HR: 1340h
AN: PP43B-1261    [Abstracts]
TI: Novel Stable Isotope Methods for Assessing Changes in Seasonality of Precipitation from Sediments of Ombrotrophic Peatlands
AU: * Nichols, J E
EM: jonathan_nichols@brown.edu
AF: Department of Geological Sciences, Brown University, 324 Brook St., Providence, RI 02912, United States
AU: Booth, R K
EM: rkb205@lehigh.edu
AF: Earth and Environmental Science Department, Lehigh University, 31 Williams Dr., Bethlehem, PA 18015, United States
AU: Jackson, S T
EM: jackson@uwyo.edu
AF: Department of Botany, University of Wyoming, 1000 E. University Ave., Laramie, WY 82071, United States
AU: Pendall, E G
EM: pendall@uwyo.edu
AF: Department of Botany, University of Wyoming, 1000 E. University Ave., Laramie, WY 82071, United States
AU: Walcott, M
EM: marie_walcott@brown.edu
AF: Department of Geological Sciences, Brown University, 324 Brook St., Providence, RI 02912, United States
AU: Bradley, R
EM: rbradley@umass.edu
AF: Department of Geosciences, University of Massachusetts, Amherst, 611 North Pleasant Street, Amherst, MA 01003, United States
AU: Pilcher, J
EM: j.pilcher@qub.ac.uk
AF: Palaeoecology Centre, Queen's University, Belfast, School of Geography, Archaeology and Palaeoecology, The Queen's University, Belfast, Belfast, BT7 1NN, United Kingdom
AU: Huang, Y
EM: yongsong_huang@brown.edu
AF: Department of Geological Sciences, Brown University, 324 Brook St., Providence, RI 02912, United States
AB: The seasonality of precipitation is a key but often elusive climate parameter in paleoclimate reconstructions. Sediments from ombrotrophic peatlands are excellent archives of past changes in precipitation/evaporation balance. Here we show that these peatland sediments can also be used to assess changes in the seasonality of precipitation. We have recently determined that distributions of Sphagnum and vascular plant biomarkers sensitively record changes in hydrologic balance (Nichols et al., 2006, Org. Geochem. 37, 1505-1513), but biomarker distributions alone do not offer detailed information for the changes in seasonal precipitation. In this study, we combine biomarker and compound-specific H and C isotope ratios to create a more comprehensive picture of the changing climate affecting these sensitive ombrotrophic systems. We present here two sets of downcore data from sites in Arctic Europe as well as Eastern North America. Basic paleohydrology is established using a ratio of Sphagnum to vascular plant biomarkers (C₂₃ and C₂₉ n-alkanes, respectively. We further describe paleohydrology using novel stable isotope proxies based on δD and δ¹³C measurements of Sphagnum and vascular plant biomarkers. Because Sphagnum has no vascular system and loses water directly by evaporation, Sphagnum biomarkers enriched in deuterium indicate an evaporative growing season (summer). Vascular plants use their root systems to take up water stored within the peatland, so deuterium-depleted vascular plant biomarkers should indicate increased winter recharge of the peatland. A methanotrophic symbiont living inside the Sphagnum's hyaline (water-holding) cells is more active when the Sphagnum is wet and therefore provides more ¹³C depleted (methane- derived) carbon dioxide for biomass production when the growing season is less evaporative. Hence, ¹³C depleted Sphagnum biomarkers indicate increased methanotrophy and therefore a wetter summer. We corroborate our stable isotope proxies by comparing them with other paleoclimatic and paleohydrological records, including testate-amoeba and pollen-inferred moisture reconstructions and sea surface temperature reconstructions. Our combination of novel stable isotope and biomarker analyses allows us to understand much more about the seasonality of precipitation throughout the Holocene than does each proxy record alone.
DE: 0424 Biosignatures and proxies
DE: 0473 Paleoclimatology and paleoceanography (3344, 4900)
DE: 1041 Stable isotope geochemistry (0454, 4870)
DE: 1605 Abrupt/rapid climate change (4901, 8408)
DE: 1637 Regional climate change
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Fall Meeting