Yongsong Huang

Brown University, Providence, Rhode Island, United States

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Publications (113)495.63 Total impact

  • James T. Dillon, Yongsong Huang
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    ABSTRACT: Liquid chromatography-mass spectrometry (LC-MS) analysis of glycerol dialkyl glycerol tetraethers (GDGTs) from sediment and soil samples has become a widely adopted approach for reconstructing past ocean and continental climate variables such as temperature and pH. The LC-MS data used for constructing these GDGT climate proxies is taken directly from the peak area values of individual GDGT [M+H]+ ions, often determined from manual peak integration due to unreliable computer integrators in commercial software, particularly in cases of complex baselines, asymmetric peak shapes and peak coelution. Manual integration is not only time consuming, but also prone to user-induced inconsistency when individuals utilize different criteria for peak/baseline definition. To overcome these problems, we have developed a user-friendly, graphical user interface (GUI) programmed in the MATLAB environment, allowing users to efficiently and reproducibly perform batch processing and peak integration of LC-MS data. The program, “TEXPRESS” v1.0 (“tetraether index express”), incorporates modern chemometric based techniques for baseline definition and deconvolution of complex chromatographic peaks and we show that LC-MS data processed using the TEXPRESS toolbox are in strong agreement with results obtained from manual peak integration. We provide a general overview of the concepts and architecture of the TEXPRESS toolbox and discuss the advantages of chemometric based peak integration methods for processing branched and isoprenoid GDGT LC-MS data.
    Organic Geochemistry 12/2014; · 2.83 Impact Factor
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    ABSTRACT: Hydrogen and carbon isotope ratios of terrestrial plant leaf wax are powerful paleoclimate and paleoenvironmental proxies. However, further research on the underlying controls of the chemical and isotopic composition is needed in order to more quantitatively infer past climate and environmental conditions. There are systematic molecular and isotopic trends along leaves of a C4 grass Miscanthus, but whether such patterns also occur in other plant types is unclear. Here we determined intra-leaf variability in leaf wax abundance and isotope ratios for five terrestrial C3 plants. All species showed a general increasing base-to-tip trend in leaf wax abundance, suggesting a physiological need for more leaf wax in outer leaf sections. The hydrogen isotope values showed base-to-tip deuterium enrichment in all plants, but carbon isotope values showed base-to-tip 13C depletion in most species. Such intra-leaf isotopic distributions are similar to those in the C4 grass Miscanthus, suggesting similar underlying controls. While leaf wax hydrogen isotopic ratio values in general followed similar trends to corresponding leaf water, we found a significant reduction in hydrogen isotopic fractionation at the base of leaves (most pronounced for Dactylis glomerata). We attribute this to the utilization of isotopically enriched glucose transported from outer leaf sections for leaf wax synthesis at the base. The transported sugars were enriched in deuterium because of preferential consumption of 2H-depleted resources during metabolism in outer sections, in addition to biosynthesis using 2H-enriched leaf water.
    Organic Geochemistry 11/2014; · 2.83 Impact Factor
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    Li Gao, Erika J Edwards, Yongbo Zeng, Yongsong Huang
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    ABSTRACT: Hydrogen isotopic ratios of terrestrial plant leaf waxes (δD) have been widely used for paleoclimate reconstructions. However, underlying controls for the observed large variations in leaf wax δD values in different terrestrial vascular plants are still poorly understood, hampering quantitative paleoclimate interpretation. Here we report plant leaf wax and source water δD values from 102 plant species grown in a common environment (New York Botanic Garden), chosen to represent all the major lineages of terrestrial vascular plants and multiple origins of common plant growth forms. We found that leaf wax hydrogen isotope fractionation relative to plant source water is best explained by membership in particular lineages, rather than by growth forms as previously suggested. Monocots, and in particular one clade of grasses, display consistently greater hydrogen isotopic fractionation than all other vascular plants, whereas lycopods, representing the earlier-diverging vascular plant lineage, display the smallest fractionation. Data from greenhouse experiments and field samples suggest that the changing leaf wax hydrogen isotopic fractionation in different terrestrial vascular plants may be related to different strategies in allocating photosynthetic substrates for metabolic and biosynthetic functions, and potential leaf water isotopic differences.
    PLoS ONE 11/2014; 9(11):e112610. · 3.53 Impact Factor
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    ABSTRACT: The chain length of long chain alkenones (LCAs) in ocean and lake sediments commonly ranges from C37 to C39. Alkenones > C40 are extremely rare: C41 and C42 alkenones have only been reported in a Cretaceous black shale (Cenomanian, ca. 95 Ma) from the Blake Bahama Basin, western North Atlantic (DSDP Leg 76, site 534). The significance of these exceptionally long chain alkenones is, however, unclear. W have conducted a systematic survey of LCAs in surface sediments from 12 lakes with a wide range of salinity (0.7 to 146.3 g/l) from arid northwestern China. They showed a general trend of increasing maximum chain length with increasing salinity. In particular, C41 and C42 LCAs occurred only in the surface sediments of hypersaline lakes (113.6 to 146.3 g/l), but were absent from lakes with lower salinity, indicating that these compounds may be produced by an unknown haptophyte species living in hypersaline environments.
    Organic Geochemistry 10/2014; · 2.83 Impact Factor
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    ABSTRACT: Improved predictions of drought require an understanding of natural and human-induced climate variability. Long-term records across glacial–interglacial cycles provide the natural component of variability, however few such records exist for the southwestern United States (US) and quantitative or semi-quantitative records of precipitation are absent. Here we use the hydrogen isotope (δD) value of C28n-alkanoic acid in lacustrine sediments of Pleistocene age to reconstruct δD values of precipitation in northern New Mexico over two glacial–interglacial cycles (∼550,000–360,000 years before present) and obtain a record of monsoon strength. Overall, reconstructed δD values range from −53.8‰ to −94.4‰, with a mean value of −77.5 ± 8‰. Remarkably, this variation falls within the measured present-day summer monsoonal and winter weighted means (−50.3 ± 3‰ and −106.4 ± 20‰ respectively), suggesting that processes similar to those of present time also controlled precipitation during Marine Isotope Stage (MIS) 13 to 10. Using the δD summer monsoonal and winter mean values as end-members, we interpret our reconstructed δD record of precipitation as a direct, and semi-quantitative, indicator of monsoon strength during MIS 13 to 10. Interglacial periods were characterized by greater monsoon strength but also greater variability compared to glacial periods. Pronounced cycles in the strength of the monsoon occurred during interglacial periods and in general were positively correlated with maximum mean annual temperatures. Our estimates of monsoon strength are supported by independent proxies of ecosystem productivity, namely, TOC, δ13C of TOC and Si/Ti ratio and warm pollen taxa Juniperus and Quercus. Interglacial variability in the strength of the monsoon resembles a response to the land-sea surface temperature contrast (LSTC) except for the early part of MIS 11. During this period, LSTC would have remained relatively strong while monsoonal strength decreased to a minimum. This minimum occurred following the warmest interval of MIS 11, suggesting a more complex driving of monsoon strength during warm periods. In addition, this period of monsoon minimum coincided with a core section of mud-cracked sediments that suggest low monsoonal precipitation was an important factor in the onset of drought. Our estimates of monsoon strength represent a record of natural variability in the region that is relevant to present time, in particular the variability during interglacial MIS 11, which is considered an analog for the current interglacial. Our results suggest that natural variability can cause significant reductions in monsoonal precipitation with the implication of a potentially adverse effect from sustained warming. http://authors.elsevier.com/a/1Pnhg-4PRZkml
    Quaternary Science Reviews 09/2014; 103:81-90. · 4.57 Impact Factor
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    ABSTRACT: Proxy records of summer monsoon moisture at Lake Qinghai on the northeastern Tibetan Plateau reveal a late Quaternary climate history that is subtly different from that of speleothems from southern and eastern China. Total organic carbon and authigenic carbonate in two independently analyzed and dated cores indicate (1) relative stability and aridity during the glacial interval, (2) small variations during the Bølling–Allerød and the Younger Dryas intervals, (3) comparatively abrupt change at the late Pleistocene/Holocene transition, and (4) relatively high variability during a wet early Holocene. Taken together, the data suggest that a climate threshold exists for penetration of Asian monsoon rainfall onto the Tibetan Plateau, a threshold that was crossed at the beginning of the Holocene. Conceptually, the threshold simply may be related to the topographic barrier that the eastern margin of the Tibetan Plateau presents to the landward penetration of the monsoon, or it may be related to non-linearities in the climate system itself, such as sudden shifts in the configuration of the Westerly jet stream. Different mechanisms for producing a threshold are not mutually exclusive and may have combined to affect the dynamics of the Asian monsoon. In any case, the threshold is related to the presence of the Tibetan Plateau, which has a profound influence on the Asia monsoon system.
    Geophysical Research Letters 07/2014; · 4.46 Impact Factor
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    ABSTRACT: The origin of homochirality and its role in the development of life on Earth are among the most intriguing questions in science. It has been suggested that carbonaceous chondrites seeded primitive Earth with the initial organic compounds necessary for the origin of life. One of the strongest pieces of evidence supporting this theory is that certain amino acids in carbonaceous chondrites display a significant L-enantiomeric excess (ee), similar to those use by terrestrial. Analyses of ee in meteoritic molecules other than amino acids would shed more light on the origins of homochirality. In this study we investigated the stereochemistry of two groups of compounds: 1) free monocarboxylic acids (MCAs) from CM2 meteorites LON 94101 and Murchison; and 2) the aliphatic side chains present in the insoluble organic matter (IOM) and extracted in the form of monocarboxylic acids (MCAs) from EET 87770 (CR2) and Orgueil (CI1). Contrary to the well-known ee observed for amino acids in meteorites, we found that meteoritic branched free and IOM-derived MCAs with 5–8 carbon atoms are essentially racemic. The racemic nature of these compounds is used to discuss the possible influence of ultraviolet circularly polarized light (UVCPL) and aqueous alterations on the parent body on chirality observed in in carbonaceous chondrites.
    Geochimica et Cosmochimica Acta 04/2014; · 4.25 Impact Factor
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    ABSTRACT: The Indo-Pacific warm pool houses the largest zone of deep atmospheric convection on Earth and plays a critical role in global climate variations. Despite the region's importance, changes in Indo-Pacific hydroclimate on orbital timescales remain poorly constrained. Here we present high-resolution geochemical records of surface runoff and vegetation from sediment cores from Lake Towuti, on the island of Sulawesi in central Indonesia, that continuously span the past 60,000 y. We show that wet conditions and rainforest ecosystems on Sulawesi present during marine isotope stage 3 (MIS3) and the Holocene were interrupted by severe drying between ∼33,000 and 16,000 y B.P. when Northern Hemisphere ice sheets expanded and global temperatures cooled. Our record reveals little direct influence of precessional orbital forcing on regional climate, and the similarity between MIS3 and Holocene climates observed in Lake Towuti suggests that exposure of the Sunda Shelf has a weaker influence on regional hydroclimate and terrestrial ecosystems than suggested previously. We infer that hydrological variability in this part of Indonesia varies strongly in response to high-latitude climate forcing, likely through reorganizations of the monsoons and the position of the intertropical convergence zone. These findings suggest an important role for the tropical western Pacific in amplifying glacial-interglacial climate variability.
    Proceedings of the National Academy of Sciences 03/2014; · 9.81 Impact Factor
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    William M Longo, Yongsong Huang
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    ABSTRACT: The Arctic is warming twice as fast as the rest of the globe and undergoing shifts in ecological disturbance regimes. These changes threaten to destabilize vast permafrost carbon reservoirs and are potential positive feedbacks to global climate change. To predict the consequences of continued arctic warming we must develop a baseline for past climate variability and its associated feedbacks using proxy records from geological archives. The goal of this research was to develop and apply two lacustrine organic geochemical proxies (alkenones and polycyclic aromatic hydrocarbons) in northeastern Alaska (NE AK) to better understand the region's climate and fire history. To develop alkenone paleothermometry in NE AK we applied our new method for alkenone analysis which uses a poly(trifluoropropylmethylsiloxane) stationary phase with gas chromatography-flame ionization detection (GC-FID). The method separated 16 alkenones from NE AK lakes and revealed 4 novel alkenones that went undetected with traditional methods. Analysis of water column particulates revealed that several indices of alkenone unsaturation were well correlated with in situ lake water temperature, allowing for a robust U K
    2014 Geological Society of America Northeastern Section Meeting, Lancaster, PA; 03/2014
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    ABSTRACT: Plants using the C4 (Hatch-Slack) photosynthetic pathway are key for global food production and account for ca 25% of terrestrial primary productivity, mostly in relatively warm, dry regions. The discovery of modern naturally-occurring C4 plant species at elevations up to 4500 m in Tibet and 3000 m in Africa and South America, however, suggests that C4 plants are present in a wider range of environments than previously thought. Environmental conditions on the Tibetan Plateau, including high irradiance, rainfall focused in summer, and saline soils, can favor C4 plants by offsetting the deleterious effects of low growing season temperature. We present evidence based on leaf wax carbon isotope ratios from Lake Qinghai that C4 plants accounted for 50% of terrestrial primary productivity on the northeastern Tibetan Plateau throughout the Lateglacial and early Holocene. Despite cold conditions, C4 plants flourished due to a combination of factors, including maximum summer insolation, pCO2 ca 250 ppmv, and sufficient summer precipitation. The modern C3 plant-dominated ecosystem around Lake Qinghai was established ca 6 thousand years ago as pCO2 increased and summer temperature and precipitation decreased. C4 plants were also intermittently abundant during the Last Glacial period; we propose that C4 plants contributed a significant portion of local primary productivity by colonizing the exposed, saline Qinghai Lake bed during low stands. Our results contrast with state-of-the-art ecosystem models that simulate <0.5% C4 plant abundance on the Tibetan Plateau in modern and past environments. The past abundance of C4 plants on the Tibetan Plateau suggests a wider temperature range for C4 plants than can be inferred from modern distributions and model simulations, and provides paleoecological evidence to support recent findings that C4 plant evolution and distribution was determined by a combination of climatic and environmental factors (temperature, irradiance, precipitation amount and seasonality, and soil salinity). Moreover, this finding highlights the exceptional sensitivity of high-elevation ecosystems to environmental change, and provides critical benchmarks for ecosystem model validation.
    Quaternary Science Reviews 03/2014; 87:24–33. · 4.57 Impact Factor
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    ABSTRACT: Glacial and early Holocene-age sediments from lakes on Mt. Kenya have documented strong responses of montane hydrology, ecosystems, and carbon cycling to past changes in temperature and atmospheric CO2 concentrations. However, little is known about climate and ecosystem variations on Mt. Kenya during the Common Era (the past ~ 2,000 years), despite mounting evidence for significant climate changes in the East African lowlands during the past millennium and recent observations of alpine glacier retreat in the East African highlands. We present a new, high-resolution record of the hydrogen and carbon isotopic composition of terrestrial plant wax compounds (δDwax, δ13Cwax) preserved in the sediments of Sacred Lake from 200C.E. to the end of the 20th century. We find that Mt. Kenya’s climate was highly variable during the past 1800 years. Droughts at Sacred Lake around ~ 200C.E., 700C.E., and 1100C.E. align with similar droughts in central Kenya and Uganda/Congo, indicating that failures of both the Indian and Atlantic monsoons caused widespread drought throughout equatorial East Africa during the early Common Era. In contrast, dry and wet periods at Sacred Lake during the past 500 years show meridional and zonal contrasts with other sites in East Africa, suggesting strong spatial heterogeneity, possibly due to independent waxing and waning of the Atlantic and Indian monsoons. Pronounced drying after ~ 1870C.E. suggests that the current dry phase observed at Sacred Lake may have begun prior to the 20th century, around the time when the retreat of Mt. Kenya’s glaciers was first observed by European explorers. Mt. Kenya’s vegetation responded strongly to these recent climate changes, highlighting the particular sensitivity of tropical montane climate and ecosystems to regional and global climate patterns, and underscoring the critical need to understand potential impacts of future climate change scenarios on this highly sensitive region.
    Palaeogeography Palaeoclimatology Palaeoecology 02/2014; · 2.75 Impact Factor
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    Li Gao, Mei Zheng, Matthew Fraser, Yongsong Huang
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    ABSTRACT: Leaf wax hydrogen isotope proxies have been widely used to reconstruct past hydrological changes. However, published reconstructions have given little consideration for the potentially variable hydrogen isotopic fractionation relative to precipitation (εwax-p) under different climate and environmental settings. Chief among various potential factors controlling fractionation is relative humidity, which is known to strongly affect oxygen isotopic ratios of plant cellulose, but its effect on hydrogen isotopic fractionation of leaf waxes is still ambiguous. Analyses of lake surface sediments and individual modern plants have provided valuable information on the variability of εwax-p, but both approaches have significant limitations. Here, we present an alternative method to obtain the integrated, time-resolved ecosystem-level εwax-p values, by analyzing modern aerosol samples collected weekly from arid (Arizona lowlands) and humid subtropical (Atlanta, Georgia) environments during the main growth season. Because aerosol samples mainly reflect regional leaf wax resources, the extreme contrast in the hydroclimate and associated vegetation assemblages between our study sites allows us to rigorously assess the impact of relative humidity and associated vegetation assemblages on leaf wax hydrogen isotopic fractionation. We show there is only minor difference (mostly <10 ‰) in the mean εwax-p values in the two endmember environments. One possible explanation is that the positive isotopic effects of low relative humidity are offset by progressive replacement of trees with grasses that have a more negative apparent fractionation. Our results represent an important step toward quantitative interpretation of leaf wax hydrogen isotopic records.
    Geochemistry Geophysics Geosystems 12/2013; · 3.05 Impact Factor
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    ABSTRACT: Two commonly used proxies based on the distribution of glycerol dialkyl glycerol tetraethers (GDGTs) are the TEX86 paleothermometer for sea-surface temperature reconstructions and the BIT index for reconstructing soil organic matter input to the ocean. An initial round-robin study of two sediment extracts, in which fifteen laboratories participated, showed relatively consistent TEX86 values (reproducibility ±3-4 °C when translated to temperature) but a large spread in BIT measurements (reproducibility ±0.41 on a scale of 0 to 1). Here we report results of a second round-robin study with thirty-five laboratories in which three sediments, one sediment extract and two mixtures of pure, isolated GDGTs were analyzed. The results for TEX86 and BIT index showed improvement compared to the previous round-robin study. The reproducibility, indicating interlaboratory variation, of TEX86 values ranged from 1.3-3.0 °C when translated to temperature. These results are similar to those of other temperature proxies used in paleoceanography. Comparison of the results obtained from one of the three sediments showed that TEX86 and BIT indices are not significantly affected by interlaboratory differences in sediment extraction techniques. BIT values of the sediments and extracts were at the extremes of the index with values close to 0 or 1, and showed good reproducibility (ranging from 0.013 to 0.042). However, the measured BIT values for the two GDGT mixtures, with known molar ratios of crenarchaeol and branched GDGTs, had intermediate BIT values and showed poor reproducibility and a large overestimation of the 'true' (i.e., molar-based) BIT index. The latter is likely due to, amongst other factors, the higher mass spectrometric response of branched GDGTs compared to crenarchaeol, which also varies among mass spectrometers. Correction for this different mass spectrometric response showed a considerable improvement in the reproducibility of BIT index measurements among laboratories, as well as a substantially improved estimation of molar-based BIT values. This suggests that standard mixtures should be used in order to obtain consistent, and molar-based, BIT values.
    Geochemistry Geophysics Geosystems 11/2013; · 3.05 Impact Factor
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    ABSTRACT: a b s t r a c t Long chain alkenones (LCAs) have played a central role in reconstructing paleo-sea surface temperature throughout much of the world oceans. The standard method for LCA separation and quantification uti-lizes gas chromatography (GC) with a non-polar column and flame ionization detection (FID). The method has remained nearly unchanged since the debut of alkenone paleothermometry over three decades ago. The conventional stationary phase used [poly(dimethylsiloxane)] is adequate for calculation of the U K0 37 index for most marine samples, but performs poorly in the separation of methyl and ethyl C 38 LCAs and fails to separate certain lacustrine LCAs, including structural isomers featuring differing double bond and carbonyl positions. Here, we demonstrate major improvements in the selectivity and resolution of numerous LCAs using a mid-polarity, dipole selective poly(trifluoropropylmethylsiloxane) GC stationary phase with FID. Various columns featuring this phase achieved baseline resolution of all C 38 LCAs in a marine sediment and Emiliania huxleyi culture samples, improving peak resolution of C 38 LCAs by > 350%. Such dipole selective stationary phases also reveal novel tri-unsaturated isomeric LCAs in lacustrine samples, for which we provide the first report and preliminary characterization. We conduct a thorough evaluation of LCA retention behavior on poly(trifluoropropylmethylsiloxane) and poly(dimethylsiloxane) columns and report an optimal range of operating conditions for both phases.
    Organic Geochemistry 10/2013; 65:94-102. · 2.83 Impact Factor
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    ABSTRACT: Omega-3 polyunsaturated fatty acids (ω-3 PUFAs) have become increasingly popular in dietary supplements worldwide and global demand for higher purity ω-3 PUFAs in clinical applications has been rising rapidly in the recent years. Traditional methods for isolating ω-3 PUFAs however, generally require multiple, cumbersome steps to obtain high purity (>95%) products. In this study, we report an efficient liquid chromatography method for purifying individual omega-3 fatty acid ethyl esters (FAEEs), eicosapentaenoic acid (EPA, C20:5) and docosahexaenoic acid (DHA, C22:6), at >95% purity using a silver(I)-mercaptopropyl stationary phase, otherwise known as silver-thiolate chromatographic material (AgTCM). We demonstrate the key variables controlling separation of FAEEs with a silver(I)-thiolate stationary phase and examine important similarities and differences between silver-thiolate and silver-ion chromatography in regards to the separation mechanism taking place. We demonstrate the separation behavior of FAEEs under various conditions such as mobile phase composition, flow rate and sample injection amount. Purification of EPA and DHA was carried out on an analytical and semi-preparative scale and the resulting purity was determined by GC-FID. We report high attainable purity for EPA (>95%) and DHA (>99%) from a single isocratic separation of fish oil FAEEs within 5-10min using a mobile phase of heptane/acetone (95:5, % v/v).
    Journal of Chromatography A 08/2013; · 4.61 Impact Factor
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    ABSTRACT: The domains of the ancient polities D’MT and Aksum in the Horn of Africa’s highlands are a superior natural system for evaluating roles of environmental change on the rise and fall of civilizations. To compare environmental changes of the times of the two polities, we analyzed stable hydrogen isotopic ratios (δD) of land-plant derived fatty acids (n-C26–30) and other proxies from soil sequences spanning the Holocene from the region. Three results suggest that trends in δD values unambiguously reflect changes in rainfall. First, increases in δD coincide with dry periods inferred from studies of eastern African lakes. Second, changes in δD values were parallel among sections during overlapping time intervals. Third, consideration of vegetation history did not alter directions of trends in δD values over time. By unambiguously recording precipitation, the δD values also enhanced interpretations of proxies that are affected by both climate and land clearing.Both D’MT (ca 2750–2350 cal y BP) and the Aksumite (ca 2100–1250 cal y BP) rose during wetter intervals of the drier part of the Holocene (after ca 6000 cal y BP). Analyses of charred matter indicated that fire had been a common agent of land clearing in all sites. The influence of climate on fire varied, however. Prior to the emergence of D’MT, δD values were correlated with C4:C3 plant ratios estimated from δ13C values. There are no C4 trees and precipitation may have been the main influence on canopy openness. After ca 4300 cal y BP, there was no significant relationship between δD and C4:C3 plant ratios suggesting that factors such as fire influenced canopy openness regardless of climate. Furthermore, the impact of land clearance differed between sites and between D’MT and the Aksumite’s times. In one site, the interval from 3550 cal y BP to the decline of D’MT had several anomalies that suggested dramatic increases in thermal severity of fire and human impact. Among these were a large contribution of charred matter to a high% total organic carbon that low hydrogen and oxygen indices suggest was severely altered by other factors than humification. These results support hypotheses about the rise of civilizations being favored by specific climatic conditions but suggest that patterns of land clearing differed during the declines of D’MT and the Aksumite.
    Geochimica et Cosmochimica Acta 06/2013; 111:140-161. · 4.25 Impact Factor
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    José C Aponte, James T Dillon, Yongsong Huang
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    ABSTRACT: Silver(I) and copper(I) are known to form reversible complexes with π bonds, which have been exploited in LC for separating unsaturated organic compounds. Prominent examples include the use of AgNO3 -impregnated silica gel in LC, and the use of copper(I) salts for selective extraction of alkenes from hydrocarbon mixtures. The Dewar-Chatt-Duncanson model is often invoked to explain the interaction between Ag(I), Cu(I), and π bonds. However, it is unclear if such a reversible interaction is directly related to their d(10) outer electronic configurations. Particularly, Au(I) has not been reported to separate olefins with different numbers of double bonds in LC. Also, there has not been a systematic comparison of the liquid chromatographic properties of other d(10) transition metal salts (e.g., Zn(II), Cd(II)), making it difficult to fully understand the observed reversible interactions of Ag(I) and Cu(I) with π bonds. We demonstrate for the first time, that silica gel impregnated with all three Group 11 transition metals with 1+ oxidation state strongly and similarly retain olefin compounds in LC, while transition metals from Groups 10 and 12 do not. We also tested a range of functionalized silica gels to improve the stability of Cu(I) and Au(I) ions on the surface of the silica. This article is protected by copyright. All rights reserved.
    Journal of Separation Science 06/2013; · 2.59 Impact Factor
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    Jonathan E Nichols, Yongsong Huang
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    ABSTRACT: Long chain alkenones (LCAs) are a class of di-, tri-, and tetra-unsaturated ketone biomarkers that have long been employed to reconstruct paleo-sea surface temperatures via the UK37 and UK'37 indices (1). Increasingly, researchers are investigating LCAs in lacustrine settings for their potential to produce continental paleoclimate records (2-4) and recent studies have provided quantitative LCA temperature records from arctic lakes (5-6). These efforts highlight lacustrine LCA paleothermometry as an effective tool for arctic paleolimnologists and they encourage further exploration of the proxy in high latitude lakes. In this study, we report the discovery of novel tri-unsaturated LCAs in the water column and surface sediments of lakes in Northeastern Alaska (NE AK). In June of 2012, we obtained water column samples and accompanying physical and chemical data from Toolik Lake (68.3°N, 149.36°E) and two neighboring lakes, E5 and F2. LCAs were present in all three lakes throughout the sampling period that began during isothermal spring mixing and persisted for three weeks through the onset of thermal stratification. Traditional gas chromatographic (GC) analyses yielded an unresolved mixture of tri-unsaturated LCAs, but novel GC techniques provided unprecedented separation and revealed that the 37-, 38-and 39-carbon homologs are composed of two positional isomers. Tentative structural identifications of the new compounds are proposed here. Analysis of LCAs from the sediments of Lake BrayaSø, Greenland—the site of a recent 6 kyr LCA temperature record (5)—reveal remarkably similar LCA profiles that include the tri-unsaturated isomers. LCAs extracted from a culture of the predominant marine haptophyte algae,Emiliana huxleyii, and from surface sediments of lower latitude lakes in North America and China, revealed no tri-unsaturated isomers using the same GC methods. Our findings suggest that these compounds are produced by a common high-latitude adapted haptophyte. The discovery of novel LCAs in Greenland and Alaska necessitates an investigation of these compounds and their correlations with temperature and environmental parameters. Many
    43rd International Arctic Workshop, Amherst, MA, USA; 03/2013

Publication Stats

2k Citations
495.63 Total Impact Points

Institutions

  • 2001–2014
    • Brown University
      • • Department of Geological Sciences
      • • Department of Chemistry
      Providence, Rhode Island, United States
  • 2012
    • University of Massachusetts Amherst
      • Climate Systems Research Center
      Amherst Center, MA, United States
  • 2008
    • Yale University
      New Haven, Connecticut, United States
  • 2007
    • Emerson College
      Boston, Massachusetts, United States
  • 2005
    • Arizona State University
      • Department of Chemistry and Biochemistry
      Mesa, AZ, United States
  • 2002
    • University of Missouri
      • Department of Geological Sciences
      Columbia, MO, United States
  • 1994–2000
    • University of Bristol
      • • School of Earth Sciences
      • • School of Chemistry
      Bristol, England, United Kingdom