HR: 0800h
AN: B11A-0054    [Abstracts]
TI: The Erosion of the Terrestrial Biosphere from Mountain Catchments and its Transfer as Particulate Organic Carbon (POC) to the Deep Ocean.
AU: * Hilton, R G
EM: rgh31@esc.cam.ac.uk
AF: Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge, CB2 3EQ, United Kingdom
AU: Galy, A
EM: albert00@esc.cam.ac.uk
AF: Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge, CB2 3EQ, United Kingdom
AU: Hovius, N
EM: nhovius@esc.cam.ac.uk
AF: Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge, CB2 3EQ, United Kingdom
AU: Horng, M
EM: mjhorng@wra.gov.tw
AF: Water Resources Agency, Ministry of Economic Affairs, Hsin-Yi Road, Taipei, 9, Taiwan
AU: Chen, H
EM: hchen@ntu.edu.tw
AF: Department of Geoscience, National Taiwan University, No.1, Sec. 4, Roosevelt Road, Taipei, 9, Taiwan
AU: Chen, M
EM: cmorgan@taroko.gov.tw
AF: Taroko National Park, Fu-Su Village, Hualien, 972, Taiwan
AB: The erosion of particulate organic carbon (POC) from the continents by rivers and its input to the oceans is an important component of the global carbon cycle. A large proportion this material is derived from mountain belts where clastic sediment yields are high. In order to assess the impact of this carbon transfer on global cycles it is extremely important to constrain the source of the POC. If POC sourced from bedrock is oxidised its influence on carbon-cycling is very different from oxidising POC derived from vegetation and soil. The same can be said if a fraction of the POC derived from vegetation and soil is buried in sediment. In addition, rivers are dynamic systems that respond to, amongst other things, climate. How is the POC source and transfer affected by this external variable? We have measured the organic carbon concentration (C_org) of suspended sediment from several rivers draining the vegetated mountain belt of Taiwan. The rivers were sampled frequently across two orders of magnitude of water discharge (Q_w) and suspended sediment concentration (SSC) (from low flow conditions and during typhoon-triggered floods). Using C_org, δ¹³C_org, N and δ¹⁵N as geochemical tracers we can determine the source of riverine POC, and differentiate between fossil (bedrock) and non-fossil (vegetation and soil) POC. Measurements of ¹⁴C (F_mod) on POC allow us to determine how much non-fossil POC is derived from eroding soil versus vegetation, and give an average soil POC residence time in the catchments. We find that the transfer of non-fossil POC is strongly controlled by climate and that at very high Q_w and SSC, non-fossil POC is enriched above the norm. Floods are extremely important in the bulk transfer of non-fossil POC from mountain hillslopes. During these flood events non-fossil and fossil POC are delivered to the ocean in hyperpycnal river plumes (where the density of the river sediment mixture is greater than seawater) which may trigger turbidity currents. The fate of the entrained POC may therefore be to remain associated with sediment for long periods of time.
DE: 0428 Carbon cycling (4806)
DE: 1055 Organic and biogenic geochemistry
DE: 1821 Floods
SC: Biogeosciences [B]
MN: 2007 Fall Meeting