Pleistocene Cold Research Articles

Laminated diatomaceous ooze from southern Mariana Trench in Late Pleistocene and Holocene for paleoclimate and paleoceanography implication

This study offers a new record of laminated ooze for paleoclimate, paleoceanography and paleoecology interpretation in the deep ocean, promoting search for other similar records in the West Pacific Ocean to improve understanding of Ethmodiscus rex ooze formation and relative paleoenvironmental change. The laminated diatomaceous ooze includes large quantities of fragmented E. rex in a box core retrieved from the Challenger Deep, Southern Mariana Trench. Radiocarbon dating of the ooze revealed the studied sediment to originate during an interval of ca. 23 400 to ca. 6620 cal. yr. BP, inserting a hiatus during ca. 19 800 - 16 800 cal. yr. BP. This is the first geochronology data to constrain the E. rex ooze time span across the Pleistocene/Holocene boundary, compared to previous studies in this West Pacific Ocean trench. In this study, the laminated diatomaceous E. rex ooze type, with increased abundance of fragmented E. rex valves is mainly documented during ca. 23 400 - 19 800 cal. yr. BP. within the Last Glacial Maximum stage, at ca. 12 900 - 11 500 cal. yr. BP. in the Younger Dryas stadial, and around 9000–7700 cal. yr. BP. in the Postglacial.These data show a response to the paleoclimatic conditions with late Pleistocene cold periods that triggered E. rex diatom bloom that strongly competed for nutrients in this principally oligotrophic region. These phenomena are likely to be linked with terrestrial nutrients input through the aeolian dust transfer by winter Monsoon and the silicon supply from Southern Ocean via thermohaline circulation. In the Postglacial, the E. rex bloom generated a high ooze accumulation rate in terms of higher flux deposition with a complicated formation mechanism.

Evolutionary dynamics of Euphorbia carniolica suggest a complex Plio-Pleistocene history of understorey species of deciduous forest in southeastern Europe.

Deciduous forests form the dominant natural vegetation of Europe today, but were restricted to small refugia during Pleistocene cold stages, implying an evolutionary past shaped by recurrent range contractions and expansions. Cold-stage forest refugia were probably widespread in southern and central Europe, with the northwestern Balkan Peninsula being of particular importance. However, the actual number and location of deciduous forest refugia, as well as the connections between them, remain disputed. Here, we address the evolutionary dynamics of the deciduous forest understorey species Euphorbia carniolica as a proxy for past forest dynamics. To do so, we obtained genomic and morphometric data from populations representing the species' entire range, investigated phylogenetic position and intraspecific genetic variation, tested explicit demographic scenarios and applied species distribution models. Our data support two disjoint groups linked to separate refugia on the northwestern and central Balkan Peninsula. We find that genetic differentiation between groups started in the early Pleistocene via vicariance, suggesting a larger distribution in the past. Both refugia acted as sources for founder events to the southeastern Alps and the Carpathians; the latter were likely colonised before the last cold stage. In line with traditional views on the pre-Pleistocene origin of many southeastern European deciduous forest species, the origin of E. carniolica was dated to the late Pliocene. The fact that E. carniolica evolved at a time when a period of continuous forestation was ending in much of Eurasia provides an interesting biogeographical perspective on the past links between Eurasian deciduous forests and their biota.

Gelasian to Calabrian (Early Pleistocene) marine ostracods and foraminifera from Mida Section (Cap Bon, Tunisia) Les ostracodes et les foraminifères marins du Gélasien au Calabrien (Pléistocène inférieur) de la coupe de Mida (Cap Bon, Tunisie)

We report for the first time a rich and well-preserved marine ostracod and foraminifera association from lower Pleistocene fossiliferous sandstones of the Mida Section (Cap Bon, NE Tunisia).Micropalaeontological analysis of nine samples taken along an eight-meter exposure revealed 46 ostracod species belonging to 34 genera, 15 species of benthic foraminifera belonging to 14 genera and 8 species of planktonic foraminifera belonging to 4 genera. The ostracod association enabled us to draw a palaeoenvironmental reconstruction of this area during the Gelasian to Calabrian time, highlighting a regressive cycle from circalittoral to shallow infralittoral palaeoenvironments. Planktonic foraminifera were used to constrain the age of the section to the end of Gelasian-beginning of Calabrian. Moreover, the discovery of Bythocythere turgida in the lower part of the section allowed to infer that these sandstones were deposited during the early Pleistocene cold periods.

Origin of the central European steppe flora: insights from palaeodistribution modelling and migration simulations

The biogeographic origin of the species‐rich steppe grasslands in central Europe has long been debated. The alternative hypotheses are long‐term species persistence in situ versus immigration from the south‐east, either after the last glacial maximum (LGM) or after the Neolithic landscape deforestation. We ask whether macroclimate‐based models of habitat suitability support either of these hypotheses and search for macroclimatically suitable ‘source areas' from which species could colonise the areas occupied in Europe today. We modelled habitat suitability for 104 species of the central European steppes and projected these models to 10 periods between the LGM and the present using downscaled CCSM3 simulations. By simulating postglacial migration, we identified potential source areas for each species in the LGM and mid‐Holocene and examined whether their location differed among three ecological and five chorological species groups.The central European macroclimate during the cold phases of the Late Pleistocene was suitable for species now typical of Asian desert steppes, whereas the warmer Bølling–Allerød and Holocene macroclimates supported the occurrence of present‐day central European steppe flora. The models suggest that the LGM source areas of these species ranged from south‐eastern France through the Adriatic region and the Balkan Peninsula to the Black‐Sea region but extended to central Europe in the mid‐Holocene. Their locations differed considerably among ecological and chorological groups in both periods. Therefore, our models support the hypothesis that during the Pleistocene cold periods, the largest populations of these species occurred in southern and south‐eastern Europe and some of them may have later colonised central Europe. If some populations occurred in central Europe during the LGM, as suggested by recent genetic analyses, they were likely restricted to microrefugia embedded in the landscape matrix of species‐poor cold steppe. The precipitation‐rich mid‐Holocene climate had no direct negative impact on the central European steppe flora.

Investigating seasonal mobility in Irish giant deer Megaloceros giganteus (Blumenbach, 1799) through strontium isotope (87Sr/86Sr) analysis

ABSTRACTGiant deer Megaloceros giganteus (Blumenbach, 1799) fossils are commonly found in Lateglacial deposits throughout Ireland. While their migrational behaviour has been suggested, it has never been researched. We hypothesise that giant deer underwent seasonal migrations, specifically during Late Pleistocene cold periods as a behavioural adaptation. Giant deer required a high nutrient uptake and were maladapted to the cold‐dry steppe of the Pleistocene glacials. Migration allowed for optimal nutrient uptake during summer, while avoiding the harsh winter conditions of the glacials by moving to sheltered, low‐lying areas. In this study strontium isotope analysis (87Sr/86Sr) of sequentially sampled dental enamel is conducted for the first time on giant deer that were previously sampled in the same manner for δ13C and δ18O, allowing correlations between the isotope data sets. One specimen from Ballybetagh, Dublin generated results indicating seasonal mobility behaviour. This individual was perhaps pushed to migrate at the Younger Dryas stadial onset as the vegetation giant deer depended on disappeared in Ireland. Adaptive mobility behaviour in response to climate was perhaps imperative to their survival through previous glacial periods, but other Eurasian populations would need to be analysed to make such a general conclusion.

Pleistocene Periglacial Processes and Landforms, Mid-Atlantic Region, Eastern United States

Just as glaciers worldwide left a record of past advances and retreats that shifted latitudinally in response to oscillating Quaternary climate changes, so too have cold-climate conditions and permafrost left topographic and sedimentary signatures in former periglacial environments. This review documents widespread occurrence of past permafrost and intense frost action that led to rock fracturing, regolith production, and regolith-mantled slopes in the mid-Atlantic region of the United States during late Pleistocene cold-climate conditions. Strong signatures of thermal contraction cracking and brecciation from frost cracking exist where rocks and sediments are most frost susceptible, as with fissile shales. On sandstone hillslopes, frost weathering produced boulder-rich sediment that episodically flowed slowly down-slope during permafrost thaw, resulting in solifluction lobes and terraces in which colluvium moved cumulatively at least a kilometer. Radiocarbon dating, optically stimulated luminescence age control, and cosmogenic isotope studies constrain some periglacial features to the Last Glacial Maximum but also indicate longer residence times of regolith. ▪ Former permafrost and areas of intensive frost cracking extended over much of the mid-Atlantic region of the eastern United States during late Pleistocene cold glacial periods. ▪ Cold-climate conditions and permafrost left long-lasting topographic and sedimentary records with limited post-depositional erosion in the formerly periglacial mid-Atlantic region. ▪ Prominent relict periglacial landforms include polygon networks and frost wedges that are the result of thermal contraction cracking and brecciated rock formed by segregated ice and frost cracking. ▪ Widespread solifluction landforms are a topographic signature of freezing, thawing, and mass movement of mobile regolith produced by frost cracking, and some were active during the Last Glacial Maximum.

Геосистемы Баргузинского хребта

The study of geosystems of geodynamically active territories and their mapping is one of the urgent tasks of modern geographical research. The long period of formation and development of the Barguzin ridge determined the specifics of geosystems and their components. The conducted research allowed us to identify five physical and geographical areas, each of which has its own unique features. Within the large tectonic faults, which are characterized by an influx of endogenous heat and hot mineral springs are common, there is the largest accumulation of Miocene-Pliocene relics that have been preserved here since the Pleistocene cold snap. The development of the dark coniferous taiga is confined to the areas of distribution of acidic granites. Currently, pyrogenic impact is of great importance in the development of geosystems of the Barguzin ridge, which is reflected in the spread of derived forests that have arisen in the places of large fires. Frequent fires can cause the disappearance of dark coniferous taiga, as the process of restoring geosystems will be replaced by their transformation. The specifics of geosystems and their current state are reflected in the medium-scale map of geosystems of the central part of the western macroslope of the Barguzin ridge, which is presented in the article. The map was made for the first time at a scale of 1: 200000 to the level of facies groups.

A contribution towards the palynostratigraphical classification of the Middle Pleistocene in Central Europe: The pollen record of the Neualbenreuth Maar, northeastern Bavaria (Germany)

Palaeoecological evidence of intra-Saalian warm stages in Central Europe, which was strongly affected by glacial and periglacial processes during the major Middle and Late Pleistocene cold periods, is ambiguous so far. Recently, the first continuous sedimentary sequence of Central Europe containing the Saalian complex (MIS 8–6) with the Eemian interglacial in stratigraphic superposition was recovered from the newly discovered Neualbenreuth Maar (NE-Bavaria). Here we present palynological results from this record allowing us to critically discuss the available biostratigraphical evidence of alternating intra-Saalian warm-cold intervals from Central Europe. The new pollen record from the Neualbenreuth Maar comprises a continuous record of vegetation and climate changes encompassing four warm stages and five cold periods. The dominance of cold and dry tolerant herbs and the sparse representation of pioneer trees and shrubs during most parts of the sequence indicate open landscapes of steppe to woody-steppe character typical of late Middle and Late Pleistocene glacial periods in Central Europe. The pollen assemblages of the warm stage in the upper part of the core clearly support its correlation with the Eemian interglacial. The three pre-Eemian warm stages represent terrestrial analogues of the marine isotope stages (MIS) 7e, 7c, and 7a. During each of these intervals forests were established, but the reduced abundances and lower diversity of thermophilous and sub-oceanic elements in comparison to the Eemian attest to a weak interglacial character. Each of these interglacials shows a similar vegetation succession and only minor differences in the vegetation composition. The intervening stadial periods represent a strong (MIS 7d) and a moderate (MIS 7b) climate deterioration, respectively. The vegetation and climate succession during the Saalian glacial-interglacial complex of Neualbenreuth is broadly in line with the respective palynological signature from the Velay record (French Massif Central) and the Hoogeveen interstadial (The Netherlands). In contrast, there is only limited correspondence with most pollen records from northern and southern Central Europe, which were hitherto classified as MIS 7.

Heavy reliance on plants for Romanian cave bears evidenced by amino acid nitrogen isotope analysis

Heavy reliance on plants is rare in Carnivora and mostly limited to relatively small species in subtropical settings. The feeding behaviors of extinct cave bears living during Pleistocene cold periods at middle latitudes have been intensely studied using various approaches including isotopic analyses of fossil collagen. In contrast to cave bears from all other regions in Europe, some individuals from Romania show exceptionally high δ15N values that might be indicative of meat consumption. Herbivory on plants with high δ15N values cannot be ruled out based on this method, however. Here we apply an approach using the δ15N values of individual amino acids from collagen that offsets the baseline δ15N variation among environments. The analysis yielded strong signals of reliance on plants for Romanian cave bears based on the δ15N values of glutamate and phenylalanine. These results could suggest that the high variability in bulk collagen δ15N values observed among cave bears in Romania reflects niche partitioning but in a general trophic context of herbivory.

A new neolepadid cirripede from a Pleistocene cold seep, Krishna-Godavari Basin, offshore India

Valves of a thoracican cirripede belonging to a new species of the Neolepadidae, Ashinkailepas indica Gale sp. nov. are described from a Late Pleistocene cold seep (52.6 ka), cored in the Krishna-Godavari Basin, offshore from the eastern coast of India. This constitutes the first fossil record of the genus, and its first occurrence in the Indian Ocean. Other fossil records of the Neolepadidae (here elevated to full family status) are discussed, and it is concluded that only Stipilepas molerensis from the Eocene of Denmark, is correctly referred to the family. Cladistic analysis of the Neolepadidae supports a basal position for Ashinkailepas, as deduced independently from molecular studies, and the Lower Cretaceous brachylepadid genus Pedupycnolepas is identified as sister taxon to Neolepadidae. Neolepadids are not Mesozoic relics as claimed, preserved in association with the highly specialised environments of cold seeps and hydrothermal vents, but are rather an early Cenozoic offshoot from the clade which also gave rise to the sessile cirripedes.

The characteristics of a relic steppe of Northeast Asia: refuges of the Pleistocene Mammoth steppe (an example from the Lower Kolyma area)

An ecosystem of a relic petrophytic steppe was studied in the Lower Kolyma River region. The soils of the steppe area significantly differed from those of the surrounding open larch forests in the following features: the presence of humus-accumulative horizons with a high content of roots; low moisture content; high heat supply; an extremely contrasting temperature regime; neutral reaction; decreased potential acidity; higher humification of organic matter; accumulation of exchangeable bases, soluble salts and organic nitrogen; and the presence of carbonate neoformations in the form of cutans on pebbly units. They also had a high microorganism saturation of the soil profile, a high share of actinomycetes in the microbial community, as is typical for arid soils, and a shift in the ratio of potential enzyme activities toward oxidoreductases, which reflects a deeper destruction of plant residues and more intensive humus formation. The petrophytic steppe had high bioproductivity. The growth rate of the aboveground phytomass (ANP) was closer to the true steppes of Central Asia than to the zonal tundras of the Arctic and Subarctic; such communities can serve as models for paleoreconstructions and study of the Late Pleistocene cold steppes - mammoth fauna large grazing mammals habitats.

Latest Villafranchian climate and landscape reconstructions at Pirro Nord (southern Italy)

Abstract Early Pleistocene terrestrial climate conditions in the Mediterranean region, especially between 1.3 and 1.7 Ma, are poorly understood. Here, the amphibian and reptile fossil record from 24 fissures (Cava Pirro) of the Pirro Nord karstic complex (southern Italy) is used to infer quantitative paleoclimatic and paleoenvironmental reconstructions. These numerical data indicate that the mean annual temperature may have been somewhat lower (–1.6 to –3.6 °C compared to modern temperatures) than that of today, and the mean annual precipitation slightly higher (+90 to +240 mm) than modern values. Seasonality was more pronounced, with cooler summers (–0.4 to –2.0 °C) and much colder winters (–1.2 to –6.0 °C). Rainfall distribution patterns during the year show more precipitation during the winter (+14 to +43 mm), with quantities of summer rainfall (–1.7 to +6.6 mm) being similar to modern values. The associated landscape comprised an open dry environment with scattered patches of woodland, locally along water courses or around swamps. This ecological scenario fits with early Pleistocene cold conditions, where the first occurrence of some eastern emigrants suggests a scenario of trans-Adriatic dispersal, as may have also occurred for the earliest European hominins.

A source of loess-like deposits and their attendant palaeoenvironment – Orava Basin, Western Carpathian Mountains, S Poland

Abstract Loess-like deposits in the Orava Basin are aeolian sediments that were laid down during Pleistocene three cold periods: MIS 2-5d, MIS 6-10, and MIS 12-19. These deposits lie at the upper portion of glaciofluvial fans associated with the Czarny Dunajec River in the Orava Basin and are the youngest lithostratigraphic division that is present there. Results of granulometric analyses place their modal grain size in the coarse silt and fine sand fractions (sediment type 1.a). Geomorphic interactions between local topography, aeolian movements of sand and distribution of dust played the leading role in formation of these deposits. Two series of sediments have been distinguished: Series A which represents proximal depositional provenance, and Series B – distal depositional provenance. The source of the loess-like deposit material must have been local as the Orava Basin is isolated from foreland by highly elevated mountain ranges. Glaciofluvial sediments were deflated then laid down on fans at the bottom of the Orava Basin by rivers draining the western Tatra Mountains. Also ‘cannibalized’ were top portions of loess-like deposits that had accumulated during earlier Pleistocene cold periods. Fine sediment was also deflated from regolith mantle that formed on the slopes of surrounding hills. This conclusion is based on the results of analyses of microtextures of sand- and silt-sized grains. Grains with surfaces that were primarily shaped by chemical weathering (coated) and by mechanical weathering (fresh fractured) predominate both fractions. These sand grains were transported over a short distance; they were not subject to repeated redeposition.

Experimental soft‐sediment deformation caused by fluidization and intrusive ice melt in sand

AbstractIdentifying the driving mechanisms of soft‐sediment deformation in the geological record is the subject of debate. Thawing of ice‐rich clayey silt above permafrost was proved experimentally to be among the processes capable of triggering deformation. However, previous work has failed so far to reproduce similar structures in sand. This study investigates fluidization and intrusive ice formation from soil models in the laboratory. Experimental conditions reproduce the growth of ice‐cored mounds caused by pore water pressure increase during freeze‐back of sand in a permafrost context. Excess pore water pressure causes hydraulic fracturing and the development of water lenses beneath the freezing front. Later freezing of the water lenses generates intrusive ice. The main structures consist of sand dykes and sills formed when the increase in pore water pressure exceeds a critical threshold, and soft‐sediment deformations induced by subsidence during ice melt. The combination of processes has resulted in diapir‐like structures. The experimental structures are similar to those described in Pleistocene sites from France. These processes constitute a credible alternative to the seismic hypothesis evoked to explain soft‐sediment deformation structures in other European regions subjected to Pleistocene cold climates.

Pleistocene periglacial imprinting on polygenetic soils and paleosols in the SW Italian Alps

Because of extensive Pleistocenic glaciations, which erased most of the previously existing soils, slope steepness and climatic conditions favoring soil erosion, most soils observed in the Alps (and in other mid-latitude mountain ranges) have developed during the Holocene or Late Glacial period. However, in few sites, particularly in the outermost sections of the Alpine range, Pleistocene glaciers covered only small and scattered surfaces, and ancient soils could be preserved for long periods on stable surfaces. In many cases, these soils retain good memories of Quaternary periglacial activity, which have never been characterized on the Alpine range. Based on both geomorphological and pedological interpretations, this work aims to investigate these environments, providing, therefore, new evidences to support paleoclimate reconstructions on the Alps.We described and sampled soils on stable surfaces in the Upper Tanaro valley, Ligurian Alps (Southwestern Piemonte, Italy). The sampling sites were between 600 and 1600 m a.s.l., under present day lower montane Ostrya carpinifolia, montane Fagus sylvatica forests or montane heath/grazed grassland, on quartz-rich substrata.The surface morphology often showed strongly developed fossil periglacial morphologies such as large-scale patterned ground, blockfields/blockstreams or solifluction sheets.The soils preserved in such Quaternary periglacial landforms normally showed stratification of different layers (units), separated by structural discontinuities, evidencing different depositional settings and different pedogenic development degree. A strong cryogenic granulometric sorting characterized all the observed soils/paleosols, with silt-enriched horizons and lateral differentiation of sand- and stone-rich parts and fine enriched ones; organic matter was irregularly distributed at depth as a result of past cryoturbation. Compact and dense layers with strong platy/lenticular structural aggregation, wedge casts and large-scale cryoturbations were described below fixed depths in all soil profiles.Thus, surface morphology and soil properties suggest the presence of permafrost during cold Pleistocene phases, with two main active layer thicknesses at 60–120 and 100–160 cm depths respectively.

Phylogeography of a west-Beringian endemic plant: An ancient seed of Stellaria jacutica Schischk. detected in permafrost deposits of the last interglacial

Beringia, the landmass connecting Eurasia and North America during Pleistocene sea level low stands, played a crucial part in the phylogeographic history of northern plants, animals and humans. Beringia was not only route for migration between both continents but, as the only unglaciated sector of the Arctic, it was also an important refugial area for northern biota during the Pleistocene. The finding of a fossil seed of Stellaria jacutica Schischk., endemic in Yakutia and the Russian Far Eastern Magadan Oblast, in permafrost deposits near Batagay demonstrates the existence of that species in the Yakutian Yana Highlands already during the last Pleistocene interglacial, about 125 ka ago. The biogeographical, ecological and seed morphological characters of S. jacutica allow for conclusions on its phylogenetic relationships. Stellaria jacutica is the only large seeded Stellaria species occurring in northeast Siberia today. According to carpological characters, S. jacutica is closely related to south Siberian large-seeded Stellaria species, which have a centre of diversity in the Altai-Sayan mountain range. This kinship is also suggested by corresponding ecological preferences and occurrence in mountain steppes and rock steppe communities mainly in the alpine belt of mountains. The spread of S. jacutica's ancestor north-eastwards assumedly happened during a Pleistocene cold stage, when the climate in Siberia was cooler, drier and more continental than during warm stages. Spread and following allopatric speciation hence occurred prior to the last interglacial, i.e. during or prior to the middle Pleistocene.

Late Pleistocene climate of Poland in the mid-European context

Proxy data from pollen and mollusc indicator species, periglacial phenomena, changes in geometry of mountain palaeoglaciers and based on selected lithological and geomorphological features enabled reconstruction of the Late Pleistocene climate characteristics in Poland and adjacent areas. Climate during the Eemian was generally stable but with a distinct west-east gradient in summer. Strong influence of the Atlantic air masses moving to the east resulted in the annual precipitation over 600 mm. Climate instability in the late Eemian as well as during stadials and interstadials of the Early Weichselian was expressed by progressive cooling and increasing temperature difference between winters and summers, reflecting stronger continentalism towards the west, accompanied by decreased precipitation. Periglacial frost crackings and polygonal patterns indicated occurrence of permafrost in Poland already at about 49 ka BP and its occurrence until the termination of the last glaciation. These periglacial structures have developed at mean annual temperatures from −9 to −4 °C, with winter extremes up to about −25 °C. Mean summer temperature reached likely around 10 °C as suggested by palaeobotanic record. Palaeoglaciological studies of mountain glaciers across Europe allowed inferring their activity and sensitivity to climatic fluctuations during the Late Weichselian. The Weichselian of central Europe was controlled mostly by the southerly and easterly circulation dominated by climate cyclones and anticyclones, respectively. An inflow of air masses from the west was significantly limited and concentrated mainly within the so-called periglacial corridor between the Scandinavian ice sheet and the Alps. Such circulation pattern determined serious reduction of precipitation during the Last Glacial Maximum that reached 60% in relation to modern conditions. The following Late Pleistocene cold phases (Oldest and Younger Dryas) were slightly warmer and wetter with increasing contribution of the westerlies that were strongly dependent on progressing shrinkage of the Northern Hemisphere ice sheets.

Middle Pleistocene human occupation in the interior of the Iberian Peninsula during cold climate conditions: Zooarchaeology and taphonomy of ETB-H02 site in the Manzanares valley (Madrid, Spain)

Evidence suggesting human occupation in the interior of the Iberian Peninsula during cold periods of the Middle Pleistocene is scarce. The Estanque de Tormentas (ETB-H02) site (Manzanares Valley, Madrid) matches with a MIS 6 or MIS 7 cold event, which allows us to tackle the study of the human occupation of the highlands of the Spanish Meseta during a cold climate event.ETB-H02 is one of the few Middle Pleistocene open air sites of the Iberian Peninsula where lithic industry associated with faunal remains has been preserved. The bone remains have been recovered from several different stratigraphic levels excavated in an area 1029 m2. It can be inferred from the taphonomic and zooarcheological analyses of those remains that occasional human occupations occurred at this site, during which lithic tools were used for processing individuals of aurochs, horses, wild donkeys and deer. In addition, carcasses of animals that probably died due to natural causes have been preserved. Some were modified by carnivores although not intensively, judging by the scarce number of tooth marks.In conclusion, ETB-H02 supports the hypothesis that the continental climate and the height of the highlands of the Iberian Peninsula were not an obstacle to occupation in the Middle Pleistocene cold times. Besides, unlike other sites of the interior of the Iberian Peninsula that show occasional occupations, in ETB-H02 the human occupation happened recurrently, as human-processed faunal remains have been recovered from different levels and sub-levels, implying repeated visits to this environment, which would offer specific advantages regarding the exploitation of animal resources.

Historical introgression among the species of Rodgersia (Saxifragaceae) in mountainous forests of southwest China

In the present study, we used genetic data and ecological niche modelling to explore possible historical introgressions among the species of Rodgersia (Saxifragaceae) in central-southwest China. Markedly differentiated chloroplast haplotypes were found in R. aesculifolia, R. sambucifolia and the Lijiang (LJ) population of R. pinnata, respectively, and differentiated chloroplast haplotypes within each of them showed the closest relationships with haplotypes from different species. ITS cloning did not reveal any shared ribotype between R. aesculifolia and the remaining species. Historical introgression between R. aesculifolia and R. sambucifolia (or R. pinnata) seems to be the most plausible explanation according to the geographical pattern and derivative status of putative introgressed chloroplast haplotypes, and also from morphological evidence. Introgressions were also found among R. sambucifolia, R. pinnata, and R. henricii from Yunnan. Frequent gene exchanges may have promoted the diversity of leaf shapes in this genus. Ecological niche modelling indicated that past secondary contact following range shifts during Pleistocene cold periods may have provided opportunities for ancient introgression between R. aesculifolia and adjacent species.

Glacial–interglacial changes and Holocene variations in Arabian Sea denitrification

Abstract. At present, the Arabian Sea has a permanent oxygen minimum zone (OMZ) at water depths between about 100 and 1200 m. Active denitrification in the upper part of the OMZ is recorded by enhanced δ15N values in the sediments. Sediment cores show a δ15N increase during the middle and late Holocene, which is contrary to the trend in the other two regions of water column denitrification in the eastern tropical North and South Pacific. We calculated composite sea surface temperature (SST) and δ15N ratios in time slices of 1000 years of the last 25 kyr to better understand the reasons for the establishment of the Arabian Sea OMZ and its response to changes in the Asian monsoon system. Low δ15N values of 4–7 ‰ during the last glacial maximum (LGM) and stadials (Younger Dryas and Heinrich events) suggest that denitrification was inactive or weak during Pleistocene cold phases, while warm interstadials (ISs) had elevated δ15N. Fast changes in upwelling intensities and OMZ ventilation from the Antarctic were responsible for these strong millennial-scale variations during the glacial. During the entire Holocene δ15N values > 6 ‰ indicate a relatively stable OMZ with enhanced denitrification. The OMZ develops parallel to the strengthening of the SW monsoon and monsoonal upwelling after the LGM. Despite the relatively stable climatic conditions of the Holocene, the δ15N records show regionally different trends in the Arabian Sea. In the upwelling areas in the western part of the basin, δ15N values are lower during the mid-Holocene (4.2–8.2 ka BP) compared to the late Holocene (< 4.2 ka BP) due to stronger ventilation of the OMZ during the period of the most intense southwest monsoonal upwelling. In contrast, δ15N values in the northern and eastern Arabian Sea rose during the last 8 kyr. The displacement of the core of the OMZ from the region of maximum productivity in the western Arabian Sea to its present position in the northeast was established during the middle and late Holocene. This was probably caused by (i) reduced ventilation due to a longer residence time of OMZ waters and (ii) augmented by rising oxygen consumption due to enhanced northeast-monsoon-driven biological productivity. This concurs with the results of the Kiel Climate Model, which show an increase in OMZ volume during the last 9 kyr related to the increasing age of the OMZ water mass.