Search Results (23)

The Mid-Piacenzian Warm Interval (MPWI) is marked by warmer temperatures and higher atmospheric CO₂ levels than today, making it an analogue for late-21st-century-warming, whereas the early Pleistocene cooling is more like today. We compare seasonal growth temperatures derived from oxygen isotope ratios (δ¹⁸O) and clumped isotopes (∆₄₇) in Mercenaria. Modern shells were previously collected from coastal NC. The fossil shells are from the Duplin (MPWI) and Waccamaw Formations (early Pleistocene), NC. Oxygen isotope ratios range from −2.2‰ to 2.3‰ (modern), −0.9‰ to 2.4‰ (MPWI), and −0.9‰ to 2.9‰ (early Pleistocene). The values of Δ₄₇ range from 0.576‰ to 0.639‰ (modern), 0.566‰ to 0.621‰ (MPWI), and 0.581‰ to 0.615‰ (early Pleistocene). We show that Mercenaria do not require a species-specific ∆₄₇ calibration. Modern and MPWI ∆₄₇-derived summer/winter temperatures (SST_∆47) and seasonal amplitudes are indistinguishable from δ¹⁸O-derived temperatures. The early Pleistocene summer SST_∆47 is indistinguishable from δ¹⁸O-derived temperatures, but the winter SST_∆47 is warmer by 5 °C and may reflect within-shell time averaging. The modern summer/winter SST_∆47 are indistinguishable from the MPWI, but the MPWI has a lower seasonal amplitude by 5 °C. Compared to our calculated δ¹⁸O_sw values, modeled values for the MPWI are within error but are much lower, and they are not within error for the early Pleistocene. Full article

Climate during the Late Cretaceous is characterized by a long-term cooling trend interrupted by several periods of increased warming. This study focuses on the terrestrial response to two rapid climate events just prior to the K-Pg boundary marked by the Chicxulub impact: the Mid-Maastrichtian Event (MME) and the Late Maastrichtian Warming Event (LMWE). These hyperthermals caused widespread biotic and greenhouse gas-related disturbances, and clarification about their timing and environmental character reveals the independent nature of all three events. Using element concentrations in bulk paleosols, as well as element concentrations in pedogenic calcite from paleosols in the Tornillo Basin of West Texas, we reconstruct mean annual precipitation (MAP) and the character of soil weathering across the K-Pg boundary. Modelled MAP indicates increased precipitation during the first half of the MME and rapid high amplitude changes in precipitation during the second half of the MME. The Tornillo Basin became increasingly dry during the LMWE followed by wet conditions that continued across the K-Pg boundary. This study documents the co-occurrence of sedimentation patterns, sea level change, and climate change caused by separate tectonic events prior to the K-Pg boundary. Full article

The Yahşihan/Kırıkkale sedimentary basin, located in Central Anatolia within the İzmir-Ankara-Erzincan suture zone, mostly consists of Upper Cretaceous to Lower Pliocene sediments developed on the Ankara Melange, which is linked to the Northern Neo-Tethys Ocean. Although the stratigraphic, sedimentological, and tectono-stratigraphic characteristics of the basin have been investigated by many researchers, its mineralogical and geochemical characteristics have not been studied extensively. In this study, the provenance, paleoclimatological properties, and tectonic structure of the sedimentary rocks were interpreted using detailed mineralogical and geochemical analysis data. Formations such as the Karadağ (Cenomanian-Campanian), Çiçekdağ (Santonian-Campanian), Samanlık (Maastrichtian), Dizilitaşlar (Paleocene-Early Eocene), Çayraz (Middle Eocene), İncik (Upper Eocene-Lower Miocene), Central Anatolia Group (Middle Miocene-Pliocene), and Quaternary alluvium were deposited in the basin. X-ray diffraction (XRD), optical microscopy, scanning electron microscopy (SEM), and geochemical analyses were employed to determine the mineralogical and chemical composition of the units. Although highly oxic paleo-environmental conditions predominated in the basin, anoxic and suboxic conditions could also be present in the Dizilitaşlar and İncik formations. The units are primarily felsic with some mafic contributions, suggesting an oceanic island arc environment with varying paleoenvironmental conditions, reflecting seasonal changes between humid and arid periods. Full article

Six up-to-date reconstructions of hemispheric and global temperatures and two indices of volcanic activity were analyzed using both Fourier and wavelet approaches over time intervals of up to 1500 years. A cyclicity with a period of 188–250 years was found to be present in both the Northern Hemisphere temperature and volcanic activity. These cycles were found to be negatively correlated with the correlation coefficients, reaching values of −0.61–−0.68 over the entire time interval. The maximum correlation coefficient is reached when volcanic variations lead to temperature variations by 20 years. The combined probability of the null hypothesis—the proposition that in the Northern Hemisphere, there is no real association between the bicentennial change in volcanic activity and temperature and that the revealed correlations arose purely by chance—was found to be no more than 1.2 × 10⁻² over the entire time interval and less than 10⁻² over the time interval of AD 1270–1980. The effect was weaker for the global temperature and was not detected in the Southern Hemisphere. It is shown that the identified bicentennial temperature variation could have made a certain contribution to the warming in the first half of the 20th century. However, this cycle has probably been in decline for the last 40–50 years and the decline should continue for the next few decades. Possible origins of the revealed bicentennial correlations are discussed, and guidelines for further research are proposed. Full article

This work aims to explore climate change as a decisive element for the transition from feudalism toward capitalism and considers the Marxist transition debate as a framework. In order to avoid the deterministic trap, climate must be considered as a condition framing the historical possibilities in a dialectical relationship with human historical agents. Thus, this paper explores the interactions between medieval English society, focusing on land use and class relation, and the conditions imposed by nature, particularly the change in rainfall and the transformation of ecological conditions around the North Sea Basin, especially on England’s east coast. Through the course of this research, we found out that the climate change that happened in the 14th century is one important condition for the rise of capitalism, as it creates certain pressures on both peasant and manorial economies that exacerbate their contradictions and sets a course for profound societal change. Full article

At the end of the Pleniglacial and the first half of the Late Glacial period, approximately between 18 and 14 ka BP, rivers of the central and southern parts of the East European Plain had channels up to 10 times as large as the present day channels of the same rivers. These ancient channels, called large meandering palaeochannels, are widespread in river floodplains and low terraces. The hydrological regime of these large rivers is of great interest in terms of the palaeoclimatology of the late Marine Isotope Stage 2 (MIS 2). In this study, we aimed at quantitative estimation of maximum flood discharges of rivers in the Dnepr, Don and Volga basins in the late MIS 2. To approach this, we used massive measurements of the morphometric characteristics of large palaeochannels on topographic maps and remote sensing data—palaeochannel width, meander wavelength and their relationships with river flow parameters. The runoff depth of the maximum flood, which corresponds to the maximum depth of daily snow thaw during the snowmelt period, was obtained for unit basins with an area of <1000 km². The mean value for the southern megaslope of the East European Plain was 44.2 mm/day (6 times the modern value), with 46 mm/day for the Volga River (5.5 times), 45 mm/day (6.3 times) for the Don River and 39 mm/day (8 times the modern value) for the Dnepr River basins. In general, the Dnepr basin was drier than the Don and Volga basins, which corresponds well to the modern distribution of humidity. At the same time, the westernmost part of the Dnepr River basin was relatively wet in the past, and the decrease in humidity from the past to the modern situation was greater there than in the eastern and central regions. The obtained results contradict the prevailing ideas, based mainly on climatic modeling and palynological data, that the climate of Europe was cold and dry during MIS 2. The reason is that palaeoclimatic reconstructions were made predominantly for the LGM epoch (23–20 ka BP). On the East European Plain, the interval 18–14 ka BP is rather poorly studied. Our results of paleoclimatological and palaeohydrological reconstructions showed that the Late Pleniglacial and the first half of the Late Glacial period was characterized by a dramatic increase in precipitation and river discharge relative to the present day. Full article

Wigry Lake represents one of the most beautiful and valuable postglacial lakes that is located in the north-eastern part of Poland. It has been an object of scientific interest for over a century, but the most intense period of research started in 1997 and resulted in the production of numerous papers of a multidisciplinary range. The lake is especially well analyzed in terms of its sediments, which were studied using geophysical methods and using traditional lake cartography based on the sampling of sediments and their geochemical characterization. Nearly two decades of research has resulted in the extraction of over 1200 sediment samples, which facilitated the analysis and the description of five main sediment types that can be found at the bottom of Wigry Lake, i.e., carbonate gyttja, lacustrine chalk, clastic sediment, fluvial-lacustrine sediment, and organic gyttja. A very thorough vertical as well as spatial examination of Wigry Lake sediments, together with paleobiological research and isotopic dating, allowed researchers to analyze the history of environmental changes in the lake and its immediate vicinity, including anthropogenic changes. Wigry Lake had been preserved as a pristine lake for a long time, and, despite the significant growth of anthropopressure, which began in the 17th century and intensified in the 20th century, it retained its natural character to a large extent. This was possible mainly due to the favorable morphometry of the lake (large depth and capacity of the reservoir) and different forms of active and passive protection, introduced mainly after the establishment of the Wigry National Park in 1989. Full article

Atmospheric oxygen is produced and consumed by life on Earth, and the ozone layer protects life on Earth from harmful solar UV radiation. The research on oxygen in the Earth system is of interest to many different geoscientific communities, from paleoclimatology to aeronomy. I provide a brief overview of the research activities and their motivations. In situ measurements and remote sensing of atmospheric oxygen are described. The global evolution, distribution, and trends of atmospheric oxygen are discussed. Full article

Northwestern Russia remains the only region in Northern Eurasia where no regional chironomid-based inference model for quantitative palaeoclimatic reconstructions has been developed. Using palaeolimnological methods, we investigated the subfossil chironomid remains in surface sediments from a data set of 98 lakes from nine subregions of the European part of Northern Russia. We identified 143 chironomid taxa in the investigated lakes. Multivariate statistical analyses of chironomid and environmental data demonstrated that the mean July air temperature (T July), distance from the tree line, water depth, pH, and altitude explain the most significant variance in chironomid distribution. T July appeared to be the most important environmental variable. We established a chironomid-based inference model for reconstructing T July from subfossil data. The resulting West Russian two-component WA-PLS model includes 96 lakes (two lakes were excluded as outliers), 143 chironomid taxa, r² = 0.84 (r² boot = 0.60), RMSEP boot = 1.34 °C, and can be recommended for application in palaeoclimatic studies in the East of Northern Eurasia. Full article

Studies of horse evolution arose during the middle of the 19th century, and several hypotheses have been proposed for their taxonomy, paleobiogeography, paleoecology and evolution. The present contribution represents a collaboration of 19 multinational experts with the goal of providing an updated summary of Pliocene and Pleistocene North, Central and South American, Eurasian and African horses. At the present time, we recognize 114 valid species across these continents, plus 4 North African species in need of further investigation. Our biochronology and biogeography sections integrate Equinae taxonomic records with their chronologic and geographic ranges recognizing regional biochronologic frameworks. The paleoecology section provides insights into paleobotany and diet utilizing both the mesowear and light microscopic methods, along with calculation of body masses. We provide a temporal sequence of maps that render paleoclimatic conditions across these continents integrated with Equinae occurrences. These records reveal a succession of extinctions of primitive lineages and the rise and diversification of more modern taxa. Two recent morphological-based cladistic analyses are presented here as competing hypotheses, with reference to molecular-based phylogenies. Our contribution represents a state-of-the art understanding of Plio-Pleistocene Equus evolution, their biochronologic and biogeographic background and paleoecological and paleoclimatic contexts. Full article

Three multi-proxy reconstructions of temperature in the Southern Hemisphere, were analyzed over the last millennium. Fourier and wavelet analysis showed that century-scale (55–120 years) and bicentennial (ca 250 years) variability is present in this series. That means that the climate of the Southern Hemisphere has periodicities similar to the solar cycles of Gleissberg and Suess. However, a comparison of the century-long variations in the Southern Hemisphere temperature records with the corresponding variation in four solar activity proxies showed that only one reconstruction of) displays century-long correlation with solar activity. The solar-like periodicities in the other two records do not show significant correlation with solar cycles. Therefore, based on the results obtained, it is difficult to draw a definite conclusion about the influence of solar activity on the climate of the Southern Hemisphere. To clarify this issue, it is necessary to obtain and analyze new independent temperature reconstructions in the Southern Hemisphere. Full article

Recent decades of warmer climate have brought drying wetlands and falling lake levels to southern Alaska. These recent changes can be placed into a longer-term context of postglacial lake-level fluctuations that include low stands that were as much as 7 m lower than present at eight lakes on the Kenai Lowland. Closed-basin lakes on the Kenai Lowland are typically ringed with old shorelines, usually as wave-cut scarps, cut several meters above modern lake levels; the scarps formed during deglaciation at 25–19 ka in a kettle moraine topography on the western Kenai Lowland. These high-water stands were followed by millennia of low stands, when closed-basin lake levels were drawn down by 5–10 m or more. Peat cores from satellite fens near or adjoining the eight closed-basin lakes show that a regional lake level rise was underway by at least 13.4 ka. At Jigsaw Lake, a detailed study of 23 pairs of overlapping sediment cores, seismic profiling, macrofossil analysis, and 58 AMS radiocarbon dates reveal rapidly rising water levels at 9–8 ka that caused large slabs of peat to slough off and sink to the lake bottom. These slabs preserve an archive of vegetation that had accumulated on a lakeshore apron exposed during the preceding drawdown period. They also preserve evidence of a brief period of lake level rise at 4.7–4.5 ka. We examined plant succession using in situ peat sequences in nine satellite fens around Jigsaw Lake that indicated increased effective moisture between 4.6 and 2.5 ka synchronous with the lake level rise. Mid- to late-Holocene lake high stands in this area are recorded by numerous ice-shoved ramparts (ISRs) along the shores. ISRs at 15 lakes show that individual ramparts typically record several shove events, separated by hundreds or thousands of years. Most ISRs date to within the last 5200 years and it is likely that older ISRs were erased by rising lake levels during the mid- to late Holocene. This study illustrates how data on vegetation changes in hydrologically coupled satellite-fen peat records can be used to constrain the water level histories in larger adjacent lakes. We suggest that this method could be more widely utilized for paleo-lake level reconstruction. Full article

Global climate and oceanic water masses have undergone profound changes during the middle Pleistocene transition; however, due to a lack of foraminiferal fossils, the nonfossiliferous pelagic deposits were less detected in previous reports. In this work, a gravity core from the Kamehameha Basin in the Central Pacific was studied in terms of magnetostratigraphy, clay mineral and geochemical elements. The main results are: (1) nine magnetozones are recognized in the core, which can be correlated to the geomagnetic polarity timescale from chrons C2n to C1n; (2) smectite is the dominant clay mineral, and the others are illite, chlorite and kaolinite; and (3) the sediments are mainly composed of Al₂O₃, Fe₂O₃, MnO, Na₂O and TiO₂. Based on these results, a geochronological framework for the study area was established, and the depositional rates are estimated as 3–7 m/Myr in the Quaternary, showing an increase during the middle Pleistocene transition. By comparing the findings to various paleoenvironmental processes, it is inferred that the increased sedimentation in the Kamehameha Basin may have resulted from the induced weathering processes and the strengthened aeolian inputs from inner Asia. Moreover, regional circulation related to bottom water evolution has experienced a rapid reorganization across the middle Pleistocene transition. All these findings illustrate the potential of deep-sea sediments in the central tropical Pacific in revealing some key features in paleoclimatology and paleoceanography, which are worthy of further investigation in the future. Full article

Nine proxies of temperature over the last 225–300 years in Southern Fennoscandia (55–63° N) were analyzed. Seven reconstructions of the mean growing season temperatures were obtained by dendroclimatological methods. Reconstructions of spring temperatures in Stockholm and winter temperatures in Tallinn were based on historical documentary sources. It was found that significant decadal (10–13 years) and bi-decadal (22–25 years) periodicities were present in many of these series during the entire time interval. Four proxy records correlated significantly with the quasi 22-year solar cycle of Hale. Three time series correlated significantly with the quasi 11-year solar cycle of Schwabe. This can be considered as evidence of a link between decadal and bi-decadal changes in solar activity and climate in Southern Fennoscandia. On the other hand, signs of correlation differed, as well as the time shift between the solar and temperature cycles. It is difficult to explain such an intricate relationship and, thus, the physical mechanism of solar−climatic linkages remains unclear. That is why assumptions about the purely occasional appearance of correlations cannot yet be rejected. Guidelines for further research are suggested. Full article

Seasonal reconstructions of streamflow are valuable because they provide water planners, policy makers, and stakeholders with information on the range and variability of water resources before the observational period. In this study, we used streamflow data from five gages near the Alabama-Florida border and centuries-long tree-ring chronologies to create and analyze seasonal flow reconstructions. Prescreening methods included correlation and temporal stability analysis of predictors to ensure practical and reliable reconstructions. Seasonal correlation analysis revealed that several regional tree-ring chronologies were significantly correlated (p ≤ 0.05) with March–October streamflow, and stepwise linear regression was used to create the reconstructions. Reconstructions spanned 1203–1985, 1652–1983, 1725–1993, 1867–2011, and 1238–1985 for the Choctawhatchee, Conecuh, Escambia, Perdido, and Pascagoula Rivers, respectively, all of which were statistically skillful (R² ≥ 0.50). The reconstructions were statistically validated using the following parameters: R² predicted validation, the sign test, the variance inflation factor (VIF), and the Durbin–Watson (D–W) statistic. The long-term streamflow variability was analyzed for the Choctawhatchee, Conecuh, Escambia, and Perdido Rivers, and the recent (2000s) drought was identified as being the most severe in the instrumental record. The 2000s drought was also identified as being one of the most severe droughts throughout the entire reconstructed paleo-record developed for all five rivers. This information is vital for the consideration of present and future conditions within the system. Full article