PP13B-1432
Microscale heterogeneities in the stable carbon and oxygen isotopic compositions of the international standard calcite materials (NBS19, NBS18, IAEA-CO-1, and IAEA-CO- 8)
The stable carbon and oxygen isotopic compositions (δ13C and δ18O) of carbonate, especially biological calcite (e.g., foraminifera and coral), are useful as environmental tracers to reconstruct paleoclimate and paleo-oceanic circulations. In recent studies, the stable isotopic analyses for sub-100 μg quantities of carbonate are needed to reconstruct high-resolution environmental fluctuations. In this study, we investigated the magnitude of grain-scale (from 6 to 88 μg) heterogeneities in carbon and oxygen isotopic compositions of international standard reference calcite materials (NBS 19, NBS 18, IAEA- CO-1, and IAEA-CO-8) in order to determine which standard reference calcite materials are suitable for a microscale, high-resolution, isotopic analysis. In order to serve this purpose, we have upgraded the analytical system reported in Ishimura et al. (2004) and improved both stability and precision during grain-scale isotopic analyses. This continuous-flow isotope ratio mass spectrometry (CF-IRMS) system realizes a simultaneous determination of both the δ13C and the δ18O values with standard deviations (S.D.) of less than 0.05 ‰ for CO2 gas. Based on the S.D. of the δ13C and δ18O values determined for CO2 gases evolved from the different grains of the same calcite material, we found that NBS19, IAEA-CO-1, and IEAE- CO-8 were homogeneous for δ13C (less than 0.10 ‰ S.D.), and only NBS19 was homogeneous for δ18O (less than 0.14 ‰ S.D.). On the level of single grains, we found that both IAEA-CO-1 and IAEA-CO-8 were heterogeneous for δ18O (1.46 ‰ and 0.76 ‰ S.D., respectively), and NBS18 was heterogeneous for both δ13C and δ18O (0.34 ‰ and 0.54 ‰ S.D., respectively). Closer inspection of NBS18 grains revealed that the highly deviated isotopic compositions were limited to the colored grains. By excluding such colored grains, we could obtain the homogeneous δ13C and δ18O values (less than 0.18 ‰ and less than 0.16 ‰ S.D., respectively) for NBS18 as well. We conclude that either NBS19, IAEA-CO-1, or pure grains in NBS18 are suitable to be used as the standard reference material for δ13C, and either NBS19 or pure grains in NBS18 are suitable to be used as that for δ18O during the grain-scale isotopic analyses of calcite. By using the standard reference calcite suitable for the grain-scale isotopic studies, we can enhance the resolution of the isotope geochemistry, climatology, and paleoceanography.
PP13B-1433
Electron Microprobe Mapping of Foraminiferal Mg/Ca Variability From Holocene and LGM Samples Obtained From Atlantic and Pacific Depth Transects
The Mg/Ca ratio of foraminiferal calcite is a widely used proxy for reconstructing past sea surface and thermocline temperatures. Dissolution lowers the Mg/Ca ratio resulting in an underestimation of past ocean temperatures (termed the 'dissolution-effect). We have used the dissolution-effect on the Mg/Ca ratio as a proxy for reconstructing deep-sea carbonate ion concentration based on the decrease in the Mg/Ca ratio with increased water depth (Fehrenbacher, et al, 2006, Fehrenbacher and Martin, in review, Paleoceanography, 2008). The dissolution effect, though well characterized, is poorly understood and warrants further investigation. Gaining insight into how dissolution lowers the bulk Mg/Ca ratio, where in the shell the Mg/Ca ratio changes the most, and how a well preserved specimen differs in shell chemistry from a poorly preserved dissolved specimen are several questions we aim to answer. In our current study, we employ a high-resolution electron microprobe analysis (EMPA) technique to determine how dissolution changes the distribution of magnesium, and thus changes the Mg/Ca ratio, within individual foraminifera shells. Recent studies have shown the utility of EMPA as a means of mapping the inter- and intratest variability of the Mg/Ca ratio in foraminiferal calcite. Results of these studies have yielded Mg/Ca maps that show large inter-species variability among samples obtained from the same interval within a core and intratest variability in excess of what can be explained by calcification temperature. We apply EMPA to map the Mg/Ca ratio within G. ruber and N. dutertrei, two species widely used in paleoceanographic studies. Our samples are from two depth transects in the tropical Atlantic (Ceara Rise; 2.8, 3.5, and 4.0 km) and tropical Pacific (Ontong Java Plateau, 1.6, 2.5, and 3.5 km) from Holocene and LGM intervals. Results show where the Mg is lost from the shell and at what depth the greatest decrease occurs. We also discuss the possibility of EMPA mapping as a means of determining if a shell is well preserved, potentially making Mg/Ca a much more powerful tool in much older samples.
PP13B-1434
Stable Isotopes of Planktonic Foraminifera From Tropical Atlantic/Caribbean Core-Tops: Implications for Reconstructing Upper Ocean Stratification
δ18O values of nine tropical-subtropical planktonic foraminiferal species with different preferential habitat depths collected from 62 core-top samples along an east-west transect across the tropical Atlantic/Caribbean were used to test the applicability of interspecific δ18O gradients for reconstructions of tropical upper ocean stratification. In general, the δ18O difference (Δδ18O) between intermediate- and shallow-dwelling species decreases, and Δδ18O between deep- and intermediate dwellers increases with increasing thermocline depth towards the west. The statistical significance of regional differences in Δδ18O highlights Δδ18O between the intermediate dwellers (in particular Globorotalia scitula and Globorotalia tumida) and the shallow dweller Globigerinoides ruber pink, as well as Δδ18O between the deep dwellers Globorotalia crassaformis or Globorotalia truncatulinoides dextral and the intermediate dwellers as most sensitive to changes in tropical Atlantic thermocline depth. Based on the observed regional variations in interspecific Δδ18O, we propose a multispecies stratification index "STRAtrop" = (δ18Ointermediate- δ18Oshallow)/(δ18Odeep-δ18Oshallow) for the tropical ocean. Statistically significant differences in STRAtrop values between the E-Atlantic and the Caribbean suggest that this index may be a useful tool to monitor variations in tropical upper ocean stratification in the geological record.
PP13B-1435
PRISM3 Pliocene Sea surface Temperature Reconstruction
The Pliocene Research, Interpretation and Synoptic Mapping (PRISM) Project provides a conceptual model and synoptic view of the earth during a considerably warmer than modern (2-3°C warmer global mean annual temperature) interval (mid-Piacenzian Age, Pliocene Epoch; ~3.3 to 3.0 Ma) through reconstruction of sea-surface temperature (SST) and other paleoenvironmental parameters. The PRISM3 SST fields include new equatorial Pacific and subpolar – polar North Atlantic components based upon multiproxy (faunal, alkenone and Mg/Ca) temperature analyses from new sites. These data are presented in 12 interpolated global fields with 2° spatial resolution representing monthly SST estimates. Results show a reduced longitudinal temperature gradient across the equatorial Pacific and extension of warm North Atlantic surface conditions into the eastern regions of the Arctic Ocean near Spitzbergen. These data are part of the PRISM3 paleoenvironmental reconstruction designed in part to provide climate modeling groups with new SST and alternative land cover reconstructions, 3-dimensional deep ocean temperature, topography and sea level. The PRISM3 reconstruction is the primary data source for the new Pliocene Climate Model Intercomparison Project (PlioMIP).
PP13B-1436
Another look at the reductive cleaning of foraminifera for Mg and trace element analysis
Trace elements in foraminifera shells, including Mg, Sr, Ba, and Cd, potentially hold a wealth of information about past oceanic conditions. However, after calcification and during burial, clays, organic matter, Fe-Mn oxides and sulfides adhere to the surface and are trapped in chambers of shells; thus, a cleaning procedure is important to obtain precise information of past oceanic conditions by isolating the shell bound signal. Applying a cleaning protocol that works for multiple metals from samples from a wide variety of environmental settings and evaluating the efficacy of that cleaning protocol is challenging because the shell-bound signal is not known. The reductive step of the cleaning procedure, included primarily for the removal of metal oxides, has received attention in several studies of sample preparation for foraminiferal Mg/Ca analysis. The step causes some dissolution, which raises concern because there is a known natural dissolution effect on Mg/Ca in some species. In addition, the step involves the use of a strong reducing reagent, hydrazine, which is a hazardous chemical requiring careful handling and storage. Although the reductive step was originally included in the protocol to remove authigenic contaminants interfering with Cd measurement, some studies have shown clear improvement of the Mg/Ca data of reductively cleaned foraminifera obtained from challenging sedimentary environments. Other studies, however, have shown that a downcore signal of reductively cleaned foraminifera can be nearly identical to a record based on foraminifera cleaned without the reductive step but simply offset to lower Mg/Ca values. It generally has been thought that the reductive reagent hydrazine is responsible for lowering the Mg/Ca, possibly due to assisting in the removal of contaminant phases. Recently, Yu et al. (2007) demonstrated that citrate alone causes lowering of the Mg/Ca and hypothesized that at least some of the decrease in Mg/Ca and other metal:Ca ratios in foraminifera shells during the reductive step is by partial dissolution, with a preferential removal of some ions (including Mg) relative to Ca. Here, we test this Çpartial dissolution hypothesis using well-preserved specimens of two different foraminifera species, Globigerinoides sacculifer and Neogloboquadrina dutertrei, whose element/Ca ratios experience different changes due to natural dissolution. We apply six different strengths of citrate solutions in the reductive step and compare the variation in element/Ca of each species associated with the increasing strengths of citrate and also with expectations of the element/Ca differences based on natural dissolution. Weak concentrations of the citrate solution lower the Mg/Ca of both species, consistent with the effect observed using stronger concentrations in the Yu's study but inconsistent with the pattern of dissolution associated with natural dissolution. More importantly, that the Mg/Ca ratios rapidly level off with increasing concentration of citrate suggests that the citrate solution is unlikely to be preferentially removing Mg from the lattice. Additional experiments demonstrate that the concentration of citrate in the standard protocol is well within the range in which Mg/Ca has leveled off, thus should aid in yielding consistent results. Given that there are settings in which Mg/Ca data do seem to be improved by reductive cleaning and that there is also a set of calibration data that have been prepared using reductive cleaning, we propose to continue to include a reductive step until experiments are conducted that reveal a detrimental effect of reductive cleaning.
PP13B-1437
Statistical algorithm to test the presence of correlation between time series with age/dating uncertainties.
To understand the Earth's climate, we must understand the inter-relations between its specific geographical areas which, in the case of paleoclimatology, can be profitably undertaken from an empirical perspective. However, assessment of the inter-relation between separate paleoclimate records is inevitably hindered by uncertainties in the absolute and relative age/dating of these climate records, because the correlation between two paleoclimate data with age uncertainty can change dramatically when variations of the age are allowed within the uncertainty limit. Through rigorous statistical analysis of the available proxy data, we can hope to gain better insight into the nature and scope of the mechanisms governing their variability. We propose a statistical algorithm to test for the presence of correlation between two paleoclimate time series with age/dating uncertainties. Previous works in this area have focused on searching for the maximum similarity out of all possible realizations of the series, either heuristically (visual wiggle matching) or through more quantitative methods (eg. cross-correlation maximizer, dynamic programming). In contrast, this algorithm seeks to determine the statistical significance of the maximum covariance. The probability of obtaining a certain maximum covariance from purely random events can provide us with an objective standard for real correlation and it is assessed using the theory of extreme order statistics, as a multivariate normal integral. Since there is no known closed form solution for a multivariate normal integral, a numerical method is used. We apply this algorithm to test for the correlation of the Dansgaard-Oeschger variability observed during MIS3 in the GISPII ice core and millennial variability recorded at cites including Botuvera Cave in Brazil, Hulu Cave in China, Eastern Indonesia, the Arabian Sea, Villa Cave in Europe, New Zealand and the Santa Barbara basin. Results of the analysis are presented as a map of the statistical significance of the covariance between GISP II and each of these sites.
PP13B-1438
Initial Results From the new Long Coring System of RV Knorr
A new long piston coring system has been designed and built for RV Knorr. The system is capable of
deploying core lengths up to 46 m and weights of ~25000 lbs. With suitable modifications to other
ships, a slightly smaller system could be deployed from other large UNOLS vessels. The handling system
was designed around a hybrid rope blend of Vectran and Plasma braided with a torque-balanced, non-
rotating construction. The rope is 7500 m long with a breaking strength (~360,000 lbs) more than 10
times greater than the pullout tensions experienced by the coring system. The high breaking strength limits
stretching during coring operations, which minimizes rebound of the rope and movement of the piston during
core penetration. An accelerometer placed on the release system documented that rope rebound was less
than 2 m after the release of a ~15000 lb core at a water depth of 4585 m. The handling system for the
new core includes a new A-frame mounted with a load transfer winch and a vertically-mounted rigging boom;
a new stern-mounted grapple for transferring the corer from starboard to stern; a new deck-mounted traction
winch for the Vectran-Plasma rope; and three new computer-controlled davit cranes along the starboard rail
to raise and lower the corer between horizontal and vertical orientations.
During testing at Bermuda Rise, core recovery exceeded 38 m, with cores generally filling 85% to 90% of
the piston core barrel length. The test location has been cored many times before and stratigraphic
correlation of the new cores with ODP Site 1063 shows that the new system recovered sediments without
stretching. Three cores exhibit some evidence of compression at about 30 mbsf, while two others do not.
These two cores were collected with a reduced-diameter core cutter, minimizing internal friction and
enhancing core recovery.
Four of the new cores completely recovered the last 150,000 years of sedimentation at Bermuda Rise with an
average sedimentation rate of greater than 25 cm kyr-1. The millennial-scale climate oscillations
characteristic of MIS 2, 3 and 4 in the Greenland ice cores are readily seen in the sediment cores. These
cores will provide an excellent archive of changes in North Atlantic deep water circulation recorded at
Bermuda Rise.
http://www.whoi.edu/projects/longcore/
PP13B-1439
A Predictive Model for Investigating Seagrass Paleoecology, Biogeography and Diversity
Seagrasses are highly productive components of coastal ecosystems that play significant roles in the flow of nutrients and the modulation of physical conditions within the world's oceans. However, in spite of the significant role seagrasses play today, the fossil record contains little evidence of the distribution and abundance of seagrass species in the past and many questions about their biology, ecology, and evolutionary history remain. We have developed, and present here, a parameter driven numerical model of global seagrass biogeography and diversity appropriate for paleontological and paleoecological investigations. The global distribution of seagrasses in our model is dependent on four input parameters, water temperature, water salinity, water depth, and photosynthetically available radiation at depth. With these limited inputs, our model captures both the location and biodiversity of modern seagrass distributions well. The simplicity of our model and its robust representation of modern conditions give it tremendous flexibility for applications throughout the ~70 Ma long history of seagrasses. Paleo ocean temperatures, salinity, water depths, and incident radiation are available from paleoclimatic/proxy datasets and/or numerical simulations of past environmental/climatic conditions, thus permitting investigations into time specific seagrass biogeography and diversity throughout its evolutionary history. In addition, the simplicity of our model allows for theoretical investigations of seagrass paleoecology and response to environmental changes. Both applications will contribute significantly to furthering our understanding of seagrasses, seagrass dominated ecosystems, and the roles they have played in the earth system over the past 70 Ma.
PP13B-1440
Late Quaternary Paleoclimates of Turkey From Glacial Records and Their Link to the Climate Change of the Past Century
Glaciers are not among the first things usually associated with Turkey. But glaciers do exist in several high mountains of Turkey, and glacial-geological evidence show that much bigger glaciers existed in Turkish mountains in the past, providing information on paleoclimate. Mount Ağri (5137 m) (also known as Mt.Ararat), in the Eastern Anatolia, has a large ice cap with several outlet glaciers. Mount Cilo (4135 m), in the Southeastern Turkey, has active glaciers up to 1.5 km long. Kaçkar Mountains (3932 m), on the Black Sea coast, have about 1 km long glacier. Mount Erciyes (3917 m) is the westernmost mountain that has a glacier today. Recent cosmogenic 10Be and 36Cl dating of glacial deposits and modeling of glacier flow on the mountains of Turkey reveal Late Quaternary paleoclimate of the region. Late Glacial Maximum glaciers were the most extensive ones in the last 22 ka (thousands years) and they developed in cold (6- 11.5°C colder than today) and wet (up to 2 times) climates. Late Glacial (14.1 ± 1.3 ka ago) climate was colder by 5 to 8°C based on 50% wetter and 25% drier conditions, respectively. Early Holocene moraines (range from 10.2 ± 0.2 ka to 8.6 ± 0.3 ka ago) in the central Turkey show that glaciers were extraordinarily large and climate was up to twice as wet as today. Glaciers present in Turkish mountains today may be remnants from the last advance (possibly the Little Ice Age) and their length change since the beginning of the century reveals a constant retreat under a warming rate of 0.9-1.2°C per century, consistent with the global warming trend.
PP13B-1441
10-Be Chronology of Late Pleistocene Outburst Floods in the Upper Arkansas River Basin, Colorado
During the Last Glacial Maximum (LGM), several eastward-flowing glaciers originating in the Sawatch Range, CO expanded into the upper Arkansas River valley. One of these glaciers, located in the Clear Creek valley, dammed the Arkansas River impounding a large lake. At least four coarse-grained (boulders >4 meters) flood terraces in the Arkansas River basin attributed to ice-dam breaches have been identified down-valley of the Clear Creek tributary. Here, we use 10-Be dating to constrain the age of the youngest two terraces (herein referred to as upper and lower). 10-Be ages of 19.3 ± 0.8 and 20.9 ± 1.0 ka on two boulders from the upper terrace provide an age for the upper terrace and a maximum age for the lower terrace. Two additional boulders from the upper terrace and two boulders from the lower terrace are currently being processed and will provide additional chronological constraint. Preliminary results indicate that flood boulders on the upper terrace are in broad agreement with the older mode (22.0 ± 1.4 ka, n = 5) of a bimodal 10-Be age distribution of clasts from a single-crested Pinedale moraine in neighboring Pine Creek valley. The younger mode in this distribution (15.2 ± 0.9 ka, n = 7) suggests that ice was near its LGM maximum extent as late as 15.2 ka and may correlate with the younger flood terrace. Additionally, we sampled four boulders and one cobble from a single-crested, left-lateral Pinedale moraine in the Clear Creek valley to further assess the connection between moraine abandonment age and flood terrace age. 10-Be ages of large flood boulders on flat terraces may serve as better sample types than moraine clasts for determining the glacial history of the upper Arkansas River basin.
PP13B-1442
Middle Holocene Unconformity in Seneca Lake, NY
The post-glacial history of the Finger Lakes, NY have involved several changes in lake levels throughout the latest Pleistocene and Holocene, resulting from the changing position of the retreating Laurentide ice sheet, river outlet position, glacial rebound, and water balance. Previous studies of high-resolution seismic reflection profiles from three Finger Lakes define a middle Holocene erosional surface at water depths as great as 26 m in the northern end of each of lake. There are two proposed hypotheses to explain the origin of the observed erosional surfaces: 1) subaerial erosion during a lake lowstand and 2) erosion resulting from increased internal seiche activity. To evaluate these hypotheses, we examined a series of 2 to 5 m long piston cores collected along a north-south transect from one of the Finger Lakes, Seneca Lake. Cores were correlated using distinctive changes in the profiles of grain size, loss-on-ignition, and magnetic susceptibility. We recognize a significant erosional unconformity of early to middle Holocene sediment at modern depths <60 m because portions of the normal deepwater sediment sequence were missing in cores and were commonly replaced by a thin zone of sand and abraded shells (bivalves, gastropods). At water depths >60 m, the unconformity continues as a conformable zone. We attribute the unconformity to wave abrasion and nearshore current winnowing of the shoreface during a lowstand. With an assumption of an effective 20 m wave base, the depth to the low level lake surface responsible for the unconformity is estimated to be 40 m. The age of the unconformity is ~6 ka, based on radiocarbon ages of lithologic boundaries in the sediment cores. Because the unconformity grades into a conformable zone in deepwater cores that display no change in lithology, we hypothesize that the large-scale lake level drop is likely not the result of climate change, but rather a change in accommodation space in the northern portion of the lake basin due to glacial rebound.
PP13B-1443
COMPARISON BETWEEN PAEOENVIRONMENTAL AND LAND USE CHANGES RECORDS IN BRAZILIAN AMAZON ECOSYSTEMS
Interpretations of biomass burn records in lacustrine sediments need a comparison among the charcoal
particle fluxes influenced by different plant communities. The charcoal fluxes, which are related with
paleofires, represent an important disturbance to the atmospheric system. These charcoal particles emitted
to the atmosphere can promote a decrease in the sunlight penetration and greenhouse gas
enhancement.Thus, the evaluation of charcoal deposition, as a consequence of regional burns, will have
great importance to determine the impact of climatic change in different tropical ecosystems. This subject will
be an important contribution for understanding the dynamics among vegetation, climate and carbon cycle
along the present interglacial. In this study, paleofires records were obtained through the charcoal particle
fluxes analysis in sediments of lakes surrounded by different vegetation, which represents the most spread
ecosystems in Brazil. The main goals were to identify major events of vegetation burn during the Holocene
and evaluate the influence of biomass availability to charcoal fluxes. Fires records were obtained through the
charcoal particles flux analyses in lacustrine sediments cores at the following locations Brazilian Amazon:
Lagoa da Pata (AM); Humaitá (AM), Lago do Saci (PA), Carajás N4, (PA); and Caracarana (RO) and
reservoirs sediments in an intense land use change region (Alta Floresta, MT). The charcoal analyses could
have also a great importance in evaluating the impact of dry climates in different ecosystems. Determination
of fire frequencies and dimensions in key areas of South America, during the Holocene, is a first step to
understand the global carbon transference between terrestrial and atmospheric systems. The synchronism
among the fires occurrences show a good relation with the middle Holocene dry climate phase in Brazil.
Discrepancy in the flux values could be attributed to differences in biomass availability provided by these
ecosystems and paleofire intensity.
http://www.uff.br/geoq
PP13B-1444
Dinosaur Footprints in Lower Cretaceous Beds in San Juan Raya, Southern Mexico and the Paleoenvironmental Implications
Dinosaur footprints were traced at San Juan Raya, an important site in Mexico, a world fossil site. This site is found at South-west of the State of Puebla, within the Biosphere Reserve of Tehuacan-Cuitcatlán, to the southwest of the Tehuacan valley. These footprints were recorded by tracing them on transparent paper at Barranca Agua Nueva, at point 18°18.56´N 97°37´W. Using Jacob´s staff a stratigraphic register was generated from 50 m ascending and descending in stratigraphically direction from the bed where footprints were founded. Bivalbes, nerineas, shell fragments, and trigonias were founded in this sequence as well as cross bedding of clays and fine grain sand, some which display ripples. Fifty two footprints were recorded and five different tracks identified, observing two different sizes. The tracks of dinosaur footprints present the common Teropode ichnites. The succession where dinosaur footprints have been found, are interpreted as a peritidal environment. This investigation contributes to an eco-tourism project of San Juan Raya.
PP13B-1445
Tropical Eastern Pacific- Interhemispheric teleconnections during the last 2000 years.
The Peruvian continental margin sediments are normally subjected to bottom water suboxic conditions as well as to high loadings of organic matter from the surface waters. However oceanic variability at different temporal scales modulate the intensity of the particle flux and water column oxygenation, which are expected to influence the inventories and downcore distributions of organic matter and trace metals. The main goal of this study is to explore the interdecadal to centennial changes in paleo-redox conditions of the Peruvian margin sediments, as inferred by the downcore variability of inorganic geochemical parameters and try to interpret them in relation to variations in redox-conditions linked to organic particle flux. Sediment cores collected off the central Peruvian coast reveal that the Medieval Climate Anomaly (MCA) was marked by stronger reducing conditions in the sediments. Proxy records from the tropical Pacific Ocean show contemporaneous changes indicating cool central and eastern tropical Pacific SSTs during this period. This MCA was followed by wetter conditions and warming coastal SSTs during the transition into the "Little Ice Age" (LIA). Comparison with other records in the Pacific and in Cariaco Basin strongly suggests the meridional change of the ITCZ as the key mechanism explaining the centennial-scale changes.
PP13B-1446
Modelling the climate of the last millennium: The relative influences of Volcanism vs. Solar radiative forcings on natural, internal variability
Climate simulations and comparisons of their results with paleoclimate reconstructions can greatly improve our understanding of the processes governing climate change over the past centuries. For the past millennium, in particular, it is likely that natural (e.g., volcanic and solar radiative) and anthropogenic (greenhouse gas and sulphate aerosol) forcings, and natural, internal variability (e.g., such as the NAO, ENSO, AMOC, etc) have played the most important roles. Most groups so far (e.g., IPPC, 2007) have applied high frequency anomalies to the solar constant to mimic the volcanism occurrences and amplitude over the last centuries. From such an approach, however, the only way to estimate the realism of the model simulations versus observations is to compare averages of hemispheric to global model results to a "blend" of proxy and/or instrumental data on the same global scale. In other words, such an approach prevents working on a regional and seasonal scale. Yet, the climatic impact of volcanism highly depends on the eruption season with a latitudinal dependence of the cooling progression in the troposphere (warming in stratosphere) for at least 2 to 3 years for the larger eruptions. Here we will present the first results of simulations for the last millennium climate conducted with the IPSL coupled ocean-atmosphere model including either solar variability or a monthly volcanic forcing that varies latitudinally to reproduce the radiative impacts of stratospheric loading of volcanic aerosols. The general aim of the present work is to estimate the possible forcing role and feedbacks of volcanism and solar forcing during the Little Ice Age and Warm Medieval Period in tropical and northern high latitudes.
PP13B-1447
Impact of the Greenland Ice Sheet on Northern Hemispheric Glacial-Interglacial Cycles
The cryosphere is considered to be one of the major influences on global climate change through the Cenozoic and into the future. Climate-ocean-cryosphere feedback mechanisms influence rapid transitions from glacial to interglacial states and vice versa. However, much of the sensitivity of the system and the dynamics involved in these abrupt transitions remain poorly understood. Here, we investigate the climatic sensitivity of the Northern Hemisphere to the removal of the Greenland ice sheet by applying a coupled GCM-ice sheet model. The focus of the study lies in analyzing the role of Greenland in the inception of continental ice sheets. Interglacial to glacial transitions are modeled using boundary conditions representative of Pliocene and late Pleistocene conditions. We use the latest (2008) version of the GENESIS GCM (version 3.0) asynchronously coupled to a standard thermomechanical ice-sheet model. Four simulations and a modern preindustrial control run are performed. A modern sensitivity test is run to investigate the effects of deglaciation on preindustrial climate conditions. The paleoclimate simulations use both modern and ice-free Greenland topography and vegetation, modern and 116ka orbits, and 250 and 400 ppmv CO2. The impact of the melted Greenland ice sheet reaches beyond the local-regional scale, with significant effects on Arctic sea ice, radiation budgets, snowfall, atmospheric circulation patterns, and moisture availability. This has an impact on internal feedback mechanisms vital for continental ice sheet inception. The effect of Greenland's interglacial survivability on Northern Hemisphere glacial cycles will be explored in a long, time continuous simulation using asynchronous GCM-ice sheet model coupling.
PP13B-1448
Using CAM3 and the Alkenone Method to Understand how Pliocene SST's Affect California and Other Climates Adjacent to Upwelling Regions
The Intergovernmental Panel on Climate Change fourth assessment report established with 90% confidence that anthropogenic climate change will result in a warmer world. In order to more fully understand possible future climate, past analogues of warm periods should be analyzed. The early Pliocene is an appropriate analogue because the continental configuration was similar to today and CO2 levels were comparable to present (~100ppm higher than pre-anthropogenic levels). This project has two objectives: 1.To test the atmospheric sensitivity to USGS PRISM2 dataset revised to better approximate proxy data indicating warmer SST's in upwelling regions and 2. To provide early-Pliocene (2.7- 3.5 Ma) SST estimates for ODP site 1018 on the California Margin (36°59.4'N, 123°16.5'W) using the UK'37 SST proxy. Recent UK'37 proxy data reveals that PRISM2 underestimates SST's in Pacific and Atlantic coastal upwelling regions. The sensitivity of the atmosphere to significantly warmer SST's in upwelling regions was tested using the National Center for Atmospheric Research (NCAR) Community Atmospheric Model, version 3 (CAM3). Initial conditions were supplied by the USGS PRISM2 project and include Pliocene SST's, vegetation cover, sea level height, topography, marine and continental ice extent. Pliocene SST's along the Californian, Peruvian, North African and South African margin were modified to reflect proxy observations from 4 sites. The lack of observational coverage (1 data point per region) required interpolation of the areal extent of the SST warming anomaly indicated by the proxies. Experiment results show increased cumulative precipitation and humidity in regions where the original PRISM2 predicted drying. The predicted North American increase in precipitation is in better agreement with geologic proxies indicating wetter conditions. Warmer SST's also causes weaker wind velocities along the North American, Peruvian, and North African margins, and stronger winds along the South Africa margin. More observations are needed to determine the influence of upwelling SST's on regional climate. UK'37 SST estimates from ODP site 1018 will further constrain SST anomalies used to test the atmospheric response of future simulations.
PP13B-1449
Interannual Variability of Seasonally Influenced Playa Lake Inundation in Northern Mexico: Possible Analogs for Wetter Holocene Climates
Playa lakes in the Chihuahuan Desert, northern Mexico respond to regional climatic signals and display large interannual variability in the timing and duration of flooding. These playas, located on the boundary of the summer North American monsoon system and the winter frontal system, are in a critical location for understanding the variability of these two precipitation modes during past and future climate change. During the Holocene, elevated beach ridges along the edges of these playas indicate the existence of at least three periods with perennial lakes and therefore effectively wetter than modern climates. Increased winter precipitation has been suggested as a mechanism for Holocene lake highstands from the Mojave Desert in the southwestern United States with similar ages to those lakes in northern Mexico. The Mojave Desert is not currently influenced by the North American monsoon, so it is important to understand the interaction between summer monsoonal versus winter frontal precipitation in maintaining wetter than modern climates in northern Mexico. We use a time series of modern playa inundation events from remotely sensed data and concurrent precipitation records to examine the relative contributions of summer and winter precipitation to playa filling. This modern precipitation-inundation analysis may aid in the interpretation of the Holocene lake highstands in northern Mexico. Playas are generally inundated with water by late summer and dry out by early to late winter. Data in a long time series derived from Landsat imagery extends into 1984 and shows a shift from larger, long-lived playa lakes toward smaller, shorter lakes following 1994. The Atlantic Multidecadal Oscillation undergoes a phase shift at the same time. The persistent El-Nino events of the early 1990s occurred at the same time as the only multi-year playa lake in the record. Data from the Moderate Imaging Spectroradiometer (MODIS) satellite has allowed the creation of a more detailed data set of the flooding and subsequent evaporation of the ephemeral lakes with a high temporal resolution. The dynamic response of the playa inundation pattern to the seasonality of regional precipitation is evident in the timing of the initial flooding event, the extent of inundation and the duration of standing water. The three playas receive inflow from separate sub-basins and are unequally affected by each seasonal precipitation regime. The analysis of the relationship of gridded precipitation data with the detailed inundation time series was used to quantify interannual variability for the period between 2000 and 2008. The high temporal resolution of the MODIS record allows us to connect the dynamics of annual playa inundation with specific precipitation events.
PP13B-1450
Historical Susceptibility of Forest Fires in the Carajas Region, Brazil
The Carajas Region in the Para state, nowadays keeps a vast area of forests protected by Units of Conservation and Indigenous Land. Despite the efforts and investments done by private companies and government agencies to prevent forest fires, they are still registered, being one of the major factors of degradation of forests, flora and fauna. Thus there is a need to improve the understanding of these burning processes at present, and its evolution in different time scales, which allows comparison between patterns of fire occurrences related to climate and human reasons. This study aims to assess the evolution of the climate of Carajas region along the Quaternary, with emphasis on natural occurrence of fires related to historical events palaeoclimatic. For this a sediment core of a lake with 450 cm of depth was collected. Chronology is being determined by the radiocarbon method. Ours specific objectives are quantify and qualify the source of sedimentary material, determine concentrations of biogenic elements and minerals, through granulometric and mineralogical analyses and of quality and quantity of organic matter through the establishment of elementary (the C/N) and isotopic ratios (ä13C and ä15N). The dimensions of processes linked to the biomass burning will be determined by quantifying of charcoal fragments resulting from fires through microscopic analysis. This seeks to reconstruct the environmental scene and paleoclimatics conditions related to events of biomass burning, demonstrating the susceptibility of this historic region to the occurrence of fires according to the different climate stages identified.
PP13B-1451
The Occurrence and Climatic Implications of a Rapid Regression of Lake Elsinore, CA, During the Last Glacial Maximum
Southern California is a densely populated region, highly sensitive to climate change and prone to potentially devastating hydrologic variability (e.g. droughts, floods, etc). In the interest of characterizing past climatic and hydrologic variability, this study analyzes a sediment core from Lake Elsinore, California with a particular focus on a possible rapid regression event at the height of the Last Glacial Maximum (LGM) (between 19,330 and 21,070 calendar yr BP). Sediment analyses (grain size, magnetic susceptibility, and total organic matter) and geochemical analyses (δ13C and molar C/N) are used to characterize and identify this event (hereafter referred to as the Last Glacial Maximum Regression Event or LGMRE). The combination of sediment characteristics of the LGMRE is not observed elsewhere in sediment core LESS02-09 suggesting that the event is unique over the period of observation. This rapid drying event is superimposed on a longer, orbital scale transgressive/regressive cycle. Given the generally wet climate of the LGM, the presence of the LGMRE is unexpected and indicates that Southern California is susceptible to rapid climate change. Evidence suggests synchrony at both orbital and centennial time scales between the Lake Elsinore climate record of the LGM and other terrestrial and marine climate records from southern California as well as the Great Basin region. Furthermore, evidence is presented for synchrony between the Lake Elsinore sediment core and the GISP 2 ice core record from Greenland, at both orbital the centennial time scales, suggesting climatic teleconnections between Southern California and the North Atlantic. It is possible that these two geographically distant areas are linked via dynamics of the altered Last Glacial Maximum jet stream.
PP13B-1452
Last Glacial Maximum Climate in the Central Rocky Mountains, USA
While the changing extent of alpine glaciers is compelling evidence of climate change, extraction of quantitative data on past climate from changes in ice extent is difficult. It is particularly difficult to separate the effects of temperature and precipitation changes. Studies in the central Rocky Mountains have used several glaciological methods, including distributed energy/mass balance modeling, degree-day modeling, and modeling by analogy to climates at equilibrium lines of modern glaciers, to determine paired values of temperature and precipitation change that would have sufficed to maintain glaciers at their Last Glacial Maximum (LGM) extents. In the Colorado Rockies different glaciological methods produce generally similar estimates of LGM temperature/precipitation change combinations, indicating that in the absence of precipitation change, temperature depression ranging from 6.4 to 8.5°C would have been necessary to sustain LGM glaciers. With precipitation halved from modern values, modeled LGM temperature depression ranges from 8.0 to 10.4°C, with twice modern precipitation, from 3.7 to 6.8°C. A distributed energy/mass balance model (Plummer and Phillips, 2003) for the LGM Middle Boulder Creek Glacier in the Colorado Front Range indicates temperature depressions of 6.8°C, 8.0°C, and 5.0°C, for no change, halving, and doubling of precipitation respectively. Comparison to studies applying the same model (Laabs et. al, 2006; Refsnider et al., 2008) indicates that LGM glaciation in the Wasatch Range of Utah required either about twice as much precipitation relative to present as did LGM glaciation in Front Range, or a 2 to 2.5°C greater temperature depression. LGM glaciers in the Uinta Mountains of Utah, geographically between the Wasatch and the Front Range, generally required intermediate temperature/precipitation changes. This pattern may reflect the effect of pluvial Lake Bonneville as a local moisture source for LGM glaciers or may reflect a broader pattern of regional differences in climate change.
PP13B-1453
Paleoclimatic Changes In The Santa Ninha Lake, Curuai floodplain, Brazil
The consequences of climate changes in the Amazon has received increasing attention from the scientific community. This makes essential to know how the Amazonian ecosystems responded to past climate change. It is known that floodplains have an elevated potential in accumulating organic matter, which provides important information about climate change occurred in the past. In this study, a sediment core was collected from the Santa Ninha lake (core TA14), Curuai floodplain, located on the right margin of the Amazon River, at 850 km of its estuary. Radiocarbon dating and analyses of sediment granulometry and organic matter elemental (organic carbon and nitrogen) and isotopic (ä13C) composition were employed to characterize the sedimentary processes and organic matter inputs. The studied core has 270 cm length, that correspond to 5700 years cal BP. The results indicated five different sedimentary environments. A flooded vegetation at the base of the core (till 5000 cal yrs BP) was substituted by graminea banks, which changed to a floodplain encompassing prolonged annual dryness at 4000 cal yrs BP. Since 700 cal yrs BP to the present day, the varzea lake, permanently overflooded, has been installed. These changes are interpreted as a response to an increase in the level of water in the river during the floods, which are consequences of climate change that occurred in the region.
PP13B-1454
Geochronology of Playas Lake, NM and Willcox Playa, Arizona
Playa lake basins contain valuable archives of late Quaternary paleoclimatic conditions in the southwestern United States. Previous research on lake basins in the region has revealed several pluvial intervals post- dating the last full glacial period; however, the timing of these intervals can only be assessed through the collective analysis of individual lake-level histories. While previous studies of lake core sediments have provided baseline data for climate modelers, the accuracy of most lake chronologies has been limited by uncertainties associated with 14C reservoir corrections. Further, most studies have used the sedimentological, chemical, and biological characteristics of lake sediments to infer relative lake-level. In contrast, radiocarbon-dated shoreline deposits—although unfortunately rare—can provide accurate information about the timing and duration of high stands, as well as a record of absolute lake-level during these events. Recent investigations of shoreline and spring sediments from playa lake basins provide preliminary geochronological and paleoenvironmental information about effective precipitation in the Southwest during the late Pleistocene and early Holocene. The results of ongoing investigations at Willcox Playa, Arizona, and Playas lake, New Mexico, are presented here.