An 11 000‐year record of driftwood delivery to the western Queen Elizabeth Islands,Arctic Canada

Fifty‐six new radiocarbon dates from driftwood (mainly Larix, Picea and Populus spp.) collected from the modern and raised shorelines of Melville and Eglinton islands (western Canadian High Arctic) are presented and compared to other driftwood collections from the Canadian Arctic Archipelago (CAA) and Greenland. By documenting the species (provenance) and spatio‐temporal distribution of driftwood at various sites across the Arctic, regional characterizations of former sea‐ice conditions and changes in Arctic Ocean circulation patterns may be deduced. The earliest postglacial invasion of the Canadian Arctic Archipelago by driftwood is recorded on central Melville Island at c. 11 cal. ka BP, suggesting that the modern circulation pattern of Arctic Ocean surface water southeast through the archipelago was established >1000 years earlier than previously proposed. Throughout most of the Holocene until c. 1.0 cal. ka BP, the rate of driftwood delivery to the western Arctic islands was low (~1 recorded stranding event per 200 years) and intermittent, with the longest break in the record occurring between c. 3.0 and 5.0 cal. ka BP. This 2000‐year hiatus is attributed to a period of colder temperatures causing severe sea‐ice conditions and effectively making the coasts of the western Arctic islands inaccessible. After c. 1.0 cal. ka BP, driftwood incursion increased to maximum Holocene levels (~1 recorded stranding event every 20 years). Driftwood identified to the genus level as Larix that was delivered at this time suggests that the Trans Polar Drift current was regularly in its most southwestern position, related to a dominantly positive Arctic Oscillation mode. The Little Ice Age appears to have had little impact on driftwood entry to the western Canadian Arctic Archipelago, indeed the general abundance in the latest Holocene may record infrequent landfast sea ice.     

The luminescence dating chronology of a deep core from Bosten Lake (NW China) in arid central Asia reveals lake evolution over the last 220 ka

The lacustrine deposits of lakes in arid central Asia (ACA) potentially record palaeoclimatic changes on orbital and suborbital time scales, but such changes are still poorly understood due to the lack of reliable chronologies. Bosten Lake, the largest freshwater inland lake in China, is located in the southern Tianshan Mountains in central ACA. A 51.6‐m‐deep lacustrine succession was retrieved from the lake and 30 samples from the succession were used for luminescence dating to establish a chronology based on multi‐grain quartz OSL and K‐feldspar post‐IR IRSL (pIRIR₂₉₀) dating. Quartz OSL ages were only used for samples from the upper part of the core. The K‐feldspar luminescence characteristics (dose recovery test, anomalous fading test, first IR stimulation temperature plateau test) are satisfactory and from the relationship amongst the quartz OSL, IR₅₀ and pIRIR₂₉₀ doses we infer that the feldspar signals are likely to be well bleached at deposition. Bacon age‐depth modelling was used to derive a chronology spanning the last c. 220 ka. The chronology, lithology and grain‐size proxy record indicate that Bosten Lake formed at least c. 220 ka ago and that lake levels fluctuated frequently thereafter. A stable deep lake occurred at c. 220, 210–180, c. 165, 70–60, 40–30 and 20–5 ka, while shallow levels occurred at c. 215, 180–165, 100–70, 60–40 and 30–20 ka. Bosten Lake levels decreased by at least ~29 m and possibly the lake even dried up between c. 160 and c. 100 ka. We suggest that the water‐level fluctuations in the lakes of ACA may not respond directly to climatic changes and may be affected by a number of complex factors.     

The Lateglacial to early Holocene tephrochronological record from Lake Hämelsee,Germany: a key site within the European tephra framework

Here we present the results of a detailed cryptotephra investigation through the Lateglacial to early Holocene transition, from a new sediment core record obtained from Lake Hämelsee, Germany. Two tephra horizons, the Laacher See Tephra (Eifel Volcanic Field) and the Saksunarvatn Ash (Iceland), have been previously described in this partially varved sediment record, indicating the potential of the location as an important Lateglacial tephrochronological site in northwest Europe. We have identified three further tephra horizons, which we correlate to: the c. 12.1 ka BP Vedde Ash (Iceland), the c. 11 ka BP Ulmener Maar tephra (Eifel Volcanic Field) and the c. 10.8 ka BP Askja‐S tephra (Iceland). Three additional cryptotephra deposits have been found (locally named HÄM_T1616, HÄM_T1470 and HÄM_T1456‐1455), which cannot be correlated to any known eruption at present. Geochemical analysis of the deposits suggests that these cryptotephras most likely have an Icelandic origin. Our discoveries provide age constraints for the new sediment records from Lake Hämelsee and enable direct stratigraphical correlations to be made with other tephra‐bearing sites across Europe. The new tephrostratigraphical record, within a partially varved Lateglacial sediment record, highlights the importance of Lake Hämelsee as a key site within the European tephra lattice.     

Changes in the inflow of saline water into the Bornholm Basin (SW Baltic Sea) during the past 7100 years – evidence from benthic foraminifera record

The Baltic Sea (~393 000 km²) is the largest brackish sea in the world and its hydrographic and environmental conditions are strongly dependent on the frequency of saline water inflows from the North Sea. To improve our understanding of the natural variability of the Baltic Sea ecosystem detailed reconstructions of past saline water inflow changes based on palaeoecological archives are needed. Here we present a high‐resolution study of benthic foraminiferal assemblages accompanied by sediment geochemistry (loss on ignition, total organic carbon) and other microfossil data (ostracods and cladocerans) from a well‐dated 8‐m‐long gravity core taken in the Bornholm Basin. The foraminiferal diversity in the core is low and dominated by species of Elphidium. The benthic foraminiferal faunas in the central Baltic require oxic bottom water conditions and salinities >11–12 PSU. Consequently, shell abundance peaks in the record reflect frequent saline water inflow phases. The first appearance of foraminiferal tests and ostracods in the investigated sediment core is dated to c. 6.9 cal. ka BP and attributed to the first inflows of saline and oxygenated bottom waters into the Bornholm Basin during the Littorina Sea transgression. The transgression terminated the Ancylus Lake phase, reflected in the studied record by abundant cladocerans. High absolute foraminiferal abundances are found within two time intervals: (i) c. 5.5–4.0 cal. ka BP (Holocene Thermal Maximum) and (ii) c. 1.3–0.75 cal. ka BP (Medieval Climate Anomaly). Our data also show three intervals of absent or low saline water inflows: (i) c. 6.5–6.0 cal. ka BP, (ii) c. 3.0–2.3 cal. ka BP and (iii) c. 0.5–0.1 cal. ka BP (Little Ice Age). Our study demonstrates a strong effect of saline and well‐oxygenated water inflows from the Atlantic Ocean on the Baltic Sea ecosystem over millennial time scales, which is linked to the major climate transitions over the last 7 ka.     

A multi‐proxy palaeoenvironmental and geochronological reconstruction of the Saalian‐Eemian‐Weichselian succession at Klein Klütz Höved,NE Germany

Here we present a multi‐proxy investigation of the Klein Klütz Höved (KKH) coastal cliff section in northeastern Germany, involving lithofacies analysis, micromorphology, micropalaeontology, palynology and luminescence dating of quartz and feldspar. We subdivide the local stratigraphy into three depositional phases. (i) Following a Saalian advance (MIS 6) of the Scandinavian Ice Sheet, the penultimate deglaciation (Termination II) at the site occurred between c. 139 and 134 ka, leading to the establishment of a braided river system and lacustrine basins under arctic‐subarctic climate conditions. (ii) In the initial phase of the Eemian interglacial lacustrine deposits were formed, containing warm‐water ostracods and a pollen spectrum indicating gradual expansion of woodlands eventually containing thermophile deciduous forest elements. A correlation of the local pollen assemblages with Eemian reference records from central Europe suggests that fewer than 750 years of the last interglacial period are preserved at KKH. The occurrence of brackish ostracods dates the onset of the Eemian marine transgression at the section at c. 300–750 years after the beginning of the last interglacial period. (iii) Directly above the Eemian record a ~10‐m‐thick sedimentary succession of MIS 2 age was deposited, implying a significant hiatus of c. 90 ka encompassing the time from middle and upper MIS 5e to late MIS 3. During the Late Weichselian, KKH featured a depositional shift from (glacio‐)lacustrine to subglacial to recessional terminoglacial facies, with the first documented Weichselian ice advance post‐dating 20±2 ka. Overall, the KKH section represents an exceptional sedimentary archive for palaeoenvironmental reconstructions, covering the period from the Saalian glaciation and subsequent Termination II to the early Eemian and Late Weichselian. The results refine the existing palaeogeographical and geochronological models of the late Quaternary history in the southwestern Baltic Sea area and allow correlations with other reference records in a wider area.     

Sediment colour reflectance spectroscopy as a proxy for wet/dry cycles at Lake El'gygytgyn,Far East Russia,during Marine Isotope Stages 8 to 12

Marine Isotope Stage 11 has been proposed as an analogue for the present interglacial interval; yet, terrestrial climate records from both this region and time interval are rare. The sediments deposited at Lake El'gygytgyn (67°30′N, 172°5′E) in Far East Russia contain a 3·56 Ma record of climate variability. This study presents a high‐resolution record of sediment colour change from Marine Isotope Stage 8 to 12 (ca 275 to 475 ka) and demonstrates the link between lake catchment processes and climate variability. The hue colour parameter, calculated from data collected via colour reflectance spectroscopy in the visible spectrum (380 to 720 nm), exhibits correspondence with global climate records. Determining the source of sediment colour changes was achieved through detailed mineralogical and sedimentological methods, and linked to colour changes through a series of colour sensitivity tests. Mineralogical data, measured by X‐ray diffraction, reveal fluctuations in concentrations of clay minerals corresponding to colour changes. Further analyses of the clay mineral assemblages show no change in relative clay mineral abundances, yet demonstrate a lake catchment dominated by physical weathering processes. Using measured mineral abundances, reconstructions of sediment colour based on colour reflectance mineral standards link mineral and clay mineral content to overall sediment colour. Colour sensitivity tests demonstrate the ability of iron oxide minerals to stain sediments red. Additionally, colour sensitivity to organic matter content was tested, suggesting that organic content drives variability in the red portion of the spectrum and darkens the overall colour signal. Sediment colour is then ultimately linked to physical weathering of bedrock minerals, with small amounts of chemical weathering producing iron oxides during wet intervals. Fluctuations in the sediment colour reveal a high‐resolution record of wet/dry cycles, and provide new information about wet periods for the Russian Arctic region not yet understood from other lake proxy records.     

Clay mineral variations in Holocene terrestrial sediments from the Indus Basin

We employed X-ray diffraction methods to quantify clay mineral assemblages in the Indus Delta and flood plains since ~ 14 ka, spanning a period of strong climatic change. Assemblages are dominated by smectite and illite, with minor chlorite and kaolinite. Delta sediments integrate clays from across the basin and show increasing smectite input between 13 and 7.5 ka, indicating stronger chemical weathering as the summer monsoon intensified. Changes in clay mineralogy postdate changes in climate by 5–3 ka, reflecting the time needed for new clay minerals to form and be transported to the delta. Samples from the flood plains in Punjab show evidence for increased chemical weathering towards the top of the sections (6–< 4 ka), counter to the trend in the delta, at a time of monsoon weakening. Clay mineral assemblages within sandy flood-plain sediment have higher smectite/(illite + chlorite) values than interbedded mudstones, suggestive of either stronger weathering or more sediment reworking since the Mid Holocene. We show that marine records are not always good proxies for weathering across the entire flood plain. Nonetheless, the delta record likely represents the most reliable record of basin-wide weathering response to climate change.     

Influence of the Laurentide Ice Sheet and relative sea‐level changes on sediment dynamics in the Estuary and Gulf of St. Lawrence since the last deglaciation

Physical properties, grain size, bulk mineralogy, elemental geochemistry and magnetic parameters of three sediment piston cores recovered in the Laurentian Channel from its head to its mouth were investigated to reconstruct changes in detrital sediment provenance and transport related to climate variability since the last deglaciation. The comparison of the detrital proxies indicates the succession of two sedimentary regimes in the Estuary and Gulf of St. Lawrence (EGSL) during the Holocene, which are associated with the melting history of the Laurentide Ice Sheet (LIS) and relative sea‐level changes. During the early Holocene (10–8.5 cal. ka BP), high sedimentation rates together with mineralogical, geochemical and magnetic signatures indicate that sedimentation in the EGSL was mainly controlled by meltwater discharges from the local retreat of the southeastern margin of the LIS on the Canadian Shield. At this time, sediment‐laden meltwater plumes caused the accumulation of fine‐grained sediments in the ice‐distal zones. Since the mid‐Holocene, postglacial movements of the continental crust, related to the withdrawal of the LIS (c. 6 cal. ka BP), have triggered significant variations in relative sea level (RSL) in the EGSL. The significant correlation between the RSL curves and the mineralogical, geochemical, magnetic and grain‐size data suggest that the RSL was the dominant force acting on the sedimentary dynamics of the EGSL during the mid‐to‐late Holocene. Beyond 6 cal. ka BP, characteristic mineralogical, geochemical, magnetic signatures and diffuse spectral reflectance data suggest that the Canadian Maritime Provinces and western Newfoundland coast are the primary sources for detrital sediments in the Gulf of St. Lawrence, with the Canadian Shield acting as a secondary source. Conversely, in the lower St. Lawrence Estuary, detrital sediments are mainly supplied by the Canadian Shield province. Finally, our results suggest that the modern sedimentation regime in the EGSL was established during the mid‐Holocene.     

Climate and environment in southwest Sweden 15.5–11.3 cal. ka BP

Lake sedimentary records that allow documentation of the distinct climatic and environmental shifts during the early part of the Last Termination are scarce for northern Europe. This multi‐proxy study of the sediments of Atteköpsmosse, southwest Sweden, therefore fills an important gap and provides detailed information regarding past hydroclimatic conditions and local environmental responses to climatic shifts. Lake infilling started c. 15.5 cal. ka BP, but low aquatic productivity, cold summer lake water temperatures, unstable catchments, and scarce herb and shrub vegetation prevailed until c. 14.7–14.5 cal. ka BP. Inflow of warmer air masses and higher July air temperatures favoured a rise in aquatic productivity and lake water summer temperatures, and the establishment of a diverse herb, shrub and dwarf shrub vegetation, which also included tree birch c. 14.5 cal. ka BP. Freshening of the moisture source region c. 13.7–13.6 cal. ka BP does not seem to have had a large impact on the ancient lake and its catchment, as lake aquatic productivity increased further and lake water summer temperatures and minimum mean July air temperatures remained around 12–14 °C. In contrast, further freshening of the moisture source region c. 13 cal. ka BP triggered a decrease in lake productivity, drier conditions and lower lake water summer temperatures. Macroscopic finds of tree Betula and Pinus sylvestris at 13–12.8 cal. ka BP demonstrate the presence of these trees in the lake's catchment. The transition into the Holocene (11.6–11.5 cal. ka BP) is marked by a change in chironomid assemblages and by a rise in lake water summer temperatures and aquatic productivity. These changes were followed by the re‐establishment of a diverse aquatic and terrestrial vegetation, including tree birch and Pinus sylvestris at 11.4 cal. ka BP.     

Holocene lake sediments from the Faiyum Oasis in Egypt: a record of environmental and climate change

The Qarun Lake in the Faiyum Oasis (Egypt) provides a unique record of Holocene environmental and climate change in an arid area largely devoid of fossil proxy records. Multiple lithological, palaeontological and geochemical proxies and 32 radiocarbon dates from the 26‐m‐long core FA‐1 provide a time series of the lake's transformation. Our results confirm that a permanent lake appeared in the Holocene at c. 10 cal. ka BP. The finely laminated lake sediments consist of diatomite, in which diatoms and ostracods together with lower concentrations of ions indicate a freshwater environment at the end of the early and middle Holocene. This freshwater supply was closely associated with regular inflows of the Nile water during flood seasons, when the Intertropical Convergence Zone (ITCZ) migrated northwards in Africa, although it has probably never reached the Faiyum Oasis. Local rainfall, possibly connected with a northern atmospheric circulation, may have been important during winter. Several phases in the lake's evolution are recognized, represented by oscillations between deep open freshwater conditions during more humid climate and shallow fresh to brackish water during drier episodes. After a long freshwater phase, the lake setting has become more brackish since c. 6.2 cal. ka BP as indicated by diatoms and increasing contents of evaporite ions in the sediment. This clearly shows that since that time the lake has occasionally become partly desiccated. This is a result of reduced discharge of the Nile. In the late Holocene the lake was mostly brackish and then gradually turned into a saline lake. This natural process was interrupted about 2.3 cal. ka BP when a man‐made canal facilitated water inflow from the Nile. The examined FA‐1 core can be used as a reference age model of climate change in the Holocene and its impact on the development and decline of ancient civilizations in northeastern Africa.     

U‐Th Zircon Dating by Laser Ablation Single Collector Inductively Coupled Plasma‐Mass Spectrometry (LA‐ICP‐MS)

Zircon crystals in the age range of ca. 10–300 ka can be dated by ²³⁰Th/²³⁸U (U‐Th) disequilibrium methods because of the strong fractionation between Th and U during crystallisation of zircon from melts. Laser ablation inductively coupled plasma‐mass spectrometry (LA‐ICP‐MS) analysis of nine commonly used reference zircons (at secular equilibrium) and a synthetic zircon indicates that corrections for abundance sensitivity and dizirconium trioxide molecular ions (Zr₂O₃⁺) are critical for reliable determination of ²³⁰Th abundances in zircon. When corrected for abundance sensitivity and interferences, mean activity ratios of (²³⁰Th)/(²³⁸U) for nine reference zircons analysed on five different days averaged 0.995 ± 0.023 (95% confidence weighted by data‐point uncertainty only, MSWD = 1.6; n = 9), consistent with their U‐Pb ages > 4 Ma that imply equilibrium for all intermediate daughter isotopes (including ²³⁰Th) within the ²³⁸U decay chain. U‐Th zircon ages generated by LA‐ICP‐MS without mitigating (e.g., by high mass resolution) or correcting for abundance sensitivity and molecular interferences on ²³⁰Th are potentially unreliable. To validate the applicability of LA‐ICP‐MS to this dating method, we acquired data from three late Quaternary volcanic units: the 41 ka Campanian Ignimbrite (plutonic clasts), the 161 ka Kos Plateau Tuff (juvenile clasts) and the 12 ka Puy de Dôme trachyte lava (all eruption ages by Ar/Ar, with zircon U‐Th ages being of equal or slightly older). A comparison of the corrected LA‐ICP‐MS results with previously published secondary ion mass spectrometry (SIMS) data for these rocks shows comparable ages with equivalent precision for LA‐ICP‐MS and SIMS, but much shorter analysis durations (~ 2 min vs. ~ 15 min) per spot with LA‐ICP‐MS and much simpler sample preparation. Previously undated zircons from the Yali eruption (Kos‐Nisyros volcanic centre, Greece) were analysed using this method. This yielded a large age spread (~ 45 to > 300 ka), suggesting significant antecryst recycling. The youngest zircon age (~ 45 ± 10 ka) provides a reasonable maximum estimate for the eruption age, in agreement with the previously published age using oxygen isotope stratigraphy (~ 31 ka).     

Deglaciation history of Lake Ladoga (northwestern Russia) based on varved sediments

Lake Ladoga in northwestern Russia is Europe's largest lake. The postglacial history of the Ladoga basin is for the first time documented continuously with high temporal resolution in the upper 13.3 m of a sediment core (Co1309) from the northwestern part of the lake. We applied a multiproxy approach including radiographic imaging, (bio‐)geochemical and granulometric analyses. Age control was established combining radiocarbon dating with varve chronology, the latter anchored to a correlated radiocarbon age from a lake close by. The age‐depth model reveals the onset of glacial varve sedimentation at 13 910±140 cal. a BP, when Lake Ladoga was part of the Baltic Ice Lake. Linear extrapolation of published retreat rates of the Scandinavian Ice Sheet provides a formation age of the Luga moraine close to Lake Ladoga's southern shore of 14.5–15.9 cal. ka BP, older than previously assumed. Varve sedimentation covers the Bølling/Allerød interstadial, the Younger Dryas stadial and the Early Holocene. Varve‐thickness variations, conjoined with grain‐size and geochemical variations, inform about the relative position of the Scandinavian Ice Sheet and the climate during the deglaciation phase. The upper limit of the varved succession marks the change from glaciolacustrine to normal lacustrine sedimentation and post‐dates the drainage of the Baltic Ice Lake as well as the formation of the Salpausselkä II moraine north of Lake Ladoga, by c. 250 years. The Holocene sediment record is divided into three periods in the following order: (i) a lower transition zone between the Holocene boundary and c. 9.5 cal. ka BP, characterized by mostly massive sediments with low organic content, (ii) a phase with increased organic content from c. 9.5 to 4.5 cal. ka BP corresponding to the Holocene Thermal Maximum, and (iii) a phase with relatively stable sedimentation in a lacustrine environment from c. 4.5 cal. ka BP until present.     

Hässeldala – a key site for Last Termination climate events in northern Europe

The Last Termination (19 000–11 000 a BP) with its rapid and distinct climate shifts provides a perfect laboratory to study the nature and regional impact of climate variability. The sedimentary succession from the ancient lake at Hässeldala Port in southern Sweden with its distinct Lateglacial/early Holocene stratigraphy (>14.1–9.5 cal. ka BP) is one of the few chronologically well‐constrained, multi‐proxy sites in Europe that capture a variety of local and regional climatic and environmental signals. Here we present Hässeldala's multi‐proxy records (lithology, geochemistry, pollen, diatoms, chironomids, biomarkers, hydrogen isotopes) in a refined age model and place the observed changes in lake status, catchment vegetation, summer temperatures and hydroclimate in a wider regional context. Reconstructed mean July temperatures increased between c. 14.1 and c. 13.1 cal. ka BP and subsequently declined. This latter cooling coincided with drier hydroclimatic conditions that were probably associated with a freshening of the Nordic Seas and started a few hundred years before the onset of Greenland Stadial 1 (c. 12.9 cal. ka BP). Our proxies suggest a further shift towards colder and drier conditions as late as c. 12.7 cal. ka BP, which was followed by the establishment of a stadial climate regime (c. 12.5–11.8 cal. ka BP). The onset of warmer and wetter conditions preceded the Holocene warming over Greenland by c. 200 years. Hässeldala's proxies thus highlight the complexity of environmental and hydrological responses across abrupt climate transitions in northern Europe.     

The timing and consequences of the blockage of the Humber Gap by the last British−Irish Ice Sheet

The eastern England terrestrial glacial sequences are critical to the spatial and temporal reconstruction of the last British−Irish Ice sheet (BIIS). Understanding glacial behaviour in the area of the Humber Gap is key as its blockage by ice created extensive proglacial lakes. This paper maps the glacial geomorphology of the Humber Gap region to establish for the first time the extent and thickness of the North Sea Lobe (NSL) of the BIIS. Findings establish the westerly maximal limit of the NSL. Ten new luminescence ages from across the region show the initial Skipsea Till advance to the maximal limits occurred regionally at c. 21.6 ka (Stage 1) and retreated off‐shore c. 18 ka (Stage 2). Punctuated retreat is evident in the south of the region whilst to the immediate north retreat was initially rapid before a series of near synchronous ice advances (including the Withernsea Till advance) occurred at c. 16.8 ka (Stage 3). Full withdrawal of BIIS ice occurred prior to c. 15 ka (Stage 4). Geomorphic mapping and stratigraphy confirms the existence of a proto Lake Humber prior to Stage 1, which persisted to Stage 3 expanding eastward as the NSL ice retreated. It appears that proglacial lakes formed wherever the NSL encountered low topography and reverse gradients during both phases of both advance and retreat. These lakes may in part help explain the dynamism of parts of the NSL, as they initiated ice draw down and associated streaming/surging. The above record of ice‐dammed lakes provides an analogue for now off‐shore parts of the BIIS where it advanced as a number of asynchronous lowland lobes.     

Sedimentary evidence of deglacial megafloods in the northern Gulf of Mexico (Pigmy Basin)

Cored sediments from the Pigmy Basin, northern Gulf of Mexico, were analyzed in order to better constrain late deglacial and early Holocene paleoenvironmental and sedimentary changes in response to North American climate evolution. Mineralogical and geochemical proxies indicate the succession of two sedimentary regimes: dominantly detrital during the deglaciation (15–12.9 cal ka BP) whereas biogenic contribution relatively increased later on during the Younger Dryas and early Holocene (12.9 and 10 cal ka BP). Geochemical data reveal that the deglacial record mainly reflects variations of terrigenous supply via the Mississippi River rather than modifications of redox conditions in the basin. Specific variations of almost all the parameters measured in this paper are synchronous with the main deglacial meltwater episode (Meltwater Spike) described or modeled in previous marine or continental studies. During this episode, most parameters display “stair-step-like” – pattern variations highlighting three successive steps within the main meltwater flow. Variations in grain-size and clay mineral assemblage recorded in the Pigmy Basin indicate that the erosional regime was very strong on land during the first part of the Meltwater Spike, and then milder, inducing more subtle modifications in the sedimentary regime in this part of the Gulf. Specific geochemical and mineralogical signatures (notably, clay minerals and trace metal geochemistry) pinpoint a dominant origin from NW North America for detrital particles reflecting meltwater outflow from the south-western Laurentide Ice Sheet (LIS) margin during the most intense freshwater discharge. The observed decrease of the sedimentation rate from about 200 to 25 cm/ka at ca 12.9 ka evidenced a drastic decrease of erosional processes during late phase of discharge, consistently with the hypotheses of major reduction of meltwater flow. The major modification at 12.9 cal ka BP is interpreted to result from both modifications of the main Mississippi fluvial regime due to eastward and northward rerouting of meltwater flow at the onset of the Younger Dryas, and the increase of sea-surface temperature linked to insolation. Finally, slight grain-size modifications suggest that some freshwater discharges may have episodically reached the Gulf of Mexico after the Younger Dryas reflecting possible small adjustments of the postglacial hydrological regime.     

Earliest Holocene deglaciation of the central Uummannaq Fjord system,West Greenland

Uummannaq Fjord, West Greenland, held the Uummannaq Ice Stream system that drained an estimated ~6% of the Greenland Ice Sheet (GrIS) during the Last Glacial Maximum. Published ages for the final deglaciation in Uummannaq Fjord vary from as early as c. 9.8 ka to as late as c. 5.3 ka. Assessing this variability requires additional chronological controls to improve the deglaciation history of central West Greenland. Here, we combine ¹⁴C dating of lake sediment cores with cosmogenic ¹⁰Be exposure dating at sites adjacent to the present GrIS margin in the central‐inland sector of the Uummannaq Fjord system. We find that ice retreated to or within the present GrIS margin at 10.8±0.2 ka (n = 6). Although this ‘final deglaciation’ to or within the present GrIS margin across the Uummannaq Fjord system varies from c. 10.8 to 5.3 ka, all chronologies indicate collapse from the continental shelf to the inner fjords at c. 11.0 ka, which occurred at a net retreat rate of 300–1100 m a⁻¹. The Uummannaq Fjord system deglaciated c. 1000 years earlier than the major fjord system to the south, Disko Bugt. However, similarly rapid retreat rates of the two palaeo‐ice stream systems suggest that their collapse may have been aided by high calving rates. The asynchronous deglaciation of the GrIS throughout the Uummannaq Fjord system probably relates to the influence of varying fjord geometry on marine glacier behaviour.     

Vegetation and climate changes in northwestern Russia during the Lateglacial and Holocene inferred from the Lake Ladoga pollen record

The new pollen record from the upper 12.75 m of a sediment core obtained in Lake Ladoga documents regional vegetation and climate changes in northwestern Russia over the last 13.9 cal. ka. The Lateglacial chronostratigraphy is based on varve chronology, while the Holocene stratigraphy is based on AMS ¹⁴C and OSL dates, supported by comparison with regional pollen records. During the Lateglacial (c. 13.9–11.2 cal. ka BP), the Lake Ladoga region experienced several climatic fluctuations as reflected in vegetation changes. Shrub and grass communities dominated between c. 13.9 and 13.2 cal. ka BP. The increase in Picea pollen at c. 13.2 cal. ka BP probably reflects the appearance of spruce in the southern Ladoga region at the beginning of the Allerød interstadial. After c. 12.6 cal. ka BP, the Younger Dryas cooling caused a significant decrease in spruce and increase in Artemisia with other herbs, indicative of tundra‐ and steppe‐like vegetation. A sharp transition from tundra‐steppe habitats to sparse birch forests characterizes the onset of Holocene warming c. 11.2 cal. ka BP. Pine forests dominated in the region from c. 9.0 to 8.1 cal. ka BP. The most favourable climatic conditions for deciduous broad‐leaved taxa existed between c. 8.1 and 5.5 cal. ka BP. Alder experiences an abrupt increase in the local vegetation c. 7.8 cal. ka BP. The decrease in tree pollen taxa (especially Picea) and the increase in herbs (mainly Poaceae) probably reflect human activity during the last 2.2 cal. ka. Pine forests have dominated the region since that time. Secale and other Cerealia pollen as well as ruderal herbs are permanently recorded since c. 0.8 cal. ka BP.     

Late Quaternary loess deposition in the southern Chaiwopu Basin of the northern Chinese Tian Shan foreland and its palaeoclimatic implications

The piedmont aeolian sediment in Central Asia is has been widely used for Quaternary palaeoclimatic reconstructions. Here we present detailed sedimentological and rock magnetic investigations on 188 samples from the ~9.4‐m‐thick Urumqi River section (URS) in the southern Chaiwopu Basin of the northern Chinese Tian Shan foreland. Optically stimulated luminescence (OSL) dating constrains the time‐span of the URS loess sedimentation from c. 28 to c. 6.8 ka. This chronology implies that the onset of the URS loess sedimentation is approximately synchronous with the Shangwangfeng Glaciation (MIS 2) in the headwaters of the Urumqi River. Analyses of sediment grain size and rock magnetic parameters indicate that sediment grain‐size composition controls magnetic properties of the URS loess, i.e. the wind intensity model, distinct from the pedogenic model interpreting the variations in magnetic properties of the loess in the Chinese Loess Plateau (CLP). Overall, the variations in sediment grain size and magnetic properties throughout the URS indicate that the present study area was dominated by a climate of strengthened wind associated with gradually intensified aridity during the latest Pleistocene. In contrast, the intensity of aridity and coldness during the early Holocene gradually became relatively weakened.     

Postglacial vegetation community change over an elevational gradient on the western Kenai Peninsula,Alaska: pollen records from Sunken Island and Choquette Lakes

The Kenai Peninsula of south‐central Alaska is a region of high topographic diversity with a complex glacial history. The sedimentary record of two small lakes [Sunken Island (SIL; 76 m a.s.l.) in the Kenai Lowlands; Choquette (CL; 527 m a.s.l.) in the Caribou Hills upland] exemplifies the postglacial development of the conifer–hardwood forest over an elevational range there. A herb–shrub tundra was established at both sites after deglaciation. By ~10.7 ka, poplar (Populus sp.) and alder (Alnus) dominated the lowland forest, while alder with minor poplar occurred at the upland site. Lake levels lower than today occurred during the early Holocene until ~8 ka. Subsequently at SIL, the near‐modern Kenai birch (Betula kenaica) – white spruce (Picea glauca) forest maintained prominence throughout the Holocene. However, at CL, alder dominated with dwarf birch and other subshrubs; small amounts of white spruce arrived ~5.2 ka. Black spruce (Picea mariana) grew around SIL by ~4 ka, but never gained prominence at CL. Fire, a prominent agent of disturbance in the Kenai Lowlands since ~8 ka, was essentially absent at the hardwood‐dominated upland site before ~6 ka, and rare thereafter. This suggests an important link between fire and spruce in Kenai forests.