PP41A-1414
Millennial-Scale Events of Asian Monsoon Records From Three Caves in Southern China During the Last Glaciation
Three stalagmites from Sanbao (Hubei province), Wulu and Dashibao (Guizhou province) Caves, provide a ~25yr-resolution δ 18O sequence from 32.5 to 20.8 ka BP, based on 876 oxygen isotope and 25 230Th measurements. Despite a distance of ~1,000 kilometers among the three sites, the oxygen isotope records from the studied sites and Hulu Cave (Jiangsu province) are essentially similar during the contemporaneous growth periods. This suggests that changes in speleothem δ 18O over the large portion of China dominantly reflect regional precipitation isotopic pattern associated with large-scale atmospheric circulation, that in turn, indicating the summer Asian monsoon (AM) intensity during the last glaciation. Throughout the whole interval of our composite record, we identified five weak monsoon events, each lasting ~ 5 to 9 centuries, centered at 31.2, 30.1, 28.1, 25.7 and 24.2 ka BP. The two events correlate to the Heinrich Event 2 and 3, and the other three to the inter-Heinrich ice-rafting events in North Atlantic. The later events, evident in our records, provide strong evidence that North Atlantic climate and AM were tightly coupled via atmospheric circulation, possibly linked by westerly winds during Greenland stadials. Based on U/Th dating, the onset of IS4 Event was estimated about 29 ± 0.2 ka BP in our records, ~ 900yr younger than the Hulu record and very close to the NGRIP chronology (GICC05) based on multi- parameter counting of annual layers. Therefore, our records refine the timing, duration and transition of millennial-scale events and support the accuracy of NGRIP time scale. Furthermore, two shorter-term strong monsoon fluctuations behind IS5 and IS3, with negative excursion as large as ~ 0.8‰ in δ 18O, match well with the analogous Greenland temperature shifts. However, the transition from H2 to IS2 shows discernable discrepancies between Greenland temperature and AM. The monsoon transition revealed a sharp decline at about 24.3 ka BP, when δ 18O decreased by approximately 1.1‰ in 140yr, followed by a stepwise reestablishment of monsoon intensity into the IS2. The IS2 event was ambiguous in our high-resolution records. These differences suggest that some changes of AM were possibly influence by the effect of Eurasian snow cover under LGM condition.
PP41A-1415
Impact of North Atlantic Abrupt Cold Events on Monsoonal Phasing
The question of orbital-scale periodicity and phasing of tropical monsoon variations has developed as a long- standing problem, due to inconsistencies between modeling results and paleo-monsoon records. In contrast to modeling studies, which point to an in-phase relation of the Monsoon system with Northern Hemisphere peak summer insolation, reconstructions from marine sediment cores showed an extended lagged response of around 8000 years. On the other hand radiometrically dated East Asian Monsoon records derived from speleothems have been interpreted to be in-phase with July insolation. Here, we present a Bromine record with a centennial scale resolution from the northern Arabian Sea capturing variability of the Indian Monsoon over the past 450 000 years together with newly derived transient modeling results including global ice volume changes. Comparing our Indian Monsoon reconstruction with speleothem records of the East Asian monsoon shows consistent patterns and a common small phase lag (2 700 to 3 800 years) with respect to June (peak summer) insolation at the precession band. Our transient model results demonstrate that ice volume variability modulates amplitude but has no impact on the precessional phase relation. We argue that abrupt cooling events (Heinrich events) in the North Atlantic consistently lead the Northern Hemisphere peak summer insolation on average by 4 500 years and delay the onset of the summer monsoon during each precession cycle. This, in combination with nonlinear response to insolation of the proxy records, introduces a small phase lag during the late Pleistocene.
PP41A-1416
Synchronous decadal changes between Asian monsoon and Greenland climates during the last glacial maximum
An annually laminated stalagmite from Hulu Cave in Southern China grew for about 3000 years starting at 21345 aBP (±85 a) as determined by lamina counting and U-Th dating. The stalagmite δ 18O time series provides a continuous history of the Asian monsoon precipitation and δ 13C may reflect the soil biogenic production, which is linked to climatic factors such as temperature and humidity. The annual layer thickness (LT) from this stalagmite can not be regarded as a direct indicator of precipitation. LT and gray level (GL) may indicate the changes in the relative humidity of the cave environment. The δ 18O record with average 3.7-year resolution precisely anchored the timing of IS2 event which was well expressed in the Greenland ice core δ 18O records. The timing of IS2 in GISP2 is close to the chronology of the stalagmite records within the uncertainty of U/Th dates. Our record, in combination with the previously-published record between 17 and 15 kaBP also from Hulu Cave, indicated that the monsoon events (H1 and H2), in terms of their structure, are quite different from the cold events in North Atlantic, which were well presented in the Greenland ice core δ 18O records. For both of the H1 and H2, the monsoon precipitation records show a rapid transition from dry to wet conditions, followed by a stepwise increasing trend, with a total duration of more than 600 years. In contrast, the Greenland δ 18O records display abrupt changes either into or out of the events. The H98 δ 18O record shows a teleconnection between the density of East Asia monsoon and polar temperature on centennial to multi-decade scales during the LGM. However, the different structure of climatic events between the low and high latitude areas also suggests that changes of East Asian monsoon were triggered not only by the North Atlantic themorhaline circulation but also by some other factors. The coupled oceanic- atmospheric circulation from tropical Pacific may be a possible forcing, it may through ENSO-PDO influences the Asian monsoon rainfall on decadal scale during the LGM.
PP41A-1417
Oxygen Isotope Composition of Phytoliths From Australian Tropical Forests: Towards a New Paleoclimate Tool for the Tropical Pacific area
Obtaining new continental δ18Ophytolith records from the tropical pacific area would help to further investigate 1) synchronicity between vegetation and climate changes, and 2) climate interactions between ocean and continent through comparison with oceanic reference δ18O records. In this aim, we produce a calibration of the thermo-dependant relationship between δ18Ophytolith and δ18Orainfall for present phytolith assemblages from Queensland rainforests (Australia). Phytoliths were extracted from soil humic horizons sampled along several elevation, temperature and rainfall gradients. Phytolith samples of 1.6mg were analyzed using a newly calibrated IR-laser fluorination technique, performed after a controlled isotopic exchanged procedure. The long term reproducibility on δ18O measurements is < ±0.5‰ (1SD), that leads to an estimated uncertainty on δ18Ophytolith close to ±0.5‰ and fit in the precision required for inter-tropical paleo-environmental reconstructions. Globular granulate phytoliths, produced in the secondary xylem of dicots, account from 60 to 90% of the phytolith assemblages. As transpiration is non-significant in the wood, δ18Owood sap should equal to δ18Osoil water. Moreover, because relative humidity is close to 100%, soil evaporation is weak and δ18Osoil water is assumed to be similar to δ18Orainfall. The obtained thermo-dependant relationship between δ18Ophytolith and δ18O mean monthly rainfall of the wet season (r=0.68) is close to the equilibrium fractionation equations obtained for quartz and diatoms. Effects of forest fires on phytoliths dehydration and δ18Ophytolith are tested through heating experiments. Provided that phytolith assemblages present a morphological tropical forest pattern, δ18Ophytolith records from sediments can now be interpreted in term of δ18Osoil water, or δ18Orainfall (provided that no soil evaporation is assumed), and temperature changes. This is a first step in further investigating synchronicity between vegetation changes, global climate changes and ENSO activity in the West-Pacific area.
PP41A-1418
Multi-proxy Evidence of Australian Summer Monsoon Variability During the Holocene: Links to the East-Asian Monsoon and the North Atlantic
The Australian summer monsoon (ASM) is the dominant factor controlling rainfall variability and terrestrial productivity in northern Australia and the Indonesian archipelago. Understanding the mechanisms that influence its variability over different time-scales, and their teleconnections with other parts of the global climate system, has proven difficult because we lack high-resolution, precisely dated records of past monsoon behaviour. Linkages between the tropics and North Atlantic have been well documented north of the equator, but the degree to which these teleconnection patterns extend into the southern sub-equatorial tropics and their effects on the ASM are undocumented. We present a precisely dated, high-resolution oxygen isotope and trace element record of ASM variability from stalagmites located on Flores (east Indonesia) over the period 13 kyr B.P. to present. The multi-proxy records are constrained by over 30 TIMS and MC-ICP-MS U-series ages. The δ18O profile displays a gradual intensification of the ASM through the Holocene, which is in phase with precipitation changes in southern Brazil but antiphased with East Asian monsoon (EAM) intensity. The low frequency trend in the oxygen isotopes tracks changes in southern hemisphere summer insolation at 25° S located directly over the heat-low region of the Australian continent. Superimposed upon the δ18O trend are multi-decadal to centennial scale increased ASM events that occur concurrently (within dating errors) with periods of decreased EAM intensity and North Atlantic ice-rafting events. Thus, late-Pleistocene/Holocene cold events in the North Atlantic, related to reductions in the Atlantic meridional overturning circulation and variations in solar output, were associated with a southward migration of the ITCZ. While precessional forcing appears to be the dominant driver of ASM circulation over orbital time-scales, the high synchroneity between the Flores isotope variations and titanium (Ti) content of Chinese lake sediments suggests that the Asian winter monsoon (AWM) may have a more dominant influence at the secular scale. The Ti content of the lake sediment, which is used as a proxy for the strength of AWM winds, shows a strong inverse relationship with the detrended δ18O (Δδ18O) record, whereby periods of strong (weak) AWM intensity correspond with intervals of high (low) ASM precipitation. This result confirms previous suggestions that the Australian monsoon is largely controlled by a 'push-pull' relationship between the Australian-East Asian monsoon systems. Overall, changes in ASM circulation during the Holocene reflect a combination of precession-controlled variations in external radiative forcing as well as internal climate dynamics associated with North Atlantic circulation and strength of the AWM winds.
PP41A-1419
Late Glacial environmental change at Lake Suigetsu, central Japan: preliminary evidence from bulk organic and compound specific isotope geochemistry.
The sediments of Lake Suigetsu, central Japan, represent a globally significant archive of climate and environmental change due the presence of annual laminae (varves) which span the past 50,000 years to present day, enabling accurate and precise chronological control and the potential for annual scale analyses. Regional palaeoclimate records, including pollen data from Lake Suigetsu (Nakagawa et al. 2003) and accumulation rates of terrestrial organic compounds in the Sea of Japan (Yokoyama et al. 2006) suggest marked climate changes occurred in Japan over the last glacial- interglacial transition (LGIT, 16-10 ka.BP) which correspond with well documented North Atlantic events, yet which differ with respect to their specific nature and timing. In order to validate and develop these findings, we aim to exploit the evidence for changes in lake primary productivity and nutrient cycling at Lake Suigetsu, as an indirect response to climate change. Compound specific carbon and nitrogen isotope analysis of chlorophyll is used to infer nutrient source and uptake over the LGIT, whilst bulk organic matter accumulation rate and C and N isotopes are used to track large scale changes in the lake/catchment environment at a higher resolution for the whole record. Lake productivity is known to respond rapidly to external forcing and therefore provides independent evidence regarding the timing and direction of climate changes. Preliminary data will be presented and discussed in relation to existing data from Lake Suigetsu and the wider region. Nakagawa, T., et al. (2003) Asynchronous Climate Changes in the North Atlantic and Japan during the Last Termination. Science 299: 688. DOI: 10.1126/science.1078235. Yokoyama, Y., et al. (2006) Dust influx reconstruction during the last 26,000 years inferred from a sedimentary leaf wax record from the Japan Sea. Global and Planetary Change 54: 239-250.
PP41A-1420
Indian Monsoon Leads the Dansgaard-Oeschger Events of Greenland: New Evidence From the Bay of Bengal
In recent years a growing body of evidence has been pouring in mainly from marine records, supporting the hypotheses that temperature changes in the Arctic and Greenland steer the intensity of the Asian Monsoon. However, the physical link between the high latitude climate and monsoons are still elusive. Here we use oxygen isotopic ratios and Mg/Ca ratios of planktonic foraminifera species Globigerinoides ruber from a sediment core in the Bay of Bengal (BOB) to reconstruct sea surface temperature (SST) and surface water oxygen isotopic values. We find that oxygen isotopic values of water (monsoon signal) and SST of BOB lead the Dansgaard-Oeschger (D-O) events. Therefore, it is proposed here that the monsoon could kick the start of millennial scale abrupt climate changes through the shifts of the Intertropical Convergence Zone (ITCZ) and associated convection, water vapor supply to the tropical troposphere and latent heat penetration.
PP41A-1421
An abnormal episode of 1991 mass coral mortality: Clues from anomalies of coral skeletal rare earth elements (REEs)
An unusual episode of mass coral mortality occurred in low-latitude coral reefs in the western Pacific and eastern Indian Oceans during 1991 late summer and fall. The mysterious disaster could not be attributed to only high summer sea surface temperature (SST) during the El Niño event. Skeletal rare earth elements (REEs) of a modern 30-cm Porites coral head with a hiatus 13.5 cm from top, collected from the Son Tra Island (16°2'59.4"N, 108°11'57.1"E), central Vietnam, western South China Sea, were determined by our developed inductively coupled plasma mass spectrometry (ICP-MS) techniques. With high- precision U-Th dating techniques (±0.5 yr, 2σ; Shen et al., 2008, GCA 72, 4201-4223), annual band counting, and elemental records, the occurrence of hiatus should be after 1991 mid-summer. Shale- normalized REE abundance patterns show distinguishable REE features recorded in the coral skeleton just below the hiatus. (1) The REE levels are 10s-100s times higher than any values during AD 1978-2005. (2) The Pr/Yb and Nd/Yb ratios of 2.5 are one order higher than those in other years. (3) The spider REE diagram indicates an abrupt input of massive igneous material. The timing of discontinuity layer and unique REE fingerprints suggest the coral mortality might be enhanced by the volcanic ash fallout following the eruption of Mount Pinatubo on June 15, 1991.
PP41A-1422
Late Glacial Tropical Savannas in Sundaland Inferred From Stable Carbon Isotope Records of Cave Guano
During the Last Glacial Period (LGP), reduced global sea level exposed the continental shelf south of Thailand to Sumatra, Java, and Borneo to form the contiguous continent of Sundaland. However, the type and extent of vegetation that existed on much of this exposed landmass during the LGP remains speculative. Extensive bird and bat guano deposits in caves throughout this region span beyond 40,000 yr BP, and contain a wealth of untapped stratigraphic palaeoenvironmental information. Stable carbon isotope ratios of insectivorous bird and bat guano contain a reliable record of the animal's diet and, through non-specific insect predation, reflect the relative abundance of major physiological pathways in plants. Various physiological pathways of carbon fixation in plants yield differing stable carbon isotope ratios. Stable carbon isotope values of C3 plants are lower than C4 vegetation due to different enzymatic discriminations of the heavy isotope through the carbon fixing pathways. In tropical locales, grasses nearly always follow the C4 photosynthetic pathway, whereas tropical rainforest uses C3 photosynthesis, providing a proxy for vegetation and therefore climate change in the past. Here we discuss four guano stable-isotope records, based on insect cuticle and n-alkane analysis, supplemented by pollen analysis. All sites suggest a C3 dominated ecosystem for the Holocene, consistent with the wet tropical forest vegetation present at all locations. Two sites from Palawan Island, Philippines, record stable carbon isotope values of guano that document a drastic change from C3 (forest) to C4 (savanna) dominated ecosystems during the Last Glacial Maximum (LGM). A third location, at Niah Great Cave, Malaysia, indicates C3-dominant vegetation throughout the record, but does display variation in stable carbon isotope values likely linked to humidity changes. A fourth location, Batu Caves in Peninsular Malaysia, also indicates open vegetation during the LGM. Vegetation models disagree as to the nature of vegetation during the LGM in Sundaland, but our results suggest major contraction of forest area with significant implications for carbon storage during the LGM and also for understanding the development of modern biogeographic and genetic patterns in the region. Additional cave guano sites will provide further constraints on the nature of environmental change in the region over the last glacial cycle.
PP41A-1423
The Enigma of Millennial-scale Rainfall Variations in the Southeast African Tropics: a Breakdown of the ITCZ Paradigm
A high-resolution, continuous, compound-specific D/H isotope and TEX86 record from Lake Tanganyika spanning the last 60 ka affords us a definitive look at past rainfall and temperature variations in the southeast African tropics. From this record, it is evident that this region experienced abrupt and dramatic episodes of aridity co-eval with known high-latitude millennial climate coolings, such as the Younger Dryas and Heinrich Events 1 and 4. Yet lithogenic and biological proxy evidence from Southeast Africa suggests that the Intertropical Convergence Zone (ITCZ) shifted south and northerly winds intensified during these events, per predictions from General Circulation Model experiments. A southward shift in the ITCZ should make the southern tropics, including Lake Tanganyika, wet, so why then is southeast Africa dry, and thus in- phase with the Northern Hemisphere? The explanation behind this "breakdown" in the ITCZ paradigm likely involves Indian Ocean dynamics, including SST variability, monsoon dynamics, and zonal reconfigurations of Walker circulation in the Indian Ocean basin – all of which modulate the amount of moisture transported into continental Africa and the strength of convergence within the ITCZ itself. These Indian Ocean dynamics may be teleconnected to the North Atlantic, thus serving as a conduit for the transmission of high-latitude abrupt climate change to continental Africa.
PP41A-1424
Modeling the Global Monsoon System During Glacial Climate Events
We employ the comprehensive NCAR Community Climate System Model (version 3) to assess the state of the global monsoon system during specific time intervals of the last glacial period. In contrast to previous studies, we take into account changes in ice-sheet distribution, greenhouse-gas concentrations and orbital parameters for marine isotope stage 3 (centered on 35 ka BP) and the last glacial maximum (LGM, centered on 21 ka BP). Both simulations result in a significant reduction of the Atlantic Ocean meridional overturning circulation. Perturbing deep-water formation in the North Atlantic Ocean in these glacial baseline simulations results in explicit representations of Dansgaard-Oeschger stadials and interstadials as well as Heinrich-type events. Glacial boundary conditions induce a large-scale drying in the West African monsoon region and a strengthening and southward shift of the African easterly jet. Through atmospheric dynamics, the effect of ice-sheets is rapidly communicated via the upper troposphere thereby also affecting the Indian and South East Asian summer monsoon systems. Dansgaard-Oeschger stadial boundary conditions lead to a pronounced intensification of the African, Indian and South East Asian summer monsoon compared to the last glacial maximum. Our Dansgaard-Oeschger interstadial simulation indicates a response pattern of all tropical monsoon systems which is similar to the stadial simulation but exhibits a stronger amplitude. This suggests a predominance of the orbital and ice sheet forcing over the imposed Dansgaard-Oeschger climate variability. Tropical inter-ocean basin teleconnections appear to be weakened during stage 3 stadials compared to the LGM as illustrated by a less pronounced covariation between tropical Atlantic hydrological conditions and the El Niño/Southern Oscillation (ENSO) in the eastern tropical Pacific.
PP41A-1425
Sedimentary response of Dansgaard/Oeschger events in the tropical South China Sea
The southern South China Sea, situated in the tropical western Pacific, exposed the broad Sunda shelf during the glacial time. Extensive drainage system developed at the low sea-level stand has greatly influenced the sediment supply to the abysmal South China Sea. Several well-developed turbidite layers were identified by using high-resolution X-ray fluorescence (XRF) core scanner major elements and laser grain size measurements at an IMAGES core MD05-2895 off the Sunda slope in the southern South China Sea. AMS C-14 dates combined with oxygen isotope and carbonate stratigraphies confirm their synchronization with all Dansgaard/Oeschger events in the past 50 kyr. The turbidite deposition was formed by rapid terrigenous discharge from the Sunda shelf and slope during the last glacial time. Such rapid sediment discharge is highly relative to heavy East Asian monsoon rains that strengthened erosion of the exposed shelf. The monsoon rains are dominant in warm seasons in Asia. Therefore, the turbidite layers in the tropical South China Sea are considered as sedimentary responses of Dansgaard/Oeschger warming events during the last glacial time, suggesting a strong teleconnection of glacial abrupt climate changes between low and high latitudes.
PP41A-1426
Dissimilarities of stalagmite stable oxygen records in caves at different regimes in East Asia during 3-4 ka
East Asian monsoon (EAM), dominated by Northern Hemisphere summer isolation, has been well-recorded in stalagmites collected from caves located in China, such as Dongge (25° 17'N, 108° 5'E), Hulu (32° 30'N, 119° 10'E), Sanbao (31° 40'N, 110° 26'E), Heshang (30° 27'N, 110° 25'E), and Shihua (39° 47'N, 115° 56'E). The stalagmite δ18O of Son La cave in northern Vietnam (21° 18'N, 104° 15'E) and of Bukit Assam cave in northern Borneo (4° N, 114° E) both show 1 per mil increase from 4 ka to 3 ka; however, only 0.5 per mil change is discovered in Chinese cave records. The 0.5-per mil offset between the continental sites in China and coastal sites adjacent to the South China Sea (SCS) suggests the regional climate in the SCS rim responds to not only the changes of EAM, but probably also the dynamics of low-latitude El Nino-Southern Oscillation in the Pacific.
PP41A-1427
Insights into changes in precipitation patterns in Brazil from oxygen isotope ratios on speleothems
Variations in tropical precipitation on millennial and orbital time scales can reflect a Hadley-cell-related anti- phasing between the Northern and Southern hemispheres due to the influence of insolation on the global summer monsoons. A new δ18O speleothem record from northeastern Brazil shows that insolation- driven changes in monsoon intensity are capable of producing a similar, zonally oriented anti-phasing within the same hemisphere. Comparison of our speleothem record with other precipitation-sensitive proxies from the central Andes and southeastern Brazil shows that precipitation in Northeastern Brazil has been out of phase with insolation and rainfall in the rest of tropical South America south of the equator since the Last Glacial Maximum. Northeastern Brazil experienced humid conditions when summer insolation was reduced and arid conditions when insolation was high. While previous interpretations of past climate change in NE South America have commonly invoked meridional displacements in ITCZ location as the main mechanism for changes in precipitation on millennial time scales, our results suggest that remote monsoon forcing is responsible for much of the observed precipitation changes on orbital time scales during the Holocene. These results demonstrate that orbitally driven out-of-phase relationships in precipitation are not limited to interhemispheric anti-phasing as demonstrated previously, but may well occur within the same hemisphere. Speleothem records also indicate contrasting climatic conditions around the Last Glacial Maximum in Brazil, characterized by marked dry and wet climates in the Nordeste and in southeastern Brazil, respectively. It is likely, however, that these regional differences primarily reflect more distant extratropical teleconnections from the Atlantic Ocean and high northern latitude changes during glacial conditions.
PP41A-1428
Transition From the LGM to the Holocene, the View From a West Virginia Cave
A stalagmite collected from a West Virginia cave provides a continuous high resolution record of climate change during the transition from the last glacial maximum (LGM) to the Holocene. The chronology is based on 14 dates obtained using U/Th dating techniques developed for carbonates and adapted for measurement on mass spectrometer. Stable isotopes were measured on a GasBench II coupled to a ThermoFinnigan DeltaPlusXP IRMS. After correcting for the ice volume effect on source water, the residual oxygen isotopic signal shows a glacial period drier than the Holocene, with numerous abrupt changes in the record, likely a response to changing circulation patterns. The Bolling-Allerod was characterized by fast growth rates, and wetter conditions than during other periods in the record. The observed variations are likely due to changes in atmospheric circulation in response to a retreating ice sheet, imposed upon a long-term warming trend. Carbon isotopes provide an additional constraint on changing moisture conditions, although there is also some evidence of changing vegetation structure during the Younger-Dryas, pre-boreal, and early Holocene.
PP41A-1429
Asian Monsoon Millennial-Scale Variability During the Last Glacial Period and its Links to North Atlantic Climate
We present an updated record of the last glacial period Asian monsoon from Dongge Cave, China. Previous low resolution work from speleothem, D4 gave an indication of millennial-scale variability during Marine Isotope Stages (MIS) 3 and 4 (Yuan et al. 2004, Science, 304, 575-578). The work presented here reexamines D4 with higher resolution oxygen isotope data and higher precision dating. Average temporal resolution is 29 years ranging from 3.5 to 110 years. Dates were obtained using a Finnigan-MAT Neptune multi-collector inductively coupled plasma mass spectrometer (MC-ICP-MS) with average 2 σ errors ~ 3.4 ‰. In addition, the record is extended to cover peak glacial conditions in MIS 2 using a side growth segment of D4. This allows for continuous coverage of MIS 2 through 4 from 22 to 65 thousand years. Significant variability in the oxygen isotope data exists (ranging from 9.5 to 5.5 ‰) indicating changes in the meteoric precipitation of monsoonal moisture. This variability correlates strongly to Dansgaard/Oeschger (D/O) events 2 through 18 observed in Greenland. The amplitude of the events recorded at Dongge is similar to that recorded in Hulu Cave (Wang et al. 2001, Science, 294, 2345), though some differences exist. Five significant shifts in the oxygen record also correspond to Heinrich events from North Atlantic marine records. This work is further evidence of the strong link between the low-latitude monsoon and the high-latitude North Atlantic region. The precise dating of D4 allows for close examination of the timing of these events with other events in well-dated records, which can help determine the physical mechanisms that link these two regions of the world.
PP41A-1430
Climate change in the mid-latitudes of North America during the marine isotope stage 11
Orbital configurations during the Marine Isotope Stage (MIS) 11 are similar to those of today's interglacial period. Study on the climate of MIS 11 may provide information on the type and magnitude of modern climate variability that could be expected under non-anthropogenic conditions. We have obtained a high-resolution calcite speleothem record from Morril's Cave (aka Worley's Cave), eastern Tennessee. The chronology was determined by U-Th dates and stable isotopic analyses were done with a sampling interval of 0.5 mm. The sample was apparently deposited under equilibrium conditions. We thus interpret its stable isotope records, spanning continuously from ~400 ka to ~342 ka, in terms of climate and environmental changes at this mid-latitude location. The carbon isotope profile shows a step-wise increase of δ13C, shifting from approximately -12‰ in the middle of MIS 11 to -8‰ near the end of MIS 11 and then to -4‰ in MIS 10. This step-wise increase may indicate a wetting to drying climate shift near the end of MIS 11. In response to the climate change, it also suggests that C3 plants probably dominated in eastern Tennessee during MIS 11, while a major transition from C3 plants to C4 plants occurred in this region when the interglacial period terminated. The oxygen isotopic value gradually increases through the record, with oscillations following the local summer insolation. The record is consistent with marine and ice core records, but also featured with prominent millennial-scale variations, which suggests climate instability during the climate transition period.
PP41A-1431
A Sub-millennial Scale Comparison Between the East Asian Monsoon and the North Atlantic Climate During the Mystery Interval
Chinese speleothem records have demonstrated a strong correlation between the East Asian monsoon (EAM) and the north Atlantic climate on millennial timescales during the last glacial-interglacial cycle. Here we evaluate this relationship at higher resolution during and immediately after the Mystery Interval. We have obtained sub-decadal-resolution oxygen isotope records, covering from 19.7 to 14.4 kyrs BP, on stalagmite samples collected from Hulu Cave and Qingtian Cave, eastern China. The chronologies of the two records are determined by U-Th dates and band counting. Replication between the records suggests that both oxygen isotopic variations primarily present EAM intensity changes. The records support a broadly millennial- scale teleconnection between EAM and northern high-latitude climate, with some differences at higher resolution. The differences include the following. (1) A relatively strong EAM at about the time of the Last Glacial Maximum and immediately thereafter (19.7-17.6 kyrs BP) compared to cold conditions in Greenland at the time. (2) A ~90-yr-long extreme weak event in EAM intensity occurred at ~16.1 kyrs BP, with the transition into the event taking 16 years or less, with resolvable structure within the transition. This event correlates with one of the major ice-rafting events within Heinrich event 1, suggesting that the monsoon change was triggered by events in the North Atlantic. (3) The monsoon transition into the Bolling-Allerod took ~370 years, much longer than the analogous Greenland oxygen isotope shift.
PP41A-1432
Decadal-scale climate change of East Asian Monsoon during the Last Glacial Maximum from stalagmite record
An average 7~8 yr resolution oxygen isotope record, based on 230Th and layer-counted data of three stalagmites from Hulu Cave in eastern China and Qingtian Cave in central China, provides a history of the Asian Monsoon(AM) from 18.4 to 14.4 kaBP. The fairly good replication of the δ 18O signals from these three stalagmites at decadal scale across their contemporaneous periods suggests a large scale regional coherence of the monsoon precipitation δ 18O variations. There are two remarkable weak summer monsoon events at ~ 17.7kaB.P.and ~16.1kaB.P.in our stalagmite δ 18O record which shows a dramatic positive shift of 2‰ in δ 18O, coincident within error with H1b and H1a in the North Atlantic, suggesting that pronounced sub-millennial variability in the summer AM was tightly coupled with climate conditions in the northern high latitudes. Our data shows a period of strong East Asian Monsoon over 18.3~17.7 kaBP, and the average intensity of which is about a half of that of Bølling Warming period. This period is corresponding to the high Atlantic meridional overturning circulation (AMOC). This gave strong evidence that the EAM climate change has a close correlation to the AMOC variability during LGM.
PP41A-1433
Did Heinrich Events Impact Climate in the Southwest Pacific? – Evidence From New Zealand Speleothems
Speleothems, layered calcium-carbonate cave deposits such as stalagmites, stalactites and flowstones, have been shown to offer much potential as paleoclimate archives. We present a new, high-resolution, independently-dated, paleoclimate record from a stalagmite which formed in Hollywood Cave (42.0°S, 171.5°E) on South Island, New Zealand. Over 700 stable oxygen and carbon isotope measurement pairs are supported by a chronology from 18 sequential 230Th dates. The stalagmite grew between 73 and 11 kyr B.P. Growth rates varied from ~1-54 mm/kyr and data resolution yields one sample per 10- 320 years. Weak covariance between δ13C and δ18O in the speleothem calcite suggests that recorded climate signals are primarily driven by mean annual precipitation amount and source. Both stable isotope proxies indicate relatively cold and dry conditions prevailed for much of the period 73-11 kyr B.P. However, abrupt-onset, millennial-scale shifts to wet and cool climate interrupt the dry conditions at 67.7-61, 56-55, 50.5-47.5, 40-39, 30.5-29, 25.5-24.3, 16.1-15, and 12.2-11.8 kyr B.P. Significantly, these eight abrupt climate changes occur synchronously with widely accepted ages for Heinrich events H6-H0 (including H5a). Many of these abrupt events can also be matched to known periods of glacier advance in the Southern Alps, New Zealand, which, arguably, were driven by increased mean annual precipitation and reduced potential for summer melting. In addition, preliminary stable isotope data (> 550 δ13C and δ18O pairs) from two North Island, New Zealand (~38°S), stalagmites will be shown that also displays abrupt shifts from relatively dry to wet climate during the period 60-6 kyr B.P. In combination, these results argue stongly for coeval climate changes in antipodean locations, and therefore provide compelling evidence for globally synchronous climate variability during the last glacial period.
PP41A-1434
Late Quaternary Paleoceanographic Changes over the Conrad Rise and off Lutzow-Holm Bay in the Indian Sector of the Southern Ocean
The Southern Ocean plays a very important role in the global climate system on the present and geologic past. The Southern Ocean has also become a region of paleoceanographic focus because of its key role in global deep-water circulation and its potential significance for the global carbon. For example, it has been proposed that primary production was higher and utilization of preformed nutrients in surface waters was more efficient in the glacial Southern Ocean than today, effectively lowering the glacial atmospheric CO2 concentration. To resolve the causes and processes of atmospheric CO2 change, it is important to understand mechanisms and processes of sub-systems in the Antarctic Cryosphere such as a change of biological productivity, sea surface temperature, surface water frontal system, sea-ice distribution, and East Antarctic ice sheet during the glacial-interglacial climate cycle. We collected three sediment cores from the Conrad Rise (COR-1PC, 54.27°S, 39.77°E, 2864m), the Gunnerus Ridge (GUR-1MC, 66.27°S, 33.42°E, 1348m), and off Lutzow-Holm Bay (LHB-3PC, 66.00°S, 40.00°E, 4469m) in the Indian Sector of the Southern Ocean during the R/V Hakuho- maru cruise KH07-4 Leg.3. Age models of the cores were established by radiocarbon dating of planktonic foraminifera, diatom biostratigraphy and relative paleointensity curve of the geomagnetic field. At the core LHB-3PC, biogenic opal contents indicate that the marine productivity was enhanced at interglacials in the high-latitudinal Southern Ocean. Based on the bathymetric mapping, subbottom profiling, and multi-channel seismic reflection survey, a dune- like bedform (mudwave) exists on the southwest slope of the Conrad Rise. The mudwaves are about 30 m in altitude and a few hundred meters in wavelength. The wave-field is located in water depths of 2000-3200 m. Similar wavy sedimentary structures are recognized below the seafloor in the seismic profile on the Conrad Rise. Such deep-sea mudwaves have been reported at the northern Weddell Sea, which influenced by the Antarctic Bottom Water (AABW) (Howe et al., 1998), and at the Gardar Drift in the North Atlantic, where is also influenced by the North Atlantic Deep Water (NADW) (e.g., Manley and Caress, 1994). Lithology of core COR-1PC is diatom ooze, and sedimentation rate is very high up to about 40 cm/ka. Thus, the sediment drift was deposited with mudwaves on the Conrad Rise, which was developed by influences of NADW and/or AABW.
PP41A-1435
Vertical distribution of living planktonic foraminifera in the tropical Indian Ocean
Planktonic foraminifera are widely used for paleoceanographic reconstructions through geochemical (e.g. d18O, Mg/Ca) and faunistics analyses. Though the global distribution of planktonic foraminifera is well established, paleo–reconstructions suffer from the limited knowledge of the vertical ecology of the different species. To assess the vertical distribution of the planktonic foraminifera in an oligotrophic gyre, we performed stratified plankton tows in the tropical Indian Ocean, ( from 7°S-100°E to 17°S- 70°E), during the GYRAFOR B cruise (July-August 2007). Planktonic foraminifera were collected by a MultiNet midi in the upper 400 meters of the water column. Countings of planktonic foraminifera in the >150µm fraction in 4 stations along the transect shed ligth on the main parameters controlling the distribution of the planktonic foraminifera. Along the transect, we observe that the most abundant species are Globorotalia menardii, Globigerinoides sacculifer and Pulleniatina obliquiloculata. The standing stock of planktonic foraminifera is decreasing from about 2600 foraminifera/m3 in the East to 770 foraminifera/m3 in the West. This trend corresponds to a deepening of the thermocline and DCM, likely linked to a decrease in nutrient availability in the mixed layer. Vertically, the assemblages of foraminifera do not display any distinctive distributional pattern. Most of the standing stock of foraminifera can be found in the mixed layer, with peaks in abundance just above the DCM, in the mixed layer. Our results contrast with previous studies that indicated a maximum abundance of foraminifera in the DCM. In the tropical Indian ocean, the main species of planktonic foraminifera used to infer past stratification changes such as P. obliquiloculata or G. menardii appear to live in surface waters rather than in and below the thermocline.
PP41A-1436
Asynchronous skeletal Mg/Ca, Sr/Ca, Ba/Ca and U/Ca seasonal cycles in a multi-decades of modern coral Porites from Nanwan, southern Taiwan
Variations of coral skeletal Mg, Sr, Ba, and U levels have widely been used for reconstructing local and regional thermal and hydrological conditions. We present decades of sub-monthly Mg/Ca, Sr/Ca, Ba/Ca and U/Ca records from a modern coral Porites core, drilled in Nanwan, southern Taiwan, analyzed on an ICP-MS, Finnigan Element II, with permil-level external precisions (2 sigma). Asynchroneity between those elemental ratios suggest different partitioning forcings. Seasonal Sr partitioning is dominated by sea surface temperature (SST) change; however, natural dynamics of Mg/Ca, Ba/Ca, and U/Ca are apparently complicated. Mg/Ca seasonal signals exhibit in-phase variations with Sr/Ca only in a few years and are consistent with the skeletal C-13 fractionation record, suggesting a metabolic mechanism. U/Ca lacked annual cycle as previously reported, but its decadal trend is similar to the Mg/Ca. Annual twin Ba/Ca summits in the spring and summer are related to a biological process during the coral spawning season and terrestrial material input in the rainfall season, respectively.
PP41A-1437
The response of the tropical Indo-Pacific warm-pool to conditions of global warmth
The Indo-Pacific warm pool (IPWP) plays an important role in both regional and global climate, but the response of this region to anthropogenic climate change is not well understood. Climate models are inconsistent in their predictions of sea surface temperature (SST) change in the region, with some models predicting warming in the IPWP due to greenhouse gas forcing and some indicating no change or a moderate cooling. While the early Pliocene warm period is not a perfect analogue for anthropogenic climate change, it is the most recent time in Earth history when global temperatures were warmer than they are today for a sustained period of time, and therefore arguable presents the best test-bed for looking at conditions of global warmth in the paleo record. We will present a Mg/Ca (G.sacculifer) sea surface temperature record from ODP site 758 in the eastern Indian Ocean and show that IPWP SST remained relatively stable through the last 5 Ma and was not warmer in the early Pliocene compared today. The stability of the IPWP through the last 5 Ma, even as SST in the EEP and coastal upwelling regions cooled significantly, presents a challenge to climate models to understand the mechanisms involved with a change from El Padre conditions to modern conditions so that we can more clearly predict future climate change.
PP41A-1438
Preliminary Comparison of the Eemian/Sahand and Holocene Hydroclimates in Northwest Iran
The exact nature of the Holocene hydroclimate in the Near East and its relationship to vegetation is still in question. Low oxygen-18 values in the first half of the Holocene, documented at numerous sites, have been interpreted in two ways. The first invokes wetter than present conditions in the Early Holocene, whereas a second interpretation suggests that the low oxygen-18 values are a function of enhanced winter precipitation and that climate was not necessarily wetter. Central to both arguments is the pollen record, which indicates a 4 kyr delay in the establishment of oak after the onset of the Holocene. Human intervention could be a significant factor in the vegetation record of the Holocene but demonstrating direct links is difficult. A new coarse-resolution isotope record, spanning the Eemian/Sahand Interglacial in Lake Urmia, Iran, provides a means to compare the hydroclimates of the last Interglacial with the Holocene. Such a comparison offers a means to examine the impact of humans on the landscape. As with the Holocene, low oxygen-18 values dominate the first part of the Eemian relative to the latter part. Thus, the overall evolution appears to be similar in both interglacials, despite differences in insolation and CO2 concentrations. Other similarities include a gradual decrease in oxygen-18 throughout the first half of the Eemian and an abrupt increase toward the latter half. One major difference is the relationship of oak to the isotopic record. In the Holocene, the peak in oak pollen occurs with the highest oxygen-isotopic values. In the Eemian, the peak in oak pollen occurs with relatively low isotopic values. Given the similarities in hydrology but differences in vegetation response between the two interglacials, human impacts are a reasonable focus of research.