Has the atmospheric supply of dissolved calcite dust to seawater influenced the evolution of marine 87Sr/86Sr ratios over the past 2.5 million years?

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Abstract

By analyzing the geochemistry of Chinese loess, this study examines if the flux of calcite dust from the Chinese Loess Plateau to the North Pacific influenced the evolution of marine 87Sr/86Sr ratios between 2.5 million years ago (Ma) and the present. Calcite comprises ∼10 wt% of Chinese loess and contains ∼1 × 104 nmol of Sr/g with an 87Sr/86Sr ratio of ∼0.711. A compilation of literature data suggests that the calcite dust flux emanating from eastern Asia has averaged either 2 × 1013 or 1 × 1014 g/yr since the onset of Northern Hemisphere cooling ∼2.5 Ma. The factor of 5 difference between the estimates reflects discrepancies inherent to methods for determining dust fluxes to seawater. At present, these discrepancies remain unresolved. Calcite dust is completely dissolved during transport in the atmosphere and ocean. Thus the marine Sr input from eolian calcite dissolution has averaged either 2 × 108 or 1 × 109 mol/yr. A mass balance model demonstrates that the lower estimate has very little influence on seawater 87Sr/86Sr ratios, whereas the higher estimate has possibly elevated seawater 87Sr/86Sr ratios by ∼18% since 2.5 Ma. When combined with previously reported effects of Northern Hemisphere glaciation on the riverine Sr flux, this shift is sufficient to reproduce the entire Plio-Pleistocene marine Sr record. While more research is required to constrain dust flux estimates, these findings suggest that the atmospheric supply of eolian calcite to seawater may represent a previously overlooked process linking climate change to the marine Sr cycle.

Original languageEnglish (US)
Article numberQ12002
JournalGeochemistry, Geophysics, Geosystems
Volume5
Issue number12
DOIs
StatePublished - Dec 2004

Keywords

  • Calcite
  • Geochemical cycle
  • Loess Plateau
  • Seawater
  • Sr/ Sr

ASJC Scopus subject areas

  • Geophysics
  • Geochemistry and Petrology

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