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SUMMARY:Orogenesis - CO2 source or sink? Insight from quantification of fo
 ssil organic carbon weathering rates in Taiwan - Robert Hilton\, Departmen
 t of Geography\, University of Durham
DTSTART:20121030T163000Z
DTEND:20121030T173000Z
UID:TALK38985@talks.cam.ac.uk
CONTACT:John Maclennan
DESCRIPTION:Physical erosion of the continents can result in the mobilisat
 ion of organic carbon (OC) from the terrestrial biosphere and its transfer
  by rivers to the ocean. If this OC is recently photosynthesised organic m
 atter (OCnon-fossil)\, then its transfer and burial in sedimentary deposit
 s contributes to geological sequestration of atmospheric CO2. Mountain bel
 ts with steep topographic gradients and high precipitation totals experien
 ce the highest rates of OCnon-fossil erosion (1)\, and its transfer along 
 with large volumes of clastic sediment can increase its likelihood of buri
 al in sedimentary deposits (2). In this way\, orogenesis can act to drawdo
 wn CO2. However in many mountain belts\, rapid fluvial incision and hillsl
 ope mass wasting processes expose fossil organic carbon (OCfossil)\, conta
 ined within sedimentary bedrock\, to the modern atmosphere and hydrosphere
 . Oxidation of OCfossil during weathering is a source of CO2 that counters
  drawdown by silicate weathering and recent organic carbon burial (3). Des
 pite this recognition\, we have very poor constraint on the rates at which
  OCfossil weathering occurs in natural environments. While it is thought t
 hat physical erosion is the primary control on this re-flux of carbon from
  the lithosphere\, the precise nature of the link remains unknown. Here\, 
 these questions are addressed using the trace element rhenium\, whose affi
 nity to OCfossil and redox-sensitive geochemical behaviour make it an idea
 l tracer of this process (4). The new data from Taiwanese rivers confirm h
 igh rates of physical erosion can enhance OCfossil weathering\, but show t
 hat they only counter half of the CO2 drawdown by terrestrial OC burial in
  marine sediments offshore. In this setting\, erosion and weathering induc
 ed cycling of OC results in a net sink of CO2.\n\n1. Hilton\, R. G.\, A. G
 aly\, N. Hovius\, S. J. Kao\, M. J. Horng\, and H. Chen (2012)\, Climatic 
 and geomorphic controls on the erosion of terrestrial biomass from subtrop
 ical mountain forest\, Global Biogeochemical Cycles\, 26\, GB3014\, doi:10
 .1029/2012GB004314\n\n2. Galy\, V.\, C. France-Lanord\, O. Beyssac\, P. Fa
 ure\, H. Kudrass\, and F. Palhol (2007)\, Efficient organic carbon burial 
 in the Bengal fan sustained by the Himalayan erosional system\, Nature\, 4
 05\, 407–410\, doi:10.1038/nature06273\n\n3. Hilton\, R.G.\, A. Galy\, N
 . Hovius\, M. J. Horng\, and H. Chen (2011)\, Efficient transport of fossi
 l organic carbon to the ocean by steep mountain rivers: An orogenic carbon
  sequestration mechanism\, Geology\, 2011\, 39\, 71-74\, doi:10.1130/G3135
 2.1\n\n4. Dalai\, T. K.\, S. K. Singh\, J. R. Trivedi\, and S. Krishnaswam
 i (2002)\, Dissolved rhenium in the Yamuna River System and the Ganga in t
 he Himalaya: Role of black shale weathering on the budgets of Re\, Os\, an
 d U in rivers and CO2 in the atmosphere\, Geochimica et Cosmochimica Acta\
 , 66\, 29-43.
LOCATION:Harker 1 seminar room\, Department of Earth Sciences
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