Carbon cycles between the earth, ocean, and atmosphere on geological timescales. The relative amount of carbon stored in each of these respective locations is one important control on Earth’s average temperature. During the last ice age 18,000 years ago, carbon moved out of the atmosphere causing decreased global temperatures. However, it remains unknown where that carbon was stored. This project uses radiocarbon dating to test whether the deep Indian Ocean stored substantial amounts of carbon across the last ice age. The researchers will study microscopic fossils in four sediment cores from across the Indian Ocean basin. These tiny fossil shells made by single-celled organisms record the radiocarbon content of the seawater they lived in at the time of their growth. By comparing the radiocarbon age recorded in these microfossils to the age of the sediment, researchers will determine if deep Indian Ocean carbon was abnormally old during the last ice age. The size of the sediment grains will reveal how quickly currents at the bottom of the ocean flowed and how quickly this old, stored carbon could be transported out of the deep Indian Ocean and released back to the atmosphere. Combined, these data will tell researchers whether changes in deep Indian Ocean carbon were—or were not—important for past changes in Earth’s temperature. The work will support early career scientists and provide research opportunities for graduate students. Seawater radiocarbon content is a power