How tiny foraminifera can play a massive role in understanding past climates

Foraminifera comprise a group of heterotrophic zooplankton, which inhabit all depths within the world's oceans from the sunlit surface ocean to the depths of the abyssal plains. Many species build a shell of calcium carbonate (predominantly calcite), which records vital geochemical information from the oceans as it grows. Studies based on microscopic foraminifera are often at the forefront of pioneering research by palaeoclimatologists into Cretaceous–Cenozoic climates. In this feature, I summarize how foraminifera are obtained from the deep ocean and describe how rapidly evolving planktic foraminifera species can be used to date marine sediments. I then explain how benthic foraminifera can be used to reconstruct high-resolution long-term climate records, focusing on the use of stable oxygen isotopes to elucidate deep ocean temperatures from the greenhouse climate of the late Paleocene–early Eocene.