HR: 0830h
AN: H51C-10    [Abstracts]
TI: Particle Dynamics in the Temporary Deposition Zone of Lake Superior: Insights From ²¹⁰Pb,¹³⁷Cs and ⁷Be
AU: * Chai, Y
EM: ychai@astate.edu
AF: Arkansas State University, Department of Chemistry and Physics, State University, AR 72467-0419 United States
AU: Urban, N R
EM: nurban@mtu.edu
AF: Michigan Technological University, Department of Civil and Environmental Engineering, Houghton, MI 49931 United States
AU: Auer, M T
EM: mtauer@mtu.edu
AF: Michigan Technological University, Department of Civil and Environmental Engineering, Houghton, MI 49931 United States
AB: With the aim of understanding particle dynamics in the slope-profundal region in coastal areas of the Great Lakes and the particulate organic carbon availability to benthic organisms, sediment cores were taken along three transects in the nearshore region of Lake Superior. Inventories of ¹³⁷Cs and excess ²¹⁰Pb and focusing factors (based on both isotopes) were calculated for 28 cores. ⁷Be was only found in the fluff layer of the sediments at most sites, but its presence in deep-water sites attests to the rapidity of sedimentation. The ²¹⁰Pb-derived focusing factors ranged from 0.04 to 2.3 with mean and median values of 0.36 and 0.15, respectively. The study region is thus categorized as a temporary deposition zone. A 2-dimensional steady-state nested-box model was developed and applied to individual transects with the 210Pb inventories as model input. Model output included isotope residence times and cross-margin fluxes of sediments and isotopes. The time scale for the particles focusing from the shelf zone to the profundal zone of the transect was on the order of 10 years. The predicted residence times also indicate the existence of local enrichment zones for both isotopes and sediments as well as depletion zones along each transect. The results suggest that food availability may explain the observed Diporeia distributions along the transects. High ratios of ¹³⁷Cs:²¹⁰Pb were interpreted to indicate longshore transport by the Keweenaw Current and the general counter-clockwise circulation in the lake. This circulation entrains older sediments into the nearshore zone where they remain for periods of 10-30 years.
DE: 1845 Limnology
DE: 4219 Continental shelf processes
DE: 4805 Biogeochemical cycles (1615)
DE: 4860 Radioactivity and radioisotopes
DE: 9345 Large bodies of water (e.g., lakes and inland seas)
SC: Hydrology [H]
MN: 2005 Joint Assembly