Four sediment cores were collected in fine-grained depositional areas of th
e southern basin of Lake Michigan. Spatial variations of aliphatic hydrocar
bons in surficial sediments were consistent with a lakeward movement of riv
erine sediments in a series of resuspension-settling cycles in which an unr
esolved complex mixture (UCM) of hydrocarbons associated with dense sedimen
ts is deposited in nearshore areas, fine-grained sediments of terrestrial o
rigin accumulate in the deep basin, and planktonic hydrocarbons are deplete
d by microbial degradation during transport to the deep basin;The rate of a
ccumulation of the,UCM (a marker of petroleum residues) in deep. basin sedi
ments has increased by more than an order of magnitude since 1880, from 60
mug m(-2).a(-1) to approximately 960 mug m(-2).a(-1) in 1980. Crude estimat
es of the atmospheric loading of the UCM (1100 mug m(-2).a(-1)) indicate th
at accumulations in deep-basin sediments might be supported by atmospheric
deposition. Agreement was poor between the atmospheric flux of the terrestr
ial n-alkanes (SigmaC(25), C-27, C-29, C-31) to the deep basin (3200 mug m(
-2).a(-1)) and the sediment accumulation rate (660 mug m(-2).a(-1)). Unders
tanding of atmospheric fluxes, estimated from the Very few available data,
would be improved by more frequent measurement of the levels of aliphatic h
ydrocarbons in air and precipitation and a better knowledge of the particle
deposition velocities and precipitation scavenging coefficients.