Younger Dryas Research Articles

Vegetation response to Early Holocene cooling events in the Moervaart region (northwestern Belgium)

A high‐resolution palynological record from northwest Belgium is presented. The record encompasses the second part of the Younger Dryas and the Early Holocene. The basal part of the pollen record reflects a relatively open landscape, characteristic for the Younger Dryas. The transition to the Holocene is marked by an expansion of birch woodland, followed by an expansion of pine in the Late Preboreal (~11.2–10.7 cal. ka BP). Subsequently, the record shows an expansion of mixed deciduous forest with hazel, elm and oak, characteristic for the Boreal (~10.7–8.6 cal. ka BP). Early Holocene forest expansion was interrupted by a number of short‐lived fluctuations, presumably driven by climatic changes. The most distinct event is the Rammelbeek phase (~11.4–11.2 cal. ka BP), during which forest development was temporarily interrupted in favour of grasses, while wildfires increased. Following this climatic event, hunter‐gatherers returned to the area after a period of almost 1.5 millennia of low population density. They most likely were attracted by the increased temperatures and abundance of edible plants present in the birch‐pine forests and on the banks of the river Kale/Durme. A temporary expansion of pine during the Boreal (~10.7–8.6 cal. ka BP) may correspond with the 9.3‐ka event. At this time, superimposed on a trend of gradual infilling of the channel, a temporary change to drier conditions is observed. The significant drop in the number of prehistoric sites in the Moervaart region clearly cannot be attributed to this short‐term climatic event alone but was most likely caused by a combination of environmental changes, such as the decreasing availability of hazelnuts as well as freshwater and edible (semi‐)aquatic plants as the Kale/Durme river gradually turned dry. The study provides insight into, partly climate‐driven, Early Holocene environmental changes and the effect this may have had on human occupation.

Rejection of Holliday et al.'s alleged refutation of the Younger Dryas impact hypothesis

Rejection of Holliday et al.'s alleged refutation of the Younger Dryas impact hypothesis

Rebuttal of Sweatman, Powell, and West's “Rejection of Holliday et al.'s alleged refutation of the Younger Dryas Impact Hypothesis”

Rebuttal of Sweatman, Powell, and West's “Rejection of Holliday et al.'s alleged refutation of the Younger Dryas Impact Hypothesis”

When environment meets culture in the arid margin of the Southern Levant

Research in the arid margins of the Southern Levant has revealed a series of cultural entities related to and interacting with analogues in the more mesic Mediterranean zone. These terminal Pleistocene (Epipalaeolithic) and early Holocene (Pre-Pottery Neolithic) foraging entities display clearly local traits reflecting restricted networking and adaptations at times when environmental conditions deteriorated, and the connections with contemporaneous cultural entities farther afield weakened, combined with connections with the wider pan-regional cultural entities. By examining the specific example of the short-lived Late Epipalaeolithic Harifian culture we attempt to illustrate the manner in which local social behaviours in the landscapes of the arid margins may have contributed to maximizing and prolonging cultural adaptations there especially during periods of variable, yet generally challenging environmental conditions during the Younger Dryas (YD), with a greater degree of isolation from the 'sown land'. Ultimately, a threshold was reached towards the end of the YD, and the Harifian adaptation ceased to be viable, so they had little choice but to abandon their former territories in the Negev and northern Sinai to more favourable environmental conditions, near and, perhaps, far. Speculatively, having to merge with different groups as conditions there were not improving and 'packing' was tight, may have contributed to the emergence of large-scale 'archaic' villages of the PPNA.

Late pleistocene glacial history of Mount Karadağ, SW Türkiye

Glacial landforms in the southwestern part of the Anatolian Peninsula are found at lower elevations than the rest, suggesting that glaciers were present during the Late Pleistocene. Karadağ, located west of the Western Taurus Mountains, provides evidence of the climatic conditions that facilitated this extensive glaciation. It is characterized by numerous peaks exceeding 2300 m above sea level (asl), with the highest peak reaching 2418 m, making it the region's largest glaciation area. This high mountain mass is composed mainly of limestone and dolomite. This study focuses on the glacial landforms in Karadağ to reconstruct the Late Pleistocene glacial chronology and palaeoclimate of the Western Taurus Mountains. We employed detailed UAV photogrammetry, extensive fieldwork and mapping, surface exposure dating with cosmogenic 36Cl, meteorological measurements, palaeoglacier reconstruction, and palaeo-equilibrium line altitude (pELA) calculations. Karadağ, a topographic barrier to humid air masses from the Mediterranean Sea, ranks as the second wettest area in the Western Taurus Mountains. At a meteorological station we installed in Karadağ, an annual precipitation of 1700 mm or more was recorded, highlighting its significant precipitation. In Karadağ, we have identified two glacial valleys with a maximum length of 4.5 km and six cirques. The glaciers reached their maximum extent around 22.4 ± 2.8 ka during the Last Glacial Maximum (LGM), facilitated by the lowering of the pELA to 2090 m. During the LGM, the glaciers covered an area of approximately 3.5 km2 and reached a maximum thickness of about 140 m. Sample TRKR 10 at 2015 m probably belongs to the LGM period. Although a single sample does not conclude definitive conclusions, the presence of the moraine at its highest position indicates the maximum thickness of the glacier. Following the LGM, two more significant glacier advances occurred during the Lateglacial (15.5 ± 2.7 ka) and the Younger Dryas (12.4 ± 1.1 ka). During the late Pleistocene glaciations, and especially during the LGM, Karadağ probably received more precipitation than today, leading to the formation of glaciers at relatively lower elevations than on the Anatolian Peninsula.

Arctic sea‐ice export as a mechanism for cold climate events during the last deglaciation

ABSTRACTRecently it was proposed that a sudden drainage of accumulated Arctic sea ice could have caused cold climate events during the last deglaciation. To explore this mechanism, we performed numerical experiments with an atmosphere–ocean–sea ice model. In these experiments, the impact of a large flush of Arctic sea ice was compared to a reference glacial state of the climate. In our results, the sea ice flush produces a major surface freshening of the North Atlantic Ocean and a 17% weakening of the strength of the Atlantic Meridional Overturning Circulation. Together with an increase in surface albedo, this weakening in ocean circulation leads to a cooling over the North Atlantic, extending to the downwind continents. Compared to our reference glacial state, the cooling reaches 5°C and lasts about 80 years. This climate anomaly is similar in magnitude and duration to relatively short cooling events during the last deglaciation, such as the Older Dryas, the Inter‐Allerød cold period and the Preboreal Oscillation. We thus conclude that the sea‐ice flush mechanism is consistent with the occurrence of such cooling events in the North Atlantic region. However, longer cooling events such as the Younger Dryas would require additional mechanisms.

Strong coupling between the East Asian summer monsoon and regional hydrological conditions as evidenced by multiproxy stalagmite records for the last deglaciation

Millennial-to centennial-scale abrupt climate events during the last glacial‒interglacial transition have significant relevance to modern-day extreme climate changes, which are occurring more frequently in the context of global warming. However, the regional expression of humidity conditions during the last deglaciation and their possible forcing mechanism in northern China are controversial. Here, combined with published δ18O data, we report 35-year-resolved δ13C and 76-year-resolved Mg/Ca and Sr/Ca records from a stalagmite from 15.3 to 10.9 ka BP from Lianhua Cave, northern China. The LH4 stalagmite δ18O record clearly records a weak monsoon event during the Younger Dryas (YD) from 12.8 to 11.6 ka BP and a strong monsoon event during the Bølling-Allerød (BA) from 14.6 to 12.8 ka BP. In addition, the δ13C and trace element ratio records, which represent local hydroclimatic changes, indicate wetter conditions during the BA and drier conditions during the YD, which appear to match well with the δ18O variations on the millennial timescale. A comparison of 28 records from 17 sites along the modern margin of the China summer monsoon revealed that the BA was characterized by wet conditions; inversely, the YD was characterized by dry conditions throughout northern China, which is obviously different from the consensus of the wet YD and the dry BA in northern northeastern China. The covariance in northern China suggests that the hydrological variation may be modulated by the advance and retreat of the large-scale East Asian summer monsoon (EASM) circulation. Further comparison revealed an anticorrelated relationship between millennial-scale precipitation changes in northern China and the middle‒lower reaches of the Yangtze River Valley during the last deglaciation. This correlation is analogous to the dipole precipitation mode at present, which is likely associated with the strength and position of the westerly jet and/or the western Pacific subtropical high, both of which play important roles in the spatial distribution of precipitation over eastern China.

Seesaw between the westerlies and Asian monsoon regulates vegetation and climate during the last deglaciation in southern Northeast China

The history and drivers of hydroclimate changes during the last deglaciation in Northeast China remain contentious. We present a high-resolution record of vegetation and climate changes from Lake Buridun in southern Northeast China (SNEC), spanning the last ∼16 kyr. Multi-proxy reconstruction reveals a slight increase in precipitation prior to the end of Heinrich Stadial 1 (HS1) and forest development during the middle Bølling warming, indicating that hydrothermal conditions regulated regional vegetation. Significant fluctuations in all millennial-scale climatic events underscore the high sensitivity of SNEC to climate change. Our record aligns with high-resolution data from both SNEC and North China, showing a persistent wetting trend during the Bølling-Allerød period. This trend coincides with changes in East Asian summer monsoon intensity and Indo-Pacific warm pool heat content but contrasts with the Greenland temperature records. During the HS1 and Younger Dryas, records show a cold-dry mode in SNEC, contrasting with the cold-wet pattern in central-eastern China caused by the prolonged Meiyu season, which corresponds to the retreat of the monsoon precipitation belt and an enhanced westerly jet. Our data, along with more comprehensive records from broader regions, suggest that hydroclimate in SNEC was dominated by the low-latitude monsoon and the high-latitude westerlies during the warm and cold phases of the last deglaciation, exhibiting a seesaw-like interaction.

Pleistocene to early Holocene paleoenvironmental evolution of the Abrolhos depression (Brazil) based on benthic foraminifera.

The paleoenvironmental evolution of the Abrolhos Depression (AD) on the southern Abrolhos Shelf during the global post-Last Glacial Maximum (LGM) transgression is investigated through benthic foraminifera analysis. Downcore sediment samples (core DA03A-5B) collected at a depth of 63m provide insights into the formation and paleoenvironmental variations of AD over the past 18 kyr BP. The core is divided into four biofacies based on foraminifera assemblages. At the base, the presence of carbonate concretions indicates a karstic surface, marking the initiation of the paleolagoon formation at approximately 13 kyr BP with low density of foraminifera, where species such as Elphidium sp. and Hanzawaia boueana (EH Biofacies) were more abundant. During the Younger Dryas (YD) (12.8-12.5 kyr BP), the AD exhibits two distinct phases: an initially confined lagoon environment with reduced circulation characterized by the dominance of the species Ammonia tepida (At Biofacies), followed by increased circulation characterized by higher density, richness, and diversity of benthic foraminifera. The end of the YD is identified by a significant biofacies change, indicative of a shallow marine environment, where the dominant species were A. tepida and Elphidium excavatum (AE Biofacies), supported by sedimentological and geochemical proxies. This paleoenvironmental shift is associated with Meltwater Pulse (MWP) -1B, suggesting a connection to a shallow marine environment. As sea levels continue to rise, the AD transitions into an open marine setting. However, around 8 kyr BP, a change occurs with the absence of A. tepida and the occurrence of planktonic and other benthic foraminifera typical of the outer shelf, indicating depths greater than 50m (HQ Biofacies). The findings highlight the complex interplay between climate fluctuations, sea-level changes, and the formation of coastal environments during the LGM transgression. This study contributes to our understanding of paleoenvironmental dynamics, adding valuable insights to the evolutionary history of AD. The results emphasize the importance of integrating benthic foraminifera analysis, radiocarbon dating, and geochemical proxies to reconstruct paleoenvironments accurately. Overall, this research enhances our knowledge of global continental shelf evolution during the post-LGM transgression and provides valuable information for future paleoenvironmental studies.

Aeolian sand cover on a granite peninsula (Hammeren, Bornholm, Baltic Sea) formed in three episodes during the past 11,600 years

Aeolian sand covers a significant part of the granite peninsula Hammeren on northernmost Bornholm in the Baltic Sea. The coastline of Hammeren is rocky and apart from one relative wide and sandy pocket beach at the east coast only few, small and gravelly pocket beaches exist. The aeolian deposits form three sand covers that stretch inland from the east and northwestern facing coasts of Hammeren. The largest sand cover forms a rising sand plain that cover the granitic landscape up to 700 m inland and reaches up to 60 m above sea level. Historical sources mention aeolian sand movement around CE 1775 in the middle of the Little Ice Age, but until this study no absolute age control has been available to confirm these observations. Luminescence dating of selected sample sites indicates that aeolian sand movement took place in three episodes. The first episode was in the last part of the Younger Dryas at about 11,500 BP, the second episode was in the Danish Late Bronze Age at about 2700 BP, and the youngest episode was indeed during the Little Ice Age around 200 BP (CE 1750). These episodes with aeolian activity all fall during relatively cold climatic intervals and add support to previous studies indicating a link between cold climates an increased storminess in Northwest Europe including the southern Baltic Sea region.

Tracking orbital and suborbital climate variability in the westernmost Mediterranean over the past 13,000 years: New insights from paleoperspectives on marine productivity responses

This study presents a comprehensive analysis of a sediment record from the Western Alboran Basin (core GP04PC), utilizing palynological and geochemical tools to investigate marine productivity responses to orbital and suborbital climate variability over the past 13,000 years. High productivity during the Younger Dryas humid phase (∼12.4–11.7 ka) and the Holocene humidity optimum (∼10.5–8.5 ka) was driven by increased local river discharges resulting from rapid mountain glaciers melting and enhanced regional precipitation. During the late Holocene, frequent flood events linked to negative North Atlantic Oscillation (NAO) incursions potentially led to multicentennial-scale productivity increases. The findings indicate that periods characterized by wet regional conditions and increased river run-off, influenced by orbital (e.g., insolation cycles) and suborbital factors (e.g., NAO and Atlantic Meridional Overturning Circulation changes), consistently enhanced marine productivity in the Western Alboran Basin. The study also reveals that the current high productivity and carbon export in the Western Alboran Basin are maintained by active upwelling and downwelling systems driven by a persistent positive NAO phase following the southward migration of the Intertropical Convergence Zone (ITCZ) that occurred around 6.5 ka. Furthermore, geochemical proxies support a strong detrital influence on trace metal concentrations, including barium (Ba), in deep Western Alboran sediments during the Holocene. This limits the use of Ba/Al ratios for accurately reconstructing productivity changes and highlights the importance of dinocyst analysis as a complementary tool for robust marine productivity reconstructions in this region. These observations provide valuable paleoperspectives on marine ecosystem responses to climate variability, contributing to the development of robust long-term productivity models essential for adapting to ongoing environmental changes in the region, and demonstrating the strong influence of North Atlantic climate and ocean dynamics on centennial-scale productivity oscillations in this region.

A Regional Paleoclimate Record of the Tropical Aeolian Sands during the Last Deglaciation in Hainan, China

The KLD segment of the Kenweiyuan section in Wenchang, Hainan, China is a set of aeolian sand deposits of the Last Deglaciation. The chemical element and heavy mineral analysis performed in this study reveals the chemical index of alteration (CIA) in the segment to be as high as 93–95, with all the heavy minerals identified as stable and extremely stable making up 38–45% of the total. Furthermore, the zircon, tourmaline, and rutile content (ZTR index) of the segment is determined to range between 48–71. The (Al2O3 + TOFE)/SiO2 ratios display obvious fluctuations from old to new strata in the segment, with the low values corresponding to Heinrich event (H1), Dansgaard-Oeschager (D-O), and Younger Dryas (YD) and the high values corresponding to Bølling and Allerød. Our study suggests that these fluctuations are attributed to the alternation of the East Asian winter and summer monsoons. Hainan Island is also impacted by the surface ocean climate of the South China Sea, and characteristics of the KLD segment may be connected to the climate changes in the North Atlantic related to the winter monsoon season or westerlies. Furthermore, the segment presents a clear response to millennium-scale climate changes during the Last Deglaciation on Hainan Island. Based on the high CIA values in the KLD segment, and particularly due to the observed stable detrital minerals, the ratios can be linked to the overall tropical climate, indicating a relatively warm tropical climate environment in the Last Deglaciation in Hainan. The high CIA values also reveal the cause of aeolian sand formation under the tropical environmental conditions in the low latitude region of China in the Late Quaternary.

Reconstruction of temperature and hydroclimate in Serling Co (Central Tibet) since the last deglaciation

Understanding the past climatic conditions and their possible driving mechanism can contribute to better constrain future climate projection, and to provide potential insights into the disputed Holocene temperature variations. In this study, we quantitatively reconstruct the mean annual air temperature (MAAT) of Serling Co since 17.3 cal kyr BP using a novel terrestrial thermometer (ring index of OH-GDGTs, RI-OH), and reconstructed the hydroclimatic evolutionary history in combination with n-alkanes and their associated proxies. Our temperature records indicate that Serling Co experienced a period of reduced temperatures during the Younger Dryas event, approximately 6 °C cooler than the present conditions. Subsequently, there was a rapid warming phase, leading to peak temperatures in the early Holocene, roughly 5.5 °C warmer than the modern MAAT, followed by a protracted cooling trend during the subsequent middle and late Holocene. The temperature and hydroclimate trends at Serling Co exhibit a synchronized evolutionary pattern since the last deglaciation, featuring an optimal hydrothermal combination in the early Holocene. This period witnessed the peak productivity of terrestrial and aquatic ecosystems, followed by a gradual decline. Summer insolation emerges as a primary controlling factor for temperature variations, with Indian Summer Monsoon intensity and internal climate system variability exerting dominance over atmospheric moisture and precipitation variations in the region.

Sedimentary record of primary productivity changes in a crater lake in Northeast China since the Last Glacial Maximum

High-resolution primary productivity records are valuable for identifying lacustrine ecosystem degradation in the context of long-term climatic variability. In this paper, we analyse primary productivity changes in a seasonally ice-covered crater lake (Lake Tuofengling) in northeast China since the Last Glacial Maximum using biogenic silica content and the carbon preference index of short-chain n-alkanes as proxies. Results show that primary productivity was lower during the cold and dry glacial period, whereas it was higher during the warm and humid Holocene. During the last deglaciation, primary productivity experienced a ∼ 1.5-kyr lagged response to Bølling-Allerød warming, and multiple oscillations during the Younger Dryas. Additionally, the peak productivity of the entire profile also occurred during this period. These fluctuations and the highest primary productivity are suggested to be the result of the combined influences of increased summer temperatures and regional permafrost melting. The current state of primary productivity in Lake Tuofengling is moderate but has been increasing since the abrupt increase in diatom productivity after ∼3 ka B.P. This stage is associated with increased dust deposition and longer ice-free periods under winter-warming conditions. We suggest that longer seasonal stratification under the current warmer winters and increased nutrient concentrations caused by decreased lake level will increase the risk of lake ecosystem degradation in the future.

Evolution process of chemical weathering and sediment sources in the Makran Continental margin since the Younger Dryas

The chemical weathering processes and sedimentary source evolution since the Younger Dryas (YD) in the low-latitude arid continental margin have been investigated. Two sediment cores, MK07G and MK09G, were retrieved from the Makran continental margin in the northern Arabian Sea and subjected to analyses of major and trace elements, along with AMS14C dating. The results show that since the YD, the weathered parent rocks of Makran sediments have remained relatively stable, predominantly consisting of felsic rocks, with some contributions from mafic rocks. The Makran sediments exhibit initial to moderate weathering, with no discernible effects from grain size sorting or disturbances from sediment recycling, indicating primary deposition. Significant contributions of terrigenous eolian dust from surrounding continents (e.g., the Indian subcontinent, Arabian Peninsula, and northeastern Africa) were identified, along with riverine inputs from the Dasht River and fine-grained components from the Late Pleistocene Indus delta sediment, as well as proximal basin sedimentation. The evolution of sediment sources in the study area is significantly influenced by the Indian Monsoon and westerly wind systems, with intensified monsoon phases and westerly conditions correlating with increased fluvial input. Furthermore, chemical weathering processes since the YD are closely linked to local precipitation patterns, where intensified rainfall enhances weathering intensity. Records from the Makran continental margin indicate a teleconnection between chemical weathering and sedimentary processes in the Arabian Sea and Bond events in the North Atlantic, highlighting the extensive influence of Northern Hemisphere climate fluctuations.

A 14,000‐Year Sediment Record of Mercury Accumulation and Isotopic Signatures From Lake Malaya Chabyda (Siberia)

AbstractEurasian permafrost soils contain large amounts of organic carbon (OC) and mercury (Hg), sequestered by vegetation during past and present interglacial periods. Lake sediment archives may help understand past OC and Hg dynamics and how they interact with climate‐related variables. We investigated Hg accumulation, OC dynamics, and Hg and OC stable isotopes in a 14,000‐year sediment record from Lake Malaya Chabyda (Central Yakutia, Russia). Sediment Hg was correlated to OC (p value < 0.01), with lower OC and Hg accumulation rates (OCAR, HgAR) during the cold Younger Dryas (YD, 12,900–11,700 cal BP), when the lake level was low. Elevated sediment Δ200Hg (0.05‰ ± 0.11‰), representing dominant HgII deposition, and low δ13C, indicates low lake primary productivity during the YD. During the early Holocene, Δ200Hg and Δ199Hg decreased, while δ13C, δ202Hg, OCAR, and HgAR increased, suggesting enhanced algal primary productivity in deeper, more turbid waters. From 4,100 cal BP to present, Hg/OC ratios and HgAR increased at constant OCAR, indicating an additional Hg source to the lake. Analysis of Hg isotopes suggests direct Hg0 uptake into lake waters, potentially driven by primary production and efficient Hg burial. Our observations suggest that the gradual climate warming since the Last Glacial Termination and into the early Holocene led to enhanced OC and Hg burial in northern lakes and watersheds. Late Holocene enhanced Hg burial, but not OC, is possibly related to a renewed increase in lake primary productivity. Continued global warming may lead to further Hg sequestration in northern aquatic ecosystems.

Plastid marker variation reveals immigration history in Scandinavian Syntrichia norvegica and S. ruralis (Pottiaceae, Bryophyta)

ABSTRACT Introduction Based on previous analyses of Syntrichia norvegica and S. ruralis, the idea of panmictic populations in Scandinavia can be rejected, despite the high dispersal capacities of wind-dispersed spores. We tested, using comprehensive European datasets, whether intraspecific phylogeographical structure reflects glacial and post-glacial history. We expected different entities to indicate immigration from known Late Glacial Maximum refugial areas, and habitat differentiation. Methods Using plastid markers (atpB–rbcL and rpl16), we investigated 45 and 190 Scandinavian and 17 and 15 non-Scandinavian specimens of Syntrichia norvegica and S. ruralis, respectively. Key results We revealed four intraspecific entities in Syntrichia norvegica. Two were from the Scandinavian mountains and the Alps, and one from the Scandinavian mountains only. The fourth was widespread across the Scandinavian mountains, the northern lowlands, and the Baltic Sea islands Öland and Gotland. For S. ruralis, we recovered five entities, of which three were from both Scandinavia and the Alps. One of these occurred in strongly calcareous habitats in southern Scandinavia and the Alps and dominated on Öland and Gotland. One entity was widely distributed only in Scandinavia. One was restricted to the border between boreo-nemoral and southern-boreal Scandinavia. Conclusions The plastid haplotype distribution patterns suggest glacial survival of Syntrichia norvegica and S. ruralis in refugia south, east and possibly within ice-covered areas of Scandinavia. We hypothesise that one S. ruralis entity evolved adaptations to strongly calcareous habitats. The dominance or prevalence of specific haplotypes of both species on Öland and Gotland contributes to the unique biodiversity of these islands.

Hydroclimatic change and vegetation response in Tropical African alpine environments over the Holocene

Future precipitation is highly uncertain, particularly in East Africa where model projections contradict modern observational trends. Climate changes in East Africa's mountains are even less well understood, yet these mountains are threatened by warming, extreme flooding, fires, and the rapid disappearance of glaciers. Paleoclimatic and paleoenvironmental records can contextualize ongoing and future changes; however, proxy records from East African mountains disagree with each other and, in some cases, differ from nearby lowland sites. It is unclear if these discrepancies are due to geographic or altitudinal gradients in climate or processes that impact the fidelity of climate proxies in these mountains. To better understand past mountain precipitation and vegetation change, we produced three new records of the hydrogen and carbon isotopic composition of terrestrial leaf waxes (δ2Hwax and δ13Cwax) spanning the Holocene using lake sediment cores collected from Lake Mahoma (2990 m asl), Lake Africa (3895 m asl), and Lake Kopello (4017 m asl) in the Rwenzori Mountains, Uganda-Democratic Republic of Congo. We find similar trends at all three sites in reconstructed precipitation hydrogen isotopic composition (δ2Hprecip), which we interpret to reflect precipitation amount. Our records show drying occurred during the Younger Dryas (∼12 cal ka BP), enhanced precipitation during the African Humid Period (∼10-5 cal ka BP) and drying in the mid to late Holocene (∼5-0 cal ka BP), similar to adjacent lowland sites. We observe a gradual termination of the African Humid Period in the Rwenzori, consistent with many regional records. We also observe distinct patterns of Holocene precipitation change in Eastern and Western Africa, indicating differences in the delivery of moisture from the Atlantic and Indian Oceans. Despite changes in precipitation over the Holocene, the carbon isotopic composition of the waxes in Rwenzori lakes indicates constant C3 vegetation and eco-hydrological stability, in contrast to sites from lower elevations. This likely indicates climate remained humid and cool enough throughout the Holocene to maintain forest and alpine plant communities at these high-elevation mountain sites.

Fossil spring records from central Sudan reveal paleoenvironmental and settlement dynamics in the Eastern Sahel during the last 30 ka

Knowledge of past environmental change and prehistoric settlement dynamics in the Sahel east of the Nile is limited due to the scarcity of suitable sedimentary archives and archaeological sites. Here we present tufa-based paleoenvironmental records from the area of NW Butana (central Sudan, ∼55 km southeast of the Nile River) which show that increased rainfall and spring activity occurred in several discrete intervals during the last ∼30,000 years. Lithostratigraphic data combined with phytolith, malacological, paleopedological, and stable carbon isotope records revealed humidity peaks during late MIS3 and the early and middle Holocene. Gaps in lithological records correlated with dry periods of the Last Glacial Maximum and Younger Dryas. Minor wet pulses coinciding with Late Glacial interstadials indicate an early intensification of the African monsoon, which implies that a sharp climatic boundary existed between the Sahel and the Sahara during this period.These new paleoenvironmental records, together with archaeological evidence from Butana, provide a unique opportunity for understanding human ecology in the eastern Sahel. The peoples who inhabited this dryland area 30+ km from the Nile Valley could not rely on its relatively predictable resources of riverine, floodplain and lake habitats. New models of subsistence and settlement, and strategies of adaptations to seasonal and interannual environmental variability are needed.

Dynamic landscape response to Younger Dryas and earliest Holocene cooling events in the European Eastern Alps (Austria)

In classic loess areas research into dust deposition and concomitant environmental changes has a long history and numerous well-investigated loess-palaeosol sequences provide insights into Late Quaternary landscape responses to climatic change on orbital to centennial time scales. This contrasts with mountain regions, where an understanding of dust deposition under rapidly changing climatic and environmental conditions is much less developed. Here we describe two sediment records from the Austrian Alps that provide rare evidence for intramontane loess accumulation. Dust deposition has been numerically constrained to the Younger Dryas (YD) to earliest Holocene interval, making these sites the first proof of significant intramontane aeolian activity during this time interval in the Eastern Alps.At study site 1, located in the Northern Calcareous Alps, a loess layer 10–20 cm in thickness and laterally exposed over more than 300 m is sandwiched into an alluvial-fan succession. Two optically-stimulated luminescence ages of quartz and four radiocarbon ages of charcoals indicate loess accumulation during the Younger Dryas to earliest Holocene. This laterally extensive loess drape suggests much drier climatic conditions compared to today, which is corroborated by palynological investigations. Macro- and micro-charcoal particles within the loess indicate regional wildfires that might have exaggerated climatically induced sedimentary processes. The second site is a Mesolithic site located ∼30 km southeast of site 1. At site two, redeposited till and pebbly scree are sharply overlain by a few centimetre thick light-grey loess layer, which is capped by the archaeological living floor hosting 14C dated fireplaces suggesting human presence as early as 10.9 ± 0.2 cal ka BP. These radiocarbon ages in combination with single-grain IRSL dating of feldspar at site two suggests concomitant aeolian deposition at site 1 and 2.Recently, a widespread drape of loess deposited immediately subsequent to the LGM was described for the same sector of the Eastern Alps (Gild et al., 2018). The present study expands on these findings and provides evidence for the recurrence of loess deposition also during the YD to earliest Holocene, and suggests a highly sensitive response of the geomorphic system in mountain ranges to abrupt post-LGM climate fluctuations. We conclude that, in addition to moraine records of Alpine glaciers and speleothems that accurately chronicle Late Glacial temperature fluctuations, the spatio-temporal pattern of inner-Alpine loess deposits records the mode and sensitivity of landscape responses to such cooling events. Because such aeolian sediment layers can be redeposited or pedologically overprinted, they are often overlooked, and are thus still severely under-researched.