Deep-Sea Sediment Cores: Reading Earth's Climate Diary

Published: 2026-01-08

Deep-sea sediment cores are cylindrical columns of seafloor material recovered by ocean drilling programs. These cores can extend hundreds of meters below the seafloor, capturing continuous records of Earth's climate stretching back tens of millions of years.

The International Ocean Discovery Program (IODP) and its predecessors have drilled at thousands of sites across the world's oceans since 1968. Each core section is carefully described, photographed, and subsampled for micropaleontological, geochemical, and physical property analyses.

The sediment itself is composed largely of the skeletal remains of planktonic organisms — foraminifera, coccolithophores, diatoms, and radiolarians — mixed with terrigenous clay and volcanic ash. By analyzing the species composition and chemistry of these microfossils at closely spaced intervals down the core, scientists reconstruct how ocean conditions changed over time.