Yongsong Huang

Brown University, Providence, Rhode Island, United States

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Publications (129)580.4 Total impact

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    ABSTRACT: Rationale: Measurements of alkenone unsaturation ratios are widely used for paleotemperature reconstructions in ocean and lake environments. Previously, we reported the discovery of a series of tri-unsaturated alkenone positional isomers (Δ(14, 21, 28) ) from oligosaline and freshwater lakes in Greenland and Alaska. In this work we provide a detailed analysis of the structures and isotopic compositions (δ(13) C and δ(2) H) of the alkenones produced by the "Greenland haptophyte". Methods: Alkenones were extracted from sediments of Lake BrayaSø, Greenland. Alkenone double-bond positions were determined by GC/EI-MS analysis of alkenone dimethyl disulfide and cyclobutylimine derivatives. Alkenones were purified by semi-preparative HPLC using a silver(I) thiolate stationary phase. Carbon and hydrogen isotope analysis was performed by gas chromatography/isotope ratio mass spectrometry (GC/IRMS). Results: A series of novel tri-unsaturated alkenone positional isomers were identified among four alkenone homologues (i.e. C37 Me , C38 Me , C38 Et , and C39 Et ) with double-bond positions at Δ(14, 21, 28) . The hydrogen isotope compositions (δ(2) H, VSMOW) of the tri-unsaturated positional isomers from C37 Me and C38 Et were slightly depleted (~ -11 ‰) relative to the common tri-unsaturated alkenone. The carbon isotope composition (δ(13) C, VPDB) of the tri-unsaturated positional isomers from the C37 Me , C38 Me , C38 Et , and C39 Et alkenones were significantly enriched (~ +4 ‰) relative to the common alkenones (di-, tri-, and tetra-unsaturated). Conclusions: The novel tri-unsaturated alkenone positional isomers produced by the Greenland haptophyte possess Δ(14, 21, 28) double-bond positions, instead of the common Δ(7, 14, 21) double-bond positions. The hydrogen isotope values suggest the novel tri-unsaturated positional isomers could be biosynthetic precursors to the tetra-unsaturated alkenones (Δ(7, 14, 21, 28) ). However, the significantly higher carbon isotope values of the tri-unsaturated positional isomers relative to the common di-, tri- and tetra-unsaturated alkenones suggest these positional isomers may have different/additional biosynthetic precursors. Copyright © 2015 John Wiley & Sons, Ltd.
    No preview · Article · Jan 2016 · Rapid Communications in Mass Spectrometry
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    ABSTRACT: Lake Qinghai, located on the northeastern Tibetan Plateau north of the modern maximum summer monsoon extent, is well situated to record northward advances of the summer monsoon. Existing paleoclimate records contain conflicting evidence for the timing of summer monsoon advance into this region: an early arrival pre-Younger Dryas or a late arrival at the beginning of the Holocene. A 30-kyr-long leaf wax hydrogen isotope (n-alkanoic acid, δ2Hwax) record from Lake Qinghai helps to address this discrepancy by elucidating changes in the three main moisture sources in this region: southerly (summer monsoon), northwesterly, and local precipitation. Lake Qinghai δ2Hwax indicates that the arid glacial period was dominated by northwesterly moisture. Extremely arid conditions prevailed from 15 to 14 ka, likely because westerly winds were weakening and the summer monsoon had not yet reached this region. This arid period ended by 13.6 ka when small amounts of summer monsoon precipitation reached Lake Qinghai. Summer monsoon moisture subsequently retreated off of the northeastern Tibetan Plateau during the Younger Dryas and re-advanced in the early Holocene. Summer monsoon precipitation decreased progressively throughout the Holocene in response to decreasing summer insolation, and the modern northwesterly- and local-dominated moisture regime was attained ca. 2.6 ka. Lake Qinghai δ2Hwax demonstrates that the summer monsoon extent was dynamic during the past 30 kyr, responding dramatically to insolation and North Atlantic circulation changes. Moreover, Lake Qinghai δ2Hwax demonstrates that local and northwesterly air masses are important moisture sources to the northeastern Tibetan Plateau, and should be considered when reconstructing past hydroclimate in this region.
    No preview · Article · Jan 2016 · Quaternary Science Reviews
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    ABSTRACT: Summer temperatures on the Tibetan Plateau (TP) significantly affect stability of glaciers that provide steady water resources to nearly half of the world population. However, lack of reliable, long-term proxy records greatly impedes understanding of regional temperature sensitivity to climate forcings. Here we present a 16-ka long, alkenone-based summer temperature record from Lake Qinghai, northeastern TP that demonstrates major regional temperature response to changes in summer insolation and Atlantic Meridional Overturning Circulation during the Holocene and late glacial. Importantly, we find a period of sustained summer temperature decline (>4oC) between 5 and 3.5 ka, which coincides with expansion of Barents Sea ice coverage, and is likely driven by intensification of the Westerlies. This unusually long and pronounced regional cooling event likely delayed permanent human settlements on the high altitude regions (>3000 m) of the TP by at least 500 years.
    No preview · Article · Dec 2015 · Geophysical Research Letters
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    ABSTRACT: Alkenone unsaturation indices, represented by either UK37 or UK′37, are important tools for paleoclimate studies. The UK37 index is a reflection of the average number of double bonds from di-, tri-, tetra-unsaturated alkenones, but UK′37 excludes the C37:4 in the calculation. Extensive studies indicate UK′37 provides better regressions against in situ Sea Surface Temperatures (SST) than UK37 and is the most widely used SST proxy. However, recent studies have shown that including C37:4 alkenones for lacustrine or brackish water haptophytes such as Ruttnera (Chrysotila) lamellosa and Isochrysis galbana improves temperature correlations although there are still significant deviations at the extreme high and low temperatures. In this study, we use new culture-based calibration experiments alongside published culture data and in situ water column or surface sediment data, to demonstrate that a further improved temperature calibration for alkenones is, in fact, achieved when the di-unsaturated alkenone is excluded from the computation of the unsaturation index. We propose new indices, termed UK″ [UK″37 = C37:3/(C37:3 + C37:4) or UK″38 = C38:3/(C38:3 + C38:4)], for lacustrine, brackish and estuarine waters. Our observation suggests that di-unsaturated alkenones play a less important role than tri- and tetra-unsaturated alkenones in regulating cell functions to temperature variations in lacustrine and brackish waters. We suggest using UK″ indices for paleotemperature reconstructions in the lacustrine and estuarine settings.
    Full-text · Article · Nov 2015 · Geochimica et Cosmochimica Acta
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    ABSTRACT: Study of meteoritic organic compounds offers a unique opportunity to understand the origins of the organic matter in the early Solar System. Meteoritic polycyclic aromatic hydrocarbons (PAHs) and heteropolycyclic aromatic compounds (HACs) have been studied for over fifty years, however; their hydrogen stable isotopic ratios (δD) have never been reported. Compound-specific measurements of PAHs and HACs are important, in part because the carbon isotopic ratios ( ) of various meteoritic PAHs cannot be readily distinguished from their terrestrial counterparts and it is difficult to rule out terrestrial contamination based on carbon isotopic ratios alone. In this study, we have extracted and identified more than sixty PAHs and HACs present in two CM2 carbonaceous chondrites Murchison and LON 94101. Their carbon and hydrogen stable isotopic ratios ( and δD) were measured and used to discuss about their synthetic environments and formation mechanisms. The concentration of aromatic compounds is ∼30% higher in Murchison than in the Antarctic meteorite LON 94101, but both samples contained similar suites of PAHs and HACs. All PAHs and HACs found exhibited positive values (up to 1100‰) consistent with an extraterrestrial origin, indicating the relatively low values are indeed an inherent feature of the meteoritic aromatic compounds. The hydrogen isotopic data suggest aromatic compounds in carbonaceous chondrites were mainly formed in the cold interstellar environments. Molecular level variations in hydrogen and carbon isotopic values offer new insights to the formation pathways for the aromatic compounds in carbonaceous chondrites.
    Full-text · Article · Sep 2015 · Earth and Planetary Science Letters
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    Full-text · Book · Apr 2015
  • 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.
    No preview · Article · Dec 2014 · Organic Geochemistry
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    Li Gao · Julia Guimond · Elizabeth Thomas · Yongsong Huang
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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.
    Full-text · Article · Nov 2014 · Organic Geochemistry
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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.
    Full-text · Article · Nov 2014 · PLoS ONE
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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.
    Full-text · Article · Oct 2014 · Organic Geochemistry
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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
    Full-text · Article · Sep 2014 · Quaternary Science Reviews
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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.
    Full-text · Article · Aug 2014 · Geophysical Research Letters

  • No preview · Dataset · Jun 2014
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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.
    Full-text · Article · Apr 2014 · Geochimica et Cosmochimica Acta
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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.
    Full-text · Article · Mar 2014 · Proceedings of the National Academy of Sciences
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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
    Full-text · Conference Paper · Mar 2014
  • James T. Dillon · Yongsong Huang

    No preview · Conference Paper · Mar 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.
    Full-text · Article · Mar 2014 · Quaternary Science Reviews
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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.
    Full-text · Article · Feb 2014 · Palaeogeography Palaeoclimatology Palaeoecology
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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.
    Full-text · Article · Feb 2014 · Geochemistry Geophysics Geosystems

Publication Stats

5k Citations
580.40 Total Impact Points

Institutions

  • 2001-2016
    • Brown University
      • Department of Geological Sciences
      Providence, Rhode Island, United States
  • 1994-2000
    • University of Bristol
      • • School of Earth Sciences
      • • School of Chemistry
      Bristol, England, United Kingdom