Stable isotopes of carbonate have long been used to reconstruct past climate and environmental conditions. The recent development of the clumped isotope paleothermometer has expanded the range of possible applications of these isotopic techniques to cover more environments and time periods. My research uses these isotopic tools to reconstruct past climate and ocean conditions during times of dynamic climate change. The end of the Cretaceous period was marked by turmoil with the massive Deccan Traps volcanic event and the Chicxulub meteorite impact combining to create the most famous of the “Big Five” mass extinctions. I will show new climate records from multiple localities spanning these final few tumultuous million years, present evidence of volcanism-induced climate change, and link these climate changes to extinction patterns. I will put these impressive climate shifts in the context of background climate conditions at the time through a global temperature dataset. Finally, I will present an investigation of intriguing isotopic results from one site that reveal information about the life cycle of an extinct bivalve species and demonstrate the breadth of possible applications of these isotopic techniques.