Interglacial Cycles Research Articles

Climatic and tectonic controls on source-to-sink processes in the tropical, ultramafic catchment of Lake Towuti, Indonesia

Humid tropical landscapes are subject to intense weathering and erosion, which strongly influence sediment mobilisation and deposition. In this setting, we aimed to understand how geomorphology and hydroclimate altered the style and intensity of erosion and sediment composition in a tropical lake and its tectonically active catchment. Lake Towuti (2.75°S, 121.5°E) is one of the oldest and deepest lakes in Indonesia, with uninterrupted lacustrine sedimentation over several glacial–interglacial cycles. Here we present results from a novel set of Lake Towuti surface sediment, bedrock and soil samples from the catchment, and two existing sediment cores that extend to 30,000 and 60,000 years before present. We studied the catchment morphology, soil properties, geochemistry, and clay and bulk mineralogy. Results from several river long profiles show clear signs of tectonic activity, which enhances river incision, favours mass movement processes, and together with remobilisation of fluvial deposits, strongly influences modern sedimentation in the lake. Material from the Mahalona River, the lake’s largest inflow, dominates modern sediment composition in Towuti’s northern basin. The river transports Al-poor and Mg-rich sediments (mainly serpentines) to the lake, indicating river incision into the Mg-rich serpentinised peridotite bedrock. Relatively small, but important additional contributions of material, come from direct laterite-derived input and the Loeha River, which both provide Al-rich and Mg-poor sediment to the lake. Over time, the Al/Mg and kaolinite-to-serpentine ratios varied strongly, primarily in response to lake-level fluctuations driven by hydroclimatic changes. In the past 60,000 years, both the Al/Mg and kaolinite-to-serpentine ratios showed variations sensitive to changes in climate boundary conditions across glacial-interglacial cycles, while tectonic activity had less influence on changes in sediment composition on these short time-scales.

Early and Middle Pleistocene environments, landforms and sediments in Scotland

ABSTRACTThis paper reviews the changing environments, developing landforms and terrestrial stratigraphy during the Early and Middle Pleistocene stages in Scotland. Cold stages after 2.7 Ma brought mountain ice caps and lowland permafrost, but larger ice sheets were short-lived. The late Early and Middle Pleistocene sedimentary record found offshore indicates more than 10 advances of ice sheets from Scotland into the North Sea but only 4–5 advances have been identified from the terrestrial stratigraphy. Two primary modes of glaciation, mountain ice cap and full ice sheet modes, can be recognised. Different zones of glacial erosion in Scotland reflect this bimodal glaciation and the spatially and temporally variable dynamics at glacier beds. Depths of glacial erosion vary from almost zero in Buchan to hundreds of metres in glens in the western Highlands and in basins both onshore and offshore. The presence of tors and blockfields indicates repeated development of patches of cold-based, non-erosive glacier ice on summits and plateaux. In lowlands, chemical weathering continued to operate during interglacials, but gruss-type saprolites are mainly of Pliocene to Early Pleistocene age. The Middle Pleistocene terrestrial stratigraphic record in Scotland, whilst fragmentary and poorly dated, provides important and accessible evidence of changing glacial, periglacial and interglacial environments over at least three stadial–interstadial–interglacial cycles. The distributions of blockfields and tors and the erratic contents of glacial sediments indicate that the configuration, thermal regime and pattern of ice flow during MIS 6 were broadly comparable to those of the last ice sheet. Improved control over the ages of Early and Middle Pleistocene sediments, soils and saprolites and on long-term rates of weathering and erosion, combined with information on palaeoenvironments, ice extent and sea level, will in future allow development and testing of new models of Pleistocene tectonics, isostasy, sea-level change and ice sheet dynamics in Scotland.

Predictive pollen-based biome modeling using machine learning.

This paper investigates suitability of supervised machine learning classification methods for classification of biomes using pollen datasets. We assign modern pollen samples from Africa and Arabia to five biome classes using a previously published African pollen dataset and a global ecosystem classification scheme. To test the applicability of traditional and machine-learning based classification models for the task of biome prediction from high dimensional modern pollen data, we train a total of eight classification models, including Linear Discriminant Analysis, Logistic Regression, Naïve Bayes, K-Nearest Neighbors, Classification Decision Tree, Random Forest, Neural Network, and Support Vector Machine. The ability of each model to predict biomes from pollen data is statistically tested on an independent test set. The Random Forest classifier outperforms other models in its ability correctly classify biomes given pollen data. Out of the eight models, the Random Forest classifier scores highest on all of the metrics used for model evaluations and is able to predict four out of five biome classes to high degree of accuracy, including arid, montane, tropical and subtropical closed and open systems, e.g. forests and savanna/grassland. The model has the potential for accurate reconstructions of past biomes and awaits application to fossil pollen sequences. The Random Forest model may be used to investigate vegetation changes on both long and short time scales, e.g. during glacial and interglacial cycles, or more recent and abrupt climatic anomalies like the African Humid Period. Such applications may contribute to a better understanding of past shifts in vegetation cover and ultimately provide valuable information on drivers of climate change.

The silicon cycle impacted by past ice sheets

Globally averaged riverine silicon (Si) concentrations and isotope composition (δ30Si) may be affected by the expansion and retreat of large ice sheets during glacial−interglacial cycles. Here we provide evidence of this based on the δ30Si composition of meltwater runoff from a Greenland Ice Sheet catchment. Glacier runoff has the lightest δ30Si measured in running waters (−0.25 ± 0.12‰), significantly lower than nonglacial rivers (1.25 ± 0.68‰), such that the overall decline in glacial runoff since the Last Glacial Maximum (LGM) may explain 0.06–0.17‰ of the observed ocean δ30Si rise (0.5–1.0‰). A marine sediment core proximal to Iceland provides further evidence for transient, low-δ30Si meltwater pulses during glacial termination. Diatom Si uptake during the LGM was likely similar to present day due to an expanded Si inventory, which raises the possibility of a feedback between ice sheet expansion, enhanced Si export to the ocean and reduced CO2 concentration in the atmosphere, because of the importance of diatoms in the biological carbon pump.

Constraining the evolution of Neogene ocean carbonate chemistry using the boron isotope pH proxy

Over the course of the Neogene, the Earth underwent profound climatic shifts from the sustained warmth of the middle Miocene to the development of Plio-Pleistocene glacial–interglacial cycles. Major perturbations in the global carbon cycle have occurred alongside these shifts, however the lack of long-term carbonate system reconstructions currently limits our understanding of the link between changes in CO2, carbon cycling, and climate over this time interval. Here we reconstruct continuous surface ocean pH, CO2, and surface ocean aragonite saturation state using boron isotopes from the planktonic foraminifer Trilobatus trilobus and we perform a sensitivity analysis of the key variables in our calculations (e.g. δ11Bsw, [Ca]sw, CCD). We show that the choice of δ11Bsw influences both seawater pH and CO2 while [Ca]sw reconstructed dissolved inorganic carbon exerts a significant influence only on CO2. Over the last 22 Myr, the lowest pH levels occurred in the Middle Miocene Climate Optimum (MMCO; 17–14 Myr ago) reaching ∼7.6±0.1 units in all our scenarios. The extended warmth of the MMCO corresponds to mean CO2 and aragonite saturation state levels of 470–630 ppm and 2.7–3.5, respectively. Despite a general correspondence between our CO2 record and climate, all CO2 scenarios show a peak at ∼9 Ma not matched by corresponding changes in climate reconstructions. This may suggest decoupling (i.e. significant CO2 change without a discernible climate response) for a limited interval in the Late Miocene (11.6–8.5 Ma), although further refinement of our understanding of the temporal evolution of the boron isotopic composition of seawater is necessary to fully evaluate the nature of the relationship between CO2 and climate. Nonetheless, from our long-term view it is clear that low-latitude open ocean marine ecosystems are unlikely to have experienced sustained surface pH and saturation levels below 7.7 and 1.7, respectively, during the past 14 million years (66% CI).

The spatial extent of the East Asian summer monsoon in arid NW China during the Holocene and Last Interglaciation

Abstract The extent to which the East Asian summer monsoon (EASM) penetrated inland during the last interglacial cycle and the Holocene remains unclear, but it is critical to understanding changing precipitation dynamics in arid NW China. Here we reconstruct high-resolution lake level changes for two closed terminal lake basins in the eastern and western Alxa Plateau (AP) at the fringe of the modern EASM. Nineteen well-preserved paleolake shoreline sequences at these two basins were systematically investigated and trenched. The chronologies for these shorelines were constructed using quartz optically stimulated luminescence dating and K-feldspar pIRIR dating. Our results indicate that: (1) lake high stands occurred in both basins of the AP during Marine Isotope Stage (MIS) 5 and the mid-late Holocene; (2) paleolake level fluctuations on the eastern and western AP are asynchronous within these two periods. Lake levels peaked in the eastern AP during MIS 5e to 5c and the mid-Holocene, while the highest lake levels occurred in the western AP during MIS 5c to 5a and the late Holocene; (3) lake level changes in the eastern AP were contemporaneous with changes in EASM intensities during MIS 5 and the Holocene, while those in the western AP were asynchronous. These differences indicate EASM–precipitation was more intense on the eastern AP during periods of maximum EASM strength. Conversely, relative aridity in the western AP indicates that the EASM did not penetrate that far inland even during phases of strong monsoonal circulation (i.e. early MIS 5 and the mid-Holocene). Instead, precipitation and lake level changes in the western AP and much of the northeastern Tibetan Plateau appears to be related to changing meridional circulation intensity (Westerlies).

Paleoceanography and ice sheet variability offshore Wilkes Land, Antarctica – Part 1: Insights from late Oligocene astronomically paced contourite sedimentation

Abstract. Antarctic ice sheet and Southern Ocean paleoceanographic configurations during the late Oligocene are not well resolved. They are however important to understand the influence of high-latitude Southern Hemisphere feedbacks on global climate under CO2 scenarios (between 400 and 750 ppm) projected by the IPCC for this century, assuming unabated CO2 emissions. Sediments recovered by the Integrated Ocean Drilling Program (IODP) at Site U1356, offshore of the Wilkes Land margin in East Antarctica, provide an opportunity to study ice sheet and paleoceanographic configurations during the late Oligocene (26–25 Ma). Our study, based on a combination of sediment facies analysis, magnetic susceptibility, density, and X-ray fluorescence geochemical data, shows that glacial and interglacial sediments are continuously reworked by bottom currents, with maximum velocities occurring during the interglacial periods. Glacial sediments record poorly ventilated, low-oxygenation bottom water conditions, interpreted as resulting from a northward shift of westerly winds and surface oceanic fronts. Interglacial sediments record more oxygenated and ventilated bottom water conditions and strong current velocities, which suggests enhanced mixing of the water masses as a result of a southward shift of the polar front. Intervals with preserved carbonated nannofossils within some of the interglacial facies are interpreted as forming under warmer paleoclimatic conditions when less corrosive warmer northern component water (e.g., North Atlantic sourced deep water) had a greater influence on the site. Spectral analysis on the late Oligocene sediment interval shows that the glacial–interglacial cyclicity and related displacements of the Southern Ocean frontal systems between 26 and 25 Ma were forced mainly by obliquity. The paucity of iceberg-rafted debris (IRD) throughout the studied interval contrasts with earlier Oligocene and post-Miocene Climate Optimum sections from Site U1356 and with late Oligocene strata from the Ross Sea, which contain IRD and evidence for coastal glaciers and sea ice. These observations, supported by elevated sea surface paleotemperatures, the absence of sea ice, and reconstructions of fossil pollen between 26 and 25 Ma at Site U1356, suggest that open-ocean water conditions prevailed. Combined, this evidence suggests that glaciers or ice caps likely occupied the topographic highs and lowlands of the now marine Wilkes Subglacial Basin (WSB). Unlike today, the continental shelf was not overdeepened and thus ice sheets in the WSB were likely land-based, and marine-based ice sheet expansion was likely limited to coastal regions.

A 190-ka biomarker record revealing interactions between sea ice, Atlantic Water inflow and ice sheet activity in eastern Fram Strait

The northeastern Fram Strait at the entrance to the Arctic Ocean represents a key observatory for sea ice reconstructions as it sensitively reacts to environmental changes. A combined biomarker approach (HBIs, sterols, alkenones) was carried out on Core PS93/006-1 from the western Svalbard margin to reconstruct sea ice conditions related to glacial–interglacial cycles of the last 190 ka. The continuous presence of sea ice demonstrates the strong influence of polar water masses in the eastern Fram Strait. Glacial intervals are characterised by extended sea ice conditions with perennial sea ice cover during early MIS 6, the Penultimate Glacial Maximum, the interstadial MIS 5d, MIS 4 and the Last Glacial Maximum. Less severe, yet highly variable, sea ice conditions with more frequent summer melt dominated the interglacial stages. The opposing sea ice conditions along the western and northern Svalbard margin highlight the different regional impact of various environmental forces in eastern Fram Strait. Thus, the major expansion of the Svalbard Barents Sea Ice Sheet favoured the formation of perennial sea ice west of Svalbard while it triggered the establishment of marginal ice cover on the Yermak Plateau.

Arctic warming induced by the Laurentide Ice Sheet topography

Abstract. It is well known that ice sheet–climate feedbacks are essential for realistically simulating the spatiotemporal evolution of continental ice sheets over glacial–interglacial cycles. However, many of these feedbacks are dependent on the ice sheet thickness, which is poorly constrained by proxy data records. For example, height estimates of the Laurentide Ice Sheet (LIS) topography at the Last Glacial Maximum (LGM; ∼ 21 000 years ago) vary by more than 1 km among different ice sheet reconstructions. In order to better constrain the LIS elevation it is therefore important to understand how the mean climate is influenced by elevation discrepancies of this magnitude. Here we use an atmospheric circulation model coupled to a slab-ocean model to analyze the LGM surface temperature response to a broad range of LIS elevations (from 0 to over 4 km). We find that raising the LIS topography induces a widespread surface warming in the Arctic region, amounting to approximately 1.5 ∘C per km of elevation increase, or about 6.5 ∘C for the highest LIS. The warming is attributed to an increased poleward energy flux by atmospheric stationary waves, amplified by surface albedo and water vapor feedbacks, which account for about two-thirds of the total temperature response. These results suggest a strong feedback between continental-scale ice sheets and the Arctic temperatures that may help constrain LIS elevation estimates for the LGM and explain differences in ice distribution between the LGM and earlier glacial periods.

A 43 kyr record of protist communities and their response to oxygen minimum zone variability in the Northeastern Arabian Sea

An extensive oxygen minimum zone (OMZ) occurs in the northeastern (NE) Arabian Sea where sedimentary records show evidence of alternating strong and weak OMZs that correlate with North Atlantic climate variability during the last glacial–interglacial cycle. OMZs are expanding world-wide, but information on long-term OMZ-ecosystem interactions is mainly limited to fossilized species, notably foraminifera. Here, we provide a first comprehensive ancient sedimentary DNA record of both fossilizing and non-fossilizing protists and their response to OMZ variability in the NE Arabian Sea over the last 43 ka. Protist communities changed significantly during strong vs. weak OMZ conditions coincident with interstadials and stadials respectively. Dinoflagellates were identified as significant indicator taxa for strong OMZs during glacial as well as interglacial interstadials, whereas diatoms were significant indicators for strong OMZs only during glacial interstadials. The chlorophyte Chlorella was found to be the main phototrophic protist in nutrient-depleted surface waters during glacial stadials. Notably, strong OMZ conditions shaped past protist communities by creating isolated habitats for those capable of sustaining oxygen depletion either by adapting a parasitic life cycle (e.g. apicomplexans) or by establishing mutualistic connections with others (e.g. radiolarians and mixotrophic dinoflagellates) or by forming cysts (e.g. colpodeans). Notably, a long-term increase in eutrophication and a decrease in the diatom/dinoflagellate ratio was observed during the late Holocene favoring the pelagic component of the marine food web. A similar scenario could be expected in the context of predicted worldwide expansion of coastal OMZs associated with global climate change.

High resolution 14C AMS ages (∼50 ka) of organic matter associated with the loess-palaeosol Holocene-Late Pleistocene (8–130 ka) sediments of Dilpur Formation, Karewa Group, Kashmir, India

Abstract High resolution 14C AMS ages from sequential layers in the late Quaternary Dilpur Formation in Indian Kashmir, reveal glacial and inter-glacial climatic changes archived in this more or less complete aeolian-palaeosol record. The 14C AMS ages are consistent and fit well within the time window of ∼45–50 ka. Considering the thicknesses (at corresponding stratigraphic heights), the ages obtained for the S1 palaeosol layer provided high resolution ages for the early Holocene period. When compared to the sedimentation rate based time estimates for the successive layers showed direct relationship between absolute ages and the time involved in the deposition. Based on the extrapolation of 14C AMS ages of the Shankerpora section, the incidences of glaciations occurred at 67–71 ka and 124–127 ka. The glacial and interglacial cycles spanning ∼130 ka encompass a variable number of palaeosols. Temporally, these observations correlate well with the two glaciations earlier reported from the loess palaeosol succession of Xiagaoyuan, Gansu Province, western Chinese Loess Plateau, suggesting perhaps that similar climatic conditions prevailed in this region.

Effects of tephra falls on vegetation: A Late‐Quaternary record from southern Italy

Abstract Impacts of tephra deposition on vegetation are recorded in a series of 10 high temporal resolution absolute pollen diagrams from Lago Grande di Monticchio, each diagram spanning a single tephra deposition event during the last glacial–interglacial cycle. Sediment accumulation rates determined by counting and measurement of annual laminations (“varves”) provide an accurate and precise chronology, enabling the minimum recovery time after a tephra fall to be determined. In most cases, pollen accumulation rate was reduced after the tephra fall, indicating reduced vegetation productivity. Tephra deposition events also led to changes in vegetation composition, although these varied in magnitude. The magnitude and duration of the impacts upon the vegetation were related to the thickness of the tephra layer deposited, the thickest layers examined (>250 mm) having minimum recovery times of up to a century and thicker layers generally having greater impacts upon pollen productivity and vegetation composition. Tephra chemistry also influenced the persistence of the impact. The nature of the prevailing vegetation prior to the tephra fall influenced the degree and persistence of the impact. Tephra layers <30 mm thick had minimum recovery times of up to 90 years when they fell on wooded steppe vegetation, whereas cold steppe recovered much more quickly, as did forest. The relative sensitivity of wooded steppe was contrary to our expectations. Of individual pollen taxa, Cupressaceae emerged as particularly sensitive to tephra deposition. Synthesis. Applying absolute pollen analytical methods to a sediment record with a well‐supported and precise chronology obtained from a lake in a volcanic region where the vegetation has been subject to numerous tephra deposition events enabled us to explore the impacts of such events. Our results provide evidence of differential impacts upon individual plant taxa and of differential sensitivity of three vegetation types that have prevailed in the region during the last glacial–interglacial cycle. The influences of tephra thickness and chemistry on minimum recovery time were substantial. Our results are relevant to forecasting the potential impacts upon ecosystems of volcanic eruptions.

Simulation of the Greenland Ice Sheet over two glacial–interglacial cycles: investigating a sub-ice- shelf melt parameterization and relative sea level forcing in an ice-sheet–ice-shelf model

Abstract. Observational evidence, including offshore moraines and sediment cores, confirm that at the Last Glacial Maximum (LGM) the Greenland ice sheet (GrIS) expanded to a significantly larger spatial extent than seen at present, grounding into Baffin Bay and out onto the continental shelf break. Given this larger spatial extent and its close proximity to the neighbouring Laurentide Ice Sheet (LIS) and Innuitian Ice Sheet (IIS), it is likely these ice sheets will have had a strong non-local influence on the spatial and temporal behaviour of the GrIS. Most previous paleo ice-sheet modelling simulations recreated an ice sheet that either did not extend out onto the continental shelf or utilized a simplified marine ice parameterization which did not fully include the effect of ice shelves or neglected the sensitivity of the GrIS to this non-local bedrock signal from the surrounding ice sheets. In this paper, we investigated the evolution of the GrIS over the two most recent glacial–interglacial cycles (240 ka BP to the present day) using the ice-sheet–ice-shelf model IMAU-ICE. We investigated the solid earth influence of the LIS and IIS via an offline relative sea level (RSL) forcing generated by a glacial isostatic adjustment (GIA) model. The RSL forcing governed the spatial and temporal pattern of sub-ice-shelf melting via changes in the water depth below the ice shelves. In the ensemble of simulations, at the glacial maximums, the GrIS coalesced with the IIS to the north and expanded to the continental shelf break to the southwest but remained too restricted to the northeast. In terms of the global mean sea level contribution, at the Last Interglacial (LIG) and LGM the ice sheet added 1.46 and −2.59 m, respectively. This LGM contribution by the GrIS is considerably higher (∼ 1.26 m) than most previous studies whereas the contribution to the LIG highstand is lower (∼ 0.7 m). The spatial and temporal behaviour of the northern margin was highly variable in all simulations, controlled by the sub-ice-shelf melting which was dictated by the RSL forcing and the glacial history of the IIS and LIS. In contrast, the southwestern part of the ice sheet was insensitive to these forcings, with a uniform response in all simulations controlled by the surface air temperature, derived from ice cores.

Modelling silicon supply during the Last Interglacial (MIS 5e) at Lake Baikal

Limnological reconstructions of primary productivity have demonstrated its response over Quaternary timescales to drivers such as climate change, landscape evolution and lake ontogeny. In particular, sediments from Lake Baikal, Siberia, provide a valuable uninterrupted and continuous sequence of biogenic silica (BSi) records, which document orbital and sub-orbital frequencies of regional climate change. We here extend these records via the application of stable isotope analysis of silica in diatom opal (δ30Sidiatom) from sediments covering the Last Interglacial cycle (Marine Isotope Stage [MIS] 5e; c. 130 to 115 ka BP) as a means to test the hypothesis that it was more productive than the Holocene. δ30Sidiatom data for the Last Interglacial range between +1.29 and +1.78‰, with highest values between c. 127 to 124 ka BP (+1.57 to +1.78‰). Results show that diatom dissolved silicon (DSi) utilisation, was significantly higher (p = 0.001) during MIS 5e than the current interglacial, which reflects increased diatom productivity over this time (concomitant with high diatom biovolume accumulation rates [BVAR] and warmer pollen-inferred vegetation reconstructions). Diatom BVAR are used, in tandem with δ30Sidiatom data, to model DSi supply to Lake Baikal surface waters, which shows that highest delivery was between c. 123 to 120 ka BP (reaching peak supply at c. 120 ka BP). When constrained by sedimentary mineralogical archives of catchment weathering indices (e.g. the Hydrolysis Index), data highlight the small degree of weathering intensity and therefore representation that catchment-weathering DSi sources had, over the duration of MIS 5e. Changes to DSi supply are therefore attributed to variations in within-lake conditions (e.g. turbulent mixing) over the period, where periods of both high productivity and modelled-DSi supply (e.g. strong convective mixing) account for the decreasing trend in δ30Sidiatom compositions (after c. 124 ka BP).

Ocean and atmosphere teleconnections modulate east tropical Pacific productivity at late to middle Pleistocene terminations

The modern Eastern Equatorial Pacific (EEP) is a key oceanographic region for regulating the Earth's climate system, accounting for between 5–10% of global marine production whilst also representing a major source of carbon dioxide efflux to the atmosphere. Changes in ocean dynamics linked to the nutrient supply from the Southern Ocean have been suggested to have played a dominant role in regulating EEP productivity over glacial–interglacial timescales of the past 500 ka. Yet, the full extent of the climate and oceanic teleconnections and the mechanisms promoting the observed increase of productivity occurring at glacial terminations remain poorly understood. Here we present multi-proxy, micropaleontological, geochemical and sedimentological records from the easternmost EEP to infer changes in atmospheric patterns and oceanic processes potentially influencing regional primary productivity over glacial–interglacial cycles of the mid-late Pleistocene (∼0–650 ka). These proxy data support a leading role for the north–south migration of the Intertropical Convergence Zone (ITCZ) in shaping past productivity variability in the EEP. Productivity increases during glacial periods and notably peaks at major and “extra” glacial terminations (those occurring 1–2 precession cycles after some major terminations) coincident with the inferred southernmost position of the ITCZ. The comparison of our reconstructions with proxy records of climate variability suggests the intensification of related extratropical atmospheric and oceanic teleconnections during deglaciation events. These processes may have re-activated the supply of southern sourced nutrients to the EEP, potentially contributing to enhanced productivity in the EEP and thus counterbalancing the oceanic carbon dioxide outgassing at glacial terminations.

Joint vegetation and mammalian records at the early Pleistocene sequence of Bòvila Ordis (Banyoles-Besalú Basin, NE Spain) and their bearing on early hominin occupation in Europe

The early Pleistocene site at Bovila Ordis (Banyoles-Besalu Basin in NE Iberia) delivered in the past a significant pollen succession which can be assigned to the upper Matuyama geomagnetic chron owing to the identification of the Cobb Mountain magnetic subchron (1.2 Ma ago). It has been previously shown by palynology that the succession of lakes recorded at Bovila Ordis corresponds to a succession of late early Pleistocene glacial–interglacial phases, between 1.2 and 1 Ma, which can be correlated with MIS 35, 33 and 31. The present investigation focuses on lake 1 (borehole BOIV) and lake 3 (boreholes BOI, BOII and BOIII and outcrops) from this site, where both fossil pollen and rodent teeth were recovered together in the same sediment, and offers the potential to provide a vegetation and climatic context to sites that are dated by rodent teeth, such as some hominin sites in Western Europe. Here we analyse the rodent content and their biostratigraphical implications in the context of early hominin dispersal in Western Europe. In lake 1, pollen data had revealed in previous analysis a complete glacial–interglacial cycle and parts of a second one. The uppermost part of BOIV sequence yielded rodent remains that can be assigned to the arvicolid species Allophaiomys chalinei and Mimomys cf. savini. Previous palynological investigations from lake 3 had revealed a temperate deciduous forest, indicative of warm and humid conditions. At the top of the section of lake 3, a regression of the forest and the spread of open landscape elements indicated drier, more steppic conditions. The palaeobiological record of lake 3 includes pollen and large (Cervus philisi, Hippopotamus antiquus and Equus stenonis) and small mammal remains (Mimomys savini and Allophaiomys lavocati). The rodent material from lake 1 clearly indicates an early Pleistocene age somewhat older than that of lake 3. According to these new biostratigraphic data in the context of previous palynological and chronological data, it is clear that Allophaiomys chalinei entered Iberia before 1 Ma ago and A. lavocati remained until 1 Ma ago. The fact that Allophaiomys lavocati and Allophaiomys chalinei, two arvicolids currently associated with the earliest evidence of hominin presence in Western Europe, appear in Bovila Ordis at a time of mild, temperate conditions reinforce the idea that the first hominin dispersal in this region was strongly dependent on favourable climatic conditions.

Land–sea coupling of early Pleistocene glacial cycles in the southern North Sea exhibit dominant Northern Hemisphere forcing

Abstract. We assess the disputed phase relations between forcing and climatic response in the early Pleistocene with a spliced Gelasian (∼2.6–1.8 Ma) multi-proxy record from the southern North Sea basin. The cored sections couple climate evolution on both land and sea during the intensification of Northern Hemisphere glaciation (NHG) in NW Europe, providing the first well-constrained stratigraphic sequence of the classic terrestrial Praetiglian stage. Terrestrial signals were derived from the Eridanos paleoriver, a major fluvial system that contributed a large amount of freshwater to the northeast Atlantic. Due to its latitudinal position, the Eridanos catchment was likely affected by early Pleistocene NHG, leading to intermittent shutdown and reactivation of river flow and sediment transport. Here we apply organic geochemistry, palynology, carbonate isotope geochemistry, and seismostratigraphy to document both vegetation changes in the Eridanos catchment and regional surface water conditions and relate them to early Pleistocene glacial–interglacial cycles and relative sea level changes. Paleomagnetic and palynological data provide a solid integrated timeframe that ties the obliquity cycles, expressed in the borehole geophysical logs, to Marine Isotope Stages (MIS) 103 to 92, independently confirmed by a local benthic oxygen isotope record. Marine and terrestrial palynological and organic geochemical records provide high-resolution reconstructions of relative terrestrial and sea surface temperature (TT and SST), vegetation, relative sea level, and coastal influence. During the prominent cold stages MIS 98 and 96, as well as 94, the record indicates increased non-arboreal vegetation, low SST and TT, and low relative sea level. During the warm stages MIS 99, 97, and 95 we infer increased stratification of the water column together with a higher percentage of arboreal vegetation, high SST, and relative sea level maxima. The early Pleistocene distinct warm–cold alterations are synchronous between land and sea, but lead the relative sea level change by 3000–8000 years. The record provides evidence for a dominantly Northern Hemisphere-driven cooling that leads the glacial buildup and varies on the obliquity timescale. Southward migration of Arctic surface water masses during glacials, indicated by cool-water dinoflagellate cyst assemblages, is furthermore relevant for the discussion on the relation between the intensity of the Atlantic meridional overturning circulation and ice sheet growth.

Cuticular analysis of new Westphalian and Stephanian Cordaites species from the USA

Four cordaitalean species from the USA are described here: Cordaites olneyensis Šimůnek, sp. nov., Cordaites daviessensis Šimůnek, sp. nov., Cordaites kinneyensis Šimůnek sp. nov. and Cordaites minshallensis Šimůnek sp. nov. They come either from below the Minshall coal or from its roof-shales in Indiana, at the Bolsovian-Asturian boundary, or from Stephanian age deposits in Illinois and New Mexico. The Westphalian cordaitaleans are from a seasonally dry habitat (between coal beds) or from a wet habitat (the roof-shales). In both cases, their cuticles have low stomatal densities on the adaxial surface; however, stomatal densities are high on the abaxial surface and stomata are arranged in stomatiferous bands. The Stephanian species come from the period where seasonal drought was more frequent, even during the wetter intervals of glacial–interglacial cycles, and cordaitalean cuticles have less variation between adaxial and abaxial surfaces. In these Late Pennsylvanian specimens, stomatal density was low on both abaxial and adaxial cuticles and stomata were arranged in stomatal rows on both sides.

Implications of Color and Lightness Characteristics for Lithostratigraphy of Bottom Sediments from the Chukchi Plateau, Arctic Ocean

Marine sediment cores from the Chukchi Plateau are used to demonstrate the efficiency of digital photographic determination of sediment color and lightness, supplemented with the statistically processed data on sediment composition, for lithostratigraphy and paleoreconstructions. Several clusters were established that correspond to brown and gray sediment layers, carbonate-rich beige interlayers and specific segments of unclear lamination and/or lens-like intercalation of brownish and grayish beds. Correlation of the studied cores with other sediment cores from the region with well-established stratigraphy revealed good correspondence (though with certain specific features) to the conventional model of the Late Pleistocene–Holocene sediment accumulation in the offshore Arctic Ocean beyond shelf areas with clearly defined glacial–interglacial cyclicity. It was shown that enhanced red-color component corresponds to the enrichment of the interglacial brown sediment layers with manganese and accompanying elements. Glacial gray layers with enhanced green-color component are enriched in iron, as well as rubidium, vanadium, titanium and yttrium and bear evidence for considerable diagenetic transformations. Blue-color component is related to the high calcium content (carbonate rock fragments) in the carbonate-rich interlayers accumulated during the periods of active disintegration of continental ice sheets and iceberg-rafting of terrigenous lithic fragments. Intermediate values of the studied parameters are likely indicative of specific sedimentation environments.

Occurrence of slender naiad (Najas flexilis (Willd.) Rostk. & W. L. E. Schmidt) during the Eemian Interglacial – An example of a palaeolake from the Hieronimowo site, NE Poland

Nowadays Najas flexilis is believed to be extinct in Poland, Germany, and Switzerland, while in other European countries it is classified as endangered or vulnerable. During the Early and Middle Holocene the species occurred throughout much of Europe, but in the Late Holocene it underwent a significant decline and reduction in range following, as it is believed, the gradual cooling of the climate and/or the eutrophication and acidification of lakes caused by human activity. The article recognizes the existence and disappearance of slender naiad in the palaeolake at the Hieronimowo site, NE Poland, during the Eemian Interglacial and at the beginning of the last glaciation (Vistulian, Weichselian), when lake transformations were caused solely by natural factors without human impact. Results of palynological and macrofossil analyses reveal that the appearance of slander naiad in the studied water body was probably triggered by the change of its pH and trophic status, resulting from the start of spruce and pine expansion stimulated by climate worsening during the younger part of the hornbeam phase (E5 R PAZ) in the middle Eemian. The appearance of spruce and pine in the area of the lake led to its acidification and oligotrophication, and that caused the strong and rapid development of N. flexilis. The species existed in the palaeolake at the Hieronimowo site through the spruce (E6 R PAZ) and pine (E7 R PAZ) phases, until the end of the Eemian Interglacial. These observations suggest that regressive transformations of the environment typical for the late part of the interglacial cycle, ‘unsupported’ by human activity, do not lead the extinction of N. flexilis. Quite the opposite, these processes promote this species. Its disappearance started only at the beginning of the Early Vistulian (Weichselian), and it was probably caused by a drastic decrease in temperatures and/or by the development of green algae, which limited light availability on the bottom of the water body.