Kyr BP Research Articles

Sedimentary evolution and lake level fluctuations of Urmia Lake (north‐west Iran) over the past 50 000 years; insights from Artemia faecal pellet records

AbstractA 25 m long sediment core from hypersaline Urmia Lake (north‐west Iran) was studied for the Late Quaternary depositional history and palaeoclimate variations using the abundance and compositional characteristics of Artemia faecal pellets. Sediment analysis is supported by scanning electron microscopy – energy dispersive X‐ray spectroscopy, organic and inorganic carbon content measurements, and stable isotopes (δ13C and δ18O) from faecal pellet carbonates. The imprecise chronology of the core back to 50 kyr bp is supported by ten radiocarbon ages from faecal pellets and bulk sediments. The palaeoenvironmental record is subdivided into four periods: (i) During much of Marine Isotope Stage 3, a period of lake level lowering is characterized by a decreasing amount of faecal pellets, and an increasing amount of coated grains, sulphate minerals and reworked shell fragments. (ii) During late Marine Isotope Stage 3 and early Marine Isotope Stage 2 a lake level lowstand and a lake floor exposure is interpreted based on the relatively low abundance of pellets, which are multicoloured and appear together with volcanic lithics and rounded sulphate minerals. (iii) During late Marine Isotope Stage 2 the record is devoid of pellets but dominated by large sulphate crystals suggesting a prolonged low lake level. (iv) During Marine Isotope Stage 1 a relative lake level highstand is rapidly established with sediments that are highly abundant in fresh pellets. The modern lake level lowstand is represented by a salt crust. The δ13C and δ18O records measured from faecal pellet carbonates suggest a link with the precipitation versus evaporation balance in the lake over time. From bottom to top the linear trend towards more negative delta values illustrates the increasing amount of precipitation arriving at the lake from the Late Pleistocene to the Holocene. Two prominent isotope minima during the Late Pleistocene and one prominent minimum in the early Holocene mark relative high lake levels, which can also be linked to Lake Van in Turkey.

Discerning the sulfur geochemical features of turbidites and methane-rich sediments from the South China sea

Upward diffusion of dissolved methane and associated anaerobic oxidation of methane (AOM) coupled with microbial sulfate reduction (MSR) are widespread in normal hemipelagic sediments of continental margins. The occurrence of authigenic sulfur enrichment in such sediments is usually regarded as an indicator of AOM; however, extensive MSR and authigenic iron sulfide generation also occur in turbidites. Therefore, research attention should be directed toward determining the geochemical features of authigenic sulfur mineralization in methane-rich background sediments and turbidites. Here we report the sedimentology and geochemical composition of sediments from four piston cores (CL30, CL44, CL47, and CL3A) containing turbidite layers from methane-rich areas of the South China Sea. The turbidite layers were deposited at 17–15 kyr BP or earlier during the last glacial period and were located above the present sulfate–methane transition zone (SMTZ). The median grain size, proportion of sand-sized grains, and Si, Ti, K, and Zr contents show marked elevation in the turbidite layers compared with the background sediments, indicating the input of large amounts of terrigenous detrital matter with coarser grains. High total sulfur (TS) contents and low δ34SAIS values (AIS: acid-insoluble sulfur) (−35.2‰ to −26.1‰) are observed within turbidite layers relative to the background hemipelagic sediments in core CL44. These results suggest that intensive sulfidization occurred as a result of enhanced organoclastic sulfate reduction rates in turbidite horizons, which were probably caused by the resultant decrease in downward oxygen flux and waning bioturbation after rapid deposition of turbidites. In comparison, TS contents are higher and δ34SAIS values are positive (0.2‰–46.8‰) within the SMTZ on account of the rapid consumption of sulfate and build-up of isotopically heavier hydrogen sulfide pools via intensive AOM. Moreover, authigenic barium (Ba) enrichments commonly occur in the depth interval immediately above the SMTZ rather than within turbidite layers; therefore, they serve as a useful indicator of the position of the SMTZ. This study presents distinct differences in the geochemical compositions of turbidity deposits and methane-rich background sediments and highlights that a multi-proxy approach including sedimentological and geochemical analyses should be used to constrain the types of MSR in deep-sea sediments, given the common occurrence of turbidites and subsurface methane release in marginal deep-sea areas. It is also suggested that if applied with caution, S–C–Ba geochemical patterns can be used to identify palaeo-SMTZs and palaeo methane-rich zones in turbidite-containing strata.

Two-phase hydrological changes during the mid-to late Holocene transition in Southwest China

The Indian summer monsoon (ISM) rainfall feeds a vast majority of the densely populated Asian continent. A deep understanding of the ISM rainfall variations and the underlying driving mechanisms during the Holocene is essential to predict its future behaviors and formulate improved mitigating strategies under the context of global warming. It has been widely recognized that the ISM intensity declined from the early to late Holocene, with a mid-to late Holocene transition. However, the nature of hydrological changes during this critical transition still remains vague. In this study, hydrological changes in Southwest China during the mid-to late Holocene transition are reconstructed based on the molecular and compound-specific carbon and hydrogen isotopic compositions of leaf waxes (δ13C and δD of n-alkanes) from the Yanjiang peat deposit in western Yunnan. Results reveal two-phase changes of hydroclimate during the mid-to late Holocene transition in Southwest China. During the first phase (5.5–4.2 cal kyr BP), Southwest China experienced an abrupt drying as indicated by the pronounced increases in both δ13C and δD values of the C29n-alkane (δ13CC29 and δDC29) by 2.2% and 26‰, respectively. The second phase (4.2–2.6 cal kyr BP) witnessed shortening in the duration of the ISM season without further aridification, as demonstrated by an increase up to 35‰ in the δDC29 values and moderate oscillations in the δ13CC29 values. Such a two-phase hydrological transition is likely to have been triggered by the changes in the summer solar insolation and amplified by the ocean-atmosphere interactions. The first phase is primarily modulated by the positive Indian Ocean Dipole mean state, while the second phase is mainly linked with a more El Niño-like mean state over the Pacific Ocean.

Vegetation, hydrology, and quantitative monsoon precipitation since the Last Glacial Maximum in Central China

The Yangtze River Basin is a crucial region in the monsoon region of China, and reconstructing its hydrological and precipitation evolution is important for developing a more robust understanding of the evolution of the East Asian Summer Monsoon. A pollen record from a strata profile (JZ2010) in the Jianghan Basin of Central China reveals variations in paleovegetation and paleoenvironmental and paleoclimatic conditions covering the last 24 cal kyr BP at ~90 years resolution. We perform a quantitative precipitation reconstruction (based on a weighted averaged partial least squares method). Results of the study show that the vegetation in the region experienced a succession from coniferous and broad-leaved mixed forest to evergreen and deciduous mixed forest and then to secondary coniferous forest. Over the past 24 kyr, the climate was relatively dry during the deglacial period, particularly during HS1 and the Younger Dryas cold event, interrupted by a warm and humid Bølling-Allerød. Precipitation in the early Holocene was at its maximum, peaking between 10.0 and 7.0 cal kyr BP followed by drier conditions between 6.5 and 4.5 cal kyr BP. Subsequent wetter conditions lasted until 3.8 cal kyr BP, after which precipitation gradually declined. Overall, the quantitative precipitation reconstruction is consistent with other proxy-based precipitation reconstructions in the Yangtze River region. However, the temporal pattern of variations in precipitation is distinct from that of the northern China monsoon region, where the precipitation peak occurred during the mid-Holocene. The study suggests that, prior to the Holocene, climate change was controlled by insolation dynamics and high latitude teleconnections, while during the Holocene it was primarily influenced by low latitude teleconnections, including the El Niño-Southern Oscillation, which controlled the dipolar rainfall pattern in the monsoon region of China. The high resolution record of changing climate in the East Asian monsoon region over a period spanning the LGM and Holocene provides a useful benchmark for modelling future precipitation change in southern and northern China against the background of global warming.

Dinoflagellate cyst distribution over the past 9 kyrs BP from offshore east Tasmania, southeast Australia

Southeastern Australia’s marine waters are notably warming, surpassing global averages. This region has emerged as a strategic location for researching planktic microfossils, particularly dinoflagellate cysts, in modern and Late Quaternary sediments, offering crucial insights into the biophysical properties of mid-latitude waters. This study examined cyst distribution in marine sediment cores near Maria Island, Tasmania, southeastern Australia, up to 9000 years before present (kyrs BP). Dominant cysts included Protoceratium reticulatum, Protoperidinium spp. (P. avellana, P. conicum, P. oblongum, P. subinerme, P. shanghaiense), and Spiniferites spp. (S. bulloideus, S. hyperacanthus, S. membranaceus, S. mirabilis, S. pachydermus, and S. ramosus). Inshore, Spiniferites spp. constituted a higher proportion (up to 61%), while offshore was dominated by P. reticulatum (up to 80%). Impagidinium spp. and Nematosphaeropsis labyrinthus were exclusively found offshore and displayed increased abundance from ∼6 kyrs BP, suggesting a shift from a shallow to a deep-water habitat. Alexandrium tamarense species complex cysts were present over 140 years inshore and approaching 9 kyrs BP offshore, indicating a longstanding endemic presence. Gymnodinium catenatum cysts were detected exclusively inshore from ∼50 years ago, indicating a relatively recent bloom phenomenon. The East Australian Current’s limited southward reach is suggested by the absence of the warm-water cyst-producing taxon Lingulodinium polyedra. Similarly, the non-detection of the cold-water species Spiniferites antarctica and Impagidinium pallidum reflects Subtropical Front boundaries against subantarctic incursions from the south. In contrast to coccolithophores in the same core, no noticeable shift from cold to warm-water dinoflagellate cyst species was observed. This documentation of dinoflagellate cysts aids in predicting environmental impacts on local communities and beyond.

Sediments as Sentinels of Pollution Episodes in the Middle Estuary of the Tinto River (SW Spain)

Estuaries are excellent environments for identifying pollution episodes that have affected river basins, as their sediments are the final destination of some of the pollutants. This paper studies the geochemical evolution of five elements (As, Co, Cu, Pb, Zn) in a core extracted from the middle estuary of the Tinto River (SW Spain). The results are based on facies interpretation, ICP atomic emission spectrometry analysis, the application of a regional background to obtain the geoaccumulation index and dating. The main objective of this communication is the detection of natural or anthropogenic pollution episodes in the middle estuary of the Tinto River (SW Spain). Four pollution episodes have been detected: (1) ~5.8 cal. kyr BP, probably caused by natural acid rock drainage processes derived from the oxidation of the Iberian Pyritic Belt deposits found in its drainage basin; (2) 4.7–4.5 kyr BP, coming from the first mining activities and characterized by a significant increase in the concentrations of the five elements analyzed; (3) 1850–1960 interval, coinciding with intensive mining and characterized by increasing values of As and, to a lesser extent, Pb (intensive mining); and (4) the second half of the 20th century, with high element concentrations from mining and industrial effluents. All episodes show an increase in their geochemical classes deduced from the geoaccumulation index. This communication can serve as an example for assessing the impact of different types of pollution in estuarine environments.

A Continuous Centennial Late Glacial-Early Holocene (15-10 cal kyr BP) Palynological Record from the Iberian Pyrenees and Regional Comparisons.

This paper presents the first continuous (gap-free) Late Glacial-Early Holocene (LGEH) pollen record for the Iberian Pyrenees resolved at centennial resolution. The main aims are (i) to provide a standard chronostratigraphic correlation framework, (ii) to unravel the relationships between vegetation shifts, climatic changes and fire, and (iii) to obtain a regional picture of LGEH vegetation for the Pyrenees and the surrounding lowlands. Seven pollen assemblage zones were obtained and correlated with the stadial/interstadial phases of the Greenland ice cores that serve as a global reference. Several well-dated datums were also derived for keystone individual taxa that are useful for correlation purposes. Four vegetation types were identified, two of them corresponding to conifer and deciduous forests (Cf, Df) and two representing open vegetation types (O1, O2) with no modern analogs, dominated by Artemisia-Poaceae and Saxifraga-Cichorioideae, respectively. Forests dominated during interstadial phases (Bølling/Allerød and Early Holocene), whereas O1 dominated during stadials (Oldest Dryas and Younger Dryas), with O2 being important only in the first half of the Younger Dryas. The use of pollen-independent proxies for temperature and moisture allowed the reconstruction of paleoclimatic trends and the responses of the four vegetation types defined. The most relevant observation in this sense was the finding of wet climates during the Younger Dryas, which challenges the traditional view of arid conditions for this phase on the basis of former pollen records. Fire incidence was low until the Early Holocene, when regional fires were exacerbated, probably due to the combination of higher temperatures and forest biomass accumulation. These results are compared with the pollen records available for the whole Pyrenean range and the surrounding lowlands within the framework of elevational, climatic and biogeographical gradients. Some potential future developments are suggested on the basis of the obtained results, with an emphasis on the reconsideration of the LGEH spatiotemporal moisture patterns and the comparison of the Pyrenees with other European ranges from different climatic and biogeographical regions.

A radiocarbon spike at 14 300 cal yr BP in subfossil trees provides the impulse response function of the global carbon cycle during the Late Glacial.

We present new 14C results measured on subfossil Scots Pines recovered in the eroded banks of the Drouzet watercourse in the Southern French Alps. About 400 new 14C ages have been analysed on 15 trees sampled at annual resolution. The resulting Δ14C record exhibits an abrupt spike occurring in a single year at 14 300-14 299 cal yr BP and a century-long event between 14 and 13.9 cal kyr BP. In order to identify the causes of these events, we compare the Drouzet Δ14C record with simulations of Δ14C based on the 10Be record in Greenland ice used as an input of a carbon cycle model. The correspondence with 10Be anomalies allows us to propose the 14.3 cal kyr BP event as a solar energetic particle event. By contrast, the 14 cal kyr BP event lasted about a century and is most probably a common Maunder-type solar minimum linked to the modulation of galactic cosmic particles by the heliomagnetic field. We also discuss and speculate about the synchroneity and the possible causes of the 14 cal kyr BP event with the brief cold phase called Older Dryas, which separates the Bølling and Allerød millennium-long warm phases of the Late Glacial period. This article is part of the Theo Murphy meeting issue 'Radiocarbon in the Anthropocene'.

Spatio‐Temporal Variations in Sediment Delivery as a Response to Rapid Quaternary Climate Change in the Lake Malawi Rift, East Africa

AbstractThe interplay of rapid climate change and tectonics drives landscape development, sediment routing, and deposition in early‐stage continental rift systems. The Lake Malawi Rift, in the Western Branch of the East African Rift, is an archetype of a juvenile rift and an ideal natural laboratory for evaluating lacustrine source‐to‐sink systems on orbital or shorter timescales. We examine the interplay of these processes over the past 140 kyr using observations from nested seismic reflection data sets tied to scientific drill cores, which calibrate numerical forward models of this closed sedimentary system. Fault slip rates measured from seismic data drive tectonic displacements in the model. Satellite‐derived precipitation maps constrain modern precipitation and are scaled to previous hydrologic balance studies to reconstruct past climates. Our model reproduces known sediment thicknesses across the rift and accounts for 96% of the estimated siliciclastic sediment deposited over the past 140 kyr. The results demonstrate that the onset of arid climate conditions (140–95 kyr BP) causes extreme drainage adjustments downstream and the formation of mega‐catchments that flow axially into a shallow restricted paleo‐lake. Sedimentation rates during this time are twice the present values due to increased sediment focusing via these axial systems into a much smaller, hydrologically closed lake. As the climate became wetter (95–50 kyr BP), the lake rapidly expanded, decreasing both erosion and sedimentation rates across the rift. This closed‐loop approach allows us to evaluate the role of high‐frequency climate change in modulating basin physiography as well as sediment fluxes in juvenile rift systems.

Sedimentary evolution of the western North Yellow Sea mud patch: A Holocene perspective

The western North Yellow Sea mud patch has a unique location, abundant sediment supply and a complex sedimentary environment. Reconstructing its sedimentary evolution is crucial for a comprehensive understanding of source to sink process in the North Yellow Sea. Using core W03 collected from the mud patch, this study unravels its Holocene history through analysis of sedimentology, mineralogy and micropalaeontology. The results indicate that core W03 can be divided into three depositional units (DU). DU3 (538-461 cm) is composed of earthy yellow clayey silt and characterized by a hard layer. It was formed in the near-coast environment between 10.3 and 9.8 cal kyr BP, a hiatus period between Melt Water Pulse 1B and 1C events. DU2 (460-341 cm) was formed during the period of 9.8–6.5 cal kyr BP. As sea level rose, the westward retreat of the Yellow River mouth caused the transportation of Yellow River-derived sediment over longer distances, leading to an increase in flaky minerals. The rising sea level also induced a shift towards a reducing environment in the western North Yellow Sea. DU1 (340-0 cm) was formed after 6.5 cal kyr BP. During this period, the study area remained in a shelf shallow sea environment characterized by relatively strong chemical hydrolysis and reducing conditions. The intensification of the Yellow Sea Warm Current and an increase in Yellow River sediment transported to the sea led to an obvious increase in sedimentation rate after 2.3 cal kyr BP.

LATE GLACIAL PALAEOENVIRONMENT AND DEVELOPMENT OF PROGLACIAL LAKES ON THE NORTHERN COAST OF THE SAMBIAN (KALININGRAD) PENINSULA<a href="#FN1"><sup>1</sup></a>

Comprehensive investigations of the northern coast of the Sambian (Kaliningrad) Peninsula, that included geomorphological survey, lithostratigraphic description of the section logs, diatom, botanical and LOI analyses, radiocarbon dating, and GNSS survey relating lithological boundaries and sampling levels to the sea level and determining terrace elevations, were performed. New data on the regional palaeogeographic settings of the Late Glacial period and the stages of development of the large proglacial basin, the Baltic Ice Lake (BIL) were obtained. It has been established that after the degradation of the last glaciation, erosional (subaquatic) processes prevailed in the coastal area, while in the interval of 14–13 cal kyr BP subaerial conditions established at the study site, and tree-moss phytocenoses formed during the Allerød warming. At the end of the warming period there was a shallow, isolated lake, with decreasing depth. During the Younger Dryas oscillation, ca. 12 000 cal kyr BP, the area was flooded by waters of a vast freshwater, ultra-oligotrophic basin with high content of suspended fine mineral particles. The conditions of a shallow bay of the BIL sheltered from the main basin by a moraine ridge at least 4–5 m high, are suggested for this period. The lake drainage took place around 11 660 cal kyr BP. Since then, no accumulation or alternating accumulation and erosion conditions prevailed in the study site until the late Holocene. The obtained results allow us to speak about two stages of flooding of the northern coast of the Sambia Peninsula during the Late Glacial, possibly caused by the BIL transgressions. The occurrence of BIL deposits in the northern part of the Sambia Peninsula above sea level suggests that the Late Glacial basin level in the study area may have exceeded the present sea level.

Vegetation, fire and climate history in central-western Tasmania (41°S), Australia, over the last ∼21,000 years

We present high resolution pollen and macroscopic charcoal records from Basin Lake, a relatively small mid-latitude (42°S) lake located in central-western Tasmania, Australia, to examine vegetation, fire and climate change since and during the Last Glacial Maximum (LGM). We find dominance of cold-resistant alpine vegetation with buttongrass moorland and scant trees between ∼21.0-17.7 cal kyr BP, with local biomass burning and low lake levels between ∼21.0-20.0 cal kyr BP and a reduction in local biomass burning and a rise in lake levels between ∼20.0-17.7 cal kyr BP. These data suggest glacial-cold conditions during the last millennia of the LGM, with relatively humid conditions between ∼21.0-20.0 cal kyr BP and a further increase in humidity between ∼20.0-17.7 cal kyr BP. These shifts suggest an intensification of the South Westerly Winds (SWW) over the site between ∼20.0-17.7 cal kyr BP. An increase in cold-temperate rainforest taxa followed between ∼17.7-16.0 cal kyr BP along with lake-level lowering, suggesting a warm pulse and southward shift of the SWW at the beginning of the Last Glacial Termination (T1). Subsequent cold-temperate conditions and increased precipitation ensued between ∼16.0-14.9 cal kyr BP promoted by increased SWW influence. A rise in cold-resistant and hygrophilous rainforest taxa and lower biomass burning activity occurred between ∼14.9-12.8 cal kyr BP under colder conditions, enhanced precipitation and major SWW influence. A multi-millennial warm/dry interval began at ∼12.8 cal kyr BP with a decline in rainforest taxa, high fire activity and low lake levels and a further opening of the vegetation in response to elevated biomass burning between ∼11.1-8.9 cal kyr BP. We suggest a decline in the SWW influence that started at ∼12.8 cal kyr BP and accentuated between ∼11.1-8.9 cal kyr BP at the beginning of the Holocene. We detect increases in precipitation between ∼8.9-5.8, ∼3.4-1.9 cal kyr BP and the last ∼900 years, with declines in the intervening intervals. Our data indicate a pronounced and sustained fire-driven shift to a more open and shrub dominant landscape after ∼5.0 cal kyr BP, in synchronous with other pollen data from Tasmania's west, reflecting an increased efficacy of Aboriginal burning under more variable and overall reduced precipitation. Our climate inferences from Basin Lake are coherent with variations of the SWW identified in other terrestrial mid-latitudes records, suggesting synchronic changes in the SWW during and since the LGM.

Formation and evolution of a loess sinkhole in the southern Chinese Loess Plateau

Sinkholes are formed by the collapse of the overlying strata or the subsidence of the ground from cracks or holes in the underlying strata, which are widely developed in the karst and loess regions over southern and northern China. These sinkholes have been explored intensively to infer their climatic and ecological significances, as well as the management of geological disasters. In this study we investigated the Sanyuan (SY) sinkhole in the southern Chinese Loess Plateau to understand how it was formed and evolved. Two 30-m cores were retrieved from the SY sinkhole and a detailed chronological framework was established by applying radionuclides dating for the top 1-m sediments as well as 14C dating for the two 30-m cores. These dating results show that SY sinkhole was formed 23.7 m below the sinkhole surface at ca. 6.0 kyr BP (before 1950 CE). Changes in lithology, sedimentation rate, magnetic susceptibility, lightness, and mean grain-size of these two cores reveal that the sinkhole has undergone two-stage evolution. The first stage was characterized by a relatively slow deposition of loess sediments during 6.0–1.9 kyr BP, and the second stage was a rapid accumulating period since 1.9 kyr BP likely affected by human activities. Our results suggest that SY sinkhole can well document the combined influence of climate change and human activities, offering an ideal archive to decipher the natural and anthropogenic imprints since the mid-Holocene.

Reconstruction of Holocene relative sea-level from beach ridges of the central west coast of India using GPR and OSL dating

The Holocene sea-level and associated shoreline regression of beach ridges in the central west coast of India have been reconstructed based on internal sedimentary architecture and luminescence chronology. For this purpose, various techniques namely ground penetrating radar (GPR), optically-stimulated luminescence (OSL) dating, and interferometry synthetic aperture radar (InSAR) have been used. The berm and beach-dune boundary of paleo beach ridges have been mapped from the high-resolution sub-surface images and converted into sea-level indicators using modern analogs and OSL ages. GPR reflection data shows a number of seaward dipping radar facies with a few landward dipping facies in paleo beach ridges. In the case of the swale, radar signal has been highly attenuated due to the presence of water and mud causing the appearance of multiple horizontal and parallel positive and negative couplets in the sedimentary layer. The results of the research reveal that the oldest beach ridge was formed around 7.7 kyr BP and sea-level was +2 m above mean sea-level. The average progradation rate of these ridges is 0.14 m/yr. From the grain size analysis, it has been found that the larger share of grain size falls into the classes of fine and moderate sand. The present displacement map of the region, which has been generated from the Sentinel-1 datasets, demonstrates that the average upliftment is 2.5 mm/yr whereas subsidence is 1 mm/yr. The fall of the Holocene relative sea-level with respect to the study region is the consequence of both global and regional events.

Early Holocene ice on the Begguya plateau (Mt. Hunter, Alaska) revealed by ice core 14C age constraints

Abstract. Investigating North Pacific climate variability during warm intervals prior to the Common Era can improve our understanding of the behavior of ocean–atmosphere teleconnections between low latitudes and the Arctic under future warming scenarios. However, most of the existing ice core records from the Alaskan and Yukon region only allow access to climate information covering the last few centuries. Here we present a surface-to-bedrock age scale for a 210 m long ice core recovered in 2013 from the summit plateau of Begguya (Mt. Hunter; Denali National Park, Central Alaska). Combining dating by annual layer counting with absolute dates from micro-radiocarbon dating, a continuous chronology for the entire ice core archive was established using an ice flow model. Calibrated 14C ages from the deepest section (209.1 m, 7.7 to 9.0 ka cal BP) indicate that basal ice on Begguya is at least of early Holocene origin. A series of samples from a shallower depth interval (199.8 to 206.6 m) were dated with near-uniform 14C ages (3 to 5 ka cal BP). Our results suggest this may be related to an increase in annual net snow accumulation rates over this period following the Northern Hemisphere Holocene Climate Optimum (around 8 to 5 kyr BP). With absolute dates constraining the timescale for the last >8 kyr BP, this paleo-archive will allow future investigations of Holocene climate and the regional evolution of spatial and temporal changes in atmospheric circulation and hydroclimate in the North Pacific.

Holocene sediment source analysis and paleoclimatic significance of core KZK01 from the eastern part of the Beibu Gulf

Identifying the sources of sediments is of great significance in reconstructing Holocene paleoclimate evolution in the Beibu Gulf and in understanding the characteristics of regional responses to changes in global climate. The Holocene paleoclimatic evolutionary history of the Beibu Gulf was investigated by chronological, geochemical, and mineralogical means using the sediments of Core KZK01 from the eastern part of the Beibu Gulf. The rare earth element (REE) distribution curves, (Gd/Yb)N and (La/Yb)N discriminant diagram, and (Gd/Lu)N and ∑LREE/∑HREE discriminant diagram indicated that the detrital materials in the eastern part of the Beibu Gulf primarily originated from Hainan Island and its proximal sources, with considerable contributions from Taiwan and Pearl River materials. Source analysis of clay minerals showed that Luzon Island was the main source of smectite, followed by Hainan Island. Rivers in Taiwan were the main sources of illite in the study area, followed by the Red River. The Red River was the main contributor of chlorite, followed by the Pearl River. Kaolinite mainly originated from Hainan Island and Guangxi. Coastal currents, surface currents, and warm currents were the main drivers of material transport. Paleoclimatic variations since the Holocene in the Beibu Gulf were divided into three stages: 12–9 cal kyr BP, 9–1.3 cal kyr BP, and 1.3 cal kyr BP to the present. During different stages of climatic evolution, drought was often accompanied by cold and humidity coexisted with warmth, and cold-dry-warm-humid alternation is characterized by significant phases. The illite crystallinity clearly recorded the extreme cold events, such as Bond Events (except Bond6) and the Younger Dryas, and the change trend was essentially consistent with the regional climate record, reflecting the control of global climate change on the process of land–sea interaction in the tropical region. Furthermore, it highlights the great potential of illite crystallinity as a proxy indicator for reconstructing the surface chemical weathering processes of the region.

Biomarker Records of Environmental Shifts on the Labrador Shelf During the Holocene

AbstractThe ultimate demise of the Laurentide Ice Sheet (LIS) and the preceding and succeeding oceanographic changes along the western Labrador Sea offer insights critically important to improve climate predictions of expected future climate warming and further melting of the Greenland ice cap. However, while the final disappearance of the LIS during the Holocene is rather well constrained, the response of sea ice during the resulting meltwater events is not fully understood. Here, we present reconstructions of paleoceanographic changes over the past 9.3 Kyr BP on the northwestern Labrador Shelf, with a special focus on the interaction between the final meltwater event around 8.2 Kyr BP and sea ice and phytoplankton productivity (e.g., IP25, HBI III (Z), brassicasterol, dinosterol, biogenic opal, total organic carbon). Our records indicate low sea‐ice cover and high phytoplankton productivity on the Labrador Shelf prior to 8.9 Kyr BP, sea‐ice formation was favored by decreased surface salinities due to the meltwater events from Lake Agassiz‐Ojibway and the Hudson Bay Ice Saddle from 8.55 Kyr BP onwards. For the past ca. 7.5 Kyr BP sea ice is mainly transported to the study area by local ocean currents such as the inner Labrador and Baffin Current. Our findings provide new insights into the response of sea ice to increased meltwater discharge as well as shifts in atmospheric and oceanic circulation.

Late Paleolithic hunter-gatherers’ resilience in the face of the transformation of the vegetation landscape and climate change in the Pre-Pyrenees

Climate change since the Last Glacial Maximum has caused both plant communities and human behaviour to adapt. Humans relied heavily on wood as fuel to sustain their daily subsistence. Thanks to efficient fuel management, they were able to persist in a challenging environment. Cova del Parco (Iberian Pre-Pyrenees) was inhabited as a settlement in different periods of the Late Pleistocene (16.4–12.7 cal kyr BP). The site has one of the most comprehensive assemblages of Magdalenian hearths, allowing several specialized and daily activity areas to be reconstructed. This study aims to provide new anthracological data regarding the transformation of the forests in the Iberian Pre-Pyrenees, as well as showing how humans adapted their behaviour as regards fuel management and the use of space around the hearths. Furthermore, we present a spatial distribution analysis of the woody taxa from Magdalenian occupations that were identified during the anthracological study. A total of 1993 charcoal fragments from Cova del Parco were identified at a taxonomic level. The anthracological results revealed the presence of 11 woody taxa, with the pine-juniper phase as a characteristic transformation of pre-forest formations in the cold climates of certain locations in the southwestern Mediterranean region. The results of our spatial analysis found that pinewood was the preferred fuel in the cave chamber, whereas juniper was most abundant in the rock shelter. However, the latest occupations revealed a shift in fuel use, with juniper becoming the primary fuel in the cave chamber. This change in behaviour is indicative of the changing needs of humans and their ability to adapt to new surroundings. It implies that strategies are contingent on context and dynamic, responding to changes in the environment. Overall, this study suggests that humans adapted to the changing environment by changing their fuel management strategies.

Paleoenvironmental changes in the coastal zone of the northwest South China Sea during the last 13 kyr

Marine sediments in coastal zones serve as valuable archives for understanding the history of silicate chemical weathering and summer monsoon rainfall in source areas, providing insights into terrigenous climate and environmental evolution. In this study, we investigated the grain size, clay minerals, and geochemistry of sediments retrieved from core KZK01 in the coastal zone of the northwest South China Sea during the past 13 thousand years before present (kyr BP). Our findings demonstrated that the illite crystallinity index served as a reliable proxy for assessing the intensity of chemical weathering in the source area. Moreover, it distinctly recorded significant climatic events such as the Younger Dryas and Bond events during the Holocene. The dominant driver of the regional East Asian summer monsoon was identified as summer solar radiation in the Northern Hemisphere at low latitudes. Cold climate events exhibited global consistency, potentially influenced by the presence of ice sheets at high latitudes. Lastly, our records revealed a distinct transition at 9.0 kyr, highlighting significant impacts of the Qiongzhou Strait and sea level rise on regional climate dynamics.

High-resolution record of temporal change in organic matter burial over the past ∼8,600 years on the northwestern continental slope of the South China Sea

Sedimentary organic matter (SOM) on continental slopes in marine regions can sensitively record climatic and environmental changes. In this study, total organic carbon content (TOC), total nitrogen content (TN), and their stable isotope compositions (δ13C and δ15N) for sediments of core G02 were investigated (at ∼24.2-year resolution) to reveal the temporal variations in organic matter sources and the main controls on the sources and distribution of buried organic matter on the northwestern continental slope of the South China Sea over the last ∼8600 years. Results of a δ13C binary mixing model reveal that ∼82.3 ± 3% of SOM is derived from marine autochthonous sources. We suggest that the carbon and nitrogen contents and compositions of SOM are governed by distinct factors. The more positive δ15N values before the Pulleniatina Minimum Event occurrence are ascribed to stronger subsurface water intrusion by the Kuroshio Current, which led to enhanced subsurface denitrification and in turn counteracted the effect of mixing with surface water caused by the East Asian winter monsoon. Sedimentary δ13C values show a fluctuant decrease during ca. 8.6–3.0 cal kyr BP and a conspicuous increase during ca. 3.0–1.4 cal kyr BP. These changes are attributed to the decrease of marine productivity induced by the continuous weakening East Asian monsoon effect and the decrease of terrigenous organic carbon input induced by the weakened Indian summer monsoon precipitation, respectively. Since ca. 1.4 cal kyr BP, human activities have become the dominant factor in controlling the production and distribution of organic carbon. The results provide an important basis for understanding of source-sink processes of organic matter and the factors influencing these processes on continental slopes in low-latitude marginal seas.