HR: 0800h
AN: PP11A-1436    [Abstracts]
TI: Water Table Depth Reconstruction in Ombrotrophic Peatlands Using Biomarker Abundance Ratios and Compound-Specific Hydrogen Isotope Composition
AU: * Nichols, J E
EM: jonathan_nichols@brown.edu
AF: Brown University Department of Geological Sciences, 324 Brook St. PO Box 1846, Providence, RI 02912
AU: Jackson, S T
EM: jackson@uwyo.edu
AF: University of Wyoming Department of Botany, Department of Botany #3165 1000 E. University Ave., Laramie, WY 82071
AU: Booth, R K
EM: rkbooth@wisc.edu
AF: Center for Climatic Research University of Wisconsin, 1153 Atmos/Ocn & Space Science Building 1225 W. Dayton Street, Madison, WI 53706
AU: Pendall, E G
EM: pendall@uwyo.edu
AF: University of Wyoming Department of Botany, Department of Botany #3165 1000 E. University Ave., Laramie, WY 82071
AU: Huang, Y
EM: yongsong_huang@brown.edu
AF: Brown University Department of Geological Sciences, 324 Brook St. PO Box 1846, Providence, RI 02912
AB: Sediment cores from ombrotrophic peat bogs provide sensitive records of changes in precipitation/evaporation (P/E) balance. Various proxies have been developed to reconstruct surface moisture conditions in peat bogs, including testate amoebae, plant macrofossils, and peat humification. Studying species composition of testate amoeba assemblages is time consuming and requires specialized training. Humification index can be influenced by environmental factors other than moisture balance. The plant macrofossil proxy is less quantitative and cannot be performed on highly decomposed samples. We demonstrate that the ratio of C₂₃ alkane to C₂₉ alkane abundance may provide a simple alternative or complementary means of tracking peatland water-table depth. Data for this proxy can be collected quickly using a small sample (100 mg dry). Water-table depth decreases during drought, and abundance of Sphagnum, the dominant peat-forming genus, decreases as vascular plants increase. Sphagnum moss produces mainly medium chain-length alkanes (C₂₁-C₂₅) while vascular plants (grasses and shrubs) produce primarily longer chain-length alkanes (C₂₇-C₃₁). Therefore, C₂₃:C₂₉ n-alkane ratios quantitatively track the water table depth fluctuations in peat bogs. We compared C₂₃:C₂₉ n-alkane ratios in a core from Minden Bog (southeastern Michigan) with water table depth reconstructions based on testate-amoeba assemblages and humification. The 184-cm core spans the past ~3kyr of continuous peat deposition in the bog. Our results indicate that the alkane ratios closely track the water table depth variations, with C₂₉ most abundant during droughts. We also explored the use of D/H ratios in Sphagnum biomarkers as a water-table depth proxy. Compound-specific hydrogen isotope ratio analyses were performed on Sphagnum biomarkers: C₂₃ and C₂₅ alkane and C₂₄ acid. Dry periods are represented in these records by an enrichment of deuterium in these Sphagnum-specific compounds. These events also correlate with drought events in the testate amoeba record and the alkane abundance ratio record. These biogeochemical proxies can be used in paleohydrological studies of ombrotrophic bogs and provide a new and complimentary source of data from these underutilized paleoclimate archives.
DE: 0454 Isotopic composition and chemistry (1041, 4870)
DE: 0473 Paleoclimatology and paleoceanography (3344, 4900)
DE: 1041 Stable isotope geochemistry (0454, 4870)
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005