Japan Geoscience Union Meeting 2015

Presentation information


Symbol B (Biogeosciences) » B-PT Paleontology

[B-PT25] Biotic history and its relation to the Earth history

Sun. May 24, 2015 6:15 PM - 7:30 PM Convention Hall (2F)

Convener:*Isao Motoyama(Department of Earth and Environmental Sciences, Yamagata University), Takao Ubukata(Division of Geology & Mineralogy, Department of Earth & Planetary Sciences, Kyoto University)

6:15 PM - 7:30 PM

[BPT25-P05] Chemotaxonomic fingerprints of alkenones and alkenoates in sediments of Lake Naga-ike on the Skarvsnes, Antarctica

*Hideto NAKAMURA1, Mayumi TAKEDA1, Ken SAWADA1, Yoshinori TAKANO2 (1.Hokkaido Univ., 2.JAMSTEC)

Keywords:alkenone, Haptophytes, chemotaxonomy, lake sediments, paleothermomater

Long chain alkenones and alkenoates are widely distributed in marine sediments and their extent of unsaturation (UK37, UK’37) is extensively used for reconstruction of paleo sea surface temperature. Alkenones and related compounds have also been detected in various lakes, although there is a wide variation in alkenone compositions and the temperature calibrations between individual settings. These variations probably reflect the difference in alkenone producing species (strains) in lakes. Indeed, recent DNA analysis revealed that multiple lineages of the order Isochrysidales are distributed among alkenone containing lakes, and is considered to be engaged in the alkenone production (2-3). Culture based investigation on temperature calibrations suggested the significant variation of calibrations among Isochrysidaceae species (Isochrysis galbana (4), Pseudoisochrysis paradoxa (5) and Chrysotila lamellosa (6)). Therefore, taxonomic identification of alkenone producers is essential to the proper selection of calibrations and thus lead to better application of alkenone paleothermometer in lakes.
To elucidate chemotaxonomic characteristics of the compositions of alkenone and related compounds, we have been cultured 9 strains covering all 3 genera (Chrysotila, Isochrysis, Tisochrysis) of the family Isochrysidaceae, and proposed that the lack of tetraunsaturated alkenones are common characteristic for genus Tisochrysis (7). In this study, cultured Isochrysidaceae strains as well as sediments of antarctic lake Naga-ike were examined further into the compositions of alkenones and alkenoates. We discuss chemotaxonomic feature of triunsaturated alkenone isomers and novel C38 alkenoate which could be identified by a recently-developed method (8) using gas chromatography column with dipole selective stationary phase. Isomer of triunsaturated alkenones have previously identified from high latitude lakes (BrayaSø, Toolik Lake), which are characterized by a significant proportion of triunsaturated isomers ranging C37-C39(8). Meanwhile, triunsaturated alkenone isomer detected from C. lamellasa were solely C38. Occurrence of C38 triunsaturated isomers along with novel C38 alkenoate are proposed as characteristics of C. lamellosa in the family Isochrysidaceae.
Lake Naga-ike is a freshwater lake on the Skarvsnes, Antarctica, and biomarker analysis has been carried out by (9) revealing ca. 3000 yrs record of alkenone compositions. Examination of the sediment of Lake Naga-ike by a new method (8) revealed that the co-occurence of C38 triunsaturated alkenone isomers and novel C38 alienate, suggesting a possible contribution of C. lamellosa. By using a calibration obtained from a culture strain C. lamellosa calibration (6), paleotemperature are calculated to be 9.2-15℃ in surface sediments of Lake Naga-ike. The estimated temperatures are concordant with a summer temperature of lake waters observed in Naga-ike, while other known culture based calibrations estimated extremely-low temperatures. This result may afford collateral evidence for the occurrence of alkenone producer closely related to C. lamellasa.

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