Computer Science
Scientific paper
Dec 2004
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004gecoa..68.4877s&link_type=abstract
Geochimica et Cosmochimica Acta, Volume 68, Issue 23, p. 4877-4889.
Computer Science
31
Scientific paper
Hydrogen isotope ratios were measured on n-alkanes (n-C12 to n-C31) extracted from recent lake surface sediments along a N-S European transect to test if modern climate variability is recorded in these biomarkers. δD values of the n-alkanes are compared to δD values of meteoric water from the IAEA-GNIP database spanning a range from -119‰ in northern Sweden to -41‰ in southern Italy, to lake water δD values, and to mean annual temperatures, varying between -2.0°C in the north and 13.7°C in the south. δD values of the short-chained n-alkanes n-C12 to n-C20, excluding algal derived n-C17 and n-C19, are higher in the north and lower in the south. The isotopic fractionation ɛ for hydrogen between meteoric water and the short-chained n-alkanes is increasing from N to S by more than 100‰ and is significantly correlated to mean annual temperature for n-C16 and n-C18. This suggests that these n-alkanes may originate from a different source in the northern lakes, possibly due to petroleum contamination, or are synthesized using a different biochemical pathway. The n-C17 and n-C19 alkanes of algal origin, the n-C21 and n-C23 alkanes originating from water plants, and the long-chain n-alkanes n-C25, n-C27, n-C29, and n-C31 of terrestrial origin, clearly correlate with δD values of meteoric water, lake water, and mean annual temperature, indicating that they excellently record the δD value of meteoric water. The mean hydrogen isotope fractionation ɛC17/w of -157‰ (SD = 13) between n-C17 and meteoric water is fairly constant over the wide range of different climates and lake environments, suggesting only minor influence of environmental factors on this biochemical fractionation. This suggests that δD values of n-C17 are suitable to reconstruct the isotopic composition of source water. The mean fractionation between the long-chain n-alkanes and water is -128‰ (SD = 12). The mean difference of 31‰ between both ɛ values is likely due to evaporative enrichment of deuterium in the leaf water. If this is the only influence on the enrichment, the difference between the δD values of terrestrial and aquatic compounds might be suitable to reconstruct terrestrial evapotranspiration of the lake environment.
Gleixner Gerd
Radke Jens
Sachse Dirk
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