Our study investigates how tropical marine ecosystems responded to climate change during the Eocene–Oligocene transition (~34 Ma). Based on microfossil and geochemical data from a Caribbean drill core, we identify enhanced terrigenous input, increased surface productivity, changes in carbonate preservation, and reduced deep-water oxygenation. Likely driven by global cooling and sea-level fall, these shifts offer new insights into low-latitude paleoenvironmental change.