Last Glacial loess in the conterminous USA

The conterminous United States contains an extensive and generally well-studied record of Last Glacial loess. The loess occurs in diverse physiographic provinces, and under a wide range of climatic and ecological conditions. Both glacial and non-glacial loess sources are present, and many properties of the loess vary systematically with distance from loess sources. United States’ mid-continent Last Glacial loess is probably the thickest in the world, and our calculated mass accumulation rates (MARs) are as high as 17,500 g/m²/yr at the Bignell Hill locality in Nebraska, and many near-source localities have MARs greater than 1500 g/m²/yr. These MARs are high relative to rates calculated in other loess provinces around the world. Recent models of Last Glacial dust sources fail to predict the extent and magnitude of dust flux from the mid-continent of the United States. A better understanding of linkages between climate, ice sheet behaviour, routing of glacial meltwater, land surface processes beyond the ice margin, and vegetation is needed to improve the predictive capabilities of models simulating dust flux from this region.     

Rerewhakaaitu Tephra,a land–sea marker for the Last Termination in New Zealand,with implications for global climate change

The Rerewhakaaiutu Tephra erupted from Okataina Volcanic Centre, North Island, New Zealand, at 14,700±95 ¹⁴C yr BP (ca 17,600 cal yr BP) at a time of rapid re-organisation of Earth's climate system at the end of the Last Glacial (Termination I). It provides a distinctive isochron in a range of different environments in North Island and in adjacent South Pacific Ocean sediments. Terrestrial evidence, based on fluvial aggradation and downcutting relationships, loess accumulation rates, palaeovegetation patterns, and buried soil development and mineralogy, shows that marked amelioration of climate occurred shortly before the Rerewhakaaitu Tephra was deposited. Similarly, marine evidence from around this time shows major changes in accumulation rates of sediment and aeolian quartz and in the abundance of various marine organisms, while foraminiferal oxygen and carbon isotope records indicate that the arrival of the glacial meltwater signal occurred close to or just after the deposition of the Rerewhakaaitu Tephra. These changes are discussed in relation to controls on climate by oceanic and atmospheric mechanisms. The re-organisation of climate commencing at ca 15,000–14,500 ¹⁴C yr BP (ca 18,000–17,400 cal yr BP) is detected elsewhere in the Southern Hemisphere and evidently was linked to orbitally forced warming which is thought to have initiated ice retreat in both hemispheres.     

Inter-profile correlation of the Chinese loess/paleosol sequences during Marine Oxygen Isotope Stage 5 and indications of pedogenesis

Low-field magnetic susceptibility has been widely used to determine the pedostratigraphy of the Chinese loess/paleosol sequences. However, uncertainties remain in correlating between the loess magnetic susceptibility and the marine oxygen isotope records because susceptibility variations are affected by both global and local paleoclimatic changes. To provide a more sound paleoclimatic interpretation of magnetic susceptibility variations, age models across Marine Oxygen Isotope Stage (MIS) 5 for the Jiuzhoutai (JZT) and Yuanbao (YB) sections, western Chinese Loess Plateau, were constructed through an integrated approach by linking the major pedostratigraphic boundaries of the loess profiles to the SPECMAP oxygen isotope curve, and by correlating relative magnetic paleointensity records with both the SINT800 global paleointensity stack from marine sediments and ³⁶Cl records from the GRIP ice core. Results indicate good correlation of SIRM_60 mT (a residual remanence of saturation isothermal remanent magnetization after a 60 mT alternating field demagnetization) variations between these two sites, which agree well with fluctuations in subtropical Atlantic sea surface temperatures. All cooling events recorded by ice-core and Atlantic marine sediments within MIS5 have counterparts in SIRM_60 mT. SIRM_60 mT is partially controlled by the degree of low-temperature oxidation, which is strongly temperature dependent. However, strong pedogenesis can decrease SIRM_60 mT due to further oxidation of partially oxidized magnetites above some critical points. Therefore, we propose that SIRM_60 mT is best suited to record paleotemperature changes in loess profiles from the western Chinese Loess Plateau, where pedogenesis is the weakest. Furthermore, by inter-profile correlation between the YB and JZT sections, we note that the seemingly uniform sub-paleosol unit with a broad susceptibility peak (previously assigned to MIS5c) between ∼34.4 and ∼37.4 m in the YB profile actually consists of two independent units (lower part of S1L1/MIS5b and S1S2/MIS5c). This indicates that susceptibility values can be strongly affected by local factors (e.g., mainly precipitation). Therefore, beside the simplistic traditional paleoclimatic interpretation of variations in loess susceptibility involving only cold/dry and warm/humid scenarios, cold/humid and warm/dry scenarios should also be considered.     

Terrestrial stable isotope records of Late Quaternary paleoclimates in the eastern Mediterranean region

Terrestrial stable isotope records (¹³C/¹²C, ¹⁸O/¹⁶O, and D/H ratios) of late Quaternary paleoclimates in the eastern Mediterranean region are reviewed. Significant paleoclimatic reconstructions come from a variety of isotopic studies. Paleogroundwaters, although they cannot be accurately dated, show oxygen and hydrogen isotopic compositions highly depleted in heavier isotopes compared to modern meteoric waters in arid regions of southern Israel, Sinai and northeastern Africa and attest to a major difference in climatic regime some time in the Pleistocene. Th-U dating of land snails showing a similar ¹⁸O depletion indicates ages of 100,000 yr and ≥300,000 yr for this climatic regime in the Negev Desert of southern Israel. Carbon isotope records of organic matter have not been studied extensively in the region, except for the record of Holocene land snails in the Negev. These document a southward shift in pure C₃ plant communities in the middle and early Holocene relative to their present distribution and indicate wetter conditions at those times. An oxygen isotope curve for the Holocene, reflecting changes in the isotopic composition of precipitation, has been established from analysis of carbonate materials—land snail shells and speleothems. The curve indicates a depletion of ca. 2‰ in ¹⁸O centered around 7000 cal yr bp, with modern levels being reached by 5000 cal yr bp. Carbon isotope analysis of soil carbonates in paleosols developed in loess in the Negev show the existence of dramatic north–south climatic gradients at the times of formation of the soils (ca. 13,000, 28,000, and ≥37,000 ¹⁴C yr bp), as occur also today due to the waning influence of Mediterranean to the south. Some isotopic methods, widely used in other regions, have received little or no attention in the eastern Mediterranean region. These include oxygen and hydrogen isotopes in wood, phosphate oxygen and organic carbon in bones and teeth, and carbon in soil organic matter.     

Revised 14C dating of ice wedge growth in interior Alaska (USA) to MIS 2 reveals cold paleoclimate and carbon recycling in ancient permafrost terrain

Establishing firm radiocarbon chronologies for Quaternary permafrost sequences remains a challenge because of the persistence of old carbon in younger deposits. To investigate carbon dynamics and establish ice wedge formation ages in Interior Alaska, we dated a late Pleistocene ice wedge, formerly assigned to Marine Isotope Stage (MIS) 3, and host sediments near Fairbanks, Alaska, with 24 radiocarbon analyses on wood, particulate organic carbon (POC), air-bubble CO₂, and dissolved organic carbon (DOC). Our new CO₂ and DOC ages are up to 11,170 yr younger than ice wedge POC ages, indicating that POC is detrital in origin. We conclude an ice wedge formation age between 28 and 22 cal ka BP during cold stadial conditions of MIS 2 and solar insolation minimum, possibly associated with Heinrich event 2 or the last glacial maximum. A DOC age for an ice lens in a thaw unconformity above the ice wedge returned a maximum age of 21,470 ± 200 cal yr BP. Our variable ¹⁴C data indicate recycling of older carbon in ancient permafrost terrain, resulting in radiocarbon ages significantly older than the period of ice-wedge activity. Release of ancient carbon with climatic warming will therefore affect the global ¹⁴C budget.     

From Pleniglacial to Holocene: a 14C chronostratigraphy of environmental changes in the Konya Plain,Turkey

In the endoreic, semi-arid Konya basin on the central Anatolian plateaux, long-term hydrological evolution has left various landforms and lacustrine deposits reflecting the regional climatic evolution, as well as human influence on the local environments. This paper presents results from a cooperative programme grouping several institutes from Turkey and France, on lacustrine, marshy and aeolian sediment sequences of Upper Pleistocene and Holocene age. The detailed study of environmental evolution is based on the reconstruction as well as on the characterization of the extension and contraction phases of wetlands occupying the lowest parts of the Konya plain. A soil and a marsh layer are ¹⁴C dated ca. 28,000–25,000 yr bp. Three phases of Pleniglacial (from ca. 22,000 to 17,000 yr bp) high lake levels are distinguished. Complementary OSL dates on aeolian dunes confirm the occurrence of two drought periods: the first occurs around the start of the Late Glacial, the second after the Mid-Holocene climatic optimum, the latter being ‘in phase’ with a similar drought in other Eastern Mediterranean regions. After 17,000 yr bp, no lacustrine phase reached as high a level as the Pleniglacial lake. During the Late Glacial, a shallow freshwater lacustrine phase is identified from >12,500 to 11,000 yr bp. The Late Glacial to Holocene transition corresponds to a general absence of deposits and dateable material, thus suggesting a period of drought, to which no aeolian features have so far been related. The Holocene environmental evolution shows a period of marsh and shallow lake extansion from 6000 to 5500 yr bp; this wetter period is interrupted by the second drought (ca. 5500 yrs bp) as indicated by aeolian dune activity. During the Late Holocene, a renewal of marshes, as well as soil development on slopes, can be interpreted either as climatic changes or as impacts of human use of water and soil resources during prehistoric and historic times.     

Sulfur cycling at the Mid-Atlantic Ridge: A multiple sulfur isotope approach

The role of sulfur in two hydrothermal vent systems, the Logatchev hydrothermal field at 14°45′N/44°58′W and several different vent sites along the southern Mid-Atlantic Ridge (SMAR) between 4°48′S and 9°33′S and between 12°22′W and 13°12′W, is examined by utilizing multiple sulfur isotope and sulfur concentration data. Isotope compositions for sulfide minerals and vent H₂S from different SMAR sites range from + 1.5 to + 8.9‰ in δ³⁴S and from + 0.001 to + 0.051‰ in Δ³³S. These data indicate mixing of mantle sulfur with sulfur from seawater sulfate. Combined δ³⁴S and Δ³³S systematics reveal that vent sulfide from SMAR is characterized by a sulfur contribution from seawater sulfate between 25 and 33%. This higher contribution, compared with EPR sulfide, indicates increased seawater sulfate reduction at MAR, because of a deeper seated magma chamber and longer fluid upflow path length, and points to fundamental differences with respect to subsurface structures and fluid evolution at slow and fast spreading mid-ocean ridges.Additionally, isotope data uncover non-equilibrium isotopic exchange between dissolved sulfide and sulfate in an anhydrite bearing zone below the vent systems at fluid temperatures between 335 and 400 °C. δ³⁴S values between + 0.2 to + 8.8‰ for dissolved and precipitated sulfide from Logatchev point to the same mixing process between mantle sulfur and sulfur from seawater sulfate as at SMAR. δ³⁴S values between ? 24.5 and + 6.5‰ and Δ³³S values between + 0.001 and + 0.125‰ for sulfide-bearing sediments and mafic/ultramafic host rocks from drill cores taken in the region of Logatchev indicate a clear contribution of biogenic sulfides formed via bacterial sulfate reduction. Basalts and basaltic glass from SMAR sites with Δ³³S = ? 0.008‰ reveal lower Δ³³S lower values than suggested on the basis of previously published isotopic measurements of terrestrial materials.We conclude that the combined use of both δ³⁴S and Δ³³S provides a more detailed picture of the sulfur cycling in hydrothermal systems at the Mid-Atlantic Ridge and uncovers systematic differences to hydrothermal sites at different mid-ocean ridge sites. Multiple sulfur isotope measurements allow identification of incomplete isotope exchange in addition to isotope mixing as a second important factor influencing the isotopic composition of dissolved sulfide during fluid upflow. Furthermore, based on Δ³³S we are able to clearly distinguish biogenic from hydrothermal sulfides in sediments even when δ³⁴S were identical.     

Insights into ore genesis of the Jinding Zn–Pb deposit,Yunnan Province,China: Evidence from Zn and in-situ S isotopes

The Jinding Zn–Pb deposit located in the Mesozoic-Cenozoic Lanping Basin of southwest China has ore reserves of ∼ 220 Mt with an average grade of 6.1% Zn and 1.3% Pb. The mineralization is hosted by sandstone in the Early Cretaceous Jingxing Formation and limestone breccia in the Paleocene Yunlong Formation. Mineralization in both types of host rocks is characterized by a paragenetic sequence beginning with marcasite–sphalerite (Stage 1) followed by pyrite–marcasite–sphalerite–galena (Stage 2), and then galena–sphalerite–pyrite–sulfate–carbonate (Stage 3). Pyrite from these stages have different δ³³S compositions with pyrite from Stage 1 averaging − 9.6‰, Stage 2 averaging − 8.9‰, and Stage 3 averaging + 0.3‰. Sphalerite hosted by the sandstone has similar δ⁶⁶Zn values ranging from 0.10 to 0.30‰ in all stages of the mineralization, but sphalerite samples from the limestone breccia-hosted ore show variable δ⁶⁶Zn values between − 0.03 and 0.20‰. Our data on sphalerite precipitated during the earlier stages of mineralization has a constant δ⁶⁶Zn value and cogenetic pyrite displays a very light sulfur isotope signature, which we believe to reflect a sulfur source that formed during bacterial sulfate reduction (BSR). The Stage 3 sphalerite and pyrite precipitated from a late influx of metal-rich basinal brine, which had a relatively constant variable δ⁶⁶Zn isotopic composition due to open system isotope fractionation, and a near zero δ³³S composition due to the influence of abiotic thermochemical sulfate reduction from observed sulfates in the host rock.     

Stable isotope composition of subfossil Cerastoderma glaucum shells from the Szczecin Bay brackish deposits and its palaeogeographical implications (South Baltic Coast,Poland)

The environmental conditions of the Szczecin Bay, which existed prior to Szczecin Lagoon, have been reconstructed on the basis of the stable carbon and oxygen isotope (¹⁸O and ¹³C) analysis and radiocarbon dates obtained for subfossil shells of Cerastoderma (Cardium) glaucum. The shells in the collected core were well preserved in their life positions, representing a geochemical record of past temperature variation over the middle Holocene. Three major periods with different thermal conditions have been distinguished in the interval ~ 6000–4300 cal yr BP, when the important Littorina regional transgression took place. During the first period, 6000–5250 cal yr BP, water temperature decreased by 1.4°C, and then remained constant over the second period (5250–4750 cal yr BP). In contrast, during the third period (4750–4300 cal yr BP) both δ-values were highly variable and the mean summer temperature (March–November) increased by about 3.5°C. During first two periods, δ¹⁸O and δ¹³C were significantly correlated, indicating stability of the environmental conditions.     

Rates and causes of recent global sea-level rise inferred from long tide gauge data records

Tide gauge data at seven sites of the Permanent Service for Mean Sea Level (PSMSL), with information for relative sea-level during the past 140–200 yr, were analyzed to examine the rates and causes of the global sea-level rise (GSLR) during the twentieth century. By subtracting linear trends for relative sea-level rise during the past 100 yr from the observed data, we get the apparent GSLRs of ∼1 mm yr⁻¹ for five sites around the Baltic Sea and Brest. The rate for San Francisco is significantly larger than this, with an optimum value ∼2 mm yr⁻¹. The spatial difference of ∼1 mm yr⁻¹ between these sites is reasonably explained by the recent melting of the Greenland ice sheet with an equivalent sea-level rise of ∼1 mm yr⁻¹. The predicted relative sea-level change for this melting scenario is 0.5 mm yr⁻¹ at sites around the Baltic Sea and Brest, and 1.5 mm yr⁻¹ for San Francisco. The residuals between observations and predictions, ∼0.5 mm yr⁻¹ at all sites, may be contributed by thermal expansion of seawater and/or other melting sources. These results suggest the rate of twentieth-century GSLR to be 1.5 mm yr⁻¹.     

Holocene aeolian development in Central Spain; chronology,regional correlations and causal processes

Extensive areas in the southern part of the Duero Tertiary Basin (Central Spain) are covered by aeolian sands. Presently, the aeolian system is relict but in its origin and development it can be described as a “wet aeolian system”. Climatic and environmental changes during the Holocene are typified by alternating humid and arid periods. These are recorded in the sedimentary record as either organic-rich sandy palaeosols or clean aeolian sand, respectively. Palaeosol dating (12 radiocarbon dated samples) and stratigraphical and sedimentological analysis of several dunefields in quarries and boreholes allow the distinction of four periods of palaeosol development since the Allerød.Aeolian sediments commonly rest on fluvial deposits, which were themselves the major source area for aeolian sands. These fluvial deposits have an age of about 14,000 cal yr BP. The first phase of aeolian activity postdates these fluvial sediments and has an upper age of about 12,000–11,700 cal yr BP, probably corresponding to the last cold oscillation of the Lateglacial (Younger Dryas). The second phase ranges from about 11,500 to 9500 cal yr BP, during which period the majority of dunes in the Tierra de Pinares area formed. This is also a major phase of aeolian activity in other areas of the Iberian Peninsula. A third and probably discontinuous phase of aeolian activity took place between 6800 and about 3000 cal yr BP. The age for this phase is supported by the presence of Visigothic burial sites covered by aeolian sands. The presence of charred material and degraded slipfaces clearly indicate stabilisation by vegetation and the final degradation of the aeolian system at the end of the fourth aeolian phase (990–540 cal yr BP). Minor aeolian activity has also occurred subsequently in this area, since aeolian sand movement was even reported in the 20th century.The aeolian phases can be tentatively correlated with aeolian phases in Europe. Aeolian activity tends to occur regionally during specific time-intervals, especially in dunefields with little human disturbance. This argues for a broad climatic forcing in Holocene aeolian accumulation, such has been previously suggested for the little ice age. The precise timing of these phases, however, is not strictly coincident, probably due to the delayed responses of aeolian environments to climatic and subsequent vegetation change.     

Holocene climate variability in Europe: Evidence from δ18O,textural and extension-rate variations in three speleothems

Time-series O isotope profiles for three U–Th dated stalagmites have revealed that for much of the Holocene, a site on the Atlantic seaboard (SW Ireland) exhibits first-order δ¹⁸O trends that are almost exactly out of phase with coupled δ¹⁸O curves from two southern European sites (SE France and NW Italy). In the Irish stalagmite (CC3 from Crag Cave, SW Ireland), low δ¹⁸O at 10,000 cal yr BP reflects cool conditions. By the early to mid-Holocene (9000–6000 cal yr BP) δ¹⁸O had increased, reflecting the onset of warmer conditions on the Atlantic seaboard. This shift to higher δ¹⁸O was accompanied by a marked increase in the stalagmite extension rate, reinforcing our interpretation that this was a period of relative warmth. Except for an episode of increased extension rate about 5500 yr ago, δ¹⁸O in the Crag stalagmite exhibits a gradual decrease, accompanied by declining extension rates between 7800 and 3500 cal yr BP, interpreted as a cooling trend. There is evidence for increases in both δ¹⁸O and stalagmite extension rate in the period from 3500 cal yr BP to the present day suggesting a return to warmer conditions on the Atlantic seaboard. In the stalagmite from NW Italy (ER76, Grotta di Ernesto, Trentino province) the early-Holocene (c. 9200-7800 cal yr BP) is characterised by high δ¹⁸O, probably indicative of warm and/or dry conditions. Exceptionally low δ¹⁸O from 7800 to 6900 cal yr BP at this site reflects a well-defined wet phase (Cerin wet phase). In the last three millennia, this stalagmite exhibits a shift to lower δ¹⁸O, interpreted as some combination of cooler and/or wetter conditions. Unlike the Irish stalagmite, the Italian sample does not show a correlation between δ¹⁸O and extension rate. Instead, its extension rate correlates roughly with δ¹³C, presumably reflecting a climate-driven vegetation change. In the early Holocene, δ¹⁸O in the French stalagmite (CL26, Grotte de Clamouse, Herault province, SE France) was low relative to its Holocene average. For much of the period since c. 3500 cal yr BP this stalagmite exhibits higher δ¹⁸O than in the early Holocene, suggesting warmer conditions. Like the Irish stalagmite, the French sample exhibits a well-defined correlation between δ¹⁸O and extension rate. Had drip-water availability been the dominant control on δ¹⁸O at this semi-arid site then higher δ¹⁸O would have been accompanied by lower, not higher extension rates. This suggests strongly that temperature rather than rainfall amount was the dominant control at this site. While conclusions regarding the patterns of climate variability on a continent scale must remain tentative because of the limited number of stalagmites studied we argue that early Holocene warm conditions on the Atlantic seaboard (Irish site) coincided with relatively cool conditions at the Clamouse site. By c. 3500 yr ago the pattern appears to have been reversed.     

Deglaciation and landscape history around Annapurna,Nepal, based on 10Be surface exposure dating

The High Himalaya is a key area for tectonic, geomorphological and climate studies, because of its extreme relief and location at the transition zone between areas with abundant monsoonal precipitation and the arid/semiarid Tibetan Plateau. We present ¹⁰Be surface exposure ages on 22 boulders from the Annapurna area in Nepal. The ages improve understanding of the Late Quaternary landscape history and the geomorphological processes operating in this part of the Himalaya.Although our study is reconnaissance in nature, it highlights the importance of catastrophic events, such as landslides and debris flows, for denudation of high mountains. Holocene exposure ages for the Dhampu–Chooya landslide (～4.1 ± 0.6 ka) and for 600 m of alluviation in Kali Gandaki Valley (～2.1 ± 0.6 ka), for example, indicate the frequent occurrence and extent of catastrophic events and their implications for natural hazards. We also offer an explanation for the differences in Late Quaternary glacial chronologies at closely spaced study sites in the Nepal Himalaya. Topographically controlled and spatially variable precipitation in the Himalaya determines the sensitivity of glaciers to changes in temperature and precipitation. Accordingly, some glaciers advanced in-phase with Northern Hemisphere ice sheets, whereas others reached their maximum extent at times of increased monsoonal precipitation during Marine Isotope Stage 3 and the early Holocene.     

Holocene climate change inferred from stratigraphy and OSL chronology of aeolian sediments in the Qaidam Basin,northeastern Qinghai–Tibetan Plateau

Paleoclimatic reconstruction based on aeolian sediments in the eastern Qaidam Basin (QB) has been hindered by the limited chronological data. Here we present 61 Optically Stimulated Luminescence (OSL) ages. On the basis of these OSL ages and the lithologic stratigraphy, we propose the ‘effective moisture index (EMI)’ for aeolian sediments to reconstruct the effective moisture change. Based on the EMI from twelve sections, the effective moisture change, moisture sources and relevant mechanisms for paleoclimatic change in the eastern QB are discussed. The results indicate that (1) aeolian deposition started at least before 12.4 ± 0.7 ka during the deglaciation, the paleosols developed at the early and mid-Holocene, and aeolian sand and loess accumulated at mid- and late Holocene; (2) effective moisture history was: hyper-arid at 12.8–11.6 ka, humid and variable at 11.6–8.3 ka, moderately humid and stable at 8.3–3.5 ka, and increasingly arid at 3.5–0 ka; (3) the effective moisture change was mainly controlled by the Asian summer monsoon (ASM), which mainly followed the change of Northern Hemispheric summer insolation, and the westerlies strengthened and increased the aridity in the QB when the ASM shrank.     

Holocene lake salinity changes in the Wimmera,southeastern Australia,provide evidence for millennial-scale climate variability

Palaeosalinity records for groundwater-influenced lakes in the southwest Murray Basin were constructed from an ostracod-based, weighted-averaging transfer function, supplemented with evidence from Campylodiscus clypeus (diatom), charophyte oogonia, Coxiella striata (gastropod), Elphidium sp. (foraminifera), Daphniopsis sp. ephippia (Cladocera), and brine shrimp (Parartemia zietziana) faecal pellets, the δ¹⁸O of ostracods, and > 130 μm quartz sand counts. The chronology is based on optically stimulated luminescence and calibrated radiocarbon ages. Relatively wet conditions are marked by lower salinities between 9600 yr and 5700 yr ago, but mutually exclusive high- and low-salinity ostracod communities suggest substantial variability in effective precipitation in the early Holocene. A drier climate was firmly in place by 4500 yr and is marked at the groundwater-dominated NW Jacka Lake by an increase in aeolian quartz and, at Jacka Lake, by a switch from surface-water to groundwater dominance. Short-lived, low-salinity events at 8800, 7200, 5900, 4800, 2400, 1300 and 400 yr are similar in timing and number to those recorded on Australia's southern continental shelf, and globally, and provide evidence for the existence of the ~ 1500-yr cycle in mainland southern Australia. We surmise that these are cool events associated with periodic equatorward shifts in the westerly wind circulation.     

Contemporary lead concentration and stable lead isotope ratio distribution in forest moss across the Czech Republic

Lead concentrations and stable lead isotopes (²⁰⁴Pb, ²⁰⁶Pb, ²⁰⁷Pb, ²⁰⁸Pb) were measured in forest moss samples (Pleurozium schreberi or Scleropodium purum) collected at 273 sites across the Czech Republic during 2010. Continuously decreasing median Pb concentrations in moss were documented over the last two decades: 1995: 11 mg/kg, 2000: 5.66 mg/kg, 2005: 4.94 mg/kg and 2010: 2.85 mg/kg. Several local anomalies have decreased in scale, the overall regional distribution patterns remained, however, the same. The regional Pb isotope ratio distributions show that the ratios show little variation for a large central part of the country and provide the large-scale background isotope ratios for the Czech Republic of about ²⁰⁴Pb/²⁰⁶Pb = 0.0550, ²⁰⁶Pb/²⁰⁷Pb = 1.167, ²⁰⁶Pb/²⁰⁸Pb = 0.478 and ²⁰⁷Pb/²⁰⁸Pb = 0.409 for 2010. This background Pb isotope ratio signal in moss has been locally (900–7500 km²) modified by specific Pb isotopic ratio signals caused by deposition of Pb emissions from known local anthropogenic Pb emission sources, such as industrial combustion of local coal, and a variety of industrial enterprises (metallurgical, engineering and glass works). At some sites where mining of uranium and polymetallic ores took place the moss samples show also a locally specific Pb isotope signal. The in terms of area affected largest deviations in the Pb-isotope ratios, e.g., in the Bohemian Massif, may be due to the input of geogenic dust.     

A late Pleistocene glacial chronology from the Kitschi-Kurumdu Valley,Tien Shan (Kyrgyzstan), based on 10Be surface exposure dating

Surface exposure dating has become a helpful tool for establishing numeric glacial chronologies, particularly in arid high-mountain regions where radiocarbon dating is challenging due to limited availability of organic material. This study presents 13 new ¹⁰Be surface exposure ages from the Kitschi-Kurumdu Valley in the At Bashi Range, Tien Shan. Three moraines were dated to ~ 15, 21 and > 56 ka, respectively, and corroborate previous findings that glacial extents in the Tien Shan during Marine Oxygen Isotope Stage (MIS) 2 were limited compared to MIS 4. This likely documents increasingly arid conditions in Central Asia during the last glacial cycle. Morphological evidence in the Kitschi-Kurumdu Valley and a detailed review of existing numeric glacial chronologies from the Tien Shan indicate that remnants of the penultimate glaciation (MIS 6) are preserved, whereas evidence for MIS 5 glacier advances remains equivocal. Reviewed and recalculated exposure ages from the Pamir mountains, on the other hand, reveal extensive MIS 5 glacial extents that may indicate increased monsoonal precipitation. The preservation of MIS 3 moraines in the Tien Shan and the southern Pamir does not require any monsoonal influence and can be explained alternatively with increased precipitation via the westerlies.     

Relict sand wedges in southern Patagonia and their stratigraphic and paleo-environmental significance

Relict sand wedges are ubiquitous in southern Patagonia. At six sites we conducted detailed investigations of stratigraphy, soils, and wedge frequency and characteristics. Some sections contain four or more buried horizons with casts. The cryogenic features are dominantly relict sand wedges with an average depth, maximum apparent width, minimum apparent width, and H/W of 78, 39, 3.8, and 2.9 cm, respectively. The host materials are fine-textured (silt loam, silty clay loam, clay loam) till and the infillings are aeolian sand. The soils are primarily Calciargidic Argixerolls that bear a legacy of climate change. Whereas the sand wedges formed during very cold (?4 to ?8 °C or colder) and dry (ca. ≤100 mm precipitation/yr) glacial periods, petrocalcic horizons from calcium carbonate contributed by dustfall formed during warmer (7 °C or warmer) and moister (≥250 mm/yr) interglacial periods. The paleo-argillic (Bt) horizons reflect unusually moist interglacial events where the mean annual precipitation may have been 400 mm/yr. Permafrost was nearly continuous in southern Patagonia during the Illinoian glacial stage (ca. 200 ka), the early to mid-Pleistocene (ca. 800–500 ka), and on two occasions during the early Pleistocene (ca. 1.0–1.1 Ma).     

Copper and iron isotope fractionation in mine tailings at the Laver and Kristineberg mines,northern Sweden

Previous research has shown that Cu and Fe isotopes are fractionated by dissolution and precipitation reactions driven by changing redox conditions. In this study, Cu isotope composition (⁶⁵Cu/⁶³Cu ratios) was studied in profiles through sulphide-bearing tailings at the former Cu mine at Laver and in a pilot-scale test cell at the Kristineberg mine, both in northern Sweden. The profile at Kristineberg was also analysed for Fe isotope composition (⁵⁶Fe/⁵⁴Fe ratios). At both sites sulphide oxidation resulted in an enrichment of the lighter Cu isotope in the oxidised zone of the tailings compared to the original isotope ratio, probably due to preferential losses of the heavier Cu isotope into the liquid phase during oxidation of sulphides. In a zone with secondary enrichment of Cu, located just below the oxidation front at Laver, δ⁶⁵Cu (compared to ERM-AE633) was as low as −4.35 ± 0.02‰, which can be compared to the original value of 1.31 ± 0.03‰ in the unoxidised tailings. Precipitation of covellite in the secondary Cu enrichment zone explains this fractionation. The Fe isotopic composition in the Kristineberg profile is similar in the oxidised zone and in the unoxidised zone, with average δ⁵⁶Fe values (relative to the IRMM-014) of −0.58 ± 0.06‰ and −0.49 ± 0.05‰, respectively. At the well-defined oxidation front, δ⁵⁶Fe was less negative, −0.24 ± 0.01‰. Processes such as Fe(II)–Fe(III) equilibrium and precipitation of Fe-(oxy)hydroxides at the oxidation front are assumed to cause this Fe isotope fractionation. This field study provides additional support for the importance of redox processes for the isotopic composition of Cu and Fe in natural systems.     

Interactions between climate and vegetation during the Lateglacial period as recorded by lake and mire sediment archives in Northern Italy and Southern Switzerland

We reconstruct the vegetational history of the southern side of the Alps at 18,000–10,000 cal yr BP using previous and new AMS-dated stratigraphic records of pollen, stomata, and macrofossils. To address potential effects of climatic change on vegetation, we compare our results with independent paleoclimatic series (e.g. isotope and chironomid records from the Alps and the Alpine forelands). The period before 16,000 cal yr BP is documented only at the lowland sites. The previous studies used for comparison with our new Palughetto record, however, shows that Alpine deglaciation must have started before 18,000–17,500 cal yr BP south of the Alps and that deglaciated sites were colonized by open woods and shrublands (Juniperus, tree Betula, Larix, Pinus cembra) at ca 17,500 cal yr BP. The vegetational history of a new site (Palughetto, 1040 m a.s.l.) is consistent with that of previous investigations in the study region. Our results show three conspicuous vegetational shifts delimited by statistically significant pollen zones, at ca 14,800–14,400, 13,300–12,800 and 11,600–11,200 cal yr BP. At sites situated above 1000 m a.s.l. (e.g. Palughetto, Pian di Gembro) forests expanded in alpine environments at ca 14,500 cal yr BP (onset of Bølling period, GI-1 in the Greenland ice record). At the same time, rather closed treeline communities of the lowlands were replaced by dense stands of Pinus sylvestris and Betula. These early forests and shrublands consisted of Larix, P. cembra, Juniperus, P. sylvestris, Pinus mugo, and Betula, and had become established at ca 16,000 cal yr BP, probably in response to a temperature increase. If combined with other records from the Southern Alps, our data suggest that treeline ascended by ca 800–1000 m in a few centuries at most, probably as a consequence of climatic warming at the beginning of the Bølling period. At 13,100–12,800 cal yr BP the onset of a long-lasting decline of P. sylvestris was accompanied by the expansion of Quercus and other thermophilous tree taxa below ca 600 m a.s.l. This vegetational change was probably induced by a shift to warmer climatic conditions before the onset of the Younger Dryas, as indicated by independent paleoclimatic records. Only a few centuries later, at ca 12,700–12,500 cal yr BP, an expansion of herbaceous taxa occurred in the lowlands as well as at higher altitudes, documenting an opening of forested habitats. This change coincided with the beginning of the Younger Dryas cooling (GS-1), which according to the paleoclimatic series (e.g. oxygen isotope series), started at 12,700–12,600 cal yr BP and lasted for about 1000 years. Environments south of the Alps responded markedly to climatic warming at the onset of the Holocene (11,600–11,500 cal yr BP). Thermophilous trees that had declined during the Younger Dryas re-expanded very rapidly in the lowlands and reached the high altitude sites below ca 1500 m a.s.l. within a few centuries at most. Our study implies that the synchronous vegetational changes observed over wide areas were probably a consequence of abrupt climatic shifts at the end of the Last Glacial Maximum (LGM) and during the Lateglacial. We emphasize that important vegetational changes such as the expansion of forests occurred millennia before the onset of similar processes in northwestern and central Europe.