Glacial Marine Isotope Stage Research Articles

Strathalan Cave revisited: Stone Age networks and environments at the foot of the Drakensberg, South Africa

The broader Drakensberg is an important region for understanding population dynamics and adaptation between the Late Pleistocene and Holocene. Here, we announce our campaign to re-excavate Strathalan Cave in the northeastern Cape of South Africa. Strathalan Cave sits at the foothills of the uKhahlamba-Drakensberg at the edge of the Great Escarpment of southern Africa. Well-known for its organic preservation, the site is important for understanding the archaeology of the region. People have occupied Strathalan Cave intermittently from ca. 29 000 years ago (ka), so exploring occupational patterns at sites such as these is a valuable means of understanding Stone Age behaviour during glacial Marine Isotope Stage 2 (ca. 29-14 ka). In this paper, we provide the first detailed description of the geological, geomorphological, sedimentary and environmental context of Strathalan Cave and review previous studies conducted on the site and region. We also introduce the goals of our re-excavation project and present a detailed map of the three cavities that make up the Strathalan Cave complex as part of a new, comprehensive, spatial control system established on site. Given the remarkable preservation of organic materials, Strathalan Cave may provide an important and rare source of archaeological and palaeoenvironmental data for this period. Future work at Strathalan will likely contribute to our understanding of the links between settlement patterns and environmental change. This is especially important given that Strathalan sits at the juncture between different environmental and geographic regions.

Glacial expansion of carbon-rich deep waters into the Southwestern Indian Ocean over the last 630 kyr

Oceanic carbon storage is one of the main sinks for atmospheric CO2, and thought to be the major contributing factor for CO2 drawdown during past glacial periods. Both physical and biogeochemical processes control the capacity of carbon storage in the ocean. During glacial periods of the Pleistocene the larger volume of deep-water masses of Southern Hemisphere origin in the Atlantic has been shown to promote carbon storage in the Southern Ocean. However, the latitudinal extension of this water mass in the Indian Ocean has been scarcely studied. In this study, we combine foraminiferal εNd and benthic δ13C of two sediment cores in the southwest Indian Ocean (MD96–2077, 33°S, 3781 m water depth; MD96–2052, 19°S, 2627 m water depth), to reconstruct the spatial and temporal evolution of glacial carbon-rich deep waters in the SW Indian over the last 630 kyr. The combined use of foraminiferal εNd and benthic δ13C allows to distinguish δ13C changes related to water mass mixing and from respired carbon accumulation within the water masses. Nutrient-rich deep waters, which cannot be explained by the enhanced proportion of southern-sourced waters, were present at core sites deeper than 2700 m during glacial periods and extended at least until 33°S into the SW Indian Ocean. From Marine Isotope Stage (MIS) 14 to MIS 10, glacial carbon storage increased gradually until reaching its highest capacity during the extreme glacial periods MIS 12 and 10. Orbital forcing (100-kyr eccentricity, 41-kyr obliquity), restricted air-sea exchange and enhanced ocean stratification, fostered higher carbon storage during periods of relatively lower eccentricity and obliquity. Furthermore, after MIS 10, a progressive transition was observed from 100-kyr eccentricity to 41-kyr obliquity cycles in benthic δ13C and δ18O records of core MD96–2077 and sea-ice cover changes derived from ice-rafted debris of the Agulhas Plateau composite core site.

Organic matter characteristics of a rapidly eroding permafrost cliff in NE Siberia (Lena Delta, Laptev Sea region)

Abstract. Organic carbon (OC) stored in Arctic permafrost represents one of Earth's largest and most vulnerable terrestrial carbon pools. Amplified climate warming across the Arctic results in widespread permafrost thaw. Permafrost deposits exposed at river cliffs and coasts are particularly susceptible to thawing processes. Accelerating erosion of terrestrial permafrost along shorelines leads to increased transfer of organic matter (OM) to nearshore waters. However, the amount of terrestrial permafrost carbon and nitrogen as well as the OM quality in these deposits is still poorly quantified. We define the OM quality as the intrinsic potential for further transformation, decomposition and mineralisation. Here, we characterise the sources and the quality of OM supplied to the Lena River at a rapidly eroding permafrost river shoreline cliff in the eastern part of the delta (Sobo-Sise Island). Our multi-proxy approach captures bulk elemental, molecular geochemical and carbon isotopic analyses of Late Pleistocene Yedoma permafrost and Holocene cover deposits, discontinuously spanning the last ∼52 kyr. We showed that the ancient permafrost exposed in the Sobo-Sise cliff has a high organic carbon content (mean of about 5 wt %). The oldest sediments stem from Marine Isotope Stage (MIS) 3 interstadial deposits (dated to 52 to 28 cal ka BP) and are overlaid by last glacial MIS 2 (dated to 28 to 15 cal ka BP) and Holocene MIS 1 (dated to 7–0 cal ka BP) deposits. The relatively high average chain length (ACL) index of n-alkanes along the cliff profile indicates a predominant contribution of vascular plants to the OM composition. The elevated ratio of iso- and anteiso-branched fatty acids (FAs) relative to mid- and long-chain (C ≥ 20) n-FAs in the interstadial MIS 3 and the interglacial MIS 1 deposits suggests stronger microbial activity and consequently higher input of bacterial biomass during these climatically warmer periods. The overall high carbon preference index (CPI) and higher plant fatty acid (HPFA) values as well as high C/N ratios point to a good quality of the preserved OM and thus to a high potential of the OM for decomposition upon thaw. A decrease in HPFA values downwards along the profile probably indicates stronger OM decomposition in the oldest (MIS 3) deposits of the cliff. The characterisation of OM from eroding permafrost leads to a better assessment of the greenhouse gas potential of the OC released into river and nearshore waters in the future.

Geochemistry and granulometry as indicators of paleoclimate, weathering, and provenance of sediments for the past 1,00,000 years in the eastern Arabian Sea

• Climate during MIS1, 3, 5a & 5c was hot and humid with intense SWM than YD, LGM, MIS2, 4, 5b. • Source area has experienced moderate to intense chemical weathering. • Provenance of sediments was felsic rocks during warm periods and mafic rocks and dust during cold periods. • Sources of sediments are ∼50% basalt , 40–80% gneiss and 10–20% dust. • Climate of lower and higher latitudes suggests inter-regional teleconnections . Geochemical and granulometric investigation of a 408 cm long sediment core raised from the Eastern Arabian Sea was carried out to decipher the climate, weathering, dust flux and provenance of sediments during the past 100 ka. The diagnostic ratio of Cr/Ni (0.99 to 1.77), Rb/Al (6.01 to 17.14), Ti/Al (0.02 to 0.03), Fe/Al (0.94 to 1.61), Mg/Al (0.31 to 0.59) and silt% (38.68 to 66.37) indicate hot and humid climate with the intensification of south-west monsoon during marine isotope stage (MIS) 1, 3, 5a and 5c and cold and dry climate with the intensification of the northeast monsoon and high dust flux during Younger Dryas cooling, last glacial maximum, MIS 2, 4 and 5b. The clay% (20.42 to 53.92), Silica–Titanium Index (71.88 to 86.28), Ruxton Ratio (2.89 to 7.22), and Th/U ratio (0.98 to 4.11) indicate moderate to intense chemical weathering in the source area during warmer climate. Th(ppm) versus Sc(ppm), La/Th versus Th/Yb, Al 2 O 3 % versus Fe 2 O 3 %, Th/Sc versus Sc(ppm), La/Sc versus Sc/Th ratios and La-Th-Sc plot indicate intermediate/mixed sources for sediment provenance. Sand% (2.82 to 25.3), Si/Al (2.74 to 7.43), ΣLREE/ΣHREE (7.65 to 10.40), La/Sc (2.24 to 3.55) indicate felsic sources from Peninsular India during warm climates and ΣREE (103.98–201.17), Rb/Ga (1.36–4.33), Ni (70.42–137.3 ppm), Rb (55.39–138.90 ppm) indicate mafic sources from Deccan Traps and Arabian desert during cold climates. The synchronous relationship between the climate of lower and higher latitudes was observed, suggesting the global teleconnections of climate during the Late Quaternary.

Geomorphic history of Lake Manix, Mojave Desert, California: Evolution of a complex terminal lake basin

Pluvial lake deposits in the Basin and Range province have long been exploited for records of hydrologic and climatic change. To obtain the most accurate reconstructions, a thorough understanding of the geomorphic evolution of such lake basins must be grounded in field stratigraphy and mapping, which are often lacking or are not well integrated with core studies. We conducted extensive stratigraphic investigation, mapping, and dating of exposed strata in the Lake Manix basin, former terminus of the Mojave River, California, during the Pleistocene to provide such a background and to supplement interpretations from a 45-m-long core.In this paper, we emphasize the geomorphic and tectonic processes that shaped the evolution of the Manix basin after the arrival of the Mojave River in the early-middle Pleistocene. The main processes include (1) sedimentary infilling of the lake basin, (2) interaction among the subbasins as controlled by internal sills and sill failures, (3) tectonics, and (4) climate change. From about 500 to 190 ka, Lake Manix was confined to its western subbasins, and fluctuated in response to climate change and perhaps to brief diversions of the river into the upstream Harper Lake basin. During this time, about 24 m of sediment accumulated near the confluence of the Mojave River and Manix Wash, and a 15-km-long clastic wedge built into the western basins, gradually filling the accommodation space.Two basin-integration events subsequently occurred, both caused by failure of sills that lay on sheared deposits along the Manix fault zone. When Lake Manix rose at the onset of glacial marine isotope stage 6, the sill on the south flank of Buwalda Ridge failed and triggered a catastrophic flood that entered the new, lower elevation, previously endorheic Afton subbasin. Subsequent lake-level changes affected both subbasins, but the thickest deposits after the flood are preserved in the Afton subbasin. The area upstream of Buwalda Ridge was only submerged during relatively high lake levels. Thus, sediment records interpreted from the core site and nearby outcrops in part reflect a geomorphic event (basin integration) rather than climatic conditions. The sill of Lake Manix after the integration event lay at the northeast end of the Afton subbasin, athwart strands of the Manix fault zone. At about 25 ka, this eastern sill was rapidly incised, and the river advanced to terminate in Lake Mojave in the Soda and Silver Lake basins. Recognition and dating of integration events, common for lake-river interactions in active tectonic settings, provide important context for interpreting paleoclimate records from sediments and provide temporal and spatial constraints on the biogeography of aquatic species.

Middle Stone Age mineral pigment procurement at Pinnacle Point 5–6 North, Western Cape province, South Africa

AbstractWe report on a multi‐method sourcing study of 35 mineral pigment artefacts from the Middle Stone Age site of Pinnacle Point 5–6 North (PP5–6 N), dating from about 90–50 ka. The artefacts were analysed and compared with geological samples from seven sources using neutron activation analysis (NAA), and supplemented by data from X‐ray diffraction (XRD) and scanning electron microscopy (SEM). Our preliminary results suggest that the occupants of PP5–6 N likely used at least two local and one currently unidentified and possibly non‐local Fe oxide mineral pigment sources. The mineral pigment artefacts derived from the latter source(s) exhibited manganese (Mn) enrichment with concentrations well above those observed in all sampled source deposits in the study area, suggesting a distinctive formation process. The proportions of the Mn‐enriched mineral pigment artefacts within the PP5–6 N assemblage vary over time, but tend to occur at higher rates in the glacial Marine Isotope Stage (MIS) 4 deposits, which holds potential implications for changes in the use of sources over time, increased mobility or increased exchange during this period.

Control Mechanisms of Primary Productivity Revealed by Calcareous Nannoplankton From Marine Isotope Stages 12 to 9 at the Shackleton Site (IODP Site U1385)

AbstractNowadays, primary productivity variations at the SW Iberian Margin (IbM) are primarily controlled by wind‐driven upwelling. Thus, major changes in atmospheric circulation and wind regimes between the Marine Isotope Stages (MIS) 12 and 9 could have driven substantial changes in phytoplankton productivity which remains poorly understood. We present a high‐resolution calcareous nannofossil record from the Shackleton Site Integrated Ocean Discovery Program Site U1385 that allow the assessment of primary productivity and changing surface conditions on orbital and suborbital timescales over the SW IbM. These records are directly compared and integrated with terrestrial – Mediterranean forest pollen – and marine – benthic and planktic oxygen stable isotopes (δ18O), alkenone concentration [C37], Uk´37‐Sea Surface Temperature and % C37:4 – proxy records from Site U1385. Our results indicate intra‐interglacial increase in primary productivity together with intensification of the Azores anticyclonic high‐pressure cell beyond the summer that suggests a two‐phase upwelling behavior during the full interglacial MIS 11c (∼420–397 ka), potentially drived by atmospheric NAO‐like variability. Primary productivity is largely enhanced during the inception of glacial MIS 10 and the early MIS 10 (∼392–356 ka), linked to intensified upwelling and associated processes during a period of strengthened atmospheric circulation. In agreement with the conditions observed during Heinrich events of the last glacial cycle, primary productivity reductions during abrupt cold episodes, including the Heinrich‐type (Ht) events 4 to 1 (∼436, 392, 384 and 339 ka) and the Terminations V and IV, seems to be the result of halocline formation induced by meltwater arrival, reducing the regional upward nutrient transference.

Drivers of river reactivation in North Africa during the last glacial cycle

North African greening phases, during which large rivers ran through the Sahara Desert, occurred repeatedly during the Quaternary and are regarded as key periods for the development of past human populations. However, the timing and mechanisms responsible for the reactivation of the presently dormant fluvial systems remain highly uncertain. Here we present hydroclimate changes over the past 160,000 years, reconstructed from analyses of the provenance of terrestrial sediments in a marine sediment record from the Gulf of Sirte (offshore Libya). By combining high-resolution proxy data with transient Earth system model simulations, we are able to identify the various drivers that led to the observed shifts in hydroclimate and landscapes. We show that river runoff occurred during warm interglacial phases of Marine Isotope Stages 1 and 5 due to precession-forced enhancements in the summer and autumn rainfall over the entire watershed, which fed presently dry river systems and intermittent coastal streams. In contrast, shorter-lasting and less-intense humid events during glacial Marine Isotope Stages 3 and 4 were related to autumn and winter precipitation over the Libyan coastal regions driven by Mediterranean storms. Our results reveal large shifts in hydroclimate environments during the last glacial cycle, which probably exerted a strong evolutionary and structural control on past human populations, potentially pacing their dispersal across northern Africa. The presence of large rivers in North Africa critical for Quaternary human migrations were controlled by a combination of orbital forcing and Mediterranean storminess, according to terrestrial proxy records from a marine core off Libya integrated with paleoclimate modelling.

Northwest Pacific ice-rafted debris at 38°N reveals episodic ice-sheet change in late Quaternary Northeast Siberia

The ice-rafted-debris (IRD) record of the open Northwest Pacific points towards the existence of substantial glacial ice on the Northeast Siberian coast during the late Quaternary. However, the scale and timing of glaciation and de-glaciation remains controversial due to the dearth of both onshore and offshore records. Existing IRD data suggests at least one event of dynamic and abrupt change during mid-late Marine Isotope Stage (MIS 3) which mimics the massive collapse of the Laurentide ice sheet during Heinrich Events. It is uncertain whether other events of this magnitude occurred during the late Quaternary. Here we present a ∼160,000 yr IRD series, planktic foraminiferal counts and an age model, derived from a benthic δ18O curve, radiocarbon dates and tephrochronology, from core ODP 1207A (37.79°N, 162.75°E), revealing the presence of low but episodic flux of IRD. We conclude that glacial Northwest Pacific icebergs spread further south than previously thought, with icebergs emanating from Northeast Siberia being transported to the transition region between the subpolar and subtropical waters, south of the subarctic front during at least the Quaternary's last two glacial periods. The episodic nature of the 1207A IRD record during the last glacial, combined with coupled climate-iceberg modelling, suggests occasional times of much enhanced ice flux from the Kamchatka-Koryak coast, with other potential sources on the Sea of Okhotsk coast. These findings support the hypothesis of a variable but extensive ice mass during the last glacial over Northeast Siberia, particularly early in the last glacial period, behaving independently of North American and Eurasian ice masses. In strong contrast, IRD was absent during much of the penultimate glacial Marine Isotope Stage (MIS) 6 suggesting the possibility of very different Northeast Siberian ice coverage between the last two glacial periods.

Records of the Laschamps geomagnetic polarity excursion from Black Sea sediments: magnetite versus greigite, discrete sample versus U-channel data

SUMMARY Magnetostratigraphic investigation of sediment cores from two different water depths in the SE Black Sea based on discrete samples, and parallel U-channels in one of the cores, yielded high-resolution records of geomagnetic field variations from the past about 68 ka. Age constrains are provided by three tephra layers of known age, accelerator mass spectrometry 14C dating, and by tuning element ratios obtained from X-ray fluorescence scanning to the oxygen isotope record from Greenland ice cores. Sedimentation rates vary from a minimum of ∼5 cm ka−1 in the Holocene to a maximum of ∼50 cm ka−1 in glacial marine isotope stage 4. Completely reversed inclinations and declinations as well as pronounced lows in relative palaeointensity around 41 ka provide evidence for the Laschamps geomagnetic polarity excursion. In one of the investigated cores also a fragmentary record of the Mono Lake excursion at 34.5 ka could be revealed. However, the palaeomagnetic records are more or less affected by greigite, a diagenetically formed magnetic iron sulphide. By definition of an exclusion criterion based on the ratio of saturation magnetization over volume susceptibility, greigite-bearing samples were removed from the palaeomagnetic data. Thus, only 25–55 per cent of the samples were left in the palaeomagnetic records obtained from sediments from the shallower coring site. The palaeomagnetic record from the deeper site, based on both discrete samples and U-channels, is much less affected by greigite. The comparison of palaeomagnetic data shows that the major features of the Laschamps polarity excursion were similarly recovered by both sampling techniques. However, several intervals had to be removed from the U-channel record due to the presence of greigite, carrying anomalous directions. By comparison to discrete sample data, also some directional artefacts in the U-channel record, caused by low-pass filtering of the broad magnetometer response functions, averaging across fast directional and large amplitude changes, can be observed. Therefore, high-resolution sampling with discrete samples should be the preferred technique when fast geomagnetic field variations, such as reversals and excursions, shall be studied from sedimentary records in the very detail.

Use-Wear Analysis of the Lithic Industry of the Lower Palaeolithic Site of Guado San Nicola (Isernia, Central Italy)

The Lower Palaeolithic site of Guado San Nicola (GSN) is located near the village of Monteroduni (Molise, Central Italy). The archaeological layers identified date to the transition between the interglacial and the glacial marine isotope stages MIS 11 (i.e. 400 ± 9 ka) and MIS 10 (i.e. 345 ± 9 ka). The bifaces and Levallois products found among the lithic assemblage of GSN make the site the earliest one bearing such tools in Italy and one of the most ancient ones in the Western European context. The aim of this work is to analyze/study/investigate the use-wear traces left on the lithic tools and to understand the activities carried out at the site. The analysis also seeks to figure out how the Levallois products were used, focusing on whether there were or not differences in the activities pursued using Levallois flakes rather than blanks obtained through different knapping methods. Moreover, the present work aims at understanding if and how the faconnage products were used. Since the research focuses on flakes, the bifaces’ flakes resulting from the faconnage process and in some cases from renewal processes are also taken in consideration, while the cores and debris are not. Results show that there were apparently no differences in the use of otherwise obtained flakes and the one resulting from the production of bifaces. Nonetheless, the examined data could be considered a hint for proposing the development of the Levallois method from the practice of faconnage sequences.

Climate variability on the Adriatic seaboard during the last glacial inception and MIS 5c from Frasassi Cave stalagmite record

A stalagmite (FR16) from Frasassi Cave, located near the Adriatic coast of the Italian peninsula, offers a 16 kyr petrographic and stable isotope record spanning from 112.8 ± 1.5 ka to 96.6 ± 1.0 ka, corresponding to the interval from marine isotope stage (MIS) 5c to MIS 5d. The physical characteristics of FR16 calcite, allowed for a thorough understanding of the processes controlling isotopic changes, because fabrics as well are controlled by the environmental parameters within the cave that reflect external climate forcing. The FR16 δ13C profile matches fabric changes where columnar fabric usually corresponds to more negative values and micrite/microsparite layers to less negative δ13C values, and with the North Greenland Ice-core Project (NGRIP) δ18O record with more negative δ13C values during interstadials GI24 and GI23. This suggests a hydrological sensitivity for the two proxies, and their variability can be linked to recharge changes. On the other hand, the response to Greenland events appears subdued in the δ18O record and the trend mimics instead the Northern Hemisphere (NH) summer insolation with more negative δ18O values corresponding to the maximum insolation centred at ca. 105 ka. This behaviour can be explained by the higher sensitivity of δ18O to rainfall seasonality, moisture source and trajectories, whose combined effect attenuated the stadials/intersadials signal in the stalagmite.

Subtropical hydroclimate during Termination V (∼430-422 ka): Annual records of extreme precipitation, drought, and interannual variability from Santa Barbara Basin

Hydroclimate extremes are expected to become more frequent and intense with anthropogenic climate forcing, but future El Niño-Southern Oscillation (ENSO) behavior is unclear. Understanding of extreme hydroclimate variability and magnitude prior to human-influences is limited by short instrumental records, however, continuous sedimentary archives of past hydroclimate variability can complement and extend these records. Laminated Santa Barbara Basin (SBB) sediment cores MV0508-33JPC, −21JPC, and −29JPC preserve annually-resolved, multi-centennial-scale precipitation records from Termination V (TV), the transition from glacial Marine Isotope Stage (MIS) 12 to interglacial MIS 11 at 424 ka. These records provide insights into the subtropical hydroclimate response to warming. Foraminiferal δ18O variations indicate rapid warming and/or salinity changes, and were used to verify the TV age assignment. A paleoprecipitation proxy was developed using the first principal component of scanning XRF elemental counts (PC1), which has high loadings for siliciclastic sediment-associated elements K, Ti, and Si. Sedimentary laminae couplets identified in PC1 were annually-tuned to investigate TV paleoprecipitation variability, as modern SBB laminae represent annual deposits. Extreme flooding and decadal-to-centennial droughts were identified, with magnitudes exceeding modern observations. ENSO-like (2–7 year) paleoprecipitation periodicities coincide with wetter intervals, but ENSO variability is reduced during droughts. A 1500-year arid interval may be related to poleward shifting of general atmospheric circulation as ice sheets melted, such that the subtropical dry zone intersected California. Southern California paleoprecipitation reconstructions from past warm climates provide insight into precipitation variability and magnitude on interannual timescales, and can reduce uncertainties in predictions of interannual climate, including ENSO.

Synoptic conditions of fine-particle transport to the last interglacial Red Sea-Dead Sea from Nd-Sr compositions of sediment cores

The sediments deposited at the depocenter of the Dead Sea comprise high-resolution archive of hydrological changes in the lake's watershed and record the desert dust transport to the region. This paper reconstructs the dust transport to the region during the termination of glacial Marine Isotope Stage 6 (MIS 6; ∼135–129 ka) and the last interglacial peak period (MIS5e, ∼129–116 ka). We use chemical and Nd and Sr isotope compositions of fine detritus material recovered from sediment core drilled at the deepest floor of the Dead Sea. The data is integrated with data achieved from cores drilled at the floor of the Red Sea, thus, forming a Red Sea-Dead Sea transect extending from the desert belt to the Mediterranean climate zone. The Dead Sea accumulated flood sediments derived from three regional surface cover types: settled desert dust, mountain loess-soils and loess-soils filling valleys in the Dead Sea watershed termed here “Valley Loess”. The Valley Loess shows a distinct 87Sr/86Sr ratio of 0.7081 ± 1, inherited from dissolved detrital calcites that originate from dried waterbodies in the Sahara and are transported with the dust to the entire transect.Our hydro-climate and synoptic conditions reconstruction illustrates the following history: During glacial period MIS6, Mediterranean cyclones governed the transport of Saharan dust and rains to the Dead Sea watershed, driving the development of both mountain soils and Valley Loess. Then, at Heinrich event 11, dry western winds blew Saharan dust over the entire Red Sea - Dead Sea transect marking latitudinal expansion of the desert belt. Later, when global sea-level rose, the Dead Sea watershed went through extreme aridity, the lake retreated, depositing salt and accumulating fine detritus of the Valley Loess. During peak interglacial MIS 5e, enhanced flooding activity flushed the mountain soils and fine detritus from all around the Dead Sea and Red Sea, marking a significant “contraction” of the desert belt. At the end of MIS 5e the effect of the regional precipitation diminished and the Dead Sea and Red Sea areas re-entered sever arid conditions with extensive salt deposition at the Dead Sea.

Surface hydrographic and water mass variability in the eastern equatorial Pacific during interglacial-like Marine Isotope Stage 14

Surface temperature and water masses variability in the Eastern Equatorial Pacific (EEP) is sensitive to global climate changes in response to either Northern/Southern Hemisphere forcing or low-latitude atmosphere-ocean feedback. High-latitude processes can influence tropical oceans via atmospheric bridges and oceanic tunnels, whereas perturbations in the low-latitude atmosphere-ocean modulate the behavior of low-latitude oceans. For climate paradoxes of prolonged warmth MIS (Marine Isotope Stage) 15–13, little has known about any causes or any possible tele-connections between the EEP and high-/low-latitudes because lack of observations. To address this issue, multiple sea surface temperature (SST) records (i.e. faunal transfer function-based, Mg/Ca ratio on mono-species, and Uk’37-derived temperature estimates) and faunal-derived water masses are generated from the EEP core ODP 1240. Our results reveal a glacial EEP MIS 14 cooling (∼1–2 °C) with higher eastern boundary current faunal abundances as compared to adjacent interglacial stages. In a glacial MIS 14 scenario, we suggest that the EEP areas would receive more nutrient-rich, cold waters from high latitudes via the Peru-Chile Current. The atmospheric bridge of a northwardly Intertropical Convergence Zone (ITCZ) shift and the resulting heat/moisture transport across the eastern equatorial Atlantic (EEA) would weaken the magnitude of the EEP cold tongue in MIS 14. We also think of another scenario in that the orbital variations in glacial MIS 14 was characterized by higher obliquity fluctuations, lower eccentricity/precession. The orbital variations shape an inter-hemispheric asymmetry with higher seasonality. This scenario could result in a stagnant/an inactive Atlantic Meridional Ocean Circulation and northward shifts in the ITCZ/southward displacement of westerlies in the southeastern Pacific during MIS 14. The retreat of the West Antarctic sea ice and enhancement of the Antarctic Circumpolar Current would also bring less high-latitude cold upwelled water (the Subantarctic Mode Water/Antarctic Intermediate Water) into the eastern tropical Pacific/Atlantic Oceans. We suggest that a diminished La Nina-like condition and a relatively weakened EEP/EEA cold tongue developed in glacial MIS 14 compared to other glacial MIS in the late Quaternary. The interglacial-like MIS 14 is therefore characterized by a small-magnitude of eastern tropical upwelling areas and greater extension of western Pacific/Atlantic warm surface waters. Such amplifications in glacial MIS 14 could lead to less fluctuation of Termination VI and persistent warmth in MIS 15–13.

Optically stimulated luminescence ages for human occupation during the penultimate glaciation in the western Loess Plateau of China

ABSTRACTThe chronology of few Palaeolithic sites in the Loess Plateau of China has been well investigated for the Middle Pleistocene. In this study, the Yangshang Palaeolithic site with significant archaeological remains, located in Gansu Province of the western Chinese Loess Plateau, was dated using blue‐stimulated optically stimulated luminescence (OSL) and infrared stimulated luminescence (IRSL) techniques on eight medium‐grained (45–63 µm) quartz and polymineral samples through the Palaeolithic sequence. Except for one sample from the upper cultural layer (55 ± 3 ka), age estimates obtained by quartz OSL dating exceed its upper datable limit, and so an elevated temperature post‐IR IRSL SAR protocol was used on 45–63 μm polymineral grains to derive a numerical chronology for the site. The luminescence ages of seven samples from six cultural layers lie between 104 ± 5 and 220 ± 11 ka; for the three main cultural layers the results varied from 149 ± 9 to 186 ± 10 ka, consistent with the presently observed stratigraphy. The dating results shown that early hominins may have occupied this region in the western Loess Plateau of China during Marine Isotope Stage (MIS) 7, early glacial MIS 6 and early interglacial MIS 5, reflecting their ability to adapt to variable environments.

Cyclic magnetite dissolution in Pleistocene sediments of the abyssal northwest Pacific Ocean: Evidence for glacial oxygen depletion and carbon trapping

The carbonate-free abyss of the North Pacific defies most paleoceanographic proxy methods and hence remains a “blank spot” in ocean and climate history. Paleomagnetic and rock magnetic, geochemical, and sedimentological methods were combined to date and analyze seven middle to late Pleistocene northwest Pacific sediment cores from water depths of 5100 to 5700 m. Besides largely coherent tephra layers, the most striking features of these records are nearly magnetite-free zones corresponding to glacial marine isotope stages (MISs) 22, 12, 10, 8, 6, and 2. Magnetite depletion is correlated with organic carbon and quartz content and anticorrelated with biogenic barite and opal content. Within interglacial sections and mid-Pleistocene transition glacial stages MIS 20, 18, 16, and 14, magnetite fractions of detrital, volcanic, and bacterial origin are all well preserved. Such alternating successions of magnetic iron mineral preservation and depletion are known from sapropel-marl cycles, which accumulated under periodically changing bottom water oxygen and redox conditions. In the open central northwest Pacific Ocean, the only conceivable mechanism to cause such abrupt change is a modified glacial bottom water circulation. During all major glaciations since MIS 12, oxygen-depleted Antarctic Bottom Water (AABW)-sourced bottom water seems to have crept into the abyssal northwest Pacific below ~5000 m depth, thereby changing redox conditions in the sediment, trapping and preserving dissolved and particulate organic matter and, in consequence, reducing and dissolving both, biogenic and detrital magnetite. At deglaciation, a downward progressing oxidation front apparently remineralized and released these sedimentary carbon reservoirs without replenishing the magnetite losses.

A pulse in the delivery of ice-rafted debris at site 704 in the southeast Atlantic during glacial Termination V

Termination V, the transition from glacial marine isotope stage 12 to interglacial stage 11–425 ka, is the largest deglaciation of the late Pleistocene and culminated with temperatures potentially warmer than present. Coastal geomorphic and stratigraphic evidence provides estimates of a sea-level high-stand 20 m above present at the time (Hearty et al. in Geology 27(4):375–378, 1999). Such sea-level rise would require disintegration of the Greenland Ice Sheet and West Antarctic Ice Sheet as well as part of the East Antarctic Ice Sheet (Raynaud et al. in Earth’s climate and orbital eccentricity: the marine isotope stage 11 question. Geophysical monograph 137. American Geophysical Union, Washington, 2003). Lithic fragments in deep-sea sediments >150 μm at Site 704 in the South Atlantic Ocean were quantified. A large multipronged peak in concentration of this ice-rafted debris consisting of clear minerals, rose-colored transparent minerals, and ash punctuates glacial Termination V. It coincides with a brief two-pronged 1 ‰ reversal to heavier isotopic values from ~2.4 to ~3.4 ‰ at ~416 ka interpreted to reflect cooling resulting from influx of a large number of icebergs. The peak in ice-rafted debris also coincides with a 1 ‰ decrease in carbon isotopic ratios interrupting the ~2 ‰ increase in carbon isotope values across the entirety of Termination V. This is interpreted to reflect a reduction or shutdown in North Atlantic Deep Water formation and attendant Circumpolar Deep Water upwelling at the site and is also consistent with a shift in storage of carbon and carbonate from the deep sea to continental shelves resulting from a dramatic sea-level high-stand. Consequently, the lithic record at Site 704 lends support for the upper end of sea-level estimates based upon land-based evidence that requires a substantial contribution from the East Antarctic Ice Sheet. However, caution is warranted as differences with lithic records from Site 1089, 1090 and 1094 suggest sea-surface temperatures may have also affected lithic concentration through controls on iceberg trajectories and decay.

Glaciomarine sedimentation and bottom current activity on the north-western and northern continental margins of Svalbard during the late Quaternary

Palaeo-bottom current strength of the West Spitsbergen Current (WSC) and the influence of the Svalbard-Barents Sea Ice Sheet (SBIS) on the depositional environment along the northern Svalbard margins are poorly known. Two gravity cores from the southern Yermak Plateau and the upper slope north of Nordaustlandet, covering marine isotope stage (MIS) 1 to MIS 5, are investigated. Five lithofacies, based on grain size distribution, silt/clay ratio, content and mean of sortable silt (SS), are distinguished to characterise the contourite-dominated sedimentary environments. In addition, depositional environments are described using total organic carbon (TOC), total sulphur (TS) and calcium carbonate (CaCO3) contents of sediments. Facies A, containing coarse SS, suggests strong bottom current activity and good bottom water ventilation conditions as inferred from low TOC content. This facies was deposited during the glacial periods MIS 4, MIS 2 and during the late Holocene. Facies B is dominated by fine SS indicating weak bottom current and poor ventilation (cf. high TOC content of 1.2–1.6%), and correlates with the MIS 4/3 and MIS 2/1 transition periods. With an equal amount of clay and sand, fine SS and high content of TOC, facies C indicates reduced bottom current strength for intervals with sediment supply from proximal sources such as icebergs, sea ice or meltwater discharge. This facies was deposited during the last glacial maximum. Facies D represents mass-flow deposits on the northern Svalbard margin attributed to the SBIS advance at or near the shelf edge. Facies E sediments indicating moderate bottom current strength were deposited during MIS 5 and MIS 3, and during parts of MIS 2. This first late Quaternary proxy record of the WSC flow and sedimentation history from the northern Svalbard margin suggests that the oceanographic conditions and ice sheet processes have exerted first-order control on sediment properties.

Unique clay assemblages in the Levant basin (Haifa Bay) subsurface reflect a land–sea transition zone and restricted environments throughout the last ~ 1 m.y.

A subsurface sequence in Haifa Bay, the Levant basin, was studied for its clay mineralogy by X-ray diffraction (XRD) in order to examine the response of clay assemblages to sea-level changes and alternating environments over a long period, apparently longer than ever recorded before. The study was conducted on continuous cores of three boreholes that represent ~1m.y. of very shallow (<40m) and shallow (40–80m) water depths alternating with wetland and terrestrial sediments, including soils. Another aim of the current study was to evaluate the constancy of clay sources along this long record within a bay located at the northern end of the Nile cell. Marine samples, regardless of water depth, are characterized by low amounts of kaolinite+illite (<25%) and variable mix-layer illite-smectite (IS) compositions, in contrast to paleosols with high amounts of kaolinite+illite (30–60%) and illite-rich IS. The sandy permeable parent material of coastal paleosols enabled efficient leaching and major pedogenic clay transformations. Maximum soil development apparently occurred when glacial marine isotope stages were more humid (MIS 6 and MIS 26). When environmental changes were rapid previous clay assemblages were preserved, as indicated by wetland sediments that display pedogenic characteristics and coastal dunes that display marine characteristics. Closely-spaced boreholes yielded two unique marine clay provinces, not known before elsewhere in the Levant basin north of the Nile delta: 1. marine sediments from two boreholes on both sides of the Carmel fault are enriched by up to 90% palygorskite; 2. clean marine sand with a clay fraction dominated by discrete smectite or smectite-rich IS that occur within dark peloids, apparently fecal pellets. Two exotic minerals are occasionally present in trace amounts: clinoptilolite, derived from the nearby northeastern hinterland; and serpentine, derived from the remote Iskenderun Bay. Both unique clay provinces prevail throughout the sequence, indicating stable environmental conditions in south Haifa Bay for the last ~1m.y.