BIOMARKER AND COMPOUND SPECIFIC ISOTOPE RATIOS AS NOVEL SENSITIVE INDICATORS OF PALEOHYDROLOGY: AN EXAMPLE FROM AN OMBROTROPHIC BOG IN COASTAL ARCTIC NORWAY

Sediments of ombrotrophic peatlands are excellent archives for reconstructing past changes in precipitation/evaporation (P/E) balance. Multiproxy analysis of these sediments is critical for better understanding of climatic events experienced by these highly sensitive systems, as each proxy responds differently to climate parameters. We have recently shown that the biomarker distributions of Sphagnum and vascular plant biomarkers are sensitive recorders of paleohydrology (Nichols et al., 2006, Org. Geochem. 37, 1505-1513). In this study, we combine biomarker and compound specific H and C isotope ratios from sediments of Bøstad Bog in coastal Arctic Norway (~68N) to reconstruct the paleohydrological change during the Holocene. We integrate our data with regional climate records and sea surface temperature changes in the Norwegian Sea and discuss various forcing mechanisms such as insolation. Sphagnum moss, the dominant peat former in ombrotrophic bogs, produces n-alkanes of different chain lengths relative to vascular plants. Under drier conditions (lower water table), vascular plants become abundant relative to Sphagnum (and vice versa). Thus, the abundance of Sphagnum relative to vascular plants is indicative of peatland hydrology. We modeled n-alkane ratios in peat based on a survey of modern plants (Nichols et al., 2006) and then applied the model to peat cores. We also measured the δD and δ¹³C values of Sphagnum biomarkers. Because ombrotrophic systems lose water only by evaporation, drier conditions cause hydrogen isotopic enrichment of bog water and Sphagnum biomarkers. In addition, decreased wetness impedes the growth of methanotrophic bacteria symbiotic with Sphagnum, causing an enrichment of δ¹³C values. Our data provide high-resolution, quantitative paleohydrological records for the study region that are consistent with other records.