Periods Of Climate Variability Research Articles

Palaeoenvironmental Framing of the O Areal Roman Saltworks and Related Anthropogenic Activities in North-western Iberia

ABSTRACT The NW Iberian city of Vigo contains buried structures of a Roman salinae that follow the ancient coastline. To investigate its environmental legacy, we studied two pedo-sedimentary profiles at the O Areal saltworks to reconstruct human activities during and after the salinae use, as well as framing them within the last two millennia of climate variability. The bottom layer consists of organic-rich sands, with marine palynomorphs, confined within the saltworks’ structures that operated during the Early Roman Empire, when the demand in fish-salted products increased and the salting industry fluorished on the Atlantic coast of Iberia. During the Late Roman Empire, salt production at the O Areal may have ended, coeval with the development of a marsh with hydro-hygrophyte vegetation and the salting industry demise. The Roman environment also experienced intense agropastoralism that triggered water eutrophication. After Roman times, a dune phase sealed the archaeologicl structures. The overall trend points to a shift from a marine to a terrestrial setting coeval to known periods of climate variability. Therefore, humans and climate impacted the coast during the last two millennia, including the very intense Roman-period saltworks, agriculture and livestock. Roman times climate would have also influenced the saltworks’ establishment and abandonment.

Paleoenvironmental reconstructions along the southern margin of Eocene Lake Uinta during a period of climatic variability

The stratigraphy preserved in the lacustrine Eocene Green River Formation suggests a variety of depositional environments that were subject to pulses of sediment and lake level fluctuations in the Uinta Basin. This paper defines 13 facies within six facies associations observed in outcrop and core from the middle to upper Green River Formation in Gate Canyon, south-central Uinta Basin, and Willow Creek/Indian Canyon, western Uinta Basin, along the margin of the ancient lake system. The facies associations are defined by dominant lithology, relative siliciclastic sediment supply, relative slope, and lake zonation, and encompass a suite of facies revealing distinct environments across a relatively small region (~35 km apart). In the lower interval, a shift from a high energy, steeper ramp setting in the east, to a lower energy, shallower ramp setting to the west suggests a transition off the main depositional axis. Correlatable siliciclastic and carbonate dominated packages reflect the impact of early Eocene hyperthermal events that followed the Paleocene-Eocene Thermal Maxi- mum, and the diverse facies present at the two study areas suggest variable responses to these climatic events. In the overlying stratigraphy, the facies are consistent in both regions and consist of organic rich and poor carbonate mudstones and siltstones. The interval thickens slightly from east to west, and the overlying Horse Bench Sandstone transitions from a wave-dominated shoreface sequence to a river-dominated deltaic sequence, indicating an overall shift in the lake depocenter towards the west. This study offers a unique glimpse at the paleoenvironmental changes along the margin of a continental interior lake system during a time of climatic variability. It also highlights the need to use multiple depositional models to accurately characterize marginal deposits in different regions of large internally-drained lake systems which, unlike typical marine depositional models, are more sensitive to basin geometry, size, and sediment fairways.

An ecological niche shift for Neanderthal populations in Western Europe 70,000\xa0years ago

Middle Paleolithic Neanderthal populations occupied Eurasia for at least 250,000 years prior to the arrival of anatomically modern humans. While a considerable body of archaeological research has focused on Neanderthal material culture and subsistence strategies, little attention has been paid to the relationship between regionally specific cultural trajectories and their associated existing fundamental ecological niches, nor to how the latter varied across periods of climatic variability. We examine the Middle Paleolithic archaeological record of a naturally constrained region of Western Europe between 82,000 and 60,000 years ago using ecological niche modeling methods. Evaluations of ecological niche estimations, in both geographic and environmental dimensions, indicate that 70,000 years ago the range of suitable habitats exploited by these Neanderthal populations contracted and shifted. These ecological niche dynamics are the result of groups continuing to occupy habitual territories that were characterized by new environmental conditions during Marine Isotope Stage 4. The development of original cultural adaptations permitted this territorial stability.

Impact of Red Sea on Climate of A Coastal and An Inland City in the Kingdom of Saudi Arabia

We analyzed the impact of the Red Sea on the climatic features of Tabukand Yanbuin the Kingdom of Saudi Arabia and used various comfort indices to determine the most suitable climatic conditions for these cities. We found that there is a clear difference between Tabuk and Yanbu with respect to the length of their comfort periods.Tabuk experiences cold periods throughout the year, with the temperature reaching the freezing point. Further, there are periods of climatic variability in Yanbu whereinthe temperaturefluctuates between hot and very cold. Furthermore, there are several periods of thermal discomfort in Tabuk and Yanbu, especially during the winter and summer.

Contemporaneity of Australopithecus, Paranthropus, and early Homo erectus in South Africa.

Understanding the extinction of Australopithecus and origins of Paranthropus and Homo in South Africa has been hampered by the perceived complex geological context of hominin fossils, poor chronological resolution, and a lack of well-preserved early Homo specimens. We describe, date, and contextualize the discovery of two hominin crania from Drimolen Main Quarry in South Africa. At ~2.04 million to 1.95 million years old, DNH 152 represents the earliest definitive occurrence of Paranthropus robustus, and DNH 134 represents the earliest occurrence of a cranium with clear affinities to Homo erectus These crania also show that Homo, Paranthropus, and Australopithecus were contemporaneous at ~2 million years ago. This high taxonomic diversity is also reflected in non-hominin species and provides evidence of endemic evolution and dispersal during a period of climatic variability.

Variability of the circulation processes in the Lower Volga Region on the background of global climate trends

In this article we consider variability of the character of atmospheric circulation during different periods of climatic variability in the Lower Volga region as part of the Atlantic-Eurasian hemisphere sector. Variability of the circulation regime is analyzed with the involvement of the regional typification of synoptic processes by V. L. Arkhangelsky - E. A. Polyanskaya. It is shown that during the phase of the second wave of global warming compared to the period of stabilization in the South-East of the Russian Plain we actually see the decrease of the polarfront cyclones occurrence frequency, the increase of cyclones frequency on the Arctic front and the intrusion of Arctic anticyclones. The revealed character of synoptic processes changes is reflected in the reconstructions of geopotential fields at the middle level of the troposphere. The climatically meaningful conclusion was also made about the stabilizing role of the atmospheric circulation and the formation of the specific features of the climatic variability that does not have analogues in the period of regular meteorological observations.

Incorporating historical and ecological genetic data for leopard grouper (Mycteroperca rosacea) into marine reserve design in the Gulf of California

Effective design of marine reserves for use in fisheries management and conservation requires a clear understanding of patterns of larval transport and sink-source dynamics between populations, as well as a clear understanding of population demography. Mitochondrial and nuclear markers were analyzed to investigate potential mechanisms impacting connectivity among and the demographic history of subpopulations of a commercially important species in the Gulf of California, the leopard grouper (Mycteroperca rosacea). Demographic history and connectivity analyses included a coalescent analysis, estimating neutrality indices, estimating global and pairwise F’ST, ΦST, or G’’ST, and a priori methodologies to identify genetically distinct units and barriers to dispersal. Average, long-term connectivity between geographic regions in the Gulf was also estimated. Divergence of mitochondrial lineages of leopard grouper dated to the late Pleistocene, with deep-water islands serving as demographically stable populations that may have acted as sources for new populations during periods of climate variability. Additionally, we observed genetically distinct units of leopard grouper in the Gulf, particularly between peninsular and mainland sites, as well as asymmetrical migration between the northern and central Gulf. Observed patterns of genetic differentiation are likely attributed to complex asymmetrical oceanographic currents and local larval retention. Based on our genetic findings and current fishing pressure in certain regions, we recommend implementing small, upstream no-take zones in the areas east of Isla Angel de la Guarda, around Isla San Lorenzo and Isla San Esteban, and north of Isla Tiburon, that would enhance connectivity among subpopulations, preserve sites with high genetic diversity, and benefit fisheries downstream of these sites.

Long‐term data suggest jarrah‐forest establishment at restored mine sites is resistant to climate variability

Summary Global climate change is projected to increase the frequency and intensity of drought in dry regions due to warming temperatures and declining rainfall. Severe drought can trigger tree mortality and drive persistent vegetation change. To date, most empirical studies have focused on drought‐induced mortality of adult trees, but this needs to be matched by similar efforts to understand drought impacts on seedling establishment if we are to understand the resilience of the world's forests to projected climate change. The Eucalyptus marginata (jarrah)‐forest ecoregion of south‐western Australia has experienced a 17% reduction in mean annual rainfall from 1975 to 2011 compared with mean rainfall from 1900 to 1974. Drought‐induced mortality of adult trees has been documented for jarrah forest, but there is limited understanding of its capacity to recover, making it difficult to predict the likelihood of persistent effects. Long‐term records of jarrah‐forest restoration following bauxite mining are available for the 19‐year period between 1992 and 2010. Records include annual data on seedling establishment in restored mine sites for 587 species in 1938 plots during a period of climatic variability. We built a structural equation model to discriminate the relative effects of climate, restoration practice, and their interactive effects on three response variables including species richness of the restored plant assemblages. Climate variability had a significant negative effect on richness, but the effect size was relatively small, being less than half that of varying restoration practice. We suggest this is due, in part, to the reliability of rainfall (i.e. no change in the coefficient of variation, seasonality or evenness, between recent and historical climates) despite a threefold difference in the absolute amount of wet‐season rainfall. Importantly, there was no evidence that restoration practices were compromised by interacting effects of increased climate variability. Synthesis. Jarrah‐forest establishment in a restoration context appears resistant to recent changes in climate. Our research highlights the importance of deriving multiple metrics of climate change to understand community responses. In particular, rainfall reliability should be a focus of future research to determine its broader significance to seedling establishment in forests subject to a drying climate.

Stability of a Neotropical microrefugium during climatic instability

AbstractAimThe primary objectives of this study were (1) to assess, in the light of palaeoecological reconstruction, the climate stability hypothesis used by evolutionary biologists to explain high diversity in historically stable areas, and (2) to identify the response mechanisms of a tropical rain forest microrefugium to climatic variability.LocationNorth‐eastern Brazil, Serra de Maranguape.MethodsVegetation and climatic changes were reconstructed using a pollen record in a sediment core from a forest hollow, and the chronology was based on accelerator mass spectrometry radiocarbon analyses.ResultsPast vegetation dynamics consisted of three main forest types, shown by major compositional changes in rain forest assemblages between 5000 and 1000 cal. yr bp. Dense ombrophilous forest was abruptly replaced by heliophilous early successional tree taxa at 4275 cal. yr bp. These early successional tree taxa were established over a period of c. 100 years, and their dominance lasted for c. 750 years and was associated with dry conditions until 3525 cal. yr bp. Subsequently, the expansion of secondary successional tree taxa over a period of c. 550 years enabled the recovery of ombrophilous forest.Main conclusionsThe vegetation changes in the Serra de Maranguape provide evidence for the high sensitivity of this rain forest microrefugium to climatic variability on a multidecadal to millennial time‐scale during the mid‐ to late Holocene. Despite the substantial compositional and climatic changes, this microrefugium apparently was continuously forested and responded to climatic instability by recruiting key species to its highly diverse stock. This evidence helps to address the joint concerns of evolutionary biologists and palaeoecologists regarding how forests can persist during periods of climatic variability by showing that some tropical regions can remain continuously forested despite reorganization during abrupt and short‐term climatic changes.

3800 Years of Quantitative Precipitation Reconstruction from the Northwest Yucatan Peninsula

Precipitation over the last 3800 years has been reconstructed using modern pollen calibration and precipitation data. A transfer function was then performed via the linear method of partial least squares. By calculating precipitation anomalies, it is estimated that precipitation deficits were greater than surpluses, reaching 21% and <9%, respectively. The period from 50 BC to 800 AD was the driest of the record. The drought related to the abandonment of the Maya Preclassic period featured a 21% reduction in precipitation, while the drought of the Maya collapse (800 to 860 AD) featured a reduction of 18%. The Medieval Climatic Anomaly was a period of positive phases (3.8–7.6%). The Little Ice Age was a period of climatic variability, with reductions in precipitation but without deficits.

Temporal buffering of climate-driven sediment flux cycles by transient catchment response

The marine sedimentary record can exhibit a systematic cyclicity that is consistent with climate variability driven by Milankovitch-scale forcing. Milankovitch-band cyclicity is widely interpreted in the hemipelagic and pelagic sediments of the marine realm, and in terrestrial paleoenvironments has been observed in lacustrine sediments, soils and river floodplain successions. It remains unclear, however, if and how mountain catchments, as a primary sediment source, respond to these high frequency (<106yr) climatic cycles, and whether particulate sediment flux signals can be expected to be recorded in the clastic sedimentary record of adjacent basin-fills. Recent field and theoretical studies suggest that mountain catchments respond transiently to high frequency forcing, and so sediment discharge from the catchment is a non-linear function of forcing variables. Using a catchment–basin model, we demonstrate that climate-driven cyclicity in particulate sediment discharge is strongly damped when the period of climate variability is shorter than the response timescale of the eroding landscape. Given that the response timescale of landscapes is of the order of 106yr, and that Milankovitch-driven climate cyclicity is of the order of 104–105yr, it is likely that climate-driven perturbation of upland catchments at these periods will be strongly damped by transient landscape behaviour. Our results therefore suggest that stratigraphy built by particulate fluxes from upland catchments, and long-term trends in the sediment delivery to the ocean, may be relatively insensitive to short-term climate variability.

Perception, history, and science: coherence or disparity in the timing of the Little Ice Age maximum in southeast Iceland?

In Iceland, studies that integrate local perceptions about the landscape with scientific evidence of change have been few. This article presents a case study from southeast Iceland that has two main objectives. Firstly, ethnographic data is used to explore the human dimension of the Little Ice Age through perceptions of landscape and climatic change and to describe the impacts that these changes had on life and livelihood. Secondly, the paper critically assesses the coherence of the scientific record regarding the Little Ice Age glacial maximum with evidence gained from the ethnographic survey and the local historical record. Although climatic deterioration from the seventeenth through nineteenth centuries ultimately affected farming viability, it was the interplay of climate with concomitant cultural and socio-economic factors that ensured effective strategies were emplaced to preserve life and livelihood in southeast Iceland. Furthermore, despite different trajectories of perception emanating from either the scientific or the local points of view, data from all sources are strongly coherent and point to a Little Ice Age maximum during the late eighteenth to early nineteenth centuries. This study also illustrates that sensitive landscapes can ‘store memories’ through the cumulative accumulation of disturbances during periods of climatic variability, eventually reaching a critical threshold and inducing landscape instability, such as occurred during the nineteenth century.

Meeting the challenge of climate variability in a major water supply system

A continuing period of climate variability affecting the south west of Western Australia has seen a 12% decrease in rainfall reduce streamflow to Perth's water supply dams by 50% during the last 27 years. A change in organisational arrangements and an evaluation of risk exposure were key triggers for the implementation of plans to restore the public drinking water supply reliability. The Water Corporation mobilised the support of customers and regulators during the recovery period. Poor and extremely low inflow events during the last five years required additional planning, regulator support and implementation strategies to minimise the impact on the Perth Community.

Climatic Variability and the European Mortality Wave of the Early 1740s

impact of climatic variability on level of mortality among preindustrial populations is examined using example of European mortality wave of early 1740s. The evidence shows that mortality peak of 1740 to 1742 coincided with a period of climatic variability. level of mortality climbed in all thirteen countries of Western Europe during 1740. steepest increase in death rates occurred in Finland location most exposed to harsh continental climatic regime. results also suggest that the differential success in neutralizing potential economic and social hardships engendered by climatic stress influenced demographic outcome more decisively than relative price of food. (EXCERPT)