Marine Isotope Stage Research Articles

The dik-diks of Guli Waabayo: Late Pleistocene net-hunting and forager sociality in eastern Africa

Net-hunting is closely linked to organized labor and hunter-gatherer cooperation in many world regions. At the Rifle Range Site (RRS) in southern Somalia, scholars have argued that Later Stone Age (LSA) foragers developed specialized dwarf antelope hunting strategies—possibly using communal net-drives—to facilitate developing concepts of territoriality around resource-rich inselberg environments during a wet period in the early and middle Holocene. Unfortunately, a lack of radiocarbon dates and faunal data limited detailed zooarchaeological perspectives on changing hunting patterns at the site. The large and well-dated dwarf antelope bone assemblage (1263 specimens) from nearby Guli Waabayo (GW) rock shelter, on the other hand, provides an opportunity to explore proposed relationships between net-hunting and LSA social and economic reorganization in southern Somalia ~ 26–6 thousand years ago (ka). Consistently high dik-dik frequencies (55.2–71.9%) and mortality profiles comprised of individuals from all age groups throughout the sequence do not support previous arguments associating specialized dwarf antelope hunting with territoriality and Holocene climatic amelioration at RRS. Instead, they suggest that LSA foraging groups regularly hunted dik-dik (genus Madoqua) using nets over a ~ 20,000-year period beginning as far back as the arid Marine Isotope Stage 2, 29–14.5 ka. Findings from this study complement recent arguments for greater economic variability in Late Pleistocene eastern Africa and push discussions of forager social change further back in time than previously considered.

Decreased Westerly moisture transport leads to abrupt vegetation change in northern Central Asia during late MIS3: Evidence from Zeketai Loess, Ili Basin

Moisture transportation to (semi-)arid Central Asia is influenced by the interplay of multiple atmospheric circulation patterns. The mechanism underlying the hydroclimate evolution in CA has recently received increasing attention. In northeastern CA, most of the precipitation falls in summer, counter to other westerly-dominated regions of CA where precipitation maximizes in boreal winter. The marine isotope stage (MIS) 3 offers a unique opportunity to examine the mechanisms driving hydroclimate variations during warm periods of the ice age in the CA. However, due in part to reliable proxies for reconstruction, the hydroclimate and vegetation change during MIS3 in northeastern CA have not been well studied. Here, we use grain size and magnetic susceptibility data from the Zeketai loess profile to reconstruct historical shifts in precipitation patterns during MIS3 in the Ili Basin from arid Central Asia (ACA). Notably, abrupt changes around 35 ka are evident in the grain size and magnetic susceptibility records, reflecting a transition to reduced wind intensity and increased aridity. Subsequent analysis of plant leaf waxes (n-alkanes), hydrogen isotopic composition of n-alkanes (δDn-alkane), and stable carbon isotope ratios of total organic carbon (δ13Corg) within the loess profile indicates a concurrent shift towards more shrubs, aligning with reduced moisture availability. The δ13Corg record further elucidates that during MIS3, the Ili Basin predominantly harbored C3 vegetation. However, the alteration in δ13Corg and δDn-alkane to more positive values at approximately 35 ka substantiates the transition to more drought-resistant vegetation. Furthermore, we link the paleo-hydroclimate variations to the decrease in solar radiation and the strengthening of the Atlantic Meridional Overturning Circulation (AMOC) and Siberian High during late MIS3. This joint influence weakens the Westerly winds and subsequently diminishes the conveyance of moisture to CA.

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.

Rapid terrace incision and Quaternary landscape evolution in central Patagonia

AbstractThe debate over isostatic uplift versus discharge as drivers of Quaternary river incision is explored here through geospatial analysis of a ~250‐m‐relief terrace sequence from the Río Pinturas (Argentine Patagonia). The geomorphic setting of the Cañadon Caracoles reach allows evaluation of discharge as a driver of terrace incision because advancing ice during Pleistocene glaciations blocked Pacific drainage and routed meltwater from an expanded ~104‐km2 catchment to the Atlantic through the dryland steppe of the study area. Twenty‐two terrace levels, some assigned to previously dated ice margins [Marine Isotope Stage (MIS) 32–36, MIS 16, MIS 8 and MIS 2], were identified. Average net incision since 800 ka (~0.34 m ka−1) exceeded regional uplift rates. The MIS 2 terraces, with ante quem and post quem age constraint on the timing of terrace formation, show that terrace incision was episodic and faster still during a transitional warming climate. Glacier recession and proglacial lake formation at ~18 ka led to rapid incision of ~11.7 m ka−1 over a few millennia. River capture and negligible flow from ~15.0 ka caused fan‐dammed lake formation on the valley floor and vertical stability during MIS 1. The Pinturas terraces demonstrate rapid incision can be driven by discharge and sediment dynamics.

Quaternary alluvial paleosols of the Atbara River, eastern Sudan: description and paleoenvironments

ABSTRACTQuaternary climatic changes in the Nile Basin and their effects on the evolution of African mammals and vegetation are poorly understood, particularly for the last 1 Ma. Pleistocene (~230 to <17 ka) alluvial sediments exposed along the middle stretches of the Atbara River in eastern Sudan are rich in fossil vertebrates and are ideal for paleoenvironmental reconstruction during this time interval. We performed petrographic, mineralogical and geochemical analyses on the middle Atbara paleosols to reconstruct the paleoclimate and paleolandscape. We describe Aridisols/Calcisols characterized by calcretes and containing gypsum and halite, and Vertisols with pedogenic slickensides and a relatively large amount of smectite. The paleosols indicate that the study area transitioned from an arid to semi‐arid climate during Marine Isotope Stage (MIS)7/6, to a more humid climate during MIS5, and then a return to more arid conditions during MIS2. The studied paleosols likely supported a range of grassland and wooded grassland savanna habitats. Our study confirms that the Atbara River Valley provided favorable living conditions for Pleistocene large mammal communities including Homo, potentially facilitating dispersals out of Africa through the Nile corridor.

Millennial-scale climate variability in the Northern Hemisphere influenced glacier dynamics in the Alps around 250,000 years ago

Mountain glaciers are sensitive recorders of natural and human-induced climate change. Therefore, it is imperative to obtain a comprehensive understanding of the interplay between climate and glacier response on both short and long timescales. Here we present an analysis of oxygen and carbon isotope data from speleothems formed mainly below a glacier-covered catchment in the Alps 300,000 to 200,000 years ago. Isotope-enabled climate model simulations reveal that δ18O of precipitation in the Alps was higher by approximately 1 ‰ during interstadials compared to stadials. This agrees with interstadial-stadial amplitudes of our new speleothem-based estimate after correcting for cave-internal effects. We propose that the variability of these cave-internal effects offers a unique tool for reconstructing long-term dynamics of warm-based Alpine palaeoglaciers. Our data thereby suggests a close link between North Atlantic interstadial-stadial variability and the meltwater dynamics of Alpine glaciers during Marine Isotope Stage 8 and 7d.

Temperature and hydrological variations during the late-glacial in the Central Mediterranean: Application of the novel ostracod-clumped isotope thermometer

This study shows, for the first time, the absence of a vital effect in the clumped isotope carbonate (Δ47) fossil ostracod signal and confirms the ability of the novel ostracod-Δ47 thermometer to reconstruct past temperatures and hydrological conditions in complex lacustrine systems. Furthermore, the application of Δ47 analyses on the ostracod species Candona angulata and Cyprideis torosa from Lake Trasimeno record (central Italy), which today precipitate their shells during the cold and the warm season respectively provides evidence that by combining biological (i.e., ostracod shell precipitation timing), paleontological (i.e., identification of ostracod species) and geochemical (i.e., Δ47) approaches, the ostracod-Δ47 thermometer accurately reconstructs past seasonality. Despite the absence of a vital effect, not all species can be combined for Δ47 analyses in environments with seasonal temperature variations; only those that precipitate their shells during the same season should be considered. The application of the ostracod-Δ47 thermometer on the Trasimeno lacustrine record gives rise to the first continental warm season paleotemperature reconstruction of the last 43 ky in central Mediterranean area. The combination of Δ47 and oxygen isotope composition (δ18Oost) measured on ostracod shells provides the isotopic composition of the water from which the carbonate precipitated (δ18Ow) and thereby, changes in the evaporation/precipitation balance in this area. Before the Last Glacial Maximum (LGM), equivalent to the Marine Isotopic Stage 3 (MIS3, from 43 to 29ky), warm season temperatures ranged from 15 ± 1.6 °C to 22 ± 2.3 °C, equivalent to 2 to 6 °C colder than today. Hydrological conditions during this period are similar to the present-day ones, characterized by a permanent lake and a high evaporation/precipitation ratio (E/P). The drastic decrease of the warm season temperatures (ranging from 10 ± 2.9 °C to 17 ± 3.1 °C) and of the E/P ratio during LGM and Late-glacial (MIS2, from 29 to 11.6 ky) correspond to the global climate cooling and low summer insolation, suggesting an amplifying role, of the latter, in the effects of the millennial scale climatic variations. At the Pleistocene/Holocene transition, both warm season temperature (25 ± 2 °C) and the E/P ratio increased in conjunction with the summer insolation. During the early Holocene, warm season temperature (23 ± 2 °C) closely resembles present-day values. However, cold season temperature (12 ± 2 °C) is approximately 4 °CC warmer than today. Notably, no hydrological differences are identified between the warm and the cold season underlying a lower seasonality contrast compared to the present, along with enhanced warm season precipitation. The good agreement between the Δ47 temperatures reconstructed for the last 1 ky and the temperatures presently recorded at Lake Trasimeno (8 °C cold and 22 °C for warm season), confirms the accuracy of the analyses and the applicability of the ostracod-Δ47 thermometer to reconstruct seasonal temperature changes.

Three‐dimensional stratigraphic architecture, secondary pore system development and the Middle Pleistocene transition, Sandy Point area, San Salvador Island, Bahamas

AbstractThe Bahamian Archipelago has been the subject of extensive studies of stratigraphy, carbonate island morphology and diagenetic overprinting for many decades. A recently‐acquired dataset comprised of high‐resolution light detection and ranging, tightly spaced cored boreholes with image logs, thin sections, porosity and permeability measurements, and isotopic geochemical analyses provides a unique opportunity to perform detailed sequence stratigraphic analysis. This multi‐faceted study first establishes a new high‐resolution sequence stratigraphic framework for the Sandy Point area of San Salvador Island, encompassing six unconformity bound sequences (exposure surfaces) representing varying lengths of missing time. The stratigraphically lowest sequence is Late Pliocene in age and is dominated by reef facies capped by an extensive laminar caliche that represents 1.5 million years of exposure. The overlying Early Pleistocene is split into two sequences, EP1 and EP2, which are both dominated by low‐energy subtidal facies. The upper three sequences are tied to the Marine Isotope Stage 11, 9 and 5e interglacials, and are distinctly different in facies composition and architecture, being dominated by higher energy facies distributed in a more complex mosaic. The new stratigraphic framework highlights significant changes in depositional style and facies architecture that can be linked to increasing sea‐level amplitude oscillations and greater climate gradient at the Mid Pleistocene Transition. The well‐constrained framework is then used to provide key context for observed complex diagenetic evolution through repeated sea‐level inundation and subaerial exposure. These results suggest that well‐developed subaerial exposure surfaces drive increases in non‐matrix features in the subsequent stratigraphic package following exposure as the well‐cemented exposure surface acts to concentrate fluid flow and dissolution. Integration of non‐matrix features within this framework highlights the importance of dissolution/cementation patterns on formation of these modified unconformity surfaces for focusing later meteoric diagenesis and creating enhanced fluid flow pathways for continued multicyclic diagenetic events.

Climate-induced surface water variability at Monte San Nicola type-section (Sicily, southern Italy): New data across the Gelasian GSSP

We present the first high-resolution results on planktonic foraminiferal stable oxygen isotopes and calcareous plankton assemblages at the Monte San Nicola GSSP section (near Gela, Sicily), the type-section for the Lower Pleistocene Gelasian Stage. The oxygen isotope profile is remarkably similar to the Eastern Mediterranean oxygen isotope record and indicates that the studied section, extending from marine isotope stage (MIS) G4 to MIS 103, clearly records glacial-interglacial variability. Cyclic changes of calcareous plankton assemblages (calcareous nannofossils and foraminifera) indicate that warmer and stratified surface waters occurred during interglacials, while cooler and unstable conditions developed during glacial phases. Signatures of further increase in surface water stratification are also captured by our surface water proxies and are coeval with enhanced monsoon run-off, developed during precession minima/insolation maxima. The surface water changes recorded at the Monte San Nicola section are in phase with North Atlantic climate variability, even at suborbital scale, and reveal evidence of the first significant southward migration of the Subarctic Front in the mid-latitudes during MIS 104, slightly below the GSSP. The overall dataset provides precise alignment of the Gelasian GSSP within MIS 103 as well as new climatostratigraphic constraints, close to the GSSP, thus improving its correlation potential outside the type-area.

Quantifying the uncertainty in the Eurasian ice-sheet geometry at the Penultimate Glacial Maximum (Marine Isotope Stage 6)

Abstract. The North Sea Last Interglacial sea level is sensitive to the fingerprint of mass loss from polar ice sheets. However, the signal is complicated by the influence of glacial isostatic adjustment driven by Penultimate Glacial Period ice-sheet changes, and yet these ice-sheet geometries remain significantly uncertain. Here, we produce new reconstructions of the Eurasian ice sheet during the Penultimate Glacial Maximum (PGM) by employing large ensemble experiments from a simple ice-sheet model that depends solely on basal shear stress, ice extent, and topography. To explore the range of uncertainty in possible ice geometries, we use a parameterised shear-stress map as input that has been developed to incorporate bedrock characteristics and the influence of ice-sheet basal processes. We perform Bayesian uncertainty quantification, utilising Gaussian process emulation, to calibrate against global ice-sheet reconstructions of the Last Deglaciation and rule out combinations of input parameters that produce unrealistic ice sheets. The refined parameter space is then applied to the PGM to create an ensemble of constrained 3D Eurasian ice-sheet geometries. Our reconstructed PGM Eurasian ice-sheet volume is 48±8 m sea-level equivalent (SLE). We find that the Barents–Kara Sea region displays both the largest mean volume and volume uncertainty of 24±8 m SLE while the British–Irish sector volume of 1.7±0.2 m SLE is the smallest. Our new workflow may be applied to other locations and periods where ice-sheet histories have limited empirical data.

The Antarctic Ice Core Chronology 2023 (AICC2023) chronological framework and associated timescale for the European Project for Ice Coring in Antarctica (EPICA) Dome C ice core

Abstract. The EPICA (European Project for Ice Coring in Antarctica) Dome C (EDC) ice core drilling in East Antarctica reaches a depth of 3260 m. The reference EDC chronology, the AICC2012 (Antarctic Ice Core Chronology 2012), provides an age vs. depth relationship covering the last 800 kyr (thousands of years), with an absolute uncertainty rising up to 8000 years at the bottom of the ice core. The origins of this relatively large uncertainty are twofold: (1) the δ18Oatm, δO2/N2 and total air content (TAC) records are poorly resolved and show large gaps over the last 800 kyr, and (2) large uncertainties are associated with their orbital targets. Here, we present new highly resolved δ18Oatm, δO2/N2 and δ15N measurements for the EDC ice core covering the last five glacial–interglacial transitions; a new low-resolution TAC record over the period 440–800 ka BP (ka: 1000 years before 1950); and novel absolute 81Kr ages. We have compiled chronological and glaciological information including novel orbital age markers from new data on the EDC ice core as well as accurate firn modeling estimates in a Bayesian dating tool to construct the new AICC2023 chronology. For the first time, three orbital tools are used simultaneously. Hence, it is possible to observe that they are consistent with each other and with the other age markers over most of the last 800 kyr (70 %). This, in turn, gives us confidence in the new AICC2023 chronology. The average uncertainty in the ice chronology is reduced from 1700 to 900 years in AICC2023 over the last 800 kyr (1σ). The new timescale diverges from AICC2012 and suggests age shifts reaching 3800 years towards older ages over marine isotope stages (MISs) 5, 11 and 19. But the coherency between the new AICC2023 timescale and independent chronologies of other archives (Italian Lacustrine succession from Sulmona Basin, Dome Fuji ice core and northern Alpine speleothems) is improved by 1000 to 2000 years over these time intervals.

Revision of the Quaternary calcareous nannofossil biochronology of Arctic Ocean sediments

Despite extensive chronological studies, the relationship between the age and sub-seafloor depth of Arctic Ocean sediments remains ambiguous. This prevents confident identification of paleoceanographic changes in the Arctic during the Quaternary. Currently, age-depth models derived from uranium-series decay in Arctic sediments diverge by hundreds of thousands of years compared to those built on known evolutionary appearances and extinctions of calcareous nannoplankton, a group of globally valuable age-markers. Here we report on high-resolution biostratigraphic analysis of late Quaternary sediments in six cores from the central Arctic Ocean (CAO). We applied paired light microscope (LM) and scanning electron microscope (SEM) imaging to improve nannofossil diagnosis. We argue that low abundances and poor preservation have led to misidentification of the true stratigraphic depth of the critical Pleistocene nannofossil bio-events that have underpinned age models for many Arctic sedimentary records for decades. The revised calcareous nannofossil biochronology provides a radically different geochronological framework for CAO sediments – indicating that what had previously been identified as Marine Isotope Stage (MIS) 7 (191–243 ka) in many sedimentary records is older than MIS 12 (424–478 ka). Furthermore, it suggests that previously inferred sub-stages of MIS 5 could represent full interglacial periods rather than interstadials. The results help reconcile the different dating approaches and provide a transformative step towards resolving the disparity in Quaternary Arctic age-depth models, bringing us one step closer to accurate paleoceanographic reconstructions based on sediment cores.

The Initial Upper Paleolithic of the Altai: New radiocarbon determinations for the Kara-Bom site

The Initial Upper Paleolithic (IUP) is one of the most important phases in the recent period of the evolution of humans. During a narrow period in the first half of Marine Isotope Stage 3 laminar industries, accompanied by developed symbolism and specific blade technology, emerged over a vast area, replacing different variants of the Middle Paleolithic. In western Eurasia, the earliest appearance of IUP technology is seen at the Boker Tachtit site, dated ca. 50 ka cal BP. The earliest evidence of IUP industries in the Balkans and Central Europe, linked to the spread of Homo sapiens, has been dated to around 48 ka cal BP. A key area of IUP dispersals are the mountains and piedmont of southern Siberia and eastern Central Asia. One of the reference assemblages here is Kara-Bom, an open-air site in the Siberian Altai. Three major settlement phases are distinguished in the sediment sequence. In this paper, we present the results of new radiocarbon determinations and Bayesian models. We find that the latest phase of the IUP, Upper Paleolithic 1 (‘UP1’) is bracketed between 43 and 35 ka cal BP (at 95.4% probability). The earliest IUP phase, ‘UP2’, begins to accumulate from ca. 49 ka cal BP and ends by ca. 45 ka cal BP. The Middle Paleolithic ‘MP2’ assemblages all fall prior to 50 ka cal BP. We can detect a spatial distribution of dates from the geographic core of the IUP beyond the Altai where it appears around 47–45 ka cal BP. The current distribution of dates suggests a west–east dispersal of the IUP technocomplex along the mountain belts of Central Asia and South Siberia.

Variations in Mid-Pleistocene glacial cycles: New insights from osmium isotopes

Reconstruction of Pleistocene glacial cycles from oxygen isotope records identifies dramatic changes in both global climate state and ice sheet size. The Mid-Pleistocene Transition (MPT) is an interval during which global ice sheets underwent a major transition from temporally symmetrical 41-thousand-year (kyr) cycles in the Early to Middle Pleistocene to asymmetrical 100-kyr cycles in the Middle to Late Pleistocene. The proposed timing of this transition and potential triggers remains contentious with possible mechanisms ranging from cryosphere dynamics to variations in Earth's energy balance. One suggested driver of the MPT involves the “Regolith Hypothesis”, which proposes that the Laurentide Ice Sheet (LIS) underwent fluctuations in ice sheet stability due to changes in subglacial substrate lithology. To empirically investigate this hypothesis, we use variations in seawater osmium (Os) isotope values from IODP sites U1302 and U1308 over an 800 kyr interval to evaluate changes in basal substrate across this transition. Our Os data identify a lithological shift beneath the LIS during the MPT that resulted in a marked change in the chemical weathering flux delivered to the ocean. We identify a pulse of glacially weathered material reaching the central North Atlantic, likely during the first Heinrich event at Marine Isotope Stage (MIS) 16, in response to increased ice sheet size post MPT. After MIS 16, the Os signal becomes less radiogenic which may correspond to a less extensive “missing glacial” which would have reduced overall weathering fluxes. Our Pleistocene Os isotope record (at ∼15 kyr resolution) contributes to our understanding of subglacial weathering of the LIS across the MPT and helps further constrain the flux of Os to the ocean during glacial-interglacial cycles.

Centennial-scale monsoon collapses during Marine Isotope Stage (MIS)7e detected in a northern Chinese stalagmite record

Centennial-scale monsoon collapses during Marine Isotope Stage (MIS)7e detected in a northern Chinese stalagmite record

Hydroclimate variability in the central Mediterranean during MIS 17 interglacial (Middle Pleistocene) highlights timing offset with monsoon activity

Mediterranean climates are characterized by warm, dry summers and mild, rainy winters. Previous studies suggest that over the last 1.36 Myr, Mediterranean winter rainfalls were in phase with the African monsoon. Here we present a high-resolution terrestrial and marine dataset for the Marine Isotope Stage 17 interglacial (Middle Pleistocene) from Southern Italy, showing that precipitation rates and regimes in the central Mediterranean varied independently of the monsoon system. Specifically, events of extreme summer precipitation were promoted by increased regional insolation rates and/or extratropical cyclones, and their magnitude was further enhanced by the advection of cool and humid North Atlantic air during stadials. Our findings provide new information on the short- to mid-term natural hydroclimatic variability of the Mediterranean basin, and offer new critical insights on land–ocean interactions at the regional scale by complementing previous analyses on the displacement of storm tracks toward southern Europe.

Atmospheric CO2 controls on the MIS 6 glaciation: 10Be chronology of moraines in the Haizishan area, southeastern Tibetan Plateau

A unifying theory interpreting the cause of ice-age cycles remains elusive, in view of the near-synchronous interhemispheric major climate shifts but anti-phased summer solar insolation signatures between hemispheres. Determining the timing and magnitude of mountain glaciations helps in shedding new light on this long-standing unsolved puzzle. Yet, robust glacial chronologies are limited for the pre-Last Glaciation time periods, impeding a full understanding of glacial histories and climatic mechanisms behind them in mountainous regions, such as the Tibetan Plateau (TP). Here, we report thirty-five new 10Be exposure-ages from moraine boulders in the Niqingqu Valley, eastern Haizishan Plateau, which adds to the existing glacial chronologies of the Hengduan Mountains, southeastern TP. The dating results indicate that four centennial to millennial-scale glacial activities occurred around 168.4 ka in the studied valley. Despite being indistinguishable in age, these high-frequency glacial fluctuations allow us to draw a conclusion that glaciers in the studied valley achieved the marine isotope stage 6 (MIS 6) glacial maximum prior to the Penultimate Glacial Maximum (PGM), inconsistent with Northern Hemisphere. We attribute the MIS 6 glacial maximum identified here to the response of glaciers to a combination of low-level atmospheric CO2 content and low northern high-latitude summer solar insolation/high summer-monsoon precipitation. The consistent local PGM and low CO2 levels suggest that low atmospheric CO2 contents are likely a necessary prerequisite for the MIS 6 glaciation.

The late Quaternary palynological record of the northern Yangtze Delta: Implication for palaeoclimate change in East Asia

Marine Isotope Stage (MIS) 3 is the latest interstadial period with unstable climate regimes that provides an indispensable key to better predict future climate change. However, paleoclimate reconstruction in the Yangtze Delta covering MIS 3 remains elusive due to limited archives with reliable age. Here, we derived a 53,000–year–long paleoclimate record from the northern Yangtze Delta, using luminescence age–based palynological data of a coastal sediment core (YZ07). The results show that the climate was relatively warm and wet during ∼53.0–37.5 ka, followed by a slightly cool but wetter condition between ∼37.5 ka and ∼33.2 ka. Afterwards, a cool and dry climate prevailed from ∼33.2 ka to ∼30.7 ka. Three cold events were identified around 48.0 ka, 39.0 ka and 31.0 ka, corresponding to the timings of Heinrich Event (HE 5), HE 4 and HE 3, respectively. From ∼30.7 ka to ∼11.5 ka, broadleaved forests and wetland herbs obviously contracted in the Yangtze Delta region, indicating cold and dry climate conditions. From the late Pleistocene to Holocene, the pollen variations in this core site were linked to coastal geomorphology under climate–induced sea–level changes. Besides, our findings suggest that the percentages of emergent vegetation in this work were negatively correlated with El Niño–Southern Oscillation (ENSO)–linked flood events during the Holocene. Overall, from mid–MIS 3 to MIS 2, the climate exhibits a ‘warm–cool–cold’ pattern in the Yangtze Delta, broadly concordant with other climate proxies in East Asian monsoon domain and beyond on suborbital or millennial timescales. We argue that the northern hemisphere summer insolation may be responsible for the paleoclimate variability and paleovegetation successions in the Yangtze Delta. However, the variability of precipitation in MIS 3 might be governed by interhemispheric insolation forcing, which accounts for a wetter climate phase occurring during late MIS 3 rather than mid–MIS 3.

An Upper Pleistocene and Holocene Black Carbon‐Related Fire Record From the SW Balkans

AbstractLake sediments are unique archives of human environment interactions. Lake Prespa is one of the oldest lakes in Europe, lying in the southwestern Balkans and thus on a possible dispersal route of anatomically modern humans from Africa. In this study, we investigated the effects of climate, vegetation and human activity on fire over the last 92,000 years in this region. Sediment samples were taken from Lake Prespa, and nearby Lake Ohrid for comparison of the regional relevance, and analyzed for benzene polycarboxylic acids as markers for burned organic carbon residues (black carbon, BC). Peaking contents of BC (up to 1 g BC kg−1 sediment) coincided with warm and humid phases, when forests expanded at marine isotope stages (MIS) 5 and 1. During the colder and more arid climates of MIS 4 and 2, BC contents were lowered by a factor of 10, with a distinct minimum during the Last Glacial Maximum (0.07 g BC kg−1). The ratio of pentacarboxylic acid to mellitic acid (B5CA/B6CA) declined from 1.2 at MIS 5 to values of 0.3 at MIS 2, confirming a change in fire regime. Overall, BC contents peaked at cycles of solar radiation, vegetation composition and fuel availability, and thus correspond to the BC signal of other environmental archives. However, in the Late Holocene and as a result of human sedentary settlement, BC production increased, independent of decreasing insolation forcing.

Limited exchange between the deep Pacific and Atlantic oceans during the warm mid-Pliocene and Marine Isotope Stage M2 “glaciation”

Abstract. The Piacenzian stage (3.6–2.6 Ma) of the Pliocene is the most recent period where Earth experienced sustained intervals of global warmth analogous to predicted near-future climates. Despite considerable efforts to characterize and understand the climate dynamics of the Piacenzian, the deep ocean and its response to this warming remain poorly understood. Here we present new mid-Piacenzian Mg/Ca and Δ47 (“clumped isotope”) temperatures from the deep Pacific and North Atlantic oceans. These records cover the transition from Marine Isotope Stage (MIS) M2 – considered the most pronounced “glacial” stage of the Pliocene prior to the intensification of Northern Hemisphere glaciation – to the warm KM5 interglacial. We find that a large (> 4 ∘C) temperature gradient existed between these two basins throughout that interval, with the deep North Atlantic considerably warmer and likely saltier than at present. We interpret our results to indicate that the deep Pacific and North Atlantic oceans were bathed by water masses with very different physical properties during the mid-Piacenzian, and that only a limited deep oceanic exchange occurred between the two basins. Our results point to a fundamentally different mode of ocean circulation or mixing compared to the present, where heat and salt are distributed from the North Atlantic into the Pacific. The amplitude of cooling observed at both sites during MIS M2 suggests that changes in benthic δ18O associated with this cold stage were mostly driven by temperature change in the deep ocean rather than by ice volume.