Phytoliths as quantitative indicators for the reconstruction of past environmental conditions in China II: palaeoenvironmental reconstruction in the Loess Plateau

Quantitative reconstruction of the climatic history of the Chinese Loess Plateau is important for understanding present and past environment and climate changes in the Northern Hemisphere. Here, we reconstructed mean annual temperature (MAT) and mean annual precipitation (MAP) trends during the last 136 ka based on the analysis of phytoliths from the Weinan loess section (34°24′N, 109°30′E) near the southern part of the Loess Plateau in northern China. The reconstructions have been carried out using a Chinese phytolith–climate calibration model based on weighted averaging partial least-squares regression. A series of cold and dry events, as indicated by the reconstructed MAT and MAP, are documented in the loess during the last glacial periods, which can be temporally correlated with the North Atlantic Heinrich events. Our MAT and MAP estimations show that the coldest and/or driest period occurred at the upper part of L2 unit (Late MIS 6), where MAT dropped to ca 4.4 °C and MAP to ca 100 mm. Two other prominent cold-dry periods occurred at lower Ll-5 (ca 77–62 ka) and L1-1 (ca 23–10.5 ka) where the MAT and MAP decreased to about 6.1–6.5 °C and 150–370 mm, respectively, ca 6.6–6.2 °C and 400–200 mm lower than today. However, the highest MAT (average 14.6 °C, max. 18.1 °C) and MAP (average 757 mm, max. 1000 mm) occurred at Sl interval (MIS 5). During the interstadial of L1-4–L1-2 (MIS 3) and during the Holocene warm-wet period, the MAT was about 1–2 °C and MAP 100–150 mm higher than today in the Weinan region. The well-dated MAT and MAP reconstructions from the Chinese Loess Plateau presented in this paper are the first quantitatively reconstructed proxy record of climatic changes at the glacial–interglacial timescale that is based on phytolith data. This study also reveals a causal link between climatic instability in the Atlantic Ocean and climate variability in the Chinese Loess Plateau.     

Age calibration of carbonate rind thickness in late Pleistocene soils for surficial deposit age estimation, Southwest USA

Carbonate rinds have been used for cross-correlation of landforms as well as a quantitative indicator of soil age. Using the measured rind thickness of clasts found within a deposit, whose age has been independently determined, allows the construction of a calibrated surface-age proxy. Measurements were taken at sites within the Mojave Desert, the northwestern Sonoran Desert, the southern Great Basin, and the western Colorado Plateau. These sites are all within about 300 km of the intersection of the borders of the states of California, Arizona, and Nevada. In the study area, elevation varied from 200 to 1200 m, MAP was from 95 to 195 mm, and MAT was from 18.4° to 23.3°C. The calibrated proxy, while not accounting for the effects of parent material or climate on rind development, does show a strong correlation (R² = 0.74, P < 0.05) between carbonate rind thickness and surface age for deposits of late to middle Pleistocene age. The calibrated chronosequence, rind thickness = 0.0889 + 0.0079 [surface age]), is in general valid over a large region of southwestern United States. This statistical relation suggests that parent material, climate, and elevation may not be as strong a control on carbonate accumulation as is age for younger soils.     

A high-resolution diatom-inferred palaeoconductivity and lake level record of the Aral Sea for the last 1600 yr

Formerly the world's fourth largest lake by area, the Aral Sea is presently undergoing extreme desiccation due to large-scale irrigation strategies implemented in the Soviet era. As part of the INTAS-funded CLIMAN project into Holocene climatic variability and the evolution of human settlement in the Aral Sea basin, fossil diatom assemblages contained within a sediment core obtained from the Aral Sea have been applied to a diatom-based inference model of conductivity (r² = 0.767, RMSEP = 0.469 log₁₀ μS cm^− 1). This has provided a high-resolution record of conductivity and lake level change over the last ca. 1600 yr. Three severe episodes of lake level regression are indicated at ca. AD 400, AD 1195–1355 and ca. AD 1780 to the present day. The first two regressions may be linked to the natural diversion of the Amu Darya away from the Aral Sea and the failure of cyclones formed in the Mediterranean to penetrate more continental regions. Human activity, however, and in particular the destruction of irrigation facilities are synchronous with these early regressions and contributed to the severity of the observed low stands.     

Modern pollen assemblages from surface lake sediments and their environmental implications on the southwestern Tibetan Plateau

The relationships amongst modern pollen assemblages, vegetation, climate and human activity are the basis for reconstructing palaeoenvironmental changes using pollen records. It is important to determine these relationships at regional scales due to the development of vegetation under different climatic conditions and human activities. In this paper, we report on an analysis of modern pollen assemblages of 31 surface lake samples from 31 lakes (one sample per lake) on the southwestern Tibetan Plateau where the knowledge of modern pollen and their relationships with vegetation, climate and human activities is insufficient. The region includes five vegetation zones: sub‐alpine shrub steppe, alpine steppe, alpine meadow and steppe ecotone, mountain desert and alpine desert. The lakes span a wide range of mean annual precipitation (50–500 mm) and mean annual temperature (?8 to 6 °C). Modern pollen assemblages from our samples mainly consist of herb taxa (Artemisia, Cyperaceae, Poaceae, Chenopodiaceae, etc.) and some tree taxa (Pinus, Fagaceae, Alnus, etc.). The results indicate that modern pollen assemblages are able to reflect the main vegetation distribution. Redundancy analysis for the main pollen types and environmental variables shows that precipitation is the leading factor that influences the pollen distribution in the study area with the first axis capturing 13.7% of the variance in the pollen data set. The Artemisia/Chenopodiaceae ratio is valid for separating the desert component (<2) from the steppe and other vegetation zones (>2) but is unable to distinguish moisture variations. The Artemisia/Cyperaceae ratio is able to identify meadows (<1) and steppes (>1) and can be used as a moisture index on the southwestern Tibetan Plateau. Our results show that an appropriate range is needed for a modern pollen data set in order to perform pollen‐based quantitative climate reconstructions in one region. It is essential to perform modern studies before using pollen ratios to reconstruct palaeovegetation and palaeoclimate at a regional scale.     

Quantitative reconstruction of Holocene precipitation changes in southern Patagonia

Holocene variations in annual precipitation (P_ann) were reconstructed from pollen data from southern Argentinian Patagonia using a transfer function developed based on a weighted-averaging partial least squares (WA-PLS) regression. The pollen–climate calibration model consisted of 112 surface soil samples and 59 pollen types from the main vegetation units, and modern precipitation values obtained from a global climate database. The performance (r² = 0.517; RMSEP = 126 mm) of the model was comparable or slightly lower than in other comparable pollen–climate models. Fossil pollen data were obtained from a sediment core from Cerro Frias site (50°24'S, 72°42'W) located at the forest-steppe ecotone. Reconstructed P_ann values of about 200 mm suggest dry conditions during the Pleistocene–Holocene transition (12,500–10,500 cal yr BP). P_ann values were about 300–350 mm from 10,500 to 8000 cal yr BP and increased to 400–500 mm between 8000 and 1000 cal yr BP. An abrupt decrease in P_ann at about 1000 cal yr BP was associated with a Nothofagus decline. The reconstructed P_ann suggests a weakening and southward shift of the westerlies during the early Holocene and intensification, with no major latitudinal shifts, during the mid-Holocene at high latitudes in southern Patagonia.     

Environmental controls on bacterial tetraether membrane lipid distribution in soils

Over the last years a novel group of branched glycerol dialkyl glycerol tetraether (GDGT) membrane lipids has been discovered in peat bogs and soils. They consist of components with 4-6 methyl groups attached to the n-alkyl chains and 0 to 2 cyclopentyl moieties in the alkyl chain. These branched membrane lipids are produced by an as yet unknown group of anaerobic soil bacteria. In this study we analysed the branched membrane lipid content of 134 soil samples from 90 globally distributed locations to study the environmental factors controlling the relative distribution of the different branched GDGT isomers. Our results show that the relative amount of cyclopentyl moieties, expressed in the cyclisation ratio of branched tetraethers (CBT), is primarily related to the pH of the soil (R² = 0.70) and not to temperature (R² = 0.03). The relative amount of methyl branches, expressed in the methylation index of branched tetraethers (MBT), is positively correlated with the annual mean air temperature (MAT) (R² = 0.62) and, to a lesser extent, negatively correlated with the pH of the soil (R² = 0.37). If both parameters are combined, however, it appears that the variation in the MBT is largely explained by both MAT and pH (R² = 0.82). These results suggest that the relative distribution of soil-derived GDGT membrane lipids can be used in palaeoenvironmental studies to estimate past annual MAT and soil pH.     

Late Holocene vegetation and climate oscillations in the Qaidam Basin of the northeastern Tibetan Plateau

Pollen evidence from sediment cores at Hurleg and Toson lakes in the Qaidam Basin was obtained to examine vegetation and climatic change in the northeastern Qinghai-Tibetan Plateau. The chronologies were controlled by ²¹⁰Pb and ¹³⁷Cs analysis and AMS ¹⁴C dating. Pollen assemblages from both lakes are dominated by Chenopodiaceae (∼ 40%), Artemisia (∼ 30-35%) and Poaceae (∼ 20-25%), with continued occurrence but low abundance of Nitraria, Ephedra, and Cyperaceae. Artemisia/Chenopodiaceae (A/C) pollen ratios from two lakes show coherent large oscillations at centennial timescale during the last 1000 yr. A/C ratios were high around AD 1170, 1270, 1450, 1700 and 1920, suggesting that the vegetation was more “steppe-like” under a relatively moist climate than that during the intervening periods. Wet-dry climate shifts at the two lakes (2800 m asl) are in opposite phases to precipitation changes derived from tree-ring records in the surrounding mountains (> 3700 m asl) and to pollen and snow accumulation records from Dunde ice core (5300 m asl), showing that a dry climate in the basin corresponds with a wet interval in the mountains, especially around AD 1600. This contrasting pattern implies that topography might have played an important role in mediating moisture changes at regional scale in this topographically complex region.     

Dependence of Near-Surface Magnetic Susceptibility on Dust Accumulation Rate and Precipitation on the Chinese Loess Plateau

Magnetic susceptibility (MS) of surface sediment varies systematically across the Loess Plateau in central China, decreasing exponentially from >200×10⁻⁸ m³/kg at the northern margin of the Qinling Shan to ≤30×10⁻⁸ m³/kg near the southern margin of the Mu Us Desert. MS correlates highly with loess median grain size (r²=0.79), which decreases south-southeastward across the plateau. It also correlates with mean annual temperature (MAT) and mean annual precipitation (MAP) (r²=0.58 and 0.60, respectively), and with their product MAT×MAP (r²=0.83), which is considered a measure of potential pedogenic activity. Because regional isopleths depicting grain size and the primary meteorological parameters are nearly parallel, it is difficult to determine their relative influence on MS. A simple MS model, based on the observed spatial variation in loess thickness, permits quantitative assessment of the effect of the dust accumulation rate on the MS signal of surface sediment and isolates the likely role of climate in the production of magnetic minerals. The model suggests that 84% of the loess MS variance is dictated by the diluting effect of dust and 10–11% is associated with meteorological factors, primarily precipitation. The observed and modeled relationships support hypotheses that attribute variations in MS in the loess-paleosol succession to varying rates of dust deposition and in situ production of magnetic minerals in the accretionary soils, both of which are controlled by monsoon climate.     

Pollen assemblages and their environmental implications in the Qaidam Basin,NW China

The Qaidam Basin is one of the most sensitive areas to climate change in China, owing to its unique geographical position and ecological condition. In this study, 32 surface‐soil pollen samples were collected to reveal the relationship between modern pollen assemblages, vegetation and precipitation in the eastern region of the Qaidam Basin. The results show that Chenopodiaceae (3.8–87%, average 48%), Artemisia (1.7–64.2%, average 17.5%) and Ephedra (0–90%, average 16.3%) are the dominant pollen types in all samples, and that different pollen assemblages correspond to different vegetation types. DCA and CCA of major pollen types demonstrate that precipitation is an important factor in the control of the distribution of vegetation in the study area. The content and concentration of the three major pollen types (Artemisia, Chenopodiaceae and Ephedra) change with the mean annual precipitation, and the optimum mean annual precipitation for Ephedra, Chenopodiaceae and Artemisia is <80, 80–200 and >160 mm, respectively. Correlation analysis between the variation in grain size of the three major pollen types and the main environmental variables shows that the grain size of the three pollen types is positively correlated with precipitation in the Qaidam Basin. The results confirm that precipitation is the most important environmental factor in the Qaidam Basin, and that it has an important effect on pollen grain size in the study area.     

Variation in foliar δN among oriental oak (Quercus variabilis) stands over eastern China: Patterns and interactions

The patterns of variation in natural abundance of foliar and soil (¹⁵N) (expressed as δ¹⁵N) related to geographical and climatic variables frequently vary over plant species or plant function groups. It is essential to identify the pattern of foliar δ¹⁵N for specific plant species which has a widespread distribution and to explore the underlying mechanisms in the context of environmental change such as global warming and anthropogenic nitrogen deposition. Oriental oak (Quercus variabilis Bl.), characterized by cork bark, is a widely distributing deciduous broadleaf tree species that can be found in temperate and subtropical areas of East Asia. In this study, the variations in foliar and soil ¹⁵N were investigated based on the data of leaf and soil samples collected in 22 stands over eastern China (from 24 to 41° N in latitude and 102 to 123° E in longitude), and the mechanisms were discussed. The results showed that for oriental oak stands, mean foliar and soil δ¹⁵N were − 4.8‰ and 2.0‰, respectively, indicating an evident ¹⁵N enrichment in the soils. The average foliar δ¹⁵N value of oriental oak in warm temperate forest was significantly lower (p < 0.01), while a higher enrichment factor was also observed in temperate forests, than that in the subtropical areas. Over the eastern China, the foliar δ¹⁵N increased linearly and significantly with increasing mean annual precipitation (MAP) (R² = 0.481 and p < 0.001) and mean annual temperature (MAT) (R² = 0.285 and p = 0.01) and decreasing pH value of rain water (R² = 0.333 and p = 0.005). With these results in eastern China, there are great implications in understanding how nitrogen dynamics of ecosystems responds to warming, drought and acid rain.     

桦甸盆地始新世孢粉特征及其古气候指示意义

系统研究了桦甸盆地始新世植物孢粉的特征,并采用共存因子分析法定量重建该区始新世气候变化。通过详细鉴定和统计,桦甸盆地始新世桦甸组共鉴定出孢粉85属100种,以被子植物花粉占绝对优势,其中栎粉、椴粉、桤木粉和榆粉含量较高,裸子植物花粉和蕨类植物孢子含量较低,孢粉组合中热带-亚热带分子较多,但含量低于温带及亚热带,属北亚热带温暖湿润气候。通过共存分析获得的桦甸盆地始新世气候参数:年均温为13.6℃~18.4℃、最热月均温23.6℃~27.9℃、最冷月均温5.5℃~7.8℃、年降雨量887~1 206 mm、最湿月降雨量187~236 mm、最干月降雨量16~41mm、最温暖月降雨量45~143 mm。相比较于吉林东部珲春盆地始新世的孢粉植物群和古气候,差异不大,均属典型的温暖湿润的气候环境。     

Distribution of glycerol dialkyl glycerol tetraether lipids along an altitudinal transect on Mt. Xiangpi,NE Qinghai-Tibetan Plateau,China

The distribution of glycerol dialkyl glycerol tetraethers (GDGTs) can reflect continental environmental changes. Recently, the distribution of branched GDGTs (bGDGTs) has been proposed as a novel tool for paleoelevation reconstructions. Here we report the variation in TEX₈₆ (tetraether index of 86 carbon atoms) of isoprenoidal GDGTs (iGDGTs) and MBT (methylation of branched tetraether index) of bGDGTs along an altitudinal transect on Mt. Xiangpi, NE Qinghai-Tibetan Plateau. Both TEX₈₆ and MBT values of surface soils showed significant linear decreases with altitude (TEX₈₆: R² = 0.65; n = 50; MBT: R² = 0.69; n = 24). We suggest that the apparent relationships between the two indices and altitude may be related to temperature. Our preliminary investigation suggests that the TEX₈₆ index can potentially be applied as a paleoelevation indicator in addition to the MBT index on the Qinghai-Tibetan Plateau.     

Global calibration of a novel,branched GDGT-based soil pH proxy

Recently, 6-methyl branched glycerol dialkyl glycerol tetraethers (brGDGTs) were separated from 5-methyl brGDGTs, which are used in brGDGT-based proxies. Here we analyzed brGDGTs in 27 soil samples along the 400 mm isoline of mean annual precipitation in China by using tandem 2D liquid chromatography. The fractional abundance of 6-methyl brGDGTs showed a positive correlation with soil pH, while that of 5-methyl brGDGTs decreased with increasing soil pH. The abundance ratio of 6-/5-methyl brGDGTs, namely the isomerization of branched tetraethers (IBT), was calculated. The correlation of IBT with pH (pH = 6.33 − 1.28 × IBT; R² 0.89; root mean squared error, RMSE, 0.24) was much stronger than that of the traditionally used cyclization index of branched tetraethers (CBT) with pH (R² 0.52; RMSE 0.49) and comparable with that of CBT′ with pH (R² 0.88; RMSE 0.25). Compiling all available data from 319 soil samples resulted in a global calibration: pH = 6.53 − 1.55 × IBT (R² 0.72; RMSE 0.65), which has a better correlation than the CBT_5ME-pH proxy (R² 0.63; RMSE 0.78), but a weaker correlation than the CBT′-pH proxy (R² 0.85; RMSE 0.52). Our result suggests that the IBT is a promising indicator for soil pH, particularly in cases when some compounds in the CBT′ index cannot be determined.     

Holocene vegetation and climate histories in the eastern Tibetan Plateau: controls by insolation-driven temperature or monsoon-derived precipitation changes?

The climates on the eastern Tibetan Plateau are strongly influenced by direct insolation heating as well as monsoon-derived precipitation change. However, the moisture and temperature influences on regional vegetation and climate have not been well documented in paleoclimate studies. Here we present a well-dated and high-resolution loss-on-ignition, peat property and fossil pollen record over the last 10,000 years from a sedge-dominated fen peatland in the central Zoige Basin on the eastern Tibetan Plateau and discuss its ecological and climatic interpretations. Lithology results indicate that organic matter content is high at 60–80% between 10 and 3 ka (1 ka = 1000 cal yr BP) and shows large-magnitude fluctuations in the last 3000 years. Ash-free bulk density, as a proxy of peat decomposition and peatland surface moisture conditions, oscillates around a mean value of 0.1 g/cm³, with low values at 6.5–4.7 ka, reflecting a wet interval, and an increasing trend from 4.7 to 2 ka, suggesting a drying trend. The time-averaged mean carbon accumulation rates are 30.6 gC/m²/yr for the last 10,000 years, higher than that from many northern peatlands. Tree pollen (mainly from Picea), mostly reflecting temperature change in this alpine meadow-forest ecotonal region, has variable values (from 3 to 34%) during the early Holocene, reaches the peak value during the mid-Holocene at 6.5 ka, and then decreases until 2 ka. The combined peat property and pollen data indicate that a warm and wet climate prevailed in the mid-Holocene (6.5–4.7 ka), representing a monsoon maximum or “optimum climate” for the region. The timing is consistent with recent paleo-monsoon records from southern China and with the idea that the interplays of summer insolation and other extratropical large-scale boundary conditions, including sea-surface temperature and sea-level change, control regional climate. The cooling and drying trend since the mid-Holocene likely reflects the decrease in insolation heating and weakening of summer monsoons. Regional synthesis of five pollen records along a south–north transect indicates that this climate pattern can be recognized all across the eastern Tibetan Plateau. The peatland and vegetation changes in the late Holocene suggest complex and dramatic responses of these lowland and upland ecosystems to changes in temperature and moisture conditions and human activities.     

A lateglacial climatic reversion in hokkaido, Northeast Asia, inferred from the Larix pollen record

At present, Larix gmelini is a main component of taiga developed in north Sakhalin, northeast China and east Siberia. During the interval from ∼11.8 to 12.4 ka BP, pollen assemblages from north Hokkaido, Japan, are dominated by Larix. Pollen assemblages of this Lateglacial climatic reversal, known as the “Kenbuchi Stadial”, are similar to pollen assemblages from the Last Glacial Maximum in north Hokkaido. Vegetation of Hokkaido inferred from these pollen assemblages — open taiga composed of Larix gmelini, Pinus pumila and Picea jezoensis and/or Picea glehnii — may have been like that of north Sakhalin today. Comparison of these fossil pollen assemblages from Hokkaido with pollen assemblages from modern surface samples in Sakhalin suggests that ∼ 11.8 to 12.4 ka BP, temperatures relative to today were at least 9°C lower in January and 7°C lower in August, and that annual precipitation was at least 735 mm lower than present.     

Continental-scale patterns in modern wood cellulose δO: Implications for interpreting paleo-wood cellulose δO

The isotopic composition of ancient wood may be a useful archive of some climatic or geochemical conditions of the past, but presently there are many uncertainties that constrain such interpretations. We sampled naturally growing, predominantly native trees in forested regions of North America and the Caribbean to evaluate the strength of the relationships among cellulose δ¹⁸O (δ¹⁸O_cel), relative humidity (RH), precipitation δ¹⁸O (δ¹⁸O_ppt), and mean annual temperature (MAT) at the continental scale, and the general range of variability in δ¹⁸O_cel associated with site hydrologic conditions and species differences. We found up to 4‰ differences among different species growing at the same site, that conifer cellulose at a site is more enriched than angiosperm cellulose by 1.5‰ (p < 0.001), and that differences in landscape position, reflecting differing access to the water table, produced differences of <1‰ in δ¹⁸O_cel. At the continental scale, δ¹⁸O_cel was strongly influenced by modeled δ¹⁸O_ppt (R² = 0.80, p < 0.001). Average summer minimum RH (RH_min) combined with δ¹⁸O_ppt explained more of the variability (R² = 0.93, p < 0.001) in δ¹⁸O_cel across North American and Caribbean forests. MAT and δ¹⁸O_cel were also strongly correlated across North America (R = 0.91 and 0.95, p < 0.001, for angiosperms and conifers, respectively). The difference between δ¹⁸O_ppt and δ¹⁸O_cel is not constant (varying from 35-44‰) and is inversely correlated with δ¹⁸O_ppt. The relationships among δ¹⁸O_ppt, RH_min, δ¹⁸O_cel, and MAT established for North America and the Caribbean applied reasonably well when δ¹⁸O_cel was used to estimate MAT and δ¹⁸O_ppt in Asia, Europe, and South America, but there were important exceptions. The most accurate predictions of MAT and δ¹⁸O_ppt from δ¹⁸O_cel require RH_min. Predictions of δ¹⁸O_ppt and MAT made from δ¹⁸O_cel alone produced errors of up to 8‰ and 16 °C, respectively.     

Connection between South Mediterranean climate and North African atmospheric circulation during the last 50,000 yr BP North Atlantic cold events

High-resolution clay mineralogical analyses were performed on sediment deposited during the last 50,000 yr in the Alboran sea (ODP Site 976). The clay mineral record is compared with pollen assemblages and with annual precipitation (Pann) and mean temperatures of the coldest month (MTCO) reconstructed with the modern analog technique (MAT). Enhanced contribution of palygorskite, a typical wind-blown clay mineral, characterizes the North Atlantic cold climatic events. Coeval development of the semi-arid vegetation (Artemisia rich) associated with a drastic fall of reconstructed precipitations and temperatures, suggest cold and arid continental conditions in the West Mediterranean area during North Atlantic cold events. The clay mineral association, especially the palygorskite content and the illite-to-kaolinite ratio, indicate western Morocco as one of the major source of the clay-size fraction during the North Atlantic cold events. The maximum abundance of Artemisia associated with the presence of Argania pollen both indicate Morocco as the main origin for pollen during these cold periods. The comparison of these pollen and clay mineral-specific features allows us to pinpoint western Morocco as the dominant source of wind-blown particles during North Atlantic cold events. These specific mineralogical composition and palynological assemblages reveal enhanced aridity over North Africa and intensification of winds favouring dust erosion and transport from North Africa toward the Alboran Sea during the North Atlantic cold events. According to atmospheric models, such a meridian transport (1) likely results from the development of strong and stable anticyclonic conditions over the tropical Atlantic and North Africa, similar to today's summer meteorological configuration and (2) implies a northward position of the westerly winds during North Atlantic cold events. Finally the synoptic situation over the West Mediterranean during the North Atlantic cold events is compared with the North Atlantic Oscillation (NAO), suggesting that during the cold Atlantic events, weather regimes over Europe and North Africa may have been systematically shifted towards a positive NAO situation.     

Last glacial pollen record from Lanzhou (Northwestern China) and possible forcing mechanisms for the MIS 3 climate change in Middle to East Asia

The vegetation on the northeastern margin of the Tibetan Plateau is highly sensitive to climatic changes and thus represents a potentially interesting environmental archive. Pollen samples from the Fanjiaping Loess section in Lanzhou on the western Chinese Loess Plateau (CLP) were analyzed in conjunction with OSL dating. The results indicate that pollen zone B (60.6–46.0 ka, correlative to the early MIS 3) had the greatest abundances of Cupressaceae, Tsuga, Gramineae and Cyperaceae of the entire section, suggesting a warm phase during the last glacial period. These pollen taxa decreased significantly in abundance in the zones C (46.0–39.0 ka) and D (39.0–27.0 ka), reflecting a substantial climate cooling from the middle MIS 3 to MIS 2. These results correlate with climate records from the South China Sea, the CLP, Baikal Lake, North America, North Atlantic Ocean and other regions, and probably correspond with the decline of northern high-latitude insolation and the increase of global ice volume from 50 to 20 ka. In particular, arboreal pollen, fern spore and algae abundances declined sharply since ～40 ka, while shrub and herb pollen reached the highest abundances. Conifer pollen Picea and Abies abundance also rose markedly and increased up the section. This implies significant climate deterioration and likely corresponded with substantial growth of the polar ice sheets since ～40 ka. The decreasing temperature caused by an insolation decline during the last glacial period probably reinforced the cooling effect in a ‘snow/ice/albedo’ feedback, which would result in less climate sensitivity to radiative forcing. Meanwhile, vegetation decline in the Northern Hemisphere during the last glacial period and tundra development at high latitudes possibly caused additional cooling, enhancing the growth of polar ice sheets since 40 ka. The development of polar ice sheets increased the polar-to-equator temperature and pressure gradients, strengthening the westerlies and supplying plenty of moisture to Northwest China during 40–30 ka. Lake sediments developed widely on the Tibetan Plateau during 40–30 ka, probably related to an increase in the seasonality of middle-to-low latitude insolation which caused an enhancement of glacier melting on the Plateau.     

Hydrogeologic characteristics of groundwater aquifers in Kathmandu Valley,Nepal

This paper reviews, compiles and comprehensively analyzes spatial variations in hydrogeologic characteristics of shallow and deep groundwater aquifers in Kathmandu Valley. To estimate transmissivity (T) (and then hydraulic conductivity) as a function of specific capacity (SC), an empirical relationship between T and SC is developed for shallow and deep aquifer. The results show that T and SC are log linearly related by an equation T = 0.8857(SC)^1.1624 [R ² = 0.79] in shallow and T = 1.1402(SC)^1.0068 [R ² = 0.85] in deep aquifer. The estimated T ranges from 163 to 1,056 m²/day in shallow aquifer and 22.5 to 737 m²/day in deep aquifer. Finally, mapping of spatial distribution in hydrogeologic characteristics (thickness, T, hydraulic conductivity and storage coefficient) in shallow and deep aquifers are accomplished using ArcGIS9.2 and such maps would be useful in delineating potential areas for groundwater development and simulating groundwater flow in the aquifer system.     

Evidence from coleopteran assemblages for a short but intense cold interlude during the latter part of the MIS11 Interglacial from Quinton, West Midlands, UK

A sequence of fossiliferous organic sediments spanning the whole of an interglacial has been investigated from Quinton, near Birmingham, United Kingdom This interglacial can be correlated on palynological grounds with the Hoxnian Interglacial of England; equivalent to the Holsteinian Interglacial of central Europe and to Marine Isotope Stage 11. A pollen diagram and coleopteran spectrum were obtained from the same series of samples. By using the mutual climatic range method on the coleopteran assemblages, it has been possible to quantify the thermal climatic conditions at this time. They show clear evidence for a sudden and intense climatic oscillation during the late temperate stage of the interglacial—named the Quinton Cold Interlude. At this time mean temperatures of the warmest month (July) declined suddenly by at least 5 °C and mean temperatures of the coldest months (January and February) by more than 10 °C. Subsequently cool-temperate conditions returned. The pollen diagram through this interval shows little or no response to this climatic event. It is too early yet to generalise about the regional significance of the Quinton Cold Interlude but a similar climatic oscillation also occurs towards the closing stage of the MIS11 Interglacial at Hoxne, Norfolk, UK, suggesting that the cold interlude was at least regional in extent. A short climatic oscillation of similar intensity has also been interpreted from coleopteran evidence towards the end of the MIS13 Interglacial at Waverley Wood Farm Pit, Warwickshire, UK, indicating that such events may characterise the later stages of other interglacials. These severe climatic oscillations towards the end of interglacials may have relevance to our understanding of the closing phase of the present interglacial.