PP43B-1243
Deglacial terrigenous organic matter input to sediments from Orca Basin, Gulf of Mexico - a combined optical and biomarker approach
In addition to paleo-salinity reconstructions, the abundance of terrigenous organic matter (OM) in marine sediments can be a valuable indicator of past changes of river outflow and/or meltwater flux. In the Gulf of Mexico, deglacial decreases in salinity indicate large input of meltwater via the Mississippi (Leventer et al. 1983, Flower et al. 2004), which probably had a strong effect on the Atlantic Meridional Overturning circulation and hence climate. Using a sediment core from the same location, we complemented these previous analyses by assessing changes in the contribution of terrigenous OM over the course of the last deglaciation. To this end, we combined optical kerogen analyses with bulk sedimentary, biomarker, and compound-specific carbon isotope analyses. During glacial times, terrigenous OM input was higher than today, as expected due to the closer proximity of the Mississippi River mouth. Furthermore, the optical analyses revealed that much of the glacial OM is reworked, i.e. of Cretaceous age or older. In contrast, the Holocene sediment contains mainly marine OM, which is exceptionally well preserved. During the last deglaciation, terrigenous input was also generally high due to the large meltwater fluxes. However, additional influences can be inferred, such as the change in distance to the river mouth, local productivity changes, and hydrodynamic particle sorting. Towards the end of the meltwater input period, the link between salinity and the abundance of terrigenous OM is weaker. Most importantly, the early part of the Younger Dryas period, around 12.5 ka, was characterized by a secondary peak in terrigenous input, although it is generally believed that meltwater flow was rerouted away from the Mississippi at this time. These results add to the growing evidence of intra-Younger Dryas variations in meltwater routing and climate and suggest that the history of deglacial meltwater inflow to the Gulf of Mexico might not yet be fully understood.
PP43B-1244
Large negative excursion of organic carbon isotope in the aftermath of the Paleoproterozoic glaciation in North America: methane-hydrate destabilization, climate recovery, and the Great Oxidation Event
The early Paleoproterozoic era (2.5 to 2.0 Ga) is a key interval in the Earth history characterized by glacial epoch and the rise of oxygen in the atmosphere. In 2.45 to 2.2 Ga, the Earth had been experienced a number of glaciations, at least one of which may have been a low-latitude glaciation. Following the glacial epoch, large positive excursions of carbon isotopic composition of carbonate are recorded in the sedimentary rocks of 2.2 to 2.0 Ga, suggesting anomalously high burial rates of organic carbon and thus massive release of oxygen to the atmosphere (called the gGreat Oxidation Eventh). Although climatic recovery in the aftermath of the glaciation is a key to understand the linkage between these two global events, the mechanism responsible for the environmental change has been largely unknown. Here we report large negative excursions of carbon isotopic composition of organic carbon (-45 to -60 permillage) from quartzites bracketed between the youngest Paleoproterozoic glacial diamictites and the carbonates recording the onset of the Great Oxidation Event both in the Chocolay Group of the Marquette Range Supergroup, USA, and in the Huronian Supergroup, Canada. Anomalous negative excursion of organic carbon isotope in deeply weathered quartzites suggests destabilization of methane hydrate as much as 50 to 150 percent of the modern hydrate pool. This may have resulted in an extreme greenhouse condition, which would have produced deeply weathered quartzites and supplied a large amount of nutrients to the oceans, resulting in the Great Oxidation Event.
PP43B-1245
Lake Surface Temperature Variability in Lake Malawi Since the Last Glacial Maximum
Previous lack of independent lacustrine temperature proxies led to shortcomings in our understanding of continental paleoclimate records. Recent advances in a molecular biomarker paleotemperature proxy, known as TEX86, have led to new insights about tropical paleoclimate. Powers et al. (2005) reported the temperature history of Lake Malawi, East Africa (9-14°S) based on a TEX86 profile in a core from the north basin of the lake. We subsequently questioned whether this thermal history reflected past regional air temperature or the intensity of upwelling in the north basin. We addressed this question by using TEX86 to reconstruct mean annual lake surface temperatures from a sediment core from the central basin of the lake, far from regions of major upwelling. We focus on a continuous, well-dated core interval from 15 ka BP to present. The earliest part of the record following the Last Glacial Maximum (LGM) displays a 1.5°C warming, followed by a 2.5°C cooling during the Younger Dryas (YD). The early Holocene shows abrupt cooling of 3°C around 9.6ka that intensified, reaching the lowest temperature of the record at 7.2ka BP (24.4°C). This cooling is coincident with early Holocene aridity in the region. This is followed by the largest temperature reversal (4°C over 1150 years), reaching the maximum temperature seen in this study, 28.3°C, at about 6ka. These maximum mid-late Holocene temperatures precede a period of extreme drought over equatorial Africa (Gasse, 2000). These results correlate well with the paleotemperature reconstruction from the northern basin of Lake Malawi (Powers et al., 2005), and confirms results as changes in thermal history for this region, and not localized differences in upwelling.
PP43B-1246
Relationship between Leaf Water and Leaf Waxes in Growing Pine Needles
There has been an increasing interest in reconstruction of paleoclimate and paleo-environment using hydrogen isotopic ratios of plant lipids extracted from sediments. It has been shown that δD of plant lipids is related to the δD of leaf water, which in turn is related to the δD of precipitation and relative humidity. However, the δD of leaf water changes significantly through the life of a leaf, it is not clear how the leaf water dynamics affects the bulk isotopic composition of lipids that are synthesized throughout the life of the leaf. This work is a detailed study of the relationship between δD values in leaf water and in leaf wax n-acids for two species of pine needles, red pine ( Pinus resinosa) and white pine ( Pinus strobus). In an earlier investigation we found that the δD of leaf water in pine needles increased as they were elongated through the needle-growing season. The leaf water of red pine needles has higher δD values than that of white pine needles at each comparable stage of growth. In addition, for a given needle, the leaf water δD also increased from the base to the tip of the needle. To examine the variation of lipid δD in relation to that of leaf water δD, we collected 4 sets of needles during their elongation period, obtained the bulk leaf water, then sectioned them into smaller segments along the length, and measured δD values of n-acids with 24 to 32 carbons. We test how the measured D/H ratios of leaf waxes vary with time, between two species, and with the position in the needle (relative distance from the tip, 0-1). A multiple regression analysis shows the following results. 1) The δD values of all types of n-acids are significantly correlated with the position of the sample; δD is lower near the base and higher near the tip. This result is consistent with the along-needle isotopic distribution of leaf water. 2) Leaf waxes of red pine needles are significantly more enriched in D than white pine needles, also consistent with leaf water δD variation between the two species. 3) Regardless of temporal increases of leaf water δD, the δD of 4 out of 5 wax n-acids shows a decreasing trend with time, although only two (C-24, 32) are statistically significant. This may reflect use of stored hydrogen (from stored carbohydrates) at earlier stages of growth. 4) The significance of the overall regression of δD against time, species and relative position increases from low carbon to high carbon number lipids (for C-24, 26, 28, 30, and 32, r2=0.34, 0.31, 0.56, 0.61, and 0.83), suggesting that longer wax n-acids are more influenced by local leaf water.
PP43B-1247
Do Strontium Isotope Ratios of Animal Bone and Teeth Really Reflect the Isotope Ratios of its birth- and growth-places?
Strontium enters the human body through the food chain as nutrients pass from bedrock through soil and water to plants and animals. Strontium substitutes for calcium in the hydroxyapatite mineral of skeletal tissue, and is stored there. 87Sr/86Sr ratios in an individualfs bone and teeth could directly reflect the isotopic ratios found in the plants and animals that she or he consumed, which reflect the isotope ratios found in the soil and bedrock of that geologic region. Therefore, 87Sr/86Sr ratios of human skeletons could be useful tools for assessing human residential mobility in prehistory, and many studies on them have been often made. In this study, to evaluate whether the 87Sr/86Sr ratio of a bone or teeth really reflects the isotopic ratios of its birth and growth places, several bone and teeth samples were measured for 87Sr/86Sr ratios, compared with 87Sr/86Sr ratios of geological samples in their growth-places. Bone and teeth samples were leached with 5% acetic acid. After drying, samples were ashed in a muffle furnace at 825°C for 8h, and then digested in nitric acid, followed by cation exchange chromatography with 2.4M hydrochloric acid. 87Sr/86Sr ratios were measured using a thermal ionization mass Spectrometer (VG Sector 54) or an inductively coupled plasma mass spectrometer (Finnigan ELEMENT2). A modern boar bone collected at Asuke, Toyota City, Aichi prefecture, Japan showed a 87Sr/86Sr of 0.71001±0.00002 (2 σ), while stream sediments in the Asuke area showed around 0.710 (Asahara et al., 2006). The 87Sr/86Sr ratio of a modern black bass bone collected from Lake Biwa, Shiga prefecture, Japan was 0.71215±0.00002, while those of surface water in Lake Biwa was 0.71233±0.00002. The similar 87Sr/86Sr ratios between bone and its provenance geology could indicate that the 87Sr/86Sr ratios of bones reflect the isotopic ratios of the birth- and growth-places. The more results of modern and fossil skeletons will be shown in our presentation.
PP43B-1248
Temporal and spatial paleoproductivity patterns associated with Eastern Mediterranean sapropels: paleoceanographic significance.
Deposition of Eastern Mediterranean sapropels has been discussed in terms of enhanced primary productivity and/or preferential preservation due to anoxic conditions in the deep basin. However, formation of these organic enriched layers is not homogeneous across the basin and through time, and temporal and spatial patterns can be observed in organic carbon concentrations and depositional conditions. We used a transect of ODP sites in the Eastern Mediterranean for the study of such variations, covering the area of major influence of the European continent and incoming waters from the Western Mediterranean basin (Ionian basin, Site 964), a region of influence of the Nile River (Levantine basin, Site 967), the central region of the basin with minor continental influence (Mediterranean Ridge, Site 969), and shallower bathymetries (Eratosthenes Seamount, Site 966). A set of paleoproductivity related proxies has been applied in order to reconstruct the paleoceanographic conditions that led to the formation of sapropels. As a whole, sapropel formation corresponds to wetter periods occurring during precessional minima and appears associated to increased productivity, evidenced by Ba/Al, and TOC-Ba mass accumulation rates maxima. δ13C data indicate intensified carbon fixation during organic carbon entrapment in sediment, where as low δ15N values provide evidence of nitrogen fixation through cyanobacteria activity as a source of increased primary and export productivity. This overwhelming export productivity led to the depletion of deep water dissolved oxygen, thus improving organic matter preservation. The above mentioned proxies show that sapropels represent periods of high productivity in an otherwise oligotrophic basin. This productivity was initiated and sustained by a change in bacterial community to nitrogen-fixing organism favored by intensified continental drainage and nutrient input. In agreement to this observation, sapropel onset generally occurred earlier in the Levantine basin, directly influenced by variations in the Nile River discharge, and progressively spread toward the western part of the basin. Thus, this change in paleoceanographic conditions is ultimately climatically driven and the evolution of the regional climate affects the intensity of the sapropel formation for the last 3 My. Intensified productivity and enhanced preservation is observed during sapropel deposition from the middle Pliocene until the lower Pleistocene. Productivity maxima occur during the late Pleistocene, coinciding with highest recorded sedimentary rate, and a relatively weak increase is observed during the deposition of the Holocene sapropel. This pattern implies that the rates of deep-water ventilation and of continental erosion generally increased in the eastern Mediterranean region as climate cooled since the mid-Pliocene.
PP43B-1249
Organic Biomarker Record of Oceanographic and Environmental Changes off Central Peru During the Last 300 Years
On the Peru margin, high surface-water productivity and associated vertical fluxes and an intense Oxygen Minimum Zone (OMZ) favours the preservation of high resolution sedimentary records of climate signals and water column processes. In the framework of the PALEOPECES project, two box cores were collected in the central Peruvian margin, in the shelf off Callao (12°00'S, 72°42'S, 184 m) and in the upper slope off Pisco (14°07'S, 76°30'S, 299 m). On-going molecular organic geochemical studies and complementary mineralogical and organic elemental analyses aim to reconstruct climatic, environmental and ecosystem variability within the last 200 years on an interannual/decadal time scale. Alkenone-SST data show variability within the last 300 years which mainly mirrors ENSO phases, although changes in the SST signal are much attenuated, and permit to extend instrumental data records. Organic biomarkers diagnostic for major phytoplankton groups are used as a tool to assess changes in the productivity patterns as a response to changing upwelling intensity and to El Nino/El Nina phases. Furthermore, patterns of higher-plant lipids are linked to changes in the eolian forcing and/or in the intensity of transport processes.
PP43B-1250
Carbon Isotope Records From Wetland Plants, and Implications for Paleohydrological Reconstructions
The carbon isotopic record of temperate tree-rings, are controlled by changes in water stress, which causes an increase in water-use-efficiency that results in a relative carbon isotope enrichment. Hence a relative decrease in rainfall during the growing season, would result in a water-stressed condition. However, plants growing in wetland environments do not necessarily respond in a similar manner. In contrast, to terrestrial plants, initial carbon isotopic results indicated that wetland plants such as pond cypress have positive relationship with precipitation. One important plant in the greater Everglades ecosystems is sawgrass ( Cladium jamaicense), which comprises an important part of the regional ecosystem. To calibrate and understand the isotopic changes that may potentially be related to changes in water level, which corresponds to hydroperiod in a temporal manner, mesocosm experiments were used to grow these plants at different water levels. 24 mesocosms were randomly assigned 4 different water treatments to simulate changes in hydroperiod and water depth, similar to the typical Everglades wet season and dry season cycle. Our initial results from this work show a strong correlation between variations in water depth and plant carbon isotope values in the shallow water treatments vs. the deeper water treatments. Further analyses are presently underway to compare assimilation with the collected carbon isotopic data. These results confirm the observations from the cypress work, and set the stage for using carbon isotopes from preserved OM and/or biomarkers to reconstruct changes in water level from wetland settings.
PP43B-1251
Mid-Holocene Climate Variability and Coastal Upwelling: Geochemical Evidence From Mytilus californianus
Oxygen isotope values in carbonate shells from the coastal zone are influenced by temperature and by the δ18O value of water, which could be 18O-depleted relative to average ocean water due to input of freshwater runoff. If Mg/Ca ratios are a reliable independent proxy for past sea-surface temperature (SST), we can reconstruct the δ18O value of coastal waters from the δ18O value of biogenic calcite as a proxy for coastal precipitation and runoff. We conducted geochemical studies (δ18O, Mg/Ca, and 14C) on shells of Mytilus californianus from archaeological middens near Pt. Año Nuevo, on the central California coast, to study shifts in upwelling and moisture regimes from ~1,000 to ~5,500 BP. The dated specimens were sectioned along the growth axis and the prismatic calcite layer sampled down the length of visible growth bands with samples split for Mg/Ca and stable isotope analysis. Seven shells have been analyzed for δ18O so far and six of these have also been analyzed for Mg/Ca ratios. Shells typically contain 3-7 years of accretionary growth that can be resolved at the monthly scale with our sampling approach. Under normal Walker circulation in central California, conditions are characterized by strong summer upwelling, relatively cool summer SSTs, and rainy winters. Interruption of normal Walker circulation due to a weak North Pacific high pressure system and therefore reduced offshore Ekman transport is reflected by warmer summer and winter SSTs, suppressed summer upwelling and even higher winter precipitation. Overall biogenic calcite Mg/Ca ratios show a negative seasonal covariation with δ18O values, as expected due to shifts in ocean temperature. Several specimens show geochemical values consistent with a breakdown in Walker circulation during several winters. With additional coupled Mg/Ca and δ18O analyses we will calculate the frequency of these events through time and will calculate the δ18O value of coastal water as a proxy for precipitation and runoff.
PP43B-1252
D/H Ratios of Terrestrial Lipids from Santa Barbara Basin: A Preliminary Assessment of Paleoclimatic Relevance
Hydrogen isotope (D/H) ratios in sedimentary lipids are increasingly used as a proxy for terrestrial paleoclimate. In arid regions such as southern California, one of the principle problems is finding long-lived lakes to provide the necessary sedimentary archive for this proxy. As a potential alternative, here we explore the D/H record of terrestrial lipids preserved in a marginal marine suboxic basin, Santa Barbara Basin (SBB). Rapid sedimentation, long continuous records, significant terrestrial inputs, and excellent organic preservation all make this site attractive from a geological perspective. But does it record terrestrial climate? To test this, we conducted a survey of lipid D/H ratios in a sediment core collected at the depocenter of SBB, extending back 1200 years before present. Long-chain fatty acids, derived from terrestrial leaf waxes, exhibit virtually no downcore variation in D/H and are uncorrelated with the record of winter Palmer Drought Severity Index (PDSI) in southern California, a proxy for regional precipitation. Long-chain n-alkanes, also derived from leaf waxes, show considerable downcore variability in D/H but are also uncorrelated with PDSI. We believe the temporal variability for n-alkanes may be caused in part by addition of D-enriched fossil hydrocarbons due to increased erosion during wet periods. Regardless, none of these leafwax compounds are a robust paleoclimate proxy in SBB at < 1000-year timescales. In contrast, D/H ratios of n-C22:0 and n-C24:0 fatty acids, commonly attributed to terrestrial aquatic sources, are well correlated with PDSI over this time interval and could serve as a viable paleoclimate proxy. We tentatively attribute the discrepancy between leaf-wax and aquatic biomarkers to a much longer soil residence time for leaf-wax compounds in the watershed, which effectively masks changes over centennial timescales.
PP43B-1253
Mid-Pleistocene Lacustrine Records of Carbon and Nitrogen Elemental and Isotopic data from Valles Caldera, New Mexico, USA
Lacustrine deposits dating back to the middle Pleistocene were recovered from Valles Caldera, located in Northern New Mexico. The core (82 m long) contained ~75 meters of lacustrine sediments. The age of the sediments was constrained by Ar-Ar dating of a primary tephra layer from the base of the core, in combination with correlation to the deep-sea marine isotope stage record along the length of the core. The lacustrine sediments span from ~350 k YBP to 552 k YBP covering two glacial-interglacial stages, from MIS 11 to MIS 14 and part of MIS 10. Total organic carbon (TOC) in the siderite free fraction (i.e. diagenetic siderite was chemically removed) ranged from <1% to 7% with the lowest values predominantly observed during glacial times and marked increases at the onset of interglacials. Particularly high TOC is observed during the long interglacial MIS 11. C/N ratios ranged from values of <2 to ~11 with lowest values in general observed during glacial times indicating increased input from aquatic sources and suggesting deepening of the lake as a result of wetter glacial climate. δ13C values measured in the siderite free fraction, ranged from -28‰ to -20‰ and remained more negative overall during glacial times. We are currently working on D/H analyses of leaf lipid biomarkers which may provide insight into the delivery of meteoric water to the region during these climatic stages, i.e. relative contributions of summer monsoonal (from the Gulfs of Mexico and California) vs. winter frontal precipitation (from the North Pacific).
PP43B-1254
A Fossil DNA Based High Resolution Record of Holocene Planktonic Taxa and Environmental Change in the Black Sea
A standard approach to study past planktonic taxa which carry information about past environments and climate variability is the microscopic determination and enumeration of microfossils. However, most planktonic taxa are soft-bodied and in cases where microfossils are absent or difficult to identify, chemical fossils (lipid biomarkers) can be used as paleoecological tools. Nevertheless, most lipids are not very specific, multiple sources are possible, or their biological source remains unknown. Recently, we and others have shown that under excellent preservation conditions, the analysis of preserved genetic signatures (fossil DNA) offers great potential to study past planktonic communities, including soft-bodied species, at the unprecedented species- and even strain-level (this work). Given the dramatic shifts in hydrography and the present anoxia that permeates most of the water column which promotes preservation of cellular materials, the Black Sea is an excellent setting to study the ancient species composition based on fossil DNA. We developed a high temporal resolution (50-100 yr) fossil DNA and lipid biomarker based stratigraphic record of planktonic community structure in the Black Sea spanning the complete Holocene development from the first post-glacial input of Mediterranean waters in the paleo-lacustrine Black Sea to the present. Preserved genetic markers for microbial communities dwelling at the surface (algal primary producers and zooplankton), the suboxic layer (marine Crenarchaeota), and the sulfidic chemocline (green sulfur bacteria) were targeted to provide information on past environmental change in the Black Sea. Specifically, we targeted markers that contributed to our understanding of past surface water temperature, salinity and stratification. Where possible, a side-by-side phylogenetic and lipid biomarker analyses was performed in order to carefully assess the validity of utilizing the former as proxies of a given biological input. As the corollary to this, we will also assess the influence of species changes in the putative biological precursors on both the distribution and isotopic composition of corresponding lipid biomarkers for which we plan to present data as well.
PP43B-1255
Sedimentary DNA from East African Rift Lakes
Ancient DNA research, especially that of environmental samples, has to date focused mainly on samples obtained from colder regions. We are characterizing present-day and historical planktonic communities in Kenyan Rift Lakes with the use of molecular genetic methods, focussing on rotifer and diatom assemblages. Within the eastern branch of the East African Rift System there are a series of shallow lakes in close proximity, yet with strikingly different hydrological and geological features. Between 15 and 5 kyrs ago the rift comprised several large lakes that were fresh and several 100's of meters deep. Tectonically separated, these lakes underwent a tremendously different development in the course of a trend towards a drier climate since 6,000 years ago. Today the lakes range in alkalinity from pH 11 (Lake Elmenteita) to pH 8 (Lake Naivasha) and in depth from less than a meter to 15 meters. Within this setting we are analyzing recent samples as well as samples obtained from sediment cores. Apart from presenting molecular tools to assess the presence and dominance of taxa meaningful for ecological reconstruction, we are also attempting to trace the population structure and history of single species in the course of severe environmental change.
PP43B-1256
An update on 11B,10B fractionation in the fundamental reaction: 10B(OH)3 + 11B(OH)4- = 11B(OH)3 + 10B(OH)4-
It has recently been demonstrated experimentally by Byrne, et al. (2006) and Klochko, et al. (2006) that the equilibrium constant for the isotopic exchange reaction: 10B(OH)3 + 11B(OH)4- = 11B(OH)3 + 10B(OH)4- (1) has a value around 1.027 for seawater at 25°C, for total B concentrations from 0.01 to 0.05 molal. These experimental studies involved essentially the accurate determination of the small pKa difference between the 11B and 10B isotopomers of boric acid. This new equilibrium constant value is significantly higher than the traditional value of 1.0194 from Kakihana, et al. (1977). This result has been obscured in recent controversies (Honisch, et al., 2007). The new value agrees well with the ab initio quantum cluster calculated values of Liu and Tossell (2005) and with the ab initio MD harmonic values of Rustad and Bylaska (2007). We will present additional calculations supporting and extending the study of Liu and Tossell (2005) and will discuss the general unsuitability of methods such as Sanchez-Valle, et al. (2005) which employ experimental spectral data. We have also established that polyborate formation in solutions as concentrated as 0.50 molal total B has little effect on the equilibrium constant. A mechanism is also presented for the interaction of B(OH)3 and B(OH)4- with HCO3- species occurring on the calcite surface. References: Byrne, et al. Deep-Sea Research I (2006) 53, 684-688. Honisch, et al. Geochim. Cosmochim. Acta (2007) 71, 1636-1641. Kakihana, et al. Bull. Chem. Soc. Jpn. (1977) 50, 158-163. Klochko, et al. Earth Planet. Sci. Lett. (2006) 248, 276-285. Liu and Tossell Geochim. Cosmochim. Acta (2005) 69, 3995-4006. Rustad and Bylaska J. Am. Chem. Soc. (2007) 129, 2222-2223. Sanchez-Valle, et al. Geochim. Cosmochim. Acta (2005) 69, 4301-4313.
PP43B-1257
Alkenone Production and UK'37 Temperature Estimates: A Time-Series Study in the Santa Barbara Basin, California
Accurate interpretations of past changes in oceanographic and climatic conditions preserved in deep sea sediments directly hinges on our understanding of the present-day factors influencing climate proxies used to estimate these conditions. In this study, the alkenone unsaturation index (UK'37) was measured in both an 11-year time series of sediment trap samples (1993-2004) and a gravity core from the Santa Barbara Basin (SBB). The UK'37 values for the sediment trap samples were correlated to concurrently measured temperature data in order to determine where in the water column this temperature signal is acquired. Our results indicate that changes in alkenone unsaturation are best correlated with temperatures at the chlorophyll maximum. Temperatures calculated from our chlorophyll maximum equation correspond closely with those calculated using the Prahl et al. (1988) equation. The majority of the sediment core UK'37 temperatures fall within ±1 SD of the weekly averaged SST record for this 13-year period, correlating best with late winter - spring SSTs. While the UK'37 ratio in the sediment trap samples clearly records seasonal and interannual temperature variability, the UK'37 record preserved in Santa Barbara Basin sediments is weighted towards spring temperatures due to highest alkenone production during this season. Comparison of the downcore UK'37 record to the Southern Oscillation Index shows a good degree of correspondence between the temperature signal preserved in the SBB and the ENSO climate signal. This study provides an important verification of the reliability of the alkenone paleotemperature proxy for determining past ocean temperature variability on a variety of time scales.
PP43B-1258
The Enigmatic Beginning of the Aptian Carbon-Cycle Perturbation
The Mid-Cretaceous is known as a period of dramatic carbon cycle perturbations, recorded in the δ13C values of both carbonate and organic matter in pelagic sediments. In particular, the Early Aptian exhibits a prominent negative δ13C spike, which precedes a positive carbon excursion. If the latter is assumed to be the result of an increased burial of organic matter caused by a greenhouse climate, the origin of this negative δ13C spike remains enigmatic. A simultaneous δ13C shift in both terrestrial and marine organic matter has been recorded at that time, indicating a substantial and abrupt input of isotopically light carbon, from 13C-depleted carbon sources to the ocean-atmosphere reservoir, may have happened at the onset of Early Aptian. Methane hydrates trapped in continental margin sediments are thought to have been released during many intervals of rapid climate warming and, have been postulated to be the cause of this massive release of isotopically light carbon. In this contribution, we will present new sedimentological organic geochemical and compound specific carbon isotope data from different Early Aptian sections exhibiting a negative isotopic carbon spike, and discuss possible origins of this negative carbon isotope excursion.
PP43B-1259
Do geostable polycyclic isoprenoids record the rise of oxygen in the ancient atmosphere?
Polycyclic terpenoids are among the most stable and abundant lipid compounds in sediments of all ages. They may record the composition of microbial communities and environmental conditions in the past, including the rise of molecular oxygen 2.7 billion years ago. A great deal is known about how some of these lipids are produced by the enzymatic cyclization of linear terpenoids by a family of triterpene cyclases, but whether and how specific polycyclic compounds reflect certain metabolisms or physiologies of modern microbes is not well understood. Here we demonstrate that a novel class of tetracyclic terpenoids is present in the spores of B. subtilis. These compounds are derived from the enzymatic cyclization of regular linear terpenoids by a protein homologous to known triterpenoid cyclases. The cyclization of regular linear terpenoids is thought to have produced the most ancient polycyclic terpenoids but, until now, there have not been any known modern microbial sources of such compounds. The presence of tetracyclic terpenoids increases the resistance of spores to hydrogen peroxide, a reactive oxygen species, establishing for the first time a physiological function of bacterial polycyclic terpenoids in vivo. Our work demonstrates that some polycyclic terpenoids play a direct role in protecting modern bacteria from reactive oxygen species. Similarly, their geostable derivatives in the rock record may imply the presence of oxidative stress related to the oxygenation of Earth's surface in the past.
PP43B-1260
Orographic and Climatic Influence on Leaf Wax Carbon and Hydrogen Isotopic Ratios: a Field Survey From Northern California
The primary objective of this research was to empirically ground-truth environmental controls on δD and δ13C values of higher plant n-alkanes, since these higher-plant specific compounds are refractory and commonly preserved in the geologic record they hold great paleoclimatic and paleoenvironmental information. Our approach was to extensively sample leaves and stems of nine species of trees across two Northern California east-west transects twice during the growing season. One hundred and ninety trees from ninety-three sites were collected along with topsoils and surface waters from most localities. Bigleaf Maple ( Acer macrophyllum), California White Oak ( Quercus lobata) and Blue Oak ( Quercus douglasii) n--alkanes δ13C have been analyzed and range from -38.0 to -29.6‰, -35.2 to - 30.4‰ and -34.5 to -30.4‰, respectively. Currently, all tree species show little to no relationship with any physical variable, such as longitude, elevation, tree height, aspect, slope, etc. The large range in tree isotope values suggests these plants are reacting to a yet unknown climatic variable or these species operate within a range of water-use efficiencies. Similarly, soil-extracted n--alkane δ13C values range between -36.5 to -29.2‰ and do not strongly correlate with any physical parameter. Surface water δD and δ18O are highly correlated and similar to the meteoric water line, however, not as robust, soil-extracted n--alkane δD show similar trends. Notably, the apparent enrichment factor between soil lipids and surface waters is not as stable as seen in other localities, varying by over 30‰, illustrating uncertainties in paleo-applications. Interestingly, water δD and δ18O from surface waters varied little between early June and mid-September and demonstrate a roughly -90‰ depletion in deuterium across the two transects. This D-depletion is reflected in the early growing season stem waters with a consistent slope to that of surface waters.
PP43B-1261
Novel Stable Isotope Methods for Assessing Changes in Seasonality of Precipitation from Sediments of Ombrotrophic Peatlands
The seasonality of precipitation is a key but often elusive climate parameter in paleoclimate reconstructions. Sediments from ombrotrophic peatlands are excellent archives of past changes in precipitation/evaporation balance. Here we show that these peatland sediments can also be used to assess changes in the seasonality of precipitation. We have recently determined that distributions of Sphagnum and vascular plant biomarkers sensitively record changes in hydrologic balance (Nichols et al., 2006, Org. Geochem. 37, 1505-1513), but biomarker distributions alone do not offer detailed information for the changes in seasonal precipitation. In this study, we combine biomarker and compound-specific H and C isotope ratios to create a more comprehensive picture of the changing climate affecting these sensitive ombrotrophic systems. We present here two sets of downcore data from sites in Arctic Europe as well as Eastern North America. Basic paleohydrology is established using a ratio of Sphagnum to vascular plant biomarkers (C23 and C29 n-alkanes, respectively. We further describe paleohydrology using novel stable isotope proxies based on δD and δ13C measurements of Sphagnum and vascular plant biomarkers. Because Sphagnum has no vascular system and loses water directly by evaporation, Sphagnum biomarkers enriched in deuterium indicate an evaporative growing season (summer). Vascular plants use their root systems to take up water stored within the peatland, so deuterium-depleted vascular plant biomarkers should indicate increased winter recharge of the peatland. A methanotrophic symbiont living inside the Sphagnum's hyaline (water-holding) cells is more active when the Sphagnum is wet and therefore provides more 13C depleted (methane- derived) carbon dioxide for biomass production when the growing season is less evaporative. Hence, 13C depleted Sphagnum biomarkers indicate increased methanotrophy and therefore a wetter summer. We corroborate our stable isotope proxies by comparing them with other paleoclimatic and paleohydrological records, including testate-amoeba and pollen-inferred moisture reconstructions and sea surface temperature reconstructions. Our combination of novel stable isotope and biomarker analyses allows us to understand much more about the seasonality of precipitation throughout the Holocene than does each proxy record alone.
PP43B-1262
Late Glaciation to early Holocene records of climatic and vegetation changes from Onepoto Crater, Auckland New Zealand: a biomarker and isotopic approach
A core taken from Onepoto Crater, a maar lake from the Auckland region of New Zealand, has excellent stratigraphy and robust age control based on well-dated and chemically distinguishable fallout tephra from the Taupo Volcanic Zone (TVZ). We present here a multi-proxy record including biomarkers and compound-specific isotopes on fatty acids that document ecological and climatological changes from the last glaciation to the early Holocene in northern New Zealand. All proxies indicate a drier and cooler climate in the glaciation followed by a rapid shift to warmer and wetter conditions at 17.6 ka that persisted until the early Holocene. The inferred arid conditions in the early part of the record are supported by markers such as charcoal abundances, but charcoal is absent after the climatic shift at 17.6 ka. New records of biomarkers and compound-specific isotopes on fatty acids from Onepoto Crater clarify changes in aridity associated with the glacial to interglacial climate shift documented by other proxies such as charcoal and pollen. Elevated abundances of marker lipids derived from biomass burning, such as dehydroabietic acid (a proxy for forest fires and by implication, aridity) and decreased 13C in terrestrially derived fatty acids indicate a return to somewhat dryer conditions during the Antarctic Cold Reversal (ACR) not present in other proxy records. The biomarker and isotopic data suggest drier conditions in the ACR that were not as intense as in the glaciation and remain unresolved by other proxies.
PP43B-1263
Carbonate `clumped isotope' thermometry in planktonic foraminifera and coccoliths
Constraints on past ocean temperatures are critical for documenting climate change and resolving its causes. The carbonate ‘clumped isotope' thermometer is a novel tool for the reconstruction of ocean temperatures. ‘Clumped isotope' thermometry in general relies on the principle that ordering, or ‘clumping', of heavy isotopes into bonds with or near each other in molecules, minerals or organic moieties is a temperature dependent phenomenon [1]. Carbonate clumped isotope thermometry in particular examines the proportion of 13C and 18O that are bound to each other within the carbonate mineral lattice [2,3]. Unlike other temperature proxies, the proportion of 13C-18O bonds in carbonates is independent of the isotopic composition of water in which the carbonate grew. In practice, this thermometer is based on analyses of 13C18O16O in CO2 produced by acid digestion of carbonates, which are reported using the variable, ‘Δ47' — a measure of the enrichment, in per mil, of 13C18O16O above the amount expected for a random distribution of isotopes. We have made the first Δ47 measurements of core-top planktonic foraminifera and coccoliths. Our initial results show that multiple species with different ecologies exhibit the same temperature dependence as inorganic calcite. We will present calibration data for mixed coccolith assemblages and multiple species of planktonic foraminifera, including: Globigerina bulloides, Neogloboquadrina dutertrei, Globigerinoides sacculifer, G. ruber, G. inflata, Globorotalia menardii, G. truncatulinoides, G. hirsuta, Globigerinella aequilateralis, and Pulleniatina obliquiloculata. In addition, data for core-top samples from a depth transect on the Ontong- Java Plateau in the Pacific Ocean will be used to assess the impact of dissolution on the Δ47 of CO2 evolved from marine carbonates. [1] Wang, Z., Schauble, E., and Eiler, J., 2004, Equilibrium thermodynamics of multiply substituted isotopologues of molecular gases, Geochimica et Cosmochimica Acta, 68, 4779-4797l [2] Schauble, E., Ghosh, P., and Eiler, J. 2006, Preferential formation of 13C-18O bonds in carbonate minerals, estimated using first-principles lattice dynamics, Geochimica et Cosmochimica Acta, 70, 2510-2529. [3] Ghosh, P., Adkins, J., Affek, H, Balta, B., Guo, W., Schauble, E, Schrag, D. and Eiler, J., 2006, 13C–18O bonds in carbonate minerals: A new kind of paleothermometer, Geochimica et Cosmochimica Acta, 70, 1439–1456.
PP43B-1264
Extending Molecular Signatures of Climatic and Environmental Change to the Mesozoic
The distributions, abundances and isotopic compositions of molecular constituents in sediments depend on their source organisms and the combination of environmental and climatic parameters that constrain or control their biosynthesis. Many such relationships are well documented and understood, thereby providing proxies of proven utility in paleoclimatic reconstructions. Thus, the temperature dependence in the extent of unsaturation in alkenones derived from prymnesiophyte algae, and in the proportion of ring structures in glycerol dibiphytanyl glycerol tetraethers (GDGTs) synthesized by crenarchaeota enables determination of sea surface paleotemperatures from sedimentary records. This molecular approach presumes temporal uniformity in the controlling factors on biosynthesis of these lipids, and their survival in the geological record, notwithstanding the challenge of establishing ancient calibrations for such proxies. Thus, alkenone records from marine sediments document cooling at the Eocene/Oligocene boundary but cannot assess changes in ocean temperatures during the Cretaceous, unlike GDGTs, which record fluctuations in ocean temperatures during the Early Cretaceous, and even survive in Jurassic strata. Other molecular measures offer less precise, yet informative, indications of climate. For example, the occurrence of sterol ethers in Valanginian sediments from the mid-Pacific suggests some cooling at that time, since these compounds are only known to occur elsewhere in cold waters or upwelling systems. Molecular compositions can also attest to levels of oxygenation in marine systems. In particular, the occurrence of 13C-depleted isorenieratane indicates the presence of photosynthetic green sulfur bacteria, and therefore anoxic conditions, albeit perhaps short-lived. Intermittent occurrences of isorenieratane often alternate with the appearance of 2-methylhopanoids, which provide separate distinct evidence for variations in oxygenation, linked to circumstances where low d15N values confirm an important role for N2-fixing cyanobacteria. In warm marine environments filamentous non-heterocystous cyanobacteria are the dominant N2-fixing organisms, and heterocystous species are excluded. Yet unicellular cyanobacteria within this latter group, wherein biosynthesis of 2-methylhopanoids is prevalent, are favored by low oxygenation levels. Thus, variations in the proportions of isorenieratane and 2-methylhopanoids observed within Cretaceous oceanic anoxic events suggest that bacterial populations varied in response to oxygenation levels during these episodes of carbon cycle perturbation.
PP43B-1265
A Multi-proxy Approach to Using Cave Sediment Carbon Isotopes for Late Holocene Paleoenvironmental Reconstruction in Florida
Carbon isotopes from cave sediments collected from Jennings Cave in Marion County, Florida were analyzed using a multi-proxy approach. Fulvic acids (FAs), humic acids (HAs), black carbon, phytoliths, and bulk organic matter were extracted from the sediments for carbon isotope analysis to determine periods of vegetation change caused by climatic influences during the Late Holocene (~\ 2,800 years BP). The carbon isotope record ranges from -35‰ to -14‰, exhibiting variability of ~\ -21‰, within the different proxies, which indicates changes between C3 and C4 vegetation. This likely indicates changes between a sub-tropical forested environment and more arid, grassy plains conditions. These changes in plant assemblages were in response to changes in available water resources, with increased temperatures and evapotranspiration leading to arid conditions and a shift toward less C3 vegetation (increased C4 vegetation) during the MWP. The cave sediment fulvic acid cabon isotopes record agrees well with ä13C values from a speleothem collected nearby that covers the same time period. Prolonged migration of the NAO and ITCZ affects precipitation in Florida and likely caused vegetation changes during these climatic shifts.
PP43B-1266
Sphagnum δ13C Values as Potential Indicators of Palaeohydrological Changes in Peat Bogs
Late-Holocene peat stratigraphy of a Canadian boreal peat bog was examined in order to evaluate the potential of Sphagnum δ13C values as a surface wetness proxy indicator. Carbon isotope-inferred past moisture levels were compared to testate amoebae-inferred water table depths, and to past decomposition levels inferred by colorimetric analyses, bulk density and carbon to nitrogen ratio measurements. Analyses were carried out at the same levels, allowing relations between the different proxies. In order to establish peat chronology, six AMS radiocarbon dates were coupled with ten 210Pb dates. Proxy records were combined and compared, and since a strong correlation was found among proxies, a valuable high-resolution surface- moisture reconstruction was obtained from the core. Although the mechanisms underlying carbon fractionation processes in peatlands are not well understood, we demonstrate that Sphagnum δ13C values have a great potential for palaeohydrological reconstructions by providing a complementary source of information.
PP43B-1267
Plant Cuticle: A Geochemical and Biophysical Sensor of the Carbon Cycle
Plant cuticle--the decay-resistant outer layer of leaves and young stems—-is the most abundant identificable component of the plant fossil record next to pollen and spores and occurs in both megafossils and phytodebris. Plant cuticles provide major information on past levels of atmospheric CO2 because of the inverse relationship between pCO2 and Stomatal Index in many modern species. Some geochemical studies have used partially decayed fossil leaf material (referred to as "plant cuticle") to reconstruct changes in atmospheric δ 13C by means of the strong correlation, in modern plants, between atmospheric δ 13C and that of plant tissue. However, the occurrence within the same piece of fossil tissue of different chemical compounds with different isotopic signatures limits the accuracy of reconstructions, because decay under anaerobic conditions distorts the original isotopic values. A standard histochemical test for plant cuticle—-namely, high resistance to oxidation in chromium trioxide—- indicates the potential for isolating pure fractions of plant cuticle from the geologic record and using these fractions to reconstruct past changes in atmospheric δ 13C. Plant cuticle macerated in chromium trioxide is 3.5‰ more negative than whole tissue, an offset similar to that for other lipids and lignin. Preliminary isotopic analysis of fossil "cuticle" suggests that much, if not most, of the fossil "cuticle" reported in the geochemical literature may represent a mixture of cuticle, remnant cellulose, and other compounds. The offset between cuticle and whole tissue appears to be consistent for plants with C3, C4, and CAM photosynthesis, indicating that plant cuticle can be used to reconstruct the path of photosynthetic carbon fixation. Plant cuticle oxidized in chromium trioxide can be identified to genus and species through light microscopy and SEM, providing much greater taxonomic resolution for isotopic studies than is possible with bulk carbon and many biomarker compounds. In addition, fossil leaf cuticle can be analyzed for Stomatal Index by light microscopy prior to its combustion for isotopic analysis, so that the same piece of cuticle can potentially provide information on levels of atmospheric CO2 and the isotopic composition of the atmosphere. Because dispersed plant cuticles can be analyzed with stratigraphic resolution close to that of pollen and spores, they can provide a high-resolution record of changes in the carbon cycle. http://www.agu.org/upchurchandmarino
PP43B-1268
Organic Matter Production And Preservation During Transgression And Highstand Of The Niobrara Cyclothem, Cretaceous Western Interior Seaway
The Upper Cretaceous Niobrara cyclothem (upper Turonian-lower Campanian) is a second-order transgressive- regressive cycle of the Cretaceous Western Interior Seaway reflecting interactions among eustatic sea level change, regional tectonic events, and sediment supply. These strata provide a unique window into Late Cretaceous sediment deposition and paleoceaonographic conditions in an epicontinental seaway. However, the response of organic matter production and burial to these forcings remains less than fully resolved. Geochemical analyses of the Montezuma Valley and Smoky Hill Members of the Mancos Shale at its principal reference section at Mesa Verde, Colorado, reveal potential relationships among organic matter abundance and composition, paleoceanographic conditions inferred from microfossils, and sea level change. These rock units represent transgression and early highstand of the Niobrara cyclothem. At Mesa Verde, the upper Smoky Hill coincides with the spatially-restricted but temporally-extended Oceanic Anoxic Event 3 of middle Coniacian to early Santonian age (~88.5-86.5 Ma). It is broadly characterized as dark-gray, foraminifer-rich calcareous shale, mudstone, and marlstone. Bulk geochemical properties, including %TOC, %CaCO3, and C/N, reflect changes in organic matter delivery and preservation, and are closely correlated to inferred water-depth and/or distance from shore. Proximity to the western paleo-shore appears to exercise a primary control over the composition of the identified biomarkers with secondary influence from redox-sensitive diagenetic processes and autochthonous microbial production, which in turn may reflect higher-order sea-level fluctuations. Changes in n-alkane, hopane, and sterane distributions are coincident with the second-order transgression of the seaway. Additionally, the presence in some samples of long-chain alkylcycloalkanes and alkylbenzenes may reflect the direct cyclization and aromatization of precursor algal and bacterial fatty acids in a reducing environment. Branched alkanes with quaternary substituted carbon atoms, thought to reflect input from chemosynthetic bacteria living near redox boundaries, are also detected. Relationships existing between sequence stratigraphy and the bulk and detailed molecular geochemistry of the Montezuma Valley and Smoky Hill members shed light on the factors, both global and regional, responsible for the composition of biogeochemical signals expressed in the sedimentary record. A better understanding of the processes affecting such signals is crucial in their use and application in paleoenvironmental and paleoceanographic reconstructions.
PP43B-1269
Bulk and Compound-Specific Isotope Analysis of Long-Chain, n-alkanes From a 85-kyr Core From Lake Peten Itza, Guatemala
Drill cores obtained from Lake Petén Itzá, Guatemala, contain a ~85-kyr record of terrestrial climate from lowland Central America. Variations in sediment lithology suggest rapid changes in precipitation during the last glacial and deglacial periods. Previous work in nearby Lake Quexil demonstrated the utility of using the carbon isotopic compositions of leaf wax n-alkanes to infer changes in terrestrial vegetation (Huang et al., 2001). Here we report carbon isotopes of bulk organic and long-chain n-alkanes in 60 samples to reconstruct changes in the relative proportion of C3 and C4 biomass in the watershed under changing climate and atmospheric CO2 conditions during the past 85 kyrs. Compound-specific carbon isotope results are compared directly with pollen analysis from the same samples. Huang, Y., F.A. Street-Perrott, S.E. Metcalfe, M. Brenner, M. Moreland, and K.H. Freeman. 2001. Climate change as the dominant control on glacial-interglacial variations in C3 and C4 plant abundance. Science 293:1647-1651.
PP43B-1270
Paleoclimatic impact on vertebrate activities: a speleothem record from Power Mill Creek Cave, Missouri
Two speleothem samples were collected from Power Mill Creek Cave (PMCC), Missouri, for uranium-series dating at the University of Minnesota and stable isotopic analyses at the University of Kentucky. The speleothem samples found in the cave were attached to the bones of an extinct ground sloth (Megalonyx jeffersonii). A femur was propped up on one stalagmite (PMCC1) and cemented to it by subsequent layers of flowstone. The other stalagmite (PMCC2) formed on top of a scapula. The ages of the speleothem samples range between 52,900 and 660 years old. Very few absolute dates on M. jefferesonii are known from the south-central United States and none of these are associated with paleoclimate data. With high-precision U-Th dates and the unique sample, PMCC1, we can narrow the age range of this M. jeffersonii to be between 42,100 ± 400 and 38,500 ± 500 years ago. In addition, we obtained carbon and oxygen isotope data on sample PMCC1 for a time period between 53 to 35 ka and reconstructed the regional climatic and vegetation changes. In general, climatic oscillations and vegetation changes in this region are consistent with the earlier study from speleothem samples of Crevice Cave, Missouri (Dorale et al., 1998). The midcontinental climate cooled and forest replaced grassland between 55 and 41 ka. Then, the temperature suddenly increased at 37 ka. Preliminary analysis of oxygen isotope oscillation shows that this warming around 37 ka was even more dramatic than that reported in the previous investigation at Crevice Cave. Based on these data, the sloth was living in a forested environment associated with a transitional climate. It is likely that these sudden cooling and subsequent warming changes between 42 and 37 ka had an impact on vertebrate communities in this region. Determining the degree of these impacts requires additional comparisons between well dated vertebrates and climatic records.
PP43B-1271
Interpreting Oxygen Isotope Ratios in Fossil Wood Cellulose
We evaluated the strength of relationships among cellulose δ18O (δ18Ocel), relative humidity, precipitation δ18O (δ18Oppt) and mean annual temperature (MAT) at the continental scale, and the range of variability in δ18Ocel associated with site hydrologic conditions and species differences. Additionally, we measured the δ18O of 45 million to 250 year-old fossil wood cellulose as a potential source of information about paleo-δ18Oppt and paleo-temperatures. We compared the crystalline structure of ancient and modern cellulose using XRD. At the oldest localities, MAT estimates derived from the modern relationship between MAT and δ18Ocel are lower than estimates derived from other biological proxies. Estimates of Pleistocene and Holocene MAT's are close to modern values at those sites. These results are consistent with other findings that the MAT/δ18Oppt relationship across North America was not constant throughout the Cenozoic. Paleo-δ18Oppt estimates derived from fossil cellulose and the modern relationship between δ18Ocel and δ18Oppt are within the current annual range of δ18Oppt values at all locations. These findings provide some evidence that a δ18Oppt signal may be retained in wood cellulose over millions of years, and that latitudinal patterns in δ18Oppt may not have changed much during the past 45 million years.
PP43B-1272
Pliocene-Pleistocene pCO2 Changes Based on Alkenone Carbon Isotopes
Climate change over the last 5 Myr includes the transition from the early Pliocene warm period to the ice age climate of the late Pliocene and Pleistocene. A moderate decrease in pCO2 is one of the many proposed causes. Here we reconstruct pCO2 changes using records of the total carbon isotopic fractionation that occurs during algal photosynthesis for the past 5 Myrs to test the overarching hypothesis that the pattern of warming during the early Pliocene warm period, as well as the subsequent cooling, was forced by a corresponding increase and decrease in pCO2. Our approach is to extract and determine the carbon isotopic value of haptophyte-derived long- chain ketone biomarkers (alkenones) from a globally dispersed set of DSDP/ODP cores. Our preliminary data from tropical and subtropical sites suggest that pCO2 during the Pliocene warm period was ~80 ppm (30%) higher than the pre-industrial level, with much of the pCO2 drop occurring prior to ~2 Ma. Reconstructions of pCO2 changes from globally distributed sites will be presented.
PP43B-1273
Pleistocene Variations in Delivery and Deposition of Organic Matter Under the Benguela Current Upwelling System - Biomarker Isotopic Evidence From Sediment Light-Dark Color Cycles
The light-dark color cycles that are distinctive features of sediment beneath the Benguela Current Upwelling System imply repetitive alternations in organic matter delivery and deposition. Organic geochemical proxies for paleoproductivity and for depositional conditions were employed to investigate the paleoceanographic processes involved in creating these cycles in two sediment sequences from ODP Site 1084 corresponding to 0.7 and 1.1 Mya. Concentrations of total organic carbon (TOC) vary between 3.5 and 17.1 wt percent, and those of calcium carbonate fluctuate inversely between 68 and 1 percent, suggesting that carbonate dissolution is involved with the light-dark cycles. Bulk organic del 13C and del 15N values that remain constant across the two light-dark sediment intervals indicate that the extent of nutrient utilization did not change in each cycle. Biomarker compositions in both sequences reflect a range of organic matter sources. Abundant n-alkanes and n-alkanols with odd-over-even and even-over-odd distributions, respectively, record land-plant inputs. Other terrestrial biomakers (e.g triterpenoid acids and alcohols) are present but in very low abundances, suggesting that the n- alkyl components derive predominantly from eolian inputs. Carbon isotopic values of n-alkanes range from –25 to –28 permil, suggesting a mixture of C3 and C4 sources. In contrast, n-alkanol isotopic compositions range from –28 to –34 permil, suggesting that they derive solely from C3 plants. Algal biomarkers are abundant and diverse, represented by 1,15-C30 diols (eustigmatophytes), 4-desmethyl and –methylsterols (diatoms, dinoflagellates), and alkenones (haptophytes). These compounds all have del 13C values ranging from ca. –22 to –24 permil, consistent with a marine origin. Systematic differences in isotopic values imply that marine productivity at 1.1 Mya was higher than at 0.7 Mya, but alkenone-based sea-surface temperatures are higher at 1.1 Mya (21 deg) than at 0.7 Mya (15 deg), which indicates that changes in water-mass properties were also involved.
PP43B-1274
Alkenone temperature and salinity: An evaluation of long chain C37 alkenone in Lake Qinghai, China
In recently years, the alkenone unsaturation index (Uk'37=C37:.2/(C37:2+ C37:3)) has been used to reconstructed paleo-temperature for lacustrine sediments. However, few studies have addressed whether the relative abundance of the C37:4 alkenone to the total C37 production (C37:4 percent) can reflect surface salinity changes in lake systems. Here we present the distribution of C37 long chain alkenone of modern lake sediments in Qinghai Lake, Qing-Tibet Plateau, to evaluate significance of abundance change of long chain C37 alkenone as an indicator of lake paleo-enviromental evolution. A group of surface sediments from different locations in the lake have been analyzed in this study. The results of long chain C37 alkenone from 28 surface sediments analyses shown relative abundance of C37:4 alkenone to total C37 production (C37:4 percent) change from 14.5 to 48.6 percent and the abundance of C37:4 alkenone is increasing with decreasing salinity of lake water. For the salinity lake in land, we suggested the relative abundance of C37:4 alkenone in lake sediments may be a indicator of paleo-silinity; We have also found that Uk'37 values are weakly correlated with salinity and C37:4 percent changes, implying that potential minor contributions of temperature and salinity effects to C37:4 percent and Uk'37 respectively cannot be excluded in this study. However, since these contributions are weak, we suggest that the C37:4 percent proxy can be used to reconstruct paleo-salinity changes at a regional scale, especially in lake systems, while Uk'37 remains as a powerful tool for reconstructions of paleo-temperature changes in the lake systems.
PP43B-1275
A Novel Tetraether Membrane Lipid Record from the Amazon Fan: The Influence of Changes in Sediment Supply on Estimates of Palaeo-Temperature, pH and Wetland Extent
Reconstructing Amazon basin paleoclimatic change is important because the region is a major component of the global carbon and hydrological cycles. Moreover, the region's tropical wetlands represent a major source of atmospheric methane. In order to provide a multiproxy 35 kyr record of terrestrial paleoclimatic change from the Amazon basin, analysis of glycerol dialkyl glycerol tetraethers (GDGTs) was carried out on sediment recovered from Ocean Drilling Program (ODP) Site 942 (Amazon Fan). The GDGTs include those with methyl-branched alkyl components, derived from unknown terrestrial bacteria (present worldwide in peat bogs and soils) which have been fluvially transported from the Amazon basin and sequestered in the Amazon fan. The catchment area supplying sediment to the Amazon fan covers a large portion of South America, including vast areas of tropical forests and wetlands; hence proxy records from ODP 942 potentially provide a spatially averaged terrestrial signal of major significance. We use recently developed indices that predict changes in: the relative fluvial input of terrestrial organic material; annual mean air temperature (MAT) and soil pH. We also use the ratios of certain alcohols as qualitative proxies for the relative inputs of wetland material. The Amazon basin shows a glacial to interglacial temperature increase of around 5°C; consistent with pollen and other geochemical records. However, this is followed by an apparent drop of 11°C at the start of the Holocene. We discuss how this seemingly counter intuitive result may be explained by changes in sediment supply from the Andean region relative to the warmer eastern Amazonia. In the glacial the soil pH increases dramatically from 13 to 11 kyr; possibly related to an (inferred) ~40 percent decrease in effective moisture in the Amazon basin. A post-glacial increase in wetland biomarkers suggests that the propagation of tropical wetlands, on continental shelves, may have been a key source of the post-glacial increase in global atmospheric methane.
PP43B-1276
Isotope Fractionations Associated With Degassing of CO2 Aqueous Solutions and its Implications for Carbonate Clumped Isotope Thermometry
Bicarbonate dehydration (HCO3-+H+→H2CO3→CO2+H2O) and dehydroxylation (HCO3-→CO2+OH-) are important reactions in solutions containing dissolved inorganic carbon (DIC) and are involved in multiple geologic processes, including cryogenic carbonate formation, speleothem deposition and air-sea CO2 exchange. Current understandings of the isotope fractionations that accompany these reactions are very limited. Here we present a model of the isotopic fractionations accompanying dehydration of carbonic acid in aqueous solution, using techniques from ab initio, transition state and statistical thermodynamic theory, and tests of this model based on measurements of experimental and natural carbonates produced by degassing of CO2 from aqueous solutions. Our model predicts that the isotopologues of carbonic acid containing heavy isotopes dehydrate more slowly than the normal isotopologues, such that fractionations between product CO2 and reactant H2CO3 are ~-25‰ for δ13C and ~-9‰ for δ18O at 300K. Expression of these isotope fractionations during degassing of CO2 from aqueous solutions should lead to increases in the δ13C and δ18O of residual DIC species, and in carbonate minerals that precipitate from that DIC; this phenomenon could explain the non-equilibrium isotopic compositions of some cryogenic carbonates and speleothems. The carbonate clumped isotope thermometer constrains carbonate formation temperatures based on the proportions of 13C-18O bonds in the carbonate mineral lattice [1]; the lower the formation temperature, the greater the proportion of 13C-18O bonds. By extending our above model to include the multiply- substituted isotopologues, we predict that isotope fractionations accompanying dehydration of carbonic acid decrease the proportion of 13C-18O bonds in the remaining DIC pool relative to their expected equilibrium abundances, and therefore lead to an apparent overestimation of carbonate formation temperatures as determined by the carbonate clumped isotope thermometer; the size of this effect, if unaccounted for, is ~10°C overestimation for every 1‰ kinetic enrichment in carbonate δ18O. We test the predictions of our model by measuring the isotopic compositions of carbonates formed by rapid freezing of CO2-saturated CaCl2 solutions. Results from these cryogenic carbonate precipitation experiments generally closely follow our predicted trend of isotope fractionations, i.e. higher in δ13C and δ18O, and lower in proportion of 13C-18O bonds. In many natural systems where CO2 degasses from aqueous solution, much of the evolved CO2 is produced by dedydroxylation of HCO3- (particularly in relatively high pH solutions). We are currently extending our modeling and experimental efforts to encompass this type of systems. Finally, we will present isotopic data for natural speleothems and compare them with the predictions of our physical chemistry model of kinetically controlled carbonate growth. Reference [1] Ghosh et. al. (2006) GCA, 70: 1439-1456.
PP43B-1277
Influence of Convective Processes on Isotopic Composition of Precipitation (Oxygen 18 and Deuterium) in the Tropics: a Single Column Model Analysis
Isotopic records (deuterium and oxygen 18) in ice cores are a valuable tools to reconstruct past climate. However, the climatic interpretation of tropical istotopic records is still debated. The amount effect, which is the observed link between precipitation amount and isotopic composition of precipitation, largely controls the isotopic composition of precipitation there. Yet physical processes underlying this effect are still poorly understood and quantified. This is partly because most of tropical precipitations are related to atmospheric convective processes, whose influence on isotopic composition of precipitation is not well known. In the present study, water stable isotopes (H2O18 and HDO) have been introduced into the Emanuel convective parametrization, and into a single column model of radiative-convective equilibrium including the convective parametrization and a parametrization of clouds and radiation. The detailed representation of processes such as mixing and rain evaporation in the Emanuel parametrization allows an investigation of the influence of convective processes on isotopic composition of precipitation (both δ D and deuterium excess). In particular, the physical processes underlying the amount effect are analyzed and their relative contributions are quantified. We show that the amount effect is actually the net effect of a combination of different convective processes. Two processes are dominant: first, the reevaporation of the falling rain and the diffusive exchange with the surrounding vapor in unsaturated downdrafts; second, the recycling of the subcloud layer vapor feeding the convective system by the mass flux driven by the reevaporation of rain. This calls for a detailed representation in models of processes associated with the reevaporation of convective rain to accurately simulate the isotopic composition of precipitation in the Tropics. We also investigate the time scales involved in the relationship between convective activity and the isotopic composition of precipitation.
PP43B-1278
Authigenic uranium in the sediments in the La Paz Bay and La Paz Basin, south-western Gulf of California
The presence of high concentrations of uranium in sediments is under research in order to explain this phenomenon, because of the possibility to use it as a proxy for reconstruction of past redox conditions in the marine environment. To characterize U sedimentary behavior in the south-western Gulf of California, four sediment cores were collected in the La Paz Lagoon, La Paz Bay and La Paz Basin. Core sediment subsamples were dried, homogenized and the contents of uranium and scandium were determined by an instrumental neutron activation analysis method. The average concentrations of the total U varied from 3.9±1.5 mg kg- 1 (core from the shallow 8 m-deep La Paz Lagoon) to 12.0±7.2 mg kg-1 (core from the 400 m-deep entrance just between La Paz Bay and the adjacent open Gulf of California), 12.9±2.6 mg kg-1 (core from the 400 m-deep suboxic Alfonso Basin of the La Paz Bay) and 13.3±2.6 mg kg-1 (core from the 745 m–deep La Paz Basin, the Gulf of California). These concentrations are not the highest compared with other studies for the areas of coastal upwelling, but are still higher than uranium average abundance in Earth´s crust (2.7 mg kg-1). The authigenic (non-lithogenic) uranium concentrations were calculated, using U/Sc crustal ratios, because Sc is a reliable indicator of terrigenous material, mainly aluminosilicates. The contribution of authigenic uranium were 46.7±21.3 % for the sediments of the La Paz Lagoon, 81.7±15.0 % for a core from the entrance at the limits of the La Paz Bay, 89.1±2.3 % for the sediments from the Alfonso Basin of the La Paz Bay and 90.6±2.2 for the sediment core from the La Paz Basin. The vertical profiles of this element in studied cores reveal different patterns of the variability of their contents in the sedimentary layers. Due to the sensibility of uranium to reducing conditions, authigenic uranium enrichments could reflect the occurrence of anoxic conditions in the water column in the past. Deeper waters in the study area are distinguished by the presence of oxygen minimum zone, which favours the less soluble uranium (IV) to precipitate on particles, whereas the dissolved uranium (VI) prevails in oxygenated upper layer of sea waters. The cores from the Alfonso Basin and La Paz Basin show some similarity and the variations of their U contents oscillate near mean value, indicating quiet conditions of the sediment accumulation. However, the core from the entrance of the La Paz Bay displays a clear change in the vertical distribution of the total U content at the 18 cm of core depth. In this core the total U content was in average 6.3±4.4 mg kg-1 for the layer of sediments from 0 to 18 cm, and then it sharply increased to 16.3±5.8 mg kg-1 for the layer from 18 to 40 cm. This pattern change could be a result of an underwater mass flow event, probably caused by tectonic seismic activity. This moved a layer of shallow sediments, depleted in authigenic uranium, to deeper places of the sea floor, characterized by higher authigenic uranium precipitation on it.
PP43B-1279
A Quantitative, High-resolution Hydrologic and Temperature Record From the Northern Great Plains, USA
The use of alkenone unsaturation ratios to reconstruct quantitative temperature records from marine sediments is well-established, while the application of this geochemical indicator is relatively new for lakes in continental settings. Here we present the first continuous, high-resolution, Holocene-length alkenone record from the North American interior, Brush Lake, MT, to quantitatively assess temperature changes from the late glacial through the Holocene (with particular emphasis on mid-Holocene maximum aridity period). We couple the alkenone analyses with measurements of the isotopic composition of short and long-chain fatty acids and other bulk geochemical measurements to reconstruct patterns of regional drought. Alkenone concentrations are generally low, but measurable, and we have generated a preliminary temperature reconstruction using a published alkenone calibration from German lakes (Zink et al. 2001). Associated with alkenone-inferred changes in temperature are shifts in the isotopic composition of leaf waxes, as well as changes in the ratio of short to long- chain acids suggestive of variability in aquatic versus terrestrial input of organic matter to the lake environment. This paleoclimate record is part of a multiproxy project to improve our understanding of the long-terms patterns of drought in central North America and the mechanism that causes drought in the Northern Great Plains. The analysis of alkenone unsaturation ratios coupled with isotope data derived from terrestrial leaf waxes has the potential to yield quantitative and independent analysis of the temperature and hydrologic drivers of drought. This study may also provide insight into the cyclic nature of drought in the Northern Great Plains and the relationship to N Atlantic and tropical Pacific SST changes, which are known to force drought in the instrumental period.
PP43B-1280
Organic Geochemical Evidence of Late Glacial-Holocene Climate Instability in the Aegean Sea: Teleconnections With North Atlantic Paleoclimate Variability
The Mediterranean Sea and its sediment record provide an ideal natural laboratory to study the history of climate changes and the responses of marine environments to these changes. Paleoceanographic and oceanographic studies highlight the Aegean Sea as an especially sensitive part of the Mediterranean Sea that is closely connected to global climatic variability. The hydrologic system of the Aegean Sea is complex, with a strong inflow of water from Black Sea and abundant rivers, and strong effects of atmospheric cooling on water mass formation and structure. Here we present a high-resolution multi-proxy study of three sediment cores collected from the north (MNB-3 and 152-SL) and central (NS-14) Aegean Sea. The cores consist of hemipelagic muds, including the sapropel layer S1 that was deposited between 9.8 to 6.4 kyr BP, along with the S1 interruption that occurred from 8.6 to 7.6 kyr BP. This study has identified important differences in multiple elemental, isotopic and molecular organic biogeochemical proxies that occurred during the late last Glacial to Holocene in response to local climate changes with the global climate variability. An important time marker and indicator for dramatic changes in the physical, chemical, and biological environment related to global climate variability is sapropel S1, a sediment layer rich in organic carbon. Our multi-proxy results identify several phases that can be related to distinct variations in paleoenvironmental conditions. Cold intervals recorded in the late last Glacial, the Younger Dryas, and during the S1 interruption show enhanced deep water convection and ventilation in response to surface water cooling probably driven by a strengthening of north winds over the NE Mediterranean Sea, related to a positive North Atlantic Oscillation phase. Warm intervals saw reduced thermohaline circulation/convection and increases in freshwater inputs related to increased intensity of the African monsoons. The warm phases caused the development of suboxic/ anoxic conditions, better organic matter preservation, and sapropel deposition during the Holocene. Interestingly, fluctuations in alkenone-SST and biogeochemical proxies within this sapropelic layer reveal that several distinct cooling events occurred during deposition of S1 that are concordant with North Atlantic Oscillations and that caused pulses of reventilation in the deep basins in the Aegean Sea.
PP43B-1281
Diversity of squalene-hopene cyclases in a tropical carbonate-rich environment
Hopanoids are isoprenoid lipids which derive primarily from bacteria and are ubiquitous in contemporary Earth surface environments. In the geologic record, hopanes found in sedimentary rocks are used as proxies to help decipher ancient biological communities. However, in contrast to the ubiquity of these lipid products, biosynthesis of hopanoids appears to be a relatively rare physiological trait among bacteria in complex environmental communities. We have recently estimated that fewer than one in ten bacterial cells in soils and fewer than one in twenty bacterial cells in the ocean contains the gene squalene-hopene cyclase (sqhC) [1]. Biosynthesis of hopanoids is rarer in natural communities than it is among species that have been propagated in pure culture [2]. Here we continue our previous work to survey the phylogeny and diversity of hopanoid producers using culture-independent methods. In particular, genes affiliated with known cyanobacterial sequences were not detected in the contemporary environments analyzed previously [1]. One possible explanation is that hopanoid-producing strains of cyanobacteria are regionally localized. It has been suggested that throughout the long-term sedimentary record there is a correlation between 2-methylhopanoid index (a putative indicator of cyanobacterial biomass) and the global prevalence of shallow carbonate platform environments [3], and in previous work we did not analyze any such environments. To address this question we surveyed a land-sea gradient across the Bahamian island of San Salvador. Samples were taken from upland soil, a hypersaline lake, a tidal creek, and the shallow open ocean. The data are remarkably similar to our previous results: environmental sqhCs average < 65% translated amino acid identity to their closest relatives in public databases, and non- cyanobacterial sequences continue to dominate. We will discuss the challenges these results pose for deciphering the global distribution of microbially-derived lipids from complex communities, and we will propose some future directions forward. [1] Pearson A, Flood Page SR, Jorgenson TL, Fischer WW, Higgins MB (2007) Novel hopanoid cyclases from the environment. Environmental Microbiology 9, 2175-2188. [2] Rohmer M, Bouvier-Nave P, Ourisson G (1984) Distribution of hopanoid triterpenes in Prokaryotes. J. Gen. Microbiol. 130, 1137-1150. [3] Summons, RE (personal communication).
PP43B-1282
Global and Regional Controls on Alkenone Sea Surface Temperature and Productivity Records for the Pleistocene From the Arabian Sea
The Arabian Sea is home to one of the modern ocean's largest upwelling zones and represents a region that is sensitive to the dynamics of the Asian monsoon system as well as glacial-interglacial climate changes. High sedimentation rates in this region enable highly resolved climate reconstructions, which provide the opportunity to evaluate the impacts of both local and global forcing of oceanographic conditions in the Arabian Sea. We present high-resolution (1.5 kyr) alkenone SST and alkenone abundance data for the last 1.8 Myr from Ocean Drilling Program Site 722 in the northwest Arabian Sea. Over the course of the Pleistocene, SST at this site ranges from 23.3°C to 27.8°C with a long term decrease of 0.7°C/Myr. Like the well-known benthic oxygen isotope record, the SST record contains a long-term increase in amplitude and a switch from 41 kyr cyclicity to 100 kyr cyclicity across the mid-Pleistocene transition. Because of the strong similarity between our Arabian Sea SST record, ice volume, carbon dioxide (where data are available), and an additional SST record from the Eastern Equatorial Pacific upwelling zone, we conclude that SST at Site 722 is strongly linked to global glacial-interglacial climate variability throughout the Pleistocene, with warmest water temperatures occurring during interglacial periods and vice versa. Our data indicate that Site 722 SST was decoupled from the monsoon system on orbital timescales and was likely driven by variations in subsurface mode water temperatures, ultimately linked to high latitude climate. Alkenone abundance, which we relate to productivity, is highly variable over the last 1.8 Myr, ranging over two orders of magnitude. Average productivity and productivity variability both decreased during the early Pleistocene and remained low through the mid-Pleistocene transition. During the late Pleistocene both average productivity and productivity variability increased. Throughout the Pleistocene, inferred productivity at Site 722 appears to be related to monsoon-driven upwelling based on the similarity between our alkenone abundance record and a grain size record from Site 722, which responds to variations in wind speed.
PP43B-1283
Characterization of the Paleoenvironmental Evolution of the Mallik Area From Gas Geochemistry Data
During drilling of the JAPEX/JNOC/GCS et al. Mallik Gas Hydrate Production Research wells (NWT, Canada), up to 35 vol-% CH4 were found in drill mud gas at 106 m depth within the permafrost. The carbon isotope composition of CH4 implies that this gas is of microbial origin (δ13C from -75‰ to - 77‰ PDB). Surprisingly, noble gas data suggest that at least some of this gas could be trapped in gas hydrates, at a depth distinctly shallower than the predicted gas hydrate stability field. Although microbes are capable of some metabolic activities at subzero temperatures, it is unlikely that production of methane under permafrost conditions can account for that amount of natural gas at this depth. Therefore, we suggest that the formation of this gas must have occurred under non-permafrost conditions. Furthermore, this gas reservoir was sealed from mixing with thermogenic gas, migrating from depth, which could be identified at the base of the permafrost at approx. 620m depth (δ13C=-42.5‰). We interpret the observed features by partially thawing of existing permafrost at least down to 106 m depth during a period of warming where the area was covered by a lake or by the ocean through inundation of the shoreline. Once the lake was drained or the shoreline was uplifted, the surface became again exposed to air and permafrost again developed on top of the unfrozen ground. As the permafrost gradually advanced downward, the water below was pressurized due to freezing and expansion of the newly formed ice, leading to pressure conditions that stabilize gas hydrates.
PP43B-1284
δ15N changes during Paleogene climatic events in organic-rich, marine clays from coastal Tanzania
A mid- to outer-shelf, passive margin sequence, consisting of organic-rich marine clays, has been cored by the Tanzanian Drilling Project (TDP) on southern coastal Tanzania. Drilling recovered an expanded Paleogene section — from latest Cretaceous to early Oligocene. Intervals cored include at least two periods of global climatic change: the Paleocene-Eocene Thermal Maximum (PETM), and the Eocene-Oligocene boundary. The organic- rich nature of these clays makes them ideal for nitrogen isotope analysis across these global climate change boundaries. Shifts in the δ15N of sediments represent changes in the primary productivity regime of the local ocean at that time. An increased or high δ15N signal in sediment corresponds to regions of greater nitrate depletion in the surface waters (i.e. higher productivity). A low δ15N signal represents a lack of nitrate uptake in the surface waters, possibly due to phytoplankton migration, phytoplankton collapse or lack of nutrient supply. A sharp and significant decrease in δ15N is seen at the onset of the PETM. This negative shift in δ15N coincides with an extinction of benthic foraminifera at this site and may indicate a broader ecosystem collapse. Productivity collapse is a likely result of switching off the nutrient supply to the planktonic biomass. This may indicate stratification of the water column — much like that seen during El Niño events, but over a longer timescale. Preliminary investigations of mineralogy across the Eocene-Oligocene boundary have indicated that through the transition, increased amounts of detrital material (e.g. SiO2) entered the coastal system. The increasing abundances of detrital quartz are coeval with increases in Ti/Al ratios, also indicating increased terrigenous input. A likely cause is the lowering of global sea-levels during initiation of glaciation on Antarctica. Analyses of the Fe/Al and Ba/Al ratios of the sediments indicate brief periods of increased productivity after the boundary, during the earliest Oligocene. A shift to higher sedimentary δ15N values would corroborate these preliminary results and further clarify the productivity conditions in the Paleogene.
PP43B-1285
A Paleoenvironmental Record From Tomales Bay, California: Organic and Geochemical Proxy Records of Anthropogenic Impacts
Coastal regions have long attracted human settlement for numerous reasons such as abundant freshwater sources, ecological and mineralogical richness, and the facilitation of trade and transport. To better understand anthropogenic impacts on coastal environments, recent sediment records of Tomales Bay, (California, U.S.A.) were examined. Tomales Bay is a secluded estuary located 50 km north of San Francisco that drains into the Pacific Ocean, for which the anthropogenic history has been very well documented. In recent history Tomales Bay has undergone changes in land-use and an increase in human populations, but impacts of these processes on the marine environment are poorly constrained. Tomales Bay is ~1.4km wide and 20km long, with sedimentation rates of 3-30mm/year. Six push-cores 15 to 20 cm in length were taken at low tide within the bay. Measurements of preserved lignin will provide a record for terrigenous DOM cycling and diagenetic processes occurring in the watershed, while also differentiating between marine and terrigenous OM sources to the sediments. The impact of environmental change over time on the presence of microfossil species (benthic foraminifera) will be presented. Temperature reconstructions and carbon cycling in the bay will be discussed based on oxygen and carbon stable isotope analyses of selected foraminiferal species. This study aims to reconstruct recent environmental changes in Tomales Bay, both natural and anthropogenic to constrain the extent to which human perturbation affects coastal environments.
PP43B-1286
Tracking Soil Organic Carbon Transport to Continental Margin Sediments Using Soil-Specific Hopanoid Biomarkers: a Case Study From the Congo Fan (ODP Site 1075)
The transport and subsequent deposition of terrestrially derived organic matter into the ocean is an important but poorly constrained aspect of the modern global carbon cycle. In regions associated with large river systems it is likely that the terrestrial input of organic carbon is much more complex than commonly considered and very difficult to trace based on established geochemical proxies. It is therefore important to develop proxies that target the movement and fate of this terrestrial organic material. The identification of bacteriohopanepolyol (BHP) biomarkers unique to soil derived organic carbon (SOC) has enabled the transport of SOC into aquatic sediments to be traced. The extreme recalcitrance of BHPs enables these source specific compounds to be used on recent and ancient sediments to identify periods of high and low SOC input into sediments. BHPs are bacterial membrane compounds with a high degree of structural variability. They are analogous to steroids in eukaryotes and have been identified in over half of all bacteria studied for their presence. BHPs have a wide range of over 40 functional groups on the side chain, with up to 6 functional groups in each structure, and with methylation and unsaturation over 100 total structures have been identified1. During the BHP analysis of a wide range of soils from around the world we consistently measure high levels adenosylhopane, known to originate from purple non-sulphur, nitrogen fixing and ammonia oxidising bacteria and 2-methyl adenosyl hopane (m/z 802)2, from nitrogen fixing bacteria. Only 3 lacustrine sediments with large SOC supply from their catchments areas have been found to contain these markers in a survey of over 40 different non-marine settings. Recent studies on Late Quaternary sediments from the Congo deep sea fan (OPD site 1075, approximately 2 km water depth) provide a strong case to expect markers for SOC3. An initial analysis of the core samples confirms the presence of soil specific BHP markers in each sample analyzed down to 89 m depth in addition to the presence of common sediment associated BHPs. Concentrations of soil markers are high in the upper sediment section down to about 49 m supporting the case for these molecular markers as novel proxies for SOC supply and burial. Distinct peaks of adenosyl and 2 methyl adenosyl hopane at about 200, 300 and 550 kyrs tentatively imply that the rate of terrestrial organic matter discharge from tropical Africa significantly increased at these times, possibly associated with periods of reduced soil stability in the Congo catchment. Analysis of the surface sediments from 4 other cores in close proximity to ODP site 1075 clearly shows that the percentage contribution of soil marker BHPs decreases with increasing distance from the river mouth, indicating that the river is the source of these BHPs. References 1. Rohmer, M. 1993. Pure and Applied Chemistry 65, 1293-1298. 2. Talbot, H.M., Rohmer, M., Farrimond, P., 2007. Rapid Communications in Mass Spectrometry (In press). 3. Holtvoeth, J., Wagner, T., Kolonic, S., 2005. Geochimica et Cosmochimica Acta, 69, 2031-2041.
PP43B-1287
Lipid biomarkers of thermal stress in scleractinian corals
Lipid content and fatty acid profiles of corals and their symbiotic dinoflagellates are known to vary in response to heat stress and bleaching. To develop lipid biomarkers of heat stress and bleaching response in scleractinian corals, clones of Symbiodinium algae of clade subtypes C1 and D1 were cultured under a range of temperatures. The predominant lipids produced are palmitic (C16) and stearic (C18) saturated fatty acids and their unsaturated analogs. Other important compounds included a C22 penta-unsaturated fatty acid, which is thought to be a specific dinoflagellate marker, and a variety of sterols. Analysis of lipids extracted from coral skeleton indicated that palmitic and stearic acids were the most abundant compounds. The amount of unsaturated C16 and C18 fatty acids in coral skeleton relative to the saturated versions of those acids was much lower in coral skeleton than in the zooxanthellae tissue. This could indicate the incorporation of lipids from outside the coral host-symbiont system into the coral aragonite, or it could reflect diagenesis. A comparison between the lipids found in cloned zooxanthellae, coral tissue, and aragonitic skeleton will be presented to assess the usefulness of lipid biomarkers as indicators of temperature stress on corals.
PP43B-1288
Molecular Markers in the Quelccaya Ice Cap, Peru Describe 20th Century Biomass Burning Variability
Organic geochemical analytical methods were applied to Andean ice core samples, resulting in a multi- molecular biomass burning record spanning 1915 to 2001 AD. The Quelccaya Ice Cap in Peru is situated on the eastern flank of the Andes at 14°S and is well situated to receive aeolian inputs of organic matter derived from Amazonian forest fire events. Compounds of interest, which occur in trace quantities in ice, were recovered by stir bar sorptive extraction and analyzed by gas chromatography/time-of-flight mass spectrometry coupled with thermal desorption. These methods permitted identification and quantitation of numerous biomarkers in sample volumes of as little as 10 ml. At least one wet and dry season sample was analyzed for every year. Observed biomarkers that may be derived from vegetation fires include several polycyclic aromatic hydrocarbons (PAHs), atraric acid, 2-ethylhexyl p-methoxycinnamate, and a range of other aromatic compounds. Abrupt changes in compound abundances were superimposed on decadal variability. Systematic offsets between wet and dry season abundances were not observed, suggesting that the biomass burning signal is not biased by seasonal depositional effects, such as dust delivery. Inputs likely reflect a combination of sources from anthropogenic burning of the Amazon rainforest as well as natural fires related to aridity, and include both high and low elevation vegetation. These compounds and techniques can be applied to older ice in this and other core locations as an independent estimate of aridity.