I will discuss the dynamics of three different climate events in the past: the Paleocene-Eocene Thermal Maximum (PETM, ∼55 million years before present) and Heinrich Events 1 and 4 (17.5-15.5ka BP and 40.2-38.8ka BP). The PETM was a period of rapid warming marked by a negative carbon isotope excursion and widespread dissolution of seafloor carbonate. These changes have been attributed to a massive release of carbon into the exogenic carbon cycle, and thus, the event provides a potential analog for future climate and environmental changes given the current anthropogenic CO2 emissions. One interesting aspect of the PETM is that acidification of deep waters was generally more extensive and severe in the Atlantic and Caribbean regions, with more modest changes in the Southern and Pacific Oceans. Here I will present a mechanism that might explain the observed spatial differences and constrain the total mass of carbon released during the PETM. In addition, I will present a model - proxy data comparison during Heinrich stadials 1 and 4 with an isotope-enabled Earth System Model. Heinrich stadials were cold periods during the past glacial associated with major discharges of icebergs into the North Atlantic. I will show that changes in surface (planktic) calcite d18O during these events can be equally attributed to changes in temperature (due to fractionation), changes in ocean circulation, precipitation and evaporation and to the addition of depleted freshwater from continental ice sheets. In contrast, the meltwater and circulation effects have only a small impact on benthic calcite d18O; significant changes in simulated deep ocean temperatures substantially influence benthic d18O records during that time.