Forecasting trends in deoxygenation is evolving to become a major task for research communities focusing on the ocean-climate system. Geological records provide great opportunities to investigate environmental perturbations occurred in the past, in order to improve constraints on the rate and magnitude of modern climate change impacts. It is beneficial to examine events across different time scales, particularly for gauging the sensitivity of various controls on ocean oxygenation. Proxy approaches are key to unveiling past ocean conditions, however, oxygenation reconstructions have their unique challenges. This talk will review results of a carbonate-based proxy iodine to calcium ratios (I/Ca). I advocate that well-established approaches in paleoceanographic studies (e.g. temperature and pH) may require adaptations to best serve the deoxygenation community.