PP11B-0513
A 20 ka Fluvial Sediment Record From The Hajar Mountain Range, N-Oman, And Its Implication For Detecting Arid - Humid Periods On The Southeastern Arabian Peninsula
Fluvial sediments from the Hajar Mountain range in northern Oman (22.83°N, 59.00°E; 1,050 m asl) document variations of the paleoenvironmental and paleoclimate conditions over the last 20 ka. Based on high-resolution OSL dating, sedimentation rates were calculated and used as a proxy for paleorainfall. The results show that the Glacial to Lateglacial was characterized by arid conditions with a following transitional period of even less rainfall. At 10.5 ka, sedimentation rates increases abruptly, indicating the onset of the early Holocene humid period (EHHP). Rainfall reaches its maximum at 9-8 ka (EHHP-2) and a decreasing sedimentation rate after 8 ka characterizes the arid period of the middle to late Holocene. Variations of the hydrological regime are associated with the intensity of the boreal summer Indian monsoon and its related position of the ITCZ. For the onset of the EHHP, a rapid northerly shift of the ITCZ is postulated, thus confirming earlier results from the southern Arabian Peninsula.
PP11B-0514
Gulf of California Sediment and Proxy SST Records Suggest a Post 6 ka Development of the Arizona Monsoon and Solar Forcing of Cycles
Summer monsoonal rains in Arizona and adjacent areas are mainly due to pulses of moisture traveling northward up the Gulf of California (GOC). Modern studies reveal that northern GOC SSTs must exceed 26 deg. C before monsoonal rainfall develops in Arizona and western New Mexico, and over 80 percent of the rainfall in this region occurs after northern GOC SSTs exceed 28.5 deg. C. Warming of GOC occurs progressively from south to north in the late spring, as northwest winds, which dominate in the late fall to early spring, decrease in strength, and tropical waters penetrate northward along the western coast of the GOC. Sediment (CaCO3 and opal) and microfossil (diatom and silicoflagellate) proxies spanning the past 15,000 years from cores in the central GOC suggest that waters of the northern GOC were too cold between ca. 11 and 6 ka to allow development of monsoonal rains in Arizona. Evidence for a post 6 ka intensification of monsoonal rains in Arizona and adjacent areas includes: 1) increased frequency of arroyo cutting in Arizona after ca. 5 ka, 2) increased evidence of paleofloods in Arizona and SW Utah after ca. 6 ka, and 3) the renewal of aggradation of alluvial fans in the Mojave Dessert at ca. 6 ka after a lull in their formation between ca. 11 and 6 ka. Supportive pollen evidence includes : 1) the late Holocene appearance of summer flowering annuals and C-{4} grasses in SE Arizona, and 2) the post 6 ka appearance of a warm, mixed biome in the highlands of northwest Mexico. Other pollen evidence and the scarcity of early and middle Holocene packrat middens in the American southwest, however, have been cited as evidence of increased monsoonal rains during the early and middle parts of the Holocene It is likely that the Gulf of Mexico was the main source of monsoonal moisture in the American southwest prior to ca. 6 ka, especially in the regions east of Arizona. A northward displacement of the Intertropical Convergence Zone in the Caribbean prior to ca. 5.4 ka possibly led to increased advection of monsoonal moisture from the Gulf of Mexico. Marked increases in tropical diatoms (Azpeitia nodulifera) and silicoflagellates (Dictyocha aculeata) in the central GOC between ca.A.D. 940 and 1020 and again between ca. A.D. 1100 and 1140 argue for substantial warming of SSTs, implying that the Arizona Monsoon was enhanced during this part of the Medieval Climate Anomaly. Detailed study of GOC sediment records of the past 2,000 years suggests that solar variability drives long-term climatic cycles there. Increased opal and an upwelling flora, normally dominant between November and April when northwest winds blow down the GOC, correspond to intervals of solar minima; whereas increased CaCO3 and tropical microfossils, which are typical of the summer to early fall, coincide with solar maxima.
PP11B-0515
Marine and terrestrial climate changes at the northern Japan margin in the northwestern Pacific during the last 23,000 years
We investigated marine and terrestrial environmental changes at the northern Japan margin in the northwestern Pacific by analyzing biomarkers in Core GH02-1030 to clarify the climate linkage between the ocean and land. The UK"37-derived temperature record was characterized by cooling events at ~19.6 ka, ~15.8 ka (Oldest Dryas), ~12.1 ka (Younger Dryas) and ~10.1 ka, and the temperature drops were attributable to the southward displacement of the subarctic boundary, which presumably resulted from both the depressed North Pacific High and the enhanced Okhotsk High. Short-chain C14-C18 n-fatty acids, derived mainly from marine organisms, showed higher concentrations during the last deglaciation, reflecting an enhanced marine production caused by the stronger Aleutian Low. Abundance ratio of long-chain n-alkanes and long-chain n-fatty acids to lignin, which are indices of herb contribution, showed maxima at ~16 ka and ~11.5 ka, indicating the expansion of grassland in a cold and dry climate. Abundant lignin indicated a higher contribution of terrigenous organic matter during the last deglaciation, reflecting an enhanced coastal erosion of terrestrial soils due to sea level rise and/or an efficient inflow of higher plant debris to river waters during this period.
PP11B-0516
Influence of Convection and Water Budget on Isotopic Composition of Precipitation (Oxygen 18 and Deuterium) During the West African Monsoon: Analysis of Rainwater Samples Collected in Niger During the 2006 AMMA Campaign
The isotopic composition of precipitation (Deuterium and Oxygen 18) is a valuable tool to reconstruct past climate variability and to better understand present and past water cycle. To better constrain the climate-isotopes and water budget-isotopes relationships, which are still poorly understood and quantified in the Tropics, precipitation samples from convective systems have been collected in the Niamey area (Niger) during the 2006 monsoon, as part of the AMMA (African Monsoon Multidisciplinary Analaysis) campaign. Isotopic composition (deuterium and deuterium excess) of precipitation are discussed in regard to the large amount of available atmospheric data collected during this campaign. On the one hand, event-scale samples were collected all along the monsoon season (from June to September 2006). The isotopic composition of rainfall reveals an abrupt change after the onset of the monsoon. The isotopic composition also depends on the degree of organization and intensity of the systems, time-averaged large-scale convective activity and low-level relative humidity. We investigate the relative influence of local convective processes, regional convective activity and large scale circulation on intra-seasonal to seasonnal time scale. On the other hand, rainwater from convective systems passing over Niamey were sampled at high frequency (time step as low as 5 minutes). Since convective processes (condensation, precipitation evaporation) are spatially differentiated in organized systems such as squall lines, we use this infra-event data to investigate the influence of convective processes on water isotopes, which is essential to better understand the climate-isotopes relationship. We also discuss the possibility of using the isotopic composition of rainfall to better constrain the water budget of squall lines (rain evaporation in particular).
PP11B-0517
Assessing Palaeomonsoon Variability During the Late Quaternary Using Evidence From the Lake Sediment Archives of Yunnan Province, China
The acquisition of well distributed, high resolution records of Asian palaeomonsoon variability remains an outstanding issue (Wang et al 2005), particularly for high altitude sites in Southwestern China where our understanding of the regional climate as a whole is limited. This sub-region is climatically sensitive because it is in the convergence zone of the Indian, East Asian and Western North Pacific monsoon subsystems of the Asian Monsoon (Yihui and Chan 2005), delineated by the line of 105°E longitude, which runs along the eastern flank of the Tibetan Plateau (Wang et al 2003). Characterising the nature, timing and magnitude of southwestern monsoon variability facilitates further understanding of the possible socio-economic and environmental consequences that may result from climate change. This NERC-funded PhD research project (2005-8) focuses on a high altitude lake sediment core extracted from Lake Shudu, Yunnan Province, China, on the southeastern edge of the Tibetan Plateau. The project aims are to produce a detailed record of southwestern monsoon variability spanning the Late Quaternary, and to compare the results with other regional records in order to better understand monsoonal patterns across western China. The sediments are being analysed using a range of proxy measures including pollen, stable isotopes (δ13C) and lithological indicators (mineral magnetics, C/N, particle size and TOC). Bulk 14C AMS dates obtained for the seven metre core suggest that it represents the last ca. 22ka cal yr BP. Six clear phases of change have been identified in the lithological and carbon isotope records. Several notable shifts in the balance of arboreal and grass pollen also appear in the pollen record. It is suggested that the core records a history of dynamic changes, initially driven by changes in climatic conditions. However, in more recent times, changes in catchment vegetation and lithology point to increased catchment disturbance associated with the onset of anthropogenic activity. The results suggest that the core may represent one of the first high-resolution palaeoclimatic records spanning the Late Glacial Interstadial Transition (LGIT) and the Early Holocene for Southwestern China.
PP11B-0518
Planktic Foraminifer Fauna and SST Variations of the Eastern Equatorial Pacific During MIS 1- 6 and MIS 13-15 (ODP Site 1240)
Numerous mechanisms have been proposed to be responsible for the mid-Brunhes transition (MBT) (0.4-0.5 Ma), whereas how well these mechanisms explain tropical Pacific climate during the MBT remains unclear. To address the MBT paleocenaographic change in surface tropical Pacific, here we conduct high-resolution planktic foraminifer fauna and sea surface temperature (SST) analyses by using cores from ODP Site 1240 (eastern equatorial Pacific). Our study focuses on two intervals: Marine Isotope Stage (MIS) 13-15 and MIS 1-6. The planktic foraminifer analysis suggests that relatively higher abundance of Globorotalia menardii (+G. tumida), and lower abundances of Globigerina bulloides and G. inflata in MIS 13-15 in comparing those in MIS 1-6. Our fauna- based SST estimates also indicate that relatively higher SST by ~2 degree Celsius and smaller variation in MIS 13-15 than MIS1-6. The different fauna and SST patterns in MIS 13-15 and 1-6 suggests different hydrographic conditions and also possibly different mechanisms driving the hydrographic changes. Furthermore, comparing our record with a planktic foraminifer fauna record from the Caribbean Sea (ODP Site 999A) (Martinez et al., 2007), where surface ocean conditions are interpreted to be more influenced by seasonal upwelling plumes and/or eddy-mediated entrainment in MIS 14, we postulate that a large-scale climatic shifting that may involve a migration of Intertropical Convergence Zone and a change of trade wind patterns in the tropical Pacific is responsible for the contrasting surface ocean hydrographies. It is probable that further works to compare our records more globally for the MBT will result thorough evaluation on other processes such as the amplification by tropical ocean-atmosphere interaction and/or changes in the Atlantic thermohaline circulation that may also affect tropical Pacific cooling.
PP11B-0519
50,000-year Late Quaternary Biogenic Sedimentation, Sea Surface Temperature, and Land Erosion Records From the Southern Papua New Guinea (IMAGES MD052928)
We present 50,000-year late Quaternary records of carbonate and total organic carbon (TOC), TEX86-SST and Uk'37-SST, and Branched Isoprenoid Tetraether (BIT) from core MD052928 (11°17.26\'S, 148°51.60É, water depth: 2250m) taken from the southeastern Papua New Guinea slope during the PECTEN cruise in 2005. The age model of the core is constructed by AMS-14C dating of planktic foraminifers, benthic foraminifer oxygen isotope stratigraphy, and paleomagnetic intensity. We found that the carbonate and TOC contents showed glacial-interglacial variations. The carbonate contents range between 15%- 50%, with higher contents in the Holocene and lower in MIS (Marine Isotope Stage) 2-3. The carbonate contents also show high frequency oscillations that mimic millennial-scale climate changes during the last deglaciation and MIS 2-3. The carbonate contents correlate well with the BIT index measured from the same core. Low carbonate events coincide with BIT indices that indicate more inputs of terrestrial organic matters, suggesting noticeable changes of soil erosion and terrestrial fluvial input on land nearby. The TOC contents range between 0.2%-0.4%, and show higher contents during MIS 2-3. High TOC contents are associated with BIT indices that reflect higher input of terrestrial organic matters. We have also conducted sea surface temperature (SST) analyses by testing two proxies: glycerol dibiphytanyl glycerol tetraether membrane lipid composition of marine crenarchaeota (TEX86) and alkenone (Uk'37). While both proxies yield similar SST during the LGM (27-28° C), SST in the Holocene derived from TEX86 is 2° C higher than that derived from Uk'37(31° C vs 29° C). Our records suggest that higher input of terrestrial organic matter is coupled to intensified soil erosion during cold periods. Whether our records implicate global climate (Antarctic vs. Arctic) or regional processes (e.g. land precipitation, high mountain glacier expansion) remains to be further investigated.
PP11B-0520
High-resolution past environmental reconstruction in East Asia using annually laminated lake sediments of Lake Megata in northeastern Japan
37 m-long non-glacial varved sequences were taken from Ichi-no-Megata maar in Oga Peninsula, Akita, northern part of Japan. Ichi-no-Megata maar occupies 0.25 km2 with a maximum water depth of ca. 45.1 m. The shape of lake is a kettle-type basin and the deepest bottom basin is very flat. We took core samples (named IMG06 core) at the center of the lake in November to December in 2006. In order to take completely continuous maar sediment, we drilled three holes and take every sample from each hole which apart only few meters. In this drilling campaign, we can 37 m-long continuous maar sediment except thick volcanic deposits from 26.5 to 31.7m in core. The sedimentological feature of IMG06 core is dominated by thin lamination clay/silt from most top part up to 37 m with turbidites characterized upward fining structure. The SEM image observation of lamination reveals that sponge-like lamina consists of diatom assemblage against dark colored lamina consists of mixture of detritus minerals, clay minerals, and diatom. It means sponge-like lamina deposits during spring season, and later one deposits during another three seasons, and then these thin lamination of IMG06 core could be identified as annual lamination (varves). This interpretation is supported by the correlation of historic event as earthquake and tunnel construction. In this IMG06 core, six volcanic ashes are found and we have also analyzed radiocarbon dating from 38 horizons of the core to use leaf and seeds inter-bedded varves. As the results, the IMG06 core covers from 25,000 to 4,000 14C yr BP with stable sedimentation rates (0.71mm/year).
PP11B-0521
The Holocene Indian Summer Monsoon Variability Recorded in a Stalagmite From NE India.
South Asian economies depend on the timely onset of the Indian Summer Monsoon (ISM), but understanding of the ISM variability is incomplete, due to lack of information on past ISM. Our stalagmite is the first well-dated climate record from the heart of the ISM region spanning the past 11,000 years. The speleothem was collected from Krem Umsynrang Cave, located 825 m above sea level in NE India. This region is influenced by the ISM, with more than 75% of annual rainfall falling during the monsoon season. The chronology of the stalagmite is based on 36 U/Th multi-collector ICP MS dates. Our data reveal profound changes in ISM rainfall and moisture balance. A strong increase of the ISM between 11.4 and 9.3 kyr BP is followed by a gradual decline over the course of the Holocene. This may be best explained by a strong coupling between ISM and the Intertropical Convergence Zone (ITCZ), with a stronger ISM during a more northerly position of the ITCZ. This long-term trend is punctuated by centennial to multi- to sub-decadal events of a weaker ISM. The most pronounced events occurred at 10.7, 8.5-8.1, 7.4, 4.4-4.0, 3.5, 1.4, 0.3 kyr BP. The δ13C record is interpreted to reflect centennial to decadal changes in the drip rate of the stalagmite. δ13C fractionation during periods of higher drip rates (i.e. times of longer residence time of percolating water) correspond with periods of a weaker ISM as inferred from our δ18O record. Our record shows in great detail periods of weaker ISM. They provide new insights on the sensitivity of terrestrial climate archives on the Indian subcontinent. Drought events recorded in our stalagmite correspond well with intervals of severe aridity known from other regions of the Asian monsoon. Moreover, our 11,000 year climate record shows that NE India experienced its driest conditions during the last three millennia.
PP11B-0522
Pacific And Atlantic SST Influences On Medieval Drought In North America Simulated By Community Atmospheric Model
Terrestrial late Holocene proxy records suggest that during medieval times (800-1300 AD) North America experienced severe centennial-scale drought. In this study, the Community Atmospheric Model (CAM) is used to investigate the role of sea surface temperatures (SSTs) anomalies from the tropical Pacific and the North Atlantic Ocean on this mega-drought. These anomalies are obtained from proxy reconstructions of SST. Four model experiments with prescribed SST anomalies in the tropical Pacific and/or North Atlantic Ocean were made. The CAM results captured the major dry features that occurred during medieval times in North America. The cold tropical Pacific alone can simulate essentially the entire drought area extent, while the warm North Atlantic alone can simulate the drought in the High Plains and the western U.S. The two working together can explain the severity and longevity of the drought. During the spring and summer rainy season, each model experiment simulated less moisture transport to the High Plains and a 15-40% decrease in rainfall there. The model results also show that changes in North America monsoon are primarily due to SST anomalies in the Atlantic Ocean. The importance of the Atlantic Ocean on medieval drought in North America suggests that attention should be paid not only to the tropical Pacific Ocean, but also to the North Atlantic Ocean in understanding the North America drought variability and predictability, both at present and during the past.
PP11B-0523
Seasonal Turnabout of the Air-Sea Correlation in Mid-latitudes and Its Effects on the Baiu Frontal Activity
In mid-latitudes, a shallow mixed layer is formed on the seasonal thermocline from spring to summer. Since the mixed layer depth (MLD) represents thermal inertia of the upper ocean, the development of shallow mixed layer alternates the polarity of air-sea correlation seasonally. When the MLD is deep (winter), the upper ocean has a potential to force atmospheric variations, while, when the MLD is shallow (summer), atmospheric variations easily modify the thermal condition in the upper ocean. Seasonal anomalies of Baiu precipitation tend to reverse the sign from May to June in the western North Pacific. The turnabout is led by the development of seasonal shallow mixed layer along 20N and to the north. The positive sea surface temperature anomalies (SSTAs) in earlier months and surrounding regions where MLD is deep form the low-level convergence on regions with the shallow mixed layer, resulting in the stronger-(weaker-)than- normal frontal activity in May, which leaves the negative (positive) SSTAs under it. The negative (positive) SSTAs then lead to weak (strong) stability and decrease (increase) Baiu precipitation in June. In the following months, the weaker (stronger) Baiu activity yields positive (negative) SSTAs in the shallow mixed layer. Thus, the seasonal anomalies of Baiu precipitation reverse the sign from May to June.
PP11B-0524
Holocene oceanography and climate recorded in laminated sediments of the southern Gulf of California, Mexico
Alfonso Basin on the western side of the Gulf of California and Pescadero Basin on the center slope of the east side are basins which have sills or shoreward slopes in the Oxygen Minimum Zone and preserve laminations whose physical and geochemical characteristics yield information on climatic and oceanographic changes. Here primary productivity and sedimentation can be considered as an imperfect proxy of climate. Cores were sampled at 1 cm intervals to produce a record of organic carbon, carbonate, opal and terrigenous content and contained laminated, hemipelagic mud, accumulating at 25-50 cm/kyr. Major changes in sedimentation began at circa 7,200 YBP with major shifts occurring at 4,200 and 3,000 YBP and smaller changes at 1500, 950, and 400 YBP in both basins. A stepwise decrease in mass accumulation rates can be correlated to northern hemisphere summer insolation, and suggests stronger NW winds and decreasing rains. Biogenic records indicate a drop in productivity and terrigenous mud records a shift from wetter to dryer conditions. At 400 YBP a recovery suggests a return to wetter less windy conditions. Three general climatic periods are recognized. Spectral analysis shows a 1-2 kyr climate rhythm in the Gulf and the data suggest that it is mediated by the migration of the Intertropical Convergence Zone (ITCZ) due to orbital precession. The records are marked by strong climate-ocean variability cycles at about 88, 150, 200 and 350 years that appear related to latitudinal shifts of the ITCZ, produced by solar cycles. The variability in all of the sediment records increases after about 2 ka.
PP11B-0525
Century-Scale Trends in the Indian Summer Monsoon During the Last 2,000 Years
Reconstructions of the Indian Summer Monsoon over the past 2,000 years reveal abrupt changes from one century to the next. Persistence of these natural changes into the future would challenge societies that are adapted to a narrow range of climate variability. New paleoclimate records of the Indian Summer Monsoon winds over the past few thousand years were derived from Arabian Sea sediments, and we compared them with other records of the monsoon, including cave deposits from Oman and India, and pollen records from Sri Lanka to create a more complete picture of century scale trends. The monsoon winds were stronger, and the ITCZ located northward, during a warm interval sometimes termed the Medieval Warm Period. The monsoon winds were weaker, and the ITCZ located farther south during the Little Ice Age, when the northern latitudes were cooler. This study reveals a natural oscillation in the monsoon upon which future change might be superimposed, and also indicates a potential relationship between northern warming (induced by greenhouse gas accumulation), the monsoons, and the ITCZ.
PP11B-0526
Indonesian Throughflow and Australasian Monsoon Variability Over the Last two Glacial Cycles
The climate and hydrography of the tropical Indian Ocean are strongly influenced by the intensity and vertical profile of the Indonesian Throughflow (ITF) and seasonal changes in wind direction associated with the southward migration of the Intertropical Convergence Zone (ITCZ) during austral summer. We use a multiproxy approach to reconstruct monsoonal wind and circulation patterns along the NW Australian continental margin as well as changes in the vertical profile of the Indonesian Throughflow on glacial, precessional and suborbital timescales. Our records from the Timor Passage and Timor Sea (Sonne 185 and IMAGES WEPAMA cruises) closely track changes in the structure of the upper water column within one of the main outflow passages of the ITF. We use (1) XRF scanning records to reconstruct continental runoff and eolian dust transport, (2) paleoproductivity proxy data related to vertical mixing of the upper water column by monsoonal winds, (3) SST, SSS and mixed layer thickness estimates from combined oxygen isotope and Mg/Ca analyses of surface and thermocline dwelling planktonic foraminifers. XRF-scanner derived terrigenous flux and paleoproductivity fluctuations over the last 460 ky were strongly influenced by monsoonal wind patterns offshore NW Australia (23 and 19 ky), the position of the ITCZ (southward shift during precession minima) and were also modulated by sea-level related variations in the intensity of the ITF (100 ky). Our results indicate that the intensity of the Australian summer monsoon over the last two glacial cycles was controlled both by summer insolation over NW Australia and by the strength of the boreal winter monsoon, as the southward migration of the ITCZ is closely linked to northern hemisphere cooling. A comparison of water mass properties within the main outflow in the Timor Strait and within the mixing zone between ITF and eastern Indian Ocean waters reveals a higher thermocline temperature gradient between the eastern Indian Ocean and Timor Strait during glacials and stadials, implying a decrease in ITF thermocline flow. Centennial records spanning Terminations I and II reveal cooling and freshening of thermocline waters during the early part of MIS5e and early Holocene, indicating a change from surface to thermocline dominated ITF flow, when the ITCZ moves southward and Australian monsoon strengthens.
PP11B-0527
Rock magnetic records of Southeast Asian monsoon variability during the past 800 kyr
Rock magnetic investigations were carried out on a sedimentary core taken from the Ninety-east ridge, the eastern equatorial Indian Ocean in order to reconstruct the South Asia monsoon variability during the past 800 kyr. A 10.2 m long piston core ÃÂ・#8216;Ã・#8216;‚Â・#202;Ã・œMR0503 -PC3ÃÂ・#8216;Ã・#8216;‚Â・#202;ï 4;¿Â½ was recovered in August 2005 during the R/V Mirai MR0503 cruise. The core site is located in the western flank of the Ninety-east ridge (1Ã・¹Ã・¡13.2'N, 88Ã・¹Ã・¡26.0'E), and water depth is 4400 m. In order to develop an age model for the MR0503-PC3 core, a relative paleointensity record (NRM30mT/IRM30mT) obtained from the core is correlated with the global stack of relative paleointensity records ÃÂ・#8216;Ã・#8216;‚Â・#202;Ã・œSint- 800ÃÂ・#8216;Ã・#8216;‚Â・#202;½ (Guyodo and Valet, 1999). Based on the developed age model, the age of the bottom of the MR0503-PC3 core is ca. 800 ka and an average sedimentation rate is 1.3 cm/kyr. A suite of rock magnetic parameters (Magnetic Susceptibility, IRM, ARM, Mrs/Ms, and S-ratio) was obtained from discrete samples collected from the half-split of the core. Magnetic Susceptibility, IRM, and ARM are used as proxies for the magnetic mineral flux. Mrs/Ms and S-ratio are used as proxies for mean grain size and magnetic mineralogical parameter, respectively. The results show that a magnetic mineral flux increases during warmer periods, whereas the flux decreases during colder periods. On the other hand, magnetic grain size increases during colder periods and decreases during warmer periods. These indicate that a supply of fine-grained magnetite (or maghemite), probably originated to pedogenesis, increases during warmer periods, suggesting intense precipitation related to the South Asian summer monsoon. During MIS 15 to 11, stepwise increases of the magnetic mineral flux accompanied with sudden drops of S-ratios are recognized. The sudden drop of S-ratio is related to intense inputs of coarse-grained hematite and maghemite, probably originated to the chemical weathering of the Himalaya-Tibet plateau. This feature suggests that intensification of the South Asian monsoon from MIS 15 to 11. This intensification of the South Asia monsoon may be related to the climate shift during the mid-Brunhes epoch observed from several regions of the western Eurasia (e.g., Chinese Loess plateau and Baikal lake).
PP11B-0528
Enhanced Circulation of the Miocene Australian Monsoon System
Paleo-botanical studies in central Australia have revealed periods of distinct seasonality throughout the Tertiary, prior to existing monsoon sedimentary records. Despite advances in the mechanisms and timing of the Australian summer monsoon, its history has remained largely unconstrained. We use the National Center for Atmospheric Research (NCAR) Community Atmosphere Model (CAM) and Community Land Model (CLM) to simulate the middle Miocene and modern Australian monsoon. Results show that southward displacement of the Australian continent in the Miocene produces higher precipitation over the monsoon trough and decreased precipitation over northern Australia. Location of precipitation maxima, sea-level pressure minima and the monsoon shear line indicates that the monsoon trough has not moved markedly between the Miocene and present. Existence of larger and warmer seas north of Australia in the Miocene, in conjunction with a more intense monsoon trough, suggests that Australia's equator ward drift has had a dampening effect on monsoon trough intensity via reduced moisture availability. Drift of the Australian continent into the zone of influence of the monsoon trough challenges classic textbook theory that high insolation over the Australian land mass is a dominant driver of the monsoon. Existence of monsoon climates significantly older than the middle Miocene therefore would most likely be driven by a classical land-sea temperature gradient as opposed to a southward reaching Inter Tropical Convergence Zone.
PP11B-0529
The variation of monsoon precipitation in central China since last deglaciation
We analyzed two stalagmites (C996-1 and C996-2) collected from Jiuxian Cave in Zhashui County, Shaanxi Province, central China. Thirty-eight 230Th dating results shown that the stalagmite C996-1 continuously deposited through last 8.5 ka BP (before present) and C996-2 grew through last 19.0ka BP except two hiatuses between 5.7 and 8.3 ka BP, and 11.9 and 15.4 ka BP, respectively. Considering dating errors and resolution differences, the δ18O variation of these two stalagmites are similar during the intervals of contemporaneous growth. Moreover, Hendy tests show that these two stalagmites deposited under isotopic equilibrium conditions. It means that oxygen isotopic variations are primarily caused by climate change. We interpret our δ18O records in terms of summer monsoon precipitation changes, although the temperature might have some minor impacts, as it affects the δ18O of the precipitation during the winter season and the fractionation between deposited calcite and drip water. The δ18O records show notable changes within the LGM, resembling other East Asian monsoon records, such as those from Hulu and Dongge Caves, suggest that significant climatic variability occurred in monsoonal eastern Asia during the LGM interval. We compared our record to other precisely dated contemporaneous speleothem records from Hoti, Hulu, Heshang and Sanbao Caves. The increasing trend of the δ18O commenced as early as 7.5 ka BP in low latitude monsoonal area, i.e. Hoti Cave, while get later toward higher latitude such as 7.0 ka BP in Dongge Cave, 5.3 kaBP in Heshang Cave, 4.7 ka BP in Sanbao Cave and 4.3 ka BP in Jiuxian Cave. It suggested that the summer monsoon precipitation in East Asia may change asynchronously in central and eastern China in the Holocene, started to decrease at different times in different regions. The asynchronous precipitation changes may be related to the responses of a coupled tropical and subtropical monsoon system to the changes of the insolation as well as the differences in the thermal forcing which result from the complex topography.
PP11B-0530
Comparison of Meteorological Data and Stable Isotope Time Series from an Indonesian Stalagmite
In the last decade, geochemical records in stalagmites have been widely recognized as a powerful tool for the elucidation of paleoclimate/environment of the terrestrial areas. The previous data are mainly reported from middle latitude. However, this study aims at reconstructing past climate variations in the Asian equatorial regions by using oxygen and carbon isotope ratios recorded in Indonesian stalagmites. Especially, we focused on the comparison of meteorological data and stable isotope time series from an Indonesia stalagmite, in order to check whether the geochemistry of stalagmite is influenced by local precipitation. We performed geological surveys in Buniayu limestone caves, Sukabumi, West Java, Indonesia, and collected a series of stalagmites/stalactites and drip water samples. A stalagmite sample was observed using thin sections to identify banding. Moreover, to construct the age model of the stalagmite, we also measured both (1) the number of bands and (2) uranium series disequilibrium ages using the MC-ICP-MS. These data suggest that each layer is annual banding dominantly. Oxygen and carbon isotope ratios were analyzed on the stalagmite for annual time scales. The carbon isotope ratio has a clear correlation with oxygen isotope ratios. Furthermore, the proxy data was compared with meteorological data set in the past 80 years, showing a good correlation between the temporal variation of oxygen/carbon isotope ratios and annual precipitation. These lines of evidence suggest that the isotopic variation is predominantly caused by kinetic mass fractionation driven by the degassing of carbon dioxide in the cave.
PP11B-0531
A High-Resolution Magnetic Rrecord of Holocene Rainfall Variations from the Western Chinese Loess Plateau: Antiphase Behaviour of the African/Indian and East Asian Summer Monsoons.
Using magnetic and clastic grain size proxies, we make quantitative estimates of past changes in Holocene rainfall and also identify variations in winter monsoon intensity from a very well-dated, high-resolution sequence of loess and palaeosols, west of the Chinese Loess Plateau. Dating by optically stimulated luminescence shows that dust deposition has been quasi-continuous at this site throughout the Holocene, whilst the intensity of soil development has varied throughout the sequence, apparently unrelated to changes in sedimentation rate. As reconstructed using an independently calibrated magnetic susceptibility/rainfall climofunction, rainfall in this region has varied from ~ 75 to ~ 375 mm/yr, with summer monsoon maxima centred on 10.5 ka, 6.5 ka and 3.5 ka BP. Rainfall minima occurred at the mid-Holocene (~ 5.5 ka) and also at ~ 11.75 ka, 9 ka, 2 ka and 1.2 ka BP. Winter monsoon intensity has intensified from ~ 9 ka BP onwards, varying in its phase relationships with summer monsoon intensity. After ~ 2.25 ka BP, extreme climatic instability is indicated by both climate proxies. This Holocene rainfall record correlates with other records regionally, in the Loess Plateau and South China Sea. Notably, it demonstrates an anti-phase relationship with records of summer monsoon intensity from N. Africa, the Near East and western Tibet. This mismatch suggests that internal feedbacks in the SE Asian region, especially reduction in the land/sea surface temperature gradient, have acted to counter the effects of solar forcing. http://geography.lancs.ac.uk/cemp/publications/06Maher&Hu.pdf
PP11B-0532
Timing of the intensification of Australian Monsoon during the last two terminations recorded in the deep sea sediment core from Timor Sea.
Timing of the past variations of the monsoon is a key to understand low to mid latitude climate in the past. We therefore examined a sediment core MD05-2970 obtained from Timor Sea to understand the evolution of the Australian monsoon since previous works proposed much lesser Australian monsoon during the ice ages. Radiocarbon dates as well as oxygen isotope of the planktonic foraminifers indicates that the core covers last 220 kyr which enables us to compare the last two glacial-to-interglacial climatic terminations. Our planktonic foraminiferal oxygen isotopic compositions range from -1.0 permil for the last glacial maximum to -2.8 permil for the Holocene which is consistent with the record previously reported from nearby locations.(Spooner et al., 2005). The present study showed the similar structures of oxygen isotopes between the penultimate glacial maximum and the last interglacial. However the oxygen isotope record obtained from the Makasser Strait indicated - 1.0permil and -4.0 permil respectively for the last two glacial maxima and the interglacials (Visser et al., 2003). No differences in the SST between the two core sites are recognized and hence any discrepancies in the oxygen isotopes are attributable to changes in the oxygen isotopes of seawater due to the hydrological differences. Modern satellites based observations show that the sea surface salinity in Makasser Strait is reduced as much as 4 psu during the Austral summer due to the transportation of the fresher water from the Banda Sea by Austral summer monsoon(Gordon et al., 2003). This creates the salinity difference between the Makasser Strait and the Timor Sea. On the other hand no salinity differences between the two sites were observed during the Austral winter. Therefore Austral summer monsoon was not as strong as today to create salinity differences between the two during the glacial times. Time series analyses of the two oxygen isotope curves would tell us the inception of the intensified Austral monsoon and we will discuss the timing of the intensification of the Austral monsoon during the last deglaciation as well as penultimate deglaciation.
PP11B-0533
Lessons Learned From the Modern Monsoon Applied to Interpretation of Paleoclimate Records
Spatial correlations of modern climate records and a description of modern atmospheric dynamics in India and SE Asia illuminate differences between and within the Indian and SE Asian monsoon systems and may improve interpretation of paleoclimate records. Land-sea heating differences and tropical circulation lead to heavy rainfall during the Indian monsoon, whose onset is consistently in June, and whose strength depends on the length of the rainy season and the number of days of rain. The SE Asian monsoon, on the other hand, depends on both mid-latitude and subtropical dynamics. Interaction between the mid-latitude jet and the subtropical high appear to control onset and amounts of springtime rains in South China, shifting northward in summer to bring rains to northern China. Yearly and rainy season precipitation totals in Northern China (near Hulu cave), Southern China (near Dongge cave) and Eastern India are not well correlated. Thus, each paleoclimate record might only describe one part of a monsoon system. Furthermore, in principle, records that are spatially well-separated allow spatial variation within a monsoon system such as that in SE Asia to be interpreted from paleoclimate records. If, as has been suggested, oxygen isotope records from Hulu and Dongge caves record precipitation amount, we do not expect these two records to co-vary over short timescales. Modern temperature records at the two sites do correlate positively however, and short-term trends in oxygen isotope records may be expected to agree if the isotope signal is largely due to temperature variation. The lack of correlations in the oxygen isotope records at decadal to centennial time scales is consistent with the modern observational record. However at longer timescales, local Milankovitch forcing and global climate events appear to dominate the variability at both sites.
PP11B-0534
A Quantitative 80 ka-Long Rainfall Record for the Chinese Loess Plateau Using 10Be and Magnetic Susceptibility in Loess
We demonstrate a new method to derive quantitative paleo-rainfall estimates for continental interior regions using 10Be in loess. We apply this technique to derive an 80,000 year long rainfall record from the Chinese Loess Plateau. The key steps in this technique are to account for variations in 10Be flux that are due to magnetic field modulation of 10Be production rate, and to account for 10Be derived from recycled dust. Aside from these two factors, variations in 10Be flux are chiefly due to changes in wet precipitation rate. We calibrate the 10Be flux dependence on rainfall rate using 7Be concentrations in modern rainfall as a proxy. In three different 7Be vs. precipitation amount studies on three continents a similar linear relationship is found. Using the average slope in these studies we convert from 7Be to 10Be using the known 10Be/7Be flux ratio in modern tropospheric precipitation. The precipitation record we derive with this method is well correlated with the speleothem delta(18)O records from Dongge and Hulu caves in S.E. China, which are widely regarded as a robust record of Asian Monsoon intensity. Our record indicates extremely low rainfall for the LGM and marine isotope stage 4 (MIS4), with precipitation rising gradually out of MIS4 to near modern levels during MIS3. After circa 35 ka BP precipitation began a long decline culminating in a 5 ka long minima during the LGM ending at circa 20 ka BP. Precipitation then increased stepwise in dramatic fashion at ~20 ka, and again at 14.3 ka. Precipitation was constant or decreased slightly between 13-11ka, followed by another abrupt precipitation increase culminating in a Holocene maximum at 9 ka BP. Precipitation then dropped rapidly to a Holocene minimum at 5.8 ka BP followed by a modest rise to 4 ka then gentle decay and another small rise to the present during the late Holocene. Two large precipitation increases are observed in our record which are roughly coeval with melt-water pulses 1 & 2 suggesting a coupling between high and low latitude climate dynamics during the deglacial. The low frequency component of our precipitation record resembles summer (JJA) solar insolation curve for 30°N, except during MIS3, when it more strongly resembles the insolation differential between 30°N and 30°S. This can be understood in terms of two of the chief elements of monsoon forcing, land/sea temperature differential, and cross-hemispheric moisture transport linked to atmospheric pressure gradient forces associated with the Mascarene High over the SW subtropical Indian ocean.
PP11B-0535
Characteristics of Anomalous Precipitation Events over Eastern China during the Past Five Centuries
Characteristics of anomalous precipitation events during the past five centuries in North China (NC) and the middle-lower Yangtze River Valley (MLYRV) were investigated using the data network of dryness/wetness index (DWI) over eastern China. The high occurrence frequency of anomalous precipitation events mainly occurred at periods of high solar forcing, active volcanic eruption, and large anthropogenic forcing (the 20th century). Coherence and dipole were the two dominant modes in spatial patterns of anomalous precipitation events. Coherent floods dominated the 18th and 19th centuries, whereas coherent droughts occurred frequently in the 17th and 20th centuries. The dipole patterns of anomalous precipitation events were the most frequent in the 20th century. NC experienced more floods in the cold periods than warm periods. Both NC and the MLYRV experienced far fewer droughts and more floods in the warm 18th century when natural climate forcing dominated, and many more droughts in the 20th century when anthropogenic forcing dominated. Coherent drought was the only spatial pattern of precipitation significantly associated with explosive low-latitude volcanic eruptions. The increased coherent droughts and dipole patterns in the 20th century support the findings of previous modeling studies that the tropospheric aerosols and human-induced land cover changes play important roles in the changes of summer rainfall over eastern China.
PP11B-0536
Indian Ocean and Asian Monsoon Influences on Indonesian Drought: Climate Signals in Tree Rings and Corals
We investigate a tree-ring and coral-based reconstruction of the Palmer Drought Severity Index (PDSI) for Java, Indonesia that preserves a history of ENSO and Indian Ocean dipole (IOD) related extremes over recent centuries. Extreme Javan droughts correspond well to known ENSO and IOD events during this period. Although Java droughts typically show the expected association with El Nino-like conditions and failed Indian monsoons, others (mainly linked to positive IOD conditions) co-occur with a strengthened Indian monsoon, suggesting linkages between the monsoon, Indonesian drought and Indian Ocean climate variability. An index of Indian Ocean dipole sea surface temperatures (SSTs), when combined with Nino-3.4 SSTs, provides a more accurate model of Java drought than Nino-3.4 SSTs alone. This result has implications for forecasting rainfall and crop productivity in the western part of the country most influenced by Indian Ocean climate variability.