Glacial-interglacial Cycles Research Articles

Retracted: Memory Effects in Salinity Profiles From Black Sea Sediments

AbstractThe current saline state of the Black Sea is only the latest of a series of freshening‐salinization episodes that have affected that body of water during past glacial–interglacial cycles. Here, we model the salinity history of the basin and its sedimentary porewaters since the end of the penultimate saline period, variously thought to have occurred in the period between ∼128 and ∼65 Kyr BP. Our model results argue that the down‐core salinity profiles of Black Sea Holocene sediments have been affected by the diffusion of salt from the penultimate saline episode. Retrodiction of these porewater profiles also requires that the Black Sea bottom waters be either fresh, or very weakly brackish (S ≤ 1), between ∼50 and ∼10 Kyr BP. In addition, we find that the timing of the first deposition of the well‐known Holocene sapropel corresponds to the time when salty bottom waters first reached the surface waters, and we speculate that increased organic matter production could have been caused by the release of nutrients stored in the saline bottom water. Finally, using current salinity proxy data, we find that the porewater salinity profiles generated from these proxies do not match the observed interstitial profiles.

Polygenetic features in Retisols, formed in Moscow (Late Saalian) glacial till

Retisols are the most spread soil in the boreal forests of the Russian Plain. Their features are usually linked to the Holocene pedogenesis. However, Retisols formed in the bipartite sediments of Moscow age (sandy cover layer on top of the glacial till) could have experienced pedogenic and cryogenic impact much earlier, starting from the last Interglacial. The subdivision of relic and modern features is still incomplete. In our work, OSL datings together with micromorphological studies indicate that the cover layer was formed by local rewashing of the glacial till during the deglaciation of the Moscow glacier. GPR investigation shows the mantle bedding of the cover layer and proves the stability of uplands and slopes since deposition, which confirms their exposure to long time pedogenesis. Detailed morphology, micromorphology, microtomography, clay mineralogy and AMS dating confirm the presence of polygenetic modern and relic features in the profile of Retisols. Within the cover layer, pedogenesis resulted in a set of embedded soil profiles that have been formed in balance with the modern environment. In the glacial till pedogenesis is mostly exhibited on the ped faces as a set of multi-layered clay and clay-humus coatings. Based on AMS dating of the inner layer of the clay infilling, it was argued that clay illuviation had started during the last interglacial (MIS5e) and continued through the Holocene. The studied soils should be considered as surface paleosols (polygenetic soils) with the palimpsest type of soil memory, reflecting environmental evolution during the last interglacial-glacial cycle and the Holocene.

Biomarker proxy records of Arctic climate change during the Mid-Pleistocene transition from Lake El'gygytgyn (Far East Russia)

Abstract. The Mid-Pleistocene Transition (MPT) is a widely recognized global climate shift occurring between approximately 1250 and 700 ka. At this time, Earth's climate underwent a major transition from dominant 40 kyr glacial–interglacial cycles to quasi-100 kyr cycles. The cause of the MPT remains a puzzling aspect of Pleistocene climate. Presently, there are few, if any, continuous MPT records from the Arctic, yet understanding the role and response of the high latitudes to the MPT is required to better evaluate the causes of this climatic shift. Here, we present new continental biomarker records of temperature and vegetation spanning 1142 to 752 ka from Lake El'gygytgyn (Far East Russia). We reconstruct warm-season temperature variations across the MPT based on branched glycerol dialkyl glycerol tetraethers (brGDGTs). The new Arctic temperature record does not display an overall cooling trend during the MPT but does exhibit strong glacial–interglacial cyclicity. Spectral analysis demonstrates persistent obliquity and precession pacing over the study interval and reveals substantial sub-orbital temperature variations at ∼900 ka during the first “skipped” interglacial. Interestingly, Marine Isotope Stage (MIS) 31, which is widely recognized as a particularly warm interglacial, does not exhibit exceptional warmth in the Lake El'gygytgyn brGDGT record. Instead, we find that MIS 29, 27, and 21 were as warm or warmer than MIS 31. In particular, MIS 21 (∼870 to 820 ka) stands out as an especially warm and long interglacial in the continental Arctic while MIS 25 is a notably cold interglacial. Throughout the MPT, Lake El'gygytgyn pollen data exhibit a long-term drying trend, with a shift to an increasingly open landscape noted after around 900 ka (Zhao et al., 2018), which is also reflected in our higher plant leaf wax (n-alkane) distributions. Although the mechanisms driving the MPT remain a matter of debate, our new climate records from the continental Arctic exhibit some similarities to changes noted around the North Pacific region. Overall, the new organic geochemical data from Lake El'gygytgyn contribute to expanding our knowledge of the high-latitude response to the MPT.

Influence of the choice of insolation forcing on the results of a conceptual glacial cycle model

Abstract. Over the Quaternary, ice volume variations are “paced” by astronomy. However, the precise way in which the astronomical parameters influence the glacial–interglacial cycles is not clear. The origin of the 100 kyr cycles over the last 1 million years and of the switch from 40 to 100 kyr cycles over the Mid-Pleistocene Transition (MPT) remain largely unexplained. By representing the climate system as oscillating between two states, glaciation and deglaciation, switching once glaciation and deglaciation thresholds are crossed, the main features of the ice volume record can be reproduced (Parrenin and Paillard, 2012). However, previous studies have only focused on the use of a single summer insolation as input. Here, we use a simple conceptual model to test and discuss the influence of the use of different summer insolation forcings, having different contributions from precession and obliquity, on the model results. We show that some features are robust. Specifically, to be able to reproduce the frequency shift over the MPT, while having all other model parameters fixed, the deglaciation threshold needs to increase over time, independently of the summer insolation used as input. The quality of the model–data agreement however depends on the chosen type of summer insolation and time period considered.

Early Oligocene—Late Miocene Wildfire History in the Northern Tibetan Plateau and Links to Temperature-Driven Precipitation Changes

Late Cenozoic wildfire evolution in Inner Asia has been attributed to both ice-volume modulating precipitation changes and surface uplift of the Tibetan Plateau. Whether this is the case or not requires additional research and wildfire records from older periods. In this study, 251 microcharcoal samples from the Huatugou section in the western Qaidam Basin are used to reconstruct the early Oligocene-middle Miocene wildfire history of the northern Tibetan Plateau. The results show that wildfires remained relatively frequent before ∼26 Ma, then reduced gradually until ∼14 Ma, and finally increased slightly but still at low level between 14 and 12 Ma. The wildfire variations can be correlated to the steppe-based dryness changes, and both of which are coincident with global temperature changes. We infer that mean annual temperature might have played a dominant role in controlling wildfire frequencies in the northern Tibetan Plateau through modulating atmospheric moisture content. This conclusion is in line with previous studies including microcharcoal-based wildfire records of 18–5 Ma successions from the Qaidam Basin as well as soot-based wildfire records from Quaternary glacial–interglacial cycles of the Chinese Loess Plateau.

Recognizing key sedimentary facies and their distribution in mixed turbidite–contourite depositional systems: The case of the Pacific margin of the Antarctic Peninsula

AbstractInterplay of deep‐water sedimentary processes is responsible for building a myriad of features and deposits across mixed turbidite–contourite systems, from <5 cm beds to >200 km long sedimentary drifts. Investigations of the spatial and temporal variability of their sedimentary facies and facies associations is crucial to reveal the dynamics between along‐slope bottom currents and down‐slope turbidity currents, as well as their impact on drift construction and channel erosion. This study focuses on extensive modern mixed (turbidite–contourite) systems, developed across the continental rise of the Pacific margin of the Antarctic Peninsula. Nine sediment cores were sampled and analysed, through grain size and geochemical methods, to study the sedimentary facies at high‐resolution (ca 1 to 20 cm). Three main facies associations have been identified across distinct morphological features (i.e. mounded drifts and trunk channels), comprising intercalations of hemipelagites, bottom current reworked sands (which include fine to coarse‐grained contourites) and gravitational facies (turbidites and mass‐transport deposits). These facies associations reflect fluctuations of the background sedimentation, oscillations of the bottom‐current velocity and of the frequency of gravity‐driven currents. The sedimentary record features cyclic alternations during the Late Quaternary (>99 kyr), suggesting that variations between along‐slope bottom currents and down‐slope turbidity currents are strongly linked to glacial–interglacial cycles during Marine Isotope Stages 1 to 6. Sedimentary records affected by bottom currents on polar margins, such as those of the Antarctic Peninsula, are essential to decipher the facies and facies sequences of bottom‐current deposits, as the low degree of bioturbation throughout most of the sediments allows us to observe the original sedimentary structures, which are poorly preserved in similar deposits from other continental margins.

Sea ice changes in the southwest Pacific sector of the Southern Ocean during the last 140 000 years

Abstract. Sea ice expansion in the Southern Ocean is believed to have contributed to glacial–interglacial atmospheric CO2 variability by inhibiting air–sea gas exchange and influencing the ocean's meridional overturning circulation. However, limited data on past sea ice coverage over the last 140 ka (a complete glacial cycle) have hindered our ability to link sea ice expansion to oceanic processes that affect atmospheric CO2 concentration. Assessments of past sea ice coverage using diatom assemblages have primarily focused on the Last Glacial Maximum (∼21 ka) to Holocene, with few quantitative reconstructions extending to the onset of glacial Termination II (∼135 ka). Here we provide new estimates of winter sea ice concentrations (WSIC) and summer sea surface temperatures (SSST) for a full glacial–interglacial cycle from the southwestern Pacific sector of the Southern Ocean using the modern analog technique (MAT) on fossil diatom assemblages from deep-sea core TAN1302-96. We examine how the timing of changes in sea ice coverage relates to ocean circulation changes and previously proposed mechanisms of early glacial CO2 drawdown. We then place SSST estimates within the context of regional SSST records to better understand how these surface temperature changes may be influencing oceanic CO2 uptake. We find that winter sea ice was absent over the core site during the early glacial period until MIS 4 (∼65 ka), suggesting that sea ice may not have been a major contributor to early glacial CO2 drawdown. Sea ice expansion throughout the glacial–interglacial cycle, however, appears to coincide with observed regional reductions in Antarctic Intermediate Water production and subduction, suggesting that sea ice may have influenced intermediate ocean circulation changes. We observe an early glacial (MIS 5d) weakening of meridional SST gradients between 42 and 59∘ S throughout the region, which may have contributed to early reductions in atmospheric CO2 concentrations through its impact on air–sea gas exchange.

Diatom community responses to environmental change in Lake Ohrid (Balkan Peninsula) during the mid-Pleistocene Transition

The Quaternary is characterized by a series of glacial-interglacial cycles and a shift in the Earth's climate state known as the mid-Pleistocene Transition (MPT, ca. 1200 ka to 720 ka). The progressive increase in glacial cycle length from approximately 41 ka to on average 100 ka affected marine and terrestrial life, but how it affected freshwater communities is far less known. Here, diatom and paleoenvironmental data between 1050 ka and 815 ka from a sediment succession of ancient Lake Ohrid are used to understand how the freshwater communities responded to environmental changes during key-periods of glacial intensification associated with the MPT. Based on stratigraphically constrained incremental sum of squares cluster (CONISS), a distinct diatom community turnover in Lake Ohrid was identified during the study period. The first community existed between 1050 and 955 ka MIS (Marine Isotope Stages) 30–25 and was mostly influenced by environmental parameters related to nutrient supply, mixing processes and primary productivity in the lake. The second community existed between 955 and 815 ka (MIS 25–21) and was largely driven by ontogenetic processes related to the ongoing deepening of the lake, changes in bottom water redox conditions and changes in mixing processes in the lake. The increased severity and duration of cold, glacial stages during the MPT shows only a weak impact on the diatom community in Lake Ohrid. Shifts in species phenotypes, abundance and composition are found in both communities, likely as adaptation in response to the changing environmental conditions. This study shows that the diatom communities were only weakly affected by the progressive intensification of the glacial intensity during the MPT, emphasizing the role of local environmental changes in regulating freshwater communities.

Evaluating refugia in recent human evolution in Africa.

Homo sapiens have adapted to an incredible diversity of habitats around the globe. This capacity to adapt to different landscapes is clearly expressed within Africa, with Late Pleistocene Homo sapiens populations occupying savannahs, woodlands, coastlines and mountainous terrain. As the only area of the world where Homo sapiens have clearly persisted through multiple glacial-interglacial cycles, Africa is the only continent where classic refugia models can be formulated and tested to examine and describe changing patterns of past distributions and human phylogeographies. The potential role of refugia has frequently been acknowledged in the Late Pleistocene palaeoanthropological literature, yet explicit identification of potential refugia has been limited by the patchy nature of palaeoenvironmental and archaeological records, and the low temporal resolution of climate or ecological models. Here, we apply potential climatic thresholds on human habitation, rooted in ethnographic studies, in combination with high-resolution model datasets for precipitation and biome distributions to identify persistent refugia spanning the Late Pleistocene (130–10 ka). We present two alternate models suggesting that between 27% and 66% of Africa may have provided refugia to Late Pleistocene human populations, and examine variability in precipitation, biome and ecotone distributions within these refugial zones.This article is part of the theme issue ‘Tropical forests in the deep human past’.

A paleoecological context to assess the development of oak forest in Colombia: A comment on Zorilla-Azcué, S., Gonzalez-Rodríguez, A., Oyama, K., González, M.A., & Rodríguez-Correa, H., The DNA history of a lonely oak: Quercus humboldtii phylogeography in the Colombian Andes. Ecology and Evolution 2021, doi: 10.100-2/ece3.7529.

The present “comment” on Zorilla‐Azcué et al.’s paper “The DNA history of a lonely oak: Quercus humboldtii phylogeography in the Colombian Andes. Ecology and Evolution 2021, doi:10.100‐2/ece3.7529” provides the paleoecological understanding of oak forest since Quercus became apparent in the Northern Andes three glacial–interglacial cycles ago. The interpretation of phylogeographical data is placed in an up‐to‐date paleoecological context. We arrived at sharper conclusions how genetic diversity between Q. humboldtii populations might have been driven by the dynamic environmental theatre of the recent Pleistocene. This paleoecological context also serves the potential future analyses of other arboreal taxa from the Andean montane forest belt. We show that hypotheses to be tested should grow out of phylogenetic analysis and paleoecological understanding together.

Depositional history of Lake Chala (Mt. Kilimanjaro, equatorial East Africa) from high-resolution seismic stratigraphy

Sediments deposited in Lake Chala (Kenya/Tanzania) constitute a high-resolution archive of past climate and environmental change in equatorial East Africa spanning two glacial-interglacial cycles. To correctly interpret the proxy records it contains, it is crucial to understand the evolution of lacustrine sedimentation in this volcanic crater basin. Building on previous seismic stratigraphic analysis by Moernaut et al. (2010) of a dense grid of 37 km high-resolution seismic reflection profiles with up to 270 ms two-way travel time (ca. 210 m depth) of sub-bottom penetration, this study presents a seismic-based reconstruction of the complete depositional history of Lake Chala as well as a first-order age model for the major documented stages in lake evolution. The seismic stratigraphic sequence comprises 16 distinct and finely-stratified units (U1-U16, youngest to oldest), grouped into five major depositional stages. Stage I (U16, ca. 249-212 ka) marks the initiation of sedimentation in an originally ring-shaped depositional area surrounding two central tuff cones emerging from the basin floor. Stage II (U15-U12, ca. 212-114 ka) represents the onset of basinwide sedimentation above the tuff cones, implying a gradual rise in lake depth and shift to more strictly hemipelagic sedimentation. Stage III (U11-U8, ca. 114-97 ka) represents the development of a relatively flat lake floor during a period of significantly reduced lake depth. Stage IV (U7-U4, ca. 97–20.5 ka) is again characterized by largely undisturbed hemipelagic sedimentation under mostly high lake-depth conditions. Stage V (U3-U1, 20.5 ka BP to Present) represents the establishment of the present-day, very broad and flat basin floor under fluctuating lake level. Reassessing the Moernaut et al. (2010) suggestion of a minor disconformity at ca. 100 m sub-bottom depth, we here interpret this seismic feature as a thick turbidite related to a mass wasting event. Consequently we can affirm continuity of lacustrine sedimentation in the depocenter of Lake Chala throughout the past ca. 250,000 years.

Ostracod response to monsoon and OMZ variability over the past 1.2 Myr

We present the first continuous middle through late Pleistocene record of fossil ostracods from the Maldives in the northern Indian Ocean, derived from sediment cores taken at Site U1467 by Expedition 359 of the International Ocean Discovery Program (IODP). Site U1467 lies at 487 m water depth in the Inner Sea of the Maldives archipelago, an ideal place for studying the effects of the South Asian Monsoon (SAM) system on primary productivity, intermediate depth ocean circulation, and the regional oxygen minimum zone (OMZ). The Inner Sea acts as a natural sediment trap that has undergone continuous sedimentation for millions of years with minor terrestrial influence. Our record spans from Marine Isotope Stage (MIS) 35 to the present, covering the mid-Pleistocene transition (1.2–0.6 Ma) and the Mid-Brunhes Event (MBE, at ~480 ka) the time when ice age cycles transitioned from occurring every 40,000 years to 100,000 years. The ostracod data is interpreted alongside the existing datasets from the same site of sedimentological (grain-size) and XRF-elemental analyses, and new organic biomarker data also from Site U1467. These datasets support the paleoenvironmental interpretation of the ostracod assemblages. Ostracods are abundant and diverse, displaying a prominent change in faunal composition at the MBE related to the increase in the amplitude of glacial-interglacial cycles, which deeply affected the monsoon system and thereby the past oceanographic conditions of the Maldives Inner Sea. Furthermore, ostracods exhibit distinctly different assemblages across glacial-interglacial cycles, particularly after the MBE, and these changes convincingly correspond to variability of the OMZ. Glacial periods are characterized by ostracod indicators of well‑oxygenated bottom water due to the intensification of the winter monsoon and the contraction of the OMZ. Abundant psychrospheric ostracods during glacials suggests that a southern sourced water mass, such as Antarctic Intermediate Water (AAIW) and/or Subantarctic Mode water, bathed the Maldives Inner Sea during glacial periods. In contrast, interglacial stages are characterized by ostracod species and biomarker data that indicate low-oxygen conditions and sluggish bottom water circulation pointing to an expansion of the regional OMZ due to the strengthening of the summer monsoon. Our results highlight the sensitivity of ostracods to oceanographic and climate variability.

Local oceanic CO<sub>2</sub> outgassing triggered by terrestrial carbon fluxes during deglacial flooding

Abstract. Exchange of carbon between the ocean and the atmosphere is a key process that influences past climates via glacial–interglacial variations of the CO2 concentration. The melting of ice sheets during deglaciations induces a sea level rise which leads to the flooding of coastal land areas, resulting in the transfer of terrestrial organic matter to the ocean. However, the consequences of such fluxes on the ocean biogeochemical cycle and on the uptake and release of CO2 are poorly constrained. Moreover, this potentially important exchange of carbon at the land–sea interface is not represented in most Earth system models. We present here the implementation of terrestrial organic matter fluxes into the ocean at the transiently changing land–sea interface in the Max Planck Institute for Meteorology Earth System Model (MPI-ESM) and investigate their effect on the biogeochemistry during the last deglaciation. Our results show that during the deglaciation, most of the terrestrial organic matter inputs to the ocean occurs during Meltwater Pulse 1a (between 15–14 ka) which leads to the transfer of 21.2 Gt C of terrestrial carbon (mostly originating from wood and humus) to the ocean. Although this additional organic matter input is relatively small in comparison to the global ocean inventory (0.06 %) and thus does not have an impact on the global CO2 flux, the terrestrial organic matter fluxes initiate oceanic outgassing in regional hotspots like in Indonesia for a few hundred years. Finally, sensitivity experiments highlight that terrestrial organic matter fluxes are the drivers of oceanic outgassing in flooded coastal regions during Meltwater Pulse 1a. Furthermore, the magnitude of outgassing is rather insensitive to higher carbon-to-nutrient ratios of the terrestrial organic matter. Our results provide a first estimate of the importance of terrestrial organic matter fluxes in a transient deglaciation simulation. Moreover, our model development is an important step towards a fully coupled carbon cycle in an Earth system model applicable to simulations at glacial–interglacial cycles.

Ideas and perspectives: Emerging contours of a dynamic exogenous kerogen cycle

Abstract. Growing evidence points to the dynamic role that kerogen is playing on Earth's surface in controlling atmospheric chemistry over geologic time. Although quantitative constraints on the weathering of kerogen remain loose, its changing weathering behavior modulated by the activity of glaciers suggests that this largest pool of reduced carbon on Earth may have played a key part in atmospheric CO2 variability across recent glacial–interglacial cycles and beyond. This work enunciates the possibility of kerogen oxidation as a major driver of atmospheric CO2 increase in the wake of glacial episodes. This hypothesis of centennial- and millennial-timescale relevance for this chemical weathering pathway is substantiated by several lines of independent evidence synthesized in this contribution, including the timing of atmospheric CO2 increase, atmospheric CO2 isotope composition (13C and 14C), kerogen oxidation kinetics, observations of kerogen reburial, and modeling results. The author hypothesizes that the deglaciation of kerogen-rich lithologies in western Canada contributed to the characteristic deglacial increase in atmospheric CO2, which reached an inflection point ≤ 300 years after the Laurentide Ice Sheet retreated into the kerogen-poor Canadian Shield. To reconcile the release of isotopically light carbon via kerogen oxidation with Earth surface carbon pool constraints, major oceanic degassing and biospheric regrowth must have acted in concert across glacial–interglacial transitions. Additionally, a process such as a strong shift in the ratio of C3 to C4-derived organic matter must be invoked to maintain isotope mass balance, a point key for reconciling the hypothesis with the carbon isotope record of marine dissolved inorganic carbon. In order to test this hypothesis, quantitative constraints on the contribution of kerogen oxidation to CO2 rise at glacial terminations are needed through systematic studies on (1) CO2 fluxes emanating from the weathering of different lithologies, (2) oxidation kinetics of kerogen along glacial chronosequences, and (3) high-resolution temporal changes in the aerial extent of glacially exposed lithological units and glacial flour.

Ice-sheet expansion from the Ross Sea into McMurdo Sound, Antarctica, during the last two glaciations

An understanding of Antarctic Ice Sheet (AIS) behavior is important for future sea-level predictions. Here, we examine past ice-sheet history in the McMurdo Sound region of the western Ross Sea over the last two glacial-interglacial cycles in order to gain insight into the drivers of ice-sheet change. Surficial mapping, along with radiocarbon dates of lacustrine algae and uranium-thorium disequilibrium dates of lacustrine carbonates from ice-dammed lakes, allow reconstruction of the timing and origin of grounded ice in McMurdo Sound during the last glacial maximum (LGM) and penultimate glaciation. During the LGM, ice-surface elevation profiles and distribution of erratics indicate ice flow into southern McMurdo Sound from the Ross Sea, rather than seaward expansion of local glaciers from the Royal Society Range. The grounded ice in McMurdo Sound flowed westward to block the mouths of valleys in the Royal Society Range and to dam proglacial lakes. In Marshall Valley, maximum ice extent during what is termed the Ross Sea glaciation, was achieved by 18 ka and remained close to this position until after 14 ka. The pattern of surficial deposits suggests that ice during the penultimate glaciation, locally named the Marshall glaciation, was slightly more extensive than that of the LGM but had a similar Ross Sea origin. Maximum ice extent in Marshall Valley occurred at ∼145–150 ka; the grounded ice may have receded from the valley mouth shortly after 138 ka. Both ice expansions occurred broadly during times of low Antarctic air temperatures, which have been linked to insolation minima. However, the lack of widespread surface melting ablation zones on the AIS indicates that the link between ice expansion and orbital forcing is likely to be indirect and possibly driven through the ocean. Closer examination of the precise timing of the glacial maxima in Marshall Valley shows that the Marshall glaciation occurred synchronously with the penultimate global maximum; ice recession took place during Termination II. In contrast, maximum ice extent during the Ross Sea glaciation along the Royal Society Range occurred after the global LGM, during Termination I. Deglaciation was primarily an early Holocene event. We attribute this delayed maximum and deglaciation (relative to global events) to the effect of rising accumulation on ice-sheet mass balance.

Luminescence dating of a sedimentary sequence in the eastern North Yellow Sea

Sediments from the Yellow Sea (YS) are important archives for investigating the stratigraphic evolution in relation to global and regional sea-level changes. Here, the upper 40-m-thick interval of a 100-m-long drill core (NYS17), retrieved from the eastern North Yellow Sea (NYS), were studied to explore the late Quaternary sedimentary history in this region. To obtain reliable chronological framework of the core, we utilized multiple luminescence signals from sediments for dating. Coarse-grained (CG) and fine-grained (FG) quartz optically stimulated luminescence (OSL), and K-feldspar/polymineral post-infrared (IR) IR stimulated luminescence (pIRIR50/150) signals were analyzed to obtain age estimates for comparison. Primary results show that quartz OSL ages are consistent with the corrected ages of IR50 and pIRIR150 signals. Chronostratigraphy of core NYS17 presents two phases of rapid accumulation. One is at the interval of 35.6–29.8 m deep, as age controls of sedimentary stratigraphy are in the period of 135–130 ka, corresponding to Marine Isotope Stage (MIS) 6/5. Another occurs in the upper section (14.5–0.9 m) as luminescence ages are constrained between 11 and 9 ka. However, the overlying deposits after 9 ka seem to be very thin in the core site. This is likely attributed to the abundant terrestrial sediment supply during the early Holocene and following starvation after further rise of the sea level and transgression. In contrast, the MIS 5–2 interval remains far to be exactly defined in the core as no age constraint is available. Regionally, correlations of chronostratigraphy of our core with other collected cores from the YS and East China Sea, show comparable depositional records for both the late Pleistocene and Holocene sedimentary successions. These findings indicate that the spatiotemporal variations of sedimentary processes in the YS shelf were closely linked to global sea-level changes during the glacial-interglacial cycles.

Intensified climate drying and cooling during the last glacial culmination (20.8–17.5 cal ka BP) in the south-eastern Asian monsoon domain inferred from a high-resolution pollen record

Recent global sea-level data indicate that a final growth of ice volume occurred towards the end of the Last Glacial Maximum (LGM). The LGM culmination, LGM-b, lasted from about 21 to 17 ka and was followed by rapid deglaciation. This finding suggests a millennial-scale state with extreme glacial conditions (at least regionally) that immediately preceded the onset of full deglaciation marked by Heinrich event 1. In order to check how regional climate and vegetation in subtropical East Asia responded to the global-scale LGM culmination and the deglaciation onset, a new high-resolution pollen record from the Lijiafang peatland (LJF: 26°36.849′N, 116°08.463′E, 270 m) in Southeast China was generated. This record demonstrates a massive expansion of herbs during LGM-b. The dominance of herbaceous pollen suggests sparse forest cover in the lowlands of the subtropical East Asian Summer Monsoon (EASM) region and indicates an approximately 3300-year-long interval of the driest climate conditions of the entire last glacial-interglacial cycle. The LJF pollen-based reconstruction is consistent with the other vegetation records from the larger region, suggesting the climate change during LGM-b significantly impacted terrestrial ecosystems. The environmental change in the EASM region is likely linked to the Sea Surface Temperatures (SSTs) decrease that weakened the Walker cell convection over the western Pacific Ocean and reduced convection and moisture content in the Intertropical Convergence Zone. The strengthened decrease in moisture supply during LGM-b seems to have resulted in extreme and widespread megadroughts in the EASM and Australian regions. Our data indicate that the cold SSTs may have also decreased air temperatures in the neighboring parts of the continents. We suggest that the widespread SSTs decline in the western Pacific may have been linked to the cooling of the Southern Ocean and the expansion of Antarctic sea ice during LGM-b.

Continuous vegetation record of the Greater Cape Floristic Region (South Africa) covering the past 300 000 years (IODP U1479)

Abstract. The Greater Cape Floristic Region (GCFR) of South Africa is a biodiversity hotspot of global significance, and its archeological record has substantially contributed to the understanding of modern human origins. For both reasons, the climate and vegetation history of southwestern South Africa is of interest to numerous fields. Currently known paleoenvironmental records cover the Holocene, the last glacial–interglacial transition and parts of the last glaciation but do not encompass a full glacial–interglacial cycle. To obtain a continuous vegetation record of the last Pleistocene glacial–interglacial cycles, we studied pollen, spores and micro-charcoal of deep-sea sediments from IODP Site U1479 retrieved from SW of Cape Town. We compare our palynological results of the Pleistocene with previously published results of Pliocene material from the same site. We find that the vegetation of the GCFR, in particular fynbos and afrotemperate forest, responds to precessional forcing of climate. The micro-charcoal record confirms the importance of fires in the fynbos vegetation. Ericaceae-rich and Asteraceae-rich types of fynbos could extend on the western part of the Paleo-Agulhas Plain (PAP), which emerged during periods of low sea level of the Pleistocene.

Soil-development differentiation across a glacial–interglacial cycle, Saalian upland, E Poland

Three soil profiles at the Koczery site (E Poland), studied through soil and sediment evaluation, reveal a polygenetic development of soils in areas unglaciated during the Weichselian glaciation (MIS 2) period. Pedogenesis had developed on glacial till (till) in period from the Saalian glaciation (MIS 6) to the Holocene (MIS 1). Wide-spectrum analyses demonstrate that the profiles represent a Planosol. Four stages (I–IV) of soil formation were distinguished in the study area. Stage I, comprising of a nutrient- and element-rich material, correlates to the accumulation of Saalian glacial till (MIS 6). Stage II, that took place during the Eemian Interglacial (MIS 5e), corresponds to the initial development of Cambisol as a result of carbonate leaching process. This was followed by the development of a Luvisol through the processes of illuviation of clay minerals and iron components. Stage III bears evidence of intensive frost weathering processes along with a development of sand-wedge cast that occurred under permafrost conditions of Weichselian glaciation (MIS 2). Further, the formation of an aeolian pavement along with erosion and removal of upper portions of the Eemian soil took place. An accumulation of coeval-age coversand led to a restart of the pedological clock, which resulted in the development of cryogenically-altered soils. Stage IV ushered the Holocene (MIS 1) delivering a progressive development of pedogenesis together with plant-succession modifications under temperate-climate conditions. Brunic or luvic horizons are formed within the coversand deposits. Pseudogleyic conditions developed along the lithological discontinuities. Of note, sand-wedge casts (SWCs) occupy specific locations in the profiles that provide the vertical migration of water, base components and iron. Reducing conditions that occurred along the bottom of ice-wedge casts favour the formation of gleyic horizon. SWCs that have been ultimately modified into ice-wedge and acted as sand-wedge-affiliated geochemical corridors (SWGC) for shallow groundwater forming natural tile drains.

Biogeographic and metabolic studies support a glacial radiation hypothesis during Chrysanthemum evolution.

Chrysanthemum (Chrysanthemum morifolium Ramat.) is an economically important plant species growing worldwide. However, its origin, especially as revealed by biogeographic and metabolomics research, remains unclear. To understand the geographic distribution of species diversity and metabolomics in three genera (Chrysanthemum, Ajania, and Phaeostigma), geographic information systems and gas chromatography–mass spectrometry were used in 19, 15, and 4 species respectively. China and Japan were two potential panbiogeographic nodes and diverse hotspots of Chrysanthemum, with species richness ratios of 58.97 and 33.33%. We studied different species from two hotspots which in similar geographical environments had closer chemotaxonomic relationships under the same cultivation conditions based on a cluster of 30 secondary metabolites. The average distribution altitude (ADA) differed significantly among Chrysanthemum, Ajania, and Phaeostigma in which it was 1227.49, 2400.12, and 3760.53 m.a.s.l. respectively, and the presence/absence of ray florets (RF) was significantly correlated with ADA (−0.62). Mountain landform was an important contributor to global Chrysanthemum diversity, playing a key role in the divergence and distribution pattern of Chrysanthemum and its allies. The Hengduan Mountains–Qinling Mountains (HDQ) in China was a potential secondary radiation and evolution center of Chrysanthemum and its related genera in the world. During the Quaternary glacial–interglacial cycles, this region became their refuge, and they radiated and evolved from this center.