MIS 5c Research Articles

Quantification of paleo-aquifer changes using clumped isotopes in subaqueous carbonate speleothems

Here we track the water-table position and temperature of the Mount San Giovanni aquifer (Iglesiente-Sulcis mining district, SW Sardinia, Italy) during the past 600 ka by determining the ages (U/Th dating) and stable isotope compositions (δ18O, δ13C and Δ47) of a variety of subaqueous carbonate speleothems (e.g. calcite spars, dogtooth calcite crystals and calcite coatings). Clumped isotopes (Δ47) provide quantitative estimates of carbonate formation temperatures (and thus water temperatures) that are independent of the oxygen isotope composition of water (δ18Ow). Then, the δ18Ow of the paleo-water has been reconstructed from the clumped isotope temperature (TΔ47) and the δ18O of the carbonate (δ18Oc). We find that some high-temperature calcite spars formed prior to 600 ka at temperatures above ~120 °C. Lower-temperature spars (~70 °C) precipitated at ~400 ka, and cold-water subaqueous speleothems (~10–20 °C) formed in perched ponds at different levels of the karst systems between 410 ka and 110 ka, while coeval precipitation of subaerial flowstones occurred in the upper level of the shallower caves until 82 ka. We infer that the groundwater level dropped by ~120 m from ~400 to ~250 ka, with a relatively rapid rate of ~0.8 mm/yr. Considering the tectonic stability of Sardinia during the Quaternary, this high rate derives from climate driven geomorphological processes at the surface rather than tectonic uplift. The δ18O values of the paleo-aquifer water range from −6.0 ± 0.7‰ during MIS 5c, and similar to modern cave water values (−5.1‰), to −7.7± 0.4‰ during the colder MIS 8. These values indicate that the groundwater reflected the δ18O signal of meteoric water, with no significant contributions from metasomatic and metamorphic waters. The observed δ18Ow variability can be explained by glacial/interglacial paleoclimate changes affecting rainfall δ18O (and thus groundwater δ18O). We conclude that clumped isotope thermometry on subaqueous carbonate speleothems is a useful tool for tracking paleo-aquifer temperatures and δ18Ow reconstructions.

A multiproxy record of the Younger Holsteinian Oscillation (YHO) in the Ossówka profile, eastern Poland

The laminated lacustrine succession at Ossówka in eastern Poland, which is largely the equivalent of MIS 11c, is amongst the best‐developed sites in Europe that cover this time period. Close inspection of the depth interval between 35.0 and 42.5 m in a 55‐m‐long core shows an environmental crisis at a depth of 40.95 m that lasted approximately 800 years and resulted in almost complete extinction of fir (Abies) from the communities existing at that time. Geochemical analyses reveal a simultaneous increase in sulphur in the deposits and a change in stable carbon and oxygen isotope ratios towards higher values, as well as a significant increase in the thickness of the laminae (up to 5 mm). Diatom studies show a clear increase in benthic diatoms in this interval, implying a decrease in water level. However, the predominance of such forms was probably caused by the elimination of planktonic diatoms by invasive blooms of Tetraedron, rather than lower lake levels, evidence of which was not noted in the pollen spectra. Hence, all these changes in the lake may have been triggered by the destruction of fir trees, the gradual decomposition of dead trunks and some inconspicuous geomorphological disturbances caused by wind throw. They resulted in a supply of micronutrients to the basin, an increase in varve thickness and rapid oscillations in the abundance and composition of algae and changes in the geochemical status of the lake. Rapid and significant drops in winter temperatures appear to be responsible for the extinction of fir. Alternatively, late frost in spring or hot and dry summers may have affected microsporophyll growth and the fir physiology as known from extant Abies populations. This environmental crisis, which is termed the Younger Holsteinian Oscillation (YHO), is noted at only a few sites. At Dethlingen (Germany), where hornbeam communities disappear at that time, a drop in summer temperatures is suggested to have been the driving force. We suggest that, at Ossówka, a drop in winter temperatures, late frost, or summer drought at the very start of the YHO are possible causes of the near‐extinction of fir.

A large mammal assemblage during MIS 5c: Artazu VII (Arrasate, northern Iberian Peninsula)

Artazu VII palaeontological site (Arrasate, Gipuzkoa) is one of the few deposits in the Iberian Peninsula in which humans did not intervene in its formation as the site acted as a natural trap. The vertebrate remains recovered are in a very good state of preservation and display great biodiversity. The large mammal assemblage from Artazu VII is studied in detail in this paper. Fourteen different species are described, including ungulates and carnivores. Morphological and osteometric descriptions are also provided, as well as a morphological study of chamois and leopard compared with the same species of similar chronology both in the surroundings of the site and in the rest of the Iberian Peninsula. The existence of biases related to the form of the shaft is tested, as these might relativize the value of the remains as a representative proxy of the fauna in the early Late Pleistocene in the Iberian Peninsula. The palaeoecology inferred from this association indicates the existence of a woodland mass alternating with meadow biotope, and with a watercourse in the surrounding area.

Unraveling the forcings controlling the vegetation and climate of the best orbital analogues for the present interglacial in SW Europe

The suitability of MIS 11c and MIS 19c as analogues of our present interglacial and its natural evolution is still debated. Here we examine the regional expression of the Holocene and its orbital analogues over SW Iberia using a model–data comparison approach. Regional tree fraction and climate based on snapshot and transient experiments using the LOVECLIM model are evaluated against the terrestrial–marine profiles from Site U1385 documenting the regional vegetation and climatic changes. The pollen-based reconstructions show a larger forest optimum during the Holocene compared to MIS 11c and MIS 19c, putting into question their analogy in SW Europe. Pollen-based and model results indicate reduced MIS 11c forest cover compared to the Holocene primarily driven by lower winter precipitation, which is critical for Mediterranean forest development. Decreased precipitation was possibly induced by the amplified MIS 11c latitudinal insolation and temperature gradient that shifted the westerlies northwards. In contrast, the reconstructed lower forest optimum at MIS 19c is not reproduced by the simulations probably due to the lack of Eurasian ice sheets and its related feedbacks in the model. Transient experiments with time-varying insolation and CO2 reveal that the SW Iberian forest dynamics over the interglacials are mostly coupled to changes in winter precipitation mainly controlled by precession, CO2 playing a negligible role. Model simulations reproduce the observed persistent vegetation changes at millennial time scales in SW Iberia and the strong forest reductions marking the end of the interglacial “optimum”.

A Last Interglacial pollen-temperature reconstruction, central North Island, New Zealand

We present new pollen-temperature reconstructions for the Last Interglacial from central North Island, New Zealand using partial least squares regression (PLS) and modern analogue technique applied with the New Zealand pre-deforestation calibration pollen dataset. The pollen-bearing organic sequence includes numerous millimetre- to decimetre- thick tephra mostly from the adjacent Tongariro Volcanic Centre and is overlain by tephric cover-beds including the c. 25.4 ka cal BP Kawakawa/Oruanui Tephra. Fine-resolution pollen and preliminary diatom analyses above and below prominent tephra layers showed that significant vegetation impact followed only the thickest ashfall event (22 cm thickness), with vegetation recovery taking several hundred years. Apart from this, changes in the longer-term pollen record are likely to be related to climate oscillations that resemble the classic five-fold subdivision of MIS 5. The warmest interval, ascribed to MIS 5e, was characterised by tall, temperate rainforest, and occurs at the base of the sequence, with mean annual temperatures reaching around 1.1 °C higher than present. Mean annual temperatures declined to ∼4 °C below present during MIS 5d and MIS 5b and were within 1–2 °C of present during MIS 5c. The PLS temperature reconstructions are corroborated by estimates derived independently from elevational changes to vegetation communities, corresponding to modern temperature controls, inferred from the Karioi pollen spectra. Temperatures reconstructed quantitatively by the modern analogue technique were up to 1.3 °C higher for MIS 5e, MIS 5d and MIS 5b, possibly reflecting weaker modern vegetation analogues for these intervals.

Palaeoenvironmental and palaeoclimatic reconstruction of the Middle to Late Pleistocene sequence of Scladina Cave (Namur, Belgium) using the small-mammal assemblages

The habitat weighting, the bioclimatic model methods and the Simpson diversity index are applied to the small-mammals assemblage of Scladina Cave (border between High and Middle Belgium) in order to reconstruct the environmental and climatic fluctuations that are reflected on the Middle to Late Pleistocene sequence of the cave. The small-mammal data analyzed come from two surveys carried out at the entrance of the cave and allow us to identify within the section one cold episode: a dry, cool phase in the upper part of the sequence (probably associated with the MIS 3). The environmental and climatic data show an alternation of open meadows and woodland formations through both sequences, punctuated by peaks in local watery environments together with lower temperatures and higher precipitations rates than at present. Finally, a comparison of the small-mammal fossil assemblage from the studied surveys with the small-mammals assemblage from the Holocene deposits of Scladina Cave shows that layers related with MIS 5 temperate sub-stages (MIS 5c and MIS 5a) present environmental characteristics similar to those prevailing nowadays (a landscape dominated by woodland formations and water streams) in the area surrounding the cave. This is coherent with the available chronostratigraphic datasets on this part of the sequence, suggesting the record of the humid and temperate phases at the beginning of the Late Pleistocene.

The Don formation, Toronto, Canada: a record of the sangamonian interglacial and early wisconsinan (warm part of MIS 5e to a MIS 5 cold substage)

Regarded as a reference unit of the Sangamonian Interglacial in North America, the Don Formation was deposited however during a longer interval of time, including the interglacial climatic optimum of MIS 5e followed by an erosive and cool phase (intra-MIS 5e or MIS 5d), a boreal phase with a fir forest (late MIS 5e transition or MIS 5c), erosive episodes and the early part of a cold stadial (MIS 5d or MIS 5b). From the planar geometry of the beds exposed at the former Don Valley Brickyard in Toronto, the formation comprises five continuous allozones with lateral variations of thickness. Each allozone corresponds to dominant conditions of sedimentation in a shoreface of Lake Coleman within a limited accommodation space. Allozone D2 is correlated to other interglacial units of Eastern Canada, with ages between 128 and 115 ka. The interglacial climatic optimum is interrupted in the area by two cool events, the first one similar to the Tunturi event of Finland, the second one probably related to a Greenland Stadial. The heterogeneous upper Allozone D5 was deposited in shallow waters when a Northern Boreal Forest prevailed in the watershed. This zone is correlated to the Deschaillons Varves of the central St. Lawrence River Valley, deposited prior to the first regional Wisconsinan glacial advance in the central St. Lawrence River Valley and the resulting glacial Lake Scarborough Formation. From the 80 ka minimalU/Th age of the Deschaillons Varves and the 98 ± 8 ka TL age of the later marine La Perade Clay, Allozone D5 was deposited during the beginning of one of the cold episodes of MIS 5.

Radiometric, isotopic, and petrographic evidence of changing interglacials over the past 550,000 years from six stalagmites from the Serra do Courel in the Cordillera Cantábrica of northwestern Spain

Seventy U-Th ages from six stalagmites from the Cordillera Cantábrica in northwestern Spain indicate deposition during interglacial, but not glacial, stages over the last 550kyr. Stable isotope data and petrographic observations suggest that, within each interglacial, conditions typically progressed from drier to wetter. Consideration of the most precise U-Th ages suggests that stalagmite deposition occurred in times more predictable from European pollen records than from the global marine isotope record. For example, during the last interglacial, ages suggest deposition in an interval better characterized as the Eemian, as opposed to MIS 5e, and during the St. Germain I or MIS 5c interval. The same holds for MIS 7, where ages suggest deposition during MIS 7a and MIS 7c but not MIS 7e. These age ranges for interglacials, consistently later than those suggested by the benthic marine record, are compatible with warm conditions maintained by thermohaline circulation that simultaneously supplied the moisture for growing ice sheets of the subsequent glaciation.Trends both within and across these six stalagmites suggest that cooler temperatures were associated with wetter conditions, both during interglacials and in conditions intermediate between interglacials and glacials in northern Spain. In contrast, other researchers' results from a stalagmite from the Last Glacial Maximum and subsequent deglaciation suggest colder temperatures were associated with drier conditions. The two trends combine to suggest wettest conditions in times intermediate between interglacials and glacials, compatible with a model in which modern climatic belts from dry Arctic to wet European to dry marginal Saharan have moved over northern Spain in the cycle from glacial to interglacial times. Extrapolation to a warmer future would suggest drier conditions in the northern Iberian Peninsula than those of today.

Speleothem evidence for MIS 5c and 5a sea level above modern level at Bermuda

The history of sea level in regions impacted by glacio-isostasy provides constraints on past ice-sheet distribution and on the characteristics of deformation of the planet in response to loading. The Western North Atlantic–Caribbean region, and Bermuda in particular, is strongly affected by the glacial forebulge that forms as a result of the Laurentide ice-sheet present during glacial periods. The timing of growth of speleothems, at elevations close to sea level can provide records of minimum relative sea level (RSL). In this study we used U–Th dating to precisely date growth periods of speleothems from Bermuda which were found close to modern-day sea level. Results suggest that RSL at this location was above modern during MIS5e, MIS5c and MIS5a. These data support controversial previous indications that Bermudian RSL was significantly higher than RSL at other locations during MIS 5c and MIS 5a. We confirm that it is possible to explain a wide range of MIS5c-a relative sea levels observed across the Western North Atlantic–Caribbean in glacial isostatic adjustment models, but only with a limited range of mantle deformation constants. This study demonstrates the particular power of Bermuda as a gauge for response of the forebulge to glacial loading, and demonstrates the potential for highstands at this location to be significantly higher than in other regions, helping to explain the high sea levels observed for Bermuda from earlier highstands.

MIS 5 environmental and climatic reconstruction in northeastern Iberia using the small-vertebrate assemblage from the terrestrial sequence of Cova del Rinoceront (Castelldefels, Barcelona)

The habitat weighting method, chorotype classification and the bioclimatic model, as well as the Simpson diversity index, are applied to the small-vertebrate assemblage of Cova del Rinoceront (Castelldefels, Barcelona) in order to reconstruct the environmental and climatic fluctuations that are reflected in the MIS 5 sequence of the cave. The small-vertebrate data analysed are from Unit 1 of the sequence, which comprises three MIS 5 layers (III to I). They allow one cool and two warm episodes to be identified within the section. The warm episodes are related with open-woodland formations and temperatures higher than at present in the area, though in layer III our data suggest moist conditions, with the precipitation higher than today, which could probably be related with the beginning of MIS 5e. Layer II is associated with drier conditions, with precipitation lower than nowadays, which could probably be related with MIS 5c. By contrast, layer I is associated with open woodland formations, but with cooler and relatively humid conditions than today to judge by the temperature and precipitation data obtained. This could probably be related with MIS 5b. Our results are consistent with the available chronological, large-mammal, bird and palaeobotanical datasets for this upper part of the sequence. They are also consistent with the pollen record from the marine margins of Iberia.

The δ18O stratigraphy of the Hoxnian lacustrine sequence at Marks Tey, Essex, UK: implications for the climatic structure of MIS 11 in Britain

ABSTRACTMarine Isotope Stage 11 (MIS 11) is considered one of the best analogues for the Holocene. In the UK the long lacustrine sequence at Marks Tey, Essex, spans the entirety of the Hoxnian interglacial, the British correlative of MIS 11c. We present multiproxy evidence from a new 18.5‐m core from this sequence. Lithostratigraphy, pollen stratigraphy and biomarker evidence indicate that these sediments span the pre‐, early and late temperate intervals of this interglacial as well as cold climate sediments that post‐date the Hoxnian. The δ18O signal of endogenic carbonate from this sequence produces several clear patterns that are interpreted as reflecting the climatic structure of the interglacial. As well as providing evidence for long‐term climate stability during the interglacial and a major post‐Hoxnian stadial/interstadial oscillation the δ18O signal provides strong evidence for abrupt cooling events during the interglacial itself. One of these isotopic events occurs in association with a short‐lived increase in non‐arboreal pollen (the NAP phase). The results presented here are discussed in the context of other MIS 11 records from Europe and the North Atlantic, particularly with respect to our understanding of the occurrence of abrupt climatic events in pre‐Holocene interglacials. Copyright © 2016 The Authors. Journal of Quaternary Science Published by John Wiley & Sons Ltd.

Late quaternary sea level changes of Gabes coastal plain and shelf: Identification of the MIS 5c and MIS 5a onshore highstands, southern Mediterranean

The continental shelf of the Gulf of Gabes is outlined, during the MIS 5c and MIS 5a onshore highstands, by the genesis of forced regressive beach ridges situated respectively at –19 m b.s.l/100 ka and –8 m b.s.l/80 ka. This area, considered as a stable domain since at least the last 130 ka (Bouaziz et al. 2003), is a particular zone for the reconstruction of the late quaternary sea-level changes in the region. Shuttle Radar Topography Mission (SRTM) data and field observations are highlighted to deduce interaction between hydrodynamic factors and antecedent topography. Variations in geomorphology were attributed to geological inheritance. Petrography and sedimentary facies of the submerged coastal ridges reveal that the palaeocoastal morphology was more agitated than today and the fluvial discharges are consistent. Actual morphologic trend deduced from different environment coasts (sandy coasts, sea cliffs and tidal flat) is marked by accumulation of marine sands and progradation.

Techno-Cultural Characterization of the MIS 5 (c. 105 - 90 Ka) Lithic Industries at Blombos Cave, Southern Cape, South Africa.

Blombos Cave is well known as an important site for understanding the evolution of symbolically mediated behaviours among Homo sapiens during the Middle Stone Age, and during the Still Bay in particular. The lower part of the archaeological sequence (M3 phase) contains 12 layers dating to MIS 5 with ages ranging from 105 to 90 ka ago (MIS 5c to 5b) that provide new perspectives on the technological behaviour of these early humans. The new data obtained from our extensive technological analysis of the lithic material enriches our currently limited knowledge of this time period in the Cape region. By comparing our results with previously described lithic assemblages from sites south of the Orange River, we draw new insights on the extent of the techno-cultural ties between these sites and the M3 phase at Blombos Cave and highlight the importance of this phase within the Middle Stone Age cultural stratigraphy.

Climate changes in south western Iberia and Mediterranean Outflow variations during two contrasting cycles of the last 1 Myrs: MIS 31–MIS 30 and MIS 12–MIS 11

Grain size analysis and physical properties of Sites U1388, U1389 and U1390 collected in the Contourite Depositional System of the Gulf of Cádiz during the Integrated Ocean Drilling Program (IODP) Expedition 339 “Mediterranean Outflow” reveal relative changes in bottom current strength, a tracer of the dynamics of the Mediterranean Outflow Water (MOW), before and after the Middle Pleistocene Transition (MPT). The comparison of MOW behavior with climate changes identified by the pollen analysis and δ18O benthic foraminifera measurements of Site U1385, the Shackleton Site, collected in the south western Iberian margin shows that the interval MIS 31–MIS 30, ~1.1–1.05millionyears ago (Ma), before the MPT, was marked by wetter climate and weaker bottom current than the interval MIS 12–MIS 11 (0.47–0.39Ma), after the MPT. Similarly, the increase in fine particles from these glacials to interglacials and in coarse fraction from interglacials to glacials was coeval with forest and semi-desert expansions, respectively, indicating the lowering/enhancement of MOW strength during periods of regional increase/decrease of moisture. While these findings may not necessarily apply to all glacial/interglacial cycles, they nonetheless serve as excellent supporting examples of the hypothesis that aridification can serve as a good tracer for MOW intensity. The strongest regional aridity during MIS 12 coincides with a remarkable increase of coarse grain size deposition and distribution that we interpret as a maximum in MOW strength. This MOW intensification may have pre-conditioned the North Atlantic by increasing salinity, thereby triggering the strong resumption of the Meridional Overturning Circulation that could contribute to the great warmth that characterizes the MIS 11c super-interglacial.

Climatic implications of the Quaternary fluvial tufa record in the NE Iberian Peninsula over the last 500 ka

The drainage area of the Iberian Ranges (NE Spain) houses one of the most extensive Quaternary fluvial tufaceous records in Europe. In this study, tufa deposits in the Añamaza, Mesa, Piedra and Ebrón river valleys were mapped, stratigraphically described and chronologically referenced from U/Th disequilibrium series, amino acid racemization and radiocarbon methods. Tufa deposits accumulated in cascades, barrage-cascades and related damming areas developed in stepped fluvial systems. The maximum frequency of tufa deposition was identified at 120ka (Marine Oxygen Isotope Stage [MIS] 5e), 102ka (MIS 5c), 85ka (~MIS 5a) and 7ka (MIS 1), probably under warmer and wetter conditions than today. Additional phases of tufa deposition appear at ~353ka (~end of MIS 11), 258–180ka (MIS 7) and 171–154ka (MIS 6). Although most tufa deposition episodes are clearly correlated with interstadial periods, the occurrence of tufa deposits during the penultimate glaciation (MIS 6) is remarkable, indicating that the onset of this stage was climatically favourable in the Iberian Peninsula. Biostatic conditions and the dynamics of karstic systems regulating tufa deposition seem to be sensitive to the precipitation regime, controlled by shifts in the position of North Atlantic atmospheric belts, and summer insolation, regulated by orbital forcing.

Increased aridity in southwestern Africa during the warmest periods of the last interglacial

Abstract. Terrestrial and marine climatic tracers from marine core MD96-2098 were used to reconstruct glacial–interglacial climate variability in southwestern Africa between 194 and 24 thousand years before present. The pollen record documented three pronounced expansions of Nama-karoo and fine-leaved savanna during the last interglacial (Marine Isotopic Stage 5 – MIS 5). These Nama-karoo and fine-leaved savanna expansions were linked to increased aridity during the three warmest substadials of MIS 5. Enhanced aridity potentially resulted from a combination of reduced Benguela Upwelling, expanded subtropical high-pressure cells, and reduced austral-summer precipitation due to a northward shift of the Intertropical Convergence Zone. Decreased austral-winter precipitation was likely linked to a southern displacement of the westerlies. In contrast, during glacial isotopic stages MIS 6, 4 and 3, fynbos expanded at the expense of Nama-karoo and fine-leaved savanna indicating a relative increase in precipitation probably concentrated during the austral winter months. Our record also suggested that warm–cold or cold–warm transitions between isotopic stages and substages were punctuated by short increases in humidity. Increased aridity during MIS 5e, 5c and 5a warm substages coincided with minima in both precessional index and global ice volume. On the other hand, austral-winter precipitation increases were associated with precession maxima at the time of well-developed Northern Hemisphere ice caps.

The continental record of Marine Isotope Stage 11 (Middle Pleistocene) on the Iberian Peninsula characterized by herpetofaunal assemblages

ABSTRACTMarine Isotope Stage (MIS) 11 in Iberia is documented at three main Acheulean archaeological sites: Gran Dolina (Burgos, Atapuerca), Áridos‐1 (Madrid) and Ambrona (Soria). As the amphibians and reptiles recovered as fossils from these sites are not extinct and their ecology can be directly studied, mutual climatic range and habitat weighting methods have been applied to the herpetofaunal assemblages to estimate climatic and environmental parameters during MIS 11. Compared with today, mean annual temperature varies from +2.7 to +0.3 °C and mean annual precipitation varies from +311.7 to +74.4 mm, suggesting, in accordance with the numerical dates for each locality, a progressive decrease in temperature and rainfall from the fully interglacial conditions of MIS 11c to the end of MIS 11. The presence of woodland areas is also well substantiated throughout the duration of MIS 11, at least during the interglacial and interstadial periods.

Terrace styles and timing of terrace formation in the Weser and Leine valleys, northern Germany: Response of a fluvial system to climate change and glaciation

In glaciated continental basins accommodation space is not only controlled by tectonics and sea-level but also by the position of ice-sheets, which may act as a regional base-level for fluvial systems. Although the Pleistocene terrace record of major river systems in northwestern Europe has been investigated by many authors, relatively little attention has been paid to base-level changes related to glacier advance–retreat cycles and how these regional changes in base-level interacted with river catchment processes. This study provides a synthesis of the stratigraphic architecture of Middle Pleistocene to Holocene fluvial terraces in the upper Weser and middle Leine valley in northern Germany and links it to glaciation, climate and base-level change. The depositional architecture of the fluvial terrace deposits has been reconstructed from outcrops and high-resolution shear wave seismic profiles. The chronology is based on luminescence ages, 230Th/U ages, 14C ages and Middle Palaeolithic archaeological assemblages.The drainage system of the study area developed during the Early Miocene. During the Pleistocene up to 170 m of fluvial incision took place. A major change in terrace style from strath terraces to cut-and-fill terraces occurred during the early Middle Pleistocene before Marine Isotope Stage MIS 12, which may correlate with climate deterioration and the onset of glaciation in northern central Europe. During this time a stable buffer zone was established within which channels avulsed and cut and filled freely without leaving these vertical confines. Climate was the dominant driver for river incision and aggradation, whereas the terrace style was controlled by base-level changes during ice-sheet growth and decay. A major effect of glacio-isostatic processes was the post-Elsterian re-direction of the River Weser and River Leine.The Middle Pleistocene fluvial terraces are vertically stacked, indicating a high aggradation to degradation ratio, corresponding with a regional base-level rise during glacier advance. At the beginning of the Late Pleistocene the terrace style changed from a vertical to a lateral stacking pattern, which is attributed to a decrease in accommodation space during glacier retreat. The formation of laterally attached terraces persisted into the Holocene.Major incision phases took place during MIS 5e, 5d, 5c, and probably early MIS 4, early MIS 3 and MIS 2 (Lateglacial). During MIS 5e and the Lateglacial the braided river systems changed into meandering rivers, indicated by preserved organic-rich flood-plain and point bar deposits. The Late Pleistocene braided river systems (MIS 5c to MIS 3) are characterized by a high sinuosity, which may be a direct effect of an increased downstream gradient after deglaciation when the channel lengthened and the river adjusted to the increased gradient by increasing sinuosity. These Middle Pleniglacial fluvial deposits are unconformably overlain by Lateglacial to Holocene meandering river deposits, which form laterally attached terraces, recording millennial-scale channel shifts. The lack of Late Pleniglacial deposits might be related to Late Weichselian forebulge formation.

The greening of Arabia: Multiple opportunities for human occupation of the Arabian Peninsula during the Late Pleistocene inferred from an ensemble of climate model simulations

Climate models are potentially useful tools for addressing human dispersals and demographic change. The Arabian Peninsula is becoming increasingly significant in the story of human dispersals out of Africa during the Late Pleistocene. Although characterised largely by arid environments today, emerging climate records indicate that the peninsula was wetter many times in the past, suggesting that the region may have been inhabited considerably more than hitherto thought. Explaining the origins and spatial distribution of increased rainfall is challenging because palaeoenvironmental research in the region is in an early developmental stage. We address environmental oscillations by assembling and analysing an ensemble of five global climate models (CCSM3, COSMOS, HadCM3, KCM, and NorESM). We focus on precipitation, as the variable is key for the development of lakes, rivers and savannas. The climate models generated here were compared with published palaeoenvironmental data such as palaeolakes, speleothems and alluvial fan records as a means of validation. All five models showed, to varying degrees, that the Arabia Peninsula was significantly wetter than today during the Last Interglacial (130ka and 126/125ka timeslices), and that the main source of increased rainfall was from the North African summer monsoon rather than the Indian Ocean monsoon or from Mediterranean climate patterns. Where available, 104ka (MIS 5c), 56ka (early MIS 3) and 21ka (LGM) timeslices showed rainfall was present but not as extensive as during the Last Interglacial. The results favour the hypothesis that humans potentially moved out of Africa and into Arabia on multiple occasions during pluvial phases of the Late Pleistocene.

Biogeography of Pleistocene conifer species from the Ziegler Reservoir fossil site, Snowmass Village, Colorado

Pleistocene biogeography of conifer species is poorly known in much of western North America. We conducted morphological studies on 201 conifer cones and cone fragments recovered from Pleistocene sediments at the Ziegler Reservoir fossil site (2705m) near Snowmass Village, Colorado. The basin, formed ~155–130ka, contains fossil-bearing lacustrine, palustrine, and colluvial sediments spanning approximately 85ka. Using a suite of morphological characters, particularly cone-scale bracts, we differentiated species of Abies, Picea, and Pseudotsuga. All fossil Abies specimens were assignable based on bract morphology to Abies concolor, which is currently absent from central Colorado (nearest populations are 160km southwest of the site). A. concolor occurs only in sediments of MIS 5d and 5c. Pseudotsuga menziesii and Picea engelmannii cones occurred in sediments corresponding to MIS 5e, 5d, 5c, and 5a. A fourth conifer species, occurring in sediments of MIS 5e, 5d, 5c, and 5a, is difficult to assign to any extant species. Bract morphology is similar to Picea pungens, which grows near the site today, but scale morphology is unlike P. pungens. These fossils may represent ancestral P. pungens, an extinct variant, or an extinct sister species.