『Abstract
Sr isotope data from soils, water, and atmospheric inputs in
a small tropical granitoid watershed in the Luquillo Mountains
of Puerto Rico constrain soil mineral development, weathering
fluxes, and atmospheric deposition. This study provides new information
on pedogenic processes and geochemical fluxes that is not apparent
in watershed mass balances based on major element alone. 87Sr/86Sr
data reveal that Saharan mineral aerosol dust contributes significantly
to atmospheric inputs. Watershed-scale Sr isotope mass balance
calculations indicate that the dust deposition flux for the watershed
is 2100±700 mg cm-2 ka-1.Nd isotope analyses
of soil and saprolite samples provide independent evidence for
the presence of Saharan dust in the regolith. Watershed-scale
Sr isotope mass balance calculations are used to calculate the
overall short-term chemical denudation velocity for the watershed,
which agrees well with previous denudation rate estimates based
on major element chemistry and cosmogenic nuclides. The dissolved
streamwater Sr flux is dominated by weathering of plagioclase
and hornblende and partial weathering of biotite in the saprock
zone. A steep gradient in regolith porewater 87Sr/86Sr
ratio with depth, from 0.70635 to as high as 0.71395, reflects
the transition from primary mineral-derived Sr to a combination
of residual biotite-derived Sr and atmospherically-derived Sr
near the surface, and allows multiple origins of kaolinite to
be identified.』
1. Introduction
2. Site description
3. Saharan dust in the Caribbean
4. Methods
5. Results
5.1. Water samples
5.2. Soil, saprolite, and bedrock samples
6. Discussion
6.1. Weathering processes
6.1.1. Bedrock weathering
6.1.2. Saprolite and soil weathering
6.1.3. Influence of precipitation inputs on soil Sr
6.1.4. Mineral separates
6.2. Weathering fluxes and Sr mass balance
6.2.1. Accounting for Sr components of weathering system
6.2.2. Testing a previous model of weathering rates in the Icacos
basin
6.2.3. Watershed Sr mass balance
6.3. Dust inputs
6.3.1. Sr isotope-based calculation
6.3.2. Nd isotope-based calculation of dust inputs
6.3.3. Summary and implications of dust input
7. Conclusions
Acknowledgments
References