New Insights into Ice Age and Post-Industrial Marine Carbonate System Dynamics Inferred from the Geochemistry of Benthic Foraminifera and a Scleractinian Coral

Doss, Whitney Crawford

Graduate Thesis Or Dissertation

New Insights into Ice Age and Post-Industrial Marine Carbonate System Dynamics Inferred from the Geochemistry of Benthic Foraminifera and a Scleractinian Coral Public Deposited

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Citeable URL: https://scholar.colorado.edu/concern/graduate_thesis_or_dissertations/dr26xx49n

Abstract

Paleoceanographic reconstructions and modern field studies of the response of marine calcifying organisms to their environment using elemental ratios are crucially dependent upon better understanding of biologically mediated fractionation. In particular, the hydrographic parameter calcium carbonate (CaCO₃) saturation state (ΔCO₃^2-) has been shown to affect biomineralization. Therefore robust empirical relationships between measurements and known seawater influences must be exactingly calibrated and supported by inclusive mechanistic explanations in order to understand past environments and also to predict future behavior. To this end, my three-part dissertation focuses on understanding and applying trace and minor element proxies in calcite and aragonite precipitated in tropical deep (by benthic foraminifera) and surface (by scleractinian coral) waters.

The influence of low latitude ocean primary productivity on Ice Age atmospheric CO₂ levels has proven challenging to reconstruct using mass accumulation rates of biogenic particulates in deep sea sediment cores. Benthic foraminiferal boron/calcium ratios (B/Ca) serve as a proxy for past seawater ΔCO₃^2-, and thereby provide a fresh perspective on this outstanding paleoceanographic problem. I employ Cibicidoides wuellerstorfi B/Ca in the Panama Basin region of the eastern equatorial Pacific (EEP) to investigate the nature of deep tropical carbon storage over the past 50,000 years.

Benthic foraminiferal Mg/Ca and Li/Ca are potentially valuable paleoceanographic tools for reconstructing deep ocean circulation and chemistry over late Pleistocene climate cycles, but only if the bottom water temperature and ΔCO₃^2-sensitivities can be isolated. Paleo-thermometry especially depends upon firm constraint of the ancillary ΔCO₃^2- effect. Here I build upon the foundation of my temperature-independent B/Ca results from the EEP and employ multi-proxy downcore intercalibration to quantify signals in simultaneously measured Li/Ca and Mg/Ca, and resolve heretofore enigmatic behavior in compiled global coretop Li/Ca.

This dissertation transitions to more recent time with relevant consideration of anthropogenic factors by measuring and interpreting elements Sr/Ca and B/Ca in the scleractinian coral species Orbicella favelolata. Using comparatively betterunderstood stable isotope signatures in conjunction with high resolution sea surface temperature measurements to constrain oceanographic conditions of the Belizean barrier reef since 1960, I test the response of coral biomineralization to environmental stressors including: ENSO and hurricane events, land-use change, and the surface ocean burden of increasing atmospheric pCO₂. Notably, this work entails a rare examination of coralline B/Ca.

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