『Abstract
The ratio of strontium isotopes, 87Sr/86Sr,
in seawater is homogeneous at any given time, yet varies considerably
throughout the geological record. This variation is thought to
stem from changes in the balance of predominantly radiogenic Sr
entering the oceans via dissolved riverine transport, and unradiogenic
Sr sourced from mid-ocean ridge hydrothermal activity. Recent
evidence suggests, however, that hydrothermal exchange at mid-ocean
ridges is a factor of 3 too low to balance Sr added to the oceans
from dissolved continental riverine fluxes. Here we present evidence
that the arrival and subsequent dissolution or riverine particulate
material in seawater is a significant contributor of both radiogenic
and unradiogenic Sr to the oceans. Batch experiments demonstrate
that between 0.15% and 27.36% of Sr is liberated from riverine
particulates to seawater within 6 months. The rates of release
are dependent on surface area and particulate composition, with
volcanic riverine material more reactive than continental riverine
particulates. The observed rapid Sr release rate from riverine
particulate material has important consequences for both chemical
and isotopic mass balances in the ocean and the application of
the 87Sr/86Sr weathering proxy to the geological
record. The dissolution of riverine particulate material is likely,
based on these findings, to at least partially account for the
imbalance between Sr sources to the oceans.
Keywords: strontium isotopes; riverine particulate material; seawater
composition; marine mass balance』
1. Introduction
2. Materials and methods
3. Results
3.1. Impact of dissolution on seawater 87Sr/86Sr
3.2. Changes in element concentrations
4. Discussion
4.1. Comparison between the experiments and the natural systems
4.2. Impact on oceanic 87Sr/86Sr and marine
budget implications
4.3. Evolution of oceanic 87Sr/86Sr
5. Conclusion
Acknowledgments
Appendix A. Supporting information
References