• DOI:10.1126/science.1182252
• Corpus ID: 22739139

Reconstructing Past Seawater Mg/Ca and Sr/Ca from Mid-Ocean Ridge Flank Calcium Carbonate Veins

@article{Coggon2010ReconstructingPS,
  title={Reconstructing Past Seawater Mg/Ca and Sr/Ca from Mid-Ocean Ridge Flank Calcium Carbonate Veins},
  author={Rosalind M. Coggon and Damon A. H. Teagle and Christopher E. Smith-Duque and Jeffrey C. Alt and Matthew J. Cooper},
  journal={Science},
  year={2010},
  volume={327},
  pages={1114 - 1117}
}

• R. Coggon, D. Teagle, +2 authors M. Cooper
• Published 26 February 2010
• Geology, Geography, Environmental Science
• Science

Cations in the Veins Major events in Earth's history, from climate change to tectonic activity, can be revealed by reconstructing past conditions of the oceans. Clues from ancient ocean chemistry can be found in the cation content of fossilized microorganisms, marine carbonates, or salt deposits from old coastal zones. As these proxies are prone to inconsistencies between samples and methodologies, Coggon et al. (p. 1114, published online 4 February; see the Perspective by Elderfield) estimated past seawater composition from the geochemistry of resistant carbonate veins precipitated within fresh basalts on the sea floor. The sudden rise to modern-day levels of ocean magnesium:calcium and strontium:calcium ratios occurred about 24 million years ago, and can be explained by a decrease in seafloor hydrothermal activity combined with a decrease in river discharge. Calcium carbonate veins from the ocean crust can be used to reconstruct past ocean cation ratios. Proxies for past seawater chemistry, such as Mg/Ca and Sr/Ca ratios, provide a record of the dynamic exchanges of elements between the solid Earth, the atmosphere, and the hydrosphere and the evolving influence of life. We estimated past oceanic Mg/Ca and Sr/Ca ratios from suites of 1.6- to 170-million-year-old calcium carbonate veins that had precipitated from seawater-derived fluids in ocean ridge flank basalts. Our data indicate that before the Neogene, oceanic Mg/Ca and Sr/Ca ratios were lower than in the modern ocean. Decreased ocean spreading since the Cretaceous and the resulting slow reduction in ocean crustal hydrothermal exchange throughout the early Tertiary may explain the recent rise in these ratios.