Late Marine Isotope Stage Research Articles

Trajectories of cultural innovation from the Middle to Later Stone Age in Eastern Africa: Personal ornaments, bone artifacts, and ocher from Panga ya Saidi, Kenya

African Middle Stone Age (MSA) populations used pigments, manufactured and wore personal ornaments, made abstract engravings, and produced fully shaped bone tools. However, ongoing research across Africa reveals variability in the emergence of cultural innovations in the MSA and their subsequent development through the Later Stone Age (LSA). When present, it appears that cultural innovations manifest regional variability, suggestive of distinct cultural traditions. In eastern Africa, several Late Pleistocene sites have produced evidence for novel activities, but the chronologies of key behavioral innovations remain unclear. The 3 m deep, well-dated, Panga ya Saidi sequence in eastern Kenya, encompassing 19 layers covering a time span of 78 kyr beginning in late Marine Isotope Stage 5, is the only known African site recording the interplay between cultural and ecological diversity in a coastal forested environment. Excavations have yielded worked and incised bones, ostrich eggshell beads (OES), beads made from seashells, worked and engraved ocher pieces, fragments of coral, and a belemnite fossil. Here, we provide, for the first time, a detailed analysis of this material. This includes a taphonomic, archeozoological, technological, and functional study of bone artifacts; a technological and morphometric analysis of personal ornaments; and a technological and geochemical analysis of ocher pieces. The interpretation of the results stemming from the analysis of OES beads is guided by an ethnoarcheological perspective and field observations. We demonstrate that key cultural innovations on the eastern African coast are evident by 67 ka and exhibit remarkable diversity through the LSA and Iron Age. We suggest the cultural trajectories evident at Panga ya Saidi were shaped by both regional traditions and cultural/demic diffusion.

Climate changes in the Qaidam Basin in NW China over the past 40 kyr

Little is known about the climate and environmental changes that have occurred in the extremely arid regions of China since MIS (Marine Isotope Stage) 3 (59–29 cal kyr BP), when most regions in northwestern China and the Tibetan Plateau featured warm and humid conditions. In this paper, we present a record of the climate changes in the Qaidam Basin in arid northwestern China over the past 40 kyr based on the mineralogy of a 35-m-long sediment core recovered from Qarhan Salt Lake. Our results show that the lake was a saline or hyper-saline lake saturated with respect to gypsum between 40 and 33 cal kyr BP. Beginning at 33 cal kyr BP, evaporite formation was dominated by halite precipitation, indicating that the lake salinity had increased extensively and that the climate became drier during 33–24.5 cal kyr BP. The lake salinity then increased continuously, resulting in the appearance of bischofite between 24.5 and 14.6 cal kyr BP. The disappearance of bischofite and the increase in gypsum indicate that the salinity of the water decreased slightly between 14.6 and 8.3cal kyr BP. However, during the last 8300 years, the lake has dried up and is now a playa. Generally, the climate was wet in late MIS 3, arid in MIS 2 (29–11.7 cal kyr BP), and hyperarid in the Holocene. The relatively humid conditions may have resulted from weak evaporation caused by the relatively low insolation and intense ice-albedo feedback in late MIS 3. The decreased insolation and dramatically increased Eurasian ice volume in MIS 2 may have led to limited precipitation, which resulted in persistent dry climate conditions in the Qaidam Basin. In the Holocene, the reduction in ice volume reduced the albedo, and this change, in conjunction with increased insolation, may have led to evaporation exceeding local precipitation, resulting in hyperarid climate conditions in the Qaidam Basin.

MIS 3 sediment stratigraphy in southern Sweden sheds new light on the complex glacial history and dynamics across southern Scandinavia

Recent studies have revealed that areas with sediments pre‐dating the Last Glacial Maximum (LGM) are more common in southern Scandinavia than previously thought. To describe and date these sediments, four deep core drillings were made in the province of Småland and one in the province of Skåne, southern Sweden, and an existing sediment core drilled in the 1960s from western Skåne was re‐examined and re‐dated, all resulting in a total of 22 AMS 14C ages and 19 OSL ages. With some variation, the Småland cores revealed a stratigraphy consisting of two tills separated by proglacial glacifluvial and glaciolacustrine sediments, dated to between 46 and 25 ka BP (Marine Isotope Stage (MIS) 3 to 2). We suggest that these sediments were deposited during the ice retreat of the MIS 3 Ristinge glaciation over southern Scandinavia and the subsequent re‐advance over the area in late MIS 3 and the transition to MIS 2, when the Fennoscandian Ice Sheet advanced towards its LGM marginal positions. This contrasts with the glacial history of southernmost Skåne, where an additional MIS 3 glacial advance through the Baltic Basin is suggested by the occurrence of a till named Allarp Till. New ages from sediments under‐ and overlying this till suggest that it was deposited by the same Baltic ice advance that deposited the Klintholm till in Denmark (Klintholm Advance, c. 34–30 ka).

Climatic control on magnetic mineralogy during the late MIS 6 - Early MIS 3 in Lake Chalco, central Mexico

Sediments from Lake Chalco in central Mexico spanning from ca. 150 to 35 ka ago provide evidence of paleoclimatic variability in the North American tropics associated with the end of Marine Isotopic Stage (MIS) 6, the transition to the last interglacial (MIS 5.5, ca. 130-115 ka ago), and part of the last glacial (MIS 5.4 to early MIS 3, 115 to 35 ka ago). We applied a multiproxy approach based on the analysis of mineral magnetism, diatom assemblages and major elements geochemistry. The reconstructed paleoenvironmental history identify the end of the globally cool MIS 6 as wetter than present, with high lake level, and a subsequent change to drier climates at the onset of the last interglacial (ca. 130 ka). Large amplitude changes in most of the analyzed parameters from ca. 130 to 74 ka are approximately coincident with MIS 5 (130-71 ka). The amplitude of these changes decreases in MIS 4 (71-57 ka) and the early part of MIS 3 (57-35 ka). We proposed that the inferred climatic oscillations follow insolation variations during MIS 6 and part of MIS 5 (150-88 ka). Low summer and spring insolation and lower seasonality inhibited evaporation and favored high lake levels. Conversely, maxima in spring and summer insolation promoted dry conditions and low lake levels. The major wet-cold glacial and dry-warm interglacial relationship found in Lake Titicaca (Bolivia) and Lake Chalco records shows the sensitivity of high altitude tropical sites to climatic variability.

Surface and deep water variability in the Western Mediterranean (ODP Site 975) during insolation cycle 74: High-resolution calcareous plankton and molecular biomarker signals

We reconstructed changes in productivity and surface/subsurface and deep-water dynamics in the Western Mediterranean through a multi-proxy study of Ocean Drilling Program Site 975 between late Marine Isotope Stage (MIS) 20 and early interglacial MIS 19. Our high-resolution study (down to ~200-year resolution) combines calcareous plankton assemblages (coccolithophores and foraminifera), biomarkers (C37-alkenones, n-alkanes, n-alcohols) and elemental proxies (total organic carbon, total nitrogen, calcium carbonate). Surface water conditions are derived (i) from high-resolution δ18O and δ13C records obtained from the planktonic foraminifer Globigerina bulloides, and (ii) from summer and winter, foraminifera-based sea surface temperature reconstructions (SSTJAS-foram, SSTJFM-foram) achieved through transfer function. The integration of the whole dataset makes it possible to identify in the Balearic Sea, and to accurately characterize for the first time, an Organic Rich Layer (ORL) during latest MIS 20-early MIS 19, close to i-cycle 74. Its presence is marked firstly by higher values of total nitrogen (TN) and an increase of total C37-alkenone and total organic carbon (TOC) preserved in the sediments. The multi-proxy approach reveals that the deglacial phase played a prominent role for ORL formation that was characterized by centennial scale phases. The alcohol preservation index (API) suggests that the shoaling of the circulation, which boosted marine productivity, started in the deglaciation and, in combination with freshening by Atlantic water inflow/riverine input and surface water buoyancy during sea level rising, culminated during the ORL event. At this time calcareous plankton proliferated on subsurface-surface waters, benefiting from ameliorating conditions, which promoted maximum marine productivity and higher organic matter preservation on the seafloor.

Palaeochannels of Australia's Riverine Plain - Reconstructing past vegetation environments across the Late Pleistocene and Holocene

Riverine Plain palaeochannels record periods of fluvial activity for Late Pleistocene southeastern Australia. In an attempt to develop a more detailed palaeoenvironmental record for this semi-arid region, we investigate the fine overbank sediments of the palaeochannel fill that cap and underlie the coarser-grained fluvial channel sands of the Tombullen (41–29 thousand years (ka) ago) and the Yanco (29–18 ka) phases. New single grain Optically Stimulated Luminescence (OSL) age determinations for the overlying palaeochannel fills suggest an overall slowing of sedimentation rates since the phase of fluvial activity in late Marine Isotope Stages 3 and 2. δ13CTOC data for the palaeochannel fill sediments range between −28‰ and −22‰, implying variable C4 contributions (0–40%) to a predominantly C3 vegetation mosaic. Modelled C4 abundance for the last 50 thousand years (kyr) decreased from 40% to 10% at around 40 ka with predicted representation remaining low towards the Last Glacial Maximum (LGM). Post LGM C4 grasses are seen to expand to 30–40% and sustained through the Holocene. Pollen preservation is restricted to the upper two metres of the cores, with the distribution showing shifts in dominance from Poaceae and Asteraceae to Eucalyptus up sequence. Increasing Eucalyptus/Poaceae ratios correspond with increasing C4 abundance suggesting that as woodland expanded in the Holocene the associated decreasing grass component shifted from C3 to C4. However, some evidence for the persistence of Poaceae and/or Asteraceae dominance argues that the likely shift from C3 to C4 grasses during the Holocene was in places independent of expanding woodland. Bulk sediment elemental ratios reveal wetting and drying cycles during the deposition of the overbank deposits. While these traits appear to be a product of local sedimentation changes, rather than regional climate, our model of C4 contraction and subsequent expansion across the last 50 kyr is likely reflecting changing summer monsoon intensity and its effects on regional aridity.

Last interglacial (MIS 5e) and Holocene paleohydrology and paleovegetation of midcontinental North America from Gulf of Mexico sediments

Marine Isotope Stage (MIS) 5e experienced slightly higher insolation and lower global ice volume compared to the pre-industrial climate, however, how climate and vegetation differ regionally during MIS 5e is poorly known. Here, we examined MIS 5e hydrologic and vegetation conditions in the Mississippi River Basin (MRB) in North America (NA) and compared this to the Holocene. To do this, we reconstructed paleohydrology and paleovegetation conditions during the last 150 kyr using plant waxes (n-alkanes) and their carbon (δ13Calk) and hydrogen (δ2Halk) isotopic compositions preserved in ODP 625B core from the northwestern Gulf of Mexico (GOM) near the MRB discharge area. In the early MIS 5e, the jet stream may have been located in its northern most position over the last 150 kyr indicated by the highest δ2Halk values resulting in high warm and moist air mass contribution from the GOM and tropical Atlantic to the MRB. This is likely caused by northern expansion of the Atlantic Warm Pool and a northward shift of the ITCZ with increased warming. The climate may have become drier towards late MIS 5e with precipitation concentrated in summer expanding the C4 grassland distribution, which persisted through the MIS 5b. We speculate that this may be due to prolonged warming and drying from early to mid MIS 5. There were notable increases in plant wax export from western dry grasslands during deglaciation (13.5 ka) and the mid-Holocene (5.3 ka). In contrast, plant wax delivery was low during the MIS 5e without significant source changes. Such contrast between the two interglacials is due to the earlier completion of the LIS retreat in late MIS 6 and an onset of a full interglacial climate during the MIS 5e compared to the Last Glacial and Holocene transition. This study presents timing and mechanisms of precipitation source and vegetation composition changes over the NA as a result of slight changes in insolation and rates of deglaciation. These results provide a baseline for understanding the sensitivity of regional hydrologic and vegetation conditions to slight changes in global climate.

Millennial-scale hydrographic changes in the northwestern Pacific during marine isotope stage 19: Teleconnections with ice melt in the North Atlantic

Marine isotope stage (MIS) 19 has been suggested as the best orbital analogue of the present interglacial period. Thus, its paleoenvironmental reconstruction will provide valuable information on future climate change, excluding anthropogenic impacts. The Kuroshio Current, the largest western boundary current in the northwestern Pacific, transports large amounts of heat and water poleward and strongly influences both East Asian and global climates. However, the responses of the Kuroshio Current to the variable intensity of the Atlantic meridional overturning circulation (AMOC) under this orbital configuration remain unknown. Here, we provide new centennial-scale resolution oxygen isotope (δ18O) records throughout MIS 19 using benthic, as well as subsurface and surface planktonic foraminifera from the Chiba composite section, a marine succession sequence in central Japan, to reconstruct detailed paleoceanographic variations in the northwestern Pacific and reveal the response of the Kuroshio Current to climate variability in the North Atlantic under this orbital configuration. The vertical water temperature structure and its gradient (ΔT) based on δ18O profiles elucidates the latitudinal oscillations of the Kuroshio Extension Front (KEF) on a millennial scale during the late MIS 19 and MIS 20–19 transition in association with AMOC disruption/reactivation due to freshwater discharges into the North Atlantic. The power spectra of the surface δ18O and ΔT show half-precession periodicity throughout MIS 19, which probably originated from equatorial insolation at equinoxes co-occurring with the orbital perihelion. This periodicity was especially strong during MIS 19c, during which paleoceanographic records from the North Atlantic show minor variations in the AMOC and freshwater discharge. Our results suggest that millennial-scale oceanographic variation and stability along the KEF under this orbital configuration are influenced by both North Atlantic climate variability and tropical insolation forcing.

Changes in the Late Pleistocene small-mammal distribution in the Italian Peninsula

Recent studies of the Late Pleistocene small-mammal sequences of the Italian Peninsula have provided a more detailed context that sheds light on numerous aspects of the faunal communities in this area. A georeferenced database with 51 Italian Peninsula sites has been built in order to investigate changes in the species range distribution and the evolution of the small-mammal community during the Late Pleistocene, with a special focus on the late Marine Isotope Stage 3 (MIS 3) to Late Glacial assemblages.From the early Late Pleistocene, the Italian Peninsula was divided into two biotic macroregions: the northern Italian Peninsula and the southern Italian Peninsula. The former was characterized by the presence of eastern European species, the latter by the presence of the endemic Savi’s vole (Microtus (Terricola) savii) and the Roman mole (Talpa romana). Three sub-regions have been recognized on the basis of the presence of Dinaromys bogdanovi (northeastern Italian Peninsula) and the presence or absence of Glis glis (southern Tyrrhenian side and southern Adriatic side, respectively).Major oscillations corresponding to Dansgaard-Oeschger (DO) cycles and Heinrich Events (HE or H) have been identified in both macroregions. In particular, the Bølling-Allerød Interstadial can be considered a moment of major faunal renewal for the small-mammal communities of the Italian Peninsula.Finally, the small-mammal communities of the Italian Peninsula follow the same general path as that recognized throughout Mediterranean Europe during the Late Pleistocene: this is characterized by variations in the spread of eastern European taxa in relation to mountain barriers and by the absence of these taxa in the southern areas of the Italian and Iberian Peninsulas, compensated by the presence of endemic species.

Climate change during the last glacial period on the southeast margin of Badain Jaran Desert, Northwest China

Reconstruction of the desert paleoclimate is important to understand the mechanisms that triggered and/or enhanced climate change. Through optically stimulated luminescence (OSL) dating, grain size, magnetic susceptibility, X-ray powder diffraction (XRD) and geochemical indicators, we provide a well-dated record of a sedimentary outcrop on the southeast margin of the Bardain Jaran Desert, Northwest China, during the last glacial period. Four Qz-OSL ages are obtained, 41.0±34 ka, 54.7±4.4 ka, 59.5±5.0 ka and 66.8±5.8 ka, corresponding to the depths of 35 cm, 70 cm, 150 cm and 200 cm respectively. Indicators like grain size, clay content, magnetic susceptibility, XRD and geochemical index (e.g. Sr, Ba, Sr/Ca) jointly indicate abrupt climate changes at the depth of 35 cm (age, ca. 41.0 ka) and 200 cm (age, ca. 67 ka). Namely, the 280 cm sedimentary outcrop perfectly records a warm wet climate stage, corresponding to the late Marine Isotope Stages (MIS) 4 to the early MIS 3. Besides, there is a trend of grain size increase after around 40 ka BP, which is most likely a signal of wind strength change. Our research supports that enhancing Siberian High pressure system during the late MIS 3 played a key role in NW East Asia climate evolution.

Enhanced Mediterranean water cycle explains increased humidity during MIS 3 in North Africa

Abstract. We report a new fluid inclusion dataset from northeastern Libyan speleothem SC-06-01, which is the largest speleothem fluid inclusion dataset for North Africa to date. The stalagmite was sampled in Susah Cave, a low-altitude coastal site, in Cyrenaica, on the northern slope of the Jebel Al-Akhdar. Speleothem fluid inclusions from the latest Marine Isotope Stage (MIS) 4 and throughout MIS 3 (∼67 to ∼30 kyr BP) confirm the hypothesis that past humid periods in this region reflect westerly rainfall advected through the Atlantic storm track. However, most of this moisture was sourced from the western Mediterranean, with little direct admixture of water evaporated from the Atlantic. Moreover, we identify a second moisture source likely associated with enhanced convective rainfall within the eastern Mediterranean. The relative importance of the western and eastern moisture sources seems to differ between the humid phases recorded in SC-06-01. During humid phases forced by precession, fluid inclusions record compositions consistent with both sources, but the 52.5–50.5 kyr interval forced by obliquity reveals only a western source. This is a key result, showing that although the amount of atmospheric moisture advections changes, the structure of the atmospheric circulation over the Mediterranean does not fundamentally change during orbital cycles. Consequently, an arid belt must have been retained between the Intertropical Convergence Zone and the midlatitude winter storm corridor during MIS 3 pluvials.

New insights on sources contributing dust to the loess record of the western edge of the Pampean Plain during the transition from the late MIS 2 to the early Holocene

High-resolution studies of palaeorecords located closer to the dust source areas of South America are relevant for increasing the knowledge on past climatic conditions in the Southern Hemisphere. In this sense, the Pampean loess archives can offer explicit records of dust source, transport, and deposition in the region, providing new insights which may be used to better understand the role of dust in future climate change scenarios. In this work, we studied a loess sequence located at the westernmost Pampean Plain. The studied sequence covers a span of time from the late Marine Isotope Stage (MIS 2) period up to the early Holocene. Loess samples from this record have two grain-size populations, indicating more than one dust source area. The dominance of a coarse-silt subpopulation during the transition from the late MIS 2 to the early Holocene suggests that proximal dust sources were dominant at that time. Two of the most proximal dust sources were analyzed as probable contributors to the Lozada site: sediments derived from the Eastern Pampean Ranges and sediments derived from the shorelines of the Mar Chiquita Lake. The geochemical data suggest that neither area was a significant dust source to the eastern Pampean Plain during the studied interval. Instead, our geochemical data suggest a dominant supply from a southern and relatively closer area, linked to the foothills of the Andes, and the increased activation during the early Holocene of a more distant source to the north in the Puna region, which contributed finer loess.

Persistent local raw material transport at Shuidonggou Locality 2

Recent methodological development indicates that the lithic cortex to volume proportion of Shuidonggou Locality 2 published in an earlier paper (Lin et al., 2019) was erroneous. Here, we describe the issue of the original method and report the revised assemblage cortex to volume ratios of the site. The updated result suggests a pattern of persistent artifact transport in the place-use history of Shuidonggou Locality 2 during late Marine Isotope Stage 3.

Intermediate water circulation changes in the Florida Straits from a 35 ka record of Mg/Li-derived temperature and Cd/Ca-derived seawater cadmium

We generated a high-resolution ocean record of bottom water temperature and seawater Cd from 546 m in the Florida Straits. The record extends to ∼35,000 yr before present, including all of Marine Isotope Stages (MIS) 2 and part of MIS 3. Previously, seawater cadmium (Cdw) has been used as a proxy for the strength of the Atlantic Meridional Overturning Circulation (AMOC) during the last deglaciation. We now consider the temperature and oxygen isotopic composition of seawater reconstructed from the same core in order to provide a fuller picture of water mass properties and circulation at this location. During the Last Glacial Maximum (LGM), Cdw levels were generally low, and a novel Mg/Li-derived temperature record reveals persistently cold temperatures (∼3.6°C, two to three degrees colder than during the Holocene or Marine Isotope Stage 3). During the Younger Dryas and early Heinrich Stadial 1, Cdw was low and temperatures were elevated compared with periods of inferred stronger AMOC. By contrast, there is no indication of AMOC variability over Heinrich Stadials 2 and 3, consistent with previous studies that conclude the AMOC is less sensitive to freshwater forcing during glaciations than during the last deglaciation. While there is some inconsistency between proxies, Cdw increases over some MIS3 Dansgaard–Oeschger interstadials, providing qualified support for a strengthening in AMOC. This is similar to our previous finding that Cdw tracks AMOC variability during the deglaciation. This study highlights the distinct nature of water masses and circulation during the LGM, relative to the stadial (weak AMOC) periods of the deglaciation and Late MIS 3.

Paleo-glacier reconstruction in southwestern British Columbia, Canada: A glaciovolcanic model

Volcanic rocks erupted within glacial environments offer powerful paleoenvironmental insights. These glaciovolcanoes and their deposits serve as proxies that inform on the paleo-presence, distribution and thickness of past glaciers. We investigate the paleoenvironmental implications of three Mid to Late Pleistocene volcanic deposits in the Garibaldi volcanic belt of southwestern British Columbia, Canada. We use these data to inform a simple geometric model that constrains paleo-glacier distributions in the southern Canadian Cordillera. The three volcanoes are used to recover: i) a coalesced mountain ice sheet in late Marine Isotope Stage (MIS) 4, and possibly into MIS 3 (up to ∼49.1 ± 5.5 ka), ii) major and rapid degradation of glaciers during the late, MIS 6 to 5e transition (by 141 ± 12.9 ka), and, iii) a coalesced mountain ice sheet, or continental ice sheet that existed during MIS 15 (598 ± 7.5 ka).

Mineralogical and isotopic evidence for the sediment provenance of the western South Yellow Sea since MIS 3 and implications for paleoenvironmental evolution

Changing sediment provenance and related paleoenvironmental evolution since marine isotope stages (MIS) 3 have been investigated based on accelerator mass spectrometry (AMS) 14C and optically stimulated luminescence (OSL) dating of core CSDP-01, recovered from the western South Yellow Sea (SYS). Based on our results, sea level fluctuations and monsoonal climate variations are identified as the principal factors driving these changes. Sea level fluctuations determined the accommodation space in the shelf area, while the monsoonal climate controlled the sediment supply capacity from river to sea. Mineral and SrNd isotopic records reveal the major contribution of the paleo-Changjiang River (Yangtze River) to the study core area during the early-mid MIS 3, which likely defined the northern limit of the paleo-Changjiang delta at that time. High sediment supply and limited accommodation space led to the development of sediment-fed systems on the SYS shelf, resulting in a high preservation potential for thick-stacking and overlapping deltaic sediments. Along with deltaic progradation, core sediment provenance gradually transformed from the paleo-Changjiang River to the paleo-Huanghe River (Yellow River) near the late MIS 3, implying that the paleo-Huanghe River likely emptied into the SYS and built a large delta during the MIS 3 interval. A strong summer monsoon during the early MIS 1 interval was favorable for the Changjiang to deliver abundant sediments to the study core area. A weak summer monsoon during the mid-late MIS 1 when the coastline had retreated to nearly its present-day position decreased the Changjiang and Huanghe supply to the study area. Low sediment supply and sufficient accommodation space gave rise to the development of sediment-starved systems during this period. ɛNd values fluctuated between the Changjiang and Huanghe sources at that time, suggesting that sea bed erosion materials are the main sediment contribution to the study area. In general, sedimentary evolution in the western SYS since MIS 3 is a good example of river-sea interaction in the marginal seas of Southeast Asia, in which sea level and monsoonal climate changes should play an important role.

Seismic morphology and infilling architecture of incised valleys in the northwest South Yellow Sea since the last glaciation

Based on the interpretation of ∼3000 km of high-resolution seismic profiles, the small local rivers that form the channel network of the northwestern South Yellow Sea are identified for the first time. Incised-valley systems orientated NW–SE and NE–SW were detected outside Dingziwan Bay and Rushan Bay, respectively. Analysis of the sedimentation and fill sequences of these valleys revealed six main types of fill architecture: horizontal or near-horizontal, lateral, undulate-wavy, concave, divergent, and chaotic. Stratigraphic sequence relationships and AMS 14C and OSL dating of two cores (QDZ03 and QDZ01) suggest that these incised valleys were formed during the period from late Marine Isotope Stage 3 (MIS 3) to MIS 1, between 30 and 11 ka BP. The incised-channel fill begins with fluvial sediments and shows a transition to estuarine sediments that are truncated by a transgressive ravinement. There is little evidence of lag deposits at the base of the fill and no evidence of capping by Holocene mud deposits. The incised-valley model presented in this paper differs from current classical sequence stratigraphic models and contributes to our understanding of incised valleys.

A 40,000-year record of aridity and dust activity at Lop Nur, Tarim Basin, northwestern China

The Taklamakan Desert is a major dust source area for northwestern China. The history of aridification and sandstorm activity of the desert is recorded in the lacustrine sediments of the Lop Nur paleolake, on the eastern margin of the desert. In this study, we used accelerator mass spectrometry 14C dating, the ln (Al/Ca) ratio, and the grain size of the non-biogenic fraction of sediment core KY01 taken from the center of Lop Nur to produce a ∼40 kyr record of local climate change. During mid–late Marine Isotope Stage (MIS) 3, increases in the ln (Al/Ca) ratio, alluvial mud content, and atmospheric dust content, and a decrease in the dust storm content indicate an overall wet climate. During MIS 2, marked decreases in the ln (Al/Ca) ratio and alluvial mud content, especially during the Last Glacial Maximum and Heinrich event 1 cold interval, indicate lowered atmospheric temperatures, as also recorded in Greenland ice cores. During MIS 2, fluvial input to the site was reduced and almost ceased, suggesting extreme aridity at Lop Nur, very strong low-altitude winds, and frequent dust storms. During early MIS 1, the contribution of dust storms to the lake sediments fell gradually and was then relatively constant, even during the Younger Dryas cold interval. This result might be ascribed to the increased supply of meltwater from snow and ice to Lop Nur, representing a response to the rise in atmospheric temperatures during the deglacial, accompanied by strong high-level winds. During 9–7 kyr BP there was an increase in the input of sediment from sandstorms, and hence an increase in low-level wind strength, possibly relating to the 8.2 kyr BP cold event. From 7.0 to ∼1.5 kyr BP there was a decrease in sandstorm input and thus a gradual weakening of the strength of low-level winds. However, after ∼1.5 kyr BP the sandstorm input increased. Overall, we conclude that dust storm activity in the region of Lop Nur since 40 kyr BP has been controlled mainly by Northern Hemisphere cold events, with atmospheric dust providing a background sedimentary component that was dominant during warm intervals. Our findings contribute to an improved understanding of the dynamics of dust transport and to the history of dust activity and the lacustrine sedimentary record in northwestern China.

Radiocarbon dates of two musk ox vertebrae reveal ice-free conditions during late Marine Isotope Stage 3 in central South Norway

One of the most reliable proofs of terrestrial ice-free conditions within Stadials is the presence of terrestrial vertebrate fauna that require access to vegetation in the winter, for example sedentary birds such as Ptarmigans and herbivorous mammals in particular. The musk ox (Ovibos moschatus) is an example of the latter; modern-day distributions of this species are limited to areas with low snow accumulations. In this paper we discuss the discovery of musk ox bones in Norway. Recently obtained radiocarbon dates on this material demonstrate the presence of this species 41–35 cal kyr B.P. in southern Norway during late Marine Isotope Stage 3 (MIS3). Furthermore the dates have implications for the interpretation of climate and environmental conditions; indicating the existence of a small ice cap in the mountains and climate and vegetation supporting a large mammal fauna in South Norway at that time.

Variações paleoclimáticas e impacto na recarga de águas subterrâneas em sistemas aquíferos multicamadas usando uma abordagem multitraçador (bacia setentrional da Aquitânia, França)

The northern Aquitaine basin (southwest France) is a large multi-layer aquifer system that contains groundwater with strong residence-time variability ranging from years to tens of thousands of years. This system constitutes an archive of paleoclimate variations. A multi-parameter approach involving isotopic tracers (14C, 18O, 2H) was used to determine the residence time of groundwater and to document climate fluctuations, while dissolved noble gases were used to estimate mean annual temperatures (noble gas recharge temperatures, NGRT) at the water table. Near-surface ground temperature reconstruction from 40 ka cal BP to the present was made using data collected from five aquifers. The coldest temperatures are recorded for late Marine Isotopic Stage (MIS) 3 and MIS 2, i.e. between 36 and 18 ka cal BP. The mean NGRT for the period 27–18 ka cal BP is estimated at 5.9 ± 0.9 °C, and a strong increase towards modern values (11–13 °C) is observed after 15 ka cal BP. The temperature change between the Holocene and the Last Glacial ranges from 5 to 7 °C, in agreement with previous NGRT studies in Europe. Since mean near-surface ground temperatures during the glacial were well above 0 °C, long-term presence of permafrost in northern Aquitaine is unlikely. However, a possible warm bias in reconstructed temperatures during the coldest events lies in the fact that NGRTs in cold regions do not reflect annual means but rather the ground temperature during the thaw months.