Younger Dryas Research Articles

The Late Palaeolithic in Toruń Basin in the light of the latest research in Brzoza, Site 50

Abstract This paper The data from the article was presented by the author during 16th SKAM Lithic Workshop (“Fossil Directeur”. A Phenomenon over Time and Space), 21–23 October 2019, Nitra, Slovak Republic, presentation: The Late Palaeolithic in Toruń Basin in the light of the latest research in Brzoza, site 50 (poster session). presents the preliminary findings related to the excavations in Brzoza site 50, commune Wielka Nieszawka, Kuyavian-Pomeranian Voivodeship (Poland). The Late Palaeolithic site complex in Brzoza – until the end of 1990s known as Toruń-Rudak – is located it Toruń Basin (Poland), in the grounds of a military shooting range on the left bank of Vistula south of the city. According to the Kuyavian-Pomeranian Voivodeship Monuments Conservator the whole complex was defined as one, site no. 50. Rescue excavations in Brzoza in years 2015–2018 were conducted by the District Museum in Toruń. In total 276 m2 were excavated, resulting in documentation of over 11 000 flint products. The research was funded from the Kuyavian-Pomeranian Voivode budget via the Kuyavian-Pomeranian Voivodeship Monuments Conservator and the District Museum in Toruń. The research consisted of archaeological exploration at the remains of the dune embankment, to locate and document undisturbed (in situ) cultural features (flint concentrations). In order to capture the stratigraphic situation in the vicinity of the planned research excavations and to locate the cultural layer with the flint materials linked to the Late Palaeolithic surveys were conducted by means of drillings. The following specialist examinations and consultations were carried out: geological and geomorphological documentation; analyzes of the geographical environment and pedostratigraphy of the research area; from selected profiles soil samples were taken for TL and OSL method analyses. Against the background of other well-known sites with tanged points in northern Poland, the area under study stands out both in terms of the number of flint products obtained and the documented flint concentrations. It must be emphasized that the context of new flint concentrations discovered in Brzoza in the years 2015–2018 is different than that of earlier investigations. Flint products were discovered in a preserved planigraphic and stratigraphic layout; not on a secondary deposit, as was the case, among others in the 1970s. New concentrations discovered in 2015–2018 are related to the Late Palaeolithic technocomplex with tanged points. Amongst flint tools there are elements typologically characteristic to Ahrensburg and Swiderian culture, and individual finds that can be associated with Bromme assemblages. At the present stage of research the acquired flint materials can be linked to the Late Palaeolithic communities present in the area presumably in the younger Dryas. Brzoza site complex occupies an important place in the research of the Late Palaeolithic of northern Poland.

From land to sea: provenance, composition, and preservation of organic matter in a marine sediment record from the North‐East Greenland shelf spanning the Younger Dryas–Holocene

The organic matter content of marine sediments is often used to infer past changes in ocean conditions. However, the organic carbon pool preserved in coastal sediments is a complex mixture derived from different sources and may not reflect in situ processes. In this study, we combine taxonomic identification of reworked palynomorphs with pyrolysis organic geochemistry and reflected‐light organic petrographic microscopy to investigate the provenance, composition and preservation of organic matter in a marine sediment core retrieved from the NE Greenland shelf. Our study reveals continuous yet variable input of land‐derived organic carbon to the marine environment throughout the late Younger Dryas–Holocene, with the highest input of inert carbon in the late Younger Dryas. Although the sediments contain some recent marine palynomorphs, there is no other evidence of fresh marine organic carbon. In contrast, our results indicate that these shelf sediments represent a significant sink of recycled organic carbon. The results of pyrolysis geochemistry revealed that ~90% of the total organic carbon in the sediments is inert. The organic petrography analyses revealed that >70–84% of the organic carbon in the sediment core is terrigenous. Reworked dinoflagellate cysts showed a continuous provenance of Cretaceous land‐derived material, most likely from the nearby Clavering Island. Our study points to the importance of constraining the organic matter origin, composition and preservation in marine sediments to achieve more accurate palaeoenvironmental reconstructions based on organic proxies.

High-northern-latitude forcing modulated fluvial‒aeolian interplay during the Last Glacial Period in the Mu Us Desert, northern central China

Substantial stratigraphic evidence from the Late Quaternary at orbital- and millennial‒scales indicates that the formation and evolution of aeolian‒sand landscapes results from the interaction between regional aeolian and fluvial‒lacustrine activity. In many deserts (sandy lands) across the planet, fluvial‒aeolian interplay at the glacial‒interglacial scale since the Late Quaternary has been responsive to monsoonal precipitation, and linked to atmospheric CO2 and periodic variations in insolation. However, the patterns of fluvial‒aeolian interplay and their relationship with climate change are not always consistent over a given timescale during the Late Pleistocene. The paucity of studies on fluvial‒aeolian interplay in the Mu Us Desert (MUD) during the Last Glacial Period (LGP) hinders our understanding of the relationships between the dynamics of aeolian and fluvial‒lacustrine landscapes and their drivers. Here, based on a comprehensive field survey and stratigraphic dating of a typical fluvial‒aeolian sequence in the MUD, we synthesized the chronology of fluvial‒lacustrine and aeolian strata during the LGP. Our results show that extensive development of a fluvial‒lacustrine environment in the MUD during the LG mainly occurred during the late Last Glacial Maximum (LGMa, 20.1–18.4 ka BP) and Bølling/Allerød interstadial (14.8–12.6 ka BP), while thicker aeolian sands extensively accumulated during the Heinrich Stadial 2, Heinrich Stadial 1, and Younger Dryas periods. However, the development of fluvial‒lacustrine environments showed considerable spatial heterogeneity, mainly occurring on the southern and eastern margins of the desert, while they were extremely rare in the central and western parts of the desert owing to strong wind erosion. Comparisons with other high-resolution geological records from the Asian monsoon region reveal that the fluvial‒aeolian interplay in the MUD during the LGP was highly consistent with the evolution pattern of the East Asian summer monsoon (EASM) on the millennial‒centennial scale, and indicate that the development of fluvial‒lacustrine environments was mainly controlled by an increase in monsoonal precipitation during strengthening of the EASM. Consistency with other broad changes at high latitudes in the Northern Hemisphere suggests that fluvial‒aeolian interplay during the LGP in northern Chinese deserts, as represented by the MUD, was mainly controlled by changes in high-northern-latitude ice volume and the Atlantic Meridional Overturning Circulation.

A world of reindeer: A technological and functional reassessment of the Last Glacial Maximum osseous industry from Cotu Miculinți (northeastern Romania)

Processing of osseous materials was an important component of the repertoire of technological innovations throughout the Palaeolithic. The study of hard animal materials assemblages therefore provides crucial information regarding hominin adaptational ranges and cultural evolution. In contrast to the wide array of studies published on this topic in western and central Europe, the Palaeolithic osseous industries from Romania received comparatively limited attention. The organic industry recovered from Cotu Miculinți, a Late Glacial Maximum (LGM) site located in the Prut Valley (northeastern Romania), provides a case at point. The present study proposes a throughout reassessment of the collection of osseous artifacts from this site, covering several key aspects – raw materials, chaîne opératoire, and the functionality of the assemblage – in an attempt of setting the site’s osseous industry into the wider context of LGM cultural adaptations in the area east of the Carpathians.The results of our analysis reveal an assemblage predominantly made of reindeer antler and document a standardization of the technical transformation scheme, by use of both segmentation and extraction. This resulted in the production of two types of blanks: segmentation produced massive pieces that were transformed into hammers or perforated batons, and extraction by grooving led to standardized rods on flat blanks used to produce barbed points or smoothers. The finished pieces were used in domestic activities (processing of hides, bark, and wood) and for hunting. The assemblage of osseous artifacts from Cotu Miculinți displays many features in common with contemporaneous sites in the area, in particular Cosăuți (Moldova), which is strongly indicative for a similar cultural and adaptive background.

Climate Induced Thermocline Aging and Ventilation in the Eastern Atlantic Over the Last 32,000 Years

AbstractThe radiocarbon analysis of uranium‐thorium‐dated cold‐water corals (CWCs) provides an excellent opportunity for qualitative reconstruction of past ocean circulation and water mass aging. While mid‐depth water mass aging has been studied in the Atlantic Ocean, the evolution of the thermocline is still largely unknown. Here we present a combined 14C and 230Th/U age record obtained from thermocline dwelling CWCs at various sites in the eastern Atlantic Ocean, with intermittently centennial resolution over the last 32 ka. Shallow dwelling CWCs off Angola, located in the South Atlantic, infer a link between the mid‐depth equatorial Atlantic and Southern Ocean. They confirm a 14C drawdown during the Last Glacial Maximum (LGM) and advocate for a consistent Southern Hemisphere radiocarbon aging of upper thermocline waters, as well as strong depth gradients and high variability. Direct comparison with 14C simulations carried out with an Ocean General Circulation Model yield good agreement for Angola. In contrast, the North Atlantic thermocline shows well‐ventilated water with strong variations near the position of today's Azores Front (AF), neither of which are captured by the model. During the Bølling‐Allerød, we confirm the important role of the AF in separating North and South Atlantic thermocline waters and provide further evidence of a 500 year long deep convection interruption within the Younger Dryas (YD). We conclude that the North and South Atlantic thermocline waters were separately acting carbon reservoirs during the LGM and subsequent deglaciation until the modern circulation was established during the YD.

High-resolution record of Paleoclimate during the late Quarternary, recovered from Con Moong cave - North Vietnam

To clarify the paleoclimatic events in Northern Vietnam during the Late Quaternary, 132 Con Moong - Thanh Hoa cave sediment samples were collected to analyze magnetic susceptibility (χ), δ18O, and δ13C. Based on the tendency in the value of χ Con Moong's sediment, 14 climate zones that change continuously from warm to cold were identified. These climate zones also correspond to the changing trend of δ18O and δ13C. The period of 14 magnetic zones is referenced from the extrapolation of four 14C data. These alternating cold-warm χ sequences correspond to the Composite Reference Section (CRS) developed in Southern Europe from a χ zonation of multiple caves. The paleoclimate characteristics, including the Heinrich H2 and H1 climate events, the Bølling/Allerød, and Younger Dryas warm-cold events, were elucidated for Northern Viet Nam from ~28.000 to ~10.000 yr BP.

Vegetation and climate dynamics at the dawn of human settlement: multiproxy palaeoenvironmental evidence from the Hashilan Wetland, western Iran

ABSTRACTThe scarcity of high‐resolution palaeoclimate records from the interior of West Asia has limited our understanding of the mechanisms of past climate change and their potential impacts on early human societies of the Eastern Fertile Crescent. Here, we present a multiproxy sedimentological, geochemical and palynological record from the Hashilan Wetland in the central Zagros Mountains, spanning the time interval from 22 to 2.2 kcal bp. Our results indicate a cold, dry climate for the last deglaciation (22 to 10 kcal bp) with amplified aridity during the Last Glacial Maximum, Heinrich Stadial 1, the Younger Dryas and the 8.2 and 3.2 ka events. The Early Holocene (11.6 to 7.8 kcal bp) is characterised by prolonged dry summers, frequent spring/summer dust storms and restricted oak woodlands that gradually expanded as summers shortened toward the second half of the Holocene (<6 kcal bp). We show an out‐of‐phase Holocene moisture variation between the interior of West Asia and the Indian Summer Monsoon domain and conclude that summer insolation‐driven latitudinal shifts of the Hadley cell played a key role in seasonality changes in the interior of West Asia by modulating the strength and pathway of the subtropical high‐pressure cells. Finally, we explore possible impacts of these changes on regional prehistoric human communities.

A window into development of a complex ice-marginal lake prior to the Late Glacial Maximum (LGM) in Austria

Abstract Although the retreat process of glaciers from the Late Glacial Maximum (LGM) is well documented, high-resolution insight into conditions prior to the maximum is lacking in the eastern European Alps, resulting in a gap in our understanding about the processes associated with this important climatic tipping point. We describe an outstanding sand and gravel outcrop at Gröbming in the Enns Valley (Ennstal), Austria, that represents the development of a delta complex that debouched into a large body of water that we name paleo-Lake Gröbming, fed by a major valley glacier. The succession consists of sands bearing climbing ripples, parallel laminations, and supercritical bed forms (bottomsets) overlain by meter-scale gravelly foresets. Topsets comprise gravels. We argue that sustained accumulation of supercritical bed forms required a jet efflux feeder mechanism best explained by a direct glacial meltwater source. Complex vertical and lateral repetition of this tripartite succession is observed, with sequence stratigraphic analysis permitting us to argue that stratal complexity is attributable to base-level changes in paleo-Lake Gröbming resulting from dam breaches of the lake. Thus, application of well-established sequence stratigraphic approaches to Quaternary ice-marginal successions in the Alps has significant potential to yield unprecedented insights into conditions prior to the LGM.

Millennial hydrological variability in the continental northern Neotropics during Marine Isotope Stages (MISs) 3–2 (59–15 cal ka BP) inferred from sediments of Lake Petén Itzá, Guatemala

Abstract. Lake Petén Itzá (Guatemala) possesses one of the longest lacustrine sediment records in the northern Neotropics, which enabled study of paleoclimate variability in the region during the last ∼400 000 years. We used geochemical (Ti, Ca/(Ti+Fe) and Mn/Fe) and mineralogical (carbonates, gypsum, quartz, clay) data from sediment core PI-2 to infer past changes in runoff, lake evaporation, organic matter sources and redox conditions in the water column, caused by hydrological changes in the northern Neotropics during Marine Isotope Stages (MISs) 3–2. From 59 to 39 cal ka BP climate conditions were relatively wet, and the lake was marked by higher primary productivity and anoxic bottom waters. This wet environment was interrupted for two periods of possible low water level at 52 and 46 cal ka BP, when our data suggest higher evaporation, high terrestrial organic matter input and persistent oxic conditions. Between 39 and 23 cal ka BP, evaporation and input of terrestrial organic matter increased considerably, lake level declined, and lake bottom waters generally became oxic. These conditions reversed during the Last Glacial Maximum (23.5–18.0 cal ka BP), when runoff and lake productivity increased, and rising lake level caused bottom waters to again become anoxic. Comparison of our hydrologic proxy data with sea surface temperature anomalies between the eastern Pacific and the Caribbean suggests that changes in the intensity of the Caribbean Low-Level Jet (CLLJ) may have influenced long-term changes in runoff during MISs 3–2. Higher intensity of the CLLJ during the onset of MIS 3 and the LGM might have led to greater runoff into the lake, whereas the MIS 3–2 transition experienced a weaker CLLJ and consequently less runoff. A refined, high-resolution age–depth model for the PI-2 sediment core enabled us to identify millennial-scale Greenland interstadials (GIs) 14–2, Greenland stadials (GSs) 14–2 and Heinrich stadials (HSs) 5–1. In general, HSs and GSs were characterized by drier conditions. In contrast to GSs and HSs, GIs were characterized by greater runoff and overall wetter conditions, with the most pronounced GI peaks between 40 and 30 cal ka BP. Whereas GSs 9, 8, 7 and 6 began with abrupt increases in evaporation and ended with gradual increases in humidity, GSs 11 and 10 showed reversed patterns. The Lake Petén Itzá paleohydrology record, along with other regional paleoclimate records, led us to conclude that shifts in the position of the Intertropical Convergence Zone (ITCZ) altered moisture delivery to the lake on millennial timescales. During GSs and HSs, high evaporation from Petén Itzá (dry climate conditions) was associated with a more southerly position of the ITCZ, whereas wetter GIs prevailed during a more northerly ITCZ position. Although abrupt millennial-scale shifts in ITCZ and hydroclimate between GSs/HSs and GIs can be linked to instabilities in the Atlantic Meridional Overturning Circulation (AMOC), longer-term changes were additionally influenced by changes in atmospheric convection linked to modulations of the CLLJ in response to ΔSST between the equatorial Pacific and tropical Atlantic.

Glyptotherium cylindricum (Cingulata, Glyptodontidae) from the Late Pleistocene of Guatemala: the most complete record of Glyptodontinae from Central America

Glyptodontinae stand out among the lineages of Glyptodontidae in having the greatest latitudinal distribution, including participation in the Great American Biotic Interchange, with significant speciation in new migration areas. The oldest records of Glyptodontinae occur in northern South America with Boreostemma from the middle Miocene–Pliocene. A later radiation incorporated the austral representatives ‘Glyptodontidium tuberifer’, ‘Paraglyptodon’ spp., Glyptodon munizi, Glyptodon reticulatus and Glyptodon jatunkhirkhi in the late Miocene–Late Pleistocene of southern South America, and the septentrional representatives Glyptotherium texanum and Glyptotherium cylindricum in the Pliocene–Late Pleistocene of North America, Central America and northeastern South America. Although knowledge of North and South American forms has increased in recent years, records from Central America are still scarce and fragmentary. Here we describe the most complete Central American glyptodontine fossils documented to date, which were recovered from the latest Pleistocene of Guatemala. The remains comprise: (1) an incomplete skull, the right and left hemimandibles, a fragmentary pelvis, cervical and caudal vertebrae, and articulated and isolated osteoderms; (2) a fragmentary pelvis, left hind limb (incomplete autopodium) and seven caudal vertebrae; (3) most of a dorsal carapace; (4) six incomplete caudal armature rings; and (5) a left hemimandible with complete dental series. Comparative assessment indicates that these remains are referrable to G. cylindricum. The presence of this species in northern Central America and northern South America during the latest Pleistocene spans more than 2200 km, suggesting a continuous distribution across this region, at least during the Last Glacial Maximum and the early Younger Dryas. Francisco Cuadrelli [ f.cuadrelli@gmail.com ]*, Juan Escamilla [ juanitoesca@gmail.com ] and Alfredo Zurita [ aezurita74@yahoo.com ], Laboratorio de Evolución de Vertebrados y Ambientes Cenozoicos–Centro de Ecología Aplicada del Litoral (CECOAL–CONICET) y Universidad Nacional del Nordeste, Corrientes, Argentina, 3400; David D. Gillette [daviddgillette@gmail.com ], 24 W. Travertine Trail, Flagstaff, AZ 86005, USA; Lorena S. Dávila [ sylodavila@gmail.com ], Colección de Fósiles, Museo Historia Natural, Universidad de San Carlos de Guatemala, Calle Mariscal Cruz 1–56, Zona 10, Ciudad de Guatemala, Guatemala, 01010.

A Holocene pollen-inferred climate reconstruction for Vermont, USA

AbstractA 13.0 cal ka BP pollen record from Twin Ponds, Vermont, provides new insights into the climate history of the northeastern United States. Modern analogs were used to produce qualitative and quantitative climate reconstructions for Twin Ponds. The Twin Ponds record was compared with nearby Knob Hill Pond to develop a Vermont reconstruction that was compared with reconstructions from two sites at a similar latitude. Postglacial warming at 11.5 cal ka BP followed a cool, wet Younger Dryas and was the largest temperature change of the record. The warmest, driest conditions occurred at ca. 9.0 cal ka BP, followed by an increase in moisture. Latitudinal and elevational shifts in the location of modern analogs from 5.7 to 4.0 cal ka BP were used to infer cooling and increased moisture during the Tsuga canadensis decline. Analysis of the timing of pollen events between the two Vermont sites suggests a more rapid decline in T. canadensis at the more northern Knob Hill Pond and further supports the possibility that colder temperatures contributed to this event. The other northern sites show similar trends until 2.5 cal ka BP, when precipitation in the easternmost site diverges, indicating the establishment of modern climatic gradients.

THREE TYPES OF INDUSTRY IN THE STONE AGE OF GOBUSTAN

In the east of the Republic of Azerbaijan, in Gobustan district, there are numerous Stone Age sites with preserved culture-bearing deposits. Interest in the richest rock art sites concentrated there overshadowed studying the stone inventory of the region’s earliest sites relegating them to the background. In this work, the author proposes a general systematization of the materials of the Gobustan Stone Age. The paper contains detailed typological lists of key sites; suggests the criteria for dividing the material into three cultural and chronological groups; and substantiates a new view on the chronology and local peculiarities of these groups that is different from previously held ones in many respects. For the sites of the Upper Palaeolithic of Gobustan, an estimated age is proposed corresponding to the period prior to maximum of the Würm glaciation (i.e., no later than approximately 25–20 thousand years ago). The lower date of the Mesolithic layers correlates roughly with the end of the Allerød and the Younger Dryas (approximately 14–12 thousand years ago). The emergence of the local Neolithic is attributed approximately to the early 6th millennium BC.

Late Quaternary fluvial environments at Abo Arroyo, New Mexico, U.S.A.: response to millennial-scale climate change

ABSTRACT Abo Arroyo is a tributary of the Rio Grande in central New Mexico. Its alluvial sequence is made up of four informal units, their age defined by 44 AMS radiocarbon dates from 12.8 ka to 0.85 ka. The earliest, unit 1, is terminal Pleistocene to early Holocene (12.8 ka to 9.0 ka), including the Scholle wet meadow (12.3 ka to 11.1 ka) related to the Younger Dryas. After an erosional gap in the record from 9 ka to 6 ka, coarse gravel (unit 2) was deposited in the channel (5.8 ka and 4.3 ka) during the middle Holocene period of aridity. Subsequently, the late Holocene wet period is characterized by fine-textured alluvium (unit 3) (3.5 ka to 0.945 ka) with shells of an aquatic snail, indicating persistent stream flow. An upper 2-m zone of dark-colored clayey silt beds with high amounts of organic carbon and carbonate accumulated from 1.7 ka to 0.945 ka. A record of C4 signatures, previously interpreted to indicate dry conditions 1.4 ka to 0.945 ka, is reinterpreted as an interval of exceptionally wet floodplain conditions with C4 grasses and sedges. Abo Arroyo and other studies indicate three major episodes of late-Quaternary channel entrenchment: 1) from the full-glacial to late glacial-Bølling/Allerød (6.1 ky), 2) during the middle Holocene (2.5 ky), and 3) during the late Holocene Medieval Warm Period (0.4 ky), each erosional event less severe and shorter duration than the preceding one, and all three represent a significant change from wet to dry climate. During the Medieval Warm Period (A.D. 900 to 1300), a shallow channel formed in unit 3 alluvium, bracketed by AMS dates A.D. 1005 in unit 3 alluvium and A. D. 1100 in unit 4 channel fill. The channel cutting occurred with the shift from wet to dry climate, although the downcutting event was preceded by 100 years of landscape adjustment to the long drought. The canyon fill was entrenched again, deep and wide, by arroyo cutting in the late nineteenth and early twentieth centuries. The regional 83-year second-century drought (A.D. 100 to A.D. 182), documented by tree rings, shows up in the stable-carbon-isotope record from Abo Arroyo alluvium. The drought was more severe than the 400-year warm period but had little effect on the preserved alluvial record. The less severe but longer-duration Medieval Warm Period resulted in channel cutting at Abo Arroyo and elsewhere in the broad region at that time, but the second-century drought did not. Finally, the similarity of Abo Arroyo and Rio Grande late Holocene alluvial records with parallel stratigraphy, sedimentology, and geochronology illustrates that tributaries and main valleys respond alike and in concert to climate and climate change.

Northern high-latitude sea ice variation linked with East Asian monsoon anomalies during the Younger Dryas

The abrupt weakening of the East Asian summer monsoon (EASM) during Younger Dryas (YD) has been attributed to freshwater discharge into the North Atlantic ocean and resultant Northern Hemisphere cooling. Recent studies have found that sea ice variability in the Nordic Sea during the YD exerted a great influence upon the northern high-latitude climate. However, the influence of sea ice upon EASM evolution during YD event remains unclear. In this paper, we report two precisely-dated speleothem oxygen isotope records from the EASM-dominated region of central China. Our records archive abrupt changes in EASM variability during the YD event. Initially, there was a significant strengthening of the EASM during the mid-YD following the gradually increased Atlantic meridional overturning circulation (AMOC). Later this trend reversed at ∼12.15 ka due to northern high-latitude sea ice fluctuations and a consequent reduction of AMOC. At the YD termination, abrupt intensification of the EASM was synchronous with the rapid decline of sea-ice and recovery of the AMOC indicating that sea ice variability was a significant influence on high latitude climate and EASM variation during the YD.

The spatio-temporal pattern of Asian summer monsoon during glacial Termination II recorded by Chinese stalagmite δ18O

The difficulty in constraining the large-scale Asian summer monsoon (ASM) variability in the Chinese monsoon region (CMR) during glacial Termination II lies in our limited knowledge of the western part, primarily due to sparse paleoclimate records. To get a better picture of the ASM during Termination II, we examined a precisely dated stalagmite δ18O record between 133.1 and 127.0 kyr B.P. from Wanxiang Cave located at the ASM's northern edge in western China. In combination with published δ18O data from this cave, we have identified the ‘Weak Monsoon Interval’ (WMI) in the Wanxiang δ18O record and confirmed that the Heinrich 11 cold event in the North Atlantic caused the weakened ASM over the CMR via reorganization of the large-scale ocean-atmospheric circulation. However, the post-WMI change in δ18O is gradual, in contrast with the abrupt shift shown in the other cave records from southern and northeastern China. The rapid northward migration of the westerly jet relative to the Qinghai-Tibet Plateau is probably responsible for this discrepancy. This northward-positioned westerly jet prevented the more 18O-depleted moisture from the Indian Ocean from reaching the study site. Simultaneously, it facilitated the earlier northward movement of the East Asian summer monsoon (EASM) rainband that carries positive precipitation δ18O to obscure the abrupt decrease in our δ18O record. After the onset of the last interglacial, no obvious Younger Dryas (YD)-like event was recorded in Wanxiang Cave. This result is consistent with most stalagmite δ18O records in the CMR and further suggests a minimal impact of the YD-like event on ASM variabilities. The relatively large amplitude of δ18O variations observed in Wanxiang Cave between the late penultimate glacial and the last interglacial corresponds to a dominant control of the Indian summer monsoon (ISM), whereas smaller δ18O amplitudes were recorded in cave sites mainly under the influence of both ISM and EASM. Therefore, we posit that the heterogeneity of the hydroclimate in the CMR during Termination II resulted from a combination of multiple processes, that is, the westerly jet, ISM and EASM, rather than a single one.

The morphostratigraphic imprint of the Baltic Ice Lake drainage event in southern Finland

Digital elevation models, based on laser scanning imageries (LiDAR-DEM) and aided by ground penetrating radar (GPR) data, were used to study glaciofluvial Gilbert-type ice-contact deltas in the Younger Dryas Salpausselkä end-moraine zone in southern Finland. The geomorphological data analysed were used to reconstruct the water-level drop of the late glacial Baltic Ice Lake to the early Holocene Yoldia Sea and tie these changes to a wider stratigraphic context. The results indicate that the sudden drainage event at around 11 650 cal. yrs BP left its imprint not only on the varved sediments but also on ice-contact glaciofluvial deltas in the Second Salpausselkä zone throughout southern Finland. This morphostratigraphic boundary can be placed at locations where the ice-contact deltas occur at two different levels; the higher-level deltas formed during the Baltic Ice Lake B III water-level stage and the lower-level deltas during the Yoldia Sea Y I water-level stage. This morphostratigraphically defined boundary in southern Finland marks the Pleistocene/Holocene chronostratigraphic boundary in southern Finland and shows the corresponding positions of the Scandinavian Ice Sheet’s Finnish Lake District Ice Lobe and the Baltic Sea Ice Lobe.

The younger Dryas layer at Boncuklu Tarla and the beginning of village life in the upper Tigris Basin

Recent archaeological excavations in the Boncuklu Tarla, Çemka Höyük, and Körtik Tepe settlements in the Upper Tigris Basin have provided a number of finds from the pre-PPNA Period, the Younger Dryas. The new data also opens up the concept of the Proto-Neolithic Period to discussion again, which has been controversial for a long time in the East Jazeera and Northwest Zagros Region. In this context, architectural remains and other small finds discovered in the Boncuklu Tarla settlement area make it possible to re-examine the transition to sedentary life in the Upper Tigris Basin during the Late Epipalaeolithic/Proto-Neolithic Period and the PPNA Period. These archaeological finds show that there were some semi-sedentary or sedentary communities in the Upper Tigris Basin, which exhibits unique geographical and climatic features, starting with the Younger Dryas Period. This is different from the Natufian culture that is thought to have emerged in the Mediterranean temperate climate zone and is known only in the Southern Levant Region.

Bipolar ice-core records constrain possible dates and global radiative forcing following the ∼74 ka Toba eruption

The Younger Toba Tuff eruption ∼74 ka ago in Indonesia, is among the largest known supereruptions in the Quaternary and its potential impact on the climate system and human evolution remains controversially debated. The eruption is dated radiometrically to 73.88 ± 0.32 ka (1σ, Storey et al., 2012) and it occurred at the abrupt cooling transition from Greenland Interstadial 20 to Greenland Stadial 20. The precise stratigraphic position of volcanic fallout detected in ice cores from both polar ice sheets has previously been narrowed down to four potential candidates. Here, we compile all available Greenland and Antarctic sulfate records, together with electrical conductivity records and recently obtained sulfur isotope records to identify, quantify and characterize these Toba candidates in terms of their likely latitudinal position of eruption, sulfur emission strength and radiative forcing. We identify that the youngest event of the four candidates is composed of two separate eruptions, both likely located in the extra-tropical Northern Hemisphere. We deem the two older events unlikely candidates for the Toba eruption because of their limited sulfur emission strengths. The second youngest event has the largest sulfur output of the Toba candidates, and it is also larger than any other volcanic event identified in ice core records over the last 60 kyr. Comparable amounts of sulfate deposits in Greenland and Antarctica strongly suggest a tropical source. We thus propose the second youngest event (74,156 years before 2000 CE) to be most likely associated with the Toba eruption. The estimated stratospheric sulfate loading of the proposed Toba eruption is 535 ± 96 Tg, which is 3 times that of Samalas 1258 CE, 6 times that of Tambora (1815) CE and 20 times that of Pinatubo (1991) CE. We derive the continuous time-series of volcanic sulfate deposition, sulfur emission strength and radiative forcing over the 74.8–73.8 ka time window, suitable for conducting experiments with climate models that either require prescribed forcing field or interactively reproduce aerosol processes. We estimate the cumulative volcanic sulfur emission strength and the radiative forcing of the two younger events and they are found to be much stronger than those at the onset of the Younger Dryas and those preceding the Little Ice Age. Stacked Greenland water isotope records show an accelerated transition trend and abrupt shift after the proposed Toba eruption and suggest that the Greenland moisture source moved southward shortly after the Toba eruption. The Toba eruption may thus have an amplifying effect on the cooling transition leading to Greenland Stadial 20.

Submarine lateglacial lake deposits from jutland bank, the north sea

Little is known about Lateglacial environments in the North Sea, the so-called Doggerland. Here we report on submerged lake sediments from the north-eastern part of the North Sea, found in sediment core JR-14. The core contained Holocene marine sand underlain by clay and clay-gyttja with plant and invertebrate remains and sand without plant remains, interpreted as glaciofluvial sand. Radiocarbon dating of terrestrial plant remains from the Lateglacial sediments gave ages between 12 300 and 14 100 cal a BP, corresponding to the early part of the Younger Dryas stadial and the Bølling-Allerød interstadial. The Lateglacial sediments contained remains of Betula nana, Salix and Dryas plants indicating a tundra-like open landscape with dwarf shrub heaths, which is typical for the region. The sediments contained a diverse assemblage of bryophytes that throws light on the Lateglacial bryoflora of the region. Remains of macrolimnophytes indicate shallow carbonate-rich, cool lake waters. Remains of larvae of Trichoptera and Chironomidae dominated the invertebrate fauna and indicate a fairly species-rich fauna. The presence of lake sediments at ∼32.9–34.5 m below sea level shows that this part of the North Sea had not been transgressed by the sea during the Lateglacial.

10Be exposure ages and paleoenvironmental significance of rock glaciers in the Western Tatra Mts., Western Carpathians

Relict rock glaciers are well-preserved features of high-elevated valleys in the Western Tatra Mts., Western Carpathians, but their chronology remained poorly constrained with numerical dating methods. We present the first robust set of 10Be exposure ages for eight rock glaciers with front elevation of 1376–1819 m asl. The results suggest that the rock glaciers stabilized throughout the Weichselian Lateglacial from ∼16.5 ka to 11 ka. This timing is consistent with the period of rock glacier stabilization in European mountain regions, but it extends the age span previously determined for rock glaciers in the Tatra Mts. There are differences between north- and south-facing valleys in the elevation and time of the stabilization of the rock glaciers, which were probably caused by contrasts in potential incoming solar radiation that affected the retreat of former glaciers and the subsequent formation of the rock glaciers. The initiation altitude of ∼1610 and ∼1830 m asl determined for the oldest and youngest dated rock glaciers is generally consistent with previous estimates of the glacier equilibrium line altitude during the Greenland Stadials 2.1 and 1, respectively. However, the lower limit of the rock glaciers is well above regional paleopermafrost features from the same periods, which suggests that rock glaciers may underestimate past permafrost extents and temperature declines disputing their regional validity for paleoenvironmental reconstructions.