The C20 highly branched isoprenoid biomarker – A new diatom-sourced proxy for summer trophic conditions? |
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| Institution: | 1. Department of Geological Sciences, Stockholm University, SE-10691 Stockholm, Sweden;2. Department of Applied Environmental Science, Stockholm University, SE-10691 Stockholm, Sweden;1. State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, Wuhan 430074, China;2. Department of Geography, Faculty of Earth Sciences, China University of Geosciences, Wuhan 430074, China;3. Department of Earth and Environmental Sciences, The University of Michigan, Ann Arbor, MI 48109-1005, USA;1. Department of Earth Sciences, Indian Institute of Science Education and Research Kolkata, Mohanpur 741246, India;2. Centre for Climate and Environmental Studies, Indian Institute of Science Education and Research Kolkata, Mohanpur 741246, India;1. Geological Survey of Denmark and Greenland (GEUS), Øster Voldgade 10, DK-1350 Copenhagen K, Denmark;2. Maersk Oil, Exploration, Esplanaden 50, DK-1263 Copenhagen, Denmark;1. Key Laboratory of Petroleum Resources, Gansu Province/Key Laboratory of Petroleum Resources Research, Institute of Geology and Geophysics, Chinese Academy of Sciences, Lanzhou 73000, PR China;2. Key Laboratory of Cenozoic Geology and Environment, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, PR China;3. University of Chinese Academy of Sciences, Beijing 100049, PR China;4. Sinopec Jianghan Oilfield Company, Wuhan 430233, PR China;5. Key Laboratory of Western China’s Environmental Systems with the Ministry of Education, Lanzhou University, Lanzhou 730000, PR China;1. Department of Geology, Faculty of Science, The M.S.University of Baroda, Vadodara 390 002, India;2. Physical Research Laboratory, Navrangpura, Ahmedabad 380 009, India;3. The Birbal Sahani Institute of Palaeobotany, 53 University Road, Lucknow 226 007, India;4. School of Environmental Sciences, Jawaharlal Nehru University, New Delhi 110 067, India;1. Department of Geoscience, University of Calgary, Calgary, Canada;2. Department of Geoscience, Kiel University, Kiel, Germany;3. Department of Geoscience, Curtin University, Perth, Australia;4. Geological Survey of Canada, Calgary, Canada |
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| Abstract: | The exact biological source of the C20 highly branched isoprenoid (HBI) present in sediments from aquatic systems is unclear. We therefore examined the relationship between the distribution of fossil diatoms and the concentration of the C20 HBI in a Late Glacial sedimentary record from the Hässeldala Port paleolake in southern Sweden. Using Bayesian multiple linear regression analysis, we show that its concentration is linked primarily to the production of the diatom taxon Gomphonema acuminatum, which accounts for the largest proportion of the temporal variability in the biomarker. By analogy with modern observations, we argue that an increasing amount of G. acuminatum biomass in our sedimentary record reflects increasing oligotrophy in the paleolake during the summer growing season, especially at times defined by subdued hydrologic flow. Our conclusions are corroborated by the δ13C composition of the C20 HBI biomarker, which points to a negative photosynthetic fractionation between atmospheric CO2 and the pool of dissolved inorganic carbon during diatom bloom, a distinct phenomenon at times of inhibited hydrological flow. Accordingly, we suggest that the C20 HBI biomarker can be effectively used to reconstruct the trophic state of the paleolake at Hässeldala Port, while its stable isotope composition can provide physicochemical information about the lake conditions during the dry summer season.Moreover, we note that the major hydrological shifts recorded in the G. acuminatum-C20 HBI stratigraphy do not coincide with the pollen zone boundaries. We thus infer that aquatic and terrestrial environmental responses to climate change are substantially decoupled through the hydrological system, which highlights the necessity for multi-proxy investigations to decipher past climate events. |
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| Keywords: | Highly branched isoprenoid Biomarkers Diatoms Late Glacial Paleolimnology |
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