Just as growth rings can offer insight into climate changes occurring during the lifespan of a tree, corals have much to tell about changes in the ocean. At Caltech, climate scientists Jess F. Adkins and Nivedita Thiagarajan use manned submersibles, like Alvin operated by the Woods Hole Oceanographic Institution, to dive thousands of meters below the surface to collect these specimens—and to shed new light on the connection between variance in carbon dioxide (CO2) levels in the deep ocean and historical glacial cycles.