36
Peter Stille and Graham Shields
G")
(./')
v
0.~
0.73
0.72
0.71
0.70
0 70
0.74
/
..
/ e
I
e /
9
9 0
9
9
/
!
I
I
0.71
0.72
0.73
86e- r ,~
( 8 7 $ r /
.~ Jsusp
Fig. 3.4. Relationship between STSr/86Sr of dissolved and suspended load. Data from
Goldstein and Jacobsen 1987 (filled circles) and Tricca 1997 (open circles: rivers from the
upper Rhine valley)
During feldspar weathering, Sr with low 87Sr/S6Sr ratios are preferentially
dissolved away first. This may also have a significant effect on the isotopic
composition of river water. Mass balance calculations demonstrate that the
dissolution of carbonates, evaporite minerals and phosphate with low S7Sr/S6Sr
ratios (<0.71 ) has likewise a decisive influence on the Sr budget of river systems
(e.g. Goldstein and Jacobsen 1987).
3.2 Nd Isotopes and the Rare Earths (REE) in River Water
The Nd and Sm concentations in rivers vary between about 3 and 3000 ng/1, and i
and 900 ng/1, respectively. Detailed investigations along individual river systems
clearly demonstrate that they resemble Sr concentrations in that they are strongly
pH dependent (Fig. 3.5; Eider'field et al. 1990). Rivers with pH values >7.5 show
concentrations between 3 and 50 ng/l, whereas rivers with a pH of <7.5 display
increasingly high Nd concentrations.
Peter Stille and Graham Shields
G")
(./')
v
0.~
0.73
0.72
0.71
0.70
0 70
0.74
/
..
/ e
I
e /
9
9 0
9
9
/
!
I
I
0.71
0.72
0.73
86e- r ,~
( 8 7 $ r /
.~ Jsusp
Fig. 3.4. Relationship between STSr/86Sr of dissolved and suspended load. Data from
Goldstein and Jacobsen 1987 (filled circles) and Tricca 1997 (open circles: rivers from the
upper Rhine valley)
During feldspar weathering, Sr with low 87Sr/S6Sr ratios are preferentially
dissolved away first. This may also have a significant effect on the isotopic
composition of river water. Mass balance calculations demonstrate that the
dissolution of carbonates, evaporite minerals and phosphate with low S7Sr/S6Sr
ratios (<0.71 ) has likewise a decisive influence on the Sr budget of river systems
(e.g. Goldstein and Jacobsen 1987).
3.2 Nd Isotopes and the Rare Earths (REE) in River Water
The Nd and Sm concentations in rivers vary between about 3 and 3000 ng/1, and i
and 900 ng/1, respectively. Detailed investigations along individual river systems
clearly demonstrate that they resemble Sr concentrations in that they are strongly
pH dependent (Fig. 3.5; Eider'field et al. 1990). Rivers with pH values >7.5 show
concentrations between 3 and 50 ng/l, whereas rivers with a pH of <7.5 display
increasingly high Nd concentrations.