persistent droughts in central Chile. We found that the extreme drought in 2019–2020 triggered shifts in vessel size and frequency that increased hydraulic safety. These significant shifts in vessel traits occurred in parallel with a decrease in pit aperture area and an increase in water-use efficiency, further increasing the resilience of K. angustifolia to extreme drought stress.ConclusionsOur results revealed coordinated shifts in vessel size and frequency and water-use efficiency in response to the megadrought, thereby reducing vulnerability to hydraulic failure. The apparent resilience of K. angustifolia to extreme droughts suggests that this adaptation to drought stress may increase its ability to tolerate novel climatic conditions of treeline environments of the Mediterranean Andes, although it is not clear whether these adaptations will be sufficient to persist in scenarios that predict intensification of climate stress. Finally, our results provide empirical evidence that integrating wood anatomical and physiological traits facilitates the understanding of resilience mechanisms that treeline forests develop in the face of increasing drought stress.

Platinum and microspherule peaks as chronostratigraphic markers for onset of the Younger Dryas at Wakulla Springs, Florida

Anomalous peak abundances of platinum and Fe-rich microspherules with high-temperature minerals have previously been demonstrated to be a chronostratigraphic marker for the lower Younger Dryas Boundary (YDB) dating to 12.8 ka. This study used Bayesian analyses to test this hypothesis in multiple sequences (units) of sandy, weakly stratified sediments at Wakulla Springs, Florida. Our investigations included platinum geochemistry, granulometry, optically stimulated luminescence (OSL) dating, and culturally dated lithics. In addition, sediments were analyzed using scanning electron microscopy and energy dispersive x-ray spectroscopy to investigate dendritic, iron-rich microspherules previously identified elsewhere in peak abundances at the onset of the Younger Dryas (YD) cool climatic episode. Our work has revealed this abundance peak in platinum and dendritic spherules in five sediment sequences at Wakulla Springs. A YDB age of ~ 12.8 ka for the platinum and spherule chronostratigraphic datum in these Wakulla Springs sequences is consistent with the archaeological data and OSL dating. This study confirms the utility of this YDB datum layer for intersequence correlation and for assessing relative ages of Paleoamerican artifacts, including those of likely Clovis, pre-Clovis, and post-Clovis age and their possible responses to environmental changes known to have occurred during the Younger Dryas cool climatic episode.

Extreme rain event highlights the lack of governance to face climate change in the Southeastern coast of Brazil

New rainfall records were registered in the southeastern region of Brazil during February 2023. The amount of rain in the north coast region of the State of São Paulo was more than 650 mm in less than two days. Landslides and tragedies with a socioeconomically vulnerable population marked this climatic extreme. The country has a regulatory system that suggests the elaboration and implementation of municipal public policies aimed at territorial organization, environmental conservation, and the prevention of disasters induced by natural hazards. In addition, both federal and state funds earmarked for such hazard's prevention have been underutilized over the last decade. In addition to this current devastating climate episode, other events were registered in this decade, reinforcing that financial governance is a key challenge to face the climate crisis in Brazil. The predicted future extreme events in different regions of Brazil will require a different governance system to minimize social inequality, seek sustainable alternatives for urban environments and manage to adapt cities for the challenges posed by climate change.

The Late Intermediate Period in the south-central Andes (AD 1000–1450): Key problems in chronology

The Late Intermediate Period (LIP, cal AD 1000–1450) in the central Andes is defined as a hiatus after the collapse of Tiwanaku and Wari, expansive state polities of the Middle Horizon (cal AD 600–1000), and before the domination of the Inca empire in the Late Horizon (cal AD 1450–1532). The LIP is often characterized as a unit, but major developments took place within this long period, including diasporic migrations and the new colonization of some regions, demographic change, intensified conflict, large-scale adverse climate episodes, and changes associated with the onset of Inca expansion. Here we make a preliminary attempt to clarify the chronology of these developments. A database of published and new radiocarbon dates is compiled for the south-central highlands and coastal valleys in order to model overall and subregional demographic trends using an updated “dates-as-data” cumulative kernel density estimate (CKDE) approach, and to examine specific LIP phenomena in two subregions. Our results indicate major demographic change including 1) substantial population growth beginning in the 13th century, 2) a marked 14th-century population surge in most, but not all, subregions included here, 3) evidence of population decline in several subregions during the same intervals when neighboring populations are expanding. Population growth was associated with intensified violence and increased physiological stress in the upper Nasca drainage. In the altiplano of Peru and Bolivia, population growth accompanied the rise of defensive hillforts and monumental cemeteries. Our date models also indicate a more complicated terminal LIP in the altiplano, with the height of classically “LIP” societies overlapping with early evidence for imperial Inca presence. This paper highlights the ways that more refined chronology can make advances in our understanding of a turbulent post-collapse era in the Andes.

A 1000-year record of paleoclimate and paleoenvironment change inferred from sedimentary organic matter in Lake Azuei, Haiti

We studied sediment organic matter (OM) to reconstruct the environment over the last millennium using a sediment core from Lake Azuei, Haiti, also known as “Etang Saumatre.” Chronology for the 84-cm-long core was established with 11 14C dates and 210Pb analysis. Total organic carbon (TOC) concentrations in the sediment were low (0.58 ‐ 4.89%), as were total nitrogen (TN) values (0.06 ‐ 0.40%). Carbon isotopic ratio (δ13C) values were relatively negative and C/N ratios were low, suggesting that algae and terrestrial C3 plants were the primary sources of OM in the lake sediment. The inverse relationship between the nitrogen isotopic ratio (δ15N) and TOC is related to denitrification in the sediment. We identified five stratigraphic zones using a δ13C vs. C/N cross diagram: 1) Medieval Climate Anomaly 1 (MCA1) (1000–1050 CE), 2) Medieval Climate Anomaly 2 (MCA2) (1050–1100 CE), 3) Transition period between Medieval Climate Anomaly and Little Ice Age (MCA-LIA) (1150–1400 CE) 4) Little Ice Age (LIA) (1400–1800 CE), 5) Current Warm Period (CWP) (1800–2000 CE). These stratigraphic zones correspond to three climate episodes. The first was applied MCA1 and LIA periods, when there was a decrease in TOC and TN as well as in plankton-derived OM. This was accompanied by an increase in δ15N, which suggests denitrification due to suboxic conditions, likely caused by an increase in lake water temperature and dry conditions. The second climate episode was the MCA-LIA transition period and was characterized by high variability of TOC, δ13C and δ15N. The organic matter deposited during this period appeared to be a mixture of material originating from both autochthonous phytoplankton and allochthonous C3 plants. There was climate instability during this period, with alternations between wet and dry conditions, and thus likely variations in lake level. The third climate episode, the MCA2 and CWP periods, was characterized by an increase in TOC and TN values, and decrease in δ13C and δ15N values. This was chiefly attributable to more organic material input which was derived from C3 terrestrial vegetation growing around the lake. A decrease in δ15N indicated a reduction in denitrification, further suggesting an increase in the input of organic matter. Sedimentation during these periods occurred when there was more transport related to wet conditions.

Mortality thresholds of juvenile trees to drought and heatwaves: implications for forest regeneration across a landscape gradient

Tree loss is increasing rapidly due to drought- and heat-related mortality and intensifying fire activity. Consequently, the fate of many forests depends on the ability of juvenile trees to withstand heightened climate and disturbance anomalies. Extreme climatic events, such as droughts and heatwaves, are increasing in frequency and severity, and trees in mountainous regions must contend with these landscape-level climate episodes. Recent research focuses on how mortality of individual tree species may be driven by drought and heatwaves, but how juvenile mortality under these conditions would vary among species spanning an elevational gradient—given concurrent variation in climate, ecohydrology, and physiology–remains unclear. We address this knowledge gap by implementing a growth chamber study, imposing extreme drought with and without a compounding heatwave, for juveniles of five species that span a forested life zones in the Southwestern United States. Overall, the length of a progressive drought required to trigger mortality differed by up to 20 weeks among species. Inclusion of a heatwave hastened mean time to mortality for all species by about 1 week. Lower-elevation species that grow in warmer ambient conditions died earlier (Pinus ponderosa in 10 weeks, Pinus edulis in 14 weeks) than did higher-elevation species from cooler ambient conditions (Picea engelmannii and Pseudotsuga menziesii in 19 weeks, and Pinus flexilis in 30 weeks). When exposed to a heatwave in conjunction with drought, mortality advanced significantly only for species from cooler ambient conditions (Pinus flexilis: 2.7 weeks earlier; Pseudotsuga menziesii: 2.0 weeks earlier). Cooler ambient temperatures may have buffered against moisture loss during drought, resulting in longer survival of higher-elevation species despite expected drought tolerance of lower-elevation species due to tree physiology. Our study suggests that droughts will play a leading role in juvenile tree mortality and will most directly impact species at warmer climate thresholds, with heatwaves in tandem with drought potentially exacerbating mortality especially of high elevation species. These responses are relevant for assessing the potential success of both natural and managed reforestation, as differential juvenile survival following episodic extreme events will determine future landscape-scale vegetation trajectories under changing climate.

A high-resolution study of planktonic foraminifera during the Holocene at the Tilos-Symi sea basin in the SE Aegean Sea

High-resolution data for planktonic foraminifera and their groups of ecological interest, including Herbivores and Carnivores, combined with benthic foraminifera and a great variety of biogeochemical indices from the SE Aegean sediment core ST5, contribute to a detailed study concerning major and minor climatic episodes during Holocene. The ST5 sediment record, retrieved from the Tilos-Symi marine basin, evidences the impact of the nearby land, the local climate, and the Rhodes Gyre imprint on the eastern Mediterranean water circulation. Pronounced environmental changes are detected during a preconditioning period of ~400 years before the onset of sapropel S1 deposition and during the deposition phases S1a (10.0–8.4 ka BP) and S1b (8.0–6.1 ka BP). Major freshwater influx episodes (10.5 ka BP, 9.2–8.9 ka BP, 7.4 ka BP, 4.5–4.3 ka BP, and few additional during the Late-Holocene) are revealed, prominent oxygen deficiency time intervals (including a distinct brief anoxic period) as well as several drier, cooler and warmer climatic events. Herbivore planktonic foraminifera alternate their dominance with the Carnivores at the preconditioning period before the S1 onset and at the Late-Holocene (2.0–1.5 ka BP) when conditions of good seawater circulation, oxygenation, and productivity alternate with stratified low oxygenation waters and high freshwater influx from the land.

Parabolic dune distribution, morphology and activity during the last 20 000 years: A global overview

AbstractParabolic dunes form and migrate in almost every climate and geographic zones of the world, ranging from the tropical coastlines to the arid continental deserts. Despite their extensive distribution and their importance within the aeolian sediment landscape, the understanding of their morphological development, activity and link with climates remains somewhat limited to local or regional scales. A good understanding of the present climate conditions under which parabolic dunes are formed and/or reactivated would be significantly helpful to constrain past climate models. Similarly, an improved knowledge of parabolic dunes behaviour during past climatic episodes would provide some valuable long‐term data to better predict their future activity. This review first aims at providing a non‐exhaustive global database on parabolic dune morphology and the present wind regimes with which they are associated. To do so, the morphology of 750 dunes distributed worldwide was first analysed using a high‐resolution global digital elevation model, suggesting an intrinsic relationship between the different measured morphoparameters. The analysis of the associated local wind regimes shows that parabolic dunes develop under strong unidirectional winds, which are more conspicuous in coastal than continental environments. Dunes of different ages are globally aligned with present prevailing winds, which suggests a prevalent control of long‐term global atmospheric circulation on dune orientations. Finally, this study explores the link between parabolic dune activity and climates over the past 20 000 years by reviewing ages from the literature and combining them with the ones compiled in the INQUA Dunes Atlas Chronologic Database. Overall, it appears that changes towards drier conditions have triggered dunes migration during both warm and cold periods of the Last Glacial Maximum, Holocene Climate Optimum, Roman Climate Optimum, Medieval Climate Optimum and Little Ice Age. The present day aeolian activity is predominantly linked with deteriorating environmental conditions caused by human disturbances.

Delayed valley incision due to karst capture (Demänová Cave System, Western Carpathians, Slovakia)

Karst systems can control the amount of water flowing on the surface and thus the fluvial erosional efficiency. Here, we used the ages of speleothems from the active cave system to determine the middle Pleistocene history of the entrenchment of the Demänová Valley. By referencing the vertical position of fluvially active and inactive cave passages to the valley bottom, we estimated the deceleration magnitude of the valley incision due to karst drainage through the Demänová Cave System. The well-developed karst system captures a significant volume of surface water and reduces surface erosion. This, in turn, causes a delay in the incision of the valley drained by the caves in comparison to the downstream positions (below the springs of sinking waters), where river-driven erosion dominates. Karst drainage has reduced the erosional efficiency in the inflow part of the Demänová Valley due to a hydraulic gradient among inputs and outputs of allochthonous waters, mostly during the middle and late Pleistocene. The cave level that contains the active underground segment of the Demänovka River, previously dated to ~350 ka, definitely existed earlier than 600 ka. The period from approximately 600 to 395 ± 5 kyr ago was characterized by relatively stable conditions with continuous deposition of flowstones, regardless of the climate episodes, including several glacial–interglacial cycles.

Modulation of East Asian monsoon strength by ENSO during the warm periods of the late Holocene: Evidence from Porites corals in the northern South China Sea

As a gauge for ocean precipitation conditions, sea surface salinity (SSS) is suspected to be an excellent indicator for variations in the global hydrological cycle. The SSS conditions in the South China Sea (SCS) are closely related to precipitation changes of the East Asian monsoon. However, the characteristics and driving mechanisms of the meridional pattern of East Asian monsoon rainfall during the warm periods of the late Holocene are not well understood because of a lack of high-resolution proxies from the SCS. Here, we present three precise chronologies of monthly stable coral skeleton oxygen isotopes (δ18O) and pair them with established composite strontium/calcium (Sr/Ca) records from the Xisha Islands to obtain a continuous reconstruction of the residual δ18O (Δδ18O, regarded as seawater δ18O) during 1980–2007 CE (Common Era), 1149–1205 CE, and 2070–2011 a BP (years before 1950 CE). The results confirm that coral Δδ18O is a good tracer for reconstructing SSS and precipitation changes in the northern SCS on seasonal and interannual timescales, with higher Δδ18O values implying more saline conditions and less precipitation. The mean value of fossil coral Δδ18O for 1149–1205 CE was higher than that of modern coral, suggesting the existence of salty surface waters and notable dry climate episodes in the northern SCS during the late Medieval Climate Anomaly (MCA). In contrast, the average coral Δδ18O for 2070–2011 a BP was significantly lighter by about 0.404‰ compared to that of recent decades, indicating that less saline and more humid conditions occurred in the northern SCS during the early Roman Warm Period (RWP). Synthesizing our coral records with other published precipitation reconstructions from eastern China suggested a meridional dipole spatial pattern of moisture variation over East Asia during the historical warm periods of the Holocene. During the MCA, drier conditions generally prevailed in the region south of the Yangtze River, and more humid conditions in the north. This may be closely related to the contemporaneous strong El Niño activity occurring at this time, which probably enhanced the East Asian summer monsoon (EASM) and caused a northward shift of the intertropical convergence zone (ITCZ), possibly inducing increased water vapor transport from the SCS to North China. During the RWP, the relatively weak El Niño–Southern Oscillation (ENSO) variability may weaken the intensity of the EASM and shift the ITCZ southward, possibly resulting in a spatial pattern of “wet south and dry north” in East Asia.

Diatom responses and geochemical feedbacks to environmental changes at Lake Rauchuagytgyn (Far East Russian Arctic)

Abstract. This study is based on multiproxy data gained from a 14C-dated 6.5 m long sediment core and a 210Pb-dated 23 cm short core retrieved from Lake Rauchuagytgyn in Chukotka, Arctic Russia. Our main objectives are to reconstruct the environmental history and ecological development of the lake during the last 29 kyr and to investigate the main drivers behind bioproduction shifts. The methods comprise age-modeling, accumulation rate estimation, and light microscope diatom species analysis of 74 samples, as well as organic carbon, nitrogen, and mercury analysis. Diatoms have appeared in the lake since 21.8 ka cal BP and are dominated by planktonic Lindavia ocellata and L. cyclopuncta. Around the Pleistocene–Holocene boundary, other taxa including planktonic Aulacoseira, benthic fragilarioid (Staurosira), and achnanthoid species increase in their abundance. There is strong correlation between variations of diatom valve accumulation rates (DARs; mean 176.1×109 valves m2 a1), organic carbon accumulation rates (OCARs; mean 4.6 g m−2 a−1), and mercury accumulation rates (HgARs; mean 63.4 µg m−2 a−1). We discuss the environmental forcings behind shifts in diatom species and find moderate responses of key taxa to the cold glacial period, postglacial warming, the Younger Dryas, and the Holocene Thermal Maximum. The short-core data likely suggest recent change of the diatom community at the beginning of the 20th century related to human-induced warming but only little evidence of atmospheric deposition of contaminants. Significant correlation between DAR and OCAR in the Holocene interglacial indicates within-lake bioproduction represents bulk organic carbon deposited in the lake sediment. During both glacial and interglacial episodes HgAR is mainly bound to organic matter in the lake associated with biochemical substrate conditions. There were only ambiguous signs of increased HgAR during the industrialization period. We conclude that if increased short-term emissions are neglected, pristine Arctic lake systems can potentially serve as long-term CO2 and Hg sinks during warm climate episodes driven by insolation-enhanced within-lake primary productivity. Maintaining intact natural lake ecosystems should therefore be of interest to future environmental policy.

Parasite communities of the golden snapper Lutjanus inermis (Perciformes: Lutjanidae): inter-annual variations during strange climatic events.

Strange oceanographic events such as El Niño and La Niña may have indirect effects on the local transmission processes of intestinal parasites due to the reduction or increase in populations of potential intermediate or definitive hosts. A total of 713 individuals of Lutjanus inermis (Peters) were collected over an 8-year period (October 2015 to July 2022) from Acapulco Bay, Mexico. Parasite communities in L. inermis were quantified and analysed to determine if they experienced interannual variations in species composition and structure as a result of local biotic and abiotic factors influenced by oceanographic events, such as El Niño-Southern Oscillation (ENSO), or La Niña, the cool phase of the ENSO climate pattern. Twenty-six taxa of metazoan parasites were recovered and identified: two Monogenea, eight Digenea, two Acanthocephala, four Nematoda, one Cestoda, seven Copepoda, and two Isopoda. Species richness at the component community level (8 to 17 species) was similar to reported richness in other species of Lutjanus Bloch. Parasite communities of L. inermis exhibited high inter-annual variation in the abundance of component species of parasite. However, the species richness and diversity were fairly stable over time. Climatic episodes of El Niño and La Niña probably generated notable changes in the structure of local food webs, thus indirectly influencing the transmission rates of intestinal parasite species. Changes in species composition and community structure of parasites possibly were due to variations in feeding behaviour during the events and differences in the host body size.