Interglacial Transition Research Articles

Synchronous or Not? The Timing of the Younger Dryas and Greenland Stadial-1 Reviewed Using Tephrochronology

The exact spatial and temporal behaviour of rapid climate shifts during the Last Glacial–Interglacial Transition are still not entirely understood. In order to investigate these events, it is necessary to have detailed palaeoenvironmental reconstructions at geographically spread study sites combined with reliable correlations between them. Tephrochronology, i.e., using volcanic ash deposits in geological archives as a dating and correlation tool, offers opportunities to examine the timing of events across wider regional scales. This study aims to review the posited asynchrony of the Younger Dryas stadial in comparison with Greenland Stadial-1 by correlating new proxy data from southernmost Sweden to previous palaeoclimate reconstructions in Europe based on the presence of the Hässeldalen Tephra, the Vedde Ash, and the Laacher See Tephra. μ-XRF core-scanning data were projected using a recently published age–depth model based on these tephras and several radiocarbon dates, and compared to previous findings, including by adapting previous chronologies to the recently proposed earlier date of the Laacher See Tephra (13,006 ± 9 cal. a BP). Although the results to some extent support the idea of a more synchronous Younger Dryas event than previously assumed, this issue requires further high-resolution proxy studies to overcome limitations of temporal precision.

Calcium Carbonate Dissolution Triggered by High Productivity During the Last Glacial–Interglacial Interval in the Deep Western South Atlantic

Studies reconstructing surface paleoproductivity and benthic environmental conditions allow us to measure the effectiveness of the biological pump, an important mechanism in the global climate system. In order to assess surface productivity changes and their effect on the seafloor, we studied the sediment core SAT-048A, spanning 43–5 ka, recovered from the continental slope (1,542 m water depth) of the southernmost Brazilian continental margin, deep western South Atlantic. We assessed the sea surface productivity, the organic matter flux to the seafloor, and calcite dissolution effects, based on micropaleontological (benthic and planktonic foraminifers, ostracods), geochemical (benthic δ13C isotopes), and sedimentological data (carbonate and bulk sand content). Superimposed on the induced changes related to the last glacial–interglacial transition, the reconstruction indicates a significant and positive correlation between the paleoproductivity proxies and the summer insolation. From the reconstructed data, it was possible to identify high (low) surface productivity, high (low) organic matter flux to the seafloor, and high (low) dissolution rates of planktonic Foraminifera tests during the glacial (postglacial). Furthermore, within the glacial, enhanced productivity was associated with higher insolation values, explained by increased northeasterly summer winds that promoted meandering and upwelling of the nutrient-rich South Atlantic Central Water. Statistical analyses support the idea that productivity is the main cause for seafloor calcium carbonate dissolution, as opposed to changes in the Atlantic Meridional Overturning Circulation (at least for the 25–4 ka period). Further efforts must be invested in the comprehension and quantification of the total organic matter and biogenic carbonate burial during time intervals with an enhanced biological pump, aiming to better understand their individual roles.

A high-resolution Lateglacial–Early Holocene tephrostratigraphy from southernmost Sweden with comments on the Borrobol–Penifiler tephra complex

We present results from a cryptotephra investigation performed at a high resolution (0.5 cm) on sediments from Körslättamossen in southernmost Sweden. Six peak concentration levels were detected and extracted for geochemical analysis by electron probe microanalyser. Five of these levels were successfully analysed and we propose correlations to the Hässeldalen Tephra, the Vedde Ash, and the Laacher See Tephra (adding new analysis results for the first geochemically confirmed finding of the latter in Sweden), as well as an undetermined Borrobol-type tephra. The tephra identifications were combined with radiocarbon dated macrofossils in order to create an age model for the sampled sediments based on Bayesian methods. Stratigraphical and chronological results were found to concur with a previous study of the site and our results form the basis for discussion concerning the issues surrounding Lateglacial Borrobol-type tephras, of which we suggest further review in order to unlock these tephras’ full potential for Quaternary studies. • 5 cryptotephras detected in sediments from the Last Glacial–Interglacial Transition. • New geochemical data of the first confirmed Laacher See Tephra finding in Sweden. • Undetermined Borrobol-type tephra highlights the Borrobol–Penifiler tephra complex.

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.

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.

Millennial-scale periodicities associated with changes in wind ansd precipitation over the last Glacial cycle (ca. 117 ± 8.5 ka BP) recorded in sediments from Lake Kai Iwi, Northland, New Zealand

Mid-latitude Southern Hemisphere proxy records of changing environment, especially those that demonstrate past variability of the South Westerly Winds (SWW), are poorly-constrained prior to the Last Glacial Interglacial Transition (LGIT; ca. 14–11.7 ka BP) and are typically located far enough south or north that they often do not reflect both tropical and SWW signals. With this deficiency in mind, we present a ca. 117 ± 8.5 ka BP lake sediment record from Lake Kai Iwi, Northland, New Zealand (~36°S), located at a latitude that demonstrates changes in precipitation associated with both the northward expansion of the SWW belt and from tropical El Niño Southern Oscillation (ENSO) variability. We converted Lake Kai Iwi μ-XRF proxy data to even time-steps in order to apply Morelet wavelet analysis for identification of millennial-scale periodicities in the data that were likely driven by orbital forcing. The results indicate that Lake Kai Iwi records a ~1 ka periodicity possibly associated with Northern Hemisphere ice sheet dynamics; a ~2–4 ka periodicity associated with ~2.4 ka Hallstatt solar cycles, and a ~9 ka periodicity linked to CO2 outgassing from upwelling in the Southern Ocean driven by changes in intensity and position of the SWW.

Stratigraphie dans la Galerie Ouest de la Grotte de Lorette (Rochefort, Belgique) : Apport de la coupe des gours suspendus

The Lorette Cave contains a wide variety of deposits within various stratigraphical contexts. This cave is a part of the complex underground meander cut-off of the Wamme and Lomme rivers, between some swallow-holes along their two talwegs near On, Jemelle and Rochefort, and the general resurgence at Eprave. The Lorette Cave is embedded within the Givetian limestone formations of the Calestienne. This cave displays the first part with a labyrinthic structure. Some parts of the karstic network are affected by recent tectonic activity, which dislocates some galleries and provokes collapses. The second part of the cave comprises the West Gallery, which contains the most complete sedimentary series. The “gours suspendus” (hanging gours) section is located at the western end of the gallery. The cave contains numerous and rich detrital deposits. The oldest sedimentary unit is a diamictite found in several galleries (e.g. Galerie Fontaine-Bagdad, Salle du Cataclysme). It is composed of large decametric-sized quartz and sandstone pebbles coming from the erosion of the Lower Devonian formations of the Ardenne. This deposit is older than the U/Th dating limit, i.e. 350 ka. The West Gallery exposes an area of collapsed blocks and ends in a vast room. This gallery is filled with a thick fluvial series of upper Pleistocene age and capped by speleothems of Tardiglacial to Holocene age. The large terminal chamber is clogged by flooded pits. A tributary gallery shows a sedimentary series in a subsiding pit, the “Fosse aux Lions” (Lions’ Pit). These deposits are made of a diamictite interbedded between two fluvial units, the upper part of which displays oblique stratifications. The dating of a summit stalagmite places this set at 120 ka. The present paper analyses a section made in the southern flank of the terminal room, close to the junction with the West Gallery: the “gours suspendus” section. A large part of this section consists of a complex fluvial deposit disconformably resting on top of a compact lower clay formation. This fluvial deposit is stratified, comprising mostly diamictites interstratified with thin levels of gravel and clay. It is capped by an upper clay unit and sealed by a flowstone. Thin strata of finer-grained size sediments (coarse sand), as well as clay lenses, occur within the lower clay. The diamictites indicate a torrential origin of the sediment. At the base, just above the lower clay, some sandy channelling strata testify that one or several fluvial deposition episodes occurred. Then, torrential and probably very short-living events are separated by decantation phases. The pebbles and smaller particles are made of quartz, sandstone and muscovite that most probably originated in the Lower Devonian formations. The “gours suspendus” section provides a new illustration of the succession of sedimentation and erosion phases in Belgian caves. It is now well demonstrated that speleothems grow mainly during temperate to hot and humid climatic phases and detrital infills are deposited in caves during cold/glacial phases. The physical erosion of sediments with ravine formations should be placed in the climatic history of the region. A gullying by a coarse detrital formation like that of the new section is due to a powerful heavy-loaded current. The deposits within caves were therefore available, which can only occur during a cold phase due to the absence of continuous vegetation cover. The sand and clay levels interstratified between levels of pebbles indicate nevertheless distinct flow regimes. However, this torrential lava in the new section seems different from the old diamictite. The deposition of the sedimentary units in the West Gallery seemingly happened during a glacial–interglacial transition. This sedimentological study sets a future perspective for dating flowstones and stalagmites at the top of or embedded within the deposit levels in order to propose a more robust chronological frame for the evolution dynamics of the cave infilling of the Lorette Cave in relation to the climatic history of the region.

Applicability of the Long Chain Diol Index (LDI) as a Sea Surface Temperature Proxy in the Arabian Sea

AbstractThe long‐chain diol index (LDI) is a relatively new proxy for sea surface temperature (SST) which has been rarely applied in upwelling regions. Here, we evaluated its application by comparison with other SST records obtained by commonly used proxies, that is, the Mg/Ca ratio of the planktonic foraminifera species Globigerinoides ruber and the alkenone paleothermometer UK´37. We focused on the last glacial–interglacial transition of four different sedimentary archives from the western and northern Arabian Sea, which are currently under the influence of monsoon‐induced upwelling and the associated development of an oxygen minimum zone. The and Mg/CaG.ruber SST records revealed an increase of 0.6–3.4°C from the Last Glacial Maximum to the late Holocene with somewhat higher amplitude in the northern part of the Arabian Sea than compared to the western part. In contrast, the LDI SSTs did not reveal major changes during the last glacial–interglacial transition which was followed by a decreasing trend during the Holocene. The LGM versus the Holocene LDI SSTs ranged between −0.2 and −2.7°C. Particularly at one record, offshore Oman, the SST decrease during the Holocene was high in amplitude, suggesting a potential cold bias, possibly related to changes in upwelling intensity. This indicates that care has to be taken when applying the LDI for annual mean SST reconstruction in upwelling regions.

Major population splits coincide with episodes of rapid climate change in a forest-dependent bird.

Climate change influences population demography by altering patterns of gene flow and reproductive isolation. Direct mutation rates offer the possibility for accurate dating on the within-species level but are currently only available for a handful of vertebrate species. Here, we use the first directly estimated mutation rate in birds to study the evolutionary history of pied flycatchers (Ficedula hypoleuca). Using a combination of demographic inference and species distribution modelling, we show that all major population splits in this forest-dependent system occurred during periods of increased climate instability and rapid global temperature change. We show that the divergent Spanish subspecies originated during the Eemian–Weichselian transition 115–104 thousand years ago (kya), and not during the last glacial maximum (26.5–19 kya), as previously suggested. The magnitude and rates of climate change during the glacial–interglacial transitions that preceded population splits in pied flycatchers were similar to, or exceeded, those predicted to occur in the course of the current, human-induced climate crisis. As such, our results provide a timely reminder of the strong impact that episodes of climate instability and rapid temperature changes can have on species' evolutionary trajectories, with important implications for the natural world in the Anthropocene.

A multi-proxy record of environmental change through the last 53,000 years recorded in the sediments of Lake Kanono, Northland, New Zealand

ABSTRACTLake sediment archives from Southern Hemisphere mid-latitude regions provide invaluable records of late Quaternary environmental change. Here, changes in depositional environment over the past ca. 53,000 years were reconstructed using a range of physical, sedimentological, geochemical, and μ-XRF elemental proxy datasets analyzed from lake sediment cores obtained from Lake Kanono, Northland, New Zealand. The Lake Kanono stratigraphy displays a terrestrial peat environment (ca. 53,700–6,670 cal yr BP), followed by a trend of increased influx of detrital sediment during the Late Glacial–Interglacial Transition (LGIT) at ca. 14,000 cal yr BP with a peak from ca. 12,000 to 9,000 cal yr BP driven by increasingly dry conditions. The increase in sediment influx continued during the early to mid-Holocene, leading to dune reactivation which altered the catchment dynamics of the region, leading to the inception of a shallow lake basin at ca. 6,670 cal yr BP. The timing of the formation of this lake basin can be associated with changes in intensity of the Southern Westerly Winds (SWW) and the appearance and increase in intensity of the El Niño Southern Oscillation (ENSO) after ca. 7,500–7,000 cal yr BP (Moy et al. 2002; Moreno et al. 2018). Drier conditions peaked from ca. 4,000 to 2,400 cal yr BP, possibly culminating in decreased lake levels that persisted from ca. 2,400 to 2,210 cal yr BP, renewed dune accumulation, and blocked stream outlets, resulting in a deep lake basin with thermal stratification that persisted to the present. Cluster analysis of the μ-XRF data demonstrates that the most prominent change in chemistry is near the onset of the Last Glacial Maximum (LGM) at ca. 26,700 cal yr BP associated with a transition to a drier, windier climate. The second most prominent change in the μ-XRF data is during the Polynesian phase of human settlement at ca. 612–575 cal yr BP (1338– 1375 CE). Hence, we can demonstrate the utility and power of a multi-proxy approach coupled with μ-XRF element data to interpret changing sediment sources to a lake basin. Such an approach allows rapid and reliable evaluation of catchment processes influenced by climate events and land-use changes at a resolution not available using other approaches.

Morphotectonic configuration of the Podtatranská Kotlina Basin and its relationship to the origin of the Western Carpathians

In tectonically active regions, many aspects of the topography can provide clues to morphotectonic development. Morphological lineaments have varying degrees of reliability as indicators of neotectonic movement. Here, eleven lines of evidence are assessed and combined for the Podtatranská Kotlina Basin (PtK) between the Tatra and Low Tatra (Nízke Tatry) Mountains, the highest topography of the Western Carpathians. This permits identification of the configuration of structural-neotectonic blocks and documentation of their behaviour. Specifically we 1) evaluate the reliability of fault mapping results, 2) assess relative uplift and subsidence accommodated by the faults, 3) evaluate the intensity of fault movement and 4) explore the role of fault movement in the tilting of blocks. We define 358 structural-neotectonic blocks in the PtK region, providing an exceptionally detailed morphotectonic analysis. Distinction of two stages of neotectonic uplift provides explanation of the regional discrepancy between intensive neotectonic activity and limited recent seismicity with Mw < 5. The first stage, in the Pliocene-Early Pleistocene, was characterized by isostatic uplift linked to delamination and/or convective removal of an over-thickened lithosphere. The second stage during the Late Quaternary involved more complex uplift, including the probable influence of episodic mantle flow induced by the load of the Scandinavian Ice Sheet on northern Europe. This resulted in a change in the extension and configuration of structural-neotectonic blocks, the movements of the Tatra block now measured by GNSS, and the interaction of neotectonic activity with effects of glacial–interglacial transitions.

Late Pleistocene–Holocene pedogenesis and palaeoclimate in western Asia from palaeosols of the Central Iranian Plateau

The Late Pleistocene and Holocene in western Asia is characterized by frequent, millennial‐scale, high‐amplitude environmental climatic changes. However, little is known about palaeoclimate conditions on the arid Central Iranian Plateau and knowledge of palaeosols and past phases of pedogenesis in relation to climatic events is scarce. Nevertheless, these palaeosols contain important information on the Last Glacial–Interglacial cycle and Holocene climate and environmental changes in the region. Three representative pedons with eight argillic horizons from the interior of the Central Iranian Plateau, namely Isfahan, Jimabad and Bajestan are selected for micromorphological, mineralogical and submicroscopic analyses. The ages of these palaeosols are constrained using the optically stimulated luminescence (OSL) signal from quartz. Micromorphological observations show clay illuviation, carbonate leaching, accumulation of secondary carbonates, calcite depletion, and other characteristic pedogenic features. These characteristics, combined with the luminescence chronology, reveal the presence of well‐developed reddish‐brown palaeoargillic horizons (Btk/Btky) with intensive soil formation processes taking place during the Last Interglacial to Middle Holocene (~107–4.5 ka) in our study area. Pedogenic evidence from the palaeosols suggests steps of polygenetic formation in the argillic horizons in response to alternating wetter and drier phases during this period. Four distinct phases of pedogenesis resulting in Btk/Btky horizons are identified: (i) Marine Isotope Stage (MIS) 5, (ii) MIS 3, (iii) the Last Glacial–Interglacial Transition Holocene, and (iv) the Late Holocene.

Ice thinning on nunataks during the glacial to interglacial transition in the Antarctic Peninsula region according to Cosmic-Ray Exposure dating: Evidence and uncertainties

The small ice caps distributed across the Antarctic Peninsula region have undergone large ice volume changes since the Last Glacial Cycle, in line with most of the Antarctic continent. While the surface extent of glacial shrinking is relatively well known, the timing of glacial oscillations and the magnitude of ice thinning remain little investigated. Cosmic-Ray Exposure (CRE) dating applied on ice-free vertical sequences can provide insights about the temporal framework of glacial oscillations. However, the potential occurrence of nuclide inheritance may overestimate the real timing of the last glacial retreat. This problem has been observed in many areas in Continental Antarctica, but similar studies have not yet been conducted in environments of the Maritime Antarctica, such as the South Shetland Islands (SSI). This research focuses on the Hurd Peninsula ice cap (HPIC, ca. 60°22′ W, 62°40’ S), located in the SW of Livingston Island, SSI. Past climate oscillations since the Last Glacial Cycle have determined the amount of ice stored in the ice cap. Today, this polythermal ice cap is surrounded by several nunataks standing out above the ice. Three of them have been selected to explore their deglaciation history and to test the potential occurrence of nuclide inheritance in deglaciated bedrocks associated with polythermal glaciers. We present a new dataset with 10 10Be exposure dates. Some of them were found to be anomalously old, evidencing that nuclide inheritance is present in bedrocks associated with polythermal ice caps and suggesting complex glacial exposure histories. We attribute this to limited erosion, given the gentle slope of the nunatak margins and the cold-based character of the surrounding ice. The remaining samples allowed to approach local surface-elevation changes of the HPIC. Our results suggest that ice thinning started during the Last Glacial Maximum (LGM) at ∼22 ka but intense glacial shrinking occurred from ∼18 to ∼13 ka, when the nunataks became exposed, being particularly intense at the end of this period (∼14–13 ka) coinciding with the time of the meltwater pulse 1a (MWP-1a) and the end of the Antarctic Cold Reversal (ACR).

Cosmogenic data about offset uplifted river terraces and erosion rates: implication regarding the central North Anatolian Fault and the Central Pontides

River terraces are geomorphological markers recording deformation. Here, we use four strath and fill river terraces along the Kızılırmak River in Turkey to unravel the deformation along the convex arc formed by the central North Anatolian Fault (NAF), a continental transform fault. 10Be, 26Al, 36Cl cosmogenic exposure ages of T3 and T2 strath terraces constrain their formation at 83 ± 15 ka and 67 ± 7 ka, respectively. We evidence frost-cracking during humid cold periods that bought younger carbonate cobbles on both terraces. T1, a younger fill terrace was probably emplaced during the MIS3 (30–40 ka) aggradational period or during the last glacial–interglacial transition. T0, the most recent fill terrace, was incised shortly before the 1668 earthquake based on 14C dating. It records a cumulated 14 ± 2 m offset linked to the 1943 and 1668 earthquakes. T3 shows a maximum offset of ~ 845 m and constrains a 10 mm/year geological slip rate that is lower than Holocene slip rates. It suggests temporal change in slip rates along the NAF. T2 and T3 also evidenced an uplift of 1 mm/year induced by transpressive deformation accommodated close to the NAF. Compared to the 0.28 mm/year obtained to the north, a larger portion of the shortening in the Central Pontides is accommodated close to the driving plate boundary. We also evidenced high cosmogenic-based erosion rates in Pontides during the Holocene, and even higher rates during T3 planation. Erosion rates were combined with present-day relief to infer a first-order minimal shortening of 12–16 km using simple mass balance principles in the Central Pontides. This long-term shortening is larger than the one induced by the Anatolian rotation suggesting a far field effect of the collision.

Evidence for centennial‐scale Lateglacial and early Holocene climatic complexity from Quoyloo Meadow, Orkney, Scotland

AbstractThe influence of the North Atlantic on the margins of Europe means the region is particularly sensitive to changes in the ocean–atmospheric system. During the Last Glacial–Interglacial Transition (16–8 cal ka bp) this system was repeatedly disrupted, leading to a series of abrupt and short‐lived shifts in climate. Despite much research, the number and magnitude of these ‘centennial‐scale’ events is not well understood. To address this, we expand upon investigations at Quoyloo Meadow, Orkney, Scotland, one of the best chronologically constrained palaeoclimate records in northern Britain. By coupling stable isotope and chironomid fossil analyses with existing data, this study identifies multiple phases of centennial‐scale disturbance at: c. 14.0, 11.1, 10.8, 10.5, 10.45 and 10.3 cal ka bp, with the events at 14.0 and 10.3 exhibiting a particularly pronounced cold‐climate signature. During the Holocene, the strongest response to climate forcing was at c. 10.3–10.0 cal ka bp, expressed as a two‐stage drop in mean July temperatures, a shift in pollen spectra indicative of ‘less‐stable’ climatic regimes, and a depletion in δ18O values. We interpret this as the first reliably dated incidence of the ‘10.3‐ka event’ in the British Isles and consider the wider impact of this climatic reversal in other Holocene records.

Declining discharge of glacier outburst floods through the Holocene in central Patagonia

Glacier outburst floods are a major hazard in glacierized catchments. Global analyses have shown reduced frequency of glacier floods over recent decades but there is limited longer-term data on event magnitude and frequency. Here, we present a Holocene palaeoflood record from the Río Baker (Chilean Patagonia), quantifying the discharge and timing of glacier floods over millennial timescales. A catastrophic flood of 110,000 m3/s (0.11 Sv) occurred at 9.6 ± 0.8 ka, during final stages of the Late Glacial Interglacial Transition, followed by five flood-phases coeval or post-dating Holocene neoglacials. Highest flood frequencies occurred at 4.3–4.4 ka, with 26 floods of minimum discharges of 10,000–11,000 m3/s, and 0.6 ka with 10 floods exceeding 4600–5700 m3/s. The largest modern outburst flood recorded surpassed ∼3810 m3/s. Thus glacier flood magnitude declines from the order of 0.1 to 0.01 Sv over the Early to Mid Holocene, and to 0.001 Sv in the instrumental record.

The Late Quaternary Evolution of the Upper Reaches of Fluvial Systems in the Southern East European Plain

Networks of dry valleys (or balkas) and hollows in the upper reaches of fluvial basins in extraglacial areas in the Penultimate Glaciation (Marine Isotope Stage 6—MIS 6) regions of the East European Plain demonstrate clear incision/aggradation rhythms corresponding to global glacial/interglacial climate cycles. The first phase of each incision/aggradation rhythm began after the global glacial maximum and was characterized by a cool and humid climate, permafrost and sparse vegetation, when high surface runoff and active linear erosion formed a dense network of gullies. The second phase occurred at the glacial–interglacial transition and the subsequent interglacial period with its warm and humid climate and dense vegetation. This phase was distinguished by the partial filling of fluvial forms with slopewash deposits, the transformation of gullies into dry valleys (balkas) and the subsequent stabilization of fluvial forms marked by the formation of mature soils on the sides and bottoms of balkas. The third phase of the rapid accumulation of balkas developed during the cold and dry part of the next glacial epoch, resulting in the balkas becoming shallow hollows filled in with sediments. The last full incision/aggradation rhythm occurred in the late MIS 6 to mid-MIS 2. The erosion network formed during the late MIS 6 was almost completely filled by mid-MIS 2, and its manifestation in the modern topography is limited to a network of shallow hollows in the upper parts of the fluvial systems. The modern (incomplete) incision/aggradation rhythm began in the late MIS 2 and caused the formation of the modern erosion landscape in the upper reaches of fluvial systems. This rhythm is now in the stabilization phase, and the main accumulation phase of this rhythm is still far in the future.

Overkill, glacial history, and the extinction of North America’s Ice Age megafauna

The end of the Pleistocene in North America saw the extinction of 38 genera of mostly large mammals. As their disappearance seemingly coincided with the arrival of people in the Americas, their extinction is often attributed to human overkill, notwithstanding a dearth of archaeological evidence of human predation. Moreover, this period saw the extinction of other species, along with significant changes in many surviving taxa, suggesting a broader cause, notably, the ecological upheaval that occurred as Earth shifted from a glacial to an interglacial climate. But, overkill advocates ask, if extinctions were due to climate changes, why did these large mammals survive previous glacial−interglacial transitions, only to vanish at the one when human hunters were present? This question rests on two assumptions: that previous glacial−interglacial transitions were similar to the end of the Pleistocene, and that the large mammal genera survived unchanged over multiple such cycles. Neither is demonstrably correct. Resolving the cause of large mammal extinctions requires greater knowledge of individual species’ histories and their adaptive tolerances, a fuller understanding of how past climatic and ecological changes impacted those animals and their biotic communities, and what changes occurred at the Pleistocene−Holocene boundary that might have led to those genera going extinct at that time. Then we will be able to ascertain whether the sole ecologically significant difference between previous glacial−interglacial transitions and the very last one was a human presence.

Structure of Late Pleistocene and Holocene Sediments in the Petrozavodsk Bay, Lake Onego (NW Russia)

Here, we present new results from seismic, geological, and geochemical studies conducted in 2015–2019 in the Petrozavodsk Bay of Lake Onego, NW Russia. The aims of these investigations were to (i) to characterize the structure of Quaternary deposits and (ii) provide new evidence of modern geodynamic movements and gas-seepage in Holocene sediments. The structure of the recovered deposits was composed of lacustrine mud, silt and sands from the Holocene, limno-glacial clays (varved clays) from the Late Glacial–Interglacial Transition, and glacial deposits (till) from the Late Pleistocene. The thickness of these deposits varied in different parts of the bay. Many pockmarks created by gases escaping and reaching sediment-water interface were observed in these deposits. Such pockmarks can play a significant role in the geochemical and biological processes in the bottom sediment surface, and gases that escape might modify the physicochemical characteristics of the environment.

Chronostratigraphy, Site Formation, and Palaeoenvironmental Context of Late Pleistocene and Holocene Occupations at Grassridge Rock Shelter (Eastern Cape, South Africa)

Grassridge rock shelter is located in the high elevation grassland foothills of the Stormberg Mountains in the Eastern Cape of South Africa. This places Grassridge at an important biogeoclimatic intersection between the Drakensberg Mountains, the South African coastal zone, and the interior arid lands of southern Africa. First excavated in 1979, the approximately 1.5 m stratigraphic sequence was divided into two major occupational components: a 50–70 cm thick Later Stone Age component dating between 7–6 ka and an underlying 50–80 cm thick Middle Stone Age component dated to 36 ka at the base. Here we present a reanalysis of the Grassridge stratigraphic sequence that combines new optically stimulated luminescence and radiocarbon age estimates with sedimentological and microbotanical analyses to evaluate site formation processes and the palaeoenvironmental context of human occupations. Results indicate a complex history of geogenic, anthropogenic, and biogenic inputs to the depositional sequence that are interspersed with pulsed human occupation from 43–28 ka, 13.5–11.6 ka, and 7.3–6.8 ka. Microbotanical remains indicate a cooler, drier grassland environment in MIS 3 that transitions to a warmer, moister grassland environment dominated by summer rainfall in the middle of MIS 1. The pulsed occupational sequence identified at Grassridge is characteristic of the Pleistocene and Holocene record across the greater high elevation grassland region of South Africa, which, based on comparison with other currently available evidence, seems linked to a complex system of forager mobility entwined with rapidly fluctuating palaeoenvironments across the last glacial to interglacial transition.