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Yongsong Huang - One of the best experts on this subject based on the ideXlab platform.
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C41 methyl and C42 ethyl Alkenones are biomarkers for Group II Isochrysidales
Organic Geochemistry, 2020Co-Authors: Sian Liao, William M. Longo, Linda A. Amaral-zettler, Yuan Yao, Li Wang, Karen J. Wang, Yongsong HuangAbstract:Abstract Alkenones are polyunsaturated long-chain methyl or ethyl ketones produced by species in the Isochrysidales, an order of haptophyte algae. Based on phylogenetic data, members of the Isochrysidales have been classified into three groups with each group showing significant differences in Alkenone profiles and preferred growth environments. Common carbon chain lengths of Alkenones range from 37 to 40. Extended C41 methyl (C41Me) and C42 ethyl (C42Et) Alkenones have been reported in hypersaline lakes in China (Lake Alahake and Lake Balikun), Canada (Lake Snakehole) and marine sediments (e.g., ∼95 Ma in Blake-Bahama Basin). It is unclear, however, if these extended Alkenones are produced by one or more groups of Isochrysidales. Here, we systematically examined Alkenones from cultures of Group II (Isochrysis nuda, Isochrysis litoralis, Ruttnera lamellosa, Isochrysis galbana and Tisochrysis lutea) and Group III (Emiliania huxleyi and Gephyrocapsa oceanica) Isochrysidales and environmental samples of Group I Isochysidales. C41Me and C42Et Alkenones were found in all Group II species with Isochrysis nuda producing the highest percentages, but not in Alkenones produced by Group I nor Group III Isochrysidales. Our results indicate that extended C41Me and C42Et Alkenones are specific biomarkers for Group II Isochrysidales. We also report the first temperature calibrations of Alkenones for Isochrysis nuda and Isochrysis litoralis using culture experiments, and find temperatures inferred from extended Alkenones in Balikun and Alahake surface sediments match warm-season temperatures based on Isochrysis nuda calibrations, which is further corroborated by genomic data indicating the dominance of Isochrysis nuda Isochrysidales.
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Phylogenetic diversity in freshwater-dwelling Isochrysidales haptophytes with implications for Alkenone production
Geobiology, 2019Co-Authors: Nora Richter, William M. Longo, Yongsong Huang, Sarabeth George, Anna Shipunova, Linda Amaral-zettlerAbstract:Members of the order Isochrysidales are unique among haptophyte lineages in being the exclusive producers of Alkenones, long-chain ketones that are commonly used for paleotemperature reconstructions. Alkenone-producing haptophytes are divided into three major groups based largely on molecular ecological data: Group I is found in freshwater lakes, Group II commonly occurs in brackish and coastal marine environments, and Group III consists of open ocean species. Each group has distinct Alkenone distributions; however, only Groups II and III Isochrysidales currently have cultured representatives. The uncultured Group I Isochrysidales are distinguished geochemically by the presence of tri-unsaturated Alkenone isomers (C37:3b Me, C38:3b Et, C38:3b Me, C39:3b Et) present in water column and sediment samples, yet their genetic diversity, morphology, and environmental controls are largely unknown. Using small-subunit (SSU) ribosomal RNA (rRNA) marker gene amplicon high-throughput sequencing of environmental water column and sediment samples, we show that Group I is monophyletic with high phylogenetic diversity and contains a well-supported clade separating the previously described "EV" clade from the "Greenland" clade. We infer the first partial large-subunit (LSU) rRNA gene Group I sequence phylogeny, which uncovered additional well-supported clades embedded within Group I. Relative to Group II, Group I revealed higher levels of genetic diversity despite conservation of Alkenone signatures and a closer evolutionary relationship with Group III. In Group I, the presence of the tri-unsaturated Alkenone isomers appears to be conserved, which is not the case for Group II. This suggests differing environmental influences on Group I and II and perhaps uncovers evolutionary constraints on Alkenone biosynthesis.
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systematic chemotaxonomic profiling and novel paleotemperature indices based on Alkenones and alkenoates potential for disentangling mixed species input
Organic Geochemistry, 2019Co-Authors: Maureen H Conte, Yinsui Zheng, Patrick Heng, Richard S Vachula, Yongsong HuangAbstract:Abstract The unsaturation indices ( U 37 K , U 37 K' ) of long chain Alkenones are powerful paleotemperature proxies and have been widely applied for sea surface temperature (SST) reconstructions in the past three decades. However, these indices encounter major difficulties in systems harboring different Alkenone-producing haptophyte species, such as saline lakes and marginal ocean environments. All haptophytes produce C37 Alkenones, but different species often display large differences in temperature calibrations and may bloom in different seasons, hindering the use of U 37 K and U 37 K' indices for reliable paleotemperature reconstructions in mixed systems. To overcome these problems, we have recently reported a new analytical method that allows comprehensive separation of up to 32 Alkenones, alkenoates and their double bond positional isomers in culture and sediment samples. Here we report a systematic analysis of Alkenones and alkenoates from six haptophyte cultures growing at a wide range of temperatures (4–25 °C). Together with a compilation of 230 previously published culture data sets, we present here systematic calibrations of temperature-sensitive indices based on all Alkenone and alkenoate homologues (including isomers). Using this dataset, we extract systematic chemotaxonomic criteria for differentiating individual haptophyte species and demonstrate such chemotaxonomic features can be encoded into a machine learning model for reliable species identifications. Specifically, we show that temperature calibrations based on C38 methyl ketones and C39 ethyl ketones are potentially useful for disentangling mixed inputs in estuarine systems where Group III (E. huxleyi) and Group II Alkenones mix, and that C36 ethyl alkenoate isomeric ratios display minimal species heterogeneity and are potentially more suited for reconstructing temperatures in mixed systems with different Group II haptophytes. Using the culture data as base profiles, we construct a mathematical model for estimating percentage inputs from Alkenones of different Isochrysidales groups in mixed systems, with potential implications for inferring past salinity changes. Overall, the results from this study demonstrate important new applications of Alkenone and alkenoate biomarkers in paleoclimate and paleoenvironmental research.
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widespread occurrence of distinct Alkenones from group i haptophytes in freshwater lakes implications for paleotemperature and paleoenvironmental reconstructions
Earth and Planetary Science Letters, 2018Co-Authors: William M. Longo, Yongsong Huang, Anne E. Giblin, Yuan Yao, Jiaju Zhao, Xian Wang, Roland Zech, Torsten Haberzettl, Ludwig JardillierAbstract:Abstract Alkenones are C35–C42 polyunsaturated ketone lipids that are commonly employed to reconstruct changes in sea surface temperature. However, their use in coastal seas and saline lakes can be hindered by species-mixing effects. We recently hypothesized that freshwater lakes are immune to species-mixing effects because they appear to exclusively host Group I haptophyte algae, which produce a distinct distribution of Alkenones with a relatively consistent response of Alkenone unsaturation to temperature. To evaluate this hypothesis and explore the geographic extent of Group I haptophytes, we analyzed Alkenones in sediment and suspended particulate matter samples from lakes distributed throughout the mid- and high latitudes of the Northern Hemisphere ( n = 30 ). Our results indicate that Group I-type Alkenone distributions are widespread in freshwater lakes from a range of different climates (mean annual air temperature range: −17.3–10.9 °C; mean annual precipitation range: 125–1657 mm yr−1; latitude range: 40–81°N), and are commonly found in neutral to basic lakes (pH > 7.0), including volcanic lakes and lakes with mafic bedrock. We show that these freshwater lakes do not feature Alkenone distributions characteristic of Group II lacustrine haptophytes, providing support for the hypothesis that freshwater lakes are immune to species-mixing effects. In lakes that underwent temporal shifts in salinity, we observed mixed Group I/II Alkenone distributions and the Alkenone contributions from each group could be quantified with the RIK37 index. Additionally, we observed significant correlations of Alkenone unsaturation ( U 37 K ) with seasonal and mean annual air temperature with this expanded freshwater lakes dataset, with the strongest correlation occurring during the spring transitional season ( U 37 K = 0.029 ⁎ T − 0.49 ; r 2 = 0.60 ; p 0.0001 ). We present new sediment trap data from two lakes in northern Alaska (Toolik Lake, 68.632°N, 149.602°W; Lake E5, 68.643°N, 149.458°W) that demonstrate the highest sedimentary fluxes of Alkenones in the spring transitional season, concurrent with the period of lake ice melt and isothermal mixing. Together, these data provide a framework for evaluating lacustrine Alkenone distributions and utilizing Alkenone unsaturation as a lake temperature proxy.
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optimizing the yield of transient mono dimethyl disulfide adducts for elucidating double bond positions of long chain Alkenones
Organic Geochemistry, 2017Co-Authors: James T. Dillon, Nora Richter, Derek Rott, Michael A Lomazzo, Christopher T Seto, Yongsong HuangAbstract:Abstract Long chain Alkenones (LCAs) are among the most successful biomarkers for paleotemperature reconstructions. However, fundamental questions regarding the biosynthesis and cellular functions of Alkenones in haptophyte algae remain poorly understood. Recent discoveries of LCAs with double bond positions and chain lengths that differ from common structures further highlight the importance of continued research into structural variations of this important class of lipid biomarkers to improve LCA applications as temperature proxies. Double bond positions on alkyl chains can be effectively determined by preparing mono-double bond adducts with dimethyl disulfide (DMDS-1), and subsequent gas chromatography–mass spectrometry (GC–MS) analysis. However, previously published procedures for adduct preparation were originally designed for mono-unsaturated fatty acids, and generally produce low product yields when applied to Alkenones. Here we demonstrate that the problem originates mainly from DMDS and Alkenone overreaction at high temperatures for long time periods, and, secondarily, insufficient amount of iodine catalyst. The overreaction results in DMDS reacting with multiple double bonds, and the possible formation of intermolecular linkages, creating non-volatile products. These products are of little use for elucidating Alkenone structures. We demonstrate that by reducing the reaction temperature and time, and by using an optimal amount of iodine, we can maximize the yield of transient DMDS-1 adducts for Alkenone structure determination.
Naomi Harada - One of the best experts on this subject based on the ideXlab platform.
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genomic and geochemical identification of the long chain Alkenone producers in the estuarine lake takahoko japan implications for temperature reconstructions
Organic Geochemistry, 2020Co-Authors: Hiroto Kajita, Naomi Harada, Hodaka Kawahata, Miyako Sato, Hideto Nakamura, Naohiko Ohkouchi, Shun TokiokaAbstract:Abstract Identifying the lacustrine haptophyte species that produce long-chain Alkenones (LCAs) is essential for using Alkenone unsaturation ratios to create lake water temperature reconstructions. We discovered LCAs in the brackish Lake Takahoko in northern Japan. The identity of LCA-producing species was investigated using 18S ribosomal DNA (rDNA) and organic geochemical analysis. Two distinct genetic groups, termed Tak-A and Tak-B, were identified within the Group II haptophyte phylotype. Tak-A was closely related to Hap-A, which was obtained from Lake George, USA; and Tak-B was identified as Isochrysis galbana. Because Hap-A and Isochrysis galbana have similar temperature calibrations, Tak-A and Tak-B were also expected to share similar calibrations. Therefore, the changes of their relative abundances in the lake should not significantly disturb paleotemperature reconstructions. The Alkenone temperature recorded in the surface sediment corresponded to the lake temperature in early to late summer. This is likely related to the haptophyte bloom season in Lake Takahoko suggesting that this lake may be a viable location for creating a lacustrine Alkenone paleotemperature record.
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Alkenone production in the East Sea/Japan Sea
Continental Shelf Research, 2014Co-Authors: Kyung Eun Lee, Sunghye Lee, Yonggi Park, Ho Jin Lee, Naomi HaradaAbstract:Abstract To test the applicability of Alkenones as a proxy for past sea surface temperature (SST) in the East Sea (Japan Sea), this study investigated the season and depth of Alkenone production in the area. Surface and subsurface seawater samples were collected from the East Sea during cruises carried out by the National Fisheries Research and Development Institute of Korea in 2008–2010. Surface samples were filtered for suspended material at two-month intervals. Subsurface samples were collected at water depths of 20, 50, 70 and 100 m by CTD bottle casts at two stations, one a coastal station and the other an offshore station. The results of Alkenone analysis show that the concentration of total C 37 Alkenones was generally high in the surface mixed layer and decreased with depth, indicating that Alkenones were most likely produced in or close to the surface mixed layer. Alkenone concentration varied seasonally: high in spring to fall and significantly reduced in winter. Comparisons of Alkenone-based temperatures with in situ seawater temperatures show that Alkenone temperatures measured from suspended particles in the surface waters were close to in situ SST in summer but were lower in winter. During winter, when Alkenone production is significantly reduced, Alkenones may be suspended for relatively long times and are likely to be advected from the north by eddies from Subpolar Front meanders. In summer when new production of Alkenones increases, the settling velocity of Alkenones appears to increase and residence time becomes shorter than in winter, suggesting that particles are less likely to be significantly advected at that time. Importantly, at the offshore station, coretop Alkenone temperature corresponds to annual-averaged SST, while at the coastal station it corresponds to summer-to-fall averaged SST.
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Freshwater impacts recorded in tetraunsaturated Alkenones and Alkenone sea surface temperatures from the Okhotsk Sea across millennial-scale cycles
Paleoceanography, 2008Co-Authors: Naomi Harada, Miyako Sato, Tatsuhiko SakamotoAbstract:[1] We present records of phytoplankton-produced Alkenones down a long piston core, which reveal changes of sea surface temperature (SST) and sea surface salinity (SSS) in the southwestern Okhotsk Sea over the past 120 ka. Between 20 and 60 ka B.P., Alkenone-derived temperatures typically increased by 6°C–8°C from periods corresponding, within a few hundred years, to stadials to those corresponding to interstadials recorded in Greenland ice cores. The abundance of C37:4 Alkenone relative to total C37 Alkenones (percent C37:4), a possible proxy for salinity, indicated that during most low SSS was associated with high SST. The warm freshwater events might be related to (1) a decline in the supply of saline water entering the Okhotsk Sea through the Soya Strait; (2) strengthening of the freshwater supply from the Amur River and precipitation over the Okhotsk Sea, associated mainly with increased Asian summer monsoon activity; and (3) the effect of melting sea ice. These findings increase our understanding of the close linkage between high and low latitudes in relation to climate change and the synchronicity of climate changes within a few centuries between the Pacific and the Atlantic sides of the Northern Hemisphere.
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Characteristics of Alkenone distributions in suspended and sinking particles in the northwestern North Pacific
Geochimica et Cosmochimica Acta, 2006Co-Authors: Naomi Harada, Miyako Sato, Aya Shiraishi, Makio C. HondaAbstract:Abstract We investigated Alkenones recorded in suspended particles and a settling particle time series collected at three stations, 40N (40°N, 165°E), KNOT (44°N, 155°E), and 50N (50°N, 165°E), in the northwestern North Pacific from December 1997 to May 1999. Emiliania huxleyi, the most abundant Alkenone producer in this area, is present in surface to subsurface (to ∼50 m depth) waters. The Alkenone concentrations recorded in the suspended particles indicated that the seasonal Alkenone particle distribution differed significantly interannually. Alkenone export fluxes at the three sediment-trap stations ranged from 0.16 to 49.3 μg m−2 day−1, and the maximum export flux, which occurred in summer to fall (July–November), was associated with a high organic carbon export flux. The amount of Alkenone produced during the maximum export season accounted for 60–80% of the total annual amount of Alkenone, and the Alkenones accumulated in the sediment below the traps had characteristics corresponding to subsurface waters during the summer–autumn season. Alkenone-derived temperatures recorded in suspended particles corresponded to the in situ temperature within ∼2 °C. Although Alkenone-derived temperatures corresponded approximately to the temperatures observed in the stratified subsurface waters at the three trap stations during the high-export season, large differences were observed during the low-export (winter–spring) period. For example, the Alkenone-derived temperatures observed at stations KNOT and 50N were much higher than the in situ subsurface temperatures reported in the World Ocean Atlas 2001. Relatively large differences between Alkenone-derived temperatures and in situ temperatures in the subarctic might be due to (1) a low-light limitation or (2) contributions of allochthonous Alkenones in particulate material transported from subtropical areas within a warm-core ring.
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characteristics of Alkenones synthesized by a bloom of emiliania huxleyi in the bering sea
Geochimica et Cosmochimica Acta, 2003Co-Authors: Naomi Harada, Kyung-hoon Shin, Akihiko Murata, Masao Uchida, Tomoko NakataniAbstract:Abstract We investigated the characteristics of the Alkenones produced by a bloom of Emiliania huxleyi in the eastern Bering Sea in 2000. Alkenones were detected in surface waters between 57°N and 63°N, where phosphate concentrations were low and the ammonium/nitrate ratio was high. The total Alkenone content (C37:2, C37:3, and C37:4) ranged from 22.0 to 349 μg g−1 in suspended particles and from 0.109 to 1.42 μg g−1 in surface sediments. This suggests that a large proportion of the particulate Alkenones synthesized in the surface water rapidly degraded within the water column and/or at the water-sediment interface of the Bering Shelf. The change in the stable carbon isotopic composition (δ13C) of C37:3 Alkenone could not be explained only by variation in [CO2(aq)] in the surface water but also depended on the growth rate of E. huxleyi. The Alkenone unsaturation index (UK′37) was converted into an Alkenone “temperature” with three equations Prahl et al 1988 , Sikes et al 1997 , Muller et al 1998 ; Sikes et al.’s (1997) equation gave the best correlation with the observed sea surface temperature (SST) in the eastern Bering Sea. However, some temperatures estimated by Sikes et al.’s (1997) equation from the UK′37 varied from the observed SST, possibly because of the rapidly changing rate of Alkenone synthesis in the logarithmic growth stage or the low rate of Alkenone synthesis when nutrients were limiting. Temperatures estimated from UK′37 in the surface sediments (6.8–8.2°C) matched the observed SST in September (7–8°C) but differed from the annual average SST of 4 to 5°C, suggesting that most of the Alkenone in the eastern Bering Sea was synthesized during limited periods, for instance, in September. The relative amounts of C37:4 Alkenone as proportions of the total Alkenones (referred to as C37:4%) were high, ranging from 18.3 to 41.4%. Low-salinity water (
Yoshihiro Shiraiwa - One of the best experts on this subject based on the ideXlab platform.
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Overexpression of Tisochrysis lutea Akd1 identifies a key cold-induced Alkenone desaturase enzyme.
Scientific reports, 2018Co-Authors: Hirotoshi Endo, Iwane Suzuki, Hiroya Araie, Yutaka Hanawa, Yoshihiro ShiraiwaAbstract:Alkenones are unusual long-chain neutral lipids that were first identified in oceanic sediments. Currently they are regarded as reliable palaeothermometers, since their unsaturation status changes depending on temperature. These molecules are synthesised by specific haptophyte algae and are stored in the lipid body as the main energy storage molecules. However, the molecular mechanisms that regulate the Alkenone biosynthetic pathway, especially the low temperature-dependent desaturation reaction, have not been elucidated. Here, using an Alkenone-producing haptophyte alga, Tisochrysis lutea, we show that the Alkenone desaturation reaction is catalysed by a newly identified desaturase. We first isolated two candidate desaturase genes and found that one of these genes was drastically upregulated in response to cold stress. Gas chromatographic analysis revealed that the overexpression of this gene, named as Akd1 finally, increased the conversion of di-unsaturated C37-Alkenone to tri-unsaturated molecule by Alkenone desaturation, even at a high temperature when endogenous desaturation is efficiently suppressed. We anticipate that the Akd1 gene will be of great help for elucidating more detailed mechanisms of temperature response of Alkenone desaturation, and identification of active species contributing Alkenone production in metagenomic and/or metatranscriptomic studies in the field of oceanic biogeochemistry.
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Composition of long chain Alkenones and alkenoates as a function of growth temperature in marine haptophyte Tisochrysis lutea
Organic Geochemistry, 2016Co-Authors: Hideto Nakamura, Ken Sawada, Hiroya Araie, Takashi Shiratori, Ken-ichiro Ishida, Iwane Suzuki, Yoshihiro ShiraiwaAbstract:Abstract We investigated the compositions of long chain Alkenones and alkenoates in cultured strains of the marine haptophyte Tisochrysis lutea CCMP463 and T. lutea NIES-2590 (formerly classified as Isochrysis galbana). Both T. lutea strains grown at various temperatures of 15–35 °C could be characterized by the lack of tetraunsaturated Alkenones and alkenoates in comparison with strains in other genera Isochrysis and Ruttnera, which are classified in the same family Isochrysidaceae and order Isochrysidales that contain Alkenone-producing haptophytes. We found that T. lutea has a distinct Alkenone response to temperature, which is characterized by high U 37 K -temperature sensitivity at 15–30 °C and continuing sensitivity at warm-end temperatures over 30 °C, where the other species fail to adapt. Both strains showed similar trends in Alkenone compositions and Alkenone unsaturation index-temperature calibrations. In addition, both strains CCMP463 and NIES-2590 showed notably close phylogenetic relationships, even those that were collected from remote regions of the Atlantic Ocean, namely the Caribbean Sea and English Channel, where their habitats, particularly the sea surface temperature, are notably different. Considering previous published datasets, three genera, Isochrysis, Ruttnera and Tisochrysis, showed very different trends in the Alkenone unsaturation index-temperature calibration. These results suggest that the lack of tetraunsaturated Alkenones, warm-water oriented growth and the high sensitivity to growth temperature serve as distinct chemotaxonomic characteristics of T. lutea in the Isochrysidaceae family.
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proteomic analysis of lipid body from the Alkenone producing marine haptophyte alga tisochrysis lutea
Proteomics, 2015Co-Authors: Qing Shi, Hiroya Araie, Iwane Suzuki, Ranjith Kumar Bakku, Yoichiro Fukao, Randeep Rakwal, Yoshihiro ShiraiwaAbstract:Lipid body (LB) is recognized as the cellular carbon and energy storage organelle in many organisms. LBs have been observed in the marine haptophyte alga Tisochrysis lutea that produces special lipids such as long-chain (C37-C40) ketones (Alkenones) with 2–4 trans-type double bonds. In this study, we succeeded in developing a modified method to isolate LB from T. lutea. Purity of isolated LBs was confirmed by the absence of chlorophyll auto-fluorescence and no contamination of the most abundant cellular protein ribulose-1,5-bisphosphate carboxylase/oxygenase. As Alkenones predominated in the LB by GC-MS analysis, the LB can be more appropriately named as “Alkenone body (AB).” Extracted AB-containing proteins were analyzed by the combination of 1DE (SDS-PAGE) and MS/MS for confident protein identification and annotated using BLAST tools at National Center for Biotechnology Information. Totally 514 proteins were identified at the maximum. The homology search identified three major proteins, V-ATPase, a hypothetical protein EMIHUDRAFT_465517 found in other Alkenone-producing haptophytes, and a lipid raft-associated SPFH domain-containing protein. Our data suggest that AB of T. lutera is surrounded by a lipid membrane originating from either the ER or the ER-derived four layer-envelopes chloroplast and function as the storage site of Alkenones and alkenes.
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Changes in Alkenone and alkenoate distributions during acclimatization to salinity change in Isochrysis galbana: Implication for Alkenone-based paleosalinity and paleothermometry
GEOCHEMICAL JOURNAL, 2012Co-Authors: Makiko Ono, Ken Sawada, Yoshihiro Shiraiwa, Masako KubotaAbstract:A cultured strain of Isochrysis galbana UTEX LB 2307 was grown at 20°C and 15°C under salinity of 35‰, 32‰, 27‰, 20‰, and 15‰, and analyzed for long chain (C37–C39) Alkenones and (C37–C38) alkyl alkenoates. It was characterized by abundant C37 Alkenones and C38 ethyl alkenoates (fatty acid ethyl ester: FAEEs) and a lack of C38 methyl Alkenones. There were no tetra-unsaturated (C37:4) Alkenones, which are frequently found in natural samples from low salinity waters. The Alkenone unsaturation index (U37) did not vary in response to change in salinity at 15°C. The Alkenone unsaturation index (U37) clearly changed in response to change in salinity at 20°C, but not at 15°C, where algal growth was and was not limited by temperature at 15°C and 20°C, respectively. The U37-temperature calibration for I. galbana UTEX LB 2307 is quite different from those of E. huxleyi and another strain of I. galbana (CCMP1323), while is resemble to that reported for C. lamellosa isolated from a Chinese lake. Also, variation in the Alkenone chain length ratio values (K37/K38) did not correlate with salinity. These results implied that a high abundance of tetra-unsaturated Alkenone and high K37/K38 values might be attributed to a taxonomic factor rather than a physiological response to salinity change. Interestingly, our culture experiments showed that the ethyl alkenoates/Alkenones ratio (EE/K37) correlates with salinity. Hence, it is suggested that the EE/K37 ratios are affected by the cellular and physiological factors against salinity condition in single haptophyte cells.
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Alkenone and alkenoic acid compositions of the membrane fractions of Emiliania huxleyi.
Phytochemistry, 2004Co-Authors: Ken Sawada, Yoshihiro ShiraiwaAbstract:Abstract The lipid classes and unsaturation ratios of long-chain Alkenones (nC37–C39), related alkyl alkenoate compounds (nC37–C38) and alkenoic acids (nC14–C22) were determined in isolated membrane and organelle fractions of Emiliania huxleyi. The percentage distribution of these compounds was predominantly high in the endoplasmic reticulum (ER) and coccolith-producing compartment (CPC)-rich membrane fraction, although Alkenones and alkenoates could be detected in all membrane fractions. In particular, the Alkenones were mainly located in CPC, since their distribution was closely correlated with that of uronic acids which are markers of CPC. In contrast, the alkenoic acids seemed to be mainly located in chloroplast (thylakoid)-rich fractions. The Alkenone unsaturation ratio and the ratio of alkenoates to Alkenones were similar in all fractions, while the unsaturation ratio of alkenoic acids in the thylakoid-rich and plasma membrane (PM)/Golgi body-rich fractions was overwhelmingly higher than that in the ER/CPC-rich fractions. Thus, alkenoic acids seemed to be typical membrane-bound lipids, and could be closely related to photosynthesis and involved in regulating membrane fluidity and rigidity in E. huxleyi. It is presumed from these results that the Alkenones and alkenoates were membrane-unbound lipids that might be associated with the function of CPC.
Maureen H Conte - One of the best experts on this subject based on the ideXlab platform.
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systematic chemotaxonomic profiling and novel paleotemperature indices based on Alkenones and alkenoates potential for disentangling mixed species input
Organic Geochemistry, 2019Co-Authors: Maureen H Conte, Yinsui Zheng, Patrick Heng, Richard S Vachula, Yongsong HuangAbstract:Abstract The unsaturation indices ( U 37 K , U 37 K' ) of long chain Alkenones are powerful paleotemperature proxies and have been widely applied for sea surface temperature (SST) reconstructions in the past three decades. However, these indices encounter major difficulties in systems harboring different Alkenone-producing haptophyte species, such as saline lakes and marginal ocean environments. All haptophytes produce C37 Alkenones, but different species often display large differences in temperature calibrations and may bloom in different seasons, hindering the use of U 37 K and U 37 K' indices for reliable paleotemperature reconstructions in mixed systems. To overcome these problems, we have recently reported a new analytical method that allows comprehensive separation of up to 32 Alkenones, alkenoates and their double bond positional isomers in culture and sediment samples. Here we report a systematic analysis of Alkenones and alkenoates from six haptophyte cultures growing at a wide range of temperatures (4–25 °C). Together with a compilation of 230 previously published culture data sets, we present here systematic calibrations of temperature-sensitive indices based on all Alkenone and alkenoate homologues (including isomers). Using this dataset, we extract systematic chemotaxonomic criteria for differentiating individual haptophyte species and demonstrate such chemotaxonomic features can be encoded into a machine learning model for reliable species identifications. Specifically, we show that temperature calibrations based on C38 methyl ketones and C39 ethyl ketones are potentially useful for disentangling mixed inputs in estuarine systems where Group III (E. huxleyi) and Group II Alkenones mix, and that C36 ethyl alkenoate isomeric ratios display minimal species heterogeneity and are potentially more suited for reconstructing temperatures in mixed systems with different Group II haptophytes. Using the culture data as base profiles, we construct a mathematical model for estimating percentage inputs from Alkenones of different Isochrysidales groups in mixed systems, with potential implications for inferring past salinity changes. Overall, the results from this study demonstrate important new applications of Alkenone and alkenoate biomarkers in paleoclimate and paleoenvironmental research.
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genetic and physiological influences on the Alkenone alkenoate versus growth temperature relationship in emiliania huxleyi and gephyrocapsa oceanica
Geochimica et Cosmochimica Acta, 1998Co-Authors: Maureen H Conte, Anthony Thompson, David Lesley, Roger P HarrisAbstract:Selected warm and cold water strains of the coccolithophorid Emiliania huxleyi and the closely related species Gephyrocapsa oceanica were cultured under controlled temperature conditions to assess genetic and physiological variability in the Alkenone/alkenoate vs. temperature relationship. Differences in the strains’ growth rates over the 6–30°C experimental temperature range were small but consistent with their cold or warm water origins. E. huxleyi and G. oceanica had similar Alkenone/alkenoate biochemistry, justifying the extension of Alkenone stratigraphy to sediments predating the appearance of E. huxleyi. These species could not be distinguished by C38/C37 Alkenone or alkenoate/Alkenone ratios as previously suggested (Volkman et al. 1995; Sawada et al. 1996) but given samples from a range of temperatures may be distinguished by a plot of the C38 ethyl vs. C38 methyl unsaturation ratios (U38EtK and U38MeK, respectively). Biochemical responses to temperature and the C37 Alkenone-based (U37K′) temperature calibrations differed significantly among the strains. The U37K′ temperature calibration was nonlinear for five of the six strains examined. A reduction in slope of the calibration at temperatures 21°C suggests the cell’s Alkenone-based adaptation to temperature is limited at the extremes of its growth temperature range. The unsaturation ratios of the C38 methyl and ethyl Alkenones (U38MeK and U38EtK) varied similarly with temperature and were strongly intercorrelated. The experiments also documented an influence of cell physiological state on both Alkenone and alkenoate composition and on Alkenone unsaturation. Cells in late logarithmic and stationary growth had significantly increased abundance of alkenoates and C38 ethyl Alkenones relative to C38 methyl Alkenone abundance. In some strains the unsaturation ratios of both C37 and C38 Alkenones also significantly decreased when cells entered the late log phase. Comparison of culture results with field data indicates that the average physiological state of Alkenone-synthesizers in the open ocean differs from cultured cells growing under exponential growth and appears to be more similar to cells in late log or stationary growth phases. Differences in Alkenone/alkenoate ratios between cultured cells and sediments underlying waters of a similar temperature most probably reflect a difference in cell physiology between cultured cells and oceanic populations and not greater diagenetic losses of Alkenones relative to alkenoates, as previously suggested (Prahl et al. 1995). Our experiments confirm that biogeographical variations observed in the Alkenone vs. temperature relationship in natural waters reflect, at least in part, differences in genetic makeup and physiological status of the local Alkenone-synthesizing populations. Hence, Alkenone-based paleo sea surface temperature estimates are subject to errors, albeit small, which arise from genetic differences between modern-day and paleo-populations. The reduction in slope of the U37K′ temperature calibration for most strains at T >24°C indicate that linear U37K′ temperature calibrations (e.g., Prahl et al. 1988) which are currently used to estimate paleo SST, and which are poorly constrained at higher temperatures, probably underestimate the magnitude of SST change for tropical and subtropical regions.
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Genetic and physiological influences on the Alkenone/alkenoate versus growth temperature relationship in Emiliania huxleyi and Gephyrocapsa oceanica
Geochimica et Cosmochimica Acta, 1998Co-Authors: Maureen H Conte, Anthony Thompson, David J Lesley, Roger HarrisAbstract:Selected warm and cold water strains of the coccolithophorid Emiliania huxleyi and the closely related species Gephyrocapsa oceanica were cultured under controlled temperature conditions to assess genetic and physiological variability in the Alkenone/alkenoate vs. temperature relationship. Differences in the strains’ growth rates over the 6–30°C experimental temperature range were small but consistent with their cold or warm water origins. E. huxleyi and G. oceanica had similar Alkenone/alkenoate biochemistry, justifying the extension of Alkenone stratigraphy to sediments predating the appearance of E. huxleyi. These species could not be distinguished by C38/C37 Alkenone or alkenoate/Alkenone ratios as previously suggested (Volkman et al. 1995; Sawada et al. 1996) but given samples from a range of temperatures may be distinguished by a plot of the C38 ethyl vs. C38 methyl unsaturation ratios (U38EtK and U38MeK, respectively). Biochemical responses to temperature and the C37 Alkenone-based (U37K′) temperature calibrations differed significantly among the strains. The U37K′ temperature calibration was nonlinear for five of the six strains examined. A reduction in slope of the calibration at temperatures 21°C suggests the cell’s Alkenone-based adaptation to temperature is limited at the extremes of its growth temperature range. The unsaturation ratios of the C38 methyl and ethyl Alkenones (U38MeK and U38EtK) varied similarly with temperature and were strongly intercorrelated. The experiments also documented an influence of cell physiological state on both Alkenone and alkenoate composition and on Alkenone unsaturation. Cells in late logarithmic and stationary growth had significantly increased abundance of alkenoates and C38 ethyl Alkenones relative to C38 methyl Alkenone abundance. In some strains the unsaturation ratios of both C37 and C38 Alkenones also significantly decreased when cells entered the late log phase. Comparison of culture results with field data indicates that the average physiological state of Alkenone-synthesizers in the open ocean differs from cultured cells growing under exponential growth and appears to be more similar to cells in late log or stationary growth phases. Differences in Alkenone/alkenoate ratios between cultured cells and sediments underlying waters of a similar temperature most probably reflect a difference in cell physiology between cultured cells and oceanic populations and not greater diagenetic losses of Alkenones relative to alkenoates, as previously suggested (Prahl et al. 1995). Our experiments confirm that biogeographical variations observed in the Alkenone vs. temperature relationship in natural waters reflect, at least in part, differences in genetic makeup and physiological status of the local Alkenone-synthesizing populations. Hence, Alkenone-based paleo sea surface temperature estimates are subject to errors, albeit small, which arise from genetic differences between modern-day and paleo-populations. The reduction in slope of the U37K′ temperature calibration for most strains at T >24°C indicate that linear U37K′ temperature calibrations (e.g., Prahl et al. 1988) which are currently used to estimate paleo SST, and which are poorly constrained at higher temperatures, probably underestimate the magnitude of SST change for tropical and subtropical regions.
Timothy I. Eglinton - One of the best experts on this subject based on the ideXlab platform.
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Unusual C35 to C38 Alkenones in mid-Holocene sediments from a restricted estuary (Charlotte Harbor, Florida)
Organic Geochemistry, 2014Co-Authors: E. E. Van Soelen, Timothy I. Eglinton, J.s. Sinninghe Damsté, J. M. Lammers, Gert-jan ReichartAbstract:Unusual C-35 to C-38 Alkenones were identified in mid-Holocene (8-3.5 kyr BP) sediments from a restricted estuary in southwest Florida (Charlotte Harbor). The distribution was dominated by a C-36 diunsaturated (omega 15,20) ethyl ketone, identical to the one present in Black Sea Unit 2 sediments. Other unusual Alkenones were tentatively assigned as a C-35:2 (omega 15,20) methyl ketone, a C-37:2 (omega 17,22) methyl ketone and a C-38:2 (omega 17,22) ethyl ketone. In late Holocene sediments < 3.5 kyr BP, the common C-37 to C-39 Alkenones were found. Compound-specific C-14, C-13, and D isotope measurements were used to constrain the possible origin of the Alkenones. Conventional radiocarbon ages of Alkenones and higher plant-derived long chain n-alcohols indicated no significant difference in age between mid-Holocene Alkenones and higher plant n-alcohols. Both alcohols and Alkenones were offset vs. calibrated ages of shell fragments in the same sediment core, which suggests they were pre-aged by 500-800 yr, implying resuspension and redistribution of the fine-grained sedimentary particles with which they are associated. The hydrogen isotopic (delta D) composition (-190 parts per thousand to -200 parts per thousand) of the C-37 and C-38 Alkenones in the late Holocene sediments is in line with values for coastal haptophytes in brackish water. However, the unusual C-36 and C-38 Alkenones from the mid Holocene sediments were enriched in D (by ca. 100 parts per thousand) vs. the late Holocene Alkenones. Also, delta C-13 values of mid-Holocene Alkenones were consistently offset compared with late Holocene Alkenones (-21 parts per thousand to 22 parts per thousand and -22 parts per thousand to -23 parts per thousand, respectively). We suggest that the Alkenones in Charlotte Harbor were produced by unknown Alkenone-producing haptophyte.
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Alkenones as tracers of surface ocean temperature and biological pump processes on the Northwest Atlantic margin
Deep Sea Research Part I: Oceanographic Research Papers, 2014Co-Authors: Jeomshik Hwang, Minkyoung Kim, Jongjin Park, Steven J. Manganini, Daniel B. Montluçon, Timothy I. EglintonAbstract:Abstract We have examined Alkenone distributions, specifically the temperature proxy U 37 K ′ , in sinking particulate organic matter (POM) intercepted at three depths by time-series sediment traps deployed between 2004 and 2007 on the Northwest Atlantic margin. The goal was to assess physical and biogeochemical processes acting upon Alkenones during passage through the water column. U 37 K ′ did not exhibit any systematic trend with increasing depth despite several-fold attenuation in Alkenone flux. Because of the extensive reduction in C 37 Alkenone flux in the water column and more efficient Alkenone degradation during the period of high Alkenone flux, the temperature bias toward that of more productive seasons was reduced with increasing trap depth. The temporal variation of U 37 K ′ and Alkenone-derived temperature compared best with the satellite-derived SST at an upstream region approximately 160 km east of the mooring site with a time lag of about 30 days, suggesting this region as the dominant source of Alkenone-bearing POM. The Alkenone-derived temperature of core-top sediments (15 °C) at the study site was lower than the flux-weighted average Alkenone-derived temperature of sinking POM at 50 m above the seafloor. This discrepancy may reflect additional supply of resuspended sediment carrying Alkenones produced in cooler waters to the northeast, and transported in bottom nepheloid layers.
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RADIOCARBON DATING OF AlkenoneS FROM MARINE SEDIMENTS: II. ASSESSMENT OF CARBON PROCESS BLANKS
Radiocarbon, 2005Co-Authors: Gesine Mollenhauer, Daniel B. Montluçon, Timothy I. EglintonAbstract:We evaluate potential process blanks associated with radiocarbon measurement of microgram to milligram quantities of Alkenones at the National Ocean Sciences Accelerator Mass Spectrometry (NOSAMS) facility. Two strategies to constrain the contribution of blanks to Alkenone 14C dates were followed: 1) dating of samples of known age and 2) multiple measurements of identical samples. We show that the potential contamination associated with the procedure does not lead to a systematic bias of the results of Alkenone dating to either younger or older ages. Our results indicate that Alkenones record ∆14C of ambient DIC with an accuracy of approximately 10‰. A conservative estimate of measurement precision is 17‰ for modern samples. Alkenone 14C ages are expected to be reliable within 500 yr for samples younger than 10,500 14C yr.
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RADIOCARBON DATING OF AlkenoneS FROM MARINE SEDIMENTS: I. ISOLATION PROTOCOL
Radiocarbon, 2005Co-Authors: Naohiko Ohkouchi, Christopher M. Reddy, Daniel B. Montluçon, Timothy I. EglintonAbstract:The chemical and isotopic compositions of long-chain (C36C39) unsaturated ketones (Alkenones), a unique class of algal lipids, encode surface ocean properties useful for paleoceanographic reconstruction. Recently, we have sought to extend the utility of Alkenones as oceanic tracers through measurement of their radiocarbon contents. Here, we describe a method for isolation of Alkenones from sediments as a compound class based on a sequence of wet chemical techniques. The steps involved, which include silica gel column chromatography, urea adduction, and silver nitrate-silica gel column chromatography, exploit various structural attributes of the Alkenones. Amounts of purified Alkenones estimated by GC/FID measurements were highly correlated with CO2 yields after sample combustion, indicating purities of greater than 90% for samples containing =100 g C. The degree of Alkenone unsaturation ( ) also varied minimally through the procedure. We also describe a high-performance liquid chromatography (HPLC) method to isolate individual Alkenones for molecular-level structural and isotopic determination.
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Asynchronous Alkenone and foraminifera records from the Benguela Upwelling System
Geochimica et Cosmochimica Acta, 2003Co-Authors: Gesine Mollenhauer, Ralph R Schneider, Timothy I. Eglinton, Peter J Müller, Naohiko Ohkouchi, Pieter Meiert Grootes, Jurgen RullkotterAbstract:Abstract Radiocarbon stratigraphy is an essential tool for high resolution paleoceanographic studies. Age models based on radiocarbon ages of foraminifera are commonly applied to a wide range of geochemical studies, including the investigation of temporal leads and lags. The critical assumption is that temporal coupling between foraminifera and other sediment constituents, including specific molecular organic compounds (biomarkers) of marine phytoplankton, e.g. Alkenones, is maintained in the sediments. To test this critical assumption in the Benguela upwelling area, we have determined radiocarbon ages of total C37-C39 Alkenones in 20 samples from two gravity cores and three multicorer cores. The cores were retrieved from the continental shelf and slope off Namibia, and samples were taken from Holocene, deglacial and Last Glacial Maximum core sections. The Alkenone radiocarbon ages were compared to those of planktic foraminifera, total organic carbon, fatty acids and fine grained carbonates from the same samples. Interestingly, the ages of Alkenones were 1000 to 4500 yr older than those of foraminifera in all samples. Such age differences may be the result of different processes: Bioturbation associated with grain size effects, lateral advection of (recycled) material and redeposition of sediment on upper continental slopes due to currents or tidal movement are examples for such processes. Based on the results of this study, the age offsets between foraminifera and Alkenones in sediments from the upper continental slope off Namibia most probably do not result from particle-selective bioturbation processes. Resuspension of organic particles in response to tidal movement of bottom waters with velocities up to 25 cm/s recorded near the core sites is the more likely explanation. Our results imply that age control established using radiocarbon measurements of foraminifera may be inadequate for the interpretation of Alkenone-based proxy data. Observed temporal leads and lags between foraminifera based data and data derived from Alkenone measurements may therefore be secondary signals, i.e. the result of processes associated with particle settling and biological activity.
