Period Of Climatic Instability Research Articles

Reconstitution of the Climate in the Municipality of Guimarães (Northern Portugal): A Regional Approach Based on Historical Information and the Record of Measured Data

Climate change is a global phenomenon that has become a focus of concern for society, mainly due to its impacts on daily lives. Despite being a global issue that affects the entire planet, these effects are not felt in the same way in all regions, so the analysis of processes from a regional or local perspective allows a better adaptation of populations to the new reality, as well as being used as a supporting tool for decision making when implementing mitigation measures. For the present analysis, a region in Northern Portugal was chosen, which is in the Mediterranean region, considered one of the hot spots for climate change. In this region of Entre Douro e Minho, more specifically in the municipality of Guimarães, the climate of the last centuries was reconstructed based on documentary information and recent data collected and modeled for the region under study. The results show a successive alternation of hot and dry periods with colder and wetter ones, where climate instability seems to be the dominant trend over the last thousand years. Currently, with the advent of a new period of climatic instability, which, unlike the periods verified previously, now have an anthropic origin, there is a tendency for a new period to occur, in which conditions will tend to be hotter and drier. Knowing this trend in advance allows informed decisions to be made to mitigate some problems that can be associated with these conditions, such as the increase in the risk of wildfires, the proliferation of invasive species, the decrease in agriculture and forests productivity, or even the occurrence of extreme weather events.

Synchronous cooling and decline in monsoonal rainfall in northeastern Tibet during the fall into the Oligocene icehouse

The fall into the Oligocene icehouse is marked by a steady decline in global temperature with punctuated cooling at the Eocene-Oligocene transition, both of which are well documented in the marine realm. However, the chronology and mechanisms of cooling on land remain unclear. Here, we use clumped isotope thermometry on northeastern Tibetan continental carbonates to reconstruct a detailed Paleogene surface temperature record for the Asian continental interior, and correlate this to an enhanced pollen data set. Our results show two successive dramatic (>9 °C) temperature drops, at 37 Ma and at 33.5 Ma. These large-magnitude decreases in continental temperatures can only be explained by a combination of both regional cooling and shifts of the rainy season to cooler months, which we interpret to reflect a decline of monsoonal intensity. Our results suggest that the response of Asian surface temperatures and monsoonal rainfall to the steady decline of atmospheric CO2 and global temperature through the late Eocene was nonlinear and occurred in two steps separated by a period of climatic instability. Our results support the onset of the Antarctic Circumpolar Current coeval to the Oligocene isotope event 1 (Oi-1) glaciation at 33.5 Ma, reshaping the distribution of surface heat worldwide; however, the origin of the 37 Ma cooling event remains less clear.

Phylogenetic relationships and biogeographic history of the Australian trapdoor spider genus Conothele (Araneae: Mygalomorphae: Halonoproctidae): diversification into arid habitats in an otherwise tropical radiation

In Australia, climate change and continental drift have given rise to a complex biota comprising mesic specialists, arid-adapted lineages, and taxa that have arrived on the continent from Asia. We explore the phylogenetic diversity and biogeographic history of the Australian trapdoor spider genus Conothele Thorell, 1878 that is widespread in Australia’s monsoonal tropics and arid zone. We sequenced three mtDNA and five nuDNA markers from 224 specimens. We reconstructed the phylogenetic relationships among specimens and estimated the number of operational taxonomic units (OTUs) using species delimitation methods. The timing of divergences was estimated and ancestral area reconstructions were conducted. We recovered 61 OTUs, grouped into four major clades; a single clade represented by an arboreal ecomorph, and three fossorial clades. The Australian Conothele had a crown age of ~19 million years, and ancestral area reconstructions showed a complex history with multiple transitions among the monsoonal tropics, central arid zone, south-west and Pilbara bioregion. Conothele arrived on the continent during periods of biotic exchange with Asia. Since then, Conothele has colonised much of the Australian arid and monsoonal zones, during a period of climatic instability. The Pilbara bioregion harbours high lineage diversity, emphasising the role of climate refugia.

Palaeoenvironment and palaeoclimate in the western Liguria region (northwestern Italy) during the Last Glacial. The small mammal sequence of Riparo Mochi (Balzi Rossi, Ventimiglia)

Riparo Mochi is considered a key site for the Middle–Upper Palaeolithic chrono-cultural sequence in the Mediterranean area. Climatic and environmental conditions have been reconstructed after the study of the small mammal assemblage by means of linear regression method and the Habitat Weighting method. The climate proxies for the late Mousterian and Proto-Aurignacian (cultural units I to G) indicate an environment with a relative high percentage of forest component during two cold and one relative warm oscillations. Open environments with low temperatures are registered for the Gravettian (cultural Unit D) allowing a possible relation to the Heinrich 3 Event. The final Gravettian (cultural Unit C) shows a relative warm peak, tentatively related to Greenland Interstadial 2. The late Epigravettian (cultural Unit A) is characterized by a high percentage of forest-related environment suggesting that this horizon formed during the Bølling–Allerød Interstadial. Finally, the Riparo Mochi sequence contributes to reconstruct the processes of faunal changes along the northern Tyrrhenian coast in a period of climatic instability, especially during the end of Marine Isotope Stage 3 when foraging groups adopted different mobility strategies between southern France and the Italian peninsula.

Oxygen isotopic evidence for high‐magnitude, abrupt climatic events during the Lateglacial Interstadial in north‐west Europe: analysis of a lacustrine sequence from the site of Tirinie, Scottish Highlands

ABSTRACTThe Last Glacial to Interglacial Transition (LGIT) is a period of climatic instability. δ18O records are ideal for investigating the LGIT as this proxy responds rapidly to even minor climatic oscillations. Lacustrine carbonates offer the opportunity to investigate spatial diversity in patterns of climatic change during the LGIT but this requires the generation of δ18O records from a range of latitudinal and longitudinal settings. This study presents a coupled pollen and stable isotopic study of lacustrine carbonates spanning the Windermere Interstadial (the British equivalent of Greenland Interstadial 1, the Lateglacial Interstadial) from the site of Tirinie in the Scottish Highlands, a region where δ18O records are absent. The Interstadial is characterized by three δ18O peaks, warm intervals, and two δ18O declines, cold episodes, the timing of which is constrained by the presence of crypto‐tephra. The landscape at Tirinie was highly responsive to these climatic oscillations as the sedimentary and pollen record respond to each isotopic shift. The paper concludes by highlighting that, across the British Isles, lacustrine δ18O records of the Interstadial have a consistent stratigraphy/structure, although the magnitude of the isotopic shifts is regionally variable. Potential causes of this variability are discussed.

Pleistocene Mitochondrial Genomes Suggest a Single Major Dispersal of Non-Africans and a Late Glacial Population Turnover in Europe

How modern humans dispersed into Eurasia and Australasia, including the number of separate expansions and their timings, is highly debated [1, 2]. Two categories of models are proposed for the dispersal of non-Africans: (1) single dispersal, i.e., a single major diffusion of modern humans across Eurasia and Australasia [3-5]; and (2) multiple dispersal, i.e., additional earlier population expansions that may have contributed to the genetic diversity of some present-day humans outside of Africa [6-9]. Many variants of these models focus largely on Asia and Australasia, neglecting human dispersal into Europe, thus explaining only a subset of the entire colonization process outside of Africa [3-5, 8, 9]. The genetic diversity of the first modern humans who spread into Europe during the Late Pleistocene and the impact of subsequent climatic events on their demography are largely unknown. Here we analyze 55 complete human mitochondrial genomes (mtDNAs) of hunter-gatherers spanning ∼35,000 years of European prehistory. We unexpectedly find mtDNA lineage M in individuals prior to the Last Glacial Maximum (LGM). This lineage is absent in contemporary Europeans, although it is found at high frequency in modern Asians, Australasians, and Native Americans. Dating the most recent common ancestor of each of the modern non-African mtDNA clades reveals their single, late, and rapid dispersal less than 55,000 years ago. Demographic modeling not only indicates an LGM genetic bottleneck, but also provides surprising evidence of a major population turnover in Europe around 14,500 years ago during the Late Glacial, a period of climatic instability at the end of the Pleistocene.

Late Quaternary landscape evolution in the Kunlun Mountains and Qaidam Basin, Northern Tibet: A framework for examining the links between glaciation, lake level changes and alluvial fan formation

The Qaidam Basin in Northern Tibet is one of the largest hyper-arid intermontane basins on Earth. Alluvial fans, pediment surfaces, shorelines and a thick succession of sediments within the basin, coupled with moraines and associated landforms in the adjacent high mountain catchments of the Kunlun Mountains, record a complex history of Late Quaternary paleoenvironmental change and landscape evolution. The region provides an ideal natural laboratory to examine the interaction between tectonics and climate within a continent–continent collision zone, and to quantify rates of landscape evolution as controlled by climate and the associated glacial and hydrological changes in hyper-arid and adjacent high-altitude environments. Geomorphic mapping, analysis of landforms and sediments, and terrestrial cosmogenic radionuclide surface exposure and optically stimulated luminescence dating serve to define the timing of formation of Late Quaternary landforms along the southern and northwestern margins of the Qaidam Basin, and in the Burhan Budai Shan of the Kunlun Mountains adjacent to the basin on the south. These dates provide a framework that suggests links between climatic amelioration, deglaciation, lake desiccation and alluvial fan evolution. At least three glacial advances are defined in the Burham Budai Shan of the Kunlun Mountains. On the northern side of this range these occurred in the penultimate glacial cycle or early in the last glacial cycle, during the Last Glacial Maximum (LGM)/Lateglacial and during the Holocene. On the south side of the range, advances occurred during the penultimate glacial cycle, MIS-3, and possibly the LGM, Lateglacial or Holocene. Several distinct phases of alluvial fan sedimentation are likewise defined. Alluvial fans formed on the southern side of the Kunlun Mountains prior to 200 ka. Ice-contact alluvial fans formed during the penultimate glacial and during MIS-3. Extensive incised alluvial fans that form the main valley fills north of the Burham Budai and extend into the Qaidam Basin are dated to ∼30 ka. These ages suggest that there was a period of alluvial fan aggradation and valley filling that persisted until desiccation of the large lakes in the Qaidam Basin post ∼30 ka led to base level lowering and active incision of streams into the valley fills. The continued Lateglacial and Holocene desiccation likely led to further degradation of the valley fills. Ice wedge casts in the Qaidam Basin date to ∼15 ka, indicating significant Lateglacial climatic amelioration, while Holocene loess deposits north of the Burham Bdudai suggest that aridity has increased in the region since the early Holocene. From these observations, we infer that the major landscape changes within high glaciated mountains and their adjacent hyper-arid intermontane basins, such as the Kunlun Mountains and Qaidam Basin, occur rapidly over millennial timescales during periods of climatic instability.

Paleoecological and climatic changes of the Upper Lerma Basin, Central Mexico during the Holocene

The record of Almoloya Lake in the Upper Lerma basin starts with the deposition of the late Pleistocene Upper Toluca Pumice layer. The data from this interval indicate a period of climatic instability that lasted until 8500 cal yr B.P., when temperature conditions stabilized, although moisture fluctuations continued until 8000 cal yr B.P. Between 8500 and 5000 cal yr B.P. a temperate climate is indicated by dominance of Pinus. From 5000 to 3000 cal yr B.P. Quercus forest expanded, suggesting a warm temperate climate: a first indication of drier environmental conditions is an increase in grassland between 4200 and 3500 cal yr B.P. During the Late Holocene (3300 to 500 cal yr B.P.) the increase of Pinus and grassland indicates temperate dry conditions, with a considerable increase of Pinus between 1100 and 950 cal yr B.P. At the end of this period, humidity increased. The main tendency during the Holocene was a change from humid to dry conditions. During the Early Holocene, Almoloya Lake was larger and deeper; the changing humidity regime resulted in a fragmented marshland, with the presence of aquatic and subaquatic vegetation types.

Palaeoclimatic significance of co-occurring wind- and water-induced sedimentary structures in the last-interglacial coastal deposits from Bermuda and the Bahamas

Abstract The late Pleistocene stratigraphic record from the Bahamas and Bermuda archipelagoes includes peculiar V-shaped coastal ridges and wedges of seaward-dipping planar beds showing fenestral porosity up to 40 m above present sea level. Judging from this porosity, these landforms were till now interpreted as resulting from the action of giant waves during a period of climatic instability at the end of the last interglacial period. The occurrence of widespread mm-thick laminae of aeolian origin (subcritically climbing translatent stratification) throughout these deposits does not agree with this hypothesis. It rather suggests that the V-shaped ridges and seaward-dipping beds represent fossil parabolic and climbing aeolian dunes, respectively. The occurrence of fenestrae high above the intertidal zone could be related to both wave splashing and rainfall action. Parabolic dunes are restricted to the NW Bahamas. They were probably formed during a time interval (ca. 500–5000 yr), when regional climatic conditions were dryer than today, and characterized by persistently blowing NE trade winds.

Late Quaternary vegetation change in the Tari Basin, Papua New Guinea

The changes in Late Quaternary vegetation at two sites in the Tari Basin, central highlands of New Guinea, are presented. Haeapugua basin (1650 m altitude) and Tugupugua basin (2300 m altitude) lie within the lower montane forest belt, where the climate is characterised by high relative humidity and low seasonality. Pollen analysis, mineral magnetics, carbonised particle analysis, and dating by radiocarbon and thermoluminescence techniques are employed to reconstruct the vegetation and sediment history. The sequences include fragmentary interglacial/interstadial records from before 50,000 yr B.P. and a continuous record from at least 28,000 yr B.P. to the present. The study shows that, prior to 21,000 yr B.P., vegetation in the basin was dominated by fluctuating proportions of tree taxa indicative of a forested environment. The montane forest taxon, Nothofagus, is important throughout the record, although other tree taxa, including Castanopsis, Myrtaceae, Dacrydium and Pandanus, attain dominance at different times under the influence of a range of environmental factors. The creation of an open environment around 21,000 yr B.P. is considered to be a consequence of the arrival of humans in the region. The late glacial transition, between 14,500 and 8500 yr B.P., is a period of climatic instability with landscape and vegetation adjustments proceeding at different rates across the highlands. Vegetational adjustments match modern ranges by about 8500 yr B.P., when swamp forest developed across the sites. At the lower altitude site there are indications of anthropogenic forest disturbance, associated with swamp forest clearance, commencing around 1700 yr B.P. and intensifying through to the present. Forest clearance is recorded only after 700 yr B.P. at the higher site, where agriculture was probably only sustainable after the introduction of sweet potato (Ipomoea batatas).

The Ecology of Seasonal Stress and the Origins of Agriculture in the Near East

The time, place, and reasons for the first domestication of cereals and legumes in the Near East can now be securely identified using combined evidence from paleoenvironmental studies, models of ecosystem dynamics, and regional archeology. The heartland of domestication was the Jordan Valley and surrounding region in the Southern Levant. Approximately 10,000 years ago, people began planting crops where the wild ancestral species had proliferated over two millenia. Impetus for domestication came from the synergistic effects of climatic change, anthropogenic environmental change, technological change, and social innovation. At the end of the Pleistocene, after a long period of climatic instability, a mediterranean climate more strongly seasonal than any today emerged with hyper‐arid summers that selected for annual species of cereals and legumes. This occurred long after people had invented tools suitable for grinding hard seeds, but the new, lengthy dry season and consequent need to use stored foods encouraged sedentism among human groups who subsequently depleted their immediate environments of wild resources. These preconditions facilitated the development of agriculture. The scenario developed here is specific to the Near East, for such case studies of specific factors in independent regions of domestication are essential before we attempt to explain cases all over the world with reference to global causes.

Effect of the advent and diversification of vascular land plants on mineral weathering through geologic time

The origin of vascular land plants in the Silurian and their subsequent diversification have had a major effect on mineral weathering through geologic tune. The presence of vascular plants reduces the stability of soil minerals through a net export of ions from soil waters and through the release of complexing organic acids by root mycorrhizae. Additional factors that dictate the nature of plant-induced mineral weathering are (1) the differences in nutrient dynamics between evergreen and deciduous species; (2) the role of specific nutrient sinks (biomass storage and secondary soil mineralization) and outputs (runoff, etc.) in plant ecosystems; and (3) the effect of long- and short-term ecosystem disturbances. First-order increases in overall mineral weathering probably took place in the middle Paleozoic and early Tertiary, following the initial colonization and diversification of land plants and the radiation of deciduous angiospenns. Second-order fluctuations would typify time intervals where paleoecosystem disturbances were maximized, such as periods of climatic instability.

Changes in the structure of the baboon hybrid zone in the Awash National Park, Ethiopia

AbstractThe zone of hybridization between anubis and hamadryas baboons in the Awash National Park, Ethiopia, evidently changed significantly in the early 1970s. When first studied, by Nagel in 1968, the distribution of adult male phenotypes suggested that the hybrid zone was a narrow, static, genetic sink. In contrast, studies during the 1970s found evidence for a broad hybrid zone intergrading with parental populations and probably expanding. A more detailed investigation of data collected in 1973, presented here, shows that between 1968 and 1973 the distribution of phenotypes changed to a more clinal pattern because of the maturation and successful integration of an extensive cohort of hybrid males. We present a provisional model that accounts for the changes in terms of climatic oscillations, with the hybrid zone tending to expand during periods of climatic instability.