Weathering of till in northern Sweden results in the formation of well-deve
loped spodosols. The till is dominated by 1.9-1.8 Ga granitic material. The
REE are among the elements most strongly depleted during weathering, and t
he loss of REE from the E-horizon decreases as the atomic number increases.
To study if weathering leads to a change of the Nd isotope composition, we
have analysed the Nd isotopic composition of the various horizons includin
g living plants and humus of two profiles of weathered till (typic haplocry
ods) in northern Sweden. As much as between 65.6 and 75.3% of the Sm and Nd
in the <0.2 mm fraction has been lost from the E-horizon, and between 32.5
and 54.7% from the B-horizon. Nd has been lost to a slightly greater exten
t than Sm. The two C-horizon samples have epsilon(Nd(0)) values of -22.1 an
d -23.2. Corresponding E-horizon values an -18.1 and -20.2. The B-horizon v
alues are intermediate between the values of the E and C horizons. It is co
ncluded that the weathering leads to a change in the Sm/Nd ratio resulting
in a change of the Sm-Nd isotope composition. The plant and humus samples d
eviate even more from the unweathered till. For one station the results cou
ld be interpreted as if the Sm and Nd taken up by the plants had similar is
otope characteristics as the amounts of these elements released by weatheri
ng in the E-horizon. For the other station it is probable that the Nd isoto
pe composition of the organic samples is dominated by Nd released by till w
eathering which, however, is mixed with another Nd-source, possibly an airb
orne component. The explanation to the change of isotope compostion in the
till is that a larger proportion of the Nd released by weathering is releas
ed from minerals with a lower Sm/Nd ratio than the bulk soil, compared with
the amount released from minerals with a higher Sm/Nd ratio. Although the
various REE-carrying minerals had the same initial Nd isotopic composition,
1.8-1.9 Ga of decay of Sm-147 to Nd-143 has resulted in a higher present N
d-143/Nd-144 ratio in the minerals with a higher Sm/Nd ratio. Copyright (C)
2000 Elsevier Science Ltd.