Quaternary Climate Change Research Articles

Long‐term climate forcings to assess vulnerability in North Africa dry argan woodlands

AbstractQuestionsNorth African dry woodlands constitute mediterranean climatic ecotone ecosystems of vital importance for human livelihoods and local biodiversity. To improve the basis for managing these key ecosystems, we selected a Tertiary relict woodland (Argania spinosa) in order to clarify the sensitivity to long‐term climate change (the present, the past glacial‐interglacial cycle and under future scenarios). We also discuss the impact of long‐term human land use for the distribution of dry woodlands in North Africa.LocationNorth Africa.MethodsTo assess whether the argan woodland is in equilibrium with current climate, we used species distribution modelling (SDM) to estimate its potential range. Then, SDM was used to estimate its potential distribution during the Last Glacial Maximum (LGM; 21,000 BP) and the Middle Holocene (Mid‐Holocene; 6,000 BP). Model predictions for past scenarios were compared with Quaternary palaeorecords to evaluate their accuracy. Finally, we forecasted changes in the potential range to year 2080 to assess its likely future range dynamics.ResultsAt the LGM, suitable areas occurred at more southern latitudes, where the Sahara Desert currently lies, while suitable areas in the Mid‐Holocene shifted northwards, occupying areas similar to those of today. The estimated past distributions are consistent with palaeorecords, providing evidence for the important role of Quaternary climate changes in driving dry woodland range dynamics. The current range‐filling constitutes 44% of the potential distribution, probably primarily reflecting anthropic land‐use effects. Future climate change is forecast not to cause latitudinal/altitudinal range shifts, but rather an overall range contraction.ConclusionsThe models reflect the high sensitivity of the dry woodland ecosystem to past climate changes, in agreement with palaeorecords. The estimated climatic sensitivity also predicts severe range contraction during future climate change. Consequently, management strategies for dry woodlands should be developed to facilitate their in situ survival, particularly by reducing the currently intensive human pressure.

Unveiling the diversification dynamics of Australasian predaceous diving beetles in the Cenozoic.

During the Cenozoic, Australia experienced major climatic shifts that have had dramatic ecological consequences for the modern biota. Mesic tropical ecosystems were progressively restricted to the coasts and replaced by arid-adapted floral and faunal communities. Whilst the role of aridification has been investigated in a wide range of terrestrial lineages, the response of freshwater clades remains poorly investigated. To gain insights into the diversification processes underlying a freshwater radiation, we studied the evolutionary history of the Australasian predaceous diving beetles of the tribe Hydroporini (147 described species). We used an integrative approach including the latest methods in phylogenetics, divergence time estimation, ancestral character state reconstruction, and likelihood-based methods of diversification rate estimation. Phylogenies and dating analyses were reconstructed with molecular data from seven genes (mitochondrial and nuclear) for 117 species (plus 12 outgroups). Robust and well-resolved phylogenies indicate a late Oligocene origin of Australasian Hydroporini. Biogeographic analyses suggest an origin in the East Coast region of Australia, and a dynamic biogeographic scenario implying dispersal events. The group successfully colonized the tropical coastal regions carved by a rampant desertification, and also colonized groundwater ecosystems in Central Australia. Diversification rate analyses suggest that the ongoing aridification of Australia initiated in the Miocene contributed to a major wave of extinctions since the late Pliocene probably attributable to an increasing aridity, range contractions and seasonally disruptions resulting from Quaternary climatic changes. When comparing subterranean and epigean genera, our results show that contrasting mechanisms drove their diversification and therefore current diversity pattern. The Australasian Hydroporini radiation reflects a combination of processes that promoted both diversification, resulting from new ecological opportunities driven by initial aridification, and a subsequent loss of mesic adapted diversity due to increasing aridity.

A similar phylogeographical structure among sympatric North American birches (Betula) is better explained by introgression than by shared biogeographical history

AbstractAimA comparative analysis of the chloroplast (cp) DNA structure of eastern North American birches (Betula) was undertaken to infer the impacts of Quaternary climate change on the phylogeographical structure of these species.LocationEastern North America.MethodsGenetic variation in chloroplast microsatellites (cpSSRs) and the psbA–trnH intergenic spacer in Betula papyrifera, Betula alleghaniensis and Betula lenta was analysed in samples from 65, 80 and 12 populations, respectively. Co‐occurring Betula uber, Betula populifolia and Betula cordifolia were also sampled to examine haplotype relationships and account for potential introgression. Haplotype networks, Bayesian analysis and comparisons of RST and GST values were used to evaluate the phylogeographical structure. Genetic diversity within and among species was compared using rarefaction analysis.ResultsThe two most widespread species, B. papyrifera and B. alleghaniensis, showed high levels of haplotype diversity, while the Appalachian endemic B. lenta possessed a single haplotype. Bayesian analysis revealed three main phylogeographical groups for B. papyrifera and four groups for B. alleghaniensis, and these two species showed extensive regional haplotype sharing and a high introgression ratio.Main conclusionsWe postulate that at least three separate refugia contributed to the recolonization of B. papyrifera and B. alleghaniensis within eastern North America, while B. lenta appears to have recolonized from a single refugium. A high haplotype diversity of B. papyrifera and B. alleghaniensis in the Great Lakes region may reflect biogeographical contact between eastern and western lineages, with the potential influence of periglacial refugia. Similar phylogeographical patterns in the distantly related B. papyrifera and B. alleghaniensis represent a geographical turnover of the same locally shared haplotypes, pointing to introgression rather than shared biogeographical history as the mechanism. Although similar phylogeographical patterns are often interpreted as evidence for common biogeographical histories, our study demonstrates that such patterns can also arise through introgression.

Late Quaternary climate change, relict populations and present‐day refugia in the northern Atacama Desert: a case study from Quebrada La Higuera (18° S)

AbstractAimIn deserts, past climate change (and particularly past rainfall variability) plays a large role in explaining current plant species distributions. We ask which species were most and which were least affected by changes in rainfall during the late Quaternary in northernmost Chile.LocationQuebrada La Higuera (QLH; 18° S), a shallow canyon that cuts east–west through the western Andean precordillera of northern Chile, connecting the Altiplano with the hyperarid Atacama Desert.MethodsWe collected and dated 22 rodent middens from elevations of 3100–3500 m in QLH. These were analysed for identifiable plant macrofossils and pollen. We also measured chinchilla rat (Abrocoma cinerea) faecal pellets in the youngest middens to explore how they relate to past ecological and climatic change.ResultsThe three oldest middens dated to more than 37 ka (thousand calibrated 14C years), four middens dated to 14.4–11.6 ka, and fifteen middens spanned the last 650 years. During all the intervals examined, extralocal species (those found today at higher elevations and indicative of positive rainfall anomalies) were present at our midden sites. In the youngest interval, Parastrephia pollen (indicating increased rainfall) increased abruptly at ad 1760 and remained high until the mid‐1800s. This increase was also seen in our faecal pellet record.Main conclusionsExtralocal species were prevalent in late Pleistocene middens at lower elevations when the climate was wetter. When combined with other regional midden records, we postulate that many species found today in the Altiplano were displaced to lower elevations during the late Pleistocene. The recent large‐scale mortality documented among arboreal cactus populations along the present upper margins of the Atacama suggests that these are relict populations that are likely to have flourished during a wetter period in the early 1800s.

Long-term cooling/drying record of North China since the middle Pleistocene from geochemical evidence of a 150 m deep drill core, Beijing plain, China

The Quaternary strata in North China primarily consist of fluvial sediments, which react strongly to East Asian Monsoon circulation. However, the records of the Quaternary climate change history in terms of these fluvial sedimentations were limited which impeded understanding the East Asian Monsoon evolution in North China. Thus, a 150 m deep drill core was collected from Changping in the Beijing plain to reconstruct the Quaternary palaeoenvironmental changes. The core was chronologically well constrained using palaeomagnetic and thermoluminescence dating. The magnetostratigraphic result indicated that the Brunhes/Matuyama boundary is at 134.2 m (0.78 Ma) and the age at the bottom of the core is 1.07 Ma. The thermoluminescence (TL) dating of the upper sand at ∼2 m was 10.4 ka. The chemical weathering history since the middle Pleistocene in Beijing plain was reconstructed by using geochemical proxies including selected major element pairs, chemical index of alteration and Al2O3–CaO*–(Na2O + K2O) diagrams. The CIA value of the Changping core ranged from 50.3 to 69.4 (average 59.2), which indicated that the sediment has experienced incipient to intermediate chemical weathering during the middle Pleistocene. The result of A–CN–K figure shows a high plagioclase to K-feldspar ratio in the source, which would be indicative of a granodiorite (Gd) source from Jundu Mountains north of the Beijing plain. All the geochemical results revealed a long-term gradual decrease of weathering since the middle Pleistocene, which implied a long-term increasing aridification/cooling in the Beijing plain.

Control of Quaternary sea‐level changes on gas seeps

AbstractGas seeping to the seafloor through structures such as pockmarks may contribute significantly to the enrichment of atmospheric greenhouse gases and global warming. Gas seeps in the Gulf of Lions, Western Mediterranean, are cyclical, and pockmark “life” is governed both by sediment accumulation on the continental margin and Quaternary climate changes. Three‐dimensional seismic data, correlated to multi‐proxy analysis of a deep borehole, have shown that these pockmarks are associated with oblique chimneys. The prograding chimney geometry demonstrates the syn‐sedimentary and long‐lasting functioning of the gas seeps. Gas chimneys have reworked chronologically constrained stratigraphic units and have functioned episodically, with maximum activity around sea level lowstands. Therefore, we argue that one of the main driving mechanisms responsible for their formation is the variation in hydrostatic pressure driven by relative sea level changes.

Phylogeography of Heliconius cydno and its closest relatives: disentangling their origin and diversification.

The origins of the extraordinary diversity within the Neotropics have long fascinated biologists and naturalists. Yet, the underlying factors that have given rise to this diversity remain controversial. To test the relative importance of Quaternary climatic change and Neogene tectonic and paleogeographic reorganizations in the generation of biodiversity, we examine intraspecific variation across the Heliconius cydno radiation and compare this variation to that within the closely related Heliconius melpomene and Heliconius timareta radiations. Our data, which consist of both mtDNA and genome-scan data from nearly 2250 amplified fragment length polymorphism (AFLP) loci, reveal a complex history of differentiation and admixture at different geographic scales. Both mtDNA and AFLP phylogenies suggest that H.timareta and H.cydno are probably geographic extremes of the same radiation that probably diverged from H.melpomene prior to the Pliocene-Pleistocene boundary, consistent with hypotheses of diversification that rely on geological events in the Pliocene. The mtDNA suggests that this radiation originated in Central America or the northwestern region of South America, with a subsequent colonization of the eastern and western slopes of the Andes. Our genome-scan data indicate significant admixture among sympatric H.cydno/H.timareta and H.melpomene populations across the extensive geographic ranges of the two radiations. Within H.cydno, both mtDNA and AFLP data indicate significant population structure at local scales, with strong genetic differences even among adjacent H.cydno colour pattern races. These genetic patterns highlight the importance of past geoclimatic events, intraspecific gene flow, and local population differentiation in the origin and establishment of new adaptive forms.

Effect of Quaternary climatic change on modern hydrological systems in the southern Chinese Loess Plateau

A systematic study was conducted to investigate the permeability, porosity, grain size, water content, mass percentage of carbonate, and magnetic susceptibility of representative Middle Pleistocene loess-palaeosol layers (from L1 to S5) on the Chinese Loess Plateau. The average infiltration rate of the loess (0.93 mm/min) was higher than the palaeosol (0.62 mm/min), and the porosity of loess was higher than that of palaeosol. The loess layers have greater water-bearing capacity and, therefore, they are more likely to form aquifers while the palaeosol layers are more prone to form aquitards. The greater permeability and the larger water-bearing space of the loess layers are largely the result of lower intensity pedogenesis due to the colder/drier climatic conditions at the time these sediments were deposited. Conversely, the weaker permeability and lesser water-bearing capacity of the palaeosol layers can be explained by the greater pedogenesis during the warmer/wetter climatic conditions. The studies demonstrate a compelling relationship between Pleistocene climate and modern hydrological systems in the southern Chinese Loess Plateau.

Tectono-geomorphic study of the Karewa Basin of Kashmir Valley

The Karewa Basin nestled between the Pir Panjal Range and the Great Himalayan Range, in Northwest India, has been studied to understand its tectono-geomorphic evolution on the basis of geomorphic indices and morphotectonic parameters supported by the field evidences. Satellite data, topographic maps and digital elevation model (DEM) were used to extract various parameters at various spatial scales. Four watersheds, representative of the entire Karewa Basin, were chosen for detailed studies on the basis of the researchable evidence of the complete sequence of the stratigraphic record and the preservation of geomorphic landscapes. The integrated analysis of the geomorphic and morphometric data provides evidence of the relative variations in the tectonic activity among the watersheds. Geomorphic indices suggest a relatively high degree of tectonic activity along the Pir Panjal side of the Karewa Basin. This variation in the relative degree of tectonic activity is consistent with the field evidence, fault/lineament locations and the landscape geometry of the Karewa Basin. Based on the results from this study, it is suggested that Late Quaternary climate changes, tectonic uplift and erosion of the Pir Panjal Range and changing geometry of the Karewa Lake have played a key role in the evolution of the geomorphic landscape of the Kashmir Valley.

Multiproxy record of late Quaternary climate change and Middle Stone Age human occupation at Wonderkrater, South Africa

Here we provide a multiproxy record of climate change and human occupation at Wonderkrater, a spring and peat mound site situated in the interior of southern Africa. Recently extracted sediment cores yielded a number of Middle Stone Age (MSA) artefacts, prompting exploratory excavation of the sediments to understand better the geomorphology of the site, age of the sediments, cultural lithic sequence, vegetation and faunal remains, and to try to establish whether human use of the site was to some extent climatically driven. Excavations yielded late Pleistocene mammal fauna and flora, and three small MSA lithic assemblages with age estimates of 30 ka, >45 ka and 138.01 ± 7.7 ka. The upper layers comprise peat that preserves macrobotanical and faunal remains, implying local fen conditions in Acacia savanna woodland at 12 ka. Below the upper peat layers, a 1 m-thick layer of white sand yielded two MSA lithic assemblages in association with faunal remains dated to between 30.8 ± 0.7 ka and >45 ka. Clay underlying the sand has an OSL age of 63.1 ± 5.8 ka, and sandy peat below it has an Infrared Stimulated Luminescence (IRSL) age of 70 ± 10 ka. Faunal remains in the lower sand levels, and dental stable carbon isotope analysis of herbivores, indicate a substantial grassland component in the landscape during late MIS 3 (>45 ka). Charcoal, phytolith and pollen data show a change from moderately warm and dry grassy savanna woodland in the lower sand levels, to cooler and wetter grassland with woody shrubs in the uppermost levels by 30 ka. The conditions that resulted in the deposition of the sand also attracted people to the site, but whether it served as an oasis in an arid landscape, or was occupied during wet phases, is unclear. The composition of the lithic assemblages, which include many tools suitable for cutting, suggest that the peat mound may have been used as a place to harvest reeds, process plant materials and butcher animals that were either deliberately or accidentally trapped in mud or peat.

Diploid hybrid origin of Ostryopsis intermedia (Betulaceae) in the Qinghai-Tibet Plateau triggered by Quaternary climate change.

Despite the well-known effects that Quaternary climate oscillations had on shaping intraspecific diversity, their role in driving homoploid hybrid speciation is less clear. Here, we examine their importance in the putative homoploid hybrid origin and evolution of Ostryopsis intermedia, a diploid species occurring in the Qinghai-Tibet Plateau (QTP), a biodiversity hotspot. We investigated interspecific relationships between this species and its only other congeners, O.davidiana and O.nobilis, based on four sets of nuclear and chloroplast population genetic data and tested alternative speciation hypotheses. All nuclear data distinguished the three species clearly and supported a close relationship between O.intermedia and the disjunctly distributed O.davidiana. Chloroplast DNA sequence variation identified two tentative lineages, which distinguished O.intermedia from O.davidiana; however, both were present in O.nobilis. Admixture analyses of genetic polymorphisms at 20 SSR loci and sequence variation at 11 nuclear loci and approximate Bayesian computation (ABC) tests supported the hypothesis that O.intermedia originated by homoploid hybrid speciation from O.davidiana and O.nobilis. We further estimated that O.davidiana and O.nobilis diverged 6-11Ma, while O.intermedia originated 0.5-1.2Ma when O.davidiana is believed to have migrated southward, contacted and hybridized with O.nobilis possibly during the largest Quaternary glaciation that occurred in this region. Our findings highlight the importance of Quaternary climate change in the QTP in causing hybrid speciation in this important biodiversity hotspot.

Late Quaternary climatic changes revealed by luminescence dating, mineral magnetism and diffuse reflectance spectroscopy of river terrace palaeosols: a new form of geoproxy data for the southern African interior

The nature, spatial patterns and forcing mechanisms of Quaternary climatic changes across southern Africa remain unresolved and contentious, principally due to the scarcity of continuous and robustly-dated proxy records. We present what we interpret to be a broadly continuous record of late Quaternary climatic change based on optically stimulated luminescence (OSL) dating, and mineral magnetic and diffuse reflectance spectroscopy (DRS) analyses of stacked palaeosols within an overbank alluvial succession along the Modder River, central South Africa. The OSL ages indicate that alluvial sedimentation occurred at a fairly steady rate, averaging ∼0.15 mm/yr from at least 44 ka until ∼0.83 ka. This suggests that the palaeosols are accretionary, having formed contemporaneously with sedimentation. Climate is identified as the key soil-forming factor controlling the intensity of pedogenesis and is reflected in the changing concentration of pedogenic ferrimagnetic minerals (magnetite/maghemite) of single domain and superparamagnetic dimensions, and by variations in the amount of hematite compared to goethite. These data indicate that the climate was generally dry (rainfall ∼200–400 mm/yr) from ∼46 to 32 ka, except for a brief peak in humidity at ∼42 ka. There was then a period of greater humidity (rainfall ∼400–600 mm/yr) from ∼32 to 28 ka, possibly reflecting enhanced moisture supply from the Atlantic Ocean associated with the equatorward migration and intensification of westerly storm tracks. Although the precise mechanism remains unresolved, this climatic change may have been linked to an obliquity minimum at ∼29 ka. After ∼28 ka, the climate became progressively cooler and drier, especially between ∼18 and 15.5 ka when rainfall was as low as ∼100–200 mm/yr. Temperatures and rainfall then increased from ∼15.5 ka onwards, with the latter possibly linked to rising sea-surface temperatures in the SW Indian Ocean and enhanced moisture supply from easterly circulation. At ∼0.83 ka, a time corresponding with part of the Medieval Climatic Anomaly (MCA, ∼900–1300 AD), rainfall reached ∼600–700 mm/yr and was higher than at present (∼400–500 mm/yr). Fluvial landforms have previously been overlooked as a source of palaeoenvironmental information in southern Africa, but this study clearly demonstrates the potential to extract robust palaeoenvironmental data from alluvial-palaeosol successions in the arid to semi-arid interior where other forms of proxy record are scarce.

Late quaternary climate changes around the elephant islands, Antarctic Peninsula

Sixty-seven species of diatoms of 28 genera were identified in Core GC03-C2 acquired from the north slope of Elephant Island, Antarctic Peninsula. The number of diatom valves per gram of dry sediment ranged from 0.2∼17.3×107g−1, and these were dominated by Fragilariopsis kerguelensis (65.8%). Diatom assemblage analysis reconstructed the Quaternary paleoclimatic change the Elephant Islands. Four diatom assemblage zones were identified according to the frequency of critical taxa as follows: zone I, from 830 to 710 cm (Antarctic Cold Reversal); zone II, from 700 to 550 cm (Deglaciation zone); zone III, from 540 to 260 cm (warm period; Holocene); and zone IV, from 250 to 0 cm (cool period; Holocene). The high abundance of reworked species includes Actinocyclus ingens, Denticulopsis hustedtii, D. praedimorpha, and D. dimorpha appeared in Zone I by turbidity currents and ice rafting in the area during the glaciations-deglaciation event.

Environmental changes in the wetlands of southern Iraq based on palynological studies: Comments

This paper suggests that the fungal fruiting bodies identified by Al-Ameri and Jassim (Arab J Geosci 4:443–461, 2011) as Plochmopellinites (Figures 6–10) is a thecamoebian taxa Arcella discoides, likewise Miliolinites nivalis (Figures 6–14) is another thecamoebian taxa Centropyxis aculeata. This conclusion is primarily based on the remarkable morphological similarity between these specimens illustrated and described by Al-Ameri and Jassim (Arab J Geosci 4:443–461, 2011) and the well-known thecamoebian taxa mentioned in this paper. These misidentified ‘fruiting fungal bodies’ were reported from the environments where thecamoebians are well known to inhabit. Thecamoebians are, by now, known to occur in the palynological slides and have become an important constituent of the non-pollen palynomorphs (NPP). Palynologists too study them as they are excellent proxies for Quaternary climatic and environmental changes.

Congruent phylogeographical patterns of eight tree species in Atlantic Central Africa provide insights into the past dynamics of forest cover

Cycles of Quaternary climatic change are assumed to be major drivers of African rainforest dynamics and evolution. However, most hypotheses on past vegetation dynamics relied on palaeobotanical records, an approach lacking spatial resolution, and on current patterns of species diversity and endemism, an approach confounding history and environmental determinism. In this context, a comparative phylogeographical study of rainforest species represents a complementary approach because Pleistocene climatic fluctuations may have left interpretable signatures in the patterns of genetic diversity within species. Using 1274 plastid DNA sequences from eight tree species (Afrostyrax kamerunensis, A.lepidophyllus, Erythrophleum suaveolens, Greenwayodendron suaveolens, Milicia excelsa, Santiria trimera, Scorodophloeus zenkeri and Symphonia globulifera) sampled in 50 populations of Atlantic Central Africa (ACA), we averaged divergence across species to produce the first map of the region synthesizing genetic distinctiveness and standardized divergence within and among localities. Significant congruence in divergence was detected mostly among five of the eight species and was stronger in the northern ACA. This pattern is compatible with a scenario of past forest fragmentation and recolonization whereby forests from eastern Cameroon and northeastern Gabon would have been more affected by past climatic change than those of western Cameroon (where one or more refugia would have occurred). By contrast, southern ACA (Gabon) displayed low congruence among species that may reflect less drastic past forest fragmentation or a more complex history of vegetation changes. Finally, we also highlight the potential impact of current environmental barriers on spatial genetic structures.

Late Quaternary molluscs from the northern San Matías Gulf (Northern Patagonia, Argentina), southwestern Atlantic: Faunistic changes and paleoenvironmental interpretation

The Late Quaternary in the coastal area of South America is represented mostly by littoral ridges, cliffs and tidal plains, with associated remains of gastropods and bivalves currently used as paleoclimatic indicators. The aim of this study is to characterize the assemblages of molluscs (bivalves and gastropods) both Pleistocene (≥MIS 9, MIS 7, MIS 5e) and Holocene (MIS 1), from the northern San Matías Gulf (Northern Patagonia, Argentina) in the southwestern Atlantic Ocean, in order to assess whether faunal change occurred together with Late Quaternary climatic change. Twenty localities were studied, seven from different interglacial stages of the Pleistocene, six Holocene, and seven modern beaches, in which 42 species were recorded, 20 bivalves and 22 gastropods. Among bivalves, euryhaline, infaunal from sandy substrates, and filter feeders, prevail. Amiantis purpurata is the dominant species of the whole mollusc assemblage. Among gastropods, although also euryhaline, the epifaunal species of rocky and sandy substrates and carnivores prevail. On the basis of descriptive statistical analyses, Bray–Curtis and AC methods, the localities formed three groups according to ages (modern vs. Pleistocene and Holocene) and/or presence/abundance of species. 70% of the marine malacofauna of MIS 7 remains during MIS 5e, decreasing to 60% during MIS 1 and to 27% when compared to the modern beaches. The most notable changes in the distribution of the species were: Tegula atra, currently extinct in the Argentine Atlantic coast, but recorded in Pleistocene interglacials MIS 7 and MIS 5e; Anomalocardia brasiliana, which only appeared in MIS 5e, and Mesodesma mactroides in MIS 1. MIS 5e was likely the warmest stage within the period considered, followed by MIS 7, both with higher SST temperatures than the present ones, and since MIS 1, molluscs of temperate-cold lineages of the Magellan malacological province are recorded.

Eastern African Quaternary Climate change and variability

Eastern African Quaternary Climate change and variability

Magnetostratigraphy of sediments from Lake El'gygytgyn ICDP Site 5011-1: paleomagnetic age constraints for the longest paleoclimate record from the continental Arctic

Abstract. Paleomagnetic measurements were performed on sediments drilled from ICDP Site 5011-1 in Lake El'gygytgyn (67°30' N, 172°05' E) located in Far East Russian Arctic. The lake partly fills a crater formed by a meteorite impact 3.58 ± 0.04 Ma ago. Sediments from three parallel cores (5011-1A, 5011-1B and 5011-1C), recovered from the middle part of the lake, yield a total of 355 m of sediment. Sediments are characterized by a variable lithology, where intervals of homogenous and laminated sediments alternate, and mass movement deposits occur frequently along the sediment profile. Mineral magnetic investigation made on sediments enclosed in core catchers suggests that magnetic carrier in these sediments is partly maghemitized Ti-rich pseudo-single domain magnetite. Its detrital origin can be shown by mineral magnetic measurements and SEM-EDS analyses performed on mini-sized cylindrical rock samples, polished rock sections and creek sediments. The intensity of the natural remanent magnetization in the sediments is high with a range from about 1 to 1000 mA m−1. Most of the sediments carry a stable magnetization interpreted as primary depositional remanent magnetization. Characteristic inclination data show alternating intervals of steep positive and negative inclinations that are used to assign magnetic polarity to the lake sediment profile. This is a rather straightforward procedure owing to the mainly high quality of data. The Matuyama/Gauss (M/G) (2.608 Ma) and Brunhes/Matuyama (B/M) (0.780 Ma) reversals were recognized in the sediments. The Mammoth and Kaena reversed subchrons were identified during the Gauss chron, and the Olduvai and Jaramillo normal subchrons as well as the Réunion and Cobb Mountain cryptochrons were identified during the Matuyama chron. Sediments also provide a record of the Olduvai precursor and Intra-Jaramillo geomagnetic excursions. Sediment deposition rate is highest at the base of the sequence laid down in the early Gauss chron, when the deposition rate is approximately 44 cm kyr−1. Sediment deposition decelerates upcore and it is an order of magnitude lower during the Brunhes chron in comparison with the early Gauss chron. Decrease in sediment deposition in the late Pliocene probably relates to atmospheric and oceanic reorganization heralding the onset of Quaternary climate change. The high-quality magnetostratigraphy reconstructed from Lake El'gygytgyn sediments provides 12 first-order tie points to pin down the age of the longest paleoclimate record from the continental Arctic.

New Light on the Evolutionary History of the Common Goby (Pomatoschistus microps) with an Emphasis on Colonization Processes in the Mediterranean Sea

Through the study of the phylogeographic structure and demographic history of the common goby, Pomatoschistus microps, the influence of Quaternary climatic changes on the evolutionary history of coastal and marine fishes is investigated. Because of its sedentary life cycle in Mediterranean lagoons, it is also a good model to study more specifically if the formation of lagoons during the Holocene had an impact on population structure and demography. Mitochondrial sequences of Northeastern Atlantic and Western Mediterranean specimens were used for phylogenetic reconstructions as well as divergence time estimates, demographic history and population structure analyses. Pomatoschistus microps was a highly supported monophyletic clade including four lineages. It may have appeared 77,000 yr ago, and the divergence of its lineages likely occured shortly thereafter (between 61,000 and 54,000 yr). Most lineages had polytomic topologies, low nucleotide diversity and demographic analyses providing evidence of population expansion. Each lineage was characterized by a large number of private haplotypes. Most haplotypes found in Mediterranean localities were endemic, and one was dominant. Complex reticulated relationships connecting North European, Atlantic and Mediterranean haplotypes were observed. Moderate to high population structure was underlined. Contrary to previous published studies, no significant differentiation was observed between Atlantic and Mediterranean populations, indicating that the Gibraltar Strait is not a phylogeographic break for P. microps. Indeed, molecular dating combined with the tree topologies, phylogeographic and demographic analyses as well as high haplotype diversity underline a recent and rapid population divergence during the last glacial. However, population structure indicates that differentiation is an ongoing process. From an ancestral population trapped in the Atlantic, this goby colonized first northern Europe and later the Mediterranean Sea. Shared haplotypes could have dispersed in the western Mediterranean basin before the lagoon formation, while most private haplotypes, evidencing a recent isolation, probably diverged in lagoons after their closure.

How do longitudinal dunes respond to climate forcing? Insights from 25 years of luminescence dating of the Australian desert dunefields

This paper presents a meta-analysis of 689 luminescence age estimates of Australian desert sand dunes. This analysis had two aims: to examine the hypothesis that Quaternary climate changes have forced dune accumulation, and to understand longitudinal dune behaviour from the age-architecture of sand dunes for which stratigraphic information is often absent or poorly known. A novel approach to the analysis of probability density curves of dune age frequency shows that in the Mallee dunefield of southeastern Australia only the period leading up to and including the last glacial maximum (LGM) (18–34 ka) experienced marked dune growth which cannot be explained by random stochastic activity. During the LGM, most, but not all, Mallee longitudinal dunes were accumulating more rapidly than before and after. In the Strzelecki dunefield source-bordering (SBD) longitudinal dune TL (n = 61) and OSL (n = 40) ages are more frequent at the Pleistocene–Holocene transition but nearby non-SBD longitudinal dunes (n = 21 ages) were only active above background levels during the LGM. However, the Strzelecki dune age data set suffers from being drawn from a small number of individual dunes (10 SBD dated using TL; 12 SBD dated by OSL; 7 non-SBD dated by OSL) with a marked bias away from surficial (young) and basal (old) depths. Even during the LGM, many dunes do not record active growth and the dunefield was most likely a mosaic of stable dune surfaces and bare mobile patches, supported by the scant pollen data from the arid zone. Hyper-aridity has not been experienced in these dunefields. These vegetated dunes exhibit conservative behaviour with limited response to the range of climate forcing experienced in the late Pleistocene. A more complete understanding of dunefield response to Quaternary climates would require an intensive and structured dating program to overcome the ‘noise’ from stochastic processes leading to small-scale activity in these dunes and the simultaneous removal of parts of the sedimentary record.