PP33D-01
Holocene Moisture Variations and Atmospheric Circulation Controls in the Qaidam Basin, Northwest China
Regional climates in NW China are controlled by the interplay between the Asian summer monsoon, extratropical westerly circulation, and the topography of the Tibetan Plateau. Here we present sedimentary evidence from three lake basins in the Qaidam Basin on the NE Tibetan Plateau to investigate variations in effective moisture and their possible connection with changes in atmospheric circulation during the Holocene. The climate history derived from multiple proxy data of two cores from Hurleg Lake, including lithology, pollen, calcite isotopes, and ostracode isotopes and trace elements, indicates a dry climate at 11-9 ka (calibrated ages), a wettest climate at 9-8 ka (including evidence of laminated sediments), a highly variable and dry mid-Holocene, and a wet climate after 3 ka. This moisture pattern appears to be out of phase with that expected from Holocene monsoon history, including the record from Qinghai Lake (250 km east of our study sites), and with other records in westerly- dominated region. We attribute this spatially-contrasting pattern to secondary vertical circulation dynamics as modulated by insolation and topography. In particular, the intense heating and uplifting of air over the Tibetan Plateau accompanied by dry subsiding air in the surrounding areas, including the Qaidam Basin, are a likely explanation for the out-of-phase relationship, as high summer insolation would cause strong monsoon in SE China and on the Tibetan Plateau, but at the same time strong subsiding air and dry climate in the surrounding regions. Also, we speculate that a threshold response to slow changes in insolation during the Holocene might have caused shifts in the relative dominance of these competing controlling factors, that is, direct monsoon precipitation, westerlies, and topography-induced subsiding air motion. This shifting dominance might explain the changes in phasing relationship at 8 ka and 6 ka between the Qaidam Basin, the westerly region and monsoonal region.
PP33D-02
Lateglacial-Holocene Environment History, Kazakhstan
Kazakhstan is located in central Asia between Caspian Sea and Tiang-Shang Mountains. Few well dated holocene sequences from the forest-steppe and steppe belt of Kazakhstan provided information about the vegetation and climate history. Mokhovoe mire was studied in the watershed of Tobol and Ubagan rivers. That's the most thick peat mire in northern Kazakhstan. Sedimentation in the Mokhovoe sequence started ca. 7800 BP. At that time regional vegetation was represented by steppes and birch-poplar forests. Pine penetrated in the Tobol region likely between 6500 and 6000 BP. Pine grew on sand terraces of Tobol River together with birch. At 3000-2900 BP Tilia, Quercus, Ulmus grew in north-west Kazakhstan.The general structure of vegetation was the same as at 6500-6000 BP. At 1900-1500 BP climate became less continental and pine forests with pure pine canopy expanded on sandy terraces of Tobol and Ubagan rivers. Soon after 1500 BP broad-leaved trees were extinct from the regional forests. Pashennoe lake is located in Karkaralinsk mountains in the most elevated part in the south-east part of the Kazakhstan lowhills. Dry grass-wormwood and wormwood steppes were spread in the region at 10500-8200 BP. Picea obovata and Hippophäe rhamnoides occurred in protected parts in intermountain valleys of Karkaralinsk mountains. Salix and Betula also occurred in valleys. Between 8000 and 6000 BP forest vegetation in Karkaralinsk mountains was represented by birch forests. Pine penetrated to Karkaralinsk mountains between 6000 and 5500 BP, but it didn't formed large forests. At the same time the maximal spread of Alnus glutinosa was reconstructed. The general structure of regional vegetation was stable up to. At 1500 BP pure pine forests expanded over Karkaralinsk mountains and around Pashennoe lake. Few lakes were investigated in Borovoe mountains in south of Kokchetav region of Kazakhstan. In early Holocene birch forests dominated in regional vegetation. Pine expanded in Borovoe at ca 7000 BP. Pine forests have been dominating in regional vegetation since 5300-5200 BP. The section of lake-bog sediment of Ozerki mire in the Irtysh river valley represents the history of vegetation and climate in southern margin of the West Siberian Lowland since 14,000 BP. Dry cold steppes grew in the Irtysh valley at 14,000 BP. Picea obovata and Hippophäe rhamnoides occurred in the Irtysh valley together with Betula and Salix. Climate became slightly warmer between 12,000 and 9500 BP. After 9500 BP Picea was extinct in the Irtysh valley and regional vegetation was represented by dry steppes and birch forests with willows near streams and lakes. At 6300-6200 BP pine penetrated to the Irtysh valley around Ozerki. Pure pine forests have been dominating in the Ozerki region since 5500 BP and the general structure of regional vegetation is very similar to the modern one.
PP33D-03
Holocene climate and cultural changes in the Lake Baikal region
The results of a suite of numerical climate simulations are presented with an emphasis on regional climate change in the Lake Baikal region through the Holocene. The model simulations incorporate the documented changes in Earth's orbital parameters as well as changing atmospheric carbon dioxide levels recorded from an Antarctic ice core. In general, the climate of central Asia warms and dries through the Holocene, consistent with the rise in global carbon dioxide levels. However, the timing of the most rapid warming and drying phase is in the mid-Holocene, 7-000-6,000 calendar years before present, coincident with a cultural hiatus deduced from mortuary sites surrounding Lake Baikal. A number of independent proxy records from both central Asia and Mongolia show that the model simulations are in quite good agreement with the data. It is therefore possible that climatic change and the concomitant changes in vegetation recorded by the proxy data played a role in the cultural hiatus. Migration of people from south to north at this time, as determined from mitochondrial DNA, is discussed in the context of a changing climate.
PP33D-04
Ice-core Evidence of Holocene Climatic and Environmental Variations Across Tibet
Since 1984 The Ohio State University, in collaboration with the Lanzhou Institute of Glaciology and Geocryology and more recently the Institute for Tibetan Plateau Research, has recovered ice cores from a number of ice fields across Tibet. The Guliya ice cap is located in the western Kunlun Mountains while the Dasuopu and Naimona`nyi ice fields are located in the Himalayas to the south. The Puruogangri ice cap is in the Tanggula Mountains that are considered a boundary between the monsoon-dominated southern region and the continental-dominated northern region. All these ice core records are complete, except Naimona`nyi, which was drilled in late 2006. Dasuopu has a high annual accumulation rate (~1 meter water equivalent per year, or w.e. a-1) along with low soluble and insoluble aerosol content and a well-defined seasonal stratigraphy. The Guliya and Puruogangri cores are from more arid regions (0.20 - 0.40 m w.e. a-1), contain high concentrations of mineral dust and ionic species and a less distinct seasonal stratigraphy. The climate of the Tibetan Plateau also varies from west to east. The Guliya ice cap provided the longest ice core record recovered to date, extending through the last glacial cycle. This likely reflects the dominance of the continental westerlies in northwestern Tibet. On the other hand, the Puruogangri, Dasuopu and Naimona`nyi ice core records appear to be much younger and those ice fields may have formed during the Holocene "Optimum" when Northern Hemisphere insolation was high and forced a more active Indian/Asian monsoon circulation. Climate models indicate that sections of High Asia were much warmer in the early Holocene than in the Late Holocene; thus, it is possible that these glaciers did not exist prior to that time. Regional and local variations in climate will be presented, using a combination of stable isotopes, soluble and insoluble aerosol concentrations, and physical stratigraphy. Special emphasis is placed on the last 2000 years when the dating control is more robust. The Holocene records from Dasuopu, Puruogangri and Guliya reflect regional variations in climate, but also display large-scale similarities over decadal and centennial time scales. For example, although the warming trend of the twentieth century is present in all the records, it is more pronounced in the Himalayan ice cores than in those from the Western Kunlun.
PP33D-05
Cultures and Climate: A Review of the Cultural Chronologies and Climate Sequences for Inner Asia.
While environmental determinism has fallen out of intellectual favor in archaeology, the role of climate change as a catalyst in cultural change is still debated in Anglo-American archaeology. Climate change is often seen as a trigger for cultural changes, accentuating trends already under way. In other cases, climate change is often seen as the primary driving force for cultural change. The purpose of this paper is to look at the absolute chronologies for the post-glacial, archaeological cultures in the Lake Hovsgol drainage of northern Mongolia, Lake Baikal in Siberia, and in the Altai-Sayan Mountains. In the case of northern Mongolia, a variety of dates for recently excavated archaeological sites in the Egiin Gol valley of northern Mongolia will be presented. The radiocarbon dates indicate that there is a shift in the burial/settlement patterns from the Bronze Age and Early Iron Age (pre-500 BC) to the Xiong-nu confederacy (200 BC?-AD 200). For the Bronze Age and Early Iron Age, burial sites and monumental architecture was found in the tributaries of the Egiin Gol river; in areas considered by current herders as being winter pasture areas. For the suceeding Xiong- nu period, settlements and cemeteries are in the flood plain of the Egiin Gol river. After the collapse of the Xiong- nu confederacy, burial/settlement shifts back to the tributaries of the Egiin Gol river. In the case of the Altai-Sayan, it is clear that a nomadic lifestyle based on horse nomadism is in place by 600 BC. The radiocarbon dates for the Kitoi, Serevo, and Glazkovo cultures of the Baikal basin will also be discussed. In all three cases, the dates for the archaeological cultures will be compared to the absolute dates for the climate sequences of these three areas. While the radiocarbon dates for the archaeological cultures may be problematic, the general trend is that cultural changes/trends precede climatic changes.
PP33D-06
Holocene Lake Productivity and Inferred Climate Histories From High-Altitude Sites Within the Baroon Taiga Mountains, Northern Mongolia
Diffuse reflectance spectroscopy, biogenic silica, and standard loss-on-ignition (LOI) analyses of radiocarbon- dated sediment core samples from Sanjin, Asgat, Ganbold, and Mustei Nuur provide a nearly 11,000 year history of aquatic productivity changes within lakes of the Baroon Taiga Mountains, northern Mongolia. Productivity within these lakes is most sensitive to temperature fluctuations because the catchments are small, nutrient poor, and located at relatively high elevations (greater than 2200 m) with very low annual average temperatures. Within the Mustei Nuur basin, long-term decreases in reflectance and LOI-inferred algal productivity follow orbitally-forced reductions in northern hemisphere solar insolation (i.e., energy receipt) after 8000 years before present (B.P.). Prior to 8000 years ago, enhanced algal productivity within the lake likely reflects increasing northern hemisphere temperature trends following late glacial conditions. Higher frequency (decadal to centennial-scale) changes in biogenic silica, organic matter, and reflectance-inferred algal pigment concentrations within the late Holocene sediment sequences of Sanjin, Asgat, and Ganbold Nuur are interpreted as representing aquatic productivity variations influenced by the length of the ice-free growing season and, by further inference, local temperature variations. Reduced productivity and inferred lower temperatures are documented between 300 and 100 years B.P., roughly coincident with the Little Ice Age, whereas warmer conditions existed from 900-1100 years B.P., and between (roughly) 100 years B.P. and the present. Inferred warming over the last century parallels instrumental data trends, numerous high-latitude (arctic) paleoenvironmental records, and several other notable northern hemisphere temperature reconstructions. Correlations between late Holocene reflectance, biogenic silica, and LOI-inferred aquatic productivity records from the Baroon Taiga alpine lakes and nearby temperature-sensitive tree-ring data sets further supports the inference that the sediment records are representative of regional temperature variations. http://www.pitt.edu/~mrosenme/central_asia.htm
PP33D-07
PRELIMINARY STUDIES OF THE RADIOCARBON RESERVOIR EFFECTS IN LAKE QINGHAI (CHINA) SEDIMENTS AND THEIR RELATIONSHIP TO IMPROVED GEOCHRONOLOGY OF LAKE QINGHAI.
A key part of any paleoclimatic reconstruction based on lake sediments is establishment of a firm geochronology for the cores. In order to determine the geochronological problems which might confront the Lake Qinghai project, we have undertaken a pilot study, to investigate the 14C reservoir effects in some cores already collected. Past studies have anticipated some of the potential concerns with radiocarbon dating of the lake sediments. Preliminary sediment trap studies were carried out in 1989 by the Institute for Saltwater Lake Studies (Xining) at a site near the Fishery village on the south shore of the lake, by Kelts et al., (1989). Subsequent studies (Henderson, 2004; Shen et al., 2005) indicated there are substantial apparent reservoir effects – with discordances between carbonate and organic material from the same horizons. A modern water sample collected by Jull (2003) also indicated there could be an input of old carbon. It appears there may be "old" carbon inputs to either the dissolved organic carbon (DOC) or dissolved inorganic carbon (DIC). Particulate matter has not been studied, and this also needs to be quantified. Jull (2003) also established that the surface water sample DIC was approximately 111 pMC in October 2003, which implies a residence time of DIC of about 10 years. Recently, Yu et al. (2007) proposed a two-box model to explain the reservoir ages observed previously of ~1100 14C yr BP (derived from Henderson, 2004) and Shen Ji et al (2003) arrived a similar average value of 1039 14C yr BP. We have therefore undertaken a fresh study, using recently-collected short cores, to compare the radiocarbon reservoir effects in organic and inorganic fractions. Our results indicate that there is a variable component to the reservoir effect, suggesting that inputs to the lake are an important contribution to these effects. Better understanding of these effects is vital to an accurate geochronology of Lake Qinghai sediments.
PP33D-08
Holocence Climatic Changes in the Mongolian Plateau
This study compares lacustrine and nearby eolian sections at sites in the Southern and Northern Mongolian Plateaus in order to test spatial climate variability during the Holocene. Based on the lithology, proxy data, and 14C dated and the interpolated ages, following observations can be made. In the northern Mongolian Plateau best developed Holocene paleosol (Mollisol) dated at ~8,600-~7000 14C yr BP at the Shaamar section and the carbonate-rich laminated layer in the Gun Nuur lake core mark the interval of warmer and dryer climate (i.e., grassland domination) during the early Holocene (~8,300-~7400 14C yr BP). Younger paleosols at the Shaamar section and corresponding organic-rich layers in the Gun Nuur core were formed under distinctly cooler and more humid conditions. Minor soils (Entisols) and associated pollen assemblages indicate that the climate in the Northern Mongolian Plateau ameliorated four times during mid-late Holocene: (1) around 4800 14C yr BP, (2) around 3800 14C yr BP, and (3) around 3000 14C yr BP, and (4) during the past 1600 14C yr BP. The Baahar Nuur lake core in the Southern Mongolian Plateau and the Dingxi eolian section in the western part of the Western Chinese Loess Plateau appear to be supportive of the notion that prolonged interval of maximum humidity prevailed in this region during the early- and mid-Holocene (9,000-4,000 14C yr BP). The late Holocene at the Dingxi section consists of three paleosol-loess couplets and the three weakly developed paleosols (i.e., Entisols) were inferred to have been formed from ~3500 to ~3100 14C yr BP, from ~2900 to ~2400 14C yr BP, and from ~2000 to ~1000 14C yr BP, respectively. The lake-core proxy data indicate that the Holocene Climatic Optimum (equivalent to the highest productivity) in the Northern Mongolian Plateau occurred from ~6000 to ~1500 14C yr BP and the Climatic Optimum occurred in the Southern Mongolian Plateau and in the western part of the Chinese Plateau from ~9000 to ~4000 14C yr BP. This discrepancy implies that the concept of the Holocene Climatic Optimum has limitations and may have to be reconsidered if it is intended to have a large-scale connotation. We also notived that the climate appeared to have changed in cycles of ~1500 years in the North (comparable with those in North Atlantic) and tt appeared to have changed in cycles of ~1000 years in the South (comparable with those in the Santa Barbara basin--- needs to be further confirmed).