Hydrogen isotope ratios of recent lacustrine sedimentary n-alkanes record modern climate variability

Hydrogen isotope ratios were measured on n-alkanes (n-C-12, to n-C-31) extracted from recent lake surface sediments along a N-S European transect to test if modern climate variability is recorded in these biomarkers. deltaD values of the n-alkanes are compared to deltaD values of meteoric water from the IAEA-GNIP database spanning a range from -119parts per thousand in northern Sweden to -41parts per thousand in southern Italy, to lake water deltaD values. and to mean annual temperatures, varying between -2.0degreesC in the north and 13.7degreesC in the South. deltaD values of the short-chained n-alkanes n-C-12 to n-C-20, excluding algal derived n-C-17, and n-C-19, are higher in the north and lower in the south. The isotopic fractionation e for hydrogen between meteoric water and the short-chained n-alkanes is increasing from N to S by more than 100parts per thousand and is significantly correlated to mean annual temperature for n-C-16 and n-C-18. 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-C-17 and n-C-19 alkanes of algal origin, the n-C-21 and n-C-23 alkanes originating from water plants, and the long-chain n-alkanes n-C-25, n-C-27, C-29, and n-C-31 of terrestrial origin, clearly correlate with deltaD values of meteoric water, lake water, and mean annual temperature, indicating that they excellently record the deltaD value of meteoric water. The mean hydrogen isotope fractionation epsilon(C17/w) of -157parts per thousand (SD = 13) between n-C-17 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 deltaD Values of n-C-17 are suitable to reconstruct the isotopic composition of source water. The mean fractionation between the long-chain n-alkanes and water is -128parts per thousand (SD = 12). The mean difference of 31parts per thousand between both epsilon 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 deltaD values of terrestrial and aquatic compounds might be suitable to reconstruct terrestrial evapotranspiration of the lake environment. Copyright (C) 2004 Elsevier Ltd.