Abstract: Magnesium/calcium data from planktonic foraminifera in equatorial Pacific sediment cores demonstrate that tropical Pacific sea surface temperatures (SSTs) were 2.8° ± 0.7°C colder than the present at the last glacial maximum. Glacial-interglacial temperature differences as great as 5°C are observed over the last 450 thousand years. Changes in SST coincide with changes in Antarctic air temperature and precede changes in continental ice volume by about 3 thousand years, suggesting that tropical cooling played a major role in driving ice-age climate. Comparison of SST estimates from eastern and western sites indicates that the equatorial Pacific zonal SST gradient was similar or somewhat larger during glacial episodes. Extraction of a salinity proxy from the magnesium/calcium and oxygen isotope data indicates that transport of water vapor into the western Pacific was enhanced during glacial episodes.

Abstract: Ice-core measurements indicate that atmospheric CO2 concentrations during glacial periods were consistently about 80 parts per million lower than during interglacial periods. Previous explanations for this observation have typically had difficulty accounting for either the estimated glacial O2 concentrations in the deep sea, 13C/12C ratios in Antarctic surface waters, or the depth of calcite saturation; also lacking is an explanation for the strong link between atmospheric CO2 and Antarctic air temperature. There is growing evidence that the amount of deep water upwelling at low latitudes is significantly overestimated in most ocean general circulation models and simpler box models previously used to investigate this problem. Here we use a box model with deep-water upwelling confined to south of 55 degrees S to investigate the glacial-interglacial linkages between Antarctic air temperature and atmospheric CO2 variations. We suggest that low glacial atmospheric CO2 levels might result from reduced deep-water ventilation associated with either year-round Antarctic sea-ice coverage, or wintertime coverage combined with ice-induced stratification during the summer. The model presented here reproduces 67 parts per million of the observed glacial-interglacial CO2 difference, as a result of reduced air-sea gas exchange in the Antarctic region, and is generally consistent with the additional observational constraints.

Abstract: There is uncertainty about the interhemispheric timing of climatic changes during the last glacial-interglacial transition. Different hypotheses, relying on different lines of evidence, point variously to the Northern Hemisphere leading the Southern Hemisphere and vice versa, or to synchrony between the hemispheres. Southern South America is well placed to test the various alternatives using both glacial and palaeoecological evidence. We argue here from a synthesis of key proxy records that there was a sudden rise in temperature that initiated deglaciation sychronously over 16° of latitude at 14 600-14 300 14 C yr BP (17 500-17 150 cal. yr). There was a second step of warming in the Chilean Lake District at 13 000-12 700 14 Cy r BP (15 650-15 350 cal. yr), which saw temperatures rise to close to modern values. A third warming step, particularly clear in the south, occurred at ca. 10 000 14 C yr BP (11 400 cal. yr), the latter achieving Holocene levels of warmth. Following the initial warming, there was a lagged response in precipitation as the westerlies, after a delay of ca. 1600 yr, migrated from their northern glacial location to their present latitude, which was attained by 12 300 14 Cy r BP (14 300 cal. yr). The latitudinal contrasts in the timing of maximum precipitation are reflected in regional contrasts in vegetation change and in glacier behaviour. The large scale of a 80-km glacier advance in the Strait of Magellan at 12 700-10 300 14 C yr BP (15 350-12 250 cal. yr), which spans the Antarctic Cold Reversal and the Younger Dryas, was influenced by the return of the westerlies to southern latitudes. The delay in the migration of the westerlies coincides with the Heinrich 1 iceberg event in the North Atlantic. The suppressed global thermohaline circulation at the time may have affected sea-surface temperatures in the South Pacific, and the return of the westerlies to their present southerly latitude only followed ocean reorganisation to its present interglacial mode. Copyright © 2000 John Wiley & Sons, Ltd.

Abstract: The late Quaternary history of water-column denitrifcation of the eastern Pacific margins and the Arabian Sea is reconstructed using sedimentary δ15N measurements. The δ15N values in six piston cores raised from these regions show remarkably similar cyclic variations, being heavy (9–10.5‰) during the interglacials and 2–3‰ lighter during the glacials. This implies that denitrification in these regions decreased substantially during the glacial periods. The glacial decline in denitrification is attributed to reduced upwelling and flux of organic material through the oxygen minimum zone. Since water-column denitrification in these areas accounts for about half of the fixed-nitrogen loss in the modern ocean, the inferred decrease in denitrification should have increased the oceanic nitrate inventory during glacial periods. Because nitrate is a limiting nutrient, oceanic productivity and attendant changes in CO2 may therefore have been modulated on glacial-interglacial timescales by variations in the oceanic NO3 content.

Abstract: In the volcanic region of Velay (Massif Central, France), lake sediment sequences derived from maar craters situated close to one another (Ribains, Praclaux and Lac du Bouchet) have been correlated on the basis of tephrostratigraphical analyses. This has enabled the construction of a sequence (2980 pollen spectra) that begins during the glaciation preceding the Holsteinian and ends in the present. This sequence covers the period from 450 ka, i.e. from the end of marine oxygen isotope stage 12, to the present time, and includes five climatic cycles. The study of a second core from the Praclaux site completed the long Velay sequence. The biostratigraphy of the whole sequence is described in detail and illustrated by a synthetic and simplified pollen diagram. Thirteen temperate forest episodes (interglacials or interstadials) and as many cold periods (glacials or stadials) are defined. Each temperate episode is characterised by particular forest development and vegetation dynamics, and all of them, with the exception of the Holocene, begin and end with a Pinus forest. The vegetation dynamics observed during the Holocene resemble more closely those recorded during the interstadials than during the interglacials. Copyright © 2000 John Wiley & Sons, Ltd.

Abstract: Sequential variations in manganese (Mn) content and color of deepsea sediments retrieved from the Lomonosov Ridge (87°N) in the central Arctic Ocean apparently mimic low-latitude δ 18 O glacial-interglacial cyclicity, thereby providing stratigraphic information that together with biostratigraphic data permit the construction of a detailed chronological model. Correlation of this Mn and color chronology to established apparent Brunhes-age estimates of geomagnetic excursions reveals a remarkable fit between these two independently derived time scales. The Mn and color cycles probably provide paleoenvironmental information about material fluxes in the Arctic Ocean over the past 1 m.y. We suggest that the primary source for the observed manganese variations in our sediment core is northern Siberia, which has extensive peat bogs and boreal forests. These Siberian source areas could operate in an off and on mode tuned to Pleistocene glacial and interglacial periods. Contrasts in ventilation of Arctic Ocean waters during interglacial-glacial cycles probably could also enhance the observed Mn and color variability.

Abstract: The Qinghai–Tibet Plateau uplifted >3000 m in the Quaternary period The average rate of uplift was 1–11 mm/year The uplifting has remolded the geomorphology of China The landform in China was changed from west-low and east-high to west-high and east-low in three steps The Qinghai-Tibet Plateau uplift is an important factor that affected the climate and the environment of China in the Quaternary period It controls atmospheric circulation and climatic change in Asia and even the northern hemisphere, by dividing the westerlies into two branches: south and north The plateau gradually became a heat source in summer and a cold source in winter The uplift had a decisive effect on the formation of the East-Asia monsoon, which increased the climatic differences between the glacial period and the interglacial period The climate and environment of China are characterized by the influences of the plateau uplift The east of China became the south-east monsoon area, whereas the south-west became the south-west monsoon area and the north-west turned into an arid inland region The Gobi and large-scale deserts that formed in the inland basins are ceaselessly extending The climate of northern China became more arid as the Qinghai-Tibet Plateau continued to uplift The Plateau uplift affected glacial evolvement and loess formation, and propelled the migration of cold- and warm-blooded animals, which differed from other regions of the world at the same latitude

Abstract: On the basis of ice core and meteorological data from the Qinghai-Tibetan (Q-T) Plateau, this article focuses on the discussion of the problems related to the sensitivity of temporal and spatial changes of the climate in high-altitude regions, particularly in the Q-T Plateau. The features of abrupt climatic changes of the past 100 ka, 2 000 a and recent years indicate that the amplitude of these changes in the Q-T Plateau was obviously larger than that in low-altitude regions. The scope of temperature change above 6 000 m in the Q-T Plateau between glacial and interglacial stages could reach over 10°C, but only about 4°C in low-elevation regions close to sea level. During the last 2 000 a, the amplitude of temperature changes at Guliya (over 6 000 m a.s.l.) in the Q-T Plateau reached 7°C, in comparison with 2°C in eastern China at low altitude. In the present age, apparent differences of climatic warming have been observed in the Q-T Plateau, indicating that the warming in high-elevation regions is much higher than that in low-elevation regions. The temperature in over 3 500 m regions of the Q-T Plateau have been increasing at a rate of 0.25×101/a in recent 30 years, but almost no change has taken place in the regions below 500 m. Thus, we concluded that high-altitude regions are more sensitive to climatic changes than the low-altitude regions.

Abstract: Five deep-sea cores from the Arabian Sea, covering a time interval of 170 ky, were sampled at high resolution and analysed for major and trace elements. The stratigraphy of the cores was obtained by comparing the Ba/Al ratio with the SPECMAP data. This method is based on the close correlation between Ba concentrations (or Ba/Al ratios) and oxygen isotope ratios (δ18O) of foraminifera in Arabian Sea sediments. Ba/Al ratios, used as a productivity proxy, are variable but high in all deep-sea cores of the Arabian Sea, indicating a basin-wide influence of nutrient-rich water masses. Compared to glacial intervals the warmer periods are characterised by higher element/Al ratios of proxies, which are directly (Ba, Ca, Sr, P, i.e. hard parts of organisms) or indirectly (U, 230Thex) related to biological productivity. 230Thex provides evidence for intense boundary scavenging caused by high productivity due to enhanced upwelling and terrigenous input from the Indus fan. The Mn distribution in a core from the western Arabian Sea shows enrichments during interglacial periods and may indicate Mn export owing to the presence of a stronger oxygen-minimum zone. Several processes limit the applicability of proxies. Intercalated turbidites in the deep-sea cores can be identified by means of Si/Al, Ti/Al and Zr/Al ratios versus depth due to the enrichment of quartz, Ti-minerals and zircon in the basal layer. These elements are also important for the reconstruction of the history and extent of the eolian dust input. Diagenetic redistribution of redox sensitive elements occurs at the boundaries between turbidites and “normal” pelagic sedimentation and may mask or destroy primary signals.

Abstract: The δ15N of surface and down-core sediments spanning the last 20–200 kyr from the entire South China Sea (SCS) ranges only from ∼3.0 to ∼6.5‰, with no correlation with discernible paleoclimatic/oceanographic changes. Detailed profiles of the uppermost sediment column, including fluff samples, indicate a minor diagenetic overprint of 0.3–1.2‰ at the sediment-water interface. The absence of any correlation with reconstructed (glacial-interglacial) changes in primary production, terrigenous input, and/or sea level related basin configuration is attributed to a complete consumption of nitrate during primary production in this marginal basin during at least the last 140,000 years. This, in turn, implies that the δ15N of the nitrate used during primary production remained approximately constant during the last climatic cycle. The proposed scenario infers an unchanged nitrogen isotopic composition of the western Pacific subsurface nitrate between glacial and interglacial stages as well as during terminations and thus constrains proposed changes in the oceanic N inventory.

Abstract: Detailed analysis of shallow penetration single-channel seismic data, integrated with piston core data, reveals that the stratigraphic architecture on the Rhone shelf of the western Mediterranean Sea is characterized by a complex stratigraphy comprising both the regressive and transgressive parts of late Pleistocene depositional sequences. Several cycles of deposition are observed and are interpreted to be associated with fourth-or possibly fifth-order cycles of relative change of sea level. The regressive parts of the sequence are inferred to have been deposited either during late highstand or during periods of relative fall of sea level. These deposits are characterized, in some instances, by discrete downstepping wedges and internal downward shift surfaces; however, in other instances this evidence is not present. The transgressive parts of the depositional sequences are characterized by backstepping wedges and isolated sand bars. In general, these types of deposits are more common on the western part of the Rhone shelf and are largely absent on the extreme eastern part of the shelf. The transgressive deposits seem to be preferentially preserved at both inner and outer shelf locations and less so in the middle shelf. The exception to this is the area near the Rhone Delta depocenter, where transgressive deposits are observed across the entire shelf. Key surfaces separating stratigraphic units include ravinement surfaces, downlap surfaces, and subaerially formed erosional surfaces. These stratal discontinuity surfaces constitute the basis for analysis of the stratigraphic architecture. This area is dominated by seismic reflection geometries suggesting a high-energy depositional environment. Relatively steeply dipping seismic reflections bounded by horizontal to irregular erosional surfaces characterize most of the upper Pleistocene section in this area. The high-energy seismic facies correspond to three types of deposits: (1) thick regressive sands of lobate delta-front origin, (2) retrogradational beach barriers overlying the regressive wedge on the outer to middle shelf, and (3) late transgressive beach sands and ridges observed at the inner shelf. The stratigraphic complexity illustrated here is likely analogous to similar, although commonly undetected, complexity that characterizes petroleum fields in shallow-shelf settings. A variety of geomorphic elements have been interpreted here. These include transgressive sand bars, wave-dominated distributary mouth bars, recurved spits, isolated shelf edge shoreface/beaches, and distributary channels. These elements are consistent with an interpretation of a depositional environment characterized by wave-dominated delta deposition. The morphology of the delta in the eastern part of the shelf (i.e., near the depocenter) seems to be consistent from the outer to inner shelf location, suggesting that the position of the shoreline relative to the shelf edge and the presence of submerged shelf outboard of the shoreline had only minor impact on deltaic deposition; moreover, climatic change and changes of fluvial discharge that likely characterized this area during the End page 119 ---------------- late Pleistocene similarly had only minor effect on delta morphology.

Abstract: It has been established that loess deposited on the Chinese Loess Plateau was derived from arid and semi-arid regions in north and northwest China, but the specific pathways of dust transport are still not proved In this study, 32 loess–palaeosol profiles of the last glacial and interglacial periods were measured for magnetic susceptibility in order to investigate the dust transport pathways of dust input to the Loess Plateau The magnetic susceptibility variations of the loess–palaeosol deposits within the last glacial cycle can be correlated with marine oxygen isotope variations to estimate the ages of boundaries of the loess units and intercalated palaeosols The sedimentation rate of each depositional unit can be obtained by dividing the thickness by the time that it represents Because sedimentation rates decrease downwind from the dust source, the spatial distribution of dust sedimentation rates shows that northwest and west winds were the two most important agents for transport of dust to the Loess Plateau during the last glacial cycle The north and northeast winds played an almost negligible role In addition, topography and dust from local sources strongly affected the dust accumulation rates at some measured sites

Abstract: Opposing models have been proposed for last glacial paleoclimates in the Mediterranean area. To discriminate between the alternative models, we calculate variations in sediment yield within a high-resolution stratigraphic framework developed for the Alkyonides basin, central Greece. Latest Quaternary highstand deposits are distinguised from lowstand Lake Corinth deposits on the basis of seismic reflection data and micropaleontological and palynological analyses of drop cores. After depth conversion and calculation of solid sediment masses in successive time slices, sediment discharge rates during the last glacial lowstand interval (ca. 70-12 ka) are shown to have exceeded discharge rates during the preceeding interglacial highstand interval (ca. 128-70 ka) by =60%, implying enhanced seasonality during the glacial period, with cool, dry summer and wet winter conditions in the region. Sediment yield calculations can thus provide an empirical test of paleoclimate models and offer input to sequence stratigraphic models.

Abstract: An almost 50-m-deep core from the Weichselian Rhine–Meuse palaeovalley, near the present Dutch coast, reveals new insights into how this continental-scale fluvial system responded to relative sea-level fluctuations associated with the last Quaternary glaciations. A multidisciplinary study of this core included sedimentological and stratigraphic analysis augmented with data on shell, diatom and pollen content to infer depositional environments. Optically stimulated luminescence dating provides a first numerical chronostratigraphy for these strata. Net fluvial incision due to relative sea-level fall associated with the Weichselian glaciation (notably oxygen-isotope stage 4) is estimated at >10 m, and we argue that this amount of incision decreases both updip and downdip, because our study area is located near the thickest part of the Eemian/Early Weichselian (oxygen-isotope stage 5) highstand coastal prisms that were particularly sensitive to erosion during ensuing relative sea-level falls. Coastal prism geometry, with a relatively steep upper shoreface, is extremely important in promoting erosion, as demonstrated by the Rhine–Meuse system that borders an exceptionally wide, low-gradient continental shelf. Our results show that fluvial deposits associated with relative sea-level fall (80–40 ka) can constitute a considerable part of preserved strata (‘falling-stage systems tract’). Interglacial transgressive and highstand systems tracts tend to have a relatively low preservation potential; in our core these are represented by estuarine deposits scoured into underlying fluvial strata. Furthermore, we note that sequence boundaries in such settings may be relatively undistinct, whereas tidal ravinement surfaces can be more conspicuous and may represent considerably longer time gaps.

Abstract: Shells belonging to the bivalve genus Corbicula occur commonly in Pleistocene interglacial deposits in NW Europe. These have usually been identified as C. fluminalis, a modern species described from the Euphrates river, although the veracity of this specific attribution remains equivocal. Corbicula has nowadays a southern distribution, and laboratory studies indicate that it is thermophilous. It is also tolerant of brackish water, one of several attributes that make this an effective colonizer. In NW Europe, Corbicula is known from the Lower Pleistocene but is absent from the Cromerian Complex, occuring again in the three interglacials following the Anglian/Elsterian. It appears to be unknown from the last interglacial, except as derived fossils.

Abstract: We evaluated changes in temperature and precipitation associated with climate change, subsidence, and erosion on a chronosequence of sites across Hawaii. The sites range in age from 0.3 to 4100 ky, and the current temperature and precipitation are similar at all sites. Interpretations of fossil pollen records suggest that cooler, dryer conditions prevailed in windward Hawaii during the last glacial period. If the previous glacial periods were similar, the 20-, 150-, and 1400-ky-old sites would have spent 60% or more of their development under relatively cool and dry conditions, whereas the 0.3- and 2.1-ky-old sites have experienced only the warmer, wetter climate of the present interglacial. Subsidence and erosion have also affected the temperature and precipitation of these sites over time; in the past, some of them have been in the dry air above the trade wind inversion or in the lee of larger mountains. Combining these components of change, we estimate that the average temperature over the history of Pleistocene-aged sites (20, 150, and 1400 ky) was up to 2.2°C cooler and that the average precipitation was only about 50% of current values. Under current conditions, it would take only 230 ky for as much water to leach through the 1400-ky-old site as we calculate has leached over 1400 ky. Incorporating more reasonable assumptions about environmental history has the potential to allow more powerful interpretations of chronosequence data and thereby improve the predictive potential of models of soil and ecosystem development.