Holocene Transition Research Articles

A Paleoenvironmental Reconstruction of Lake Vrana on the Island of Cres (Croatia) Based on the Geochemistry and Mineralogy of the Late Pleistocene and Holocene Sediments

A 7.4 m long sediment core has been retrieved from the central part of Lake Vrana on the island of Cres to reconstruct the paleoenvironmental conditions. Lake Vrana is the deepest freshwater lake in Croatia, located in the karst region of the eastern Adriatic coast. A dated sediment sequence in Lake Vrana of 4.4 m has spanned the past 16.4 kyr, and it featured a dynamic sediment deposition until the beginning of the Holocene, including strong sediment input and supply to the lake by runoff sediments of dolomitic origin from the catchment in the period 16.4–14.4 cal kyr BP. High organic carbon content, which originates from mixed terrestrial and aquatic origins in the periods 14.4–13.3 cal kyr BP and 12.7–11.7 cal kyr BP, indicates fluctuating lake levels in shallow water environments during the Late Glacial to Holocene transition. The Holocene sequence indicates the development of more stable conditions and continuous sediment deposition, characterized by an increasing trend of siliciclastic sediments delivered into the lake during the early Holocene (11.7–10 cal kyr BP) and dominantly from 8 to 4.4 cal kyr BP, indicating enhanced input and erosion, which coincides with the humid and pluvial period recorded in the central Mediterranean region. It is followed by sediments with high organic carbon content between 4.4 and 1.6 cal kyr BP, which points to higher lake productivity. Calcite sedimentation prevailed between 1.6 to 0.4 cal kyr BP, indicating stable deeper-lake conditions. Predominantly, siliciclastic sediments from 0.4 to 0.1 cal kyr BP pointed to erosion during the Little Ice Age (LIA), with enhanced precipitation and sediment discharge from the catchment. The re-establishment of calcite sedimentation has been observed over the last 100 years.

Palaeoenvironmental Analysis of the Southern Part of the Danube–Tisza Interfluve (Hungary): The Northern Loess Wall of Katymár and the Hay Meadows and Loess Banks of Hajós

This study presents a comprehensive palaeoenvironmental reconstruction of the southern part of the Danube–Tisza interfluve in the Carpathian Basin from the Late Pleistocene to Early Holocene, addressing the region’s response to global climate forcings and local environmental factors based on multi-proxy analyses of two key protected areas: the Katymár brickyard and the hay meadows and loess banks of Hajós. By integrating radiocarbon-dated malacological, macrobotanical, pollen, phytolith, geochemical, and sedimentological analyses, it was possible to provide a picture of past climate–ecosystem interactions. The Katymár North sequence provides an extended chronology from Marine Isotope Stage 3 (MIS3, ca. 36,000 cal BP) through the Last Glacial Maximum (LGM) and into the Early Holocene, while the Hajós sequence offers high-resolution data for the LGM–Holocene transition. By the late Ice Age, humidity and surface moisture superseded temperature as primary palaeoecological limiting factors, promoting ecotone-like forest–steppe environments during cooling periods.

Higher abundance of disturbance‐favoured trees and shrubs in European temperate woodlands prior to the late‐quaternary extinction of megafauna

Abstract Large herbivorous mammals strongly influence vegetation structure by creating and maintaining open areas and causing disturbance within closed woody habitats. The herbivores alive today in Europe are only a small remnant of the large species that existed in high diversity and abundance before modern humans. The extinction of so many large herbivores during the last 50,000 years, and the loss of megaherbivores (body weight ≥1000 kg) from most of the continent before the Pleistocene–Holocene transition, is likely to have had cascading effects on vegetation structure and composition. To evaluate these effects within the European temperate forest biome, we examine the abundance change of three important European woody taxa (deciduous oaks, Quercus spp.; hazel, Corylus [mainly C. avellana]; and yew, Taxus baccata) before and after the late‐Quaternary downgrading of the region''s large herbivore fauna. These taxa are disturbance‐favoured, depend on canopy openings for regeneration, and tend to decline in closed dense forests. Quercus and Corylus may thrive in systems affected by megafauna herbivory or fire, whilst Taxus is fire‐sensitive but can thrive in grazed systems. Using pollen‐based reconstructions (REVEALS), we investigated the proportional cover of these three focal taxa in the Last Interglacial (129,000–116,000 before present [BP]) and early–mid‐Holocene (8700–5700 BP). We found that woodlands in the Last Interglacial exhibited higher cover of Corylus and Taxus relative to the Holocene, with the former reaching very high percentage cover; meanwhile, Quercus had a consistent, moderately high percentage cover in both periods. Furthermore, we found that the cover of Corylus and Taxus appeared to be influenced more by unmeasured, non‐climatic factors than Quercus. Synthesis: The abundance of Taxus suggests a limited role of fire; whilst the observed levels of Taxus, Corylus and Quercus align with the potential influence of megafauna herbivory; however, a direct quantitative link remains to be established. Our results suggest that vegetation was structurally and compositionally affected by differences in disturbance regimes between the Last Interglacial and early–mid‐Holocene, with the loss of diverse disturbance regimes likely contributing to the divergence of Holocene vegetation from long‐term ecological baselines.

Historical vegetation shifts in southeastern Amazonia: Unraveling ecotone dynamics in the Carajás region over the last ∼14000 cal yr BP

This study investigates the Pleistocene–Holocene transition in Serra Leste, a highly endangered southeastern Amazonian ecotone, with a focus on the lake-filling process, climate changes, and potential consequences to forest and savanna dynamics. The lake's development began at approximately 14000 cal yr BP, resulting from the collapse of the fractured lateritic crust. Sedimentation patterns and geochemical, palynological and micro-charcoal proxies reveal shifts in detrital input and redox conditions, forest/savanna areas, and local and regional fire events, indicating a highly dynamic environmental history. The evolution of the lake is characterized by initial deltaic lobe deposition and forest dominance, followed in the Middle Holocene by sedimentary gaps or reduced detrital input; woody vegetation dominance, with a notable shift toward a more open landscape; and savanna and semideciduous dry forest, accompanied by a decrease in ombrophilous forests. A resurgence in arboreal elements recorded in the Late Holocene indicates an expansion of ombrophilous forests under wetter climate conditions and the establishment of a more continuous forest matrix, with the presence of likely “hyperdominant” taxa. Frequent local fire events and the occurrence of temporarily correlated archeological sites in the Serra Leste region suggest the influence of ancient indigenous communities on vegetation changes during the Late Holocene.

Large herbivore δ18O as a proxy for aridity in the South African winter and year-round rainfall zone

Abstract This study explores patterning in δ18O values of tooth enamel in contemporary African herbivores from mainly C3-dominated ecosystems. Evapotranspiration causes plants to lose H216O to a greater extent than H218O, leaving leaves enriched in 18O. In eastern Africa, ES species (evaporation-sensitive species: those obtaining water from food) tend to have more positive δ18Oenamel values than EI species (evaporation-insensitive species: those heavily dependent on drinking water); the magnitude of the difference increases with increasing aridity. We find the same pattern applies in the winter and year-round rainfall region of southern Africa, allowing us to use δ18Oenamel in fossil animals to examine paleo-aridity. We apply this approach to infer aridity at Quaternary fossil assemblages from present-day winter and year-round rainfall zones, including Elandsfontein (ca. 1–0.6 Ma), Hoedjiespunt (ca. 300–130 ka), and Nelson Bay Cave (23.5–3 ka). This analysis suggests that (1) at various times during the Pleistocene, Elandsfontein and Hoedjiespunt environments were wetter than last glacial maximum (LGM) to Holocene environments at Nelson Bay Cave (year-round rainfall zone); and (2) considered alongside other evidence from the year-round rainfall zone, wetter conditions across the Pleistocene–Holocene transition at Nelson Bay Cave suggests that climate changes at near-coastal sites may be out of phase with the adjacent interior.

Hydraulic damage in subglacial conduits: Evidence from rock hydrofracture and hydraulic jacking for high fluid pressures during rapid melt of the Fennoscandian Ice Sheet

When large volumes of meltwater arrive suddenly at the glacier bed, the capacity of subglacial conduits is exceeded, generating transiently high fluid pressures. Yet we currently lack reliable markers for where such conditions developed on the beds of former glaciers. Here, we describe hydraulic damage that developed at close to or above overpressure (Pw > Pi) at the bed of the last Fennoscandian Ice Sheet in Uppland, east-central Sweden. Hydraulic damage is mostly confined within sharp lateral and vertical limits at the boundaries of former large subglacial conduits. The conduits include large Röthlisberger- and Nye-channels - eskers, esker corridors, and meltwater channels – that operated at full pipeflow. Wider (0.4–1.5 km) meltwater corridors opened under sheetflow with broad, shallow Hooke-channels. Hydraulic damage found in Precambrian gneiss and granite bedrock includes hydrofracturing and hydraulic jacking, with fracture propagation, dilation, and block displacement. Dilated fractures are often plugged by massive sands and diamicts or laminated silts. The fracture fills represent brief, single and multi-phase, injections of viscous, sediment-laden fluids at the ice sheet bed. The most spectacular effects of hydraulic damage are seen in the distension, disruption, and bursting of 1–20 m high rock bumps and hills. We present a detailed taxonomy for hydraulic damage and the consequent glacitectonic damage sustained during glacial ripping.Industrial fracking provides a well understood analogue for hydrofracture in nature. In subglacial settings, pathways for the flow of pressurised fluids are determined by the tensile strengths and hydraulic transmissivity of ice, till, and rock. The easiest flow path is across the glacier bed beneath sliding ice. Abrupt increases in meltwater flow force ice-bed separation. Opening of conduits under high fluid pressures triggers further propagation of hydrofractures into ice, till, and rock. On the floors of subglacial conduits, pressurised fluids entered the hard rock bed via old, mineral coated fractures. Under Poiseuille's law, fracture flow was initially slow due to the narrow apertures, but flow accelerated rapidly as fluid wedging dilated fractures. Fluid pressures in old fractures are constrained by published measurements for near-surface fracture toughness of ≤0.7 MPa at Forsmark, east-central Sweden. Formation of new rock hydrofractures overcame gneiss tensile strengths of 8–18 MPa. Hydraulic jacking required accommodation space that developed during conduit opening. Due to buoyancy and ice bed separation, lower excess pressures of <0.3 MPa were required to lift rock sheets up to 10 m thick. Hydraulic bursting developed in large conduits under very high, but rapidly fluctuating fluid pressures as dilating rock fractures extended to the glacier bed. Distension of rock surfaces was brief due to rapid leak-off and the inherent instability of overpressured conditions in dilatant, fractured rock masses.Hydraulic damage developed in Uppland when accelerating ablation generated large subglacial meltwater fluxes in response to abrupt warming at the Younger Dryas-early Holocene transition (∼10.8 ka). The large volumes of subglacial meltwater, the sudden increases in subglacial water flow and fluid pressures, and the release and transport of 2 m b-axis boulders in esker tunnels suggest that hydraulic damage was triggered at the onset of large subglacial floods. Ice thicknesses at distances of up to 50 km behind the grounding line at the retreating subaqueous ice margin indicate that steady-state hydrostatic pressures were ∼2.9–4.5 MPa. Such pressures are consistent with (i) extensive, but brief ice-bed separation in meltwater corridors under overpressure and (ii) the development of hydraulic damage in conduits close to the ice margin. More extreme fluid pressures developed instantaneously under hydraulic shock, as rapid subglacial pipeflow was suddenly stopped or diverted. The taxonomy of hydraulic damage presented here can be applied to any hard glacier bed to identify where large volumes of subglacial meltwater reached high pressures. Similar markers are widely reported from modern and former glacier beds.

Temperature changes of the Mid-Late Holocene transition in North China and their implications for regional cultural succession

Evaluating the influence of temperature on cultural successions in North China during the Mid-Late Holocene transition (MLHT) is a significant research problem. We used a lacustrine sedimentary profile (BG-2019) from Lake Baiyangdian, in the hinterland of the North China Plain, to quantitatively reconstruct temperature changes during the MLHT, using branched glycerol dialkyl glycerol tetraethers (brGDGTs). We then integrated this record with selected quantitative paleotemperature records from North China to explore the effects of temperature change on the evolution of Neolithic cultures in this region. The results show that the mean annual temperature (MAT) in the hinterland of the North China Plain during the MLHT averaged ∼15.7 °C (∼3.6 °C higher than today); and that three significant cooling events occurred (the 5.3 ka event, 4.8 ka event, and 4.2 ka event), at ∼5300-5100 cal yr BP, 4800 cal yr BP, and ∼4500-4300 cal yr BP, respectively, with cooling between −2.1 °C and −3.4 °C. Integration of our results with other regional quantitative paleotemperature records shows that these three cooling events are well documented in North China, with spatial consistency in their magnitude and onset of cooling. These cooling events are temporally correlated to two cultural transitions in North China: the cooling event at ∼5300-4800 cal yr BP corresponds to the decline of the Yangshao culture in the Central Plains region, and the decline of the Hongshan culture in the Yanliao region, which evolved into the Xiaoheyan culture. Additionally, we suggest that the cooling event at ∼5300-4800 cal yr BP, combined with the weakening of the summer monsoon, contributed to the end of the Yangshao culture and the rise of the Longshan culture in the Central Plains region, and that it accelerated the end of the Xiaoheyan culture and the rise of the Xiajiadian Lower Culture in the Yanliao region.

Holocene ecosystem and temperature development inferred from invertebrate remains in Zminje Jezero (Dinaric Alps, Montenegro)

AbstractLake Zminje Jezero (1535 m a.s.l.) in Montenegro was studied for chironomid and other aquatic invertebrate remains in a sediment sequence dating back to 12,000 calibrated 14C years before present (cal yr BP), providing, to our knowledge, the first lake-sediment record studied for chironomids and other associated chitinous aquatic invertebrate remains in the Dinaric Alps. Changes in chironomid and other invertebrate remains along the record make it possible to constrain changes of relevant environmental variables for aquatic invertebrates in the lake including temperature, oxygen availability, trophic status and water depth. The results suggest moderate changes in trophic conditions with chironomid assemblages indicating meso- to eutrophic conditions during the analysed interval. Invertebrate assemblages were typical for lakes with relatively high oxygen availability with a minor trend during the middle to late Holocene to conditions observed in lakes that are more hypoxic. A change in temperature is suggested in the earlier part of the record when the share of chironomid taxa adapted to warmer conditions increased, at the Younger Dryas to Holocene transition, whereas later no particularly pronounced shifts in temperature-sensitive taxa were observed. July air temperatures were estimated based on chironomid assemblages using a transfer function based on calibration data consisting of 117 lakes sampled in the Swiss Alps and northern Switzerland. The results suggest that temperatures rapidly increased by 5 °C at the onset of the Holocene (11,500 cal yr BP) leading to a relatively warm early to mid-Holocene and thereafter slightly decreased during the late Holocene. Reconstructed temperatures are discussed together with a previously published pollen record for our study site and are broadly consistent with other chironomid-based temperature reconstructions from Central, Eastern and Southern Europe. From ca. 3000 cal yr BP sedimentation rates increased and from ca. 500 cal yr BP onwards pollen data suggest that the vegetation and lake catchment were affected by human activities, possibly influencing chironomid and other invertebrate assemblages in the lake and thereby also reconstructed temperatures. Overall, our results show that combining analyses of chironomid and other invertebrate assemblages can provide valuable insights into long-term environmental changes and can provide temperature reconstructions for small mountain lakes in the Balkans, such as Zminje Jezero.

Holocene insolation and sea surface temperature influences on the polar front jet stream and precipitation in the midcontinental United States

Variability in the source and seasonality of precipitation in the midcontinental United States during the Holocene was investigated using isotopic and sedimentological data from Martin Lake, northeastern Indiana, USA. Between 7100 and 4000 years before present (yr BP; present = 1950 CE), high δ18Ocal and δ13Ccal values with low variability indicate that moisture was predominantly derived from subtropical, southerly sources and delivered primarily during the warm season. Mean state shifts toward lower δ18Ocal and δ13Ccal occurred at ca. 4000 and 2550 yr BP, respectively, indicating an increase in northerly-sourced cold-season precipitation during the Late Holocene (i.e., the past 4200 years) and a subsequent reduction in warm season duration after 2550 yr BP. Record low %lithics from ca. 5000 to 4000 yr BP indicates major reductions in warm-season rain storms, consistent with regional evidence of drought at this time. An increase in the amplitude of centennial-scale variability in δ18Ocal, δ13Ccal, and %lithics after 1900 yr BP indicates greater precipitation source variability during the Common Era. During this interval, precipitation fluctuated between southerly-sourced, convective rainstorms when the Northern Hemisphere (NH) was warm (e.g., during the Medieval Climate Anomaly; 700–1000 yr BP) and northerly-sourced rain and snow when the NH was cool (e.g., during the Little Ice Age; 150–550 yr BP). These trends, especially the change at ca. 4000 yr BP, are consistent with other North American paleoclimate records that collectively suggest a continental-scale shift in precipitation seasonality during the Middle to Late Holocene transition as the tropical Pacific Ocean transitioned from La Niña-like conditions to a more El Niño-like mean state. Concurrent NH cooling and persistent El Niño-like conditions during the Late Holocene would have favored a southerly polar front jet stream with enhanced ridge and trough atmospheric circulation over North America – conditions resembling the positive mode of the Pacific-North American teleconnection (PNA). This would have increased interactions between high-latitude and subtropical airmasses over the midcontinent, increasing the proportion of northerly precipitation with low δ18O delivered during the cold season (i.e., snowfall) and during extended periods with +PNA-like atmospheric circulation (e.g., the Little Ice Age).

The fossil avian assemblage from Cova Foradada (Calafell, Spain) during the Late Pleistocene to Holocene transition

The end of the Pleistocene to the Holocene is a moment of particular interest, as several environmental changes coincided with some significant culture shifts: the Middle-to-Upper Palaeolithic and the Palaeolithic to Neolithic transitions. Here we present the analysis of the environmental conditions during this period in the Northeast Iberian Peninsula, based on the bird remains from Cova Foradada (Calafell, Tarragona), a site known for its archaeological record, including the symbolic use of imperial eagle phalanges. The stratigraphic sequence of the site is divided into five units, spanning from the Late Pleistocene (Units V to III) to the Northgrippian (Units II and I). A total of 1310 avian remains from these five units have been analysed, revealing the presence of at least 25 bird taxa. This suggests a landscape dominated by open areas with forest or scattered trees. The presence of four species, currently absent around the site, could be related to habitat expansions during colder periods, or to sporadic visits to the area. The layers in Unit IV show a trend towards a reduction in woodlands and an increase of open areas, which may be related to the Heinrich 4 event (ca. 40Ka). The layers in Unit III show the lowest proportion of woodlands and the highest proportions or rocky areas in the sequence. In the Holocene units the presence of water bodies is indicated by the presence of aquatic taxa. Diurnal birds of prey appear to be the main contributors to the bird accumulation, and probably also contributed to the accumulation of leporids. The impact of humans on birds at the site has been documented in several remains, confirming the mixed origin of the avian accumulation and contributing to increasing cases of interaction between humans and large diurnal raptors during Iberian prehistory.

First automatic size measurements for the separation of dwarf birch and tree birch pollen in MIS 6 to MIS 1 records from Northern Germany.

During past glacial periods, the land cover of Northern Eurasia and North America repeatedly shifted between open steppe tundra and boreal/temperate forest. Tracking these changes and estimating the coverage of open versus forested vegetation in past glacial and interglacial landscapes is notoriously difficult because the characteristic dwarf birches of the tundra and the tree birches of the boreal and temperate forests produce similar pollen grains that are difficult to distinguish in the pollen record. One objective approach to separating dwarf birch pollen from tree birch pollen is to use grain size statistics. However, the required grain size measurements are time-consuming and, therefore, rarely produced. Here, we present an approach to automatic size measurement based on image recognition with convolutional neural networks and machine learning. It includes three main steps. First, the TOFSI algorithm is applied to detect and classify pollen, including birch pollen, in lake sediment samples. Second, a Resnet-18 neural network is applied to select the birch pollen suitable for measurement. Third, semantic segmentation is applied to detect the outline and the area and mean width of each detected birch pollen grain. Test applications with two pollen records from Northern Germany, one covering the Lateglacial-Early Holocene transition and the other covering the Mid to Late Pleistocene transition, show that the new technical approach is well suited to measure the area and mean width of birch pollen rapidly (>1000 per hour) and with high accuracy. Our new network-based tool facilitates more regular size measurements of birch pollen. Expanded analysis of modern birch pollen will help to better understand size variations in birch pollen between birch species and in response to environmental factors as well as differential sample preparation. Analysis of fossil samples will allow better quantification of dwarf birch versus tree birch in past environments.

Numerical Reconstruction of Landslide Paleotsunami Using Geological Records in Alpine Lake Aiguebelette

AbstractMass movements and delta collapses are significant sources of tsunamis in lacustrine environments, impacting human societies enormously. Paleotsunamis studies play an essential role in understanding historical events and their consequences, along with their return periods. This study investigates a paleotsunami induced by a subaqueous mass movement during the Younger Dryas to Early Holocene transition, ca. 11,700 years ago in Lake Aiguebelette (NW Alps, France). Utilizing high‐resolution seismic and bathymetric surveys associated with sedimentological, geochemical, and magnetic analyses, we uncovered a paleotsunami triggered by a seismically induced mass transport deposit. Numerical simulations of mass movement have been conducted using a visco‐plastic Herschel‐Bulkley rheological model and corresponding tsunami wave modeled with dispersive and nondispersive models. Our findings reveal for the first time that dispersive effects may be negligible for subaqueous landslides in a relatively small lake. This research reconstructs a previously unreported paleotsunami event and enhances our understanding of tsunami dynamics in lacustrine environments.

Transformation of regional vegetation driven by climate change during the last deglacial–early Holocene at Chaohu Lake, eastern China: New pollen insights

Reconstructing the vegetation history of east China during the last glacial–interglacial transition is crucial for understanding the East Asian Summer Monsoon (EASM) evolution. Here, we present a new high-resolution pollen record from Chaohu Lake to determine the detailed process of regional lowland vegetation succession and its response to the EASM changes during the last glacial–Holocene transition (13.9–9.1 cal ka BP) in the lower Yangtze Valley, eastern China. During the Older Dryas (OD, 13.9–13.5 cal ka BP) period, regional forest-steppe indicative of co–dominance of Artemisia, Poaceae, and deciduous Quercus was present under a cool and dry climate. During the Allerød Interstadial (AI, 13.5–12.9 cal ka BP), significant arboreal expansions of deciduous Quercus, Hydrangea type and evergreen Quercus occurred, while herbs retreated significantly, presumably driven by the relatively warm, humid climate. Forest-steppe readvanced during the Younger Dryas (YD) interval, as indicated by increases in Poaceae and Artemisia, suggesting a cool and dry climate. During the early Holocene, extensive oak-pine forest flourished as regional vegetation, responding to pronounced climatic amelioration.Our pollen-based climatic record is closely correlated with stalagmites δ18O records from EASM region and Greenland ice cores δ18O records, indicating the teleconnection between EASM variation and North Atlantic climate during the last deglacial–early Holocene. However, our record indicates an intensified EASM during the early AI and a prolonged onset excursion during the YD, diverging from North Atlantic climate but closely correlated to sea surface temperature (SST) variations in the western tropical Pacific.

Late Pleistocene-Holocene sea level and climate changes in the Gulf of Saros: Evidence from seismostratigraphic record and sediment core data

A detailed record of sea level changes and climate oscillations in the Gulf of Saros during the late Pleistocene to the Holocene is provided by high-resolution seismic reflection profiles and analysis of a sediment core. The seismic stratigraphy reveals the formation of four main depositional units bounded by prominent reflection surfaces, reflecting high sea level variations. The Last Glacial Maximum period in the gulf is associated with the lowstand sea level, forming the deepest marine terrace at −148 m. The increasing sea level due to post-glacial warming was accompanied by the deposition of transgressive units characterized by coastal onlaps together with local channel-fills. This transgressive phase was modulated by three brief still-stands sea levels at 17 cal ka BP, 14.6 cal ka BP and 13.6 cal ka BP, producing the younger marine terraces in the gulf at −135 m, −112 m and −90 m, respectively. A comparison of their depths with the global sea level curve reveals elevation differences with decreasing subsidence rates from the older to younger ages, implying tectonic subsidence along the gulf floor.The close correlation of multi-proxy data from core SAG-22 in the gulf with the northern Aegean and Anatolia data strongly indicates that the timings of the past climate events generally agree with the global and regional climate patterns. The warm climate around the gulf during the late phase of Bølling/Allerød (13.3–12.6 cal ka BP) is represented by high marine biological productivity and improved ventilation in the deeper water due to subsequent transgression. Permafrost formation in the catchment area during the following cold and dry Younger Dryas period (12.6–11.7 cal ka BP) resulted in reduced soil erosion and sediment input to the gulf. Noticeable warming during the Early Holocene between 11.2 cal ka BP and 9.4 cal ka BP is recorded by the multi-proxy data of the core when the enhanced marine biological productivity occurred above the poorly oxygenated deep water column. The climatic deterioration to a cooler and drier phase during the Early to Middle Holocene transition (9.4–7.8 cal ka BP) resulted in intense physical weathering and erosion, causing the highest sedimentation in the gulf. The later period of the Holocene is associated with the formation of two discrete sapropels at 7.8 cal ka BP and 5.4 cal ka BP that were accompanied by warm and wet climates around the gulf.

A Social Network Analysis of Traditional Labrets and Horizontal Relationships in the Salish Sea Region of Northwestern North America

AbstractIn the Salish Sea region, labret adornment with lip plugs signify particular identities, and they are interpreted as emblematic of both membership in horizontal relationships and achieved status for traditional cultures associated with labret wearing on the Northwest Coast (NWC) of North America. Labrets are part of a shared symbolic language in the region, one that we argue facilitated access to beneficial horizontal relationships (e.g., Angelbeck and Grier 2012; Rorabaugh and Shantry 2017). We employ social network analysis (SNA) to examine labrets from 31 dated site components in the Salish Sea region spanning between 3500 and 1500 cal BP. Following this period, the more widely distributed practice of cranial modification as a social marker of status developed in the region. The SNA of labret data shows an elaboration and expansion of antecedent social networks prior to the practice of cranial modification. Understandings of status on the NWC work backward from direct contact with Indigenous societies. Labret wearing begins at the Middle-Late Holocene transition, setting an earlier stage for the horizontal social relationships seen in the ethnohistoric period. These findings are consistent with the practice as signifying restricted group membership based on affinal ties and achieved social status.

Biostratigraphic analysis of a Late Pleistocene to Holocene section from Punta Pescador, eastern Venezuela

A biostratigraphic study was undertaken on a shallow borehole drilled to 90 meters in the easternmost Orinoco Delta, Venezuela. Twenty-eight samples were analyzed for palynomorphs and foraminifera. Palynomorphs were recovered in all except one sample consisting of 178 entities. Foraminifera assemblages of low diversity were recovered in 17 of the 28 samples. The analysis provides some insight into the vegetation, climate, and depositional history allowing comparisons with other Late Pleistocene to Holocene studies in the northern South America region. The Late Pleistocene to Early Holocene transition is marked by an unconformity, where the vegetation changes from a diverse flora of Mauritia flexuosa, grasses (Poaceae), ferns, and mangroves (Rhizophora, Avicennia) to one dominated by Rhizophora around 10,000 years BP. This transition also contains reworked palynomorphs and abundant black wood (inertinite), indicative of erosion and oxidation. The absence of foraminifera suggests an exposed continental shelf and lowering of sea level. The Early Holocene mangrove flora is replaced by vegetation dominated by Mauritia flexuosa, with Symphonia globuliflora, grasses, and ferns. The palynological signature for the upper 42 m of the section compares favorably with a previous study of the Holocene in the Orinoco Delta. Radiocarbon dating indicates there is an unconformity or condensed section at the vegetation change, representing as much as 5500 ± years. Foraminifera indicate an open shelf environment immediately above this horizon followed by a significant shallowing to nearshore transitional environments near the top of the section. Local climate and/or human influence may have been a factor in the abundance of Mauritia flexuosa as suggested by other studies.

Abrupt cooling of cold seasons at the middle-late Holocene transition revealed by alkenone records from North China

In saline lakes, the paleoenvironmental interpretation of long-chain alkenones (LCAs) is difficult due to the inputs of Isochrysidales Group 2i, which are ice-related bloomers. Here, we perform detailed analysis of LCAs and long-chain alkenoates in sediment cores from Lake Daihai in north China. During the late Holocene, alkenone-inferred temperatures and the Group 2i species abundance indicate a long-term warming trend in cold seasons (winter and early spring), possibly driven by regional insolation and by atmospheric CO2 concentrations. Notably, our records indicate cold climate conditions during the period of 4.3–3.0 cal ka BP, possibly linked to the abrupt expansion of Arctic winter sea ice in a given of low insolation and atmospheric CO2 concentration conditions. The abrupt cooling may have led to the collapse of the East Aian Summer Monsoon (EASM) and the deterioration of the ecosystems in northern China during the middle to late Holocene transition, and thus likely accounted for the nearly synchronous Chinese Neolithic cultural collapses.

Earliest Records of Holocene Cetaceans in the Black Sea

ABSTRACTThe timing of the Holocene transition of the Black Sea from a brackish lake to a marine sea has long been debated. Here, we report on the earliest records of cetaceans in the Black Sea region as a proxy for the connection with the Mediterranean and the transition from a brackish to marine environment. We base our analysis on cetacean skeletal finds and archival data on cetacean skeletal remains from the Bosphorus, the western, northern and eastern Black Sea, and the Kerch Strait. We find that all three contemporary cetacean species in the Black Sea – the harbour porpoise, bottlenose dolphin and common dolphin – had migrated out of the Mediterranean to the Bosphorus and the Black Sea at least 8000–7000 years ago and reached the northern Black Sea by 5500 years ago at the latest. Our study suggests the establishment of a Mediterranean–Black Sea biogeographical connection for marine vertebrates at least 7000 years ago. The early presence of cetaceans in the Black Sea has implications for understanding its Holocene transition, as well as the evolutionary and ecological history of these species more generally.

The Enmynveem mammoth and vegetation changes in arctic Chukotka during the Late Quaternary

Abstract Mining operations in the Enmynveem valley, northeastern Siberia, exposed a well-preserved right hind leg of Mammuthus primigenius (woolly mammoth), dated to ca. 37,500 cal yr BP. The leg had a fracture that crosscut the midsections of the tibia and fibula. Additional skeletal and soft tissue remains, including two mummified adults (Berezovka, ca. 47,200 cal yr BP; Bolshoi Lyakhovsky, ca. 37,000 cal yr BP), document the presence of mammoths in interior mountain valleys and across both northern and southern coasts of far northeastern Siberia during Marine Isotope Stage (MIS) 3. A mosaic of herb-dominated tundra communities characterized the vegetation of the Enmynveem site during late to middle MIS 3 and MIS 2 (ca. 37,000–17,000 cal yr BP). Shrubs were limited to Salix during the late Pleistocene, whereas Betula also may have been present in sheltered sites during MIS 3. Herb communities remained dominant during the late Pleistocene–Early Holocene transition, although shrub Betula increased during this interval. By ca. 10,200 cal yr BP, the vegetation was Betula–Alnus shrub tundra. Larix and Pinus pumila were established in the valley by ca. 8700 cal yr BP and ca. 5700 cal yr BP, respectively.

Geochemical Record of Late Quaternary Paleodepositional Environment from Lacustrine Sediments of Soda Lake, Carrizo Plain, California

This study investigates the responses of the depositional environments of Soda Lake sediments to climatic shifts from the Last Glacial Maximum to the Holocene epoch based on the results of major and trace elements of the North Soda Lake (NSL) NSL1A core. The NSL1A core records the sedimentary evolution of the Soda Lake watershed since at least 25 cal ka BP. Element analyses provide evidence that Soda Lake sediments are mostly derived from marine sequences in the Southern Coast Ranges of California. Variation in proxies for paleoweathering, paleoclimate, paleosalinity, paleoproductivity, paleoredox, and water depth is utilized to reconstruct the evolution of the sedimentary environment. The Chemical Index of Alteration (CIA) values indicate low to moderate chemical weathering in the sediment source regions. Paleoredox proxies indicate that the NSL1A core formed in a mainly subreduction environment. The NSL1A core is divided into four zones based on the results of the proxies. Zone 4 (5.0–5.8 m) of the sediment core indicates stable hydroclimatic conditions with low and constant sand and silt content, suggesting a warm and relatively humid environment. Zone 3 (3.35–5.0 m) represents the early half of the Last Glacial Maximum interval and a high lake stand. The elevated sand content suggests postflood events due to the northerly migration of westerly storm tracks. Zone 2 (1.075–3.35 m) reveals nuanced changes, including decreasing salinity, slight increases in wetness, detrital trace metals, and paleoproductivity. These subtle shifts suggest a multifaceted environmental evolution: a trend toward wetter conditions alongside a prolonged shift from cooler to warmer periods. Zone 1 (0.15–1.075 m) spans the Lateglacial to Holocene transition as well as Early and Middle Holocene, marked by significant hydrologic and ecologic variability including rapid warming during the Bølling–Allerød and rapid cooling linked to the Younger Dryas.