HR: 08:30h
AN: PP41B-03    [Abstracts]
TI: Using Multiproxy Influx Data to Clarify the Origin of Carbon-Isotope Signals in Organic Matter from Late Quaternary Lake Sediments: Application to an Altitudinal Transect of Lakes on Mt. Kenya, East Africa
AU: * Street-Perrott, F A
EM: f.a.street-perrott@swan.ac.uk
AF: University of Wales Swansea, Department of Geography, Singleton Park, Swansea, SA2 8PP United Kingdom
AU: Barker, P A
EM: p.barker@lancaster.ac.uk
AF: Lancaster University, Hysed, Department of Geography, Lancaster, LA1 4YB United Kingdom
AU: Ficken, K J
EM: k.j.ficken@swan.ac.uk
AF: University of Wales Swansea, Department of Geography, Singleton Park, Swansea, SA2 8PP United Kingdom
AU: Huang, Y
EM: yongsong\_huang@brown.edu
AF: Brown University, Dept of Geological Sciences, Providence, RI 02912 United States
AU: Eglinton, G
EM: Geoffrey.Eglinton@dartmouth.edu
AF: University of Bristol, Biogeochemistry Research Centre, Department of Geology, Bristol, BS1 1RJ United Kingdom
AB: Considerable ambiguities arise in the interpretation of both bulk and molecular stable-isotope analyses from tropical lake sediments, due to past variations in the relative importance of different local organic-matter sources, including C3 and C4 terrestrial plants and emergent macrophytes, submerged aquatic macrophytes, algae, and bacteria, as well as atmospheric particulates. Although comparisons are often made between isotope curves and other sedimentological, geochemical, or palaeoecological indicators, these usually rely on concentration or percentage data, which may be biased by large temporal fluctuations in sedimentation rate, bulk density, and proportions of major sediment components or common fossil taxa. It is also difficult to make interlake comparisons by this means. We present new insights into the 13C records from four small lakes at 2350 - 4595m a.s.l. on Mt. Kenya, spanning the period 38,000 - 0 cal. yr BP, based on the accumulation rates (influxes) of an array of sediment components, including total sediment, magnetic minerals, TOC, TN, n-alkyl lipids, pollen, charred grass fragments, diatoms, diatom C and N, and green microalgae. The results suggest that Sacred Lake (2350m a.s.l.) has always been oligotrophic and dominated by organic-matter inputs from surrounding rainforest and aquatic macrophytes, whereas the higher algal productivity of lakes above treeline ($>$3000m a.s.l.) was stimulated by nutrients transported by periglacial activity from surrounding slopes, and aeolian inputs of dust and organic detritus. Comparisons between lakes help to distinguish between isotopic coherence resulting from shared atmospheric forcing, and purely local signals reflecting differences in lake depth, hydrology, vegetation, and geomorphological processes.
DE: 9305 Africa
DE: 3344 Paleoclimatology
DE: 1845 Limnology
DE: 1040 Isotopic composition/chemistry
DE: 1615 Biogeochemical processes (4805)
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting