wAbstract
@Greenland is by far the dominant source of glacial runoff to
the oceans but the controls on the chemical and isotopic composition
of this runoff are poorly known. To better constrain glacial effects
on weathering processes, we have conducted elemental and lithium
isotope analyses of glacial and non-glacial rivers in gneiss catchments
in West Greenland. The glacial rivers have high total suspended
solids (0.5 g l-1) and low total dissolved solids (12ΚScm-1)
relative to the non-glacial rivers, and they contain a higher
proportion of dissolved Ca2+ and K+ because
of subglacial, preferential, weathering of trace carbonates and
biotite. The glacial rivers also have high SO42-
because of the oxidation of trace sulphides under the ice. Both
glacial and non-glacial rivers have high Β7Li (respectively,
`26ρ and `30ρ) relative to the rocks from which that Li is derived
(`8ρ). Saturation state modelling suggests that this is due to
the formation of Fe-oxyhydroxides in the non-glacial rivers, with
preferential uptake of 6Li during inner sphere sorption
of Li+ on the Fe-oxyhydroxide surface. Glacial rivers,
however, are undersaturated with respect to clay minerals and
Fe-oxyhydroxides. Nevertheless, leaching of suspended sediments
indicates that `65 of the Li in these sediments is associated
with Fe-oxyhydroxide phases, and the Β7Li value of
this Li is low, `5ρ. These results suggest that these Fe-oxyhydroxides
formed under the ice, as a product of sulphide oxidation, with
preferential uptake of 6Li onto the mineral surface.
Solubilisation of Li from these Fe-oxyhydroxide phases is unlikely
to represent a significant flux of Li to the oceans. Moreover,
because the difference between the Β7Li values of glacial
vs non-glacial rivers is small, glaciation has not had a significant
impact on the Li isotopic composition of the riverine flux delivered
to the oceans in the past, even at the height of the last deglaciation.
Keywords: lithium isotopes; glacial weathering; Greenland; weathering
fluxesx
1. Introduction
2. Geology, climate and river settings
3. Field and analytical techniques
@3.1. Sample collection and preparation
@3.2. Cation and anion analyses
@3.3. Leaching experiment
@3.4. Li isotope analyses
4. Results
@4.1. In situ measurements
@4.2. Major and trace elements
@@4.2.1. Dissolved load
@@4.2.2. Colloidal and ultrafiltered fractions
@@4.2.3. Solid phases
@4.3. Leaching experiments
@4.4. Lithium and lithium isotopes
5. Discussion
@5.1. Physical and chemical erosion rates
@5.2. Chemistry of glacial vs non-glacial rivers
@5.3. Lithium and lithium isotope systematics
@5.4. Glacial weathering: effects on the Li and Li isotope composition
of global runoff
6. Conclusions
Acknowledgements
References