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Yongsong Huang - One of the best experts on this subject based on the ideXlab platform.

  • identification of methyl branched Alkenones with up to five double bonds in saline lakes
    30th International Meeting on Organic Geochemistry (IMOG 2021), 2021
    Co-Authors: Sian Liao, Carsten J. Schubert, Karen J. Wang, Yazhen Xue, Ewerton Santos, Jianbo Wang, Yongsong Huang
    Abstract:

    Summary We demonstrate new C38 and C39 found in Lake Van and Lake Fryxell are methyl-branched Alkenones (brC38Me and brC39Et). Previous assignments of these compounds as straight chain C38Me and C39Et were incorrect. Double bond positions, determined based on mass spectra of corresponding DMDS adducts, are Δ 4, Δ 7, Δ 14, Δ 21 and Δ 28 for penta-unsaturated branched Alkenones. Based on published DNA data and changes of branched alkenone percentages of Lake Van, we hypothesize that branched Alkenones function as storage of energy and are produced by a yet unknown species of Isochrysidales. UKbr38Me based on brC38Me Alkenones has a similar trend with UK37 in the past 270 ka of Lake Van, suggesting the high temperature sensitivity of branched Alkenones, same as other straight chain Alkenones. Such proxies based on branched Alkenones might be more reliable than UK37 and UK'37 to provide temperature record in sites with mixed alkenone productions.

  • novel methyl branched Alkenones with up to five double bonds in saline lakes
    Organic Geochemistry, 2021
    Co-Authors: Sian Liao, Carsten J. Schubert, Karen J. Wang, Yazhen Xue, Ewerton Santos, Jianbo Wang, Jingfeng Huo, Yongsong Huang
    Abstract:

    Abstract Long-chain Alkenones, a class of highly specific and widely used lipid biomarkers found in ocean and lake sediments, have been so far found as straight-chain alkyl ketones with 2 to 4 double bonds. Jaraula et al. (2010) reported assignments of a series of tri- to penta-unsaturated Alkenones as straight-chain C38 methyl (C38Me) and C39 ethyl (C39Et) Alkenones in Lake Fryxell, Antarctica. The same series of compounds were later found in sediments from Lake Van (Randlett et al., 2014). The structure assignments by Jaraula et al (2010) were primarily based on strong ions at [M−43]+ for C38 Alkenones and [M−57]+ for C39 Alkenones, which were interpreted as a loss of CH3CO and CH3CH2CO groups. However, such fragmentation is atypical for common straight-chain methyl and ethyl Alkenones. In this study, we reanalyzed Lake Van sediment samples. We show these new C38 and C39 Alkenones elute earlier than the common straight-chain C38Me and C39Et Alkenones on a mid-polarity GC column. After hydrogenation, mass spectra of these new Alkenones show distinct peaks at m/z 72 or 86 caused by McLafferty rearrangement, indicating a methyl substitution at the α position of the carbonyl group in these C38 and C39 Alkenones (i.e., α-methyl-branched C38Me and C39Et). Our new assignments as methyl-branched Alkenones are further confirmed by the synthesis of an analog α-methyl C25 methyl ketone and comparison of mass spectra. Double bond positions for branched C38:5Me (brC38:5Me) are found to be Δ4, Δ7, Δ14, Δ21 and Δ28 based on the mass spectrum of corresponding dimethyl disulfide adducts. Analysis of Lake Van alkenone data reveals that U b r 38 M e K ∗ based on brC38Me shows a trend similar to U 37 K for the past 270 ka, suggesting that the degree of unsaturation of branched Alkenones is also sensitive to temperature.

  • Group 2i Isochrysidales produce characteristic Alkenones reflecting sea ice distribution.
    Nature communications, 2021
    Co-Authors: Karen Jiaxi Wang, Yongsong Huang, Nora Richter, Timothy D. Herbert, Sian Liao, Markus Majaneva, Simon T. Belt, Joseph B. Novak, Tyler R. Kartzinel, Patricia Cabedo-sanz
    Abstract:

    Alkenones are biomarkers produced solely by algae in the order Isochrysidales that have been used to reconstruct sea surface temperature (SST) since the 1980s. However, alkenone-based SST reconstructions in the northern high latitude oceans show significant bias towards warmer temperatures in core-tops, diverge from other SST proxies in down core records, and are often accompanied by anomalously high relative abundance of the C37 tetra-unsaturated methyl alkenone (%C37:4). Elevated %C37:4 is widely interpreted as an indicator of low sea surface salinity from polar water masses, but its biological source has thus far remained elusive. Here we identify a lineage of Isochrysidales that is responsible for elevated C37:4 methyl alkenone in the northern high latitude oceans through next-generation sequencing and lab-culture experiments. This Isochrysidales lineage co-occurs widely with sea ice in marine environments and is distinct from other known marine alkenone-producers, namely Emiliania huxleyi and Gephyrocapsa oceanica. More importantly, the %C37:4 in seawater filtered particulate organic matter and surface sediments is significantly correlated with annual mean sea ice concentrations. In sediment cores from the Svalbard region, the %C37:4 concentration aligns with the Greenland temperature record and other qualitative regional sea ice records spanning the past 14 kyrs, reflecting sea ice concentrations quantitatively. Our findings imply that %C37:4 is a powerful proxy for reconstructing sea ice conditions in the high latitude oceans on thousand- and, potentially, on million-year timescales.

  • C41 methyl and C42 ethyl Alkenones are biomarkers for Group II Isochrysidales
    Organic Geochemistry, 2020
    Co-Authors: Sian Liao, William M. Longo, Linda A. Amaral-zettler, Yuan Yao, Li Wang, Karen J. Wang, Yongsong Huang
    Abstract:

    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.

  • Phylogenetic diversity in freshwater-dwelling Isochrysidales haptophytes with implications for alkenone production
    Geobiology, 2019
    Co-Authors: Nora Richter, William M. Longo, Yongsong Huang, Sarabeth George, Anna Shipunova, Linda Amaral-zettler
    Abstract:

    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.

Yoshihiro Shiraiwa - One of the best experts on this subject based on the ideXlab platform.

  • Cold-induced metabolic conversion of haptophyte di- to tri-unsaturated C37 Alkenones used as palaeothermometer molecules.
    Scientific reports, 2018
    Co-Authors: Eri Kitamura, Ken Sawada, Iwane Suzuki, Tomonori Kotajima, Yoshihiro Shiraiwa
    Abstract:

    The cosmopolitan marine haptophyte alga Emiliania huxleyi accumulates very long-chain (C37-C40) alkyl ketones with two to four trans-type carbon-carbon double bonds (Alkenones). These compounds are used as biomarkers of haptophytes and as palaeothermometers for estimating sea-surface temperatures in biogeochemistry. However, the biosynthetic pathway of Alkenones in algal cells remains enigmatic, although it is well known that the C37 tri-unsaturated alkenone (K37:3) becomes dominant at low temperatures, either by desaturation of K37:2 or by a separate pathway involving the elongation of tri-unsaturated alkenone precursors. Here, we present experimental evidence regarding K37:3 synthesis. Using the well-known cosmopolitan alkenone producer E. huxleyi, we labelled K37:2 with 13C by incubating cells with 13C-bicarbonate in the light at 25 °C under conditions of little if any K37:3 production. After stabilisation of the 13C-K37:2 level by depleting 13C-bicarbonate from the medium, the temperature was suddenly reduced to 15 °C. The 13C-K37:2 level rapidly decreased, and the 13C-K37:3 level increased, whereas the total 13C-K37 level-namely [K37:2 + K37:3]-remained constant. These 13C-pulse-chase-like experimental results indicate that 13C-K37:2 is converted directly to 13C-K37:3 by a desaturation reaction that is promoted by a cold signal. This clear-cut experimental evidence is indicative of the existence of a cold-signal-triggered desaturation reaction in alkenone biosynthesis.

  • Composition of long chain Alkenones and alkenoates as a function of growth temperature in marine haptophyte Tisochrysis lutea
    Organic Geochemistry, 2016
    Co-Authors: Hideto Nakamura, Ken Sawada, Hiroya Araie, Takashi Shiratori, Ken-ichiro Ishida, Iwane Suzuki, Yoshihiro Shiraiwa
    Abstract:

    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.

  • Rapid detection and quantification of haptophyte Alkenones by Fourier transform infrared spectroscopy (FTIR)
    Algal Research, 2016
    Co-Authors: Angela Pelusi, Hiroya Araie, Iwane Suzuki, Yutaka Hanawa, Mario Giordano, Yoshihiro Shiraiwa
    Abstract:

    Abstract Several haptophyte algae produce unique neutral long-chain (C 37 C 40 ) ketones (Alkenones) with two to four trans -carbon-carbon double (C C) bonds and a keto-group. These molecules are of great biological interest and may have substantial commercial relevance as biofuel sources. Unfortunately, their detection and quantification, involving extraction from cells with organic solvents and fractionation of lipids through columns, are rather cumbersome. Hence, we developed a method for the rapid and reliable quantification of Alkenones in intact cells using Fourier transform infrared spectroscopy (FTIR). The method is based on the absorption band at 962.5 cm − 1 , which corresponds to a trans -C C bond that is unequivocally attributable to Alkenones. This peak was exclusively observed in alkenone-producing haptophytes such as Emiliania huxleyi NIES-837, Emiliania huxleyi CCMP 2090, Tisochrysis lutea (former Isochrysis galbana T-iso), Tisochrysis lutea CCMP 463, and Chrysotila lamellosa CCMP 1307, as well as in appropriate standards. We compared our FTIR method with a typical GC analysis method. The alkenone quantity determined by these two methods showed similar values. Nevertheless, the FTIR method developed in this study does not require complex extraction procedures and is therefore a much easier and rapid quantification method. This FTIR method can also be used for the screening of strains and the optimization of culture conditions for alkenone production.

  • proteomic analysis of lipid body from the alkenone producing marine haptophyte alga tisochrysis lutea
    Proteomics, 2015
    Co-Authors: Qing Shi, Hiroya Araie, Iwane Suzuki, Ranjith Kumar Bakku, Yoichiro Fukao, Randeep Rakwal, Yoshihiro Shiraiwa
    Abstract:

    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.

  • P433-TH CHANGE OF UNSATURATION DEGREE OF Alkenones DURING ACCLIMATION TO SALINITY CHANGE IN ISOCHRYSIS GALBANA WITH REFERENCES TO PALEOSALINITY PROXY
    2015
    Co-Authors: Makiko Ono, Ken Sawada, Masako Kubota, Yoshihiro Shiraiwa
    Abstract:

    Long-chain (C37–C39) Alkenones, which are derived from Haptophycean algae, especially Gephyrocapsaceae and Isocrysidaceae, have been well used as the proxy for paleotemperatures of sea surface water, as reviewed by Brassell (1993). Recently, it was reported that the relative abundance of 4-unsaturated Alkenones (e.g. C37:4 alkenone) increased with decreasing salinity, and therefore, the unsaturation ratios and the compositions of the Alkenones could be potentially used as a proxy for paleosalinity of ambient waters (Rosell-Mele, 1998; Harada et al., 2003). We have been investigated variations of the unsaturation ratios of the Alkenones for culture strains of Haptophycean algae Emiliania huxleyi and Gephyrocapsa oceanica, which are typical source organisms in marine environment, against the changes of salinity in order to clarify the relationships between alkenone unsaturation ratio and salinity (Sawada et al., 2001). Nevertheless, the 4-unsaturated Alkenones could not be detected in both low and high salinity conditions of these algae. Thus, in this study, the variations of the alkenone unsaturation ratios of a culture strain Isocrysis galbana, which is generally coastal Haptophycean species, were investigated and the potential for paleosalinity proxy in the 4-unsaturated Alkenones was examined

Ken Sawada - One of the best experts on this subject based on the ideXlab platform.

  • Cold-induced metabolic conversion of haptophyte di- to tri-unsaturated C37 Alkenones used as palaeothermometer molecules.
    Scientific reports, 2018
    Co-Authors: Eri Kitamura, Ken Sawada, Iwane Suzuki, Tomonori Kotajima, Yoshihiro Shiraiwa
    Abstract:

    The cosmopolitan marine haptophyte alga Emiliania huxleyi accumulates very long-chain (C37-C40) alkyl ketones with two to four trans-type carbon-carbon double bonds (Alkenones). These compounds are used as biomarkers of haptophytes and as palaeothermometers for estimating sea-surface temperatures in biogeochemistry. However, the biosynthetic pathway of Alkenones in algal cells remains enigmatic, although it is well known that the C37 tri-unsaturated alkenone (K37:3) becomes dominant at low temperatures, either by desaturation of K37:2 or by a separate pathway involving the elongation of tri-unsaturated alkenone precursors. Here, we present experimental evidence regarding K37:3 synthesis. Using the well-known cosmopolitan alkenone producer E. huxleyi, we labelled K37:2 with 13C by incubating cells with 13C-bicarbonate in the light at 25 °C under conditions of little if any K37:3 production. After stabilisation of the 13C-K37:2 level by depleting 13C-bicarbonate from the medium, the temperature was suddenly reduced to 15 °C. The 13C-K37:2 level rapidly decreased, and the 13C-K37:3 level increased, whereas the total 13C-K37 level-namely [K37:2 + K37:3]-remained constant. These 13C-pulse-chase-like experimental results indicate that 13C-K37:2 is converted directly to 13C-K37:3 by a desaturation reaction that is promoted by a cold signal. This clear-cut experimental evidence is indicative of the existence of a cold-signal-triggered desaturation reaction in alkenone biosynthesis.

  • Novel alkenone-producing strains of genus Isochrysis (Haptophyta) isolated from Canadian saline lakes show temperature sensitivity of Alkenones and alkenoates
    Organic Geochemistry, 2018
    Co-Authors: Hiroya Araie, Julien Plancq, Jaime L. Toney, Hideto Nakamura, Takashi Shiratori, Ken-ichiro Ishida, Osamu Seki, Heather A. Haig, Peter R. Leavitt, Ken Sawada
    Abstract:

    Abstract Alkenone-producing species have been recently found in diverse lacustrine environments, albeit with taxonomic information derived indirectly from environmental genomic techniques. In this study, we isolated alkenone-producing algal species from Canadian saline lakes and established unialgal cultures of individual strains to identify their taxonomical and molecular biological characteristics. Water and sediments collected from the lakes were first enriched in artificial seawater medium over a range of salinities (5–40 g/L) to cultivate taxa in vitro. Unialgal cultures of seven haptophyte strains were isolated and categorized in the Isochrysis clade using SSU and LSU rRNA gene analysis. The alkenone distributions within isolated strains were determined to be novel compared with other previously reported alkenone-producing haptophytes. While all strains produced the typical C37 and C38 range of isomers, one strain isolated from Canadian salt lakes also produced novel C41 and C42 Alkenones that are temperature sensitive. In addition, we showed that all alkenone unsaturation indices (e.g., U 37 K and U 37 K ′ ) are temperature-dependent in culture experiments, and that alkenoate indices (e.g., U 37 A , U 38 A , RIA38 and A37/A38) provide alternative options for temperature calibration based on these new lacustrine algal strains. Importantly, these indices show temperature dependence in culture experiments at temperatures below 10 °C, where traditional alkenone proxies were not as sensitive. We hypothesize that this suite of calibrations may be used for reconstructions of past water temperature in a broad range of lakes in the Canadian prairies.

  • Composition of long chain Alkenones and alkenoates as a function of growth temperature in marine haptophyte Tisochrysis lutea
    Organic Geochemistry, 2016
    Co-Authors: Hideto Nakamura, Ken Sawada, Hiroya Araie, Takashi Shiratori, Ken-ichiro Ishida, Iwane Suzuki, Yoshihiro Shiraiwa
    Abstract:

    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.

  • P433-TH CHANGE OF UNSATURATION DEGREE OF Alkenones DURING ACCLIMATION TO SALINITY CHANGE IN ISOCHRYSIS GALBANA WITH REFERENCES TO PALEOSALINITY PROXY
    2015
    Co-Authors: Makiko Ono, Ken Sawada, Masako Kubota, Yoshihiro Shiraiwa
    Abstract:

    Long-chain (C37–C39) Alkenones, which are derived from Haptophycean algae, especially Gephyrocapsaceae and Isocrysidaceae, have been well used as the proxy for paleotemperatures of sea surface water, as reviewed by Brassell (1993). Recently, it was reported that the relative abundance of 4-unsaturated Alkenones (e.g. C37:4 alkenone) increased with decreasing salinity, and therefore, the unsaturation ratios and the compositions of the Alkenones could be potentially used as a proxy for paleosalinity of ambient waters (Rosell-Mele, 1998; Harada et al., 2003). We have been investigated variations of the unsaturation ratios of the Alkenones for culture strains of Haptophycean algae Emiliania huxleyi and Gephyrocapsa oceanica, which are typical source organisms in marine environment, against the changes of salinity in order to clarify the relationships between alkenone unsaturation ratio and salinity (Sawada et al., 2001). Nevertheless, the 4-unsaturated Alkenones could not be detected in both low and high salinity conditions of these algae. Thus, in this study, the variations of the alkenone unsaturation ratios of a culture strain Isocrysis galbana, which is generally coastal Haptophycean species, were investigated and the potential for paleosalinity proxy in the 4-unsaturated Alkenones was examined

  • long chain alkenes Alkenones and alkenoates produced by the haptophyte alga chrysotila lamellosa ccmp1307 isolated from a salt marsh
    Organic Geochemistry, 2014
    Co-Authors: Hideto Nakamura, Ken Sawada, Hiroya Araie, Iwane Suzuki, Yoshihiro Shiraiwa
    Abstract:

    Abstract The compositions of long chain alkenes, Alkenones and alkenoates in a cultured strain of the haptophyte Chrysotila lamellosa CCMP1307, isolated from a salt marsh, were investigated. The biomarker patterns were distinctive and showed a high proportion of tetraunsaturated Alkenones and alkenoates, with a pronounced proportion of C 40 Alkenones and a lack of C 38 methyl and C 39 ethyl Alkenones. Linear regression of the alkenone unsaturation degree ( U 37 K ) with growth temperature ( T ) was obtained over the range of possible CCMP1307 growth temperature values (4–20 °C): U 37 K  = 0.045 ×  T (°C) − 1.016, ( n  = 13, r 2 0.96), while the U 37 K ′ values were weakly correlated with T : U 37 K ′  = 0.0035 T (°C) + 0.0511 ( n  = 18, r 2 0.70). The U 37 K calibration exhibited a low y-intercept in comparison with that of a Chinese inland lake strain reported previously. The data show significant intraspecific variation in U 37 K for C. lamellosa between strains from different geographic origins. C. lamellosa CCMP1307 reproduced typical U 37 K values observed in C 37:4 rich lakes, especially at lower temperature ( 29:2 , C 31:1 , C 31:2 and C 31:3 alkenes, and found that the unsaturation degree of C 31 alkenes ( U 31 en ), calculated with C 31:1 and C 31:2 alkenes, might also be a useful index of growth temperature for the haptophyte C. lamellosa .

Stefan Schouten - One of the best experts on this subject based on the ideXlab platform.

  • constraining the application of hydrogen isotopic composition of Alkenones as a salinity proxy using marine surface sediments
    Geochimica et Cosmochimica Acta, 2019
    Co-Authors: Gabriella M Weiss, Stefan Schouten, Jaap Sinninghe S Damste, Marcel T. J. Van Der Meer
    Abstract:

    Sea surface salinity is an essential environmental parameter necessary to understand past changes in global climate. However, reconstructing absolute salinity of the surface ocean with high enough accuracy and precision remains a complicated task. Hydrogen isotope ratios of long-chain Alkenones (δ 2 H C37 ) have been shown to reflect salinity in culture studies and have been proposed as a tool to reconstruct sea surface salinity in the geologic record. The correlation between δ 2 H C37 – salinity in culture is prominently caused by the relationship between δ 2 H H2O and salinity, as well as the increase in fractionation factor α with increasing salinity. The δ 2 H C37 – salinity relationship in the natural environment is poorly understood. Here, surface sediments from a variety of environments covering a wide range of salinities were analyzed to constrain the environmental relationship between salinity and hydrogen isotopes of Alkenones. δ 2 H C37 correlates significantly (r = 0.75, p < 0.0001) with annual mean salinity. Interestingly, the biological hydrogen isotope fractionation (α C37 ) seems independent of salinity. These findings are different from what has previously been observed in culture experiments, but align with other environmental datasets and suggest that the salinity effect on biological hydrogen isotope fractionation observed in culture is not apparent in sediments. The absence of a correlation between α C37 and salinity for marine surface sediments might be best explained by a mixing of multiple alkenone-producing species contributing to the sedimentary alkenone signal that fractionate in distinct ways. Nevertheless, sedimentary δ 2 H C37 ratios still correlate with salinity and δ 2 H H2O , suggesting that δ 2 H C37 ratios are useful for paleosalinity reconstructions. Our surface sediment calibration presented here can be used when different species contribute to the sedimentary alkenone pool and substantial changes in salinity are expected.

  • constraining the applicability of organic paleotemperature proxies for the last 90 myrs
    Organic Geochemistry, 2019
    Co-Authors: Marijke W De Bar, Sebastiaan W Rampen, Ellen C Hopmans, Jaap Sinninghe S Damste, Stefan Schouten
    Abstract:

    Abstract We evaluated changes in the distributions of long-chain Alkenones, long-chain diols and GDGTs, lipids commonly used for paleothermometry, over the last 90 Myrs for sediments deposited on the New Jersey shelf (the Bass River site) and assessed potential effects of different ancestral producers and diagenesis on their distributions and their impact on the associated temperature proxies. As reported before, the Paleogene distributions of Alkenones are generally similar to those in modern haptophytes, but unusual alkenone distributions, characterized by a dominant di-unsaturated C40 alkenone, are observed for Late Cretaceous sediments, suggesting different ancestral source organisms for Alkenones in this interval. The isoprenoid GDGT distributions remained comparable to modern-day distributions, suggesting that TEX86 can be applied up to ca. 90 Ma. The Miocene long-chain diol distributions are similar to modern-day distributions, but the older sediments reveal unusual distributions, dominated by the C28 1,12- and C26 1,13-diols, suggesting different source organisms before ∼30 Ma. Accordingly, the LDI does not match other paleotemperature proxies, suggesting its applicability might be compromised for sediments older than the Miocene. Our results indicate that of the three proxies, the TEX86 seems to be the most applicable for deep time temperature reconstructions.

  • effects of alkalinity and salinity at low and high light intensity on hydrogen isotope fractionation of long chain Alkenones produced by emiliania huxleyi
    Biogeosciences, 2017
    Co-Authors: Gabriella M Weiss, Stefan Schouten, Eva Y Pfannerstill, Marcel T J Van Der Meer
    Abstract:

    Abstract. Over the last decade, hydrogen isotopes of long-chain Alkenones have been shown to be a promising proxy for reconstructing paleo sea surface salinity due to a strong hydrogen isotope fractionation response to salinity across different environmental conditions. However, to date, the decoupling of the effects of alkalinity and salinity, parameters that co-vary in the surface ocean, on hydrogen isotope fractionation of Alkenones has not been assessed. Furthermore, as the alkenone-producing haptophyte, Emiliania huxleyi, is known to grow in large blooms under high light intensities, the effect of salinity on hydrogen isotope fractionation under these high irradiances is important to constrain before using δDC37 to reconstruct paleosalinity. Batch cultures of the marine haptophyte E. huxleyi strain CCMP 1516 were grown to investigate the hydrogen isotope fractionation response to salinity at high light intensity and independently assess the effects of salinity and alkalinity under low-light conditions. Our results suggest that alkalinity does not significantly influence hydrogen isotope fractionation of Alkenones, but salinity does have a strong effect. Additionally, no significant difference was observed between the fractionation responses to salinity recorded in Alkenones grown under both high- and low-light conditions. Comparison with previous studies suggests that the fractionation response to salinity in culture is similar under different environmental conditions, strengthening the use of hydrogen isotope fractionation as a paleosalinity proxy.

  • testing the alkenone d h ratio as a paleo indicator of sea surface salinity in a coastal ocean margin mozambique channel
    Organic Geochemistry, 2015
    Co-Authors: Sebastian Kasper, M.t.j. Van Der Meer, Jaap Sinninghe S Damste, Isla S. Castañeda, Rik Tjallingii, Geertjan A Brummer, Stefan Schouten
    Abstract:

    Abstract Reconstructing past ocean salinity is important for assessing paleoceanographic change and therefore past climatic dynamics. Commonly, sea water salinity reconstruction is based on planktonic foraminifera oxygen isotope values combined with sea surface temperature reconstruction. However, the approach relies on multiple proxies, resulting in rather large uncertainty and, consequently, relatively low accuracy of salinity estimates. An alternative tool for past ocean salinity reconstruction is the hydrogen isotope composition of long chain (C37) Alkenones (δDalkenone). Here, we have applied δDalkenone to a 39 ka sedimentary record from the Eastern South African continental shelf in the Mozambique Channel, close to the Zambezi River mouth. Despite changes in global seawater δD related to glacial – interglacial ice volume effects, no clear changes were observed in the δDalkenone record throughout the entire 39 ka. The BIT index record from the same core, which provides information on relative contributions of soil organic matter (OM) vs. marine input, indicates high soil OM input during the glacial and low input during the Holocene. This suggests a more pronounced freshwater influence at the core location during the glacial, resulting in Alkenones depleted in D during that time, thereby explaining the lack of a clear glacial-interglacial alkenone δD shift. The correlation between the BIT index and δDalkenone during the glacial period suggests that increased continental runoff potentially changed the growth conditions of the alkenone-producing haptophytes, promoting coastal haptophyte species with generally more enriched δDalkenone values. We therefore suggest that the application of δDalkenone for reconstructing past salinity in coastal settings may be complicated by changes in the alkenone-producing haptophyte community.

  • the effects of growth phase and salinity on the hydrogen isotopic composition of Alkenones produced by coastal haptophyte algae
    Geochimica et Cosmochimica Acta, 2014
    Co-Authors: David Chivall, Stefan Schouten, Jaap Sinninghe S Damste, Daniela Mboule, Danielle Sinkeschoen, Marcel T. J. Van Der Meer
    Abstract:

    The isotopic fractionation of hydrogen during the biosynthesis of Alkenones produced by marine haptophyte algae has been shown to depend on salinity and, as such, the hydrogen isotopic composition of Alkenones is emerging as a palaeosalinity proxy. The relationship between fractionation and salinity has previously only been determined during exponential growth, whilst it is not yet known in which growth phases natural haptophyte populations predominantly exist. We have therefore determined the relationship between the fractionation factor, αAlkenones-water, and salinity for C37 Alkenones produced in different growth phases of batch cultures of the major alkenone-producing coastal haptophytes Isochrysis galbana (strain CCMP 1323) and Chrysotila lamellosa (strain CCMP 1307) over a range in salinity from ca. 10 to 35. αAlkenones-water was similar in both species, ranging over 0.841-0.900 for I. galbana and 0.838-0.865 for C. lamellosa. A strong (0.85≤R2≤0.97; p<0.0001) relationship between salinity and fractionation factor was observed in both species at all growth phases investigated. This suggests that alkenone δD has the potential to be used as a salinity proxy in neritic areas where haptophyte communities are dominated by these coastal species. However, there was a marked difference in the sensitivity of αAlkenones-water to salinity between different growth phases: in the exponential growth phase of I. galbana, αAlkenones-water increased by 0.0019 per salinity unit (S-1), but was less sensitive at 0.0010 and 0.0008S-1 during the stationary and decline phases, respectively. Similarly, in C. lamellosa αAlkenones-water increased by 0.0010S-1 in the early stationary phase and by 0.0008S-1 during the late stationary phase. Assuming the shift in sensitivity of αAlkenones-water to salinity observed at the end of exponential growth in I. galbana is similar in other alkenone-producing species, the predominant growth phase of natural populations of haptophytes will affect the sensitivity of the alkenone salinity proxy. The proxy is likely to be most sensitive to salinity when Alkenones are produced in a state similar to exponential growth. © 2014 Elsevier Ltd.

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  • constraining the application of hydrogen isotopic composition of Alkenones as a salinity proxy using marine surface sediments
    Geochimica et Cosmochimica Acta, 2019
    Co-Authors: Gabriella M Weiss, Stefan Schouten, Jaap Sinninghe S Damste, Marcel T. J. Van Der Meer
    Abstract:

    Sea surface salinity is an essential environmental parameter necessary to understand past changes in global climate. However, reconstructing absolute salinity of the surface ocean with high enough accuracy and precision remains a complicated task. Hydrogen isotope ratios of long-chain Alkenones (δ 2 H C37 ) have been shown to reflect salinity in culture studies and have been proposed as a tool to reconstruct sea surface salinity in the geologic record. The correlation between δ 2 H C37 – salinity in culture is prominently caused by the relationship between δ 2 H H2O and salinity, as well as the increase in fractionation factor α with increasing salinity. The δ 2 H C37 – salinity relationship in the natural environment is poorly understood. Here, surface sediments from a variety of environments covering a wide range of salinities were analyzed to constrain the environmental relationship between salinity and hydrogen isotopes of Alkenones. δ 2 H C37 correlates significantly (r = 0.75, p < 0.0001) with annual mean salinity. Interestingly, the biological hydrogen isotope fractionation (α C37 ) seems independent of salinity. These findings are different from what has previously been observed in culture experiments, but align with other environmental datasets and suggest that the salinity effect on biological hydrogen isotope fractionation observed in culture is not apparent in sediments. The absence of a correlation between α C37 and salinity for marine surface sediments might be best explained by a mixing of multiple alkenone-producing species contributing to the sedimentary alkenone signal that fractionate in distinct ways. Nevertheless, sedimentary δ 2 H C37 ratios still correlate with salinity and δ 2 H H2O , suggesting that δ 2 H C37 ratios are useful for paleosalinity reconstructions. Our surface sediment calibration presented here can be used when different species contribute to the sedimentary alkenone pool and substantial changes in salinity are expected.

  • Long-chain Alkenones in Baltic Sea surface sediments: New insights
    Organic Geochemistry, 2017
    Co-Authors: Jérôme Kaiser, Marcel T. J. Van Der Meer, Helge W Arz
    Abstract:

    Abstract C 37 Alkenones produced by certain haptophytes of the Isochrysidales are valuable sedimentary biomarkers used to estimate sea surface temperature (SST) in the open ocean. However, in coastal seas the role of salinity gradients on alkenone producing species and SST estimates is poorly known. Alkenones were analyzed in surface sediments from the marine Skagerrak region and the entire brackish Baltic Sea. Three types of alkenone distribution patterns were identified: type A distribution, which resembles the distribution in Emiliania huxleyi , type B distribution, which is similar to Ruttnera lamellosa , Isochrysis galbana and Pseudoisochrysis paradoxa distributions, although these haptophytes are absent from the Baltic Sea, and type C distribution, which is also found in worldwide lake sediments. These types of distribution are apparent in the percentage of C 37:4 alkenone (%C 37:4 ), which is significantly negatively correlated to sea surface salinity (SSS). The distribution of Alkenones very likely results from distinct alkenone-producing haptophytes, whose spatial distribution is ultimately related to SSS, as supported by the hydrogen isotope fractionation (α) between Alkenones and water. U 37 K and U 37 K ″ correlate more significantly than U 37 K ′ with both SST and SSS, probably due to the superimposed effect of changing alkenone-producing species. The application of U 37 K and U 37 K ″ as SST proxies results in unrealistic Holocene temperature records for the southern Baltic Sea, but %C 37:4 as a SSS proxy reveals reasonable salinity changes. Interestingly, a C 32 hopanoic acid was found abundantly as the methyl ester in the ketone fractions and may represent a marker for (cyano)bacterial biomass in the Baltic Sea.

  • the effects of growth phase and salinity on the hydrogen isotopic composition of Alkenones produced by coastal haptophyte algae
    Geochimica et Cosmochimica Acta, 2014
    Co-Authors: David Chivall, Stefan Schouten, Jaap Sinninghe S Damste, Daniela Mboule, Danielle Sinkeschoen, Marcel T. J. Van Der Meer
    Abstract:

    The isotopic fractionation of hydrogen during the biosynthesis of Alkenones produced by marine haptophyte algae has been shown to depend on salinity and, as such, the hydrogen isotopic composition of Alkenones is emerging as a palaeosalinity proxy. The relationship between fractionation and salinity has previously only been determined during exponential growth, whilst it is not yet known in which growth phases natural haptophyte populations predominantly exist. We have therefore determined the relationship between the fractionation factor, αAlkenones-water, and salinity for C37 Alkenones produced in different growth phases of batch cultures of the major alkenone-producing coastal haptophytes Isochrysis galbana (strain CCMP 1323) and Chrysotila lamellosa (strain CCMP 1307) over a range in salinity from ca. 10 to 35. αAlkenones-water was similar in both species, ranging over 0.841-0.900 for I. galbana and 0.838-0.865 for C. lamellosa. A strong (0.85≤R2≤0.97; p<0.0001) relationship between salinity and fractionation factor was observed in both species at all growth phases investigated. This suggests that alkenone δD has the potential to be used as a salinity proxy in neritic areas where haptophyte communities are dominated by these coastal species. However, there was a marked difference in the sensitivity of αAlkenones-water to salinity between different growth phases: in the exponential growth phase of I. galbana, αAlkenones-water increased by 0.0019 per salinity unit (S-1), but was less sensitive at 0.0010 and 0.0008S-1 during the stationary and decline phases, respectively. Similarly, in C. lamellosa αAlkenones-water increased by 0.0010S-1 in the early stationary phase and by 0.0008S-1 during the late stationary phase. Assuming the shift in sensitivity of αAlkenones-water to salinity observed at the end of exponential growth in I. galbana is similar in other alkenone-producing species, the predominant growth phase of natural populations of haptophytes will affect the sensitivity of the alkenone salinity proxy. The proxy is likely to be most sensitive to salinity when Alkenones are produced in a state similar to exponential growth. © 2014 Elsevier Ltd.

  • Salinity dependent hydrogen isotope fractionation in Alkenones produced by coastal and open ocean haptophyte algae
    Geochimica et Cosmochimica Acta, 2014
    Co-Authors: Daniela M'boule, Stefan Schouten, Jaap Sinninghe S Damste, David Chivall, Daniëlle Sinke-schoen, Marcel T. J. Van Der Meer
    Abstract:

    Abstract The hydrogen isotope fractionation in Alkenones produced by haptophyte algae is a promising new proxy for paleosalinity reconstructions. To constrain and further develop this proxy the coastal haptophyte Isochrysis galbana and the open ocean haptophyte alga Emiliania huxleyi were cultured at different salinities. The fractionation factor, αAlkenones–water, ranged between 0.853 and 0.902 for I. galbana and 0.789 and 0.822 for E. huxleyi. The results show a strong linear correlation between the fractionation factor α and salinity for E. huxleyi, in agreement with earlier studies, but also for I. galbana. Both haptophytes show the same response to changes in salinity, represented by the slopes of the α–salinity relationship (∼0.002 per salinity unit). This suggests that the same process, in both coastal as well as open ocean haptophytes, is responsible for reducing fractionation with increasing salinity. However, there is a significant difference in absolute isotope fractionation between E. huxleyi and I. galbana, i.e. E. huxleyi produces Alkenones which are 90‰ more depleted in D under the same culturing conditions than I. galbana. Our data suggest that the δD of Alkenones can be used to reconstruct relative shifts in paleosalinity in coastal as well as open ocean environments with careful consideration of species composition and other complicating factors especially in coastal regions.