The stable isotope composition of strontium dissolved in the ocean offers a new and relatively unexplored tracer of carbon cycle processes fundamental to the regulation of Earth’s climate system. Seawater stable strontium isotope ratios (δ88/86Sr) vary over million-year timescales in response to changes in continental weathering and the marine carbonate sink. Reconstructing δ88/86Sr variations through time consequently provides insight to long-term carbon cycle processes and, most critically, their positive or negative feedbacks on climate. The canonical view of conservative elements in the ocean suggests that seawater δ88/86Sr should not respond to shorter-term carbon cycle changes, but mounting evidence suggests that the ocean Sr budget may have been imbalanced over the glacial/interglacial cycles of the Pleistocene. This dissertation addresses the outstanding question of whether the ocean Sr budget was sensitive to perturbation by changing carbonate burial and weathering fluxes on relatively short timescales during major climate transitions.

In Chapter 2, I reviewed our current quantitative understanding of carbonate burial in the ocean over the past 2.5 million years and concluded that the shallow carbonate sink, past and present, remains vastly underconstrained. My review introduced δ88/86Sr as a potential proxy for past changes in carbonate burial during the Quaternary ices ages if the isotope ratio is shown to be sensitive to carbonate fluxes on these timescales. In Chapters 3 and 4 I investigated two different archives of paleo seawater chemistry – pore fluids preserved in a Maldives carbonate platform and marine barite accumulated in deep sea sediments – to determine whether seawater δ88/86Sr varied over glacial/interglacial cycles. Both archives revealed measurable fluctuations in seawater δ88/86Sr over the past 250 kyr. These observations were combined with model simulations to explore the potential links between glacial/interglacial sea level, marine carbonate burial and weathering, and Sr cycling. Finally, I looked at another period of glaciation in Earth history, the Eocene/Oligocene Transition, in Chapter 5 and found that seawater δ88/86Sr was not sensitive to the major carbon cycle perturbation during this time. Together, these chapters provide the first geochemical records of seawater δ88/86Sr during abrupt climate events and inform our evolving understanding of how carbon cycle changes have impacted elements in seawater.