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.
Project Overview
Processes affecting ocean chemistry
Hydrothermal CCVs
CCVs precipitate from seawater-derived hydrothermal fluids, recording their temperature and composition (
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Sr/
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Sr, 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.
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.
