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The University of Southampton
Ocean and Earth Science, National Oceanography Centre Southampton

Research project: Calcium carbonate veins as recorders of past ocean chemistry

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Seawater chemistry reflects the balance between the supply and removal of elements to and from the oceans, e.g. by rivers, hydrothermal exchange or sediment burial. Fundamental global processes such as tectonics, climate, and biological productivity control these fluxes (Fig 1). Consequently, changes in past ocean chemistry help us understand the evolution of the Earth system. Calcium carbonate veins (CCV) formed during ridge flank hydrothermal circulation record past ocean Mg/Ca and Sr/Ca ratios.

Fig. 1. Processes that affect seawater chemistry, after Coggon (2011)
Processes affecting ocean chemistry

Hydrothermal CCVs

CCVs precipitate from seawater-derived hydrothermal fluids, recording their temperature and composition (87Sr/86Sr, Sr/Ca and Mg/Ca). CCVs from young (<3.6 Ma) ocean crust across the eastern Juan de Fuca Ridge Flank record the chemical evolution of the fluid, away from its initial modern seawater composition, as it heats and reacts with the rock. Similarly, CCVs from ancient ocean crust record trends of past basement fluid evolution that project back to the composition of contemporaneous seawater.

Fig. 2. Ridge flank hydrothermal CCV formation (After Coggon, 2011).
Ridge flank CCV formation

Past seawater Mg/Ca and Sr/Ca

CCVs from old crust were used to estimate past ocean Mg/Ca and Sr/Ca. The CCVs corroborate previous estimates of past seawater Mg/Ca, but indicate lower Sr/Ca ratios from 170 to 25 Ma than previous estimate from biogenic carbonates, perhaps due to uncertainties in biogenic Sr-partitioning.

Changes in seawater chemistry reflect perturbations to the balance between ocean inputs and outputs. The CCVs record increases in both seawater Sr/Ca and Mg/Ca since 25 Ma that coulf be accounted for by decreased mid-ocean ridge spreading and hydrothermal exchange.

Fig. 3. Reconstructing past seawater Sr/Ca and Mg/Ca using CCVs (After Coggon et al., 2010 and Coggon et al., 2011)
Sr/Ca and Mg/Ca reconstruction
Fig. 4. Records of past seawater Sr/Ca and Mg/Ca (After Coggon et al., 2010)
Seawater Sr/Ca and Mg/Ca records

Key Contacts

Dr. Rosalind Coggon (Principal Investigator)

Prof. Damon Teagle (Principal Investigator)

Dr. Michelle Harris (Post Doctoral Researcher)

PhDs and Other Opportunities


Associated research themes

Past Present and Future Environmental Change

Formation and Evolution of the Ocean Crust

Hydrothermal Processes and mineral deposits

Related research groups


Key Publication


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