PP43A-0589 1340h
Calibration of transfer functions between phytolith, vegetation and climate for integration of grassland dynamics in vegetation models. Application to a 50,000 yr crater lake core in Tanzania.
Global vegetation models provide a way to translate the outputs from climate models into maps of potential vegetation distribution for present, past and future. Validation of these models goes through the comparison between model outputs and vegetation proxies for well constrained past climatic periods. Grass-dominated biomes are widespread and numerous. This diversity is hardly mirrored by common proxies such as pollen, charcoal or carbon isotopes. Phytoliths are amorphous silica that precipitate in and/or between living plant cells. They are commonly used to trace grasslands dynamics. However, calibration between phytolith assemblages, vegetation, and climate parameters are scarce. This work introduces transfer functions between phytolith indices, inter-tropical grassland physiognomy, and bio-climatic data that will be available for model/data comparisons. The Iph phytolith index discriminates tall from short grass savannas in West Africa. A transfer function allows to estimate evapo-transpiration AET/PET. The Ic phytolith index accurately estimates the proportion of Pooideae and Panicoideae grass sub-families, and potentially the C4/C3 grass dominance on East African mountains. The D/P index appears as a good proxy of Leaf Area Index (LAI) in tropical areas. These environmental parameters are commonly used as vegetation model outputs, but have been, up to now, hardly estimated by vegetation proxies. These transfer functions are applied to a 50,000 yr phytolith sequence from a crater lake (9°S; 33°E Tanzania). The record is compared to the pollen vegetation reconstruction and confronted to simulations of the LPJ-GUESS vegetation model (Stitch et. al, 2003).
PP43A-0590 1340h
Long Distance Pollen Transport to the Arctic: a Useful Proxy to Calibrate Atmospheric Circulation?
Tracing modern atmosphere dynamics is important to constrain models used for past climate reconstruction. The main types of tracers of arctic air masses are chemical and show different patterns. Dust in the ice at the summit of the Greenland ice cap has been shown, through isotope analyses, to have originated from Chinese deserts, mostly the Takla Makan and Gobi. Conversely, the chemical composition of the aerosols reaching the summit of the ice cap associated with backward air masses trajectories points to source areas in North America, Europe and Asia. A total of four pollen traps have been displayed on both western and eastern coasts of Greenland during the last four years in order to assess long distance transport in the Arctic domain and to identify potential vegetation source areas associated with air mass pathways. We are demonstrating the long distance transport of pollen originating from North America, Great Lakes area to southern Greenland at least during two consecutives years, 2002 and 2003. Thus a regular pattern of air masses responsible for the transport of pollen grains from North America to Greenland should be constant, as already described for anthropogenic pollutants. Another pollen trap was installed on the sea ice during the ice-sea drift expedition from North Pole of French explorer Dr. Jean-Louis Etienne in 2002. In that case we demonstrate two long distance transport to the North Pole from two different Eurasian regions during 2002: western Europe and eastern Siberia. Until now the use of pollen as an air mass tracer had not yet been investigated. Here we show that first evidence pollen represents a biological alternative to understand both present and past air mass dynamics in the Arctic and its associated relationship with biosphere changes.
PP43A-0591 1340h
Seasonal Climate Dynamics Inferred From High Resolution Modern Diatom Data
keywords: seasonal, sediment-traps, diatoms, lakes To understand and predict future climatic changes, we study past climate dynamics, using subfossil diatoms deposited in lake sediments. A training set consisting of surface lake sediments integrating diatom assemblages over recent years is the classical approach to reconstruct past environmental conditions in palaeolimnological research. However, not only annual temperatures and average limnological conditions are relevant but also seasonal thermal and limnological variability, as evidenced by spring and autumn diatom blooms. As high temporal resolution plays an important role in understanding the diatom ecology and its use in palaeolimnological reconstructions, we investigated diatom succession and seasonal limnological variability on a bi-weekly basis using sediment traps. In order to better understand the impact of climate on the seasonality of diatoms we studied 6 lakes distributed over an altitudinal gradient from 330 to 950 m a.s.l., in the Laurentides Provincial Park region north of Quebec-City, Canada. Multivariate statistics was applied to explore the main biological and limnological patterns in the modern data, revealing that the climatic gradient explained most of the biological variance. One advantage of sediment traps is that, compared to surface sediment samples, the time of deposition is exactly known, thus changes in environmental variables can be better related to shifts in the biological assemblages. From one of the study lakes, at 830 m altitude, a sediment core was taken. Fossil diatoms of the past 9500 years were analysed at high resolution (about 15 years/sample) and modern seasonal diatom distribution was used to interpret changes in fossil diatom assemblages. From ca. 9.5 until ca. 8 ka cal. BP, spring bloom species that are presently found in the low altitude lakes occurred with ca. 30%, whereas an autumn bloom species typical of autumnal diatom communities in the highest elevation lake occurred with 50%. In the more recent sediments of the core, autumn bloom taxa typical of the lowest altitude lakes increased upcore to 20%. These patterns could be related to a cooling of spring temperatures and warming of autumn temperatures during the Holocene, which are in agreement with changes in spring and autumn solar insolation patterns of the Milankovitch orbital cycles. Contrary to the surface sediment sample technique, our novel approach using sediment traps with high temporal resolution of modern data may allow inferences about past seasonal climate dynamics.
http://www.cen.ulaval.ca/paleo/Sonja/Hausmann.html
PP43A-0592 1340h
Record of the Southwest Monsoon from Gulf of Mexico Sediment Cores
Summer monsoonal rains are an important source of moisture to portions of southwestern United States and northern Mexico. Changes in the amount and seasonal distribution of precipitation in this semi-arid region of North America influence overall water supply and severity of fires. Historical records demonstrate that precipitation in the southwestern U.S. is quite variable, but the long-term (millennial-scale) variability of the monsoon system is not well known. Studies based on tree rings can provide highly resolved records of past conditions, but separating temperature and precipitation signals can be difficult, and determining seasonality of precipitation is challenging. In addition, tree-ring records usually represent short intervals of the Holocene, and they often reflect local conditions. In this study, we show that variations in the abundance of the planktic foraminifer Globigerinoides sacculifer in marine sediments from the Gulf of Mexico are a proxy for the southwest monsoon on millennial and sub-millennial time scales. The marine record confirms a severe multi-century drought centered at ~ 1600 calendar years BP as well as several multidecadal droughts that have been identified in a long tree-ring record spanning the last 2000 calendar years from west-central New Mexico. Analyses of the marine and tree-ring records indicate that decadal- and century-scale changes in monsoon intensity are related to solar variability. The marine monsoon proxy provides the potential for constructing a highly resolved, well-dated, and continuous history of the southwest monsoon for the entire Holocene.
PP43A-0593 1340h
Deciphering the Depositional History of the Hudson Estuary and Estimating Summertime Precipitation Changes in the New York City area from the mid to late Holocene (7-1 ka)
Paleosalinity estimates and sedimentation rates inferred from core samples from the Hudson Estuary indicate the influence of both the estuarine turbidity maximum (ETM) and climate changes in the evolution of the estuary from centennial to millennial timescales. Cores examined in this study are located in the segment of the Hudson Estuary 26 to 50 km upstream from Battery Park, the southern tip of Manhattan. An age model was constructed using C-14 dating. Paleoenvironmental interpretations are based upon paleosalinity estimates, grain size variability, and sedimentary structures. Summertime paleosalinity estimates were inferred from a new method using $\delta$$^{18}$O and $\delta$$^{13}$C records, as well as foraminiferal studies. Isotopic analyses were obtained from a narrow size fraction (1.0-1.7 mm) of bivalve shells of a single species ({\it Gemma gemma}). This represents the summer growth of a first-year bivalve shell, thereby reducing the uncertainty related to annual changes in temperature. Oxygen isotopes are dependent on temperature, whereas $\delta$$^{13}$C are not. The fact that both of the isotopic records correlate well indicates temperature played a minor role in the $\delta$$^{18}$O record. A good correlation in $\delta$$^{18}$O records exist among the cores of this study indicating that this new method for reconstructing a paleosalinity record is robust. Because salinity changes in the Hudson River are controlled by runoff/precipitation, these data can be used as a proxy for summertime precipitation changes in the Hudson River. These results suggest that the mid Holocene was characterized by major dry periods and greater variability in summertime precipitation during the mid Holocene (6-5 ka) with an abrupt increase in summertime precipitation occurring between 3 and 2 ka. Sedimentation rates in the Hudson estuary during the mid to late Holocene are generally low and are similar to the rate of sea-level rise in the Hudson River. Exceptions are high sedimentation rates observed in cores on the western side of the Hudson River in water depths of $>$4 m. These high sedimentation rates migrated during the Holocene and are related to a location of the ETM some 20 km upstream of its present position at 3.5 ka. The results of this study are consistent with the idea that at any time, estuarine sedimentation is highly localized, suggesting a more complex depositional pattern than previously indicated in estuarine stratigraphic models.
PP43A-0594 1340h
Understanding the Recent Paleolimnological Record From Lake Monroe, FL
Calibration studies of lake sediments allows for an improved understanding of past changes in the climate system, which can also impact the biogeochemistry of a particular system. However, in shallow open basin lake systems, first-order changes in a climate system can impact these records in many ways. A relative rise in base level accompanying the rising sea-level since the last deglaciation can complicate lake sedimentological records near coastal zones. Here we present the preliminary multi-proxy paleolimnological investigation of Lake Monroe from a paleoclimatic and biogeochemical perspective. In order to further understand the spatial differences within the sedimentary record, 20 intact sediment cores (between 0.5m to 1m) were collected from the lake in October 2003 using a modified 5.4 cm inside diameter Wright-Livingston piston corer. Our approach combines geochemical, nutrient, and diatom analyses to reconstruct paleoclimate and biogeochemical changes in the study basin over the last 20,000 years of available material, using the modern record (last 100 yrs) as the calibration period. The lake, which is part of the upper St. Johns River, is shallow and hypereutrophic, and today is strongly affected by fluvial processes. However, our analyses thus far indicate that around 14,000 yrs ago the lake appeared to be more like a wetland. It is important to consider how first-order climate change can affect an archive's paleo-record before quantitative analyses can be conducted.
PP43A-0595 1340h
Enhancing spatial and temporal resolution of trace elements in sediment cores
Sediment cores provide an historical record of seasonality, yearly pollution inputs and longer term climate changes if the resolution of the sampling tool matches that needed for the analysis of the sediment record. While X-ray florescence has been routinely used for elemental analysis in environmental samples, the intense beam of X-rays produced at the Advanced Light Source, Lawrence Berkeley National Laboratory on beamline 10.3.1 provides a unique opportunity to quantitatively probe trace element concentrations in wet samples at sub-millimeter resolution. Detailed analyses of both sediment standards and prepared mixtures of sediment standards have demonstrated linear calibration over three orders of magnitude dynamic range. Calibration was established for eleven elements including; Ti, Fe, Cu, Zn, Mn, Cr, Sr, Pb, Ca, Cl, K. The nondestructive technique rapidly (i.e. less than 20 seconds per spot) quantifies multi-element concentrations at specified locations. Collimating slits are used to control the vertical and horizontal width of the analysis area, varying from 50 to 500 microns. Analysis of frozen wet sediment cores from the former Alameda Naval Air Station's Seaplane Lagoon have resolved trends in the spatial variability of trace metal deposition corresponding to seasonal timescales. Although this method was developed for estuarine sediments, it is well suited to analyze a wide range of linear timescale samples from ice cores to deep ocean sediment cores.
PP43A-0596 1340h
Chironomid $\delta$^{18}$O and $\delta$D as Paleoclimate Proxies: Progress and Puzzles
An increasing number of paleolimnological studies are aimed at reconstructing lakewater isotopic composition, and thus (in appropriate hydrologic settings) the isotopic composition of paleo-precipitation. Records of \delta$^{18}$O and $\delta$D of paleo-precipitation are used to infer changes in climate, including changes in site temperature and storm tracks. This study investigates the viability of using the \delta$^{18}$O and $\delta$D of subfossil chironomid head capsules preserved in lake sediments to reconstruct lakewater isotopic composition. Chironomids (Chironomidae, or non-biting midges) spend much of their life cycle as aquatic larvae, and their chitinous larval head capsules are well preserved in many lake sediments. Wooller et al. (2004) demonstrated that chironomid \delta$^{18}$O and precipitation \delta$^{18}$O are strongly correlated along a transect from Greenland to Vermont (n=4, r$^{2}$=0.96). The goal of the current research is to further investigate the relationships between mean annual temperature (MAT) and the stable isotopic composition (\delta$^{18}$O and $\delta$D) of chironomids, lakewater, and precipitation. We have analyzed more than 100 samples from lakes in Iceland and Arctic Canada, including surface sediments from a transect of lakes representing a broad modern climatic gradient. Results confirm a correlation between chironomid \delta$^{18}$O and both lakewater \delta$^{18}$O and MAT. Chironomid $\delta$D also correlates with lakewater $\delta$D and MAT. On the other hand, preliminary results suggest differences in isotopic fractionation between taxa. Ongoing experiments are aimed at evaluating taxonomic differences and refining our methodology.
PP43A-0597 1340h
A Modified Method for Saline Lake Calcite Isotope Analysis: Application to a Study of Climate Change over 200,000 Years in Death Valley, California.
The standard method of oxygen and carbon isotope analyses for carbonate minerals was first reported by McCrea (1950). Carbonates are converted to CO2 by the reaction of carbonates with 100% phosphoric acid at temperatures between 25 and 95$\deg$C for C- and O-isotope analyses: 3CaCO3 + 2H3PO4 = 3CO2 + 3H2O + Ca3(PO4)2 The reaction time for this method can vary depending on different minerals and temperature. For example, at room temperature, the reaction time could be an hour or less for calcite and aragonite, three days for dolomite, two weeks for magnesite, and several months for siderite. This method is very reliable for almost every carbonate-dominated sample or even trace carbonates in silicate rocks. However, Death Valley saline core sediments showed that this standard method could be problematic for chloride-rich or soluble sulfate-rich carbonate samples because of the production of SO2 and/or HCl gas by partial reaction of the chloride or sulfate minerals with 100% H3PO4. The SO2 and HCl gases can affect the $\delta$-values significantly in two ways: (1) The contaminating gases may react with the CO2 in the mass spectrometer source region, isotopically fractionating the CO2 and/or generating background peaks in the CO2 + spectrum; and (2) The SO2 and HCl may react with interior parts of the mass spectrometer reducing its stability and/or sensitivity. In this study, we choose 85% H3PO4 to react with the lacustrine calcite at room temperature by off-line "Y" tube preparation for 2 to 3 minutes. This modification to the traditional method has resulted in negligible SO2 and HCl production. The CO2 gas generated from each bulk lacustrine sediment sample was manually introduced into a VG 609 mass spectrometer for C and O isotope analyses. The analytical precision is better than $\pm$0.2$\permil$ for both $\delta$13C and $\delta$18O. This modification of the method of McCrea (1950) was applied to determining carbon and oxygen isotopic compositions of lacustrine calcite in bulk saline lake sediments. For a continuous 200,000-year $\delta$18O record of lacustrine calcite from a 186-meter sediment core from Badwater Basin, Death Valley, California, a two-level climatic fluctuation model is suggested.. This record provides new insight to the debate on the timing and driving forces of late Quaternary paleoclimatic changes. Excursions in calcite $\delta$18O are similar to those of $\delta$18O in sulfate in the Death Valley core, as well as to those in marine carbonate (SPECMAP) and polar ice in the Summit ice core (GRIP), Greenland. The Death Valley record shows periodicities of 96000, 39000, 21000, 14000 and 8000 years. The longer-term (96000, 39000 & 21000 years) fluctuations match Milankovitch orbital forcing, and are thus likely to be global in origin; the shorter-term (14000 and 8000 years) fluctuations probably reflect regional climatic and/or hydrologic forcing.
PP43A-0598 1340h
A New Model for Interpretation of Carbon Isotope Values of Lacustrine Sediment: Influence of Summer Moisture
We propose that changes in summer moisture stress force variations in terrestrial organic matter $\delta$$^{13}$C values that are recorded in lake calcite. This relationship should be especially strong in small oligotrophic lakes. Lake sediment $\delta$$^{13}$C(CaCO$_{3}$) values serve as a proxy for summer moisture conditions whereby high summer precipitation and low moisture stress yield terrestrial vegetation with lower $\delta$$^{13}$C(organic) values. This variation is superimposed upon aquatic productivity that is related to supply of nutrients, temperature and light availability. Decay of terrestrial vegetation with low $\delta$$^{13}$C(organic) values decrease the $\delta$$^{13}$C value of the lake's dissolved inorganic carbon (DIC) resulting in lower $\delta$$^{13}$C(CaCO$_{3}$) sediment values. $\delta$$^{13}$C(CaCO$_{3}$) values are linked to atmospheric circulation that drives dry/wet periods and therefore high/low $\delta$$^{13}$C(organic) values. Wet periods are associated with mid-tropospheric troughing over the eastern United States, similar to conditions experienced there during summer 2004. To evaluate this hypothesis, we examined the relationship between various measures of summer moisture and $\delta$$^{13}$C(CaCO$_{3}$) values of carbonate varves from a box core recovered at 22 m water depth in Fayetteville Green Lake, central New York State. Calcite $\delta$$^{13}$C(CaCO$_{3}$) values were determined for the historic period (A.D. 1892-1986) on the summer, calcitic portion of individual varves. Multiple correlations were performed between the carbon isotope values and various measures of moisture stress. We compared $\delta$$^{13}$C(CaCO$_{3}$) values to total precipitation, the Palmer drought Z-index, moisture surplus, moisture deficit, and precipitation-potential evapotranspiration (P-PE). Statistically significant correlations include the 5-year auto weighted average for precipitation (-0.357), surplus (-0.432), deficit (0.387), P-PE (-0.409), and Z-index (-0.288). The strength of the five-year weighting reflects the lag in decay and transport of terrestrial organic matter. This carbon isotope-moisture stress hypothesis provides an alternative interpretation, but is not exclusive of, the traditional productivity model.
PP43A-0599 1340h
Holocene Climate History of North Central Minnesota, Interpreted From $\delta$D and $\delta$$\^{18}$O of Lake Sediments
Stable isotopes of authigenic carbonates in lake sediments are routinely used to reconstruct past climate. When carbonates are absent, other stable isotope records such as cellulose oxygen and $\delta$D of specific organic compounds such as palmitic acid (PA) are being used to infer water temperature. Here we show that $\delta$D of PA can be used to reconstruct aridity in appropriate climatic settings. Cored sediment from Moody Lake, located near the base of the Crow Wing River watershed, was analyzed for lithological variations indicative of lake-level, total organic and inorganic carbon, pollen, O and C isotopes of authigenic calcite and H isotopes of PA. Modern sediments in Moody Lake contain no authigenic carbonates, but lower sections contain 5$\sim$10% total inorganic carbon. Total organic carbon varies between 10$\sim$35% in the deep-water core. The $\delta$$\^{18}$O values varies from -8$\permil$ at about 11ka $\^{14}$C increasing to -2$\permil$ at ca. 4ka $\^{14}$C. The $\delta$D values are approximately -210$\permil$ at 11ka $\^{14}$C and -180$\permil$ at the top, with a peak of -170$\permil$ in the mid-section. The $\delta$D values of PA can be converted to that of water using a published equation. If we assume that authigenic carbonate is formed only during warm summer months, say at $25\deg$C, the small temperature dependence of carbonate oxygen isotope fractionation allows us to estimate the $\delta$$\^{18}$O of water without introducing a large error, given the range of 6$\permil$ in $\delta$$\^{18}$O values. When the two calculated isotope values are compared to the Global Meteoric Water Line and to local (Minneapolis) precipitation, they fall on an evaporation line of slope $\sim$5, a typical slope observed for the region. Mid-Holocene values are farthest from the local meteoric precipitation indicating greater aridity, and early Holocene values closer to the meteoric precipitation. The overall pattern is interpreted as reflecting cooler and wetter conditions in the early Holocene, gradually increasing temperatures toward the mid-Holocene, much higher aridity during the mid-Holocene, and a return to cooler and wetter conditions during the late-Holocene. Lake-level history derived from stratigraphic correlation of sand layers in shoreline transects is broadly coincident with mid-Holocene aridity. The start of the increase of oak pollen and the highest concentration of herb pollen indicating increased aridity and warmth at $\sim$8ka $\^{14}$C coincide with the beginning of the highest values in $\delta$D and $\delta$$\^{18}$O.
PP43A-0600 1340h
A Holocene Record of Climate Change from the Sierra Nevada, CA, USA: A Paleolimnological Perspective of California Drought
Drought has had disastrous impacts on western North American ecosystems, economies and society, and for many regions is predicted to be a likely consequence of future climate change. The instrumental record, however, spans too short a period to provide the full range of drought variability (including frequency, duration and magnitude), which is critical information to anticipate and prepare for future drought events. Paleolimnology provides a means to reconstruct long-term (1000s of years) climate records from which to determine drought variability. Here we present a Holocene drought record from the eastern Sierra Nevada, CA, USA, and compare this record to similar records from western North America in order to explore spatial variability of Holocene drought. A 3.1 m sediment core was retrieved from Kirman Lake (2,174 m a.s.l.), located west of Bridgeport, CA. At present, Kirman Lake is a relatively small (11.9 ha), shallow (3.8 m), slightly alkaline (pH=7.6), freshwater (salinity=92.7 mg/L), oligotrophic (TP=13.9 μg/L) lake with no inflow and only seasonal outflow. Vegetation surrounding the lake is dominated by sagebrush with some pinyon pine and western juniper in the catchment. Diatoms were identified and enumerated every ~1cm for the top 256cm, which provides a chronological resolution of between 18 to 99 years per sample. Robust diatom-inference models for lake depth and salinity were developed from a 60-lake calibration data set from the Sierra Nevada and applied to fossil diatoms identified in the Kirman Lake sediment core. Results indicate that between ~8,000 and ~3,000 calendar years B.P. conditions were considerably drier than present. A dramatic change in effective moisture (precipitation-evaporation) occurred at approximately 3,000 calender years B.P., when conditions became generally wetter, but also more variable. These conditions have continued to the present. Isotope and mollusc data from the same Kirman Lake core support this interpretation, as do charcoal records from nearby lakes. The striking change in drought conditions at ~3,000 years is approximately coincident with changes in the frequency of El Ni\~{n}o events. The Kirman Lake record is compared to similar records from western North America, and the spatial variability of this change provides clues to the possible forcing mechanisms driving this change.
PP43A-0601 1340h
Ostracode and Organic Biomarker Evidence for Changes in Lake Productivity and Hydrodynamics Since the Late 19th Century in Central Europe
Ostracode species assemblages and organic biomarkers from a 87 cm long core taken at 178 m water depth in Lake Constance (southern Germany) reflect the eutrophication history and changes in lake hydrodynamics. Age control is provided by flood layers, magnetic susceptibility, TOC concentrations, and lead and zinc distribution compared to other, well-dated sediment cores from Lake Constance. As in most deep lakes, the profundal ostracode community is comparatively simple; being composed of a few benthonic species living in and on the sediment (Leucocythere, Limnocythere, Fabaeformiscandona, and Cytherissa) and bentho-nektonic species that swim above it (Cypria). Organic biomarkers comprise autochthonous biomarkers such as dinosterol, brassicasterol, and tetrahymanol and allochthonous biomarkers such as sitosterol, amyrenones, and n-alkanes. Eutrophication in Lake Constance started in the 1940's and reached its maximum in the 1970's as shown by the distribution of dinosterol, tetrahymanol and brassicasterol. The ratios of long- to short-chain alkanes display high values in historical flood layers. Land-plant derived sterols and amyrenones also reflect changes in autochthonous and allochthonous sedimentation. Leucocythere shows maximum abundances during the oligotrophic stage, Limnocythere prefers oligotrophic-mesotrophic lake water. During maximum eutrophication, species diversity is reduced to two species, Fabaeformiscandona and Cypria. The return to meso-oligotrophic conditions at the beginning of the 1990's allowed Limnocythere to recolonize the profundal, and provided optimum conditions for Cytherissa. Leucocythere on the other hand has not yet been able to return to the lake bottom. Stable oxygen and carbon isotopes from Limnocythere and Leucocythere are used to reconstruct changes in oxygen supply of the bottom waters that is ultimately controlled by the North Atlantic Oscillation.
PP43A-0602 1340h
Isotopic Evidence for C4 Grass Expansion During the Last Glacial Maximum and Younger Dryas in Northern Australia
In northern and central Australia, late Quaternary records of terrestrial environmental change are rare due to generally poor preservation of pollen grains and a derth of long-term, continuous lacustrine sedimentary deposits. The Wombe mound spring in the Keep River National Park, Northern Territory, is an organic mound and isolated patch of monsoon vine thicket thought to have formed tens of thousands of years ago. In an effort to obtain a record of paleovegetation and fire history from northern Australia, a 3.4 m sediment core was recovered from the Wombe mound spring and subject to multiple types of analyses. The core represents a continuous depositional sequence with radiocarbon ages spanning the last 35 ka cal years (hereafter referred to as 35 ka). Paleovegetation was reconstructed using a combination of pollen and carbon isotopes in bulk sediment and higher plant leaf wax (HPLW) lipid biomarkers. The fire history was reconstructed from paired graphitic black carbon (GBC) and polycyclic aromatic hydrocarbon (PAH) analyses of the core sediments. Between 35 and 11 ka, the bulk organic carbon (OC) isotope data fluctuate between -22 and -15%, with the most isotopically enriched values measured at 11.4 ka. Between 12.3 and 6.8 ka, OC isotope values decrease by 13%, and remain steady from 6.8 ka to the present at -28%. There are two distinct peaks of isotopic enrichment in the higher plant leaf wax biomarkers. These two peaks coincide with the Last Glacial Maximum (LGM; 21 ka) and the Younger Dryas (YD; 11.4 ka) and represent maximum increases in C4 grasses relative to C3 plants. Relative increases in C4 grasses during the LGM in other parts of the tropics (i.e., Sacred Lake, Mt. Kenya) have been attributed to the competitive advantage of C4 plants relative to C3 plants under reduced atmospheric pCO2 and is likely the cause for C4 expansion in northern Australia. The increase in C4 grasses during the YD is reflected in the bulk sediment and HPLW isotope data and is also documented in the Sacred Lake record and may result from an increase in intensity of the easterly trade winds. GBC and PAH analyses are correlated to each other with maximum concentrations of each occurring between 28 and 30 ka and between 13 and 18 ka. The fact that these records are correlated suggests that each is an independent proxy for fire frequency at the Wombe mound spring. These periods of increased fire frequency may be associated with excessive fuel build-up and burn, or increased vulnerability of the vegetation to periods of enhanced aridity. Low GBC and PAH concentrations at approximately 20 ka and 11 ka are attributed to relatively reduced fuel loads during extreme dry events of the LGM and YD. Low GBC and PAH values during the Holocene coupled with establishment of the C3 mound spring indicate that there is very little evidence of fire over the last 8 ka preserved at the site. This likely reflects the moist microenvironment of the mound spring and not the regional fire history of the area.
PP43A-0603 1340h
Reconstruction of the West Pacific ENSO precipitation anomaly using the compound-specific hydrogen isotopic record of marine lake sediments of Palau
There is still much uncertainty whether the El Niño Southern Oscillation (ENSO) will become stronger or more frequent in a warming global climate. A principal reason for this uncertainty stems from a glaring lack of paleoclimate data in the equatorial Pacific, which hampers model validation. To partly resolve this data deficiency, sediments of three marine anoxic lakes were cored in Palau, an island group that lies in the heart of the West Pacific Warm Pool. The lakes contain seawater that seeps through fissures in the surrounding karst, and they are permanently stratified due to fresh water input provided by the year-round wet climate (map 1970-2000 = 3.7m). During ENSO events, however, the islands suffer from drought. The surface water hydrogen isotopic compositions in the lakes are sensitive to the relative proportions of D-depleted rainwater and D-enriched seawater, and are therefore sensitive to ENSO events. The lake surface water H/D values are recorded by algal and bacterial biomarkers that are preserved well in the highly organic and anoxic sediments, which accumulate relatively fast (mean 1 mm/yr). Ongoing down core measurement will eventually result in a precipitation proxy record of the islands. To obtain endmember D/H values, a comprehensive set of water samples from sea, lakes and rain water was obtained, as well as suspended particulate matter. Higher plant biomarker D/H values derived from the jungle vegetation surrounding the lakes may render supporting climatic proxy data, being influenced by evapotranspiration. Some lakes are inhabited by millions of jellyfish (Mastigias) that live in symbiosis with zooxanthellae. The jellyfish of one of the investigated lakes disappeared completely after the last large ENSO event in 1998 (returning in 2000-01), and a correlation is suggested. To reconstruct the history of jellyfish occurrence, jellyfish and sedimentary lipids were extracted and compared. In addition to a possible ENSO proxy record, this information will contribute to a better understanding of the lake system and ecology of the jellyfish, providing a better basis for conservation efforts.
PP43A-0604 1340h
Compound-specific hydrogen isotope ratios of sedimentary n-alkanes - a new paleoclimate proxy
Hydrogen isotope ratios (deltaD) of sedimentary biomarkers are suggested to record the hydrogen isotope composition of environmental water and to preserve it over geological timescales. Therefore, changes in earth's water cycle, like changing evapotranspiration rates or atmospheric circulation patterns, which are necessary to understand climate variability, could be reconstructed using deltaD values of biomarkers. However, so far no study exists that proves this theory for n-alkanes. Here we present the first systematic approach calibrating deltaD values of recent sedimentary n-alkanes (n-C12 to n-C31) to modern meteoric water deltaD values. deltaD values from n-alkanes (n-C17 to n-C31) extracted from lake sediments along a N-S European climatic gradient from northern Finland to southern Italy are significantly correlated with deltaD values of meteoric water. This clearly demonstrates that sedimentary n-alkanes record the source water deltaD value. The observed isotope fractionation during biosynthesis (epsilon) for the n-C17 alkane of algal origin is constant at -158 permil over a wide range of climates and lakes of different trophic states. This suggests a constant biosynthetic hydrogen fractionation driving the hydrogen isotope composition of aquatic biomarkers. Moreover, evapotranspiration enriches deuterium in terrestrial n-alkanes (n-C25 to n-C31) relative to aquatic biomarkers. This opens the additional possibility to reconstruct paleo-transpiration rates. Our results prove that deltaD values from sedimentary n-alkanes (n-C17 to n-C31) record the hydrogen isotope composition of meteoric water and may be applied to study paleohydrology of lake systems, changes in atmospheric circulation and hence climate history.
PP43A-0605 1340h
Lacustrine Organic Matter Elemental and Isotopic Compositions as Markers of Environmental and Paleoenvironmental Changes: Examples from Lagoa do Caco (Maranhao State, Brazil)
Organic matter is important to the reconstruction of paleoenvironmental changes from lacustrine sediments. Organic matter and its allochtonous and autochtonous fractions provide information about the evolution of ecosystems in the lake catchment and in the sedimentation basin and about physical and chemical water column conditions. Most studies that use organic matter as a marker of paleoenvironmental changes have been limited to relative descriptions of lake evolution because they lack calibration to modern conditions. We present the results of our study of modern sedimentation of organic matter in Lagoa do Caco and their application to reconstruction of late-glacial environmental changes in northeastern Brazil. We measured C/N ratios and carbon and nitrogen isotopic compositions of organic matter in surficial sediments collected along four transverse transects and one longitudinal transect of this lake. Each transverse profile starts from a margin dominated by emergent macrophytes, crosses the central part of the lake, and finishes on the opposite margin. The elemental and isotopic results characterise the different depth-related lake environments and enable interpretation of variations in sediment bulk organic matter and its properties. C/N and del 13C values decrease and del 15N values increase from the lake edge to 4m water depth before stabilizing as algae replace macrophytes as the predominant sources of organic matter. We applied these results to reconstruct a 20-ky sediment-core history of lake level changes based on organic matter properties that reflects the evolution of regional late-glacial and Holocene climate.
PP43A-0606 1340h
Variations in Composition and Preservation of Peat Deposited Since 27 ka in the Baoxiu Basin, Southwestern China: Implications for Environmental and Climatic Changes
Multi-proxy organic geochemical paleoclimate records have been obtained from a 200-cm peat core extending back to about 27 ka cal from the Baoxiu Lake Basin, Yunnan Province of southwestern China. Relatively low del 13C values (-26.3 to -24.3 per mil) of total organic carbon (TOC) and of n-fatty acids (-30.4 to -33.0 per mil), high TOC/TN ratios (17 to 64), and the presence of p-hydroxyphenyl, guaiacyl, and syringyl phenylpropanyl lignin units in pyrolysates show that the source of organic matter is dominated by terrestrial C3 grasses (herbaceous angiosperms) throughout this peat profile. Decomposition of peat is indicated by shortening of alkyl side-chains of methoxyphenols, an increase of oxidation products, and demethylation of methoxy groups of the lignin/polyphenol fraction. Lower amounts of these decomposition proxies below 100 cm indicate good preservation of peat from 26.8 to 22.6 ka and imply good reliability of climatic information derived from this time range in the peat profile. From 26.8 to 23.3 ka , lower inputs of terrestrial plants and lower aquatic productivity are suggested by relatively low concentrations of TOC and phosphorus, mirroring decreased precipitation. Relatively heavier carbon isotopic compositions of plant wax n-fatty acids (C24 - C30) indicate larger contributions of C4 plants, providing a further hint of dry climate. Intermediate del 13C values of TOC and of mid-chain n-fatty acids (C20 - C22) result from an overprint of organic matter from aquatic algae. From 23.3 to 22.6 ka, a rapid increase of precipitation and a resultant C3 land-plant expansion is documented by maxima in concentrations of TOC and phosphorus, a minimum in TOC del 13C, and relatively negative del 13C values of plant-wax n-fatty acids. Since 22.6 ka, climate reconstruction is not reliable because of disturbance of the peat layers. The disturbance is most likely caused by human activities, a conclusion that is supported by a rapid increase in peat decomposition as indicated by more phenol proxies and higher concentrations of phosphorus.
PP43A-0607 1340h
Carbon Isotopic Ratio Of Individual Lignin Moieties In Stalagmite As A Novel Indicator Of Past C3/C4 Plant Variations
Oxygen isotopes,layer thickness,and trace elements of stalagmite provide excellent records of past climatic and environmental change.However,carbon isotopic ratios of speleothem are difficult to interpret,because multiple sources of carbon contribute to the formation of calcite.Organic humic substances inbeded in the stalagmite layers are potential paleoenvironmental archives,but their molecular compositions have not been characterized.Here we report the first molecular-level characterization of stalagmite organic matter using pyrolysis-gas chromatograph-mass spectrometry.Py-GC/MS analyses reveal that speleothems contain a large suite of lignin derived aromatic moeties,and the sample-to-sample variations in composition are relatively small.These compounds were fragments of microbial-oxidized lignin macromolecules,which were derived from vegetation growing in the overlaying soil.Py-GC/IRMS was used to measure isotopic ratio of the compounds found in stalagmites.Two sets of samples were studied.The first set of samples was collected along the longitudinal section of a speleothem,TS0302,from Shihua Cave,Beijing.The \delta$^{13}$C records of organic compounds show temporal variation, which is compared with the \delta$^{13}$C of bulk carbonate. The other set of samples was the top sediment of five speleothems in China (TS0301,Shihua Cave(39.83N,115.67E),Beijing;TW02,Water Cave(41.31N,124.1E),Liaoning;YMB01,Bailong Cave(24.38N, 102.71E),Yunnan;TJ9401,Jiguan Cave(33.75N,111.6E),Henan).The \delta$^{13}$C of organic compounds in these samples is roughly consistent with the C4 grass photosynthesis.Based on the results,we have developed a new approach to unravel the past changes in C3/C4 plant ratios based on carbon isotopic ratios of individual monomeric lignin molecules by using Py-GC/IRMS.Our approach overcomes the problems associated with interpreting carbon isotopic data of speleothem calcite.The new approach allows high resolution reconstruction of past regional variations in the abundance of C3 and C4 plants.
PP43A-0608 1340h
Records of Rainfall and ENSO in the South Pacific From Speleothem Growth Bands
Actively growing stalagmites were collected from the Avaiki cave on the island of Niue in the austral winter of 2002 in order to establish the dominant factors controlling the observed variability in the thickness of their annual growth increments. The isolated island is located (19\deg 05' S; 169\deg 50' W) at the SE fringes of the Pacific Warm Water Pool (WWP) and the instrumental records kept on the island since 1905 indicate that annual rainfall variability is directly linked to the incidence of ENSO. The pronounced rainfall seasonality leaves a mark on the stalagmites such that a layer of clear calcite (ca. 250 microns thick) typically forms during the wet monsoon season (December to April, monthly mean rainfall of 307 mm and mean air temperature of 26\deg C) and a thin dark layer of calcite (ca. 150 microns thick) forms during the dry season (May to November, monthly mean rainfall of 84 mm and average air temperature of 24\deg C). The chronology of four stalagmites, spanning a time interval of up to 200 years, was established on the basis of annual couplet counting and verified by AMS radiocarbon dating corrected for dead carbon contribution. Our study shows good agreement between the annual couplet and the historical rainfall records such that periods of extreme rainfall match faster speleothem growth while droughts correspond to slower stalagmite growth. Power spectra analysis of the couplet thickness data exhibits significant periodicities of 17-20, 10-12, 5-8, 3-4 and 2 years that agree well with the periodicities unraveled in the historical rainfall data. The most prominent cycles revealed in the rainfall data of 3-8 years matches the ENSO cycle (3-7 years) suggesting an ENSO control of rainfall in the region. Lower ranked periodicities of 10-15 years may be related to either a solar variability cycle of 11 years or periodic fluctuations in the expanse of the WWP driven by the Pacific Decadal periodicity (PDO). Our results highlight the potential of high resolution growth band records archived in stalagmites to serve as proxies of climate variability on decadal, century and millennial time scales in the South Pacific region.
http://www.geo.ua.edu/asil
PP43A-0609 1340h
A High-Resolution Climate Record for the Last Millennium From a Scottish Stalagmite
Stalagmites are recognised as important continental archives of palaeoenvironmental information, they can be accurately dated and their subterranean location means that they can accumulate undisturbed for thousands of years. This work takes advantage of the recent developments in the High-Resolution analysis technique of Laser Ablation Gas Chromatography Isotope Ratio Mass Spectrometry (LA-GC-IRMS) to produce High-Resolution stable isotope records and hence a climate record for Northwest Scotland. NW Scotland is a site located on the North Atlantic Seaboard and an area which is thought to be climatically sensitive, particularly in the relationships between precipitation and the NAO and temperature and ocean circulation via the North Atlantic Drift. Initial laser ablation d18O results on a 1000 year old annually laminated stalagmite show oxygen isotope variations in the stalagmite calcite which is greater than can be attributed to temperature change alone. This suggests that the stalagmite is recording a combination of environmental factors and highlights the need for detailed calibration of the modern cave system. An understanding of how these surface climate signals are transmitted through an 18O proxy to a stalagmite via the soil and groundwater system is essential. The cave system from which the stalagmite was sampled was monitored over a 12 month period. Surface and cave drip waters were collected and analysed for a variety of isotopic and geochemical parameters including d18O, dD, d13C. Cave climatology was monitored for temperature, humidity and carbon dioxide concentration. Drip rates were monitored in order to understand the hydrology of the overlying karst system. Initial monitoring results indicate a seasonally variable cave temperature (4-9 degrees C), high relative humidity (100 %); cave air CO2 concentration also follows a seasonal pattern. Waters collected from the surface show seasonal variation in d18O and d2H composition with more positive values in summer. Drip waters show little isotopic variation indicating a substantial degree of mixing in the epikarst. Monitoring suggests that the cave is sensitive to a number of parameters whose dominance may change through time. The role of ventilation and hence kinetic effects upon isotopic fractionation may also play a part.
http://www.gees.bham.ac.uk/research/ascribe/
PP43A-0610 1340h
Climate Change Recorded in Aragonite Speleothems from Central Alabama
The driving forces of global climate change are poorly understood in part due to the lack of high-resolution terrestrial climatic records. The study of carbonate cave formations (stalagmites) often provides uninterrupted annual to millennial records of past terrestrial climate conditions. It is well documented that the growth and isotopic composition of stalagmites are primarily controlled by climatic factors including air temperature, soil microbial activity, and rainfall. Stable isotope analysis of an aragonitic speleothem from DeSoto Caverns (Childersburg, AL) suggests the cave deposits reflect historic and prehistoric climate variations. The stalagmite provides approximately 350 years (determined by annual couplet counting) of climate record for central Alabama with $\delta$$^1$$^8$O values ranging from $\sim$ - 2 to - 5 ($\permil$ PDB) and $\delta$$^1$$^3$C ranging from $\sim$ -4 to - 10 ($\permil$ PDB). High-resolution micro-sampling ($\sim$ 200 $\mu$m) along the growth axis reveals a significant negative shift at about 1850 AD in both $\delta$$^1$$^8$O and $\delta$$^1$$^3$C proxy records suggestive of changing land practices and increased air temperature. The proximity of the cave to the laboratory allows for detailed study of temperature, relative humidity, and $\rho$CO$_{2}$ both inside and outside the cave allowing for a more complete understanding of the relationship between local climate factors and cave deposits. Future stalagmite analysis in DeSoto Caverns may reveal climate conditions for the southeastern United States during the Little Ice Age, Medieval Warm Period, and the 8200-year cold event. Additionally, the location of the study site may provide valuable information regarding the source of moisture (Gulf of Mexico) for the buildup and starvation of the Laurentide Ice Sheet during the last glacial maximum and the subsequent deglaciation.
http://www.geo.ua.edu/asil
PP43A-0611 1340h
High-Resolution Speleothem Records of the Indian Ocean Monsoon Variability of the Last 6 ka and 0,5 ka From Soqotra Island, Yemen
Soqotra is an arid tropical island in the Indian Ocean, situated between the Horn of Africa and the Arabian Peninsula. The inter-tropical convergence zone (ITCZ) passes there twice each year, resulting in a bi-annual rainy season. High-resolution \delta$^{18}$O and \delta$^{13}$C ratios of speleothems from two different caves are used to reconstruct changes in the Monsoon intensity and/or variability. Based on 10 TIMS $^{234}$U/$^{230}$Th dating, two active speleothems from Hoq (S-STM1) and Kazekas Caves (S-STM5) have formed over a period of 6 ka BP and 0,5 ka BP, respectively. To obtain a detailed climate reconstruction more than 1000 \delta$^{13}$C and \delta$^{18}$O measurements were carried out, providing a time resolution between 2,5 and 10 years. In S-STM1 \delta$^{18}$O -values range between -4,5\permil and -1,5\permil and \delta$^{13}$C -values between -10,5\permil and -5,5\permil; while for S-STM5 these values range respectively between -4\permil and -2\permil and -7\permil and -3\permil (vs VPDB). Based on the comparison between \delta$^{18}$O excursions and historical meteorological data, the amount of precipitation is reflected in the \delta$^{18}$O signal. Different mechanisms for the \delta$^{13}$C are considered, such as a diminution of the C$_{4}$-type vegetation during droughts, resulting in more positive \delta$^{13}$C -value or kinetic effects during the calcification process itself. Throughout the time series, co-variation occur between \delta$^{13}$C and \delta$^{18}$O -values (R$^{2}$= 0,69) exhibiting long term (millennial) and short term (decadal) variations. In both stalagmites, layers of white porous calcite (WPC) (0,1-0,5mm) and dark dense calcite (DDC) (0,01-0,1mm) alternate, most probably due to seasonal variations. The WPC has more positive \delta$^{13}$C and \delta$^{18}$O -values, while the DDC shows more negative values, clearly demonstrated by high-resolution micro sampling up to a monthly to bi-weekly resolution. A positive correlation between the greyscale variations in the calcite fabric, the presumably annual growth banding and the inverse stable isotope ratios records support this hypothesis. During dry periods, less precipitation enters the cave-system, resulting in a whitish porous calcite deposition, thinner annual banding and more negative stable isotope ratios and vice versa. To better understand the climatic significance of these records, adapted Environmental Data Acquisition Systems (EDAS) are installed in and near Hoq Cave to obtain information on the actual transfer functions between climate and the proxy data in our speleothems.
PP43A-0612 1340h
Non-equilibrium $^{18}O and $^{13}C Enrichments in Modern Speleothems
The application of speleothem stable isotope records requires an understanding of the extent to which speleothem isotopic compositions reflect the compositions of the cave waters from which they precipitate. In order to test for equilibrium precipitation, we sampled modern speleothem calcite by coring actively growing speleothems and by growing calcite on glass plates under active drips, thereby allowing the direct comparison of the C and O isotopic composition of the calcite and the water from which it precipitated. At individual sites, only the lowest $\delta^{13}$C values and none of the plate $\delta^{18}$O values correspond to equilibrium values. On glass plates, speleothem calcite $\delta^{18}$O and $\delta^{13}$C values increase linearly away from the growth axis, with up to 6.6 per mil $^{13}$C and 1.7 per mil $^{18}$O enrichments. The positive $\delta^{13}$C vs. $\delta^{18}$O trends can be accounted for by Rayleigh-distillation of the HCO$_{3}$^{-}$ reservoir due to progressive CO$_{2}$ degassing and CaCO$_{3}$ precipitation, resulting in progressive $^{13}$C and $^{18}$O enrichment. The $\delta^{13}$C vs. $\delta^{18}$O slope is likely controlled by the ability of CO$_{2}$ hydration/hydroxylation reactions to buffer the O isotopic composition of the HCO$_{3}$$^{-}$ reservoir during calcite precipitation. Complete O isotopic buffering of the HCO$_{3}$^{-}$ reservoir by CO$^{2}$ hydration/hydroxylation reactions will produce a vertical $\delta^{13}$C vs. $\delta^{18}$O slope in calcite sampled along a growth layer. As O isotopic buffering of the HCO$_{3}$^{-}$ reservoir decreases to no buffering, the modeled $\delta^{13}$C vs. $\delta^{18}$O slope in calcite sampled along a growth layer will decrease from vertical to 0.4 at 26.6° C. The glass-plate calcite sampled along the growth layer has a $\delta^{13}$C vs. $\delta^{18}$O slope of 3.9, indicating incomplete O isotopic buffering of the HCO$_{3}$^{-}$ reservoir during calcite precipitation. We compiled 158 published speleothem stable isotope records with a global distribution and found that the majority of these records show a positive covariation between $\delta^{13}$C and $\delta^{18}$O values. In addition, speleothem records that show positive correlation, no correlation and negative correlation between $\delta^{13}$C and $\delta^{18}$O values for the entire record may contain short intervals that show strong positive correlation between $\delta^{13}$C and $\delta^{18}$O values. It is likely that the stable isotopic composition of many speleothems is influenced by the non-equilibrium processes. Direct application of equilibrium fractionation factors may be unwarranted when interpreting speleothem stable isotopic variability in most studies.
PP43A-0613 1340h
A Detailed and Comprehensive Reconstruction of the Northern Annular Mode and Pacific North America Pattern Using Tree Rings
The cross-validated skill of existing multi-proxy climate variability reconstructions is difficult to assess due to a variety of factors. The use of statistical methods that cloud interpretation of the physical links between predictors and predictand and the use of non-standard cross-validation techniques or intervals are common problems. In this study, we generate reconstructions of the Northern Annular Mode and Pacific North America patterns using extratropical Northern Hemisphere tree ring width site chronology time series. Four independent methods of predictor selection are employed: 1) mean ring width time series, generated to represent particular species over subjectively chosen regions where a consistent temperature or precipitation growth signal occurs, are used as predictors, 2) significant principal components generated from the matrix of ring width data are used as predictors, 3) natural clusters are formed from the matrix of ring width data and used as predictors and 4) individual site chronologies are used as predictors. Each method has two variants, one based on multivariate linear regression and another based solely on the covariance between individual predictors and the predictand. The calibrated and cross-validated skill of each reconstruction variant are compared in a consistent manner. Results indicate that essentially the same few records provide the bulk of the cross-validated skill in the Northern Annular Mode reconstruction, regardless of the selection method employed. The same can loosely be said of the Pacific North America reconstruction. Many of the candidate ring width site chronologies are not very useful for this particular effort because they either are located in the wrong area or are obtained from a relatively insensitive species. The tree ring based reconstructions are also frequency dependent and the high-frequency component is the most robust. In addition to creating well-verified reconstructions, we are able to explore the utility of particular records and groups of records with this relatively detailed and comprehensive approach.
http://www.atmos.washington.edu/~justinjw/AGU2004
PP43A-0614 1340h
Seasonal $\delta$$^{13}$C Variability in Tree Rings From China: Environmental Regulation And Its Relationship to East Asia Monsoon
Carbon isotope analyses of $\alpha$-cellulose from modern tree-rings (A.D.1966 to 1995) sampled along the path of the yearly East Asia monsoon invasion (Shennongjia and Huangling) in China show distinct seasonal variations in $\delta$$^{13}$C of up to 3.0 $\permil$ PDB in a single ring. The seasonal patterns of $\delta$$^{13}$C, as well as the annual $\delta$$^{13}$C values, reveal a negative correlation with relative humidity, suggesting environmental regulation on $\delta$$^{13}$C. Four seasonal $\delta$$^{13}$C patterns of tree rings are classified in this study: late-growing season maximum (pattern I); mid-growing season minimum (pattern II); mid-growing season maximum (pattern III), and early-growing season maximum (pattern IV). Various patterns and amplitudes of seasonal $\delta$$^{13}$C variability concurrently occurring in single tree further support the view of environmental regulation on isotopic compositions. The seasonal $\delta$$^{13}$C patterns exhibit distinct regional characteristics in Huangling and Shennongjia. The tree-rings from Huangling, located in the northwest Chinese loess plateau, show that the more negative $\delta$$^{13}$C values usually appear in latewood (autumn growth). In contrast, negative values predominate in earlywood of tree-rings from Shennongjia, a humid area to the southeast. The change in the relative position of more negative $\delta$$^{13}$C values is considered to be the consequence of seasonal East Asia monsoon precipitation which exhibits a systematic shift in the timing of the rainy season from the southeast coast to the northwest inland of China. Normal seasonal $\delta$$^{13}$C patterns have been identified for both sites. In a normal year of East Asia monsoon activity, the tree-rings show a normal $\delta$$^{13}$C pattern: more negative values appear in latewood from Huangling, where precipitation is greatest in autumn, but in earlywood of tree-rings from Shennongjia, where the rainy season begins earlier in the growing season. Abnormal patterns of seasonal $\delta$$^{13}$C in a single ring may thus reveal abnormal East Asia monsoon activity, including seasonal drought or advancement or delay of the rainy season. This study suggests that seasonal patterns of $\delta$$^{13}$C in tree-rings could be used as a proxy index of seasonal climate variability and reveal abnormal activities of East Asia monsoon.
PP43A-0615 1340h
Multi-proxy reconstructions of South American precipitation from oxygen isotopes and growth rings in tropical trees
Most of our knowledge about climate variability is restricted to the high latitudes of the Northern Hemisphere. Although the tropics constitute 40% of the Earth's surface, very little is known about temperature and precipitation variability, even during the last century. By analyzing the growth and isotopic variability of tropical trees, we may resolve intra-annual fluctuations in precipitation. Certain taxa of tropical trees are known to possess annual growth rings and some taxa exceed 1,000 years old. Recent progress in tropical dendrochronology, has established a strong relationship between growth and precipitation amount, especially during the growth season. The relationship between \delta$^{18}$O in precipitation and precipitation amount has been well established; and is moderately significant for certain regions of the neotropics (r= -65). Although much of the variability in the \delta$^{18}$O of precipitation has been ascribed to changes in sea surface temperatures resulting from El Niño events, longer periods (12 yr.) of variability in \delta$^{18}$O remain unexplained. Here we combine measures of tree ring growth and \delta$^{18}$O in the cellulose of several tropical trees to capture the inter-annual variability in precipitation. Samples from the Andean genus Polylepis were cross-dated and analyzed for \delta$^{18}$O. The resulting 146-year time series reveals pronounced inter-annual variability in \delta$^{18}$O, as well as low frequency variability similar to the \delta$^{18}$O. An appreciable amount of regional precipitation is described by the ring-width and the high pass-filtered \delta$^{18}$O data. To validate the relationship between growth and cellulose \delta$^{18}$O, we also analyzed samples from Dipterix spp. and Tachigali spp. from the Amazon. In both taxa growth maxima and cellulose \delta$^{18}$O minima coincided during the rainy season (DJF). The analysis of \delta$^{13}$C, another isotope known to be fractionated under arid conditions may increase our ability to reconstruct precipitation over the last 500 years.
PP43A-0616 1340h
Annual growth bands in Hymenaea courbaril: implications for utilization in tropical paleoclimate reconstructions.
Instrumental records of environmental variables such as temperature and precipitation are necessary to understand climate patterns and variability. In general, such observations from the tropics do not exist prior to the late 19th century, and existing records contain large spatial and temporal gaps and are sparsely distributed. An important source of annual temperature and precipitation proxy-data comes from the regular annual growth rings of wood formed by trees. Tree growth rings occur in response to periodic seasonal changes in the environment. Although expansive and diverse in number and ecology, a vast majority of tropical trees do not produce distinct annual growth rings. Because of this, tropical dendrochronology and paleoclimate reconstructions have lagged behind their temperate and higher latitude cousins. Distinct secondary growth rings were investigated in a single individual of the tropical hardwood legume Hymenaea courbaril felled within the City of David, Republic of Panama. Rings that maintained circuitry were considered annual and were sampled for 14C. Radiocarbon values from the secondary growth rings from this specimen were compared with annual reference radiocarbon values from wood and air in North America, New Zealand and Germany. This comparison demonstrated that the secondary growth rings formed by H. courbaril were determined to be annual in nature in this one stem disk specimen. To confirm the consistency of the annual nature of the secondary growth rings in H. courbaril, nine (9) additional specimens were recovered from the small hamlet of San Carlos y Algarobbo in western Panama between the town of David and the cordillera approximately ~30km from the site of the first tree sample. Of the nine specimens, four were chosen for ring counts and isotope analyses. "Annual" rings were counted and samples corresponding to the equivalent time of the bomb-14C peak were sampled. In addition a small subset of years within one tree specimen were sub-annually sampled for d18O cellulose. Radiocarbon and 18Ocellulose are consistent with the secondary rings being annual. These results imply that H. courbaril may be suitable for extended paleoclimate reconstructions.
PP43A-0617 1340h
Summer Temperatures of Late Eocene to Early Oligocene Freshwaters: a Multi-proxy Approach
We report northern hemisphere summer palaeotemperatures derived from multiple palaeoproxies from the Hamphire Basin Eocene-Oligocene succession. Continental freshwater \delta$^{18}$O values have been determined at six horizons spanning a 3 ma interval across the Eocene-Oligocene boundary from large sets of analyses of rodent tooth enamel phosphate. Surface water \delta$^{18}$O values permit use of associated carbonate and phosphate thermometers (gastropods, charophyte gyrogonites and fish otoliths) to bracket either the mean summer growing season temperature (gastropods), the mean temperature of the warmest months of the growing season (fish otoliths) and the mean temperature of a single month in the latter part of the growing season (charophtyte gyrogonites). We argue that calculated temperatures, which range from 26\deg C to 37\deg C are independent of freshwater evaporation effects and of variations in initial seawater \delta$^{18}$O that may be modified by distal changes in ice volume. The time averaged mean palaeotemperatures for each fossil horizon are generally indicative of warm mesothermal conditions. However, the large standard deviations on each of the summer season palaeotemperatures suggest climate perturbations during these times and/or that the period of mineralization of the rodent teeth encompasses some seasonal variation. This succession is a key interval where the positive \delta$^{18}$O shift in the early Oligocene marine foraminiferal isotope record identifies the onset of the Antarctic Oi-1 glaciation. The data suggest there was no significant summer temperature fall across the Oi-1 glaciation itself. This result is concordant with several other recent studies in suggesting that the majority of the isotopic shift in the marine realm across the Oi-1 glaciation is linked to ice volume, not temperature change. Our new approach has allowed us to put numerical values on summer season temperatures as well as to reconstruct relative temperature change across this key interval of the Eocene-Oligocene transition.
PP43A-0618 1340h
Medieval Warmth, Little Ice Age Cooling, and 20th Century Warming Reconstructed from Icelandic Lake Sediments
Historical records from Iceland provide one of the most compelling lines of evidence for North Atlantic warmth and reduced sea ice during Medieval times, colder summers and expanded sea ice during the Little Ice Age, followed by ameliorated conditions during the 20th century. Icelandic terrestrial records, particularly those derived from lake sediments, tend instead to be over-printed by the ancillary effects associated with colonization, especially by soil erosion that resulted from deforestation and overgrazing. Here we present data for the past 2000 years from Haukadalsvatn, a large (3.3 km2), deep (42 m) lake set in a large catchment (172 km2), resulting in high sedimentation rates that exceed 1.5 m ka-1 in the central basin. Much of the catchment is at high elevation, and was probably never forested, reducing the anthropogenic signature. Two cores recovered with the GLAD200 Hydraulic Piston Corer in 2003 capture the entire sediment fill, consisting of 30 m of sediment; the upper 16 m are lacustrine, the lower 14 m are marine. The lacustrine sediments are finely laminated and interspersed with diagnostic tephra that provide additional age control. The last 2000 years is represented by the uppermost 4.5 m of sediment. Total organic carbon has been measured in continuous 1-cm-samples, providing a continuous record at ca. 3-year resolution. Studies of modern terrestrial and aquatic vegetation document a large difference in their d13C, with terrestrial vegetation typically 8 per mil lighter. The d13C of total organic carbon from Haukadalsvatn sediment indicates that carbon stored in the lake sediments is dominated by terrestrial carbon sources. However, intervals of low total carbon concentrations are also periods of relatively heavy d13C, suggesting that they represent intervals of reduced terrestrial erosion with a stronger contribution from aquatic sources. Overall, the interval from 2000 to 900 BP is characterized by relatively low rates of soil erosion, and slow rates of change. Sharp increases in soil erosion begin about 900 BP, and intensify after 600 BP, ending late in the 19th century, broadly coincident with the Little Ice Age. This period of landscape instability is punctuated by about a century of landscape stability about 400 BP. This pattern broadly follows the historical record of sea ice variability off the coast of Iceland.
PP43A-0619 1340h
Quantitative reconstruction of paleoclimate - Air and ground temperature tracking from Emigrant Pass Observatory
Borehole temperature-depth profiles contain information about surface ground temperatures histories and provide a useful complement to proxy indicators of climate change. An inherent assumption in borehole temperature reconstructions is that air and ground temperatures are coupled through heat diffusion track each other at annual and longer periods. The Emigrant Pass Observatory (EPO), located in the Grouse Creek Mountains of northwestern Utah, is designed to test ground-air temperature tracking. Analyses of 10 years of observations at EPO demonstrate the following: 1) Ground temperatures track air temperatures at annual and longer periods exceptionally well at the site. Divergence between the observed temperatures at 1 m in the subsurface and air temperatures modeled as a boundary layer forcing is less than 0.04 K per annum. 2) Seasonal variations in incident solar radiation are ~200 Wm$^{-2}$ leading to an average annual difference between ground and air temperatures, $\Delta$T$_{g-a}$, of 2.55 K ($\pm$0.01) from 1993-2003. The temperature difference varies from -5 K to +10 K when averaged over a diurnal cycle, and from 2.50 K to 2.60 K over an annual cycle. However, inter-annual variations in insulation are less than 1 Wm$^{-2}$; consequently, solar radiation is not observed to affect the inter-annual tracking at the site. 3) Model studies snow-ground thermal interactions at EPO demonstrate that seasonal snow cover can either warm or cool the ground relative to the annual mean air temperature and that the winter snow effect is an order of magnitude smaller than the summer radiation effect at the site. 4) Temperature observations at various depths within the granite and soils at the site allow us to make estimates of in-situ thermal diffusivity and its changes with time. The "apparent" thermal diffusivity of the upper meter of granite at EPO ranges from 0.88-0.98 x 10$^{-6}$ m$^{2}$s$^{-1}$ while the soil varies from 0.57-0.68 x 10$^{-6}$ m$^{2}$s$^{-1}$. The accumulation of data at EPO leads to a quantitative understanding of paleoclimate signals in rock temperatures without the need for an empirical calibration.
PP43A-0620 1340h
Resumed Activity of the Dead Sea Ca-Cl Brine and the Northward Migration of the Levant Rain System Upon the MIS5/4 Transition
Terminal lakes in the arid and semi-arid region of the Dead Sea basin expanded significantly or contracted and dried up depending on the way the hydrological system is reacting to the regional and global climate during the late Pleistocene-Holocene periods. We reconstructed the precipitation and hydrological history of the drainage area of the Dead Sea basin during the transition from the last Interglacial (MIS5) to the last Glacial period (MIS4). Thus, the lakes are considered as a large rain gauges and faithful monitors of the regional hydrological-climate system. Our assessment is based on lithological, mineralogical, isotopic and chemical evidence stored in the sedimentary-limnological record of Samra (Amora) and Lisan lakes that filled the Dead Sea basin during the late Pleistocene. Deposition of CaCO3 as authigenic aragonite or calcite from the lakes depends on the relative contribution of the ancient Dead Sea Ca-Cl brine to the lake waters. During the uppermost Pleistocene time (approximately 120-80 ka) mainly authigenic calcite was deposited in the lake suggesting minor contribution of the Ca-Cl brine relative to the freshwater input. The transition from the last Interglacial to last Glacial periods (the MIS5/4 transition at approximately 70 ka) was marked by resumed activity of freshwater springs in the vicinity of the Dead Sea (depositing travertines) and enhanced activity of the Ca-Cl brines, leading to precipitation of salt and authigenic aragonite. The MIS5/4 freshwater-brine change was associated with a regional migration of rainstorms to the north of the Negev desert. Since then, during the past 70 ka rainstorms were mostly limited to the drainage area of the Jordan River and Dead Sea shoulders.
PP43A-0621 1340h
The Oxygen and Hydrogen Isotope Composition of Lake Huron
Over 150 water samples collected along transects of Lake Huron and Georgian Bay during late April-early May 2004 have average oxygen and hydrogen isotope compositions of -7.5 and -57$\permil$ (VSMOW), respectively. These values are very similar to averages obtained using monthly samples collected over the last seven years from a single location (Grand Bend, Ontario) near Lake Huron's southern outlet. At the time of the 2004 sampling, Lake Huron and Georgian Bay were receiving waters with lower-than-average oxygen and hydrogen isotope compositions, both from Lake Superior (via the St. Mary's River), and from fluvial inputs into the North Channel and Saginaw Bay. Conversely, inflow from Lake Michigan via the Straits of Mackinac supplied waters with higher-than-average oxygen and hydrogen isotope values. These regions of contrasting isotopic composition were localized, and the lake was regulated to values typical of the average within a short distance from these inputs. Vertical profiles from several locations throughout Lake Huron and Georgian Bay likewise showed little variation in oxygen and hydrogen isotope composition from top to bottom of the water column. Porewater samples were also extracted at 10-cm intervals from two Lake Huron sediment cores, which were obtained from the Manitoulin and Goderich basins in spring 2004. In the Manitoulin basin, the oxygen isotope values of porewater decreased systematically from about -7.2$\permil$ at the sediment-water interface to about -9.0$\permil$ at 11 m depth. Porewater from the Goderich basin showed similar variation in oxygen isotope values, from about -7.6$\permil$ at the sediment-water interface to -9.7$\permil$ at 12.3 m depth. The oxygen isotope composition of porewater then increased to -9.3$\permil$ by the core's end at 13.3 m. This latter variation may reflect upward infiltration of groundwater or contamination during coring. Overall, however, we suggest that these changes in porewater oxygen isotope composition may be a useful proxy for variations in the composition of Lake Huron over the time required to deposit these sediments.
PP43A-0622 1340h
Two Glacial-Interglacial Cycles of Lake-Level Change in Equatorial East Africa Documented by High-Resolution Seismic Sequence Stratigraphy from Lake Challa (Kenya)
A high-resolution (3.5 kHz) reflection seismic survey of Lake Challa (Kenya-Tanzania), a 97-m deep volcanic crater lake on the lower East slope of Mt. Kilimanjaro, revealed at least 215 meters of acoustically stratified lake deposits. Analysis of seismic facies and onlapping features, in conjuncton with 14C-dating and sedimentology of a 3-m surface core, indicates that the 10 major stratigraphic units (and their sub-units) recognised in the seismic sequence represent distinct phases of lacustrine sedimentation associated with late-Quaternary lake-level fluctuations. At least the uppermost units, which represent late-Glacial and Holocene sedimentation, seem to be mainly composed of fine-grained authigenic and aeolian detrital mineral inputs, intercalated only at the periphery by occasional mass-flow deposits from local collapse of the inner crater wall. Isopach mapping of each stratigraphic (sub-)unit over the dense seismic grid (mean interval 150 meter) reveals repeating patterns of sediment distribution across the lake floor, tracing quantifiable lake-level fluctuations during the Holocene, the late-Glacial period, the Last Glacial Maximum, and the penultimate glaciation. Extrapolation of available radiometric ages on the uppermost units together with the inferred sequence of late-Quaternary lake-level change suggests that the acoustically visible lacustrine infill of Lake Challa covers the two last glacial/interglacial cycles.
PP43A-0623 1340h
Sediment thickness and Holocene erosion rates derived from a seismic survey of Hvitarvatn, central Iceland
More than 100 km of seismic reflection profiles of the sediment fill in the glacier-dominated lake Hvitarvatn, central Iceland, reveal over 65 m of stratified postglacial sediment in the main depositional basin. Five diagnostic seismostratigraphic units, defined on the basis of acoustic properties tied to lithostratigraphic breaks in sediment cores from the lake, can be traced throughout the sediment fill. Compiled data were entered into a Geographic Information System (GIS) for further analysis of changes in bathymetry and unit thicknesses, using ArcGIS v8.2. Isopach maps of the lithostratigraphic units exhibit different spatial patterns, suggesting significant changes in the primary sediment delivery systems through the Holocene. The mass of sediment in the lake is estimated to be between 55 x 1010 kg and 109 x 1010 kg. Suspended sediment loss from the lake currently averages 5 x 107 kg of fine sediment each year. From these figures the average Holocene bedrock erosion rate across the catchment is calculated to be between 2 and 5 cm ka-1.
PP43A-0624 1340h
Modelling the Climate of Last Glacial Maximum Europe Through Reconstructions of Glacial Mass Balances
The state of a glacier and its equilibrium line are closely related to local and regional climatic conditions. Any alterations to the climate will cause fluctuations in the glacier system. Numerical models that use glaciological and meteorological inputs to calculate glacier mass balance can therefore be used to quantify climatic differences between time periods with known differences in glaciological condition. During the Last Glacial Maximum (LGM) southern Europe became glaciated with a range of ice cap and mountain glacier systems. Mass balance models constrained by records of glacial extent can be used to estimate glacial condition and equilibrium line altitude. By modelling both the present day and Last Glacial Maximum (LGM) conditions across Europe potential anomalies in climatic parameters, such as temperature and precipitation, can be derived. This modelling approach provides a new method of deriving palaeoclimate estimates in both times and spaces where a palaeo-glaciological record is present. The results can be compared to other palaeoclimate reconstructions especially General Circulation Models (GCM's).
PP43A-0625 1340h
An Open Source Implementation of the Modern Analog Technique (MAT) Within the R Computing Environment.
We present the development of a complete analytical solution for Quaternary geoscientists applying the Modern Analog Technique (MAT) to fossil biological assemblages. We present a package called MATTOOLS that implements the MAT and offers new calibration techniques related to Monte-Carlo simulation and response operating curves (ROC), both of which are used in assessing the critical thresholds of biological assemblage dissimilarity. MATTOOLS is a complete open-source solution to the MAT and has the advantage of operating in the R language environment and is packaged as a standard R extension. MATTOOLS therefore offers an easily extensible solution for individual research endeavors in both marine/ocean and terrestrial paleoclimate calibration exercises. We review current solutions for MAT calculations and provide an example modern calibration using MATTOOLS.
PP43A-0626 1340h
Extraordinary Climatic Greenhouse Conditions in Middle Miocene: Evidence From Xenoliths in Basalts
Although Paleoclimate records have been obtained mostly from the study of sedimentary rocks, some high-temperature rocks may contain useful climatic information. Here we show that unusual tridymite-hercynite xenoliths in Niutoushan basalts from the southeast coastal area of China preserve evidence of extraordinary climatic greenhouse conditions in middle Miocene. These xenoliths are composed of hercynite (FeAl$_{2}$O$_{4}$), tridymite (SiO$_{2}$) and glasses, and are characterized by positive cerium anomalies and extremely high Al$_{2}$O$_{3}$ (32-34 wt.%) and total iron oxide (20-22%). Their chemical and Nd, Sr, Pb and O isotopic compositions suggest that these xenoliths represent preserved aluminous lateritic paleosols that are not genetically related to host basalts. These lateritic paleosols with strongly desilicated minerals were formed by intense chemical weathering under warm and humid tropical conditions (with annual average temperature of $>$$19\deg$C and the annual rainfall of $>$165 cm) in SE China during the interval from 17 to 15 million years (Ma). The formation age of the paleosols corresponds to a period characterized by slow uplift of the Himalayan-Tibetan Plateau region (and thus less consumption of CO$_{2}$) after 17 Ma, and eruptions of 17-15 Ma Columbia River flood basalts, the Vogelsberg basalts, and eastern China basalts (and thus more input of CO$_{2}$ into the atmosphere). The contributions of Niutoushan and nearby basalts to our understanding of middle Miocene climate are (1) to preserve the geochemical record of lateritic paleosols captured and transformed in the basalts; and (2) to provide robust constraints on the ages of the lateritic paleosols.