How oxygen levels in Earth's atmosphere and oceans evolved has always been a central question in Earth System Science. Researchers have developed numerous tracers to tackle this question, utilizing geochemical characteristics of different elements. Iodine incorporated in calcium carbonate (including biogenic) minerals, reported as I/Ca, is a proxy for dissolved oxygen in seawater. Here we review the rationale behind this proxy, its recent applications and some potential future research directions.
2. Proxy systematics
4. Sample materials and post-depositional alterations
5. Long-term I/Ca trends through Earth history
6. Short-term ocean deoxygenation events
7. Quaternary glacial-interglacial cycles
8. Future prospects