210Pb and Mass Flux Imbalance Between the Settling Particulates and Sediments at a Sediment Trap

HR: 0830h
AN: OS11A-06 [Abstracts]
TI: 210Pb and Mass Flux Imbalance Between the Settling Particulates and Sediments at a Sediment Trap
AU: * Wu, C
EM: ycchung@mail.nsysu.edu.tw
AF: Institute of Marine Geology and Chemistry, National Sun Yat-sen University, Kaohsiung, 80424 Taiwan
AU: Chung, Y
EM: ycchung@mail.nsysu.edu.tw
AF: Institute of Marine Geology and Chemistry, National Sun Yat-sen University, Kaohsiung, 80424 Taiwan
AU: Hung, G
EM: gwhung@mail.nsysu.edu.tw
AF: National Center for Ocean Research, National Taiwan University, Taipei, 106 Taiwan
AB: In order to evaluate the mass balance problems between the settling particulates and the underlying sediments, sediment traps were deployed at M1 site (21o32İN, 119o28İE; 2948m) where a box core was taken recently. The sediment trap results were previously published (Chung et al., 2004: Continental Shelf Research). We report here the 210Pb profile measured on this box core by determining its daughter, 210Po, with alpha spectrometry, assuming the paired nuclides are in radioactive equilibrium. The box core (33 cm long, taken in June, 2004) was analyzed for the distributions of its water content, loss on ignition (LOI), and 210Pb. The water content decreases with depth and averages about 55 percent; the LOI as a measure of the total organic matter (TOM) is fairly constant at about 12 percent. The 210Pb profile shows a general exponential decrease with depth, yielding a maximum sedimentation rate of 0.26cm/y, applying a constant flux and constant sedimentation rate model. This rate translates to a mass flux of 0.31g/cm2/y or about 8.5g/m2/d with a dry bulk density of 1.2g/cm3. Based on the excess 210Pb inventory integrated over the core length, the 210Pb flux is estimated at about 19.2dpm/cm2/y or 526dpm/cm2/d assuming at steady state. The 210Pb and mass fluxes obtained from the deepest trap at M1 were only 129dpm/m2/d and 0.55g/m2/d, respectively. The large excess" of the 210Pb and mass fluxes in the sediments over those measured from the sediment trap (4 times in 210Pb flux and 14 times in mass flux) suggests either the sedimentation rate was overestimated due to neglect of the mixing effect, and/or large additional particulates, as resuspended sediments which contain less 210Pb, have been transported laterally near the bottom from elsewhere.
DE: 1050 Marine geochemistry (4835, 4850)
DE: 4835 Inorganic marine chemistry
DE: 4850 Organic marine chemistry
SC: Ocean Sciences [OS]
MN: 2005 Joint Assembly